Improvements of the TRANSURANUS code for FBR fuel performance analysis

Recent developments of the TRANSURANUS code concering the modelling and simulation of nuclear fuel rods for fast breeder reactors (FBR) are presented. The work deals with the following main topics: extension of the burnup model (TUBRNP) for fast spectrum, plutonium and oxygen redistribution, normal grain growth and helium release. The extended version of TUBRNP allows now to perfom nuclide analysis also for FBRs. This is actually an important task for fuel performances codes since it allows describing the major and minor actinides transport and evolution across the fuell pellet, which represents a key issue for the behaviour of FBR fuel pins. To this purpose, the models of transparent phenomenia involving plutonium and oxygen redistribution have been revised and improved. Based on the multi-scale philosophy (in paricular, making use of neutron transport calculation results and experimental data coming from out-of-pile experiments) neutron cross sections and fissions yields for FBRs were included and oxygen and plutonium diffusion coefficients were upgraded. As concerns helium production and release, which in an important issue during irradation and strorage, a simplified model was aslo implemented that makes use of experimental data from separate effect exeriments. Further code improvements for FBR that are underway are outlined and discussed.JRC.E.3-Materials researc