Structural analysis of a reactor vessel in a sodium-cooled fast reactor under extremely high temperature conditions

To enhance resilience of next-generation nuclear structures, it is necessary to develop design methodology that mitigates impacts of failure caused by extremely high temperature conditions which might lead to a severe accident. The purpose of this study is to understand its deformation behavior under extremely high temperature conditions and to identify the areas that should be focused on to mitigate impacts of failure. For this purpose, this study has conducted a detailed structural analysis of a reactor vessel (RV) in a loop-type sodium-cooled fast reactor using a commercial finite element analysis code, FINAS/STAR. In a postulated scenario of loss of heat removal system, the RV was heated from the normal operation condition to the sodium boiling temperature in the upper sodium plenum for 20 hours, assuming depressurization. The analysis has revealed less significant stress and strain which were sufficiently lower than failure criteria. The upper body of the RV was identified as the important area in terms of mitigation of structural failure. The RV was eventually deformed downward about 160 mm, but it resulted in no failure. This analysis implies maintaining the RV sodium level in a long term, thereby enhancing the RV resilience.