How the 4th block of the Chernobyl Nuclear Power Plant actually blew up: why the “poisoned” reactor could not be removed from the “hole”

How could the events leading up to the accident have influenced the fate of the reactor?

After the SIUR errors in reactor control or/and as a result of xenon poisoning, or power reduction for vibration testing, the reactor stalls. We discussed this in detail in the previous article. There is an extremely important hypothesis of the possibility of xenon poisoning of the reactor, created both as a result of a planned power reduction by 50% on the eve of the experiment, and the subsequent delay in its reduction due to the ban of Kyivenergo. Let us briefly recall these points.

During the process of reducing the power of the unit on April 25, 1986, during the shift of A.F. Akimov (from 0:8 to 7:10), at 13,2:15 a.m., the ORM, according to the calculated data, reached a value of XNUMX rods, i.e. it became lower than the permissible value of XNUMX rods.

From the testimony of Rogozhkin, the station shift supervisor:

"The unit was unloaded, but Akimov and I had doubts that the reactivity margin would not fall below 15 RR rods. By 8:00, that's what happened, it became 13,2 rods. I noted this at the selector operational meeting at 8:00. Frolovsky asked again: "How much, how much?", to which Fomin said: "We will discuss this issue separately...". According to the regulations, we should shut down the reactor. But the unit was about to be shut down, so we reported this to the management and that was it. We decided to do without extremes, since this parameter was not listed as the main one in the instructions and regulations."

Then the process of reducing power (unloading the unit) was unexpectedly interrupted at a level of 50% of the reactor's design capacity at the request of the Kievenergo dispatcher on 25.04.1986 at 14:00, who prohibited reducing power due to problems at the Tripolskaya GRES (according to another version - the South Ukrainian NPP), and was continued only at 23:10.

According to V. Komarov (former deputy director for science at the Smolensk NPP, participant in the accident investigation):

“This… absolutely should not have been done!
But the telex from KyivEnergo was duplicated by a telephone call from the Central Committee of the CPSU... And... the order was carried out...”

According to Deputy Minister of Energy G.A. Shasharin:

"The delay of the experiment... significantly reduced the reactivity margin, reducing the number of control rods immersed in the active zone due to additional poisoning of the reactor (iodine pit). All this created conditions for a pre-accident state."

This circumstance was of an external nature, the management could adjust the program. However, all this required additional time, which the group did not have.

In the book by N. Karpan there is evidence from M.A. Yelshin (NS CTAI), confirming this hypothesis:

"During the process of reducing power, the SIUR failed to maintain the unit at power and "dropped" it. The apparatus was heavily "poisoned", and the SIUR failed to maintain it..."

As the author of the textbook, V. L. Gurachevsky, writes (“Introduction to Nuclear Energy”, Rosatom library):

"According to another version, the night shift of A. F. Akimov accepted the reactor while it was running, during a rapid decrease in power from the level of 1600 MW in the presence of xenon poisoning. The senior reactor control engineer who came on duty, L. F. Toptunov, did not have time to understand the difficult current situation and simply could not stabilize the power at the required level..."

Let's see how the designer of the RBMK-1000 reactor, academician N. Dollezhal, comments on this moment:

"...There followed... a request from the Kyivenergo dispatcher to delay the shutdown of the second turbogenerator... What should the senior reactor control engineer (senior operator) have done? Ignore the dispatcher's request and continue the planned reduction of the reactor's power in accordance with the instructions available on this matter. This is what a qualified specialist who is aware of his responsibility would have done on a completely legal basis."

Assessing the degree of poisoning of the reactor after 23 p.m., he writes:

“...it was obviously already deep, since after almost 2 hours the reactor was poisoned to a state called an “iodine pit,” i.e. inoperable.”

Next, Dyatlov gives an order to increase the power, which was established during the judicial investigation, although he denies it. The reactor begins to be raised from the pit - this was done quite quickly, from 00:38 to 00:42 - in 4 minutes the power was raised to 160 MW, and a little later, by 01:03, to the planned 200 MW. The main questions that arise in this key episode:

- was it possible to increase the power;
- at the expense of what it was done;
- were the regulatory documents for reactor management observed?

Let's see how the participants in the events themselves, official commissions and experts evaluate these events.

Technical news feed

00:05 - by order of Dyatlov A.S., the reactor power began to be reduced to the level of its own needs (200 MW).

00h 28m - LAR is switched off, AR-1 is switched on. AR-1 is switched off according to the VK, AR-2 is not switched on due to an unacceptable imbalance. The thermal power of the reactor is falling.

00h 30m 50s - signal of malfunction of the measuring part of AR-2.

00h 31m 35s - 00h 32m 46s - activation of BRU-K2 TG-8.

00h 34m 03s - 00h 37m 49s - emergency level deviation signal in BS.

00h 35m - the AP setting was reduced using the “quick power reduction” button.

00h 36m 24s - the AZ setpoint for reducing pressure in the BS was switched from 55 to 50 kg/cm2.

00h 38m - N(T) = 0 -:-30 MW. Raising power to the SN level by order of Dyatlov.

00h 39m 32s - 00h 43m 35s - the DREG program did not work (4m 03s).

The reason is the preparation of the magnetic tape of the DREG by SDIVT for recording the tests.

00h 42m - N(T1 = 160 MW. AR-1 is switched on. Unacceptable imbalance on AR-2 is removed. AR-2 is brought to readiness. OZR = 19,7 st. RR according to VU "Rocks" (according to data from NSB Tregub and NSS Rogozhkin).

Wan = 0, par on BRU-K.

00h 42m - measurement of idle vibration of TG-8 with an excited generator.

00h 43m 27s - output of protection AZ-5 by disconnecting TWO TGs.
........................ ..
01h 03m - N(T) = 200 MW. Disconnection of TG-8 from the network, measurement of vibration XX with the generator disconnected.

Personnel actions and regulations

According to the interpretation of INSAG-7, which also indicates xenon poisoning:

“The consequence of the failed actions taken to control the reactor was that in order to compensate for the additional negative reactivity that arose due to xenon poisoning of the active zone during a power reduction, as well as during the subsequent increase in power to 200 MW, it was necessary to remove some of the operating reserve rods from the reactor, which, as the Commission believes, with or without awareness of the severity of the consequences, the personnel transferred the reactor to an unscheduled state, in which the emergency protection ceased to be a guarantee of quenching the nuclear reaction….

At 01:22:30, the SKALA central control system recorded the power unit parameters on magnetic tape, and operational calculations using the PRIZMA program were not performed at that time. They were performed after the accident using the magnetic tape removed from the central control system using the PRIZMA-ANALOG program outside the Chernobyl Nuclear Power Plant (at the Smolensk Nuclear Power Plant). The control room personnel and the SKALA system personnel did not have the results of operational calculations and did not know the calculated parameters, including the ORM value, at that time."

Before the accident, the personnel operated the reactor as if blindly. But when they raised the reactor from the pit, they should have had an understanding of the situation. The entire experiment was supposed to be carried out by one, the most experienced shift, but by a fatal coincidence, the most inexperienced one ended up on duty. What N. Dollezhal writes about this:

“…Did the personnel who came on duty just an hour before the accident know how the reactor power had been reduced the day before? That it was in such a state of poisoning that reaching power without observing the necessary conditions was unacceptable? Did the personnel know that to conduct the generator coastdown experiment, a reactor thermal power of 700 MW was needed, since this was probably the power that ensured the turbine’s idle speed, i.e. the minimum turbine power at which the generator’s nominal speed required for the experiment was maintained? Did they know that the emergency cooldown system had been switched off? Did they know that maintaining the reactor power at the 200 MW that had been achieved with difficulty was pointless and that the reactor had to be shut down altogether? And finally, did they know that two more main circulation pumps were planned to be switched on?”

The Chernobyl Nuclear Power Plant control room before the accident

IXBT Forum:

"Combining the TG-8 vibration test experiment with increasing reactor power violates clause 6.3 of the TR, which is an integral part of the short-term shutdown regulations, which they are formally obliged to follow by clause 6.6.10. According to clause 6.3 of the TR, first reach stage 2, wait, load the RCPs according to the map, and then operate at power according to section 8 of the TR. Including conduct at least one or two tests during operation at power, after formal completion of the power increase procedures according to section 6 of the TR. In their case, clause 6.7 of the TR refers to the "power increase regulations after a short-term shutdown without an iodine pit." Not to the increase regulations after unloading, but specifically after a shutdown. That is, all actions within the framework of paragraph 6.7 must be carried out according to the formal procedure of the entire 6th section - as if they were briefly stopped."

According to the Regulations, paragraph 6.2, the reactor had to be shut down, since a rise from a power of less than 50% of the design power is only permitted if the ORM before the shutdown was not lower than 30 rods, and the reactor had 24 (see scan below). This situation put the personnel in an extremely difficult situation: whether to shut down the reactor, as required by the regulations, or continue the chain of violations, which, as is now known, ended in disaster. The first time we missed it was the day before, when it was 13,2 instead of 15. What if we miss it again? The reactor began to "poison" itself again.

Scan of item 6 of the Technological Regulations for the RBMK-1000 reactor

For clarity, let us present a graph with changes in reactor power and reactor reactivity margin with Site – V. Dmitriev (VNIIAES).

According to the court's determination:

"The fact that on April 25-26, 1986, the reactor of the fourth power unit was operated with an operational reactivity margin of less than 26 rods is confirmed by the entries in the logs of the shift supervisor and the SIUR of unit No. 4, examined during the court hearing, as well as a photocopy of the printout of the centralized control system "Skala", according to which at 1 hour 22 minutes 30 seconds on April 26, 1986, the reactivity margin was 6-8 rods. According to the recording of another device - the SFKRE recorder - at 00 hours 28 minutes on April 26, 1986, the reactor power dropped to zero, and then rose to 180-200 MW. This was done in violation of paragraph 6.2 of the Regulations, without passing the iodine pit, in the absence of the minimum required reactivity margin."

Gurachevsky V.L.:

"...Some witnesses testified that the order to raise the reactor power came from A.S. Dyatlov. Dyatlov writes in his book: "I agreed with Sasha Akimov's proposal to raise the power to 200 MW after the failure for a very simple reason: according to the Regulations, it is necessary to raise it to 700 MW in no less than half an hour, and we have work for half an hour, such power is not needed either for measuring the vibration of the turbine, or for the experiment under the TG rundown program - under the latter, the reactor was completely shut down."

So where could they go? - opinion of a forum member IXBT:

"- But where should they [go]? If at 700 MW as provided by the program, then it is 0,5 + 0,5 + 0,5 + 0,5 + 3,0 + 1,40 (+ 5 to work so that the parameters stabilize?), - i.e. until the morning. In fact, I understand it would be even longer, since according to the table in paragraph 6.6.10 there is a paragraph that in this case refers to another table in paragraph 5.5.2 of the TR, and there the time intervals are even longer;

- If at 500 MW, which, judging by the graph, they almost reached before stalling, then it’s still 0,5+0,5+0,5+0,5+3,0 and only then experiments or other types of work at this power level;

- But they improvised on the fly because they were in a hurry (and the dispatcher's postponement of the tests plus this unplanned failure pushed them even further away from the goal)... Whether Metlenko or Dyatlov himself figured out from the table p.6.6.10 where they could quickly climb out, formally remaining within the TR, is no longer important. But it seems to take them 200 hours to climb to 0,5 MW, plus they need to work for 0,5 hours to settle down."

Obviously, it was impossible to reach 700 MW without going through the iodine pit when the reactor was poisoned. 200 MW in those conditions was the real limit.

As stated in the INSAG-1 report:

"It was only by 1:00 a.m. on April 26, 1986, that it was possible to stabilize it at a level of 200 MW. Due to the fact that the reactor was being "poisoned" during this period, further increase in power was difficult due to the small operational reactivity reserve, which by this time was significantly lower than the regulatory one."

Next, the most knowledgeable researcher of the accident, O. Yu. Novoselsky, gives an answer to the question – was it possible to remove the reactor from the pit:

"During this reduction, the operator failed to maintain the power, and the reactor was shut down. Was it possible to raise the power? The operating regulations permit this operation if the operating reactivity margin (ORM), measured in the manual control rods (RCR) fully immersed in the core, exceeds 30 RCRs. Otherwise, the emergency protection rods and all the control rods should be immersed in the core and the reactor should be depoisoned for at least 20 hours, i.e., it is necessary to pass through the "iodine pit". It seems that none of the two shifts (the previous one had not yet left the control room) remembered about this unfortunate ORM, and this margin, as it turned out later, was much less than 15 RCRs, i.e., a mandatory reactor shutdown with passage through the "iodine pit" was required. By removing almost all the absorber rods from the xenon-poisoned active zone, it was possible to raise the power to 160 MW, and to measure the vibrations of TG-8. By 1.03.00 on April 26, the power was raised to 200 MW..."

