Graphite materials in salt-cooled high temperature reactors: Known issues from past experience and proposed path forward for their mitigation

Since the successful completion of Molten Salt Reactor Experiment (MSRE) at Oak Ridge National Laboratory, nuclear and material scientists continue to expand their knowledge on materials and conditions that would ensure safe and efficient operation of high temperature reactors with molten salt coolant. Carbon materials will be present in the reactor core as graphite moderators and reflectors in liquid-fuel molten salt reactor, MSR, and also as fuel matrix carbons in the fuel pebbles of thermal fluoride high temperature reactors (FHR). This paper summarizes the knowledge progress on carbon and graphite materials for molten-salt reactors starting from the lessons learned after the MSRE up to the newly revived interest for MSR in the last decade. Some unsolved items and knowledge gaps which require more research are emphasized.