Study on Eutectic Melting Behavior of Control Rod Materials in Severe Accidents of Sodium-Cooled Fast Reactors (2) Modeling of Multi-Phase Eutectic Reaction Behavior

Abstract

The eutectic reaction between boron carbide (B₄C) and stainless steel (SS) and the relocation of reaction products in a damaged core are important phenomena to be considered in the safety analysis of severe accident (SA) in sodium-cooled fast reactors (SFRs). In this study, a multiphase eutectic reaction model was developed to simulate eutectic reactions and relocation of reaction products in the damaged core and incorporated into the fast reactor safety analysis codes SIMMER-III and SIMMER-IV. The eutectic reaction model was coupled with the multi-fluid model, the fluid dynamic model of the SIMMER codes, because the reaction products cause thermal and hydraulic interactions with multiphase core materials in the damaged core. In addition, the equation of state and thermophysical property models of the SIMMER codes were extended to allow for the B₄C concentration dependence of the physical properties of the eutectic reaction products. The developed eutectic reaction model was validated for its capability by analyzing a B₄C-SS eutectic reaction experiment in which a B₄C pellet was immersed in a molten SS pool. In the validation analysis, quantitative comparisons were made on the measured thinning of a B₄C pellet due to the eutectic reaction and the distribution of a boron component dispersed in the molten SS pool along with the melt of the reaction product. Validation results indicate that the SIMMER-III code incorporating the developed eutectic reaction model has the potential capability to evaluate the eutectic reaction and the relocation behavior of reaction products during SA of SFR.