Structural behavior of an ablated reactor pressure vessel wall with external cooling

Abstract

In a severe accident scenario of a nuclear power plant involving core meltdown and relocation to the lower head of the reactor pressure vessel (RPV), the vessel may undergo serious deformation and even failure due to extreme thermo-mechanical loads from the relocated core melt. Proper material models and detailed structural analysis are paramount in predicting the timing and mode of possible vessel failure.This paper presents a strain hardening creep model with optimal parameters to simulate the material behavior of the reactor steel 16MND5 under extreme thermo-mechanical loads. First, validations against two experiments, a tensile-creep test and the EU-REVISA RUPTHER #14 test, show that the proposed model is best overall compared to three previous models. Next, the creep model is implemented for the thermo-mechanical analysis of an ablated RPV under a severe accident scenario with external vessel cooling as a mitigation strategy. The effect of internal pressures from 3 to 50 bars is investigated with the assumption that the corners of the ablated part of the vessel have sharp corners. In this case, we found that the vessel fails above 40 bars. However, if we model the corners with varying smoothness or fillet sizes, we found significant delay in failure time and an increase in failure internal pressure.