FUEL-SODIUM REACTION-PRODUCT AND ITS INFLUENCE ON BREACHED MIXED-OXIDE FUEL-PINS

The formation and consequences of fuel-sodium reaction product (FSRP) in mixed-oxide fuel pins that were irradiated in EBR-II are described. These results indicated that the amount of FSRP that forms as a result of sodium entering a pin with failed cladding is limited by oxygen availability and sodium availability at a favorable fuel temperature. The formation of FSRP is limited to an outer band of the fuel during normal operating conditions. FSRP results in an effective increase in the smeared density of the fuel since the density of FSRP is about half that of the fuel. The FSRP also lowers the O/M of the fuel which reduces its thermal conductivity and increases its thermal expansion. Results from the irradiation tests indicate that the FSRP formation in-reactor is consistent with the characteristics found for sodium uranate and sodium uranoplutonate in the laboratory.