Study on Eutectic Melting Behavior of Control Rod Materials in Core Disruptive Accidents of Sodium-Cooled Fast Reactors: (5) Validation of a multi-phase model for eutectic reaction between molten stainless steel and B4C

摘要

Investigation of the eutectic reaction in a coredisruptive accident of sodium cooled reactor is ofimportance since reactor criticality will be affected by thechange in reactivity after eutectic reaction. In this study,we performed 1st step of validation analysis using a fastreactor safety analysis code, SIMMER-Ⅲ, with thedeveloped model based on a new series of experiments,where a B_4C pellet was immersed into a molten stainlesssteel (SS) pool. The simulation results showed the generalbehavior of eutectic material formation measured in theexperiments reasonably. The eutectic reaction consumessolid B_4C and liquid SS, and then the liquid eutecticcomposition is produced at the early stage of reaction dueto the high temperature of molten SS. Movement of theeutectic material in the molten pool leads to theredistribution of boron element. Molten SS pool thenfreezes to solid SS and movement of eutectic material isstopped by surrounding solid SS. Boron concentration inthe pool was measured after molten SS freezes into a solid.Simulation results indicate that boron tends to accumulatein the upper part of the molten pool. This is attributed tothe buoyancy force acting on lighter boron in the moltenSS pool. A parametric study was also conducted bychanging the initial temperature of B_4C pellet and SS toinvestigate the temperature sensitivity on the eutecticreaction behavior.