GB1126396A - Nuclear reactor fuel element and method of manufacturing same - Google Patents

Abstract

1,126,396. Fuel elements. ATOMIC ENERGY OF CANADA Ltd. 22 June, 1967 [18 July, 1966], No. 28965/67. Heading G6C. A fuel element comprises a core 10 of nuclear metal fuel with a void space 11 surrounded by a sheathing assembly consisting of inner and outer sheaths 12, 14 separated by and in contact with a continuous ductile interlayer 13. The core 10 is preferably formed from U metal having minor alloying additions to reduce swelling upon irradiation. The U may contain up to 1.5 wt. per cent of any of Fe, C, Cr or Si either individually or in combination and should be heat treated by being beta quenched from about 750‹ C. and annealed at about 550‹ C. for several hours to produce a fine grained randomly oriented structure containing a fine precipitate. Other U alloys which may be used contain up to 10 wt. per cent Zr or Al, or up to 1 wt. per cent Mo or Nb. The void volume is between 2 and 15%, preferably about 5% of the U volume. Natural or enriched U, or alternatively other fuel metals and their alloys such as Pu, Th, Pu-U, Th-U may be used. The inner and outer sheaths 12, 14 are formed from a corrosion-resistant Zr alloy, preferably Zircaloy-2, with Zircaloy-4 and Zr containing about 2À5 wt. per cent Nb also being suitable. Circumstances may occur in which stainless steel or a Ni-Cr alloy is suitable for the sheaths. The preferred material for the interlayer 13 is extremely ductile material formed by alloying A1 with from 0 to 25 wt. per cent U, preferably about 10 wt. per cent. The U alloy provides a monitoring signal on fracture of the outer sheath 14. A non-fissile material such as Pb or a ductile alloy may, however, also be used for the interlayer 13. The end cap assemblies each consist of two portions 15, 16, portion 16 being welded to the inner sheath 12 and portion 15 to the outer sheath 14. The fuel element is fabricated by: (a) co-extrusion of the core 10 and the inner sheath 12 followed by slip fit assembly inside the interlayer 13 and the outer sheath 14, the outer sheath then being reduced in diameter by swaging or drawing to provide intimate contact between the layers, (b) individual fabrication of the component parts and slip fit assembly followed by swaging or drawing, or (c) assembly of the core 10 and the inner sheath 12 by co-extrusion or slip fit assembly followed by extrusion cladding of the interlayer 13, the assembly so produced then being slip fitted into the outer sheath 14.