ROSA/LSTF test on nitrogen gas behavior during reflux cooling and RELAP5 analysis

Takeda, Takeshi ; Otsu, Iwao 

The primary coolant inventory may affect degradation in the primary depressurization due to failure of accumulator system isolation in PWR accidents. A separate-effect experiment with the ROSA/LSTF was thus conducted focusing on nitrogen gas behavior under reflux cooling condition at low pressures. The test showed primary pressure and flow behavior in steam generator (SG) U-tubes were dependent on amount of the gas accumulated. In addition, RELAP5/MOD3.3 code indicated remaining problems in the predictions of the primary pressure and SG U-tube fluid temperature after the nitrogen gas inflow.