Modelling guidelines for safety analysis of Station Black Out sequences based on experiments at the PKL test facility

After the Fukushima accident, “stress-test” activities carried out worldwide pointed out the need to study additional accident management measures to deal with prolonged Station Black Out (SBO) scenarios. Without any operator actions, a total loss of the secondary side heat sink leads to core uncovery, to core damage and ultimately to a melt-down scenario. The international NEA/OECD PKL-3 project has addressed the efficiency of possible accident management actions to re-establish core cooling by experiments at the PKL test facility. Since best estimate system codes were mainly developed to simulate LOCA scenarios, their performance and the general guidelines followed to simulate PWR power plants are called into question. In this paper, RELAP5 simulations of three SBO experiments are presented. An assessment of the code for the particular phenomenology in the experiments have been conducted. Specific guidelines on modelling and a list of the most important sources of uncertainties are provided.