A Study on Mechanism of Early Failure of Inner Duct Wall within Fuel Subassembly with High Heat Flux from Molten Core Materials based on Analysis of an EAGLE Experiment Simulating Core Disruptive Accidents in an LMFBR

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. Conˆrming the principle eŠectiveness 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 clariˆcation of heat transfer from a hightemperature mixture of molten fuel and steel to the duct. As a result, the duct failure caused by high heat ‰ux from the mixture was identiˆed as one of an important mechanisms of early duct failure in FAIDUS. It was also suggested from this study that the high heat ‰ux from the mixture is caused by the direct contact of molten steel in the absence of fuel crust on the duct wall. Based on theseˆndings, it is judged that the mechanism of early duct failure with high heat ‰ux obtained in the ID1 test satisˆes 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.

A preliminary evaluation of unprotected loss-of-flow accident for a prototype fast-breeder reactor

“…The neutronics portion provides a nuclear heat source based on the mass and energy distributions calculated by the other portions. The experimental knowledge and physical models obtained in the EAGLE programs were efficiently reflected and appropriately validated in the current SIMMER-III/IV [15,16].…”