[en] Almost 3500 kg of high enriched uranium (HEU) has been removed from research reactor sites worldwide over the last few decades as part of global efforts supported by the IAEA. Upon the request of Member States, the IAEA has assisted with the conversion of research reactor fuels to low enriched uranium (LEU) in order to reduce the proliferation risks associated with HEU, which contains more than 20% fissile uranium-235. While most research reactors were built in the 1960s and 70s with technology that required HEU to perform experiments intended for scientific research, today much of this research can be carried out using LEU, in which the concentration of radioactive uranium-235 is below 20%.