Earthquakes: Nuclear bunker busters
In the material "Knockin' on the Bottom: The Limits of Bunker-Breaker Munitions" We have considered the capabilities of conventional bunker-busting munitions. In many ways, their evolution has stopped, they are based on theoretical developments from the early 20th century, design materials and explosives have become better, but not by orders of magnitude or even by several times.
In fact, if we compare bunker-busting munitions from the Second World War (WWII) with modern munitions of comparable caliber, their effectiveness has become only 1,5–2 times higher, at best, and the increase in effectiveness is mainly due to the fact that bunker-busting munitions have become “highly accurate”, and since the theoretical calculations of the English design engineer Barnes Wallace, the founder of bunker-busting weapons, almost a hundred years have passed.
On the other hand, the military has not had any particular incentive to develop conventional bunker busters since the advent of nuclear weapons. It is clear that their power is not comparable to conventional explosives, so humanity has focused on nuclear "bunker busters."
One of the first nuclear bunker buster munitions was the Mark 8 nuclear bomb, which entered service with the US Armed Forces in April 8. It was a very interesting munition, made using a cannon design - in its simplest form, two pieces of enriched uranium fired towards each other. The design was ineffective in terms of efficiency, but simple and reliable.
Mark 8 aerial bomb
The Mark 8 bomb had a very simple detonation system, with no electrical circuits at all. Three pyrotechnic delay fuses were used to detonate the powder charge that initiated the nuclear explosion, one installed in the nose and two in the middle, on both sides of the hull. The delay was from 60 to 180 seconds and was set from the carrier aircraft before dropping, the fuses ignited at the moment of separation from the aircraft.
According to open data, the Mark 8 nuclear aerial bomb could penetrate 6,7 meters into reinforced concrete, 27 meters into compacted sand, 37 meters into clay, or 13 centimeters into hardened armor steel. The TNT equivalent of the Mark 8 nuclear aerial bomb was 15-20 kilotons, each bomb required about 50 kilograms of uranium-235 enriched to 90%.
Cannon scheme
Theoretically, this is where the review of nuclear bunker-busting munitions could end, but not because they have not developed or evolved further, but because their real capabilities are tightly hidden behind a veil of secrecy. It is clear that nuclear bunker-busting munitions can penetrate 40-60 meters deep, just like their non-nuclear “brothers”, but what next, what is their destructive power?
Despite the opinion of a significant part of the population that even a few nuclear explosions would lead to a catastrophe, in reality over two thousand nuclear tests were carried out, a significant part of which were underground, and nothing terrible happened on a global scale.
On August 5, 1963, the Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water was signed in Moscow. The parties to the treaty were the USSR, the USA, and Great Britain. The treaty entered into force on October 10, 1963, and was later joined by another 131 countries.
Geography of the Treaty Banning Nuclear Weapon Tests in the Atmosphere, Outer Space, and Under Water. Image: Wikimedia Commons / Allstar86
In this regard, a significant portion of underground nuclear explosions were carried out for the purpose of testing new munitions and checking the functionality of old ones, but a significant number of underground nuclear explosions were carried out at different depths in order to assess the impact of nuclear weapons on the earth's crust and their use for various peaceful purposes.
Thus, some understanding of the destructive power of underground nuclear explosions can be gained from information about the peaceful use of nuclear charges - this information was not so taboo, and some of it is freely available.
Today we will talk about such nuclear explosions carried out in the USA and the USSR, and based on the information received we will try to form an idea of the real capabilities of nuclear bunker-busting munitions.
USA
In the summer of 1957, the American Atomic Energy Commission adopted the Plowshare program, the goal of which was to study the possibilities of using nuclear explosions for industrial and scientific purposes.
"Hardhat"
As part of this program, on February 15, 1962, at the Nevada Test Site, during the Hardhat experiment, American specialists detonated an explosive device with a capacity of 4,5 kilotons, located at a depth of 290 meters in granite rock, as a result of which a cavity with a diameter of about 38 meters was formed.
"Danny Boy"
During the Danny Boy test on March 5, 1962, a nuclear explosion of ultra-low yield, equivalent to only 420 tons, was carried out at the Nevada Test Site. The charge was placed in basalt rocks at a depth of 34 meters.
