Measurement of non-condensable gas in a PWR small-break LOCA simulation test with LSTF for OECD/NEA ROSA project and RELAP5 post-test analysis

PWR小破断LOCAに関するOECD/NEA ROSAプロジェクトLSTF実験での非凝縮性ガス計測とRELAP5実験後解析

竹田 武司 ; 大和田 明彦; 中村 秀夫  

Takeda, Takeshi; Owada, Akihiko; Nakamura, Hideo

An OECD/NEA ROSA Project experiment was conducted simulating a PWR 0.5% cold leg small-break LOCA with steam generator (SG) secondary-side depressurization as an accident management measure to clarify such complex phenomena as non-uniform flow among the SG U-tubes under natural circulation (NC) with air as non-condensable gas. The gas concentration was measured at the SG outlet plenum by using a gas measurement device to measure oxygen concentration in steam-gas mixture that is developed employing a Zirconia sensor. Non-uniform flow behaviors were observed in the SG U-tubes with non-condensable gas ingress. Air concentration in steam-gas mixture was estimated to be about 40-50% at the SG outlet plena after the U-tube downflow side became empty of liquid. Post-test analysis by RELAP5/MOD3.2.1.2 code revealed that the code underpredicts the primary pressure a bit after the gas inflow with some discrepancies in the SG U-tube liquid level and the NC mass flow rate.