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In Russia (JSC NIKIET) a project of a fast reactor BREST-1200 is being developed. The article analyzes the safety of the BREST reactor with maximum limiting power (BREST-2000, -2400). In BREST reactors with an electric power of 1200 MW and more, the void reactivity effect of can be positive. The most dangerous scenario is associated with the entrainment of bubbles into the central part of the core (with a volume fraction of bubbles of 50 … 60%). In this case, the magnitude of the void reactivity effect is several times higher than the effective fraction of delayed neutrons β. For the BREST-2400 reactor, the maximum void reactivity effect is about 7 β (for BREST-2000, about 6 β). When other ATWS are implemented against the background of erosion and corrosion of structural steel, the total introduced reactivity can also exceed β, which will lead to an accident. To ensure safety, it is necessary to adjust the design solutions. When used as a coolant, lead extracted from thorium ores (with a concentration of 208Pb isotope from 75 to 98%) and tungsten coatings of fuel claddings, the void reactivity effect is negative even in the BREST-2400 reactor, and when switching to a new cermet fuel (0.8 MN - 0.2 U) it is easy to ensure the safety of the reactor.

Abnormally high pressure or temperature can significantly reduce the lifetime of atomic nuclei including stable. A hypothesis on stable nuclei decays caused by mechanical collision of macro-objects containing these nuclei is put forward. Mechanisms of such decays are presented. At the same time the distance between interacting nuclei can be significantly higher than the range of nuclear interaction (as manifestations of strong interaction). In decays initiated by external impact, the mean lifetime with respect to particular decay can change depending on these factors. The hypothesis is verified experimentally. When a bismuth bullet collides with a steel flat target, we see different types of stable bismuth isotope decay including cluster one, which is not found in nature (if there is no external impacts). This new class of physical processes can be related to the collective radioactive decay of atomic nuclei initiated by an external mechanical impact.

The main purpose of the article is to substantiate the safety of a lead-cooled fast reactor of high power. Thermal power of the reactor is about 5600 MW, electric power is about 2400 MW. The design is similar to the BREST-OD-300 project developed at NIKIET JSC. The safety of a high-power reactor is ensured only with the use of innovative core materials (previously the author proposed to use fuel based on micrograins of UN-PuN mononitride and uranium metal nanopowder, a coolant based on lead of thorium ores, fuel element cladding based on EP823 steel with nanopowder of titanium oxide and yttrium, tungsten-coated cladding are used). Research methods are mathematical modeling of the reactor and reactor emergency modes. The most dangerous emergency modes (ATWS – anticipated transients without scram and their combinations, taking into account the non-simultaneous start) are considered. The studies used the codes developed by the author (Dragon-M, FRISS-2D) and the well-known code for precision neutron-physical calculations (MCU). A safe reactor corresponds to the fulfillment of restrictions for a number of functionals characterizing emergency modes. Studies have shown that when using innovative core materials, any combination of emergency modes does not lead to unacceptable releases of radioactive substances outside the Nuclear Power Plant. The results of the study show the possibility of developing reliable, safe, environmentally acceptable nuclear power based on reactors of this type.