1. Thermal neutron generation

Current nuclear power reactors require the production of thermal neutrons to achieve a stable chain reaction. A research reactor designed to produce thermal neutron beams differs little in principle. Since the main aim is to produce neutrons rather than heat, thermal power and core size are kept to a minimum: the reactor with the highest flux in the world reaches just 57 MW: the high-flux reactor at the Institut Laue-Langevin, Grenoble (RHF). A small-diameter core enables a high density of thermal neutrons to be generated in its vicinity, all the more so if a fuel with a high fissile material density and heavy water as moderator is used. As deuterium is much less absorbent than hydrogen, the peak thermal neutron flux is greater than in the case of light water and, above all, much more radially spread out. This facilitates installation of the neutron extraction devices, the channels, which...