GB1070204A - Method for tightly closing tubes made of ceramic-metal composite materials, for example sheaths for the fuel elements of nuclear reactors - Google Patents

Abstract

1,070,204. Welding by fusion; brazing; stamping. EUROPEAN ATOMIC ENERGY COMMUNITY (Euratom). Aug. 5 1964 [Aug. 6, 1963], No. 31767/64. Headings B3Q and B3R. [Also in Division G6] A method of closing the ends of tubular elements made of ceramic metal composite materials comprises the steps of closing the end of the tubular element with a plug having a projecting flange which co-operates with the element to form an annular cavity around the mouth of the element, securing the plug in the element, inserting in the cavity a ring of the same metal as the matrix of the composite material, said ring having a size to project from the cavity and heating the ring so that it melts and the metal diffuses into the element and the flange of the plug. A tube 13 made of sintered aluminium containing a high percentage of alumina and forming the sheath of a nuclear fuel element is internally threaded at 19 and has a counterbore 20. The plug 15 of the same material has external threads 18 and a flange 17, which is reduced in diameter at 21 to form, with the element an annular cavity which receives an aluminium ring 22. The thickness of the metal of the sheath and plug on each side of the ring is the same and is equal to the projection of the ring above the cavity. Preferably the thickness (i.e. the axial length) of the plug 15 is ten times the wall thickness of the tubular element, and twice the axial length of the ring 22. The plug is secured in the element by swaging and is then rotated at 2 r.p.m. and bombarded by an electron gun 23 which causes fusion of the ring to produce the joint shown in Fig. 7. Argon or helium shielded arc-welding using a tungsten electrode may be used in which case the ends of the tube and the plug flange are chamfered at 45 degrees to contain the molten metal of the ring. In a modification, the threads 18 and 19 are omitted and the plug is formed with a cannelure (27), Fig. 10 (not shown), into which the tubular element is electromagnetically swaged. In a second modification, Fig. 11 (not shown), the counterbore 20 is omitted from the element and the full radial depth of the cavity is formed by machining the plug. In a third modification, Fig. 12 (not shown), the method is applied to special sheathing tubes having a solid plug (30) through which thermocouples extend. The ring (32) has an angular crosssection and is received in a cavity comprising a counterbore (34) in the sheath and a V- groove formed by chamfered flange (31) on the plug and the chamfered end of the tube. In a further modification the plug is coated with silver and heated to obtain a mechanical connection by diffusion.