压水堆核电厂严重事故卸压阀能力评估

Evaluation of SADV Capacity in PWR Nuclear Power Plant

在百万千瓦级压水堆核电厂中为防止高压熔堆严重事故发生时发生高压熔喷(HPME)和安全壳直接加热(DCH),参考EPR堆型在稳压器上额外设置严重事故卸压阀(SADV),对主系统进行快速卸压。建立百万千瓦级压水堆核电厂事故分析模型,选取丧失厂外电叠加汽动辅助给水泵失效,一回路管道小破口以及丧失主给水三条典型严重事故序列,进行系统热工水力及卸压能力分析。计算结果表明:如果不开启严重事故卸压阀,三条事故序列在压力容器下封头失效时一回路压力均较高,有发生高压熔喷和安全壳直接加热的风险。根据严重事故管理导则开启严重事故卸压阀,可以有效降低一回路压力,三条事故序列均可以防止高压熔喷和安全壳直接加热发生。针对卸压阀阀门面积的影响进行分析,表明阀门面积减小到4.8×10-3 m2后下封头失效时RCS压力会有所增加,仍然能够满足RCS的卸压要求,且可延迟下封头失效时间。

To prevent high-pressure melt-spray event （HPME） and direct containment heat （DCH）, dedicated severe accident depressurization valve （SADV） is added to the pressurizer with the reference of EPR design. The mechanism model for 1000 MWe PWR nuclear power plant is built and three sequences of TMLB＇, SBLOCA and LOFW are selected to be investigated. Thermohydraulic and depressurization of RCS is analyzed, which shows that： without opening SADV, the RCS pressure is high enough to induce large risk of HPME and DCH when lower head of the RPV fails for the selected typical severe accident sequences~ while with opening SADV according to severe accident management guidelines, the RCS pressure is low enough to prevent HPME and DCH for the selected typical severe accident sequences. The effect of SADV area is also analyzed, which shows that the RCS pressure will increase by decreasing the valve area to 4. 8e-3 m2 when lower head of the RPV fails; while the criterion for RCS depressurization is still satisfied and the time for lower head of the RPV failure is also delayed.