Study on Eutectic Melting Behavior of Control Rod Materials in Severe Accidents of Sodium-Cooled Fast Reactors (1) Project Overview and Progress Until 2022

It is necessary to simulate a eutectic reaction and relocation behavior of boron carbide (B4C) as a control rod material and stainless steel (SS) during a severe accident in a next-generation sodium-cooled fast reactor designed in Japan. On that account, Japan Atomic Energy Agency with academic and industrial partners have been conducting a research project consisting of thermophysical property measurement of the B4C-SS eutectic melt, B4C-SS eutectic melting and relocation experiments, eutectic reaction mechanism investigation, and physical model development for a severe accident simulation code and its application to the reactor. This project has accomplished the development of a basic physical model to simulate the B4CSS eutectic reaction in Phase 1 (2016-2019). The objective of Phase 2 (2020-2024) is to upgrade the physical model for the improvement of reactor analysis accuracy. The model improvement is characterized by implementing a variable B4C mass fraction for the B4C-SS eutectic material. This paper describes the project overview including progress until JFY2022. As one of the state-of-the-art results in the experimental studies, this paper also presents a first freezing experiment using the B4C-SS eutectic material.