Reactor hall of the Chernobyl Nuclear Power Plant

According to Arkady Uskov, senior engineer for the operation of reactor shop No. 1 (RS-1) of Unit 1 of the Chernobyl Nuclear Power Plant, the personnel were not sufficiently informed about this problem:

"But the most important thing is why the personnel violated the Regulations that night (and this is also a law!) - because of the lack of a clear explanation: why it is categorically forbidden to work with an operational reactivity reserve of less than 15 rods. The guys could not even imagine that they were in a nuclear-hazardous mode!

Not even half a line was mentioned anywhere about this. And even from the institute bench it was firmly hammered into my head: the reactor cannot explode! It was only after the accident that the operational reserve would be set at 30 (!) rods, and no less. It was already in October 1986 that a stern warning would be introduced into the Regulations: "...with a reserve of less than 30 rods, the reactor goes into a nuclear-hazardous state!"

This is partially true, but, as we have seen above, not entirely. The problem was different. These events very well demonstrate the attitude of the personnel of the Chernobyl Nuclear Power Plant to the regulations, which is confirmed by the testimony of I.I. Kazachkov, the head of the day shift of the 4th unit: "I will say this: we have repeatedly had less than the permissible number of rods - and nothing ...", "... none of us imagined that this was fraught with a nuclear accident. We knew that we should not do this, but we did not think ..." At the Chernobyl Nuclear Power Plant, they often worked in violation of the regulations (there is a court ruling on this) - but the situation was saved, most likely, by the fact that this happened at higher capacities than those fateful 200 MW that A. Dyatlov chose.

This is confirmed by another highly authoritative expert who investigated the causes of the accident, Valentin Zhiltsov:

"...I have witnessed when it was necessary to work with significantly smaller reactivity reserves, when the power was increased after a short-term shutdown (especially after a false activation of the A3) and when the requirement to pass the "iodine pit" was optional. But what is the risk of this?.. This was really not mentioned anywhere."

But the main thing was something completely different: Anatoly Dyatlov, having strict instructions from the management to complete the experiment, nevertheless gave an absolutely fatal order to increase the power to those very 200 MW that he needed.

This is how he justifies his actions:

“Prosecutor: When you saw that the reactor’s capacity was 30 MW, why did you allow the rise and not give the command to shut down?

Dyatlov: A drop in power to 30 MW is not a shutdown, but a partial load reduction. Even a working AP can go into automatic mode at thirty megawatts. That is why I did not give the command to stop."

According to the court's determination:

"At 00:30 on the same day, in the presence of Dyatlov, SIUR Toptunov, due to inexperience, reduced the reactor installation's power to zero, as a result of which the reactor was "poisoned" with xenon, after which, on the instructions of Dyatlov, who acted contrary to the requirements of the Regulations on immediate shutdown of the reactor in such a case, he began to raise its power, without having a minimum reactivity reserve. Approximately 10 minutes later, on the instructions of Dyatlov, another gross violation of Chapter 3 of the Regulations was committed - the shift personnel disabled the AZ-5 protection for a number of parameters. Contrary to paragraph 2.1 of the test program, Dyatlov ordered that they be conducted with the reactor operating at a power of 200 MW instead of the 700-1000 MW required for safe operation. According to the conclusion of the forensic technical examination, the above violations, taken together, led to intensive steam formation in the reactor core, the creation of positive reactivity and uncontrolled acceleration of the reactor on prompt neutrons, and then to a strong thermal explosion at the 4th power unit of the station."

According to the State Penitentiary Service:

“A conclusion on the legitimacy of the personnel’s actions after the reactor power failure (section 4.7.3 of this report) can only be made after additional research.”

How does Academician V. Legasov assess the general actions of the staff in his notes:

“…the mistakes made by the operators are in themselves monstrous; the behavior of the station’s management is difficult to explain; the punishment of the culprits is correct, because the actions did not comply with regulatory requirements and showed a discrepancy with the job requirements of those people who acted in this situation… This is the fault of the officials.”

THE FOURTH (FATAL) TRAGIC MISTAKE – INCREASE IN POWER AFTER SELF-SHUTDOWN OF THE REACTOR.

How the reactor was raised from the “pit”

As the former deputy director of the Chernobyl Nuclear Power Plant, Alexander Kovalenko, testifies:

"The tests were supervised by Deputy Chief Engineer Anatoly Dyatlov. It is clear from the recording of the telephone conversation that the operational personnel understood that the reactor power could not be increased. But Dyatlov received a call from an employee of the all-powerful CPSU Central Committee [an official in the sector for supervision of the nuclear power plant]… and ordered that the fourth reactor be brought up to power. In 1986, there were rumors at the station that these tests were needed for [someone's] dissertation… And Dyatlov wanted to conduct them at any cost, because he promised to appoint him chief engineer or director of the station [or, if unsuccessful, send him into retirement]…. In one of our conversations, Raymond Brize (Deputy Chairman of the Supreme Court of the USSR - he presided over the trial on the disaster) also mentioned the existence of such a recording, which was then classified."

Here is information from the leading specialist in nuclear power plant safety in Russia, V. Asmolov (First Deputy Director General of Rosenergoatom, co-author of the first report for the IAEA):

“Then the operator, switching to the mode of this experiment in a new state, was practically unable to stabilize in this mode... He dropped the reactor to zero... And the reactor cannot be started in this state according to the instructions for days 2-3. [But] this was our operator. An engineer with a higher education. A person who wanted to conduct this experiment. For him, this was a super task. A challenge. And he pulled the reactor out of the iodine pit... But it did not go... And then he began to remove all the emergency protection rods from the zone in order to... reach some power... There are 240 emergency rods in this reactor. Less than 30 - the chief engineer of the station gives permission. Less than 15 - no one gives permission. He... pulled the reactor out, leaving 6 rods in the zone. The reactor resisted, saying: "Get away from me, don't touch me, let me rest for two days." As the director of the Chernobyl Nuclear Power Plant Bryukhanov testified in court: “It was necessary to go through the iodine pit after the loss of power to zero. And not to turn off the AZ-5 protection.”

Let's see how G. Medvedev describes this dramatic situation in very fine detail:

"...Dyatlov, with an agility uncharacteristic of him, ran around the control panels of the operators' console... The reactor is being poisoned by decay products. It is necessary either to immediately increase the power, or to wait a day for it to be de-poisoned. And it was necessary to wait...

But he did not want to stop... SIUR Leonid Toptunov and the block shift supervisor Akimov thought about it... It was clear to him that he would hardly be able to rise to the previous power level, that is, to 50 percent, and if he did succeed, then with a sharp decrease in the number of rods immersed in the zone, which required an immediate shutdown of the reactor... Toptunov made the only correct decision.

- I will not rise! - firmly said Toptunov. Akimov supported him. Both expressed their concerns Dyatlov.

- What are you lying about, Japanese crucian carp! - Dyatlov pounced on Toptunov, - After a fall from 80 percent, the regulations allow a rise in 50 hours, and you fell from 26 percent! The regulations do not prohibit it. And if you don’t rise, Tregub will rise... (Yuri Tregub, the block shift supervisor, who handed over the shift to Akimov and stayed to watch how the tests were going, was nearby)... Leonid Toptunov was frightened by the shout from his superiors, and betrayed his professional intuition. He was young, of course, only XNUMX years old, inexperienced... But he was already calculating:

“…To compensate for the poisoning, I’ll have to pull out another five to seven rods from the reserve group... Maybe I’ll get through... If I disobey, I’ll be fired...”

Leonid Toptunov began increasing the power, thereby signing a death warrant for himself and many of his comrades... Further increasing the power was hampered by the small operational reactivity reserve, which by that time was much lower than the regulatory one. (According to the USSR report to the IAEA, it was 6-8 rods, according to the statement of the dying Toptunov, who looked at the printout of the "Skala" machine seven minutes before the explosion, it was 18 rods.)...

This is explained by the fact that Toptunov, leaving the “iodine pit”, removed several rods from the emergency reserve group...

And yet it was decided to continue the tests, although the reactor was already practically uncontrollable. Apparently, there was great... hope that it would not fail this time, that the reactor would be saved [by pressing the AZ-5 protection reset button]... Over the past 35 years, there have been no accidents at nuclear power plants of a global nature... And the operators themselves were young and not vigilant enough.

The increase in power was achieved by removing an unacceptably large number of control rods

The moment when the reactor actually shut itself down was actually a turning point. Fate gave a real chance to avoid the accident - if the personnel had shut down the reactor, there would have been no accident!

However, according to Komarov, an official from a department (or sector) of the Central Committee of the CPSU may have given instructions to A. Dyatlov to increase the capacity and conduct the experiment, threatening him with retirement. The capacity was only raised to 200 MW (t), which was a gross violation of the test program, which provided for a coastdown at 700 MW.

What is most important is that the increase in power to 200 MW due to xenon poisoning of the reactor was achieved by removing the maximum possible number of rods, while their number in the zone became unacceptably low (see the next point), becoming a gross violation of the Regulations. The reactor was poisoned, and its condition was uneven. And this was a fatal mistake of the personnel.
According to the GPAN report (1991), this event led to the accident:

"...to compensate for the additional negative reactivity that arose due to xenon poisoning of the reactor core during a power reduction, as well as during the subsequent increase in reactor power to 200 MW, it was necessary to remove some of the operating reserve rods (ORR) from the reactor. By doing this...the personnel transferred the reactor to an unscheduled state, in which the emergency protection ceased to be a guarantee of quenching the nuclear reaction...The "failure" of the reactor power at 00:28 and the subsequent increase in its power largely determined the tragic outcome of the process. The change in the reactor operating mode, which took place between 00:28 and approximately 00:33, initiated a new xenon process of restructuring the energy release fields in the reactor, which the personnel had no way of controlling."

According to the memoirs of V. I. Borets, at such power levels the reactor behaved unpredictably and unstable; spontaneous acceleration could begin at any moment.

Forum participants often say that nowhere was it said that it was impossible to work at this capacity. Formally yes, but, as follows quite clearly from the regulations, the capacity of 200 MW is only one of the initial stages of increasing the capacity before bringing the reactor to the operating level.

IXBT forum member:

“200 MW is dangerous due to the unstable operation of the level regulators in the BS, which leads to a deterioration in the reactor’s controllability... It was the poisoning of the reactor that led to the emergence of instability at 200 MW.”

V. Asmolov again:

"It stabilized at a power of 200 megawatts. That is, less than 10 percent... For us in the project, this was an unexplored power level. Because the reactor lives at this power either when it starts up or when it stops."

Another important point is that at low reactor power, the water temperature becomes close to the saturation (boiling) temperature. The water temperature is determined by the saturation temperature in the BS (drum separator), the flow rate through the reactor, and the temperature and flow rate of the feedwater. Feedwater is formed as a result of the condensation of exhaust steam. The lower the reactor power, the lower the flow rate of "cold" feedwater, and the temperature becomes closer to the saturation (boiling) temperature.

According to Dmitriev, and according to N. Karpan, in the period from 00:43 to 01:00 the reactor operated unstably, since there were emergency signals about the deviation of the water level in the BS and the activation of the BRUK-K (excess steam pressure).

The most important thing is that although the reactor was poisoned with xenon, it had zones free of rods, and under certain circumstances (for a specific accident – ​​steaming of the zone) an uncontrolled runaway could begin in them, which is what actually happened, the accident (destruction of the zone) began in the south-eastern quadrant of the reactor.

THE FIFTH FATAL MISTAKE OF THE STAFF IS INCREASING POWER BY REMOVING A LARGE PART OF THE CONTROL SYSTEM RODS FROM THE CRITICAL ZONE.

Links:
Chernobyl: KOMAROV'S TESTIMONY
Shasharin G. Chernobyl tragedy // Novy mir, No. 9, 1991, p. 164.
Dollezhal N.A. At the origins of the man-made world. Notes of a designer. — 2010
TECHNOLOGICAL REGULATIONS for the operation of power units 3 and 4 of the Chernobyl NPP with RBMK-1000 1E-S-11 reactors
Valery Alekseevich Legasov, About the Chernobyl Nuclear Power Plant Accident, Text from five tape cassettes dictated by Academician V.A. Legasov.
The Cause of the Chernobyl Disaster Is Hidden in a Secret Call from the Central Committee
Vladimir Asmolov about Chernobyl
Grigory Medvedev. Chernobyl notebook
On the causes and circumstances of the accident at Unit 4 of the Chernobyl nuclear power plant on April 26, 1986, Report of the USSR Gospromatnadzor Commission
How the Chernobyl explosion was prepared. (Memoirs of V.I. Borets.)
Victor Dmitriev, Chernobyl disaster. Its causes are known
N.V. Karpan, CHERNOBYL REVENGE OF THE PEACEFUL ATOM
A.G. Tarapon, RECONSTRUCTION OF THE CAUSE OF THE ACCIDENT AT THE CHERNOBYL NUCLEAR POWER PLANT AND THE PROCESSES OF DESTRUCTION OF THE REACTOR AND PREMISES OF UNIT IV

Comments

[Same lech]

Human factor...there was no default technical protection at the nuclear power plant against incorrect actions of personnel and orders from the dispatcher.

[dmi.pris1]

There are no technical measures for the human factor. There are organizational ones. Do not allow poorly trained personnel to operate. There is also training and exams. About the call from the Central Committee - nonsense.

