Comparison of various partial light water reactor core loadings with inert matrix and mixed-oxide fuel

Two types of plutonium-containing cores have been compared, each comprising of four different stages of plutonium deployment in an actual 1000 MW (electric) pressurized water reactor. 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, core loadings with inert matrix fuel (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 loadings, the IMF rods with the highest power ratings were identified. The data depend on a pin power reconstruction of three-dimensional nodal calculations, and a partial verification of the pin power values was carried out using the transport codes CASMO and HELIOS as well as the Monte Carlo code MCNP. Fuel behaviour calculations were then performed for the highest power-rating rods employing models partly validated via recent data from the comparatory 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.