Liquid metal cooled fast neutron nuclear reactor

In a fast-neutron nuclear reactor cooled by a liquid metal the emerging free shells of the internal structures (28) are equipped, on the hot collector (32) side, with troughs (36) filled with liquid metal. The bottom of these troughs is at a level below the minimum level (Nmin) of the liquid metal in the hot collector, while at least one passage (40a) permits free communication between the troughs (36) and the hot collector when the level of liquid metal in the latter reaches a maximum value (Nmax) corresponding to the nominal regime of the reactor. The thermal stresses in the emerging shells of the internal structures (28) are thus greatly reduced.