Patent Number: 043366147
Section: summary

BACKGROUND OF THE INVENTION This invention relates to tube-in-shell heat exchangers and is directed towards intermediate heat exchangers for use in liquid metal cooled fast breeder nuclear reactor constructions. A tube-in-shell heat exchanger comprises a closed shell housing a bundle of heat exchange tubes which pass through the shell by way of a transverse tube sheet or sheets. In use a first fluid flows through the shell in heat exchange with a second fluid flowing through the tubes. In one kind of tube-in-shell heat exchanger used as an intermediate heat exchanger in a liquid metal cooled fast breeder nuclear reactor constructions, the tubes being elongate and extending between opposed tubes sheets incorporate expansion bends and therefore are subject to severe vibration due to fluid flow through the shell. One expedient to prevent vibrational movement is to support the tubes transversely by a series of longitudinally spaced grids of which successive grids radially displace the tubes from their nominal in-line positions in opposed directions in order to strain the tubes. However, tube support provided by this expedient can be too rigid, and the differential movement of the tubes relative to the other parts of the structure thereby induces severe stress. SUMMARY OF THE INVENTION According to the invention in a tube-in-shell heat exchanger wherein the heat exchange tubes are arranged in a bundle and braced transversely by a longitudinal series of spaced grids, the grids are resiliently supported from a central spine of the tube bundle. The resilient supports provide flexibility in the mountings of the tube bundle on the central spine so that groups of heat exchange tubes can be longitudinally displaced relative to the spine and to adjoining groups of tubes to accommodate differential linear thermal expansion. In a preferred construction of heat exchanger the spine has an annular series of radially outwardly extending forked brackets and each grid has an annular series of radially inwardly extending forked brackets, each bracket of one annular series being interposed between two neighbouring brackets of the other annular series, and there is a resilient annular member disposed to interengage each forked bracket. In a liquid metal cooled fast breeder nuclear reactor construction of the kind comprising a nuclear fuel assembly submerged in a pool of coolant in a primary vessel, and a tube-in-shell intermediate heat exchanger according to the invention, the intermediate heat exchanger comprises a bundle of heat exchange tubes having a central spine extending longitudinally through the shell and a series of longitudinally spaced transverse grids resiliently mounted on the central spine within the shell and disposed to provide transverse support for bracing the tubes apart, successive grids displacing the tubes from their nominal in-line positions in opposed directions, resilient mountings for the grids on the central spine each comprising an annular series of brackets rigidly secured to the spine, the brackets each having a pair of radially outwardly extending forked arms, a complementary annular series of forked brackets having radially inwardly extending arms rigidly secured to a grid, each bracket of one series being interposed between two neighbouring brackets of the complementary series, and a resilient annular member disposed transversely to the spine in engagement with the forked arms of both complementary series of brackets.