Fuel integrity evaluation for the shutdown BWR-4 plant during LOCA event

Abstract

Two BWR units in the Chinshan stopped operation since 2017. However, the spent fuel assemblies still reside in the reactor core, and the plant staffs defined this configuration as the Mode 5 condition. If a Loss-of-Coolant Accident (LOCA) occurs in this condition, the water level will drop and then maintain at approximately 2/3 of the height of the reactor core. The upper 1/3 of the fuel will be exposed to air, and then the fuel cladding temperature will increase significantly. This study use RELAP5 to investigate the effect of different Emergency Core Cooling System (ECCS) to mitigate the LOCA. It is found that the core spray (CS) system can sufficiently suppress the fuel temperature. However, the temperature increase of the uncovered fuel becomes larger if the low pressure coolant injection (LPCI) system which does not provide direct core injection is operable. Based on the results, the peak cladding temperature of both cases are still below the acceptance criteria of 600 °C.