WSMR非能动安全系统在全厂断电事故下的事故缓解能力分析

Accident mitigation ability analysis of WSMR passive safety system under station blackout accident

先进的小型模块化反应堆(简称小堆)设计广泛地采用一体化结构设计与非能动安全理念,使小堆固有安全性显著提升.然而,在实现小堆广泛商用化之前,需要对其安全性进行全面评估.该研究利用严重事故分析程序MELCOR,对WSMR(Westinghouse small modular reactor)进行建模,以全厂断电事故为基础事故序列,分析了全厂断电事故在WSMR中的事故进程;同时对非能动安全系统在全厂断电事故下的缓解能力进行了研究,其中着重探讨堆芯补水箱的事故缓解作用,并针对堆芯补水箱的有效运行数量与启用时间进行了敏感性分析.研究结果表明:全厂断电事故会导致堆芯冷却能力下降,从而造成堆芯坍塌失效;而堆芯补水箱能够为反应堆提供额外的冷却剂,且利用余热移除热交换器将堆芯余热移至外部最终热阱水箱中,从而保证堆芯的长期冷却.相关敏感性分析结果表明:在其他非能动安全设施全部失效的情况下,至少需要2个正常运行的堆芯补水箱才能有效缓解事故;在堆芯补水箱启动失败的情况下,若考虑重新启用堆芯补水箱,重启时间应不晚于52.5 ks才能避免堆芯结构损坏.该研究结果可为相关小堆的严重事故管理导则的制定和改进提供参考,从而增强对全厂断电事故的应对能力,同时有利于提升模块化小堆非能动安全系统的事故缓解能力.

The design of advanced small modular reactors widely uses integrated system design and passive safety concept to significantly improve the inherent safety of small modular reactors.However,before achieving the commercialization of small modular reactors,their safety performance needs to be fully evaluated.In this study,severe accident analysis program MELCOR was used to model the Westinghouse small modular reactor(WSMR).Then,the station blackout was introduced to the WSMR and the development process of the accident was analyzed.The mitigation ability of the passive safety system under the station blackout accident was analyzed afterwards.Furthermore,the sensitivity analyses of the number of effectively operated core makeup tank and its reinvesting time were carried out as well.The results show that the station blackout accident causes the core cooling capacity to drop,which leads to core collapse.The core makeup tank is able to provide additional coolant for the reactor and to transfer the residual heat to the external ultimate heat sink tanks through residual heat removal heat exchangers,thus guarantees the long term cooling of the core.The results of the sensitivity analysis show that in the case of total failure of other passive safety features,at least two core makeup tanks need to function normally in order to effectively mitigate the accident.In the case that the core makeup tanks fail to start initially,if they can be restarted,the restart time should be no later than 52.5 ks to avoid core damages.The results of this study will supply references for the development and improvement of related severe accident management guidelines for small modular reactors,thereby enhancing the ability to cope with the station blackout accident,as well as helping to improve the accident mitigation ability of the passive safety system of small modular reactors.