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 temperatures 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: T-m = 3, 133.8 - 460X(1) - 980X(2) - 0.66X(3) + 0.0008(X-3)(2), where T-m is the expected melting temperature (K); X-1 the plutonium fraction (Pu/(Pu+U)), X-2 the americium fraction (Am/(Pu+U+Am)), and X-3 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-ray intensity profiles of Nd and Y.