<br/>Molten salt reactors (MSRs) represent a completely different paradigm of fission and activation product volatility in comparison to ceramic-fueled reactors. In the latter, fission gases are contained during reactor operation. Safety systems in containment are designed to handle rare, high pressure releases under severe accident conditions. For a salt-fueled MSR, gases evolve continuously during normal operation and are treated and confined within a dedicated off-gas system that operates at pressures only slightly above ambient. The chemical and physical phenomena that affect fission product volatility include: the redox state of the salt; bubble formation and release, or void fraction; metal precipitation and relocation in the primary circuit; generation of mists, airborne particles, and aerosols in the pump bowl headspace; decay of noble gas fission products; headspace purging with inert gas; and radiolysis. This talk will review historical data on fission product release from MSRs that operated at Oak Ridge National Laboratory, including the Molten Salt Reactor Experiment (MSRE). Recent developments on salt redox chemistry will be discussed including preparation of a thermodynamic database for chemical species relevant to MSRs. The database includes binary and ternary systems of actinides, lanthanides, fission products, and transition elements, the latter primarily coming from corrosion of reactor materials. The effect of redox chemistry on speciation and volatility of fission products will be presented, along with preliminary experiments investigating salt volatility using a dedicated thermogravimetric analysis instrument equipped with a differentially pumped quadruple mass spectrometer. These experimental results can be analyzed to provide missing thermodynamic data on salt species that are missing from the fore-mentioned database. They will be compared with alternative methods to determine thermodynamic properties in molten salts, including electrochemical methods.<br/>

Fission product volatility in molten salt reactors

2019 Fall National Meeting

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