Interactions Between U-Bearing Fluoride Fuel Salts and Graphite

A thorough understanding of interactions between graphite and fluoride fuel salts is crucial, as graphite is a promising candidate for the moderator of molten salt reactors. This study investigates the infiltration of fluoride fuel salts into graphite and the fluorination of graphite by these salts under various pressures and temperatures. A high-pressure salt infiltration test apparatus was developed to examine the infiltration of NaF-KF-UF₄ and NaF-BeF₂-UF₄-ZrF₄ fuel salts into two types of graphite at high temperatures. For tests using NaF-BeF₂-UF₄-ZrF₄, two different temperatures were selected to assess the impact of temperature on threshold pressure. The study observed salt infiltration into graphite at pressures exceeding its threshold pressure, and the threshold pressure for infiltration was lower at the higher temperature. In addition, the formation of carbon fluorides on the surface of post-test graphite specimens was identified.