堆芯熔化严重事故下反应堆压力容器下封头高温蠕变分析

核电厂在发生堆芯熔化严重事故时，采用堆内熔融物滞留（IVR）策略将熔融物包容在反应堆压力容器（RPV）内是一项重要缓解措施。在IVR策略期间，RPV下封头在熔融物的极高温度载荷和力学载荷的共同作用下很有可能因过度蠕变变形而失效。因此，有必要对熔融物滞留条件下RPV下封头进行蠕变变形分析，以保证RPV结构完整性。该文在假定IVR条件下，采用有限元方法对RPV下封头进行热-结构耦合分析，通过计算得到容器壁的温度场和应力场，以及下封头的塑性和蠕变变形，并结合塑性和蠕变断裂判据对下封头进行失效分析。结果表明，考虑蠕变影响后，结构的变形将大大增加；严重事故下采取熔融物滞留策略期间，RPV下封头的主要失效模式为蠕变失效而非塑性失效；内压对蠕变变形量和蠕变失效时间有较大影响。该文为严重事故下RPV下封头的蠕变和失效研究提供了分析方法。 

Creep Analysis of Reactor Pressure Vessel Lower Head under Core Meltdown Severe Accident

During the core meltdown severe accident?in the nuclear power plants, the strategy?of In-Vessel Retention (IVR) to contain the melt in the Reactor Pressure Vessel (RPV) is a key mitigation measure.?During the implementation of IVR strategy, the RPV?lower head is likely to fail due to excessive creep deformation under the combined action of extremely high temperature loads and mechanical loads. Therefore, it is necessary to perform the analysis of the creep deformation of the RPV lower head,?to ensure the structural integrity of the RPV under the condition of melt retention. In this paper, under the assumption of IVR, the finite element method is used to perform the thermal-structural?coupling analysis of the RPV lower head. The temperature and stress fields of the vessel wall, and the plasticity and creep deformation of the lower head are calculated. Combining the plasticity and creep rupture criteria, the failure?was?analyzed. ?Results show that the deformation of the structure will be greatly increased when creep is considered.?During the IVR?strategy under severe accident, the main failure mode of the RPV lower head is creep failure instead of plastic failure. Further analysis implies that the?internal pressure has?a significant influence on the?creep deformation and?failure time.?This paper provides the method for the creep and failure analysis of the RPV lower head under severe accident.