TRANSURANUS modelling of irradiated inert matrix fuels from Halden IFA-652 experiment

Inert matrix fuels are a possible option to reduce plutonium stockpiles by burning it in Light Water Reactors (LWR). These fuels, that host plutonium in a U-free inert matrix (IM) phase, may reach high burning efficiency while preventing new plutonium build-up under irradiation. A first in-reactor testing of these innovative fuels, has been performed through the IFA-652 experiment in the OECD Halden HBWR. Irradiation conditions were similar to the Westinghouse AP-600 fuel with 45 MWd/kgUeq burnup as target. The test-rig consists of a six-rod bundle loaded with fuel pins. Pins are equipped with fuel temperature thermocouple, internal pressure gauge and fuel stack elongation sensor. In this paper, a TRANSURANUS modelling (TU) of inert matrix fuels is discussed. In particular, a comparison of the code predictions with IM IFA-652 experimental data has been performed up to 40 MWd/kgUeq average discharge burnup. Concerning the complex behaviour of the fuel (densification, fission gas release and swelling) TU models have been adjusted to fit the IFA-652 experimental data. It appears that TU overestimates the experimental data concerning fuel temperature by less than 10% in the great part of the burnup range but in some locations where a calculated pellet-cladding strong interaction takes place, fuel temperature predictions degrade. Similar statements can be made for the pin inner pressure