Assessment of Thermal Behaviour of Spent Nuclear Fuel Storage Pool in the Exsiccation Accident

The accident at the Japanese nuclear power plant (NPP) Fukushima-1 in March 2011 showed that possibility of accidents with potentially serious radiation consequences could not be excluded with large-scale measures for improvement of safety level. For spent nuclear fuel storage facilities, one of such accidents may be the interruption of heat removal from spent nuclear fuel (SNF) due to the failure of the cooling system as a result of disruption of the power supply system with the failure of backup power sources or rapid full dehydration of the wet SNF storage as a result of the destruction of building structures and its depressurization. The decision to take preventive measures in advance to minimize exposure to personnel and the public is based on conservative estimates of possible radioactive discharges. To perform such assessments, the operating organizations carry out a calculated justification of the thermal and hydraulic characteristics of the SNF system in the accident scenarios with long-term blackout and a violation of heat removal. APROS is one of the software tools that are used in SEC NRS for calculating the thermal-hydraulic characteristics of systems in transient modes by solving the equations of heat and mass transfer in a steam-water mixture. For more detailed calculations of the structural elements of spent fuel assemblies (SFA) temperature, the ANSYS software is used, which implements the finite element method. The results obtained with the help of the above simulation tools are used by specialists of SEC NRS to assess the protective measures developed by operating organizations.