Computation methods and techniques for solution of coupled multiphysics problems in precision calculations of VVER type reactors

Precise simulation of the isotopic composition of nuclear fuel and temperatures during reactor operation requires solution of two coupled tasks from two different fields of physics: neutron-physical calculation and thermal physics calculation. Simple way is based on models using averaged temperature, thermal conductivity factors, and heat power density. In practical situations, changing of isotopic composition and changing of temperature distribution over fuel assembly influence each other. In this paper, coupled approach is presented, based on modern algorithms, methods and codes to solve consistent tasks of thermal conductivity, neutron transport, and nuclide transformation kinetics. It allows to perform neutron-physical and thermal-physical calculation of the reactor with detailed temperature distribution, with account of temperature-depending thermal conductivity and other characteristics. It was applied to studies of fuel cell of the VVER-1000 reactor.