Safety Analysis at Increasing Heat Conductivity of Uo2-Fuel of Nuclear Power Plants

Abstract

One of the modern directions of improving the safety and operational efficiency of nuclear UO2 fuel is related to the modernization of its thermal conductivity. However, an increase in the thermal conductivity of UO2 fuel, ceteris paribus during accidents with violations of heat removal from the reactor core, can lead to a corresponding increase in the temperature of the cladding of fuel rods and a violation of safety conditions for the maximum allowable temperature of the cladding of the fuel rods. In this case, design basis accidents become trans-design basis and a corresponding decrease in the overall level of nuclear safety occurs.Such provisions determine the need to optimize the modernization of increasing the thermal conductivity of UO2 fuel.Based on the previously developed express method of safety analysis during the modernization of nuclear power plants and the known results of computational modeling with the RELAP5 / M3.2 code of the maximum design basis accident (with two-sided rupture of the main circulation pipe) for serial power units with VVER-1000, it was determined that a rational increase in the thermal conductivity UO2 -Fuel is not more than 100% of the design.With a large increase in the thermal conductivity of UO2 fuel, the safety conditions are violated for the maximum permissible temperature of the zirconium cladding of the fuel elements.