This paper presents the current status of the experiments performed at INE within the Work-packages 2 and 3 of the EURATOM FP7 Collaborative Project, “Fast / Instant Release of Safety Relevant Radionuclides from Spent Nuclear Fuel (CP FIRST-Nuclides)”. The segment N0204 from the pressure water reactor of Gösgen (KKG) nuclear power plant was selected to carry out this project. In a first approach and before the performance of leaching experiment, the fission gas release of this segment was determined to be 8.35% (in vol.). Leaching experiment of a cladded fuel pellet in bicarbonate water (19 mM NaHCO3 + 1 mM NaCl) under an Ar and H2 atmosphere with a total pressure of (40 ± 1) bar (pH2: 3 ± 1bar) were started. After a cumulative contact time of 57 days, 4.3% of the Xe and 17% of the Kr inventories of the cladded fuel pellet segment was released into the gas phase.