Patent GB-1519546-A (GB)
Title: Nuclear reactor
IPC: G21C7/00
Filed: 1976-09-22
Abstract: 1519546 Reactors COMMISSARIAT A L'ENERGIE ATOMIQUE 22 Sept 1976 [20 Oct 1975 (2)] 39323/76 Heading G6C A nuclear reactor, e.g. a pressurized water reactor, comprises a lower support grid 3 rigidly fixed to the reactor pressure vessel (not shown), a plurality of fuel wrappers 2 removably attached at their lower ends to the grid 3, each fuel wrapper 2 being intended to contain two plate-type fuel assemblies 4 suspended side-by-side from the top of the wrapper which consists of four rigidly fixed vertical walls 16 and is open at its upper end and closed at its lower end by a rectangular base plate 18 provided with a bore 20, and units 10 for the position-maintenance of the fuel assemblies 4 in the wrappers 2. The means of removable attachment of each fuel wrapper 2 to the lower support grid 3 consists of a tube 50, Fig. 4, rigidly fixed to the grid 3 and extending into the bore 20 in the base plate 18, the tube 50 being formed of a material having a higher thermal expansion than that of the base plate 18 to effect a clamping of the base plate 18 against the tube 50 at the operating temperature. For safety reasons, however, the mounting of the wrapper 2 is completed by means of a number of screws 54. The fuel plates 6 forming each fuel assembly 4 are attached at their upper ends to an end component 22 braced by ribs 24 with a centring sleeve 26, Fig. 3, each fuel assembly 4 being supported by the wrapper 2 by means of bosses 30 on the end component 22 engaging recesses 28 in plates 16 of the wrapper 2. The wrappers 2 are uniformly spaced with the intervening spaces housing either stationary neutron absorbing rods 34 formed of burnable poisons or movable control rods 36. Both types of rod 34, 36 are of cruciform section. Spacer members 40 are provided at the ends of the arms 35 of the stationary rods 34 in order to maintain the spacing between the walls of adjacent wrappers 2. The lower portion of each fuel wrapper 2 is provided with a removable diaphragm 42 comprising apertures 74 which serves to regulate the coolant flow rate. As shown in Fig. 4, the diaphragm 42 is mounted on a number of units, such as the unit 60 which comprises a rod 64 spring- loaded within a body 62 and terminating in a point 70 which bears on the tap face of the base plate 18. The body 62 traverses the diaphragm 42 through a bore 72 and is welded thereto. Ribs 68 are fixed on the diaphragm 42 at right angles to the fuel plates 6, the lower ends of which they contact. As shown in Fig. 8, each position-maintaining unit 10 has an upper flange unit 104 which serves to secure and centre the unit 10 within the upper core support grid 12. A connection between the main cylindrical body 100 of the unit 10 and the flange unit 104 is ensured by a helical spring 118 located within a skirt 116 of the flange unit 104 and surrounding an extension 112 of the body 100, engaging a face 120 of the flange unit 104 and an annular shoulder 122 formed on the body 100. The units 10 serve both to guide the movable control rods 36 and to maintain the fuel assemblies 4 within the individual fuel wrappers 2. Each unit 10 serves to guide the control rod 36 assigned to four juxtaposed fuel wrappers 2. Guiding is effected by means of partitions 130 which extend up to the full height of the body 100 and form a central cylindrical passage 132 through which the control rod drive unit can be inserted, also four radial slots 134 which permit the passage of the arms 136 of the control rod. Position-maintenance of the fuel assemblies is effected by means of four spring devices 150d connected to the lower shell portion 102 of the body 100 by radial arms 152d and each comprising a spring-loaded locking pin 156d traversing an intermediate grid 14 through a bore 158d to penetrate into a sleeve 26 in a fuel assembly end component.