Analysis of beyond design basis accidents in spent fuel pools of the ignalina NPP

The main problem in nuclear energy is providing of safety at all stages of lifetime of nuclear installations in conditions of normal operation and accidents. Prevention of radioactive substances release in an environment or minimization of releases is the primary goal of the organizations operating nuclear power plants. Usually the means of safety improvement are based on the analysis of transients, design and beyond design basis accidents (BDBA). Consideration of BDBA development as a result of which the failure of nuclear fuel can occur, is actual not only for accidents with the core degradation, but for accidents in spent fuel pools as well. The analysis of BDBA in spent fuel pools in the given paper is carried out with the purpose of determination of critical stages of accident development (failures of fuel element claddings, start of fuel melting, generation of hydrogen, etc.). The analysis was performed using the ATHLET-CD model of spent fuel pools of RBMK-1500 in Ignalina NPP Unit-2. Two cases: (1) loss of water due to loss of heat removal and (2) loss of water due to leakage accident, were selected for the analysis, because they cover all possible phenomena and uncertainties in boundary conditions of initiating event and modeling approach except the transport of fission products and aerosols to the environment. (authors)