压水堆核电厂冷停堆状态下防止堆芯裸露的措施

Preventive Measures to Avoid Core Uncovering in Cold Shutdown for Pressurized Water Reactor Nuclear Power Plants

压水堆核电厂冷停堆期间,余热排出泵可能因产生涡流导致气蚀失效,存在堆芯裸露甚至融化的风险。为了有效预防反应堆冷停堆状态下发生堆芯裸露事故,通过对冷停堆期间反应堆堆芯冷却系统各种水位阶段的分析并参考国外核电厂发生的反应堆余热排出系统失效情况,结合大亚湾核电站的运行经验,提出对反应堆堆芯冷却系统水位测量、余热排出泵入口的涡流探测及丧失余热排出功能后自动补水系统的多种改进措施。概率风险分析结果表明,实施这些改进措施,可有效降低反应堆堆芯裸露的风险。

During cold shutdown, the loss of residual removal function （unavailable of the RHR pump） due to the vortex suction or cavitations distinctly increases the core uncovering possibility, which might lead to core meltdown. In order to prevent the core uncovering accident during cold shutdown, the water motion in the reactor primary circuit and the RHR degrade incidents occurred in nuclear power plants in the world are analyzed and the three following preventive measurement are proposed： RCP water level measurement, RHR pump vortex detection and water makeup after loss of RHR function. The measures are based on experiences of Daya Bay nuclear power plant. The Probability Risk Analysis indicates that these three modifications decrease core uncovering efficiently.