基于热力学分析的核反应堆压力容器下封头完整性研究

Under severe accident conditions, the core will melt due to insufficient cooling, and a large amount of molten material will be relocated to the lower plenum of reactor pressure vessel(RPV), which may lead to lower head failure and radioactive release to the environment. In-vessel retention(IVR) is a very effective and critical mitigation measure for severe accidents. As the main component of IVR strategy, the integrity research of the lower head under high temperature environment is of great significance for the successful implementation of the IVR strategy. Based on the theoretical mechanical analysis of plates and shells, combined with the stress-strain constitutive relationship, and using a variety of failure criteria, the integrity of the lower head is further studied. Through the numerical simulation of OLHF-1 experiment, the integrity and thermodynamic behavior of the head under RPV were analyzed. The results show that the mechanical model of the lower head developed in this paper can better judge the mechanical failure behavior of the lower head, and the calculated results are in good agreement with the existing data. At the same time, in a high-temperature environment, the wall thickness at the failure location of the lower head rapidly decreases due to creep and the stress suddenly increases. Under this condition, the lower head typically fails at the location of maximum strain, with strains exceeding 20% upon failure.