Patent GB-1003020-A (GB)
Title: Nuclear reactor control rod operating device
Inventor: FILLOLEAU ETIENNE
IPC: G21C13/073
Filed: 1962-06-20
Abstract: 1,003,020. Controlling reactors. COMMISSARIAT A L'ENERGIE ATOMIQUE. June 20, 1962 [June 27, 1961], No. 23791/62. Heading G6C. [Also in Division F2] A nuclear reactor control rod operating device comprises, in combination, a control differential gear having an output element which produces the displacements of the control rod, a first input element adapted to be rotated in both directions, preferably at different speeds, by a power unit, and a second input element adapted to be rotated in the direction that moves the control rod towards its shut-down position by an actuating device, preferably of the spring type. Referring to Fig. 3, the output element consists of a first ring gear 42 producing the displacement of a control rod through a rack 44 with which it meshes, the control rod being supported from an operating bar 45 carrying the rack 44; the first input element consists of a shaft 48 carrying a planet wheel carrier 49b, a wheel 49 of which meshes with the ring gear 42; and the second input element consists of a ring gear 57 meshing with a wheel 49a of the planet wheel carrier 49b and being fixed on a sleeve 58 carrying a pinion 59 rotatable so as to move the control rod to its shut-down position by an actuating device 60 (Fig. 4). The power unit 50 (Fig. 3) comprises two electric motors 66, 67 (one of which is reversible) co-operating with differential gears 70 and 77 so as to rotate an intermediate shaft 77a to drive the input shaft 48 of the control differential gear 41 and hence the control rod, the latter downwardly at a medium speed (e.g. 1 mm./sec.) and upwardly at a slow speed (e.g. 0.1 mm/sec). In case of failure of the motors 66, 67, the shaft 77a may be rotated manually by means of a crank 87 and spring-loaded clutch 89. The position of the control rod is indicated by two selsyn transmitters 95a, 96a of fine and coarse adjustment, respectively, driven by two pairs of pinions 87a, 88a transmitting the rotation of the ring gear 42 to a toothed wheel 89a connected to the transmitters by gear transmissions 90a, 92a. The device 60 which produces the shutdown movement of the control rod comprises springs 61 (only one shown in Fig. 4) compressed between a fixed top plate 102 and a sliding bottom plate 103 which carries on one side a rack 62 and on the other side a rod 104 surrounded by the springs 61. The rack 62 actuates pinion 59 through toothed wheels 63, 64 and 65. The rod 104 carries a head 105 which, in the withdrawn position of the control rod shown in Fig. 4, is gripped by links 106 pivoted at 107 and held thus by a wedge 108 fixed to a plunger core 109 and held in position, compressing a spring 110, by an electromagnet 111. In case of emergency, the feed current to the electromagnet 111 is cut off and the plunger 109 rises rapidly under the action of the spring 110, the links 106 releasing the head 105 and the springs 61 exerting a strong downward thrust upon the plate 103 and rack 62. The rapid downward movement of operating bar 45 which results is braked at the end of the movement and the shook is absorbed by a mechanism 117 shown diagrammatically in Fig. 4 (see Division F2). The control rod 43 (Fig. 11d comprises a body 176 containing a hollow cylinder of a substance rich in boron (e.g. natural boron carbide for the shim rods and boron-10 carbide for the regulating and shut-down rods) and connected to a head 47 by a rod 175. The head 47 is engaged by tongs 46 pivotally mounted on a head 133 of a rod 132b extending downwardly from a screw 131 (Fig. 4) which engages a nut 130 driven by a motor 135. Hooks 171 at the lower ends of the legs 134 of the tongs 46 surround the head 47 and are normally kept in holding position by a guiding ring 172, screwed into the lower end of a tube 150a surrounding the rod 132b and by a central core 173. The legs 134 also have notches 174 of the same profile as the guiding ring 172, a pivoting of the legs 134 and consequent release of the head 47 occurring when the rod 132b is lowered so that the guiding ring 172 enters the notches 174. The above control rod operating device may be used with a fast reactor of the converter type, such as that shown in Fig. 1, the tank 1 housing a cylindrical set of fuel assemblies 2 to form a core 3 of fissile material (uranium enriched in U-235 or Pu) and a blanket 4 of fertile material (natural uranium or uranium depleted in U-235) surrounded by a neutron shield 6 and immersed in a bath 7 of