[Olgovich]

Quote from: dmi.pris1

About the call from the Central Committee - that's nonsense.

Blatant stupidity is when public the organization is meddling in something that isn't its business instructions for technical questions:

- in the early 1980s, the Central Committee of the CPSU created Department for Supervision of Nuclear Power Plants (NPP), which included V. Maryin and G. Kopchinsky. This department was subordinate to the Secretary of the Central Committee of the CPSU, who supervised this area.

And then an official from the Department for Supervision of Nuclear Power Plants under the Central Committee of the CPSU (subordinate to the Secretary of the Central Committee of the CPSU V. Dolgikh), who had previously been the deputy chief engineer of the Chernobyl Nuclear Power Plant for science (1973-1980), called the unit and ordered Dyatlov to continue the tests: "Carry out an inspection! Either you retire or you become the chief engineer of the new Chernobyl NPP-2." This certificate was based on the fact of wiretapping of telephone conversations on the block during his participation in the investigation of the cause of the accident and confirmed by him also in two television interviews. The fact of the call is also confirmed by the former deputy director of the Chernobyl Nuclear Power Plant, Alexander Kovalenko.

It is clear that the station's technical specialists are still to blame, but pressure is unacceptable in any case.

[Doctor]

No one called. Why the author is repeating this nonsense for the 4th time is unclear.
Here is an interview with the "caller" Kopchinsky:

https://gak-2000.livejournal.com/655.html?ysclid=mf899zh3gf494397428

There are videos, and more than one, where all this has been discussed a long time ago.

[Olgovich]

Quote: Arzt

https://gak-2000.livejournal.com/655.html?ysclid=mf899zh3gf494397428

I read it, thank you.

Kopchinsky is convincing, I agree, I think that there was no call after all.

[Podvodnik]

. interferes in other people's business - with instructions on

In the navy I have repeatedly encountered situations where "big stars", not understanding the essence of the issue, gave illiterate instructions or made demands that went beyond the capabilities of the equipment. And it was impossible to convince them otherwise.

[barbos]

There are no technical measures for human factors

A lot of automation is designed with the Black Sea Fleet in mind, much of it is designed to exclude the Black Sea Fleet if possible.

There are organizational ones. Do not allow poorly trained personnel to operate.

At one time, Academician Sakharov was categorically against handing over nuclear facilities to power engineers. He saw with his own eyes the difference between the responsibility of military and civilian power engineers.

[dmi.pris1]

I myself worked at a power plant, a thermal one, though. 20 years in the thermal automation and measurements shop. I did my internship in Desnogorsk. In the electronics shop. The AZ is done in no time. True, all this is recorded and reported to the DIS, the shift supervisors of the shops where the work takes place. Later, all this was tightened. The responsibility of the military and civilians is very controversial. But you are right about the design of automation, blocking, protection.

[barbos]

In the electronics shop.AZ is a piece of cake

You haven't seen the control panel of an automatic sorting hump yet, where all the switches are sealed. But even that doesn't help!

[dmi.pris1]

I readily believe it, I did it myself. But again, by order, with an entry in the log of orders and instructions

[barbos]

Here's a question for you as a person in the subject. Which emergency in a military unit is more terrible:
- the missing machine gun from the KHO?
or
- a broken seal on special communications equipment?

[dmi.pris1]

The special agents will immediately work on the broken seal. So, it will be more scary. Although for the loss from the KHS the soul will also be taken out.

[Alexander Odintsov]

You are right, at that time the personnel could turn off many important protections themselves, which was done so that the shutdown of the reactor by these means of protection could not interfere with the experiment to a victorious end. And so all the necessary protections were there, but a number of important ones, primarily for the shutdown of both turbo generators, were turned off.

[Podvodnik]

. but a number of important .... . were disabled

I once asked my reactor operators at sea to read the log of accidents and breakdowns. There are ALL nuclear accidents and incidents. My answer was: "Why do you need this, I'll tell you anyway..." Well, I told you. The main point was the absolutely illiterate actions of the personnel, violating everything possible, a complete lack of understanding of the processes occurring in the reactor. Well, and the result... .
The accident was caused by the actions of the personnel, which were absolutely illiterate and criminal. No defense will help here.
A few years ago, a plane crashed in the mountains in Europe. Everyone died.
When we listened to the flight recorders, our hair stood on end. One of the pilots went to the toilet, and the other closed the door, set the altitude in the autopilot to "zero" and just sat there. And on the recording, screams from the cabin and attempts to open the door were heard. Is the plane to blame? Was there no "fool" protection?
In Chernobyl they also acted consciously, but due to ignorance they did not understand where they would “land”.

[Doctor]

You are right, at that time the personnel could turn off many important protections themselves, which was done so that the shutdown of the reactor by these means of protection could not interfere with the experiment to a victorious end. And so all the necessary protections were there, but a number of important ones, primarily for the shutdown of both turbo generators, were turned off.

Alexander, one more simple question.

WHY did the staff turn off the protection?

[Alexander Odintsov]

The staff allegedly intended to repeat the experiments in case of failure. According to the report (No. 1 INSAG-1): "The existing A3 for closing the SRK of two TGs (TG No. 7 was disconnected in the afternoon on April 25, 1986) was blocked to be able to repeat the test if the first attempt was unsuccessful. Thus, another deviation from the test program was made…."

[Subtext]

I subscribed to the Kommunist magazine. At the end of the year, a sealed brown envelope arrived by mail, containing a special issue of the Kommunist magazine dedicated to the Chernobyl accident. Lots of words, but the thesis about the specialists was reinforced. The manager is assembling his team. At the Chernobyl Nuclear Power Plant, the turbine managers skewed in favor of the turbine specialists. They wrote like that in 86. Like, it had an effect too.

[Podvodnik]

. .there was no default technical protection against incorrect actions at the nuclear power plant

How could it not be? Everything was there. And everything worked. You just shouldn't allow ignoramuses to work with complex technology. It's like a monkey with a grenade.
The reactor was driven into this mode deliberately, manually. Maybe it will pass. And even stupid adherence to the regulations would have prevented the catastrophe. But there are "smart" and "devoted to the cause of the CPSU".
And if the personnel had an idea of ​​the processes they were managing, it would not have come close to an accident. If there is no understanding in the head of what is happening, the result is unambiguous.

[Mikhail Drabkin]

For whom is this written in all the glory of the techno-dialect for nuclear engineers, and why is this an overwhelming dialogue of scientists and experts, with graphs and instructions?

Why is Academician Legasov, this almost Sakharov, mentioned, and Boris Evdokimovich Shcherbina, Deputy Chairman of the Council of Ministers of the USSR, and the true driving force behind all the most important steps to mitigate the immediate risks and consequences of the accident, not mentioned? That is where the positive human factor and the true courage of the responsible person were…

[123_123]

The passage about the call from the Central Committee was possibly a hoax to denigrate the CPSU, as part of the process of liberalizing the country.

[your1970]

Quote: 123_123

The passage about the call from the Central Committee was possibly a hoax to denigrate the CPSU, as part of the process of liberalizing the country.

The investigation would either confirm or deny. If it didn't confirm, it's a lie in the testimony, another article.
It's not a matter of throwing something in...

[Doctor]

The investigation would either confirm or deny. If it didn't confirm, it's a lie in the testimony, another article.
It's not a matter of throwing something in...

During the investigation, there was no talk of any calls. And Dyatlov didn't even hint at anything like that, although he could have been given a death sentence.
He would certainly have used all the opportunities and would not have tried to cover up the mythical official from the Central Committee. And the official himself would not have been spared, as you rightly say - that would not have been the case...

And this official got promoted after Chernobyl.
A pure fabrication, Komarov’s personal motives.
https://gak-2000.livejournal.com/655.html?ysclid=mf899zh3gf494397428

[Alexander Odintsov]

There was no denigration. These facts were confirmed by Komarov.

[Doctor]

The passage about the call from the Central Committee was possibly a hoax to denigrate the CPSU, as part of the process of liberalizing the country.

There are personal showdowns between a boss and a subordinate:

https://gak-2000.livejournal.com/655.html?ysclid=mf899zh3gf494397428

[Alexander Odintsov]

The fact of the call is also confirmed by the former deputy director of the Chernobyl Nuclear Power Plant, Alexander Kovalenko. However, the said person categorically denies such a possibility.

[Same lech]

Quote from: dmi.pris1

There are no technical measures for human factors

There are...for example...the polarity of devices, the diameter of the threads in the sensors...their geometry does not allow them to be inserted into the mounting places differently, and so on...
Remember the incident with our rocket with 17 satellites... somehow the assemblers managed to insert the most important sensor the wrong way around... that's the human factor... the sensor had to be made in such a way that even out of stupidity it couldn't be inserted anywhere else... except where it was intended.

[Alexander Odintsov]

Yes, there was no foolproofing there. Academician Aleksandrov spoke about this exactly. In general, the RBMK was raw and unfinished at that time. They were in a hurry or built a lot for development and economic reasons. The project itself, compared to VVER, is not safe and complex, but its economics were good.

[Non-fighter]

Naive!!! You underestimate the strength of our specialists!!! They are really STRONG, at least I saw two connected plug-in connectors of the "male" type when I worked at the plant in the 90s, that is, the pin parts of the connectors were connected to each other and 380V power was supplied to this structure!!!! In short, then we had to re-solder this entire structure (the electricians there were no longer trusted), and there were about 50 contacts:(
P.S. Let me remind you that all this happened in about 1995, valuable specialists had not yet been brought in.

[Podvodnik]

. I saw two connected male-type plugs,

Somehow we managed to organize training on the use of GPD. No one had loaded these products into the database or used them before us.
Well, they installed a "tray" outside (they are loaded into "grids" inside a light body). They put the product down with a crane. The miner is in charge... And suddenly he runs up, confused: "Do you have a drill?"
I was also confused: "Why?"
- There, "daddy doesn't fit in with mommy"!!!!!
-?
- I'm shocked myself, the contacts are geometrically correct, but "daddy doesn't love mommy."
Had to drill.

Well, the miner did it, I saw all the products in the seas as they should be, the tasks were solved, the shooting went well. But "mom and dad..."

[Non-fighter]

Um... maybe there was a letter in the name of some connector that was "wrong", or they installed the wrong one but "from stock", or there were two ALMOST identical connectors under one index, or maybe there was just a factory defect in the "father" or "mother".

[stankow]

On the top row, the "dad" must have identical rods. Otherwise, it will not connect.

[Conrad1045]

I remember one emergency at work. I arrived at work in the morning, an electrician came up and invited me to go up on the roof. We went up, and there was a ladder by one of the air exhaust pipes. The electrician suggested sniffing the air - the air smelled like burning. We went down, went into the process room, touched the reactor lid with his hand, and it was hot, which shouldn't be at all. So there was a process in the reactor with the release of heat. An emergency situation was declared, everything was prepared, the bolts were removed from the lid, the lid was lifted, and the smoldering was poured with water. In the process of eliminating the consequences of the emergency, it was discovered that the level sensors were not working properly - an error by the installers.

[Valery Mamai]

According to V. Komarov (former deputy director for science at the Smolensk NPP, participant in the accident investigation):

“This… absolutely should not have been done!
But the telex from KyivEnergo was duplicated by a telephone call from the Central Committee of the CPSU... And... the order was carried out...”
Worked in the technological production of the USSR for 18 years (Chief Technologist). I have never seen a service instruction for the Chief Dispatcher of the enterprise that the Chief Dispatcher of the enterprise must carry out the orders of the Central Committee of the CPSU.

[Alexander Odintsov]

The man who worked as the head of the sector previously worked at the Chernobyl Nuclear Power Plant, they say he tried in every way to show who was boss

[Valery Mamai]

The head of the Central Committee sector could prove whatever he wanted.
Only the owners of the enterprise in the USSR were the ministries, they determined the technical policy of the enterprise, and not the Central Committee. Ultimately, the director and the chief engineer are responsible for everything that happens at the enterprise. For which they paid.

[Doctor]

Worked in the technological production of the USSR for 18 years (Chief Technologist). Never once in the service instructions for the Chief Dispatcher of the enterprise did I see a clause that the Chief Dispatcher of the enterprise must carry out the orders of the Central Committee of the CPSU.

Nobody carried them out in Chernobyl. Because there were no calls))

https://gak-2000.livejournal.com/655.html?ysclid=mf899zh3gf494397428

[Non-fighter]

Well, Academician Dollezhal made me happy. Specialists must make a responsible decision! Well, you as an academician can make it, you have already earned your pension, but will you cover for those specialists in front of the Central Committee? Academician Legasov also made his mark, well, yes, you were not in the reactor control room at that moment.
The reactor was pulled in four directions at once, and the requirements in all three directions were contradictory. Let me remind you that the reactor was shut down, the dispatcher's requirement to maintain power was met, and two experiments on turbogenerator rundown and vibration measurements on it were carried out simultaneously (this is from the previous article in the series). By the way, on the screenshot of the technical regulations, paragraph 6.3 directly prohibits switching and especially experiments, or am I mistaken?

