Studies on the chemical behaviour of failed fuel pins in LMFBRs

The chemical interactions between sodium vapour of low activity and urania-plutonia and urania-plutonia containing added cations in solid solution have been studied at 16000C. The results show that the reaction with urania-30%-plutonia is limited below a sodium activity of ∼6x10-4. Indications that reaction had occurred with the doped urania-plutonia at a sodium activity of ∼1.9x10-6 were due to precipitation of certain of the added cations at the grain boundaries. The influence of the sodium-fuel reaction on the release of caesium, tellurium, iodine and fuel particles has been investigated by a series of tests involving samples that simulate small fuel pins. The results indicate that the extent of release is dependent on the chemical state of the constituents after pin failure and their solubility in liquid sodium