Melting Temperature of Simulated High-Burnup Mixed Oxide Fuels for Fast Reactors

The melting (solidus) temperatures were measured for fuel simulating burnups of 50, 90, 130, 170, 210 and 250 GWd/t (SIMFUEL) which were added non-radioactive soluble fission products (FPs) to unirradiated fast reactor MOX fuel. The melting temperatures for fuels of 250 GWd/t which were blended non-radioactive soluble FPs and irradiated fuels of 110.6 and 119.0 GWd/t were also compared to the SIMFUEL of 250 GWd/t. The melting temperature decrease of the SIMFUEL tended to saturate with increasing burnup and the melting temperature appeared virtually constant above 170 GWd/t. An equation for melting temperature was obtained from the proposed equation in the previous report by revising the coefficient of the fifth term: Tm=3, 133.8-460X1-980X2-0.66X3+0.0008(X3)2, where Tm is the expected melting temperature (K), X1 the plutonium faction (Pu/(Pu+U)), X2 the americium fraction (Am/(Pu+U+Am)), and X3 the burnup (GWd/t). After the temperature measurement, the radial distribution of eight FP oxide additives in SIMFUEL of 250 GWd/t was measured by X-ray microanalysis. Relative characteristic X-ray intensities of Zr, Ce, La and Sr had the same radial profiles, whilst they did not correspond to the X-rey intensity profiles of Nd and Y.