On the Chemistry of the Fission Process in Reactor Fuels Containing UF₄ and UO₂

Electrical neutrality must be maintained in nuclear reactor fuels. The consequences of this requirement are illustrated for two fuel materials: solid UO₂ and dilute solutions of UF₄ in molten fluorides. In both systems, changes with time of the valencies of several fission product elements are sufficient to maintain the necessary electroneutrality. In the molten fluorides, however, the situation is more complex than in the oxide, due to the possibility that certain fission product species may react with the container. The importance of rare gas removal in this regard is demonstrated.