Separate effect studies at the Halden reactor project related to fuel thermal performance and modelling

The fuels and materials testing programmes carried out at the OECD Halden Reactor Project are aimed at providing data in support of a mechanistic understanding of phenomena, especially as related to high burn-up fuel. The investigations are focused on identifying long term property changes, and irradiation techniques and instrumentation have been developed over the years which enable to assess fuel behaviour and properties in-pile. Selected examples from separate effects studies are discussed with emphasis on the influence of the fuel-clad gap on thermal behaviour, pellet-clad mechanical interaction and aspects of gas communication and mixing. The data provide a basis for the understanding of fuel performance up to high burn-up and can be used for fuel behaviour model development and verification as well as in safety analyses. (author)