ROSA/LSTF test and RELAP5 code analyses on PWR hot leg small-break LOCA with accident management measure based on core exit temperature and PKL counterpart test

An experiment was performed for the OECD/NEA ROSA-2 Project using the large scale test facility (LSTF), which simulated a hot leg small-break loss-of-coolant accident with steam generator (SG) secondary-side depressurization as an accident management measure based on core exit temperature in a pressurized water reactor (PWR). This experiment was conducted under two conditions of high-pressure to meet the PWR pressure condition and of low-pressure to meet the Primӓrkreislӓufe Versuchsanlage (PKL) condition. Core uncovery took place by core boil-off with no reflux coolant from the SGs in the LSTF test. The increase rate of the cladding surface temperatures from top to center of the core relative to the core exit temperature increased according to the linear heat rate in the LSTF test. Some discrepancies appeared between the LSTF low-pressure phase and PKL test results for the core exit temperature increase due to differences in low-temperature structures around the core exit. The RELAP5/MOD3.3 code indicated a remaining problem in the prediction of the core exit temperature due to pseudo coolant mixing. Results of uncertainty analysis for the LSTF low-pressure phase test clarified influences of the combination of the multiple uncertain parameters on peak cladding temperature within the defined uncertain ranges.