严重事故下封头失效机理分析

Analysis for the Lower Head Failure Mechanism under Severe Accident Condition

严重事故下堆芯熔融物坍塌到下封头,可能造成压力容器失效。本文针对造成压力容器失效的五个机制,运用一体化严重事故分析程序,分析全场断电分别叠加破口失水、主蒸汽输送管线破裂和蒸汽发生器传热管破裂事故对下封头完整性的影响。研究结果表明,三类事故均造成压力容器失效,全场断电叠加中破口失水事故由于破口位于热管段,距离稳压器和压力容器较近,事故响应更快,比全场断电分别叠加蒸汽发生器传热管破裂和主蒸汽输送管线破裂提前失效约20000 s;全场断电叠加中破口失水事故中作用于贯穿件上的压力载荷超出贯穿件及其焊缝所能承受的最大载荷之和使得贯穿件弹出造成下封头失效;全场断电分别叠加蒸汽发生器传热管破裂和主蒸汽输送管线破裂均是因高温熔融物对下封头节点的损伤份额大于1使得下封头蠕变破裂造成压力容器失效。

In a severe accident,the core melt collapses to the lower head,which may cause the failure of the pressure vessel.In this paper,aiming at the five mechanisms that cause the failure of pressure vessels,the integrated serious accident analysis program is used to analyze the completeness of the lower head due to station blackout to superimpose coolant loss accidents respectively,the rupture of the main steam transmission pipeline,and the rupture of the steam generator heat transfer tube.The study results show that the three types of accidents all caused the failure of the pressure vessel.In the superposition of the station blackout,the coolant loss accident occurred at the break because the break was located in the heat pipe section 3,which was close to the pressurizer and the pressure vessel,and the accident response was faster.Compared with the station blackout superimposed on the rupture of the steam generator heat transfer tube and the rupture of the main steam transmission pipeline,the failure was about 20000 s earlier.The pressure load acting on the penetration in the accident of loss of coolant from the break in the superposition of the power outage exceeds the sum of the maximum load that the penetration and its weld can withstand,causing the penetration to pop out and cause the failure of the lower head.The station blackout was superimposed on the rupture of the steam generator heat transfer tube and the rupture of the main steam transmission pipeline,both of which were caused by the damaged fraction of the high temperature melt to the lower head node greater than 1,which caused the failure of the pressure vessel due to the creep rupture of the lower head.