Lessons Learned from the Result Comparison of Calculations of a Reference Severe Accident Sequence on a TMI-2 Like PWR Reactor of 900 MWe with the Integral Codes ASTEC and MELCOR

This report presents the activity performed in the frame of LP1, Objective A (Acquisition, development and validation of methods and codes for sustainable and safety studies and analyses), Task A3.3 of PAR2013, ADP ENEA-MSE. In this study the integral codes ASTEC and MELCOR have been applied for the calculation of a reference severe accident sequence (SBLOCA) on the TMI-2 plant (PWR of 900 MWe). Several insights on the reliability and consistency of code response have been gained from a detailed comparison of the main code results. The reasons of the differences in code results have been thoroughly investigated and tentatively explained. Recommendations have been made for sensitivity studies on important and uncertain core degradation parameters and model options, in order to better understand the different code behavior and make proposals for further code model improvements.