The explosion resulted in a crater 65 meters in diameter and 19 meters in height, a base wave 884 meters in diameter and 305 meters in height arose, and 30 minutes after the explosion the dust cloud reached a height of 610 meters. Only about 4% of the radioactive particles fell as precipitation, which mostly settled within a radius of 3,2 kilometers from the explosion point.
"Sedan"
On July 6, 1962, the United States conducted another nuclear experiment as part of Project Sedan.
Modern penetrating gravity nuclear aerial bombs can have a variable charge power from 5 to 100 kilotons (according to some data, the adjustable range is even wider - from 2 to 320 kilotons)
A nuclear charge with a capacity of 100 kilotons, which is quite consistent with the parameters of modern nuclear warheads, was placed in a mine at a depth of 194 meters. As a result of the explosion, a funnel with a diameter of 366 meters, a depth of 98 meters, and a total volume of about 5 million cubic meters was formed in the ground.
As with the Hardhat and Danny Boy experiments and other underground nuclear tests, most of the radioactive particles that emerged from the crater were deposited in the immediate vicinity. The blast wave was one-fifth to one-tenth that of a comparable surface explosion, and the zone of dangerous seismic impact extends for about four kilometers.
The crater from the explosion carried out as part of the Sedan project is shown in the image at the beginning of the article.
the USSR
Considerable attention was paid to peaceful nuclear energy in the USSR as well; among the first proposals considered was the creation of reservoirs with a capacity of 3-5 million cubic meters for agricultural needs in the arid regions of Siberia.
On January 15, 1965, a 178-kiloton nuclear charge was detonated at a depth of 140 meters at the Semipalatinsk test site in Kazakhstan. The resulting crater had a diameter of 408 meters and a depth of 100 meters, the crater crest rose by 20-35 meters. About 20% of the radioactive products of nuclear decay entered the atmosphere, and within a few days the radiation level on the collapse ridge rose to 20-30 roentgens per hour (R/h) - that's a lot.
On October 10, 1965, a second experimental explosion was conducted – a nuclear charge with a capacity of 1,1 kilotons was placed at the Semipalatinsk test site at a depth of 48 meters. The resulting funnel was initially 107 meters in diameter and 31 meters deep. Over the next three months, under the influence of artesian water, the diameter of the funnel increased to 124 meters, and the depth decreased to 20 meters.
Only 3,5% of the radioactive products of nuclear decay entered the atmosphere, and five days after the explosion, the radiation level on the collapse ridge reached 2-3 R/h.
"Taiga"
On March 23, 1971, as part of the work to create the Kama-Pechora Canal, it was decided to conduct a nuclear experiment called "Taiga", during which three nuclear charges with a capacity of 100 kilotons each were simultaneously detonated 128 km north of the city of Krasnovishersk at a depth of 15 meters. As a result, a series of craters about 700 meters long and 340 meters wide were formed.
An artificial lake formed as a result of explosions during the Taiga experiment. Image – archive of the Stil-MG agency
An hour later, a radiation dose of 50-200 R/h was recorded at the testing site; after eight days, at a distance of 8 kilometers downwind, the radiation was only 23-25 microroentgens per hour (μR/h) – for comparison, in an ordinary apartment in most Russian cities the background radiation is about 10-15 μR/h.
"Crystal"
On October 2, 1974, as part of the Crystal program, a nuclear charge with a capacity of 98 kilotons was detonated at a depth of 1,7 meters under the Siberian settlement of Udachny. The work was carried out by order of the USSR Ministry of Non-Ferrous Metallurgy and the diamond mining company Yakutalmaz with the aim of creating a small lake for storing mining waste.
The result was a dome-shaped embankment with a diameter of 180 meters and an initial height of 60 meters, which over time settled to an average height of 10 meters above the original surface.
Trace of the underground nuclear explosion "Crystal" (additionally covered over in 1992)
Limited opportunities
In fact, there were significantly more peaceful nuclear explosions; only those closest in depth of use to the possible point of detonation of a bunker-busting nuclear weapon are selected above – it hardly makes sense to consider the option where a nuclear charge is buried underground for a kilometer or more and only then detonates.
Most likely, a nuclear bunker buster will be able to reach approximately the same depth as a non-nuclear bunker buster, that is, about 50-60 meters.
How can the peaceful nuclear explosions discussed above be assessed in relation to the impact on highly protected underground bunkers?
