A modern nuclear warhead (YABZ) contains a central plutonium part (pit) made in the form of a metal sphere and contains, over 90, a percent of the fissioning Pu-239 isotope (weapon grade plutonium) as an integral element.
For the production of such material, the two superpowers used specially created water-graphite reactors during the Cold War years - weapons plutonium accumulators. In the USA, 14 of such installations was built, in the USSR - 13. By 1993, all American plutonium reactors were shut down, but three of their counterparts continued to operate in Russia (two in Seversk, Tomsk Oblast and one in Zheleznogorsk, Krasnoyarsk Krai), which annually produced about 1,5 tons of weapons-grade plutonium sufficient to manufacture 300 nuclear warheads. It was not possible to stop these reactors, since in parallel with the production of plutonium they served as a source of heat and electricity for the corresponding Siberian regions, and there was no one-time replacement for them. Due to the fact that the defense order for weapons-grade plutonium was canceled at that time due to overproduction (there are no official data on this score, however, according to some Western experts, in the USSR over 40 tons of weapons-grade plutonium were accumulated over the 100 years) work "at the warehouse."
In 2003, an agreement was signed between the Russian Federation and the United States on the provision of American assistance in the construction of replacement energy facilities, ensuring the production of equivalent amounts of heat and electricity in the event of the closure of the three remaining Russian plutonium reactors. Two US companies were involved in this work, the total amount of contracts was 460 million dollars.
In 2008, the reconstruction of the coal-fired CHP plant in Seversk was completed and at the same time two plutonium reactors were decommissioned. In Zheleznogorsk, the reactor was shut down at 2010 after completing the construction of a new coal-fired power plant.
It is assumed that the weapons-grade plutonium accumulated in the special warehouses of the two cities will later be used to manufacture mixed uranium-plutonium (MOX) fuel for burning in Russian fast-neutron power reactors in accordance with the Russian-American agreement.
It should be noted that among the characteristic features of plutonium producing reactors is the use of natural uranium as fuel rather than uranium enriched in contrast to power reactors (natural uranium contains the 99,3 percentage of the non-dividing isotope U-238, which is transformed into weapon-grade plutonium under the influence of the nuclear reaction and only the 0,7 percentage of the fissioning isotope U-235).
It is fundamentally important that the fuel campaign of such reactors does not exceed two to three months (as opposed to the three to four years characteristic of NPP power reactors). This condition is connected with the need to limit the volume (no more than 10 percent) of the Pu-240 isotope "harmful" for a nuclear warhead that is simultaneously accumulated in the fuel.
The negative properties of this isotope include the probability of spontaneous (spontaneous) neutron radiation (which is fraught with uncontrolled launching of the chain fission reaction and reduction of the calculated explosion power), a large specific heat release (the need for arresting which inevitably leads to weight and size parameters of the special product) also a high level of radioactivity (this significantly complicates the process of production and long-term storage of YABZ).
For comparison, it is interesting to cite the following figures: if the ratio of Pu-239 and Pu-240 isotopes in a reactor that produces plutonium is nine to one, in the case of an NPP power reactor, the Pu-240 content can reach 25 percentages in the overall composition of the reactor plutonium. At the same time, in both types of reactors, the amount of plutonium produced amounts to about one percent of the mass of fresh fuel loaded (the typical mass of the annual load for power reactors is 20 – 30 tons).
In 1962, in the United States, as an experiment, a nuclear explosive device with a power of 20 kilotons based on plutonium isolated from spent nuclear reactor SNF (reactor grade plutonium) was designed, manufactured and tested. As follows from the data on the results of the experiment officially published in 1977, in this case it wasn’t actually a nuclear warhead, because to overcome the above negative properties of the Pu-240 isotope, developers had to resort to such technical tricks that made it possible to achieve 20 kilotons only for the account of transforming the YABZ into a primitive nuclear explosive device, unsuitable for use.
In this regard, it cannot be denied that “intruders” may, in principle, try to repeat this experiment using SNF from a power reactor at their disposal, but this possibility seems unlikely for two reasons. First of all, to carry out this kind of work requires an exceptionally high level of professionalism of the developers, who are unlikely to have “home-builders”. And secondly, to isolate plutonium, it is necessary to design and build a plant for reprocessing spent nuclear fuel, which is difficult to accomplish covertly and also very costly. For example, the construction of a civilian spent fuel reprocessing plant in Rokkas-mura (Japan) took 15 years and cost more than 20 billions of dollars.
Considering the above, we can conclude that the fears expressed by some foreign and Russian experts and broadcast through the media that nuclear power, especially in the context of large-scale plans for the construction of nuclear power plants in some developing countries, may pose a real threat to the non-proliferation regime. grounds.
A good example of this is the construction of Bushehr NPP in Iran. At the first stage of work on the part of the American leadership, there were calls for Russia to break the relevant contract with reference to the fact that, they say, there is a risk that Iranians will not illegally extract plutonium from the spent nuclear fuel of a nuclear power reactor. Somewhat later, such fears disappeared, including for the reasons stated above, and also taking into account the fact that an agreement was reached with Iran on returning SNF to Russia from Bushehr NPP during the entire life cycle of the plant.