[en] A representative selection of high chromium steels of fusion relevance has been irradiated in the BR2 reactor, in the framework of a collaborative project between ORNL (Oak Ridge National Laboratory, US) and SCK-CEN. The experiment, denominated FRISCO-F (Fusion and Reactor Materials Irradiation SCK-CEN/ORNL - Fusion materials), included tensile and miniature C(T) fracture toughness specimens of the following materials: EUROFER97, F82H, CLAM (Chinese Low Activation Material) and four ORNL developmental alloys (⁹Cr, ⁵Cr, ³Cr, ³Cr⁺Ta); in addition, we also irradiated samples of the well-known ferritic/martensitic steel T91, which is not relevant for fusion (its chemical composition cannot be considered reduced-activation) but is regarded as one of the reference materials for applications such as accelerated-driven systems (ADS) and future high temperature nuclear energy systems (Gen IV). Irradiation of RPV Steels for ORNL (US) The primary goal of the Heavy-Section Steel Irradiation (HSSI) Program is to provide a thorough, quantitative assessment of the effects of neutron irradiation on the material behaviour, and in particular the fracture toughness properties, of typical pressure vessel steels as they relate to light-water RPV integrity. The program includes studies of the effects of irradiation on the degradation of mechanical and fracture properties of vessel materials augmented by enhanced examinations and modelling of the accompanying microstructural changes. Effects of: specimen size; material chemistry; product form and microstructure; irradiation fluence, flux, temperature, and spectrum; and post-irradiation mitigation are being examined on a wide range of fracture properties. Results from the HSSI studies are incorporated into codes and standards directly applicable to resolving major regulatory issues that involve RPV irradiation embrittlement such as pressurized-thermal shock, operating pressure-temperature limits, low-temperature over pressurization, and the specialized problems associated with low upper-shelf welds. The HSSI Program, funded by the U.S. Nuclear Regulatory Commission (USNRC) at Oak Ridge National Laboratory (ORNL), has contracted with SCK-CEN on a project aimed at investigating the effects of relatively high, fast neutron flux on RPV steels. Irradiation of RPV Steels for CRIEPI (Japan) Neutron irradiation embrittlement of RPV steels at high fluences is a common concern worldwide for the light water reactors, especially in countries where long term operation of such reactors is planned. Irradiation in test reactors is an important tool to study embrittlement at high fluences, although full understanding and consensus has not yet been reached on the effect of the difference in neutron flux (dose rate) between commercial and test reactors. The objective of the collaborative project between CRIEPI and SCK-CEN denominated IRPEC (Irradiation of RPV StEels for CRIEPI) is the irradiation in BR2 of a low Cu reactor pressure vessel steel up to high fluences