For example, during the Hardhat experiment, a 4,5-kiloton explosion created a cavity 38 meters in diameter in granite rock at a depth of 290 meters.
An underground cavity formed during the Gnome nuclear explosion carried out by American specialists on December 10, 1961
Underground nuclear explosions with a yield of 100-140 kilotons at a depth of 100-200 meters created craters several hundred meters in diameter on the surface. Even the detonation of a nuclear weapon equivalent to only 420 tons at a depth of 34 meters created a crater 65 meters in diameter and 19 meters high.
Of course, the rule "where it's thinnest, it breaks" has not been cancelled, so it is logical that most of the energy of a nuclear explosion spreads upwards, not downwards. Nevertheless, in cases where the products of a nuclear explosion did not reach the surface, cavities of a fairly large diameter formed in soils, even in such strong ones as granite or basalt.
Thus, it turns out that the shallower the bunker buster munition is buried and the higher its power, the higher the probability that most of the explosion energy will go upward without harming the underground bunker. Accordingly, the critical factor is the ability of a nuclear bunker buster munition to go to the maximum depth before detonation.
The impact of the underground bunker's protective belts is questionable. On the one hand, a strong concrete cover can prevent a nuclear weapon from penetrating to a significant depth. On the other hand, if it is nevertheless breached and the nuclear charge detonates, the concrete pad can act as a screen, directing most of the explosion energy downwards, compared to the situation where there would be no concrete pad.
Thus, another important factor is understanding the structure of the defense of the attacked underground bunker, which will allow choosing the optimal charge power and the depth of its detonation.
It can be assumed that highly protected underground bunkers located at a depth of about 300 meters are completely invulnerable to non-nuclear bunker-busting munitions and are fairly well protected from single nuclear bunker-busting munitions, regardless of their power.
Highly protected underground bunkers located at a depth of about 200 meters are most likely also invulnerable to non-nuclear bunker-busting munitions, but their protection against nuclear bunker-busting munitions is already questionable.
It is clear that all highly protected underground bunkers located deeper than the specified values will be protected even better. Of course, the composition of the soils in which the shelter is located will play a significant role here, for example, granite rocks will have a clear advantage here.
Doomsday Bunker - NORAD's Underground Complex in Cheyenne Mountain
Potentially, it is possible to reach an underground bunker located at great depth by using several nuclear weapons in succession, but here it is necessary to understand with what frequency these charges need to be used.
If they go in a dense group, the first exploded charge can destroy the rest. If they are used with a significant delay, a situation may arise where the collapse and sintering of the rock in the funnel of a nuclear explosion will partially neutralize the effect of the explosion of the previous charge.
It's like digging a hole in the sand, the walls of which will always crumble - it's unlikely that anyone can count on successive nuclear explosions being able to "drill" a vertical shaft.
It is also worth mentioning the exits from underground bunkers, which are highly likely to be blocked in the event of an attack, especially with the use of nuclear bunker-busting munitions – there are many questions and assumptions here.
Yes, the exits directly above the bunker will likely be blocked, but how many emergency exits are there? Are they all known? How far do they extend beyond the bunker?
Is it possible that there are a certain number of exits to some other underground structures, for example, metro lines, which would be difficult to collapse completely? It is possible that there are some reserve exits from the bunkers, which initially go horizontally from the bunker, and then rise to the surface, but do not exit, that is, at the end there is some equipment capable of passing the remaining several dozen meters.
Where is the guarantee that the tunneling equipment is not mothballed in the most important bunkers? There are now quite compact and very effective models - by the way, this is also an important topic for discussion.
Conclusions
Based on the testing and use of nuclear charges for peaceful purposes, it can be concluded that with the help of single nuclear bunker-busting munitions it is possible to guarantee the destruction of any highly protected underground bunker located at depths of about 100 meters.
Highly protected underground bunkers located at depths of about 200 meters are at risk.
Highly protected underground bunkers located at depths of approximately 300 meters are relatively safe from single nuclear bunker buster munitions, but they could potentially be destroyed by the sequential impact of two or more nuclear bunker buster munitions.
As for highly protected underground bunkers located at much greater depths, we will put this issue “out of the equation” for now – certain theoretical studies and modeling have been conducted on the destruction of such targets, and perhaps we will return to this topic later.
The underground nuclear explosions examined in this material allow us to form a number of interesting conclusions, which we will discuss in the next material.
Information