小破口冷却剂丧失始发安全壳失效事故源项行为分析

Analysis of Source Term under Containment Failure Severe Accident Induced by SB– LOCA

采用一体化严重事故仿真程序对600MW压水堆核电厂小破口冷却剂丧失(SB-LOCA)始发安全壳隔离失效、安全壳早期失效和晚期失效三类事故的源项行为进行分析。分析结果表明:(1)由于沉积作用或残留在熔融物中,挥发类和非挥发类裂变产物相对于惰性气体类,释入环境份额较小;(2)事故进程中安全壳与环境之间较小的压差和安全壳较晚的失效时间,分别使得在安全壳隔离失效和晚期失效事故中裂变产物较为缓慢地释入环境;(3)安全壳早期失效事故中,在安全壳直接加热(DCH)现象发生后熔融物颗粒与安全壳大气换热过程中,从熔融物释出的挥发性与非挥发性裂变产物在安全壳失效后快速地释入环境。上述结论可为严重事故源项缓解措施研究、厂外后果评价以及应急策略制定提供技术支持。

With an integral severe accident analysis computer code,fission products behavior is analyzed during containment isolation failure,containment early and late failure accidents induced by small-break loss-of-coolant accident（SB-LOCA）for600MWe PWR NPP.The results are as follows：（1）Fractions of volatile and nonvolatile fission products,releasing into environment,are smaller than that of noble gases because of deposition or remaining in the corium.（2）The small pressure between the containment and environment,and the lateoccurrence of the containment failure,respectively leads to the fission products releasing slowly into environment under containment isolation failure,and containment late failure accidents.（3）Under the early containment failure accident,in the process of heat exchange between corium particles and atmosphere in containment following direct containment heating（DCH）,volatile and nonvolatile fission products are released from the corium.They release quickly into environment after the containment failure.The results can give some supports for research of source term measures under severe accidents,assessment of the accident consequences and development of emergency strategy.