Abstract: The space formed between the primary vessel of a sodium-cooled fast reactor and a leak jacket surrounding the vessel is filled with an inert gas which is maintained at a pressure in the vicinity of atmospheric. A vacuum is created within the space formed between the leak jacket and the concrete reactor vault and means are provided for detecting the presence of inert gas within the evacuated space and thus continuously testing the jacket for leak-tightness and mechanical resistance.

Abstract: In a fast reactor in which each cooling loop comprises the primary sodium circuit which exchanges heat with the sodium of a secondary circuit by means of an intermediate heat exchanger, each cooling loop comprises in parallel with the secondary sodium circuit an auxiliary secondary circuit in which a chemically inert gas extracts heat from the primary sodium, said secondary auxiliary circuit being equipped with at least one gas turbine which is supplied with the inert gas and operates in a closed energy-producing gas cycle.

Abstract: Conventional fuel elements within the core of a nuclear reactor and especially a fast reactor are at least partly replaced by "safety elements" each formed by a stack of fissile fuel pellets enclosed in a can. Each pellet is provided with a central orifice so as to form an axial flow duct of sufficiently large cross-sectional area to ensure that the portion of fuel which is liable to melt as a result of a neutron-flux excursion flows under gravity to the bottom of the fuel element and has the effect of reducing the reactivity without damaging the fuel can.