Patent GB-1423058-A (GB)
Title: Fuel element for a liquid-cooled nuclear reactor and a method for charging or recharging it
IPC: G21C3/34
Filed: 1973-04-24
Abstract: 1423058 Fuel elements STICHTING REACTOR CENTRUM NEDERLAND 24 April 1973 [20 April 1972] 19217/73 Heading G6C A fuel element for use in, e.g. a boiling water reactor, comprises an array of fuel rods 2 supported within a sleeve 10, the sleeve 10 being permanently connected at its lower end to a base 16 which supports the fuel rods 2 and a head member 12 being detachably connected to the sleeve at its upper end by means of a plurality of bolts mounted in the head member 12 with their bolt-heads 28 disposed downwards to engage releasably with the sleeve 10. To permit of easy mounting and removal of the fuel rods, their ends are gripped in the base 16 by snap connections. Each connection consists of a pin 38 integral with the end of a fuel rod 2 and a cylinder 41 securely fixed to the base 16, the cylinder 41 being rendered resilient by means of a saw-cut 45. The pin 38 is provided with a collar 40 and the cylinder 41 with a co-operating neck 44. Thus when a fuel rod 2 is pressed downwards, the conical nose 39 of its pin 38 enters a flared portion 43 of the cylinder 41 and spreads it apart until the collar 40 passes the neck 44, whereupon the parts of the flare 43 snap back into position to hold the lower end of the fuel rod. The detachable clamping bolt between the sleeve 10 and the head member 12 may comprise tilting bolts each having a clawlike bolt-head 28 (Fig. 6) which, when in the screwed-up position, engages by claw 29 in an aperture 35 in the sleeve 10. Pivot bolts (Fig. 13, not shown) may be used instead of the tilting bolts. The fuel element comprises a number of intermediate lattices 3 and these, together with the sleeve 10, head members 12 and base 16 can be used several times so that, with recharging of the fuel element, only the fuel rods need be changed. The lattices 3 are secured to the sleeve 10 by means of resilient retainers each comprising an endwise extension of the outer jacket of a lattice in the form of a tongue 7 carrying at its up per end a peg 9 which locks into an aperture in the sleeve 10. The procedure for mounting a bundle of fuel rods 2 into such a fuel element consists in assembling the fuel rods 2 upside down in the intermediate lattices 3, the whole being mounted in a mould having the same internal dimensions as the sleeve 10, after which the mould is filled with demineralized water to such an extent that the ends of the rods (i.e. the pins 38) project above the water. The water is then frozen, a lifting eye being frozen in with it to provide a holding means during transport. The resultant prismatic column of ice is introduced into the sleeve 10 and pressed down so that the pins 38 are forced into the resilient flared portions 43 of the cylinders 41. The head member 12 is then mounted on the element and the ice thawed. The tongues 7 are held in the pressed-in condition during the charging of the element either by means of a dowel-type pin 46 on the side of the tongue 7 opposite peg 9 (Fig. 8, left hand side) which fastens as an anchoring device into the ice mass, or by means of a hook or eye 47 made of ice (Fig. 8, right hand side) which holds the tongue 7 in the deflected position.