中压安注对RRA连接模式下严重事故进程影响分析

针对中国改进型百万千瓦级压水堆（CPR1000）核电机组在中间停堆反应堆余热排出系统（RRA）连接模式下失去高低压安注和喷淋的冷却剂丧失事故（LOCA），采用MAAP5程序对参考机组的反应堆堆芯、反应堆冷却剂系统以及安全壳系统进行模拟计算，同时结合计算结果分析中压安注系统对该严重事故序列进程的影响，并研究其对事故的缓解作用。分析结果表明，在RRA连接模式下出现LOCA导致的堆芯裸露和升温过程中，中压安注的及时注入能有效地限制堆芯的升温行为，并可对严重事故进程起到重要的缓解作用，甚至为事故工况下失去高低压安注和喷淋时避免堆芯完整性遭到破坏提供可能。最后，根据分析结果针对现行核电机组的运行规程提出改进建议:对于中压安注箱的行政隔离行为，只对其电气开关做相应的隔离操作，而对安全壳厂房内的阀门就地部分做挂牌警示，不做现场挂锁的操作，这样不仅可避免在正常运行工况下中压安注箱误注入行为的发生，同时能够在RRA连接模式下发生LOCA时有效地保障堆芯的完整性，在保证电厂正常安全运行的同时，提高了机组在该模式下发生严重事故的缓解能力。 

Analysis of Impact of Medium Pressure Safety Injection on Severe Accident Process under RRA Connected Mode

Aiming at the loss of coolant accident (LOCA) of China's improved million kilowatt PWR (CPR1000) Nuclear Power Unit losing high and low pressure safety injection and spray in reactor residual heat removal system (RRA) connected mode of intermediate shutdown, the reactor core, reactor coolant system and containment system of the reference unit are simulated and calculated by using MAAP5 program, at the same time the impact of medium pressure safety injection on the severe accident process is analyzed by combining with the calculation results, and the mitigation effect on the accident is studied. The results show that the timely injection of medium pressure safety injection can effectively limit the temperature rising behavior of the core, and play an important role in mitigating the process of severe accidents during the process of core exposure and temperature rise caused by LOCA under RRA connected mode, and even it is possible to avoid core integrity damage when high and low pressure safety injection and spray is lost under accident conditions. Finally, according to the analysis results, the improvement suggestions are put forward for the current operation regulations of nuclear power units. For the administrative isolation behavior of the medium pressure safety injection tank, only the corresponding isolation operation is performed for its electrical switch, while the local part of the valves in the containment building is provided with a tag warning, and the on-site padlock operation is not performed, which can not only avoid the misinjection of the medium pressure safety injection tank under normal operation conditions, the integrity of the reactor core can be also effectively guaranteed after the occurrence of LOCA under RRA connected mode. The normal and safe operation of the power plant can be ensured, and the mitigation ability of severe accidents of the unit under this mode can be improved.