SAFETY JUSTIFICATION FOR WASHING ВВЕР-440 REACTOR FUEL ASSEMBLIES IN THE FRAMATOME CLEANING TANK

The primary objective of conducting this research is to obtain a more accurate estimation of the residual heat release from fuel assemblies after their removal from the reactor core and to determine, based on calculation results, the optimal method applicable for assemblies from different years of operation. The application of an advanced methodology [1] proposed by the U.S. Nuclear Regulatory Commission (NRC) enabled the consideration of various heat sources, while the residual heat release calculations in the standards of the SE “NNEGC “Energoatom” employed the SCALE software package, which accounts for the specific characteristics of the fuel. The approach suggested by the NRC allows for the identification of the heat contribution generated by each component, namely: heat release due to actinide decay, neutron capture, activation of structural elements, and fission product decay. The sum of these contributions defines the total heat release of the fuel assembly. The calculations indicated that for assemblies in their fifth year of operation, it is more appropriate to use the NNEGC Standard method, whereas for assemblies from the first to fourth years of operation, the approach proposed by the NRC is preferable. This approach will allow for more conservative results, which can subsequently be used to substantiate safety.