- Charles Forsberg, Massachusetts Institute of Technology, Cambridge, Massachusetts
All salt reactors [e.g., fluoride salt-cooled high-temperature reactors (FHRs), molten salt reactors (MSRs), and salt-cooled fusion reactors] require salt coolant cleanup systems for corrosion control and removal of impurities (corrosion products, activation products and fission products) with solidification of the waste products. From 1950 to the 1970s there was significant work on salt processing associated with MSR programs—but very little research for the following 40 years. During this time major technology advances in other fields have occurred that enable new salt processing options. We describe some of the new options: (1) removal of noble metals in MSRs, (2) atmospheric-pressure high-temperature distillation enabled by additive manufacture of high-temperature distillation equipment, and (3) conversion of fluoride or chloride wastes to either borosilicate or iron phosphate waste forms suitable for geological disposal with recovery of the chloride or fluoride anions for recycle.
Research and development is under way on three classes of salt reactors: with fluoride salts for cooling and tritium production. While these different technologies use different salts with different requirements, the salt processing requirements are similar and thus there are a set of technologies applicable to all three reactors. For the FHR and fusion coolant salts, the impurities are measured in parts per million while MSRs require large-scale removal of fission products.