Abstract
In the design of a Japanese sodium-cooled fast reactor (JSFR), a design measure (fuel subassembly with an inner duct structure; FAIDUS) is considered to prevent severe recriticality events even in the case of core disruptive accidents by molten fuel ejection out of the core region through the duct equipped within the fuel subassembly. Confirming the principle effectiveness of such a design measure is important. In this study, the systematic heat transfer behavior in the ID1 test, which was conducted in the impulse graphite reactor (IGR) in Republic of Kazakhstan, was evaluated by applying a heat conduction code TAC2D and a reactor safety analysis code SIMMER-III focusing on the clarification of heat transfer from a high-temperature mixture of molten fuel and steel to the duct. As a result, the duct failure caused by high heat flux from the mixture was identified as one of an important mechanisms of early duct failure in FAIDUS. It was also suggested from this study that the high heat flux from the mixture is caused by the direct contact of molten steel in the absence of fuel crust on the duct wall. Based on these findings, it is judged that the mechanism of early duct failure with high heat flux obtained in the ID1 test satisfies the required condition for FAIDUS, i.e., the inner duct of FAIDUS should fail at an early phase of core disruptive accident in advance of wrapper tube failure so that the produced molten fuel can escape from the core region, which supports the feasibility of the FAIDUS concept.