[Alexander Odintsov]

You are right. People were artificially put in conditions where they succeeded, what succeeded. There are a lot of questions here. All this is described in the two previous parts

[Doctor]

Well, Academician Dollezhal made me happy. Specialists must make a responsible decision! Well, you as an academician can make it, you have already earned your pension, but will you cover for those specialists in front of the Central Committee? Academician Legasov also made his mark, well, yes, you were not in the reactor control room at that moment.
The reactor was pulled in four directions at once, and the requirements in all three directions were contradictory. Let me remind you that the reactor was shut down, the dispatcher's requirement to maintain power was met, and two experiments on turbogenerator rundown and vibration measurements on it were carried out simultaneously (this is from the previous article in the series). By the way, on the screenshot of the technical regulations, paragraph 6.3 directly prohibits switching and especially experiments, or am I mistaken?

There was nothing simultaneous. Everything was sequential and according to the Regulations.

[Doctor]

Again, they pulled out a lot of rods, and even came up with some kind of "emergency reserve"!

A simple question for the author. THE SIMPLEST.

WHY DIDN'T THE REACTOR ACCELERATE ON FAST NEUTRONS IMMEDIATELY AFTER THEY PULLED OUT A LOT OF RODS?!

Why did he let the test go ahead and go bang 7 seconds AFTER THE RODS WENT DOWN?!

How do you explain this paradox?

[Alexander Odintsov]

The reactor was poisoned. In fact, they were able to accelerate some local zone where all this happened. And in the reactor, the acceleration process began approximately from the beginning of the rundown experiment. The rods have nothing to do with it. They saw this and pressed AZ-5, but it was too late.

[Doctor]

The reactor was poisoned. In fact, they were able to accelerate some local zone where all this happened. And in the reactor, the acceleration process began approximately from the beginning of the rundown experiment. The rods have nothing to do with it. They saw this and pressed AZ-5, but it was too late.

Well, let's say they dispersed the local zone. What does that change?
The reaction on fast neutrons is lightning fast, the reactor should have exploded IMMEDIATELY after they PULLED OUT the rods.

No AZ-5 rods would have had time to enter the zone. And they were sticking out there by a third according to the arrows.

That is THE FAST NEUTRON REACTOR ACCELERATION WAS INITIATED BY THE INTRODUCTION OF AZ RODS, and not by raising for acceleration. And this is RECORDED AND CONFIRMED BY THE COMMISSIONS.

[Alexander Odintsov]

The main argument against the official version is extremely simple - according to the same information about the accident "From the entry in the operational log... "01:24 Strong impacts, the control rods stopped before reaching the NK (lower limit switches). The clutch power key was disconnected."
The fact that the rods did not go all the way down indicates that by the time the button was pressed, the emergency process was already in full swing and its results were obvious: the active zone and channels were partially damaged, which prevented the emergency protection from working. That is, the operating reactor as such no longer existed at that moment!
It should be noted that in the first report made for the IAEA, Report No. 1 (INSAG-1), in 1986, the end effect of the rods as a factor in the accident was not considered at all.
It is also known that the AZ5 button was pressed twice (it was pressed once by the operator at 1.23.39, the second AZM-AZRS signal was generated by the automation at 1.23.41), although it had to be held down continuously for the rods to move without stopping (in the pre-accident design). This fact, according to O. Novoselsky (NIKIET), casts doubt on the effectiveness of the "displacement" effect itself: "the AZ-5 button is pressed. But the power increase is rapid, and the speed of the emergency protection rods is only 0,4 m/s. The operator decides to speed up the introduction of the absorber rods: he releases the AZ-5 button and turns to the KOM key, de-energizing the clutches of the CPS rod drives. As soon as the operator released the AZ-5 button, the absorber rods stopped. The button was held for approximately one second… during which time the rods managed to move only 0,3 m in accordance with the acceleration characteristics.”
From the absolutely authoritative testimony of Yu. Tregub, the head of the previous shift of the 4th block, it follows that the first signs of the accident were clearly audible at the moment the coastdown tests began at 01:23:04 on April 26, 1986 (before pressing the AZ5 button - time 01:23:39 on the teletype):
"The coasting experiment begins... We didn't know how the coasting equipment worked, ... the first seconds ... some kind of bad sound appeared. I thought it was the sound of a braking turbine... as if a Volga at full speed began to brake and skid. Such a sound: du-du-du-du... Turning into a roar. The building began to vibrate. Yes, I thought it was bad. But what is it - probably a coasting situation.
The control room was shaking. But not like an earthquake. If you count to ten seconds, you could hear a roar, the frequency of the vibrations was falling. And their power was growing. Then there was a bang. Because I was closer to the turbine, I thought a blade had flown out. But that's just subjective, because I've never seen anything like that before...
Kirshenbaum shouted: "Water hammer in the deaerators!" This blow was not very strong. Compared to what happened later. Although a strong blow. It shook the control room. And when the SIUT shouted, I noticed that the alarm of the main safety valves went off. Flashed through my mind: "Eight valves... open!" I jumped back, and at that moment the second blow followed. Now that was a very strong blow. Plaster fell, the whole building was going dark... the lights went out, then the emergency power was restored... The opening of one GPK [author's note - the main safety valve, designed for emergency steam release] is an emergency situation, but eight GPK - that was already something... supernatural..."
There is more than one such evidence. That same bad sound that Tregub (and not only he) heard was the real beginning of the emergency situation development, when the core was steamed, and then, due to the heat transfer crisis (lack of normal cooling of the fuel channels), the destruction of the fuel assemblies (FA) began. Those same hydraulic shocks that many also heard were a consequence of the breakdown (see below) and cavitation of the main circulation pumps. [Author's note: Cavitation is the process of formation and subsequent collapse of bubbles in a liquid flow, accompanied by noise and hydraulic shocks... As a result of the collapse of the bubbles, shock waves are formed that damage metal surfaces.] Then an explosion occurred in the reactor. Perhaps, at the very first signs of an accident, it was still possible to reset the emergency protection (but only until the moment the channels began to collapse) and start the criminally blocked emergency cooling system of the reactor SAOR.

[Doctor]

The main argument against the official version is extremely simple - according to the same information about the accident "From the entry in the operational log... "01:24 Strong impacts, the control rods stopped before reaching the NK (lower limit switches). The clutch power key was disconnected."
The fact that the rods did not go all the way down indicates that by the time the button was pressed, the emergency process was already in full swing and its results were obvious: the active zone and channels were partially damaged, which prevented the emergency protection from working. That is, the operating reactor as such no longer existed at that moment!

What do you mean "the emergency process was in full swing", the channels started to collapse? Then the sensors should already be screaming!

And they have complete silence, everything is going according to plan, the process of increasing power began suddenly, in a few seconds, AFTER pressing the AZ.
Look at your graph in the article, it is clearly visible there.

And of course the rods did not have time to enter the channels, with fast neutrons the increase in the neutron flux K1000 is in a fraction of a second!

[Alexander Odintsov]

All sensors worked as they should. As Boris Gorbachev (ISTC "Shelter" of the National Academy of Sciences of Ukraine) asks:
"... why in November 1975, at the imperfect reactor of the 1st unit of the Leningrad NPP, the automatic emergency protection system worked and shut down the reactor, and on April 26, 1986, at the much more perfect 4th unit of the Chernobyl NPP, the automatic emergency protection system did not "respond" to the emergency signal "AZM" (signal of excess power), nor to the emergency signal "AZS" (signal of excess power increase rate), nor to eight emergency signals to turn off all eight MCPs (main circulation pumps), nor to eight emergency signals for all eight UZM (power protection amplifiers), and the control system in response did not generate an emergency signal of the highest, 5th category "AZ-5" at all? ... I wonder if any of the veterans of the Chernobyl NPP will dare to reveal this "shop secret" of theirs, which ... all the official commissions did not want to reveal, and ... even the fact of its existence is carefully hushed up to this day."

[Doctor]

All sensors worked as they should. As Boris Gorbachev (ISTC "Shelter" of the National Academy of Sciences of Ukraine) asks:
"... why in November 1975, at the imperfect reactor of the 1st unit of the Leningrad NPP, the automatic emergency protection system worked and shut down the reactor, and on April 26, 1986, at the much more perfect 4th unit of the Chernobyl NPP, the automatic emergency protection system did not "respond" to the emergency signal "AZM" (signal of excess power), nor to the emergency signal "AZS" (signal of excess power increase rate), nor to eight emergency signals to turn off all eight MCPs (main circulation pumps), nor to eight emergency signals for all eight UZM (power protection amplifiers), and the control system in response did not generate an emergency signal of the highest, 5th category "AZ-5" at all? ... I wonder if any of the veterans of the Chernobyl NPP will dare to reveal this "shop secret" of theirs, which ... all the official commissions did not want to reveal, and ... even the fact of its existence is carefully hushed up to this day."

Do not confuse the SIGNAL from the sensor and AUTOMATIC protection activation.

For example, they actually blocked the protection for the AUTOMATIC shutdown of two TGs, otherwise it would not have allowed the experiment to be carried out and would have shut down the TGs back at 00.43.

But SIGNALS from the sensors went to the control panel, and if an emergency situation began to develop, the control panel would squeal. He squealed, but AFTER pressing AZ.

[Alexander Odintsov]

For example, they actually blocked the protection for the AUTOMATIC shutdown of two TGs, otherwise it would not have allowed the experiment to be carried out and would have shut down the TGs back at 00.43.

Perhaps the unit personnel did not fully appreciate the risks of closing the SRK on the remaining turbine, although the more experienced of them should have understood everything. Perhaps from their experience it followed that when the reactor was operating at 200 MW, the pressure increase would be slow. Steam could be discharged into the condensers through the device for bleeding excess steam (when the pressure increases) BRU-K.
The main steam drain in a working reactor is through the turbine. If the turbine is switched off, the drain is blocked, but the reactor continues to generate steam, which leads to an increase in pressure. This protection was created to prevent a pressure surge in the primary circuit associated with the shutdown of the turbines, when they stop consuming steam.
According to Yu. A. Potemkin, former deputy head of the GVP (Main Military Prosecutor's Office) of the USSR: "...they turned off both turbines while the reactor was running. This is madness, to put it bluntly. This led to an explosion."
As a result, the blocking of protection to block both turbogenerators under specific conditions of the accident development (see below, a sharp decrease in the feedwater level, slowdown in operation and failure of the main circulation pump) was one of the factors in the development of the accident.
As stated in the court ruling: “Fomin, Dyatlov, Kovalenko… did not regulate the removal of excess steam from the circuit.”

[Doctor]

Perhaps the unit personnel did not fully appreciate the risks of closing the SRK on the remaining turbine, although the more experienced of them should have understood everything. Perhaps from their experience it followed that when the reactor was operating at 200 MW, the pressure increase would be slow. Steam could be discharged into the condensers through the device for bleeding excess steam (when the pressure increases) BRU-K.
The main steam drain in a working reactor is through the turbine. If the turbine is switched off, the drain is blocked, but the reactor continues to generate steam, which leads to an increase in pressure. This protection was created to prevent a pressure surge in the primary circuit associated with the shutdown of the turbines, when they stop consuming steam.
According to Yu. A. Potemkin, former deputy head of the GVP (Main Military Prosecutor's Office) of the USSR: "...they turned off both turbines while the reactor was running. This is madness, to put it bluntly. This led to an explosion."
As a result, the blocking of protection to block both turbogenerators under specific conditions of the accident development (see below, a sharp decrease in the feedwater level, slowdown in operation and failure of the main circulation pump) was one of the factors in the development of the accident.
As stated in the court ruling: “Fomin, Dyatlov, Kovalenko… did not regulate the removal of excess steam from the circuit.”

Alexander, well, think for yourself, is it really true that in such a large samovar as the RBMK, there is no way to regulate steam?
This is the main dangerous factor of steam mechanisms, thermal power plants also work on this principle. And here, on a single-circuit scheme, where the steam is radioactive... Prosecutor Potemkin probably thought that without turbines there was nowhere for the couple to go. There, even at maximum power, both turbines can be turned off, the steam will simply go into the whistle, although yes, the protection will shut down the reactor in this case.

But the main thing is that all these fabrications of Zhiltsov and others are not confirmed by documents based on sensor data.
The pressure in the circuit was EQUAL until the AZ was pressed, and the reactor power according to the intra-zone sensors of the SFKRE was the same.
Look again at your chart - from 0.40 after the failure it grew a little, and from 01.00 it was a plateau.
Although it should jump according to your logic, there is already steam instead of water.

