Feasibility of partial LWR core loadings with inert-matrix fuel

Three types of plutonium-containing cores have been compared, each comprising of four different stages of plutonium deployment in an actual 1 000 MWe pressurised water reactor (PWR). In a first step, core-follow calculations for four real-life cores with increasingly larger mixed-oxide (MOX) loadings were validated against measured plant data. In a second step, all MOX assemblies were substituted by optimised Pu-Er-Zr oxide, inert-matrix fuel (IMF) assemblies. Finally, core loadings with IMF have been designed and considered which contain, on the average, the same amounts of plutonium as the four partial MOX loadings. From the latter, more realistic IMF loadings, the IMF rods with the highest power ratings were identified. Fuel behaviour calculations were then performed for these rods employing models partly validated via recent data from the comparative IMF/MOX irradiation test currently under way at Halden. Based on the various results obtained, conclusions have been drawn regarding IMF rod designs most likely to yield (in partial IMF core loadings) fuel behaviour similar to that of UO2 fuel.