Low temperature steam generator

A steam generator comprising within a common enclosure a molten-salt nuclear reactor having a reactor core, a fluidized-bed heat exchanger located above the reactor core in said common enclosure, a molten-salt circuit, said reactor core and said heat exchanger being components of said molten-salt circuit, said heat exchanger comprising a vessel having a first bank of primary tubes and a second bank of secondary tubes which are spaced from said primary tubes, said secondary tubes comprising part of a secondary coolant circuit, said molten salt being circulated within the primary tube elements of said heat exchanger whilst water is circulated within the secondary tube elements and is discharged in the form of steam, the two banks of tube elements being immersed in a particle bed means for subjecting said particle bed to agitation by a stream of inert gas wherein heat is transferred from the molten-salt in said primary tubes to the water in said secondary tubes by means of the particles in said bed.