[Alexander Odintsov]

The acceleration initially occurred in a narrow zone. Then the process went into fractions and milliseconds. According to the GPAN report (1991), immediately before the tests at 01:22:30:
“Under the conditions that arose, a small increase in reactor power (for any reason) due to a small underheating of the coolant to boiling could lead to an increase in the volumetric steam content in the lower part of the active zone... Thus, before the start of the tests, the parameters of the active zone caused an increased susceptibility of the reactor to the self-acceleration process in the lower part of the active zone... such a condition was created not only because there was an increased coolant flow rate compared to the usual..., but above all because of the low value of the reactor power.”
The reactor remained running at capacity with both turbogenerators switched off! Since the steam flow stopped, its pressure began to increase due to the reduction in steam consumption from the BS.
The increase in steam content was predetermined by the slowdown of half of the operating MCPs, which were connected to the current source from the running-down (stopping) turbine. According to the opinion of the RBMK chief designer, an additional reason that led to the rapid onset of steam generation in the reactor core immediately before its acceleration could have been the shutdown of the running-down MCPs by their own protections for reducing the current in the stator windings of the pump motors. According to K. Checherov, as a result of the operation of the first stage of the minimum voltage protection, four of the eight MCPs were switched off within 0,7 s in the period from 1.23'39,9" to 1.23'40,6".
After disconnecting the MCPs, powered by TG8 voltage protection, the supply of the remaining MCPs was disrupted due to cavitation during flow overload (insufficient suction pressure).
As K. Checherov writes: "The reduction in feedwater supply to the run-down PENs was more intense with a decrease in the network frequency. As a result, the TG run-down mode (and a certain time interval before it began) occurred with a virtually complete absence of feedwater supply to the reactor under conditions of virtually complete extraction of the absorber rods from the active zone...
The increase in the neutron flux density, which ensured an increase in the thermal power of the reactor, should have led to a sharp decrease in xenon poisoning of the reactor and an even greater increase in the neutron flux density and a corresponding increase in energy release."
According to O.Yu. Novoselsky, after almost complete cessation of the feedwater supply, boiling occurs in the upper part of the fuel channels. From the active zone, the steam-water mixture begins to flow into the drums - separators, the process of replacing the main water volume of the separators with water at the saturation (boiling) temperature is underway. After the start of the rundown tests, at 1.23.04, the steam supply to the turbine is stopped, but the reactor continues to operate and the pressure in the circuit begins to increase. Saturated (boiling) water flows into the pipes from the separators, after 2530-XNUMX seconds, due to the proximity of the water temperature to the saturation (boiling) point, cavitation develops on the SRV [author's note - shut-off and control valve, a device designed to regulate and control the flow of water through process channels].
Cavitation is the formation of cavities (cavitation bubbles, or caverns) in a liquid filled with steam... Moving with the flow... the cavitation bubble collapses, emitting a shock wave and a significant release of energy.
The version about coolant cavitation in the SAM is based on experimental data proving that when the coolant temperature at the reactor inlet is close to the boiling point, the coolant boils in the SAM grooves, and the steam generated in this process gets to the inlets of the reactor fuel channels.
The length of the water communication pipelines from the air defense missile system to the inputs to the process channels is from 5,5 to 24 m; the steam-water mixture travels this distance in one to six seconds and then enters the inputs to the various fuel channels.
Then there is a sharp increase in steam formation in the channels due to the positive steam effect of reactivity, associated with the fact that steam, due to its low density, is a worse absorber of neutrons than water, which provokes a sharp increase in the reactor power due to acceleration on prompt neutrons. This process is accelerated by a powerful positive feedback mechanism: the increase in steam content causes an increase in energy release, in turn, provoking even greater steam production, etc. In addition, acceleration includes the process of "burning" xenon, which also intensifies the chain reaction. These processes cause the destruction of technological channels and the explosion of the reactor.
According to INSAG-1 report No. 1, the increase in steam pressure against the background of a sharp drop in the supply of feedwater to the BS with a decrease in the flow of water through the reactor caused an increase in the reactor power, which was most likely the reason for pressing the AZ button.
From the story of witness Lysyuk G.V. (master of the EC), it follows that before Toptunov pressed AZ-5, he managed to shout: “The reactor power is growing at an emergency rate!”

[Doctor]

According to INSAG-1 report No. 1, the increase in steam pressure against the background of a sharp drop in the supply of feedwater to the BS with a decrease in the flow of water through the reactor caused an increase in the reactor power, which was most likely the reason for pressing the AZ button.
From the story of witness Lysyuk G.V. (master of the EC), it follows that before Toptunov pressed AZ-5, he managed to shout: “The reactor power is growing at an emergency rate!”

BEFORE the AZ button was pressed, there was NO increase in steam pressure, so it did NOT CAUSE an increase in reactor power. See the graphs in the comment above again.

Lysyuk is quite a witness, he forgot to press his button, and came to after Metlenko’s command. He was at the other end of the console and did not hear Akimov's first calm command to Toptunov. But Metlenko was nearby and heard:
".....The rundown lasted for about 40 seconds, and then there was a failure. Before that, I believe, everything was done in full compliance with the test program. As far as I know, according to the program and in fact, 8 MCPs were operating during the rundown. I did not observe any deviations from the norm in the operation of the MCPs. The rundown itself lasts no more than 1-2 minutes. The MPA button was practically operated by foreman Mole, he did its installation, and the button was pressed on my command by senior foreman Lysyuk. When all this was done, the turbo generator calmly began to reduce its speed, I was monitoring the speed. When it was about 2500 rpm, the unit shift supervisor, turning to the reactor operators, calmly gave the command "shut down the reactor". After that, some more time passed, the speed dropped to 2100 rpm and at that time the explosion occurred...."

[Alexander Odintsov]

Dear Arzt! You reason competently, but this reasoning is formal. And the facts are that the reactor flew up into the clouds and this is the dry residue. The version of the reactor acceleration due to the end effect is questionable. It was invented to hide the real causes of the accident. Including possible sabotage. The second hypothesis is simple, that the personnel brought the reactor into a state in which it could accelerate at any moment. Just give it a push. And this is indicated by the official conclusions of the commissions cited above and the opinions of professional experts. Choose whatever you like. There is no point in saying that the personnel are not guilty. To say that they were all framed, including Dyatlov - that is true. The accident was provoked by a sector of the CPSU Central Committee and this is an obvious fact, although not legally proven. There will be a new investigation and all this will be revealed.

[Doctor]

Dear Arzt! You reason competently, but this reasoning is formal. And the facts are that the reactor flew up into the clouds and this is the dry residue. The version of the reactor acceleration due to the end effect is questionable. It was invented to hide the real causes of the accident. Including possible sabotage. The second hypothesis is simple, that the personnel brought the reactor into a state in which it could accelerate at any moment. Just give it a push. And this is indicated by the official conclusions of the commissions cited above and the opinions of professional experts. Choose whatever you like. There is no point in saying that the personnel are not guilty. To say that they were all framed, including Dyatlov - that is true. The accident was provoked by a sector of the CPSU Central Committee and this is an obvious fact, although not legally proven. There will be a new investigation and all this will be revealed.

It is precisely all these murky versions that are dubious. Because they are not supported by facts.
And as for the end effect, everything has been proven, but if not, suggest to the guys from NIKIET to remake the rods back, as they were in Chernobyl.

[Alexander Odintsov]

There is another version - sabotage. It was also published on VO. Why was it decided to conduct the experiment at the Chernobyl Nuclear Power Plant, which "was the only nuclear power plant where neither the director nor the chief engineer were nuclear specialists at all..."? Why was the main motive of the personnel's behavior the desire to finish the tests faster or, more precisely, to complete them at all costs? Why was the personnel not familiarized with the experiment program in advance? Why were the tests assigned to the most inexperienced shift, which was not reinforced by more experienced specialists!? Why were representatives of the nuclear safety department not present during the tests!? Why was it necessary to burden the experiment with another complex program of vibration tests of the turbine, given that these two experiments are incompatible!? Why was it necessary to turn off a significant part of the automatic reactor protection systems and the emergency cooling system (ECCS)!? What was the need to conduct the experiment on a working reactor, which contradicted the entire previous history of these tests!? Why was it necessary to conduct tests at a low (6% of nominal) power of 200 MW, which is not intended for reactor operation, when the program required operation at a power of 700 MW!? Why did the personnel not stop the experiment either after the reactor shut down itself or after the number of rods in the zone fell below the standard? ... etc. Are there too many oddities for this whole story?

[Doctor]

There is another version - sabotage. It was also published on VO. Why did they decide to conduct the experiment at the Chernobyl Nuclear Power Plant, which "was the only nuclear power plant where neither the director nor the chief engineer were nuclear specialists at all..."?

The experiment had to be timed to coincide with the reactor shutdown for repairs. After the fundamental decision to conduct it was made, the first one to be shut down was the 3rd power unit at ChASE in 1982. That's where it was conducted for the first time.
And then the topic was fixed on the Chernobyl Nuclear Power Plant, they supposedly already have experience...

[Doctor]

Why was the main motive of the personnel's behavior the desire to finish the tests faster, or more precisely, to bring them to completion, no matter what?

A natural desire in the USSR. There was no "at all costs". Reduced power - increased power, that's all.

Nobody knew that this couldn’t be done (by the way, it can be done, but the ignition rods must be normal).

[Doctor]

Why wasn't the staff familiarized with the experimental program in advance? Why were the tests assigned to the most inexperienced shift, which was not reinforced by more experienced specialists!?

And it was not entrusted to the most inexperienced shift, you yourself write in your investigations:
"The experiment was planned to be carried out on Friday, April 25, 1986, during the day, during Igor Ivanovich Kazachkov's shift, which worked from 8 a.m. to 16 p.m. On that day, the fourth unit of the Chernobyl Nuclear Power Plant was scheduled to be shut down for scheduled repairs."

That's why they didn't introduce it. For Akimov and others it was an impromptu.

Moreover, Tregub and other "experienced" were present at the BShChU-4 and actively participated in the work:

"I told Toptunov which rods were best to choose. He did as he knew.
I also noticed Dyatlov behind me. And when we raised the reactor power to 200 MW, I returned to the SIUT control panel. When I looked at the distribution field for the last time before the accident, the SIUR had pulled out about half of the rods close to the limit switches, and the rest were about two meters away. The last ORM value that I saw was that there were about 19 rods in the active zone."

Do you get the point? Experienced Tregub SUGGESTED, but got away with it. And inexperienced Toptunov was buried.

[Doctor]

Why weren't representatives from the nuclear safety department present during the tests!?

This was a routine experiment, it was not the first time. I think you are aware that even now, despite the accident, many different experiments are being conducted at our nuclear power plants. And representatives of nuclear safety are not always present there.

[Doctor]

Why was it necessary to burden the experiment with another complex program of vibration tests of the turbine, given that these two experiments are incompatible!?

There was nothing particularly complicated there; for the reactor operators, it was the usual work of shutting down, and the rest was handled by specialists in the field, including those who arrived from the turbine plant.
The tests were carried out SEQUENTIALLY.

[Alexander Odintsov]

Here we can make the most important and very significant conclusion - if the vibration tests had been conducted earlier and there had been no combination of both tests, the accident could most likely have been avoided. But here a fatal coincidence occurred.
Let's see what the main expert on the accident, O. Novoselsky (NIKIET), writes about this:
“Two tests were to be carried out (who came up with this idea?): first, measuring the vibrations of TG8 at idle, then testing the TG8 rundown with a load of four RCPs and one feed pump. “On the go,” having familiarized themselves with the test programs, the shift began work. To conduct the first tests at idle of TG8, it was necessary to reduce the steam capacity, i.e. the reactor power. ... Rundown tests began. At 1.23.04, the turbine RVC closed, and the TG8 rundown began with a load of four RCPs and one feed pump. However, the reactor remained at power, since the connection between the RVC and the AZ-5 logic was broken [for this purpose, the protection for blocking the RVC of both turbines was disabled]. This connection interfered with the previous tests - measuring the vibrations of TG8 at idle. For these tests, it was necessary to almost completely close the RVC in order to ensure the minimum steam consumption required for idle. There was a risk of "touching" the AZ-5 setting and shutting down the reactor. And the TG8 rundown test program required the reactor to be at 700 MW in the initial state. Here, the nuclear reactor was treated like a heating boiler: the power was reduced to almost zero, the vibrations were measured, and now we will raise it to the program value of 700 MW. No one remembered about any xenon poisoning or reactivity reserves…"
Novoselsky writes about the obvious fact that in order to conduct vibration tests it was necessary to reduce the reactor power, and also that the connection of the SRK with the AZ-5 (i.e. protection for disconnecting both TGs) was broken. V. Zhiltsov also says this - in order to conduct vibration tests the personnel turned off the protection for both TGs, but then "forgot" to turn it on:
“In order to conduct vibration tests on the turbo generator, they removed one protection, and after they completed these tests, they forgot to put this protection back in…
The reactor was supposed to be automatically shut down by the signal "disconnection of two turbines". But one turbine was already stopped, and on the 8th, on which that ill-fated "rundown" was checked, the protection was blocked, since they "forgot" to unlock it after the end of the vibration tests. This is a serious fault of the personnel. Therefore, the reactor continued to operate for almost 30 seconds [which caused the reactor to run away] after the turbine was disconnected, after which an attempt was made to shut it down with the AZ-5 button.. "

[Doctor]

