MELTING TEMPERATURE OF IRRADIATED FAST-REACTOR MIXED-OXIDE FUELS

The melting (solidus) temperatures of irradiated mixed oxide fuels wer e measured and the compositions of the fuels on the temperature measur ement date were calculated. The fuels contained about 29 wt% Pu initia lly and were irradiated up to 124 GWd/t in the experimental fast react or JOYO. A melting temperature correlation was obtained by an experime ntal regression analysis using 21 measurements: (T) over cap(m) = 3, 1 33.8 - 460X(1) - 980X(2) - 0.66X(3) + 0.0013(X-3)(2), where (T) over c ap(m) is the expected melting temperature (K), X-1 the plutonium fract ion (Pu/(Pu+U)) and X-2 the americium fraction (Am/(Pu+U+Am)) at the m easurement, and X-3 the burnup (GWd/t). The equation shows that the me lting temperature decreases by 5, 4, and 3K per 10 GWd/t at 50, 100 an d 150 GWd/t, respectively. The effects of actinides, such as Pu and Am , on melting temperature could be explained by an ideal solution model . However, the decreases caused by soluble fission products could not be well explained in terms of the ideal solution model.