Comparison of Codes and Neutronics Data Used in the United States and Russia for the TOPAZ‐2 Nuclear Safety Assessment

The TOPAZ‐2 reactor system is a heterogeneous epithermal system fueled with highly‐enriched fuel based on uranium oxide, cooled by a sodium‐potassium liquid metal (NaK), using a zirconium hydride moderator, with 37 thermionic fuel elements (TFEs) built into the core. The core is surrounded by a radial beryllium reflector which contains rotating regulating drums with moderating segments. An important problem is the guaranteeing of nuclear safety upon the accidental falling of the TOPAZ‐2 reactor into water, which leads to the growth of the reactivity of the reactor. It has turned out that it is necessary to use the Monte‐Carlo method for the conduct of neutronics calculations of such a complex reactor. In the United States (U.S.) and Russia, different codes based on the Monte‐Carlo method are used for calculations — the MCNP code in the U.S., and the MCU‐2 code in Russia. The goal of this work is the comparison of the codes and neutronics data used in the U.S. and Russia for the basis of the TOPAZ‐2 nuclea...