Here we can make the most important and very significant conclusion - if the vibration tests had been conducted earlier and there had been no combination of both tests, the accident could most likely have been avoided. But here a fatal coincidence occurred.
Let's see what the main expert on the accident, O. Novoselsky (NIKIET), writes about this:
“Two tests were to be carried out (who came up with this idea?): first, measuring the vibrations of TG8 at idle, then testing the TG8 rundown with a load of four RCPs and one feed pump. “On the go,” having familiarized themselves with the test programs, the shift began work. To conduct the first tests at idle of TG8, it was necessary to reduce the steam capacity, i.e. the reactor power. ... Rundown tests began. At 1.23.04, the turbine RVC closed, and the TG8 rundown began with a load of four RCPs and one feed pump. However, the reactor remained at power, since the connection between the RVC and the AZ-5 logic was broken [for this purpose, the protection for blocking the RVC of both turbines was disabled]. This connection interfered with the previous tests - measuring the vibrations of TG8 at idle. For these tests, it was necessary to almost completely close the RVC in order to ensure the minimum steam consumption required for idle. There was a risk of "touching" the AZ-5 setting and shutting down the reactor. And the TG8 rundown test program required the reactor to be at 700 MW in the initial state. Here, the nuclear reactor was treated like a heating boiler: the power was reduced to almost zero, the vibrations were measured, and now we will raise it to the program value of 700 MW. No one remembered about any xenon poisoning or reactivity reserves…"
Novoselsky writes about the obvious fact that in order to conduct vibration tests it was necessary to reduce the reactor power, and also that the connection of the SRK with the AZ-5 (i.e. protection for disconnecting both TGs) was broken. V. Zhiltsov also says this - in order to conduct vibration tests the personnel turned off the protection for both TGs, but then "forgot" to turn it on:
“In order to conduct vibration tests on the turbo generator, they removed one protection, and after they completed these tests, they forgot to put this protection back in…
The reactor was supposed to be automatically shut down by the signal "disconnection of two turbines". But one turbine was already stopped, and on the 8th, on which that ill-fated "rundown" was checked, the protection was blocked, since they "forgot" to unlock it after the end of the vibration tests. This is a serious fault of the personnel. Therefore, the reactor continued to operate for almost 30 seconds [which caused the reactor to run away] after the turbine was disconnected, after which an attempt was made to shut it down with the AZ-5 button.. "

Novoseltsev writes in a rather vague way; it’s unclear what happened when.

Take another look at the graph:
0.30 - power failure. They start to rise.
0.42 approximately, when the power is about 150 MW - vibration measurements begin.
01.16 approximately - finish measuring vibration. 34 minutes approximately - measurement.
01.23.04 - closed the valves to the turbine. Approximately 7 minutes after the end of the vibration measurement.
The run-out experiment has begun.
01.23.40 - AZ pressed. After 3 seconds, emergency signals started flying, after 7 seconds - explosion.
The AZ button was pressed late, that's true. It should have been pressed right after closing. Why Toptunov was so slow - no one will ever know, he was probably worried, Akimov told him - "turn it off".

But there is no objective data, either on the oscilloscope or on the sensors, that a reaction has started in these seconds. Neither pressure, nor neutron flux density - nothing. Everything is calm, like in Baghdad.
This is not surprising, the power is only 200, the reactor is "smoldering" and not burning, the steam flow to the turbine was already at a minimum, they simply closed the valves. Everything is in balance, in short.

Once again, this is OBJECTIVE DATA.

And only after pressing AZ - it started.

[Doctor]

Why was it necessary to turn off a significant part of the automatic reactor protection systems and the emergency cooling system (ECS)!? What was the need to conduct an experiment on a working reactor, which contradicted the entire previous history of these tests!?

All questions to the author of the program. You don't think that Dyatlov decided to have fun on the reactor out of boredom. Dollezhal and Co. invented it.

But I see that you don’t know the true background of this program’s appearance...

[Alexander Odintsov]

Let us cite the court's ruling regarding the testing program: "... the testing program was drawn up by the Dontekhenergo brigade engineer Metlenko G.P., who did not have the necessary knowledge and experience in operating nuclear reactors. This program was not properly developed by Bryukhanov, Fomin, Dyatlov and Kovalenko, although it contained significant deviations from the technological regulations. Despite this, Fomin, Dyatlov and Kovalenko signed it. In accordance with this program, the personnel subsequently carried out the tests that ended in the accident on April 26, 1986... The testing program had to be agreed upon with the Scientific Director, Chief Designer, Chief Engineer, Gosatomenergonadzor and the deputy chief engineer of the station for science, but this was not done either."

[Doctor]

Let us cite the court's ruling regarding the testing program: "... the testing program was drawn up by the Dontekhenergo brigade engineer Metlenko G.P., who did not have the necessary knowledge and experience in operating nuclear reactors. This program was not properly developed by Bryukhanov, Fomin, Dyatlov and Kovalenko, although it contained significant deviations from the technological regulations. Despite this, Fomin, Dyatlov and Kovalenko signed it. In accordance with this program, the personnel subsequently carried out the tests that ended in the accident on April 26, 1986... The testing program had to be agreed upon with the Scientific Director, Chief Designer, Chief Engineer, Gosatomenergonadzor and the deputy chief engineer of the station for science, but this was not done either."

Alexander, just post it here:

1. "On the coasting mode". Letter from NIKIET, outgoing No. 040-9253 dated 24.11.76/XNUMX/XNUMX.
2. Letter from the Institute GIDROPROEKT dated 12.02.82, No. 11, RZ –70 – 1292.

And we will honor...

[Alexander Odintsov]

Ok, I'll post it when I have time. But no one has approved the program itself, that's a fact.

[Doctor]

Why was it necessary to conduct tests at a low (6% of the nominal) power of 200 MW, which is not intended for reactor operation, when the program required operation at a power of 700 MW!?

Power is not important. What is important is the initial TURBINE SPEED. They also measured the dynamics of its decrease.
It just so happened that we failed, it happened to everyone, as Dyatlov writes.

[Doctor]

Why didn’t the staff stop the experiment either after the reactor shut down itself or after the number of rods in the zone fell below the standard?

So, this is an unusual situation, we decided to speed it up a bit, but this is not prohibited by the regulations.

There was no drop below the standard, Tregub said in court - 19 rods.
He also testifies:
- The control rods became the fuse of the accident. The station would not have exploded due to the mistakes made by the personnel.

[tank64rus]

He participated in the emergency response at the Chernobyl Nuclear Power Plant in 1986-1987. He went to Unit 4 with volunteers in October 1986. He heard rumors of sabotage at the plant from plant personnel.

[Alexander Odintsov]

Thank you, I was there at Unit 3 in early 1986. Honestly, no one at NIKIET or VNIIAES talked about it at the time. I was there a lot in 1988-89, and I knew the Chernobyl Nuclear Power Plant management, but no one said anything. But now it's clear that this was a possibility. Thanks for the information!

[Alexander Odintsov]

Let us cite the authoritative opinion of O.Yu. Novoselsky (NIKIET) on the popularity of the end effect version: "the version was liked... for two reasons: firstly, the pointer was automatically transferred to the chief designer; secondly, it is a very clear and simple explanation of what happened at the 4th power unit of the Chernobyl Nuclear Power Plant on April 26, 1986. The operating personnel especially liked the version, their position is clear: why admit to some incorrect actions, all the blame will be on them anyway. Which, by the way, is what happened at the initial stage of the investigation."
The second most important reason for concealing the true causes of the accident is that it paints a rather paradoxical picture of the accident: if you dig to the very end, find out who was the direct customer of the experiment, then who supervised the "experiment" (and the "ends" go to the level of the Central Committee of the CPSU (!) see item I), think about who in turn stood behind them - then who (!) or what will be there? Therefore, all this still (!) well-organized massive PR of the official and other false versions (earthquake, various connections with the Chernobyl 2 radar station "Duga" (see the paradoxical film "Russian Woodpecker" filmed by the trio Ukraine, Great Britain, USA, about how the accident was allegedly fabricated by a high-ranking official from Moscow in order to conceal the failure of "Duga"), the explosion of ammunition under the reactor, etc.) is aimed at concealing this information. To this day, you can find a lot of experts from the "Chernobyl party" on forums who will prove that "everything was fine" before the AZ-5 button was pressed. And this also does not look at all accidental.

[Doctor]

Let us cite the authoritative opinion of O.Yu. Novoselsky (NIKIET) on the popularity of the end effect version: "the version was liked... for two reasons: firstly, the pointer was automatically transferred to the chief designer; secondly, it is a very clear and simple explanation of what happened at the 4th power unit of the Chernobyl Nuclear Power Plant on April 26, 1986. The operating personnel especially liked the version, their position is clear: why admit to some incorrect actions, all the blame will be on them anyway. Which, by the way, is what happened at the initial stage of the investigation."
The second most important reason for concealing the true causes of the accident is that it paints a rather paradoxical picture of the accident: if you dig to the very end, find out who was the direct customer of the experiment, then who supervised the "experiment" (and the "ends" go to the level of the Central Committee of the CPSU (!) see item I), think about who in turn stood behind them - then who (!) or what will be there? Therefore, all this still (!) well-organized massive PR of the official and other false versions (earthquake, various connections with the Chernobyl 2 radar station "Duga" (see the paradoxical film "Russian Woodpecker" filmed by the trio Ukraine, Great Britain, USA, about how the accident was allegedly fabricated by a high-ranking official from Moscow in order to conceal the failure of "Duga"), the explosion of ammunition under the reactor, etc.) is aimed at concealing this information. To this day, you can find a lot of experts from the "Chernobyl party" on forums who will prove that "everything was fine" before the AZ-5 button was pressed. And this also does not look at all accidental.

Alexander, you are partly right, but you are digging in the wrong direction a little.

If the Central Committee is involved here, then the main question should be:

WHAT FOR?

Why was some ordinary experiment, at one of the many nuclear power plants in the USSR, needed even by the Central Committee itself?

[Alexander Odintsov]

The solution to the question of the time of the explosion and the pressing of the button was proposed by a very interesting hypothesis by Boris Gorbachev (the Shelter Center of the National Academy of Sciences of Ukraine), who is the most consistent critic of the official version:
“… in 1997, a serious scientific work was published, in which, based on the analysis of seismograms obtained at three seismic stations located at a distance of 100-180 km from the Chernobyl Nuclear Power Plant, the most accurate data on this incident were obtained. From them it followed that at 1 hour 23 minutes 39 seconds (±1 second) local time, 10 km to the east of the Chernobyl Nuclear Power Plant, a “weak seismic event” occurred… The TNT equivalent of its intensity was 10 tons…”
According to Gorbachev's version, which has very strong objective grounds, this signal could only have been caused by an explosion at the Chernobyl Nuclear Power Plant itself, since the version that the Chernobyl accident was caused by some mysterious earthquake that occurred 10 seconds before the accident does not stand up to criticism. It follows that most likely, the explosion occurred not 10 seconds later (at 01:23:49, approximately at 1:24 am) after the button was pressed, but immediately before it was pressed (or at the moment of pressing), while, according to B. Gorbachev, the main primary data on the accident could have been falsified (!) The time of recording the shock coincides amazingly precisely with the time the AZ5 button was pressed (!). It should be said that exactly the same analysis was conducted back in 1999 by the legendary accident researcher K. Checherov, however, the text of his work is difficult to find and little known.

[Alexander Odintsov]

There is another version (see Zhiltsov) that they kind of forgot to turn it on. Let's see what the main expert on the accident, O. Novoselsky (NIKIET), writes about it:
“Two tests were to be carried out (who came up with this idea?): first, measuring the vibrations of TG8 at idle, then testing the TG8 rundown with a load of four RCPs and one feed pump. “On the go,” having familiarized themselves with the test programs, the shift began work. To conduct the first tests at idle of TG8, it was necessary to reduce the steam capacity, i.e. the reactor power. ... Rundown tests began. At 1.23.04, the turbine RVC closed, and TG8 rundown began with a load of four RCPs and one feed pump. However, the reactor remained at power, since the connection between the RVC and the AZ-5 logic was broken [for this purpose, the protection for blocking the RVC of both turbines was disabled]. This connection interfered with the previous tests of measuring the vibrations of TG8 at idle. For these tests, it was necessary to almost completely close the RVC in order to ensure the minimum steam consumption required for idle. There was a risk of "touching" the AZ-5 setting and shutting down the reactor. And the TG8 rundown test program required the reactor to be at 700 MW in the initial state. Here, the nuclear reactor was treated like a heating boiler: the power was reduced to almost zero, the vibrations were measured, and now we will raise it to the program value of 700 MW. No one remembered about any xenon poisoning or reactivity reserves…"
Novoselsky writes about the obvious fact that in order to conduct vibration tests it was necessary to reduce the reactor power, and also that the connection of the SRK with the AZ-5 (i.e. protection for disconnecting both TGs) was broken. V. Zhiltsov also says this: in order to conduct vibration tests the personnel switched off the protection for both TGs, but then "forgot" to turn it on:
“In order to conduct vibration tests on the turbo generator, they removed one protection, and after they completed these tests, they forgot to put this protection back in…
The reactor was supposed to be automatically shut down by the signal "shutdown of two turbines"But one turbine was already in operation, and on the 8th, on which that ill-fated "run-down" was tested, the protection was blocked, since they "forgot" to unblock it after the end of the vibration tests. The personnel are seriously at fault for this. That is why the reactor continued to operate for almost 30 seconds [which caused the reactor to run away] after the turbine was turned off, after which an attempt was made to shut it down with the AZ-5 button..»

