The HELIOS irradiation experiment is the latest of a series of experiments on americium transmutation, and has been carried out in the framework of EURATOM's 6th Framework Programme (FP6) project EUROTRANS, which has been completed in March 2010. The transmutation of Minor Actinide (MA) is a fundamental step in order to be able to close the cycle of the nuclear fuel. Past experimental activities in the field of transmutation and testing of innovative nuclear fuel containing Am has proved that the release or trapping of helium is a key issue for the design of such kind of fuel or targets. Therefore, the main objective of the HELIOS experiment is the study of the in-pile behaviour of U-free fuels such as (Pu,Am,Zr,Y)O2 or (Am,Zr,Y)O2, CERCER (Am2Zr2O7+MgO), CERMET ((Pu,Am)O2+Mo) or ((Am,Zr,Y)O2+Mo) in order to gain knowledge on the role of the fuel microstructure and of the operating temperature on gas release and fuel swelling. The HELIOS irradiation experiment started in the HFR (High Flux Reactor) in Petten (The Netherlands) on the 29th of April 2010 and finished on the 19th of February after 9 reactor cycles (~241 full power days). Although only the Post Irradiation Examination (not performed yet) conducted on the CERCER and CERMET target fuel tested during the HELIOS irradiation experiment will show the performance of the fuel, the behaviour of such targets during the irradiation did not show any difficulties. It is possible to conclude that from an operational point of view, these kinds of fuel targets which have been developed mainly having in mind the possibility to burn MA in a in a subcritical nuclear system, did not show significant issues. This paper summarises the main experimental data obtained during the 9-cycle irradiation of the HELIOS experiment in the HFR. ; JRC.F.4-Safety of future nuclear reactors