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The results of a verification of the BONUS method as regards predictions of the time dependence of the mass and activity of fission products produced in thermal reactors are presented. Different standard regimes of fuel irradiation in VVER-1000 are examined, and the results calculated using the autonomous version of the BONUS code and as a module integrated into SOCRAT code are compared with the results obtained using other codes, including precision program complexes. On the whole, the calculation shows good agreement between BONUS and alternative codes; the standard deviation variance is 6-13.5% for fission product mass and activity, which is comparable to the discrepancies between different variants of the alternative calculations themselves.It is obvious that the moduli of a well-balanced integrated code that describes the complex physicochemical processes occurring in a reactor facility in standard and emergency situations must conform to an overall targeted accuracy. Specifically, considering the simplification of the models used to describe fission-product transport in a reactor facility as well as the uncertainty of the parameters and input data, high-accuracy cumbersome computational methods can hardly be regarded as the optimal choice for describing effects associated with radioactive intertransmuting actinides and fission products. In this connection, the BONUS method was developed at the Institute of Problems in the Safe Development of Nuclear Energy (IBRAE) to perform simplified calculations of the time dependence of the concentration, activity, and energy release of fission products. The method is implemented as a separate program module to be included in computer codes, such as the MFPR code [1,2], that simulate the behavior of fuel and the yield of fission products in different operating regimes or in integrated codes, such as SOCRAT [3], that simulate processes occurring inside and outside vessels during anticipated and unanticipated accidents.The BONUS method describes in the one-group approximation the change of the concentration of actinides under neutron irradiation as well as the concentration of fission products taking account of their production as a result of fission, γ and β decay, and radiative capture of slow neutrons. Of course, the evolution of the radionuclide composition of the fuel after the reactor is stopped is also simulated. Actually, the BONUS module incorporated in an external code is used to calculate the production of actinides and fission products in an individual spatial cell. It is supposed that the time dependence of the specific energy release in a given cell or the thermal-neutron flux density is given in at the irradiation stage. The par-

As a result of catastrophic events on the nuclear power plant “Fukushima” the European organizations on regulation of nuclear power (ENSREG) initiated wide-scale measures for complex designs revision of already operating and under construction European and Russian NPPs. Inspection was made about resistance of power units to external influences of the natural character, being accompanied by multiple failures of safety systems. Within these works stress tests for constructed power units of LAES-2 and the Baltic NPP were executed. The structure of these checks included the settlement analysis of a condition of NPP at accident with loss of all AC power supply sources which results are presented in report materials. Accident calculations with a full blackout were executed on the best-estimated heat-hydraulics code KORSAR/GP for justification of power unit preservations in the intact condition within 72 hours from the accident beginning by means of SG PHRS. The system is developed for feed of the SG PHRS tanks and the fuel pool for working capacity extension the SG PHRS and power unit preservation in a stable condition more than 72 hours from the accident beginning. Use of system for feed of tanks the SG PHRS and the fuel pool allows to increase significantly resistance of the NPP to external influences of the natural character and to increase time of preservation of the blackout power unit in a stable condition more than 5 days.