[Doctor]

It should be noted that in the first report made for the IAEA, Report No. 1 (INSAG-1), in 1986, the end effect of the rods as a factor in the accident was not considered at all.
It is also known that the AZ5 button was pressed twice (it was pressed once by the operator at 1.23.39, the second AZM-AZRS signal was generated by the automation at 1.23.41), although it had to be held down continuously for the rods to move without stopping (in the pre-accident design). This fact, according to O. Novoselsky (NIKIET), casts doubt on the effectiveness of the "displacement" effect itself: "the AZ-5 button is pressed. But the power increase is rapid, and the speed of the emergency protection rods is only 0,4 m/s. The operator decides to speed up the introduction of the absorber rods: he releases the AZ-5 button and turns to the KOM key, de-energizing the clutches of the CPS rod drives. As soon as the operator released the AZ-5 button, the absorber rods stopped. The button was held for approximately one second… during which time the rods managed to move only 0,3 m in accordance with the acceleration characteristics.”
From the absolutely authoritative testimony of Yu. Tregub, the head of the previous shift of the 4th block, it follows that the first signs of the accident were clearly audible at the moment the coastdown tests began at 01:23:04 on April 26, 1986 (before pressing the AZ5 button - time 01:23:39 on the teletype):
"The coasting experiment begins... We didn't know how the coasting equipment worked, ... the first seconds ... some kind of bad sound appeared. I thought it was the sound of a braking turbine... as if a Volga at full speed began to brake and skid. Such a sound: du-du-du-du... Turning into a roar. The building began to vibrate. Yes, I thought it was bad. But what is it - probably a coasting situation.
The control room was shaking. But not like an earthquake. If you count to ten seconds, you could hear a roar, the frequency of the vibrations was falling. And their power was growing. Then there was a bang. Because I was closer to the turbine, I thought a blade had flown out. But that's just subjective, because I've never seen anything like that before...
Kirshenbaum shouted: "Water hammer in the deaerators!" This blow was not very strong. Compared to what happened later. Although a strong blow. It shook the control room. And when the SIUT shouted, I noticed that the alarm of the main safety valves went off. Flashed through my mind: "Eight valves... open!" I jumped back, and at that moment the second blow followed. Now that was a very strong blow. Plaster fell, the whole building was going dark... the lights went out, then the emergency power was restored... The opening of one GPK [author's note - the main safety valve, designed for emergency steam release] is an emergency situation, but eight GPK - that was already something... supernatural..."
There is more than one such evidence. That same bad sound that Tregub (and not only he) heard was the real beginning of the emergency situation development, when the core was steamed, and then, due to the heat transfer crisis (lack of normal cooling of the fuel channels), the destruction of the fuel assemblies (FA) began. Those same hydraulic shocks that many also heard were a consequence of the breakdown (see below) and cavitation of the main circulation pumps. [Author's note: Cavitation is the process of formation and subsequent collapse of bubbles in a liquid flow, accompanied by noise and hydraulic shocks... As a result of the collapse of the bubbles, shock waves are formed that damage metal surfaces.] Then an explosion occurred in the reactor. Perhaps, at the very first signs of an accident, it was still possible to reset the emergency protection (but only until the moment the channels began to collapse) and start the criminally blocked emergency cooling system of the reactor SAOR.

Well, it's clear that the developers immediately threw in a version about steaming, which was later not confirmed. By the way, I do not exclude that they really thought so at first, and did not try to confuse the investigation, this is a common mistake of operators)).

But here it’s the same case as with the AZ button, the time parameters don’t match.

The fact is that the 7th and 8th main circulation pumps were started at 01.03 and 01.07 respectively, i.e. 20 MINUTES BEFORE THE EXPLOSION.
If they had taken the water out of the reactor and steamed it, the steam generation process would have started much earlier, and the pressure and level in the BS would have also jumped earlier.

But there is nothing like that, the graphs clearly show that everything started at 01.23.40, AFTER PRESSING THE AZ BUTTON.

[Alexander Odintsov]

When, in the opinion of the operator, the reactor parameters returned to normal, he sharply reduced the feedwater consumption, practically to zero, which became a fatal step, since it led to an increase in the coolant temperature at the reactor inlet, i.e. additionally increased steam production.
According to the INSAG-7 report (1993):
"01:09" The feed water consumption is sharply reduced to 90 t/h on the right side and to 180 t/h on the left side with a total flow rate along the circuit of 56-000 t/h. As a result, the suction temperature [approx. author - entrance] MCP was 58°C (left side) and 000°C (right side).” This level - 280,8 t/h - is practically equal to zero within the limits of instrument error. The water temperature at the reactor inlet became close to the saturation (boiling) temperature.
But as the GPAN report (1991) believes: “…this was a return of feedwater consumption to some average consumption corresponding to a reactor capacity of 200 MW and equal to approximately a consumption of 120 tons/hour on each side of the reactor.”
According to A.G. Tarapon, Institute for Problems of Modeling in Power Engineering named after G.E. Pukhov of the National Academy of Sciences of Ukraine (Ukraine, Kyiv), the accident process began earlier, immediately after the start of the coastdown tests at the moment of closing the SRK damper, and the accident process itself developed for about 15 minutes: “This entry [author's note: a sharp decrease in feedwater consumption] recorded the beginning of a heat exchange crisis of the second kind…., while the integral power of the reactor remained at the level of 200 MW, which allows us to draw two conclusions: the power was increased only in one (southeastern) quadrant, and in the others it remained at the level of 13.5 MW (residual heat release); in the indicated quadrant, heat exchange completely ceased."
In fact, the temperature at the inlet/outlet of the channels is normally 270/284,5, i.e. the water temperature at the inlet of the main circulation pump was 280,8°C (left side) and 283,2°C (right side), which is more than 10 degrees higher than normal and approximately corresponds to the temperature of boiling water at the outlet of the channels 284,5.
When the unit personnel began the coastdown tests (01h 23m 04s), the steam outlet to the turbine was disconnected and the shutoff and control valves (SRVs) were closed to ensure that the generator entered the inertial run. In the absence of steam flow from the BS (the drum-separator, where steam is separated for feeding to the turbine), the pressure in the circuit began to increase. The experiment was started without resetting the reactor protection, the protection for shutting down both turbines was blocked to possibly have the opportunity to repeat the experiment.
As a result of the sharp increase and then decrease in feedwater consumption, two successive coolant fronts were formed in the reactor circuit at the entrance to the active zone: the first with a lower temperature and, after some time, the second, with a temperature close to the boiling point of water. By a fatal coincidence, the last front of the "heated" coolant approached the entrance to the active zone at the time of the experiment.
According to the report of the State Nuclear Academy of Sciences (1991), immediately before the tests at 01:22:30:
“Under the conditions that arose, a small increase in reactor power (for any reason) due to a small underheating of the coolant to boiling could lead to an increase in the volumetric steam content in the lower part of the active zone... Thus, before the start of the tests, the parameters of the active zone caused an increased susceptibility of the reactor to the self-acceleration process in the lower part of the active zone... such a condition was created not only because there was an increased coolant flow rate compared to the usual..., but above all because of the low value of the reactor power.”
Thus, the complex of actions of the personnel (low reactor power, connection of additional main circulation pumps, closure of the recovery valve and a sharp decrease in the feedwater level) were the most important factors in the development of the accident, which led to the destruction of the reactor.

[Podvodnik]

The guys couldn't even imagine,

So you should have read books! Fucking C students. You broke everything you could. Maybe it will pass... . It didn't.
And again, telephone law. Again, someone super-literate gave the command to do something that he understood like a pig understands oranges.

[Darkdimon]

The main mistake was the transfer of the nuclear power plant from the military to the civilian sector, which resulted in a deterioration in the level of personnel.

[Vladimir_Tver]

Let's start from scratch - any testing program is written down from beginning to end, any deviation from it, in this case, is a crime. And he must have a last name, first name, patronymic.
When I was servicing RSBN - RSDN, I first studied the technical maps, then passed the test and when performing routine maintenance, I carried them out precisely, because I understood that the lives of people depended on the quality of my work, albeit indirectly.

[Dometer]

It is necessary to distinguish:
The Test Program; what WE call the Test Program; the name of the Test Program...
I looked at http://accidont.ru/ - I find it difficult to classify...

[Doctor]

Let's start from scratch - any testing program is written down from beginning to end, any deviation from it, in this case, is a crime. And he must have a last name, first name, patronymic.
When I was servicing RSBN - RSDN, I first studied the technical maps, then passed the test and when performing routine maintenance, I carried them out precisely, because I understood that the lives of people depended on the quality of my work, albeit indirectly.

Here you unexpectedly came to the most important thing.
Disabling protections was WRITTEN into the program. But some deviations were quite acceptable if the essence of the test was preserved.

The point was to measure the inertia run-out time of the turbogenerator. Which is generally located in the next room. And it doesn't matter in principle what power it was done with, the initial number of revolutions is important.

[Alexander Odintsov]

Disabling protection was WRITTEN into the program.

Only disabling the SAOR is a violation.

[Doctor]

Only disabling the SAOR is a violation.

Then a couple more questions.
1. WHY was the program written to disable the SAOR? How could this interfere with the experiment on the TG, which is actually located in the neighboring building?
2. WHO turned off the SAOR?

[Alexander Odintsov]

According to G. Medvedev, the SAOR was switched off "...for fear of thermal shock to the reactor, that is, cold water entering the hot reactor... The SAOR was... switched off, the valves on the water supply line to the reactor were de-energized in advance and locked so that they could not be opened even manually if necessary.... But... It is better to supply cold water to the hot reactor than to leave the red-hot active zone without water... After all, when... the reactor is left without cooling water, 350 cubic meters of emergency water from the SAOR tanks could have saved the situation by extinguishing the steam effect of reactivity, the most significant of all. Who knows what the outcome would have been. But...."
Why was it necessary to block it? Paradoxically, after the accident Akimov tried to turn it on, asking G. Metlenko about it: "Be a friend, go to the turbine hall, help turn the valves. Everything is de-energized. It takes at least four hours to open or close each one manually. The diameters are huge..."
According to V.A. Vinokurov, Ph.D., VMII: "When non-stationary processes began in the power unit on the night of 26.04.1986, the shift supervisor, noticing that the upper part of the main circulation pump was oscillating with an amplitude of 1 m..., gave the command to immediately open the emergency reactor cooling system valves, which were closed to ensure the purity of the turbo unit rundown experiment. One of the two people killed in the first minutes of the disaster was the very person who opened the emergency reactor cooling valves."

[Doctor]

According to G. Medvedev, the SAOR was switched off "...for fear of thermal shock to the reactor, that is, cold water entering the hot reactor... The SAOR was... switched off, the valves on the water supply line to the reactor were de-energized in advance and locked so that they could not be opened even manually if necessary.... But... It is better to supply cold water to the hot reactor than to leave the red-hot active zone without water... After all, when... the reactor is left without cooling water, 350 cubic meters of emergency water from the SAOR tanks could have saved the situation by extinguishing the steam effect of reactivity, the most significant of all. Who knows what the outcome would have been. But...."
Why was it necessary to block it? Paradoxically, after the accident Akimov tried to turn it on, asking G. Metlenko about it: "Be a friend, go to the turbine hall, help turn the valves. Everything is de-energized. It takes at least four hours to open or close each one manually. The diameters are huge..."
According to V.A. Vinokurov, Ph.D., VMII: "When non-stationary processes began in the power unit on the night of 26.04.1986, the shift supervisor, noticing that the upper part of the main circulation pump was oscillating with an amplitude of 1 m..., gave the command to immediately open the emergency reactor cooling system valves, which were closed to ensure the purity of the turbo unit rundown experiment. One of the two people killed in the first minutes of the disaster was the very person who opened the emergency reactor cooling valves."

Funny. Medvedev apparently decided to cool the reactor with boiling water in case of emergencies. The colder the better, there is no heat stroke here.

In fact, the program says: "Close the manual valves to prevent water from flowing into the main circulation system through all three subsystems of the SAOR."

There was no signal to turn it on automatically, so it doesn’t matter whether the valves were closed or not.

The most important thing is that everyone blames Akimov's shift for the shutdown of SAOR.
Although the SAOR was switched off by Kazachkov's shift, even before Tregub's shift!

This is what Yuri Tregub writes:
"The SAOR (emergency reactor cooling system) began to be put into operation
Kazachkov's replacement. This is a very big job - after all, we have manual reinforcement.
Just imagine, one valve takes about forty-five minutes. The valve is
like a steering wheel on a sailboat, only a little smaller and horizontal.
To close it, it requires the efforts of two people, or better yet, three. That's all.
is done manually. Kazachkov needed almost the entire shift
bringing the system to an emergency stop. This is very hard work."

[Alexander Odintsov]

You are writing everything correctly. Although in the specific conditions of the accident, the SAOR hardly helped.

[Dometer]

Quote: Arzt

During the investigation, there was no talk of any calls. And Dyatlov didn't even hint at anything like that, although he could have been given a death sentence.
(approx. call from a CPSU functionary)

The seasoned Soviet man understood that any attacks on the CPSU would destroy his chances of survival.

[Doctor]

The seasoned Soviet man understood that any attacks on the CPSU would destroy his chances of survival.

Funny.
He himself is a member of the CPSU, a holder of the Order of the Red Banner of Labor and the Badge of Honor. More than 30 years in the profession, an excellent combat and political worker, etc.
At that time, NOT REPORTING such a call meant the end)).
Where is the guarantee that such conversations are not written down?

[to sing]

As someone who works at a Chernobyl-type reactor, I'll add a little.
If we are to believe the pressure graph in the drum separators (DS) presented by Arzt, the pressure in the DS at the start of the tests was about 65 kgf/cm2. At this pressure, the saturation temperature of water/steam was 281 degrees C. That is, there was no reserve to the saturation temperature. Which is logical, since 200 cubic meters of feedwater with a temperature of 170 degrees is nothing compared to 56000 cubic meters of the total flow rate of the MCC from the MCP with a temperature of 281 degrees.
Furthermore, no hot water front came to the zone after the supply to the drives stopped for the simple reason that all the water makes a circle around the MCC in about 40 seconds (650 cubic meters of water volume of the MCC at a flow rate of 56000 cubic meters per hour, you can calculate it yourself). Accordingly, the water in the MCC was already on the saturation line for quite a long time by the standards of that night. By the way, I am writing the flow rate in cubic meters to make it easier to compare. In fact, the flow rate is measured in tons per hour, so it will be even more in cubic meters, but that is not important here.
Now about the reactor power.
After the reactor is brought to the minimum power level (no more than 160 MW thermal) and heated to nominal parameters (69 kgf and 284,5 degrees in the BS), the MCP pumps water to the saturation line without any underheating, since the steam consumption and, accordingly, the feedwater is negligible. Steam is not supplied to the turbine, but is discharged into the turbine condensers through the BRU-K. The turbine is pushed only at a reactor power of 700 MW (!!!). All the time before the turbine push, the reactor operates without supplying steam to the turbine. After that, the turbogenerator gains electrical power of 150 MW and they begin to further increase the reactor power. All this to say that there is nothing terrible in the operation of the reactor without supplying steam to the turbine up to 700 MW. The BRU-K copes well. Simply, the higher the steam consumption to the turbine, the faster the pressure in the BS will increase to the BRU-K response settings of 71,5 kgf, and possibly the protection against pressure of 74 kgf will be triggered if the BRU-K fails, and the reactor will be shut down. With further pressure growth, the GPK (main safety valves) are already opened. Perhaps for this reason, the reactor power was reduced to 200 MW, after all, closing the SRV at a TG power of 150 MW is not at 40 MW. Here it is also important to understand that opening the BRU-K entails a decrease in pressure in the MCC, an increase in steam formation in the core and, accordingly, an increase in power due to a large steam coefficient of reactivity. The more BRU-Ks open simultaneously (there are only 4 of them), the faster the pressure will decrease, the faster the power will increase.
Now let's consider the power reduction to 200 MW. It began with an ORM of 26 control rods (since the reactor had been poisoned 12 hours before). If they had quickly reduced it, conducted experiments and shut it down, everything would have been fine, since the peak of the iodine pit occurs 3-4 hours after the power reduction began. But then the reactor self-shutdown factor intervened (as a result of either an error by the reactor safety engineer or someone's trick with the regulators), and not only did the iodine pit become "deeper", but they also had to pull out additional control rods to raise the reactor power. That's why they got those same 6-8 rods, and most likely even less, which will not help in any way with sharp reactivity surges. Under those conditions, for that reactor design with large positive reactivity coefficients, any sharp change in the parameters in the core could give a jump of more than one beta and cause a runaway on prompt neutrons. Whether this was caused by the group opening of the BRU-K, the shutdown of the run-down MCPs by the minimum voltage protection, the end effect of the control rod displacers, or a combination of all of the above, we will most likely never know.
The only fact is that the design flaws of the RBMK-1000 were known, known not only in the USSR, and it is entirely possible to plan a sabotage in collusion with the right people. Especially if you remember how many man-made disasters there were in the Union after the beginning of perestroika.
On the other hand, in 1985, a submarine reactor exploded near the pier in Chazhma Bay after the active zone was overloaded due to negligence. There were also fatalities, radioactive contamination of the area. That accident was classified, and most likely no measures were taken in the civilian part of the industry. Therefore, in Chernobyl, it was probably just negligence.

[Alexander Odintsov]

Nikolay, thank you for the interesting information!

[Doctor]

Now let's consider the power reduction to 200 MW. It began with an ORM of 26 control rods (since the reactor had been poisoned 12 hours before). If they had quickly reduced it, conducted experiments and shut it down, everything would have been fine, since the peak of the iodine pit occurs 3-4 hours after the power reduction began. But then the reactor self-shutdown factor intervened (as a result of either an error by the reactor safety engineer or someone's trick with the regulators), and not only did the iodine pit become "deeper", but they also had to pull out additional control rods to raise the reactor power. That's why they got those same 6-8 rods, and most likely even less, which will not help in any way with sharp reactivity surges. Under those conditions, for that reactor design with large positive reactivity coefficients, any sharp change in the parameters in the core could give a jump of more than one beta and cause a runaway on prompt neutrons. Whether this was caused by the group opening of the BRU-K, the shutdown of the run-down MCPs by the minimum voltage protection, the end effect of the control rod displacers, or a combination of all of the above, we will most likely never know.

Thanks for the addition, it's always interesting to hear from a real operator.

I have always been interested in this question, I have asked experts many times, but I have never received a clear answer.

If I understand correctly, when a reactor is completely shut down, either on a planned or emergency basis, they use the AZ and many rods, about 180, go down at the same time.
In your experience or that of your colleagues, have you ever observed a short-term power surge in these cases? Or does the minimum reserve always compensate for it, and only Chernobyl experienced a critical situation?

And one more thing. The reactor was poisoned, so why didn't the xenon interfere with the fast-neutron acceleration?

[to sing]

In 1986, during a reactor shutdown, all control rods that were not fully immersed in the core were pulled into the reactor core. There were 223 rods in total. Accordingly, the more rods were on the upper limit switches, i.e., completely withdrawn from the core, the greater the end effect of the displacers (with all control rods fully withdrawn, approximately 1,5 beta). The rods traveled from the upper to the lower limit switches in the core in approximately 14 seconds, i.e., the response time was not very good. It should be noted that the rod speed during a planned shutdown and an emergency shutdown was the same.
Immediately after the accident, all RBMK-1000 reactors underwent modernization, including a redesign of the control rods, eliminating the displacer end effect. A fast-acting emergency shutdown system (FAS) with a response time of 2.2 seconds was also implemented. To achieve this, 24 rods were replaced with completely different designs. These 24 rods were supposed to be sufficient for a rapid emergency shutdown of the reactor. In the 2010s, after another modernization, the number of such rods increased to 33. During a normal or planned shutdown, the remaining 190 FAS rods are used in the core. The 33 FAS rods do not enter the core (only in emergency mode).
I can't tell you anything about the power surge during reactor shutdown, since I had no one to ask (I started working at a nuclear power plant in the 2000s). I've only heard that some reactor maintenance workers back in the 80s shut down the reactor manually, using several rods at a time, rather than pressing the emergency shutdown button. The fewer rods in the reactor core (the lower the ORM), the less neutron absorber there is, the more neutrons are absorbed in the fuel during reactivity surges, and, consequently, the better the fission reaction.
So, yes, the reactor was decommissioned, and xenon also absorbed neutrons and interfered with the fission reaction. The only problem is that xenon concentration is impossible to control. The core undergoes competing processes of xenon accumulation and decay. So, as reactor power increases, xenon burns out, its concentration decreases, thus reducing the amount of neutron absorber in the core and introducing additional positive reactivity. Uneven xenon poisoning across the core also plays a role. It's more in some places, less in others (the RBMK core is very large), so prompt neutron runaway could have started in one part of the core and then spread throughout the entire volume as the xenon burns out. However, all this took only a second or two (the prompt neutron lifetime is 10e-3 sec).

[Doctor]

So, yes, the reactor was decommissioned, and xenon also absorbed neutrons and interfered with the fission reaction. The only problem is that xenon concentration is impossible to control. The core undergoes competing processes of xenon accumulation and decay. So, as reactor power increases, xenon burns out, its concentration decreases, thus reducing the amount of neutron absorber in the core and introducing additional positive reactivity. Uneven xenon poisoning across the core also plays a role. It's more in some places, less in others (the RBMK core is very large), so prompt neutron runaway could have started in one part of the core and then spread throughout the entire volume as the xenon burns out. However, all this took only a second or two (the prompt neutron lifetime is 10e-3 sec).

As far as I know, xenon is five times heavier than air, and in theory, it should have accumulated in the lower part of the accelerator, slowing down the reaction. But the accident simulation quite reliably shows that the acceleration began at the bottom. That's the paradox!

As for the ORM, yes, you wrote about the Smolensk NPP and I talked to others – they left fewer than 5, 4, and 3 rods and nothing happened! But here, at the start of the experiment, it was almost 20, damn!

And he went boom.

The mechanism is not fully understood, but it is obvious that these power fluctuations played a role.

[to sing]

You seem to have a misconception about the design of a nuclear reactor in general and nuclear fuel in particular. It's not some barrel containing air, water, and fuel. I won't describe the reactor's design here; there's plenty of it online. I'll just say that xenon doesn't move around in a reactor like air. Xenon is a product of the fission of heavy nuclei (uranium and plutonium). Xenon is contained within the nuclear fuel and doesn't escape. The nuclear fuel is contained within the fuel element cladding. There are approximately 60,000 fuel elements in a reactor, assembled into fuel assemblies (FAs)—two bundles of 18 elements each. Each fuel channel (FC) contains one fuel assembly, washed by pressurized water (the coolant). The nuclear fuel doesn't come into contact with the coolant, meaning the xenon doesn't escape, but remains where the neutron-driven fission of uranium and plutonium occurs. That is, where the energy release is currently higher, over time there will be more xenon, and the energy release will decrease. Accordingly, in another part of the core, where the energy release is lower, there will be less xenon, and the energy release will increase. This process is called xenon oscillations. With a rapid decrease in reactor power, the poisoning will be uneven across the core volume.
At the start of the experiment, 20 rods were missing their ORM; 26 were missing when the power began to decline at 23:10 PM the previous day, as I've already written about. Various sources report ORMs ranging from 6-8 to 2-3 rods.
And the fact that it didn’t work before was most likely due to a combination of factors, I also wrote about this.

[Doctor]

You seem to have a misconception about the design of a nuclear reactor in general and nuclear fuel in particular. It's not some barrel containing air, water, and fuel. I won't describe the reactor's design here; there's plenty of it online. I'll just say that xenon doesn't move around in a reactor like air. Xenon is a product of the fission of heavy nuclei (uranium and plutonium). Xenon is contained within the nuclear fuel and doesn't escape. The nuclear fuel is contained within the fuel element cladding. There are approximately 60,000 fuel elements in a reactor, assembled into fuel assemblies (FAs)—two bundles of 18 elements each. Each fuel channel (FC) contains one fuel assembly, washed by pressurized water (the coolant). The nuclear fuel doesn't come into contact with the coolant, meaning the xenon doesn't escape, but remains where the neutron-driven fission of uranium and plutonium occurs. That is, where the energy release is currently higher, over time there will be more xenon, and the energy release will decrease. Accordingly, in another part of the core, where the energy release is lower, there will be less xenon, and the energy release will increase. This process is called xenon oscillations. With a rapid decrease in reactor power, the poisoning will be uneven across the core volume.
At the start of the experiment, 20 rods were missing their ORM; 26 were missing when the power began to decline at 23:10 PM the previous day, as I've already written about. Various sources report ORMs ranging from 6-8 to 2-3 rods.
And the fact that it didn’t work before was most likely due to a combination of factors, I also wrote about this.

Got it, thanks. Regarding xenon, yes, for some reason I imagined it in gaseous form)).

Back then, with such a large active zone, locally unpredictable processes could only have occurred with computer modeling. But back then, with slide rules…

It's surprising that Chernobyl didn't happen earlier.

[to sing]

I completely agree with you here 🙂

[Jager]

Very interesting stuff.
We can argue for a long time about the causes of the disaster, but we will never know the truth. Where did Legasov's notes disappear? What other secrets do the classified archives hold? We will never know.
One can only speculate on a range of hypotheses.
But, for example, sabotage is the weakest of all.
There is no doubt that the personnel and those personally responsible for the reactor made HUGE mistakes. Yes, the reactor was damp. But in normal mode, RBMKs worked quite successfully before the accident and are working now.
Accidents are usually not the fault of one person, but a chain of someone's carelessness, incompetence, greed, indifference and negligence.
"Maybe it will pass, we've done it a hundred times and it's okay, let's do it quickly." The result was human casualties and destruction.

[Kruglov]

Hmm... It was as if they were all trying to prove the axiom: Everything man has created, he can always break! They succeeded.