The EURATOM FP7 Collaborative Project “Fast / Instant Release of Safety Relevant Radionuclides from Spent Nuclear Fuel (CP FIRST-Nuclides)” is established with the overall objective to provide for improved understanding of the fast / instantly released radionuclides from disposed high burn-up UO2 spent nuclear fuel. This issue is given a high priority in the SRA of the IGD-TP. The outcome of the project is relevant for all types of host rocks in Europe.European experimental facilities with specialised equipment for work with highly radioactive materials collaborate for improving the knowledge relevant for the period after loss of the disposed canister integrity.The project provides for experiments combined with modelling studies on integration of the different results as well as for up-scaling from experimental conditions to entire LWR fuel rods. Spent fuel materials are selected and characterized that have known initial enrichment, burn-up and irradiation histories. Experiments and modelling studies access the correlation between the fast release of fission gases and non-gaseous fission products. They also cover the chemical speciation of relevant fission/activation products and the retention of radionuclides in the rim and grain boundaries of the fuel. Complementary, existing data from previous investigations are evaluated.The 3 years project is implemented by a consortium with 10 Beneficiaries consisting of large Research Institutions and SME’s from 7 EURATOM Signatory States, and the EC Institute for Transuranium Elements. National Waste Management Organizations contribute to the project by participation in the End-User Group, by co-funding to Beneficiaries, and provide for knowledge and information.