The European Commission funded Collaborative Project FIRST-Nuclides aimed on quantification of the rapid release of radionuclides (IRF) from high burn-up used fuel after canister failure in an underground disposal. The investigations were performed with different types of fuel, sample preparations and experimental methods, independent on specific host rocks or disposal strategies. The results obtained cover the IRF of cesium and iodine (prioritized in my talk at the 2015 International High-Level Radioactive Waste Management Conference). Results to be presented extend to fission gas release (FGR), speciation of 14C in the plenum gas, binding state of selenium in the fuel matrix, etc. Furthermore, short-term releases of matrix elements were determined. The talk presents experimental result and modelling studies, as well as the IRF database which was elaborated for demonstrating the state-of-the-art with respect to the rapid release of radionuclides. Correlations of the IRF with burn-up, power rating and FGR are shown. Within the project, an excellent cooperation was established between the partners, Associated Groups and the waste man ... mehragement organizations (End-Users). The added value of FIRST-Nuclides achievements is highlighted.