严重事故下正常余热排出系统向堆芯注水策略分析

选取导致堆芯熔化频率最高的始发严重事故--直接注入（DVI）管线断裂事故，以及典型高压熔堆事故--丧失主给水始发事故(LOFW)，利用MAAP4程序，分析反应堆堆芯热工水力行为，并对正常余热排出系统（RNS）堆芯注水策略的有效性与负面效应进行评估。分析结果表明，在DVI管线断裂事故和LOFW严重事故序列中，利用RNS进行堆芯注水可有效终止堆芯熔化进程，维持堆芯长期冷却。但堆芯再淹没会产生更多的氢气，存在增加安全壳氢气燃烧风险的可能性。此外通过分析利用严重事故管理导则中辅助计算文件给出的堆芯最小流量实施堆芯注水策略，讨论注水流量对堆芯冷却的影响，结果表明，在实施堆芯注水策略时，建议在系统允许的情况下采用更高的流速进行堆芯冷却。

Analysis of RCS Injection Strategy by RNS during Severe Accident

In order to evaluate the effectiveness of normal residual heat removal system (RNS) for RCS injection strategy during severe accidents ,two typical severe accident sequences were selected and analyzed with MAAP4 code ,including direct vessel injec‐tion (DVI) line break induced severe accident w hich contributes most to the core damage frequency ,and loss of feed water (LOFW) induced severe accident which is a typical high‐pressure core melt accident .Both mitigation effect and negative impact of the RNS injection strategy were evaluated .The results show that RNS injection can effectively terminate core melt progression and keep long‐term core cooling in two typical severe accident sequences .However ,more hydrogen generates in core during core reflooding stage w hich may lead to hydrogen hazard in the containment . Furthermore , the influence of injection flowrate was discussed with the minimum injection flowrate for long term decay heat removal given by the computational aid documents from the severe accident management guideline .T he analysis results indicate that higher flow rate should be preferred for RCS injection strategy during severe accidents if the injection system would be available .