Out-of-pile chemical compatibility of hyperstoichiometric (Pu_0.7U_0.3)C with stainless steel cladding and sodium coolant

Abstract

Chemical compatibility experiments of the hitherto unknown fuel (Pu_0.7U_0.3)C_1+x with sodium coolant and SS 316 (20% cold-worked) cladding were carried out at 973 K for 1000 h for its out-of-pile 'proof testing'. Any possible chemical interaction was assessed by metallographic examination and microhardness measurements of SS 316 cladding specimens. Hyperstoichiometric (Pu_0.7U_0.3)C containing upto 0.7% oxygen and 20% mixed sesquicarbide (M₂C₃) did not interact at all with sodium and caused insignificant carburization of the SS 316 cladding. Mixed carbide pellets containing high 'O' (~1%) and high M₂C₃(~60%) caused clad carburization to a depth of around 90 μm. These experiments generated valuable informations in support of choosing plutonium rich mixed carbide as the driver fuel for the fast breeder test reactor (FBTR).