The effect of surface oxidation of uranium carbide powder on its compatibility behaviour with stainless steels

Vacuum-bonded and sodium-bonded compatibility tests between stainless steels 316, 321 and 347, and both stoichiometric and hyperstoichiometric UC powders which had been surface-oxidised, were carried out for 1000h at 700° C. Results prove that the free carbon liberated during surface oxidation of UC powders is an important source of carbon during carburisation of the cladding, and can cause substantial embrittlement of the cladding even in a stoichiometric carbide fuel powder in both vacuum-bonded and sodium-bonded tests. A model is proposed for the transfer of carbon from an oxidised fuel powder of this kind, to the cladding in a vacuum-bonded test in which a suitable CO/CO₂ and/or CH₄/H₂ gas atmosphere is established and acts as a transfer medium for the carbon between the fuel and the cladding. Comparison of this model with the experimental results for a stoichiometric fuel powder yielded reasonable agreement.