Study on Eutectic Melting Behavior of Control Rod Materials in Severe Accidents of Sodium-Cooled Fast Reactors (3) Material Analysis of Boron Carbide Immersed in Molten Stainless-Steel

Abstract

Interest in eutectic reactions between boron carbide, used as control rod material and stainless steel used such as cladding tubes, is growing to improve the accuracy of severe accident analysis codes. Immersion experiments of boron carbide pellets into molten stainless steel were performed between 1,773 and 1,973 K. The eutectic melting behavior of the pellet was investigated by observing the cross-section of the pellet using an optical microscope, a scanning-type electron microscope. The elemental distribution and crystal structure of the reaction products were analyzed using an energy-dispersive X-ray spectrometer, X-ray diffraction, and electron–beam diffraction by a transmission electron microscope to clarify the eutectic reaction behavior. Based on the thickness reduction of the pellet cross-section, the reaction rate constants between boron carbide and stainless steel were evaluated under various contact temperatures and times to develop an evaluation formula of the reaction rate constants, which would be incorporated into severe accident analysis codes.