GB1162578A - Improvements in and relating to a Nuclear Reactor Fuel Element Assembly - Google Patents

Abstract

1,162,578. Fuel elements. COMMISSARIAT A L'ENERGIE ATOMIQUE. 10 July, 1967 [12 Aug., 1966]. No. 31641/67. Heading G6C. A transverse support grid for a cluster-type fuel element assembly is formed of spigot rings 5 which fit over and are secured to the upper ends of the fuel pencils 1 and coupling members 11 which connect each ring 5 to at least one adjacent ring and have internal ducts 12 for providing communication between spaces 4 between the cans 2 and the fuel 3 at the upper ends of the fuel pencils 1. A number of solid discs 13 are disposed around the periphery of the support grid and engage in recesses 15 in tie-rods 14. The tie-rods 14 are coupled to each other by means of a metallic sleeve 16 welded to the tie-rods at 17 and surrounded by an outer metallic sleeve 18. The two sleeves 16, 18 are coupled together at one end by means of a circular collar 19 and at the other end by means of a circular collar 46. At this latter end, the sleeve 18 terminates short of the sleeve 16. The ends of each tie-rod 14 are so shaped (Fig. 3, not shown) as to provide a male portion and a female portion, with the result that the tierods of two fuel element assemblies which are superposed in a nuclear reactor fuel channel can be interengaged and the fuel pencils of each cluster axially positioned in the line of extension of each other. The spigot rings 5 are closed at the top by caps 8. The ducts 12 of the coupling members 11 and a number of peripheral fuel pencils 1 are connected to funnel-type components 24 in each of which is formed an axial bore 25 closed at the top by a cap 26. Each component 24 has an arm 27 engaging in a recess 28 of the circular collar 19 and provided with an internal duct 29 through which fission product gases released from the fuel pencils 1 are conveyed to an expansion chamber 30 located between the two sleeves 16, 18. The chamber 30 is delimited by a casing 31 applied against the outer sleeve 18 and a casing 32 separated from the inner sleeve 16 by a layer 34 of heat-insulating material. The two casings 31, 32 are sufficiently thin to deform under the effect of variations of pressure. In the position shown in Fig. 2, the volume of chamber 30 is a maximum as during normal operation. In the event of a shut-down, the two casings 31, 32 can contract and thereby reduce the volume of chamber 30. The fuel cluster is completed at the lower end of the fuel pencils by a member which permits of free expansion of the pencils. The cans 2 are sealed at their lower end by end caps 35 in each of which is formed a blind-end bore 36 in which is mounted a ball 37 and a stud 38. After insertion through seals 39, the studs are secured to a simple grid 40, the ends 41 of which are fitted in a channel 42 formed at the base of the tie-rods 14. Each fuel pencil 1 is divided at the centre by a plug provided with radial fins for the purpose of bracing the fuel cluster. The collar 46 formed either of graphite or silica is radially proud of the sleeve 18 and is applied against the wall of the fuel channel to prevent any coolant flowing between the channel wall and the sleeve 18. The cans 2 may be formed of Zr alloy, Be, Si, graphite or SiC whilst the tie-rods 14 may be formed of impregnated graphite, Si or SiC and the support grids and sleeves 16, 18 of Nb, Zr alloy or steel.