Severe accident analysis of a PWR spent fuel pool in case of loss of pool coolant

Abstract

The Fukushima Daiichi nuclear accident shows that it is necessary to study potential severe accidents and corresponding mitigation measures for the spent fuel pool (SFP) of a nuclear power plant (NPP). This study presents the analysis of loss-of-pool-coolant accident scenarios and the discussion of mitigation measures for the SFP at a pressurized water reactor (PWR) NPP with the MAAP5 code. Analysis of uncompensated loss of water due to the loss-of-pool-coolant has been performed. Scenarios of the accident such as overheating of uncovered fuel assemblies, oxidation of claddings and hydrogen generation, loss of intactness of fuel rod claddings, and release of radioactive fission products were predicted with the assumption that mitigation measures were unavailable. Furthermore, emergency injection is an important mitigation measure for the SFP safety concerns in case of pool leakage accident. It provides reflooding of the spent fuels from below, reducing clad temperatures or even quenching the molten corium. However, to recover the pool water inventory, the injection rate should be large enough so as to replenish the lost pool water due to leakage and vaporization. Considering that there may be very high radiation levels in the SFP building, sources of injection water should be available from a remote point.