Plutonium redistribution in the outer regions of hypostoichiometric mixed oxide fuel

Plutonium redistribution in the outer region of mixed-oxide fuel was observed in fuel pins irradiated in EBR-II. The observations indicate that the occurence and radial distribution of plutonium depends on initial fuel o/m and burnup. Analysis of the effects of plutonium redistribution at high burnup, approximately 12.5 at. percent, indicates an approximate 8 percent decrease in the power-to-incipient fuel melting could occur in fuel composed of 75 wt percent natural uranium dioxide and 25 wt percent plutonium dioxide due to this phenomenon.