百万千瓦级压水堆严重事故后再注水的有效性评价

根据现有的设计资料,使用一体化严重事故分析程序MELCOR1.8.6建立了核电厂一、二回路系统,非能动堆芯冷却系统和安全壳系统的模型,并模拟冷段2英寸(5.08cm)小破口叠加重力注入失效的严重事故发生后,将冷却剂注入堆芯的情形,分析其对严重事故进程的缓解能力。本文选取3个严重事故的不同阶段,将冷却剂分别以小流量(10kg/s)、中流量(50kg/s)和大流量(200kg/s)的速率注入堆芯,通过比较氢气产生量、堆芯放射性产生量及堆芯温度等数据来评估在严重事故不同阶段再注水的可行性。结果表明:在堆芯损伤初期,可认为10kg/s以上的流量足以冷却百万千瓦级事故安全。而当严重事故发展到堆芯开始坍塌阶段,200kg/s的注水流量可认为是基本可行的,而小于此流量的注水应慎重考虑。

Water Reflooding Effectiveness Assessment for 1 000 MWe PWR under Severe Accident Condition

The MELCOR1.8.6 code was applied to a severe accident model of a 1 000 MWe PWR which includes primary system, secondary system, passive core cooling system and containment system. For the transient case, a small break LOCA with 2 inch (5.08 cm) break at the cold leg concurrent with failure of gravity injection was selected. After the core was damaged due to the failure of gravity injection, it was assumed that the coolant was injected into the pressure vessel, and then the water reflooding effectiveness was evaluated and analyzed. In this calculation, the coolant injection into reactor core with the small (10 kg/s), medium (50 kg/s) and large (200 kg/s) mass flow rates respectively at 3 different time stages of the severe accident was simulated. The effectiveness of water reflooding was assessed through hydrogen production, radioactive materials released from core, and core temperature. The results show that the mass flow rate above 10 kg/s is believed to be efficient for cooling a 1 000 MWe reactor at the beginning of core damage. However, with the accident developing to core relocation, a large mass flow rate of 200 kg/s is considered to be applicable for core cooling. As a result, the mass flow rate below this value should be carefully considered when injecting water into the core.