Decommissioning considerations for molten salt type reactors

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Molten salt type small modular reactors are presently being developed as an option for providing electricity and alternative energy forms. The current proposed designs do not document how decommissioning will be addressed. The decontamination activities necessary for these reactor technologies upon their shut-down are not available in the open literature. The intent of the experiments performed in this work is to investigate the decommissioning considerations that are associated with molten salt reactors as well as identify some of the concerns that will need to be addressed. Two separate experimental systems were used: one for the synthesis of FLiNaK salt and the other for the remelting and drainage of residue FLiNaK from a Hastelloy-C276 segment. The results of these experiments have demonstrated that FLiNaK salt, given contact with atmospheric moisture, tends to change in condition over time and migrate from one location to another as a result of hygroscopy and deliquescence. Consequently, the technical challenges that may arise during molten salt reactor decommissioning as a result of this phenomenon are also discussed and explored. Similarly, the application of heating and pressure reduction to assist in collecting the salt for removal processes was also examined to better determine suitable decontamination and end-of-life options for molten salt reactors. The results of this experiment demonstrated that it would be difficult to completely drain solidified molten salts in a reactor system by reheating the structure only once; residual salt is likely to be present, and the use of flush salt would increase the volume of waste.
Molten salt reactors, FLiNaK, Nuclear decommissioning, Salt migration, Salt preparation