Boil-off experiments with the PSI-NEPTUN facility: Analysis and code assessment overview report

Abstract A series of experiments was performed in the NEPTUN test facility consisting of ten boil-off (core uncovery) and one adiabatic heat-up tests. In these tests rod power, system pressure and initial coolant subcooling were varied. The repeatability of the experiments was also demonstrated. Some of the boil-off data obtained from the NEPTUN test facility are used for the assessment of the thermal-hydraulic transient computer codes. These calculations were performed extensively using the frozen version of TRAC-BD1/MOD1 (version 22). A limited number of assessment calculations were also done with RELAP5/MOD2 (version 36.02). In this report the main results and conclusions of these calculations are presented with the identification of problem areas in relation to the models relevant to boil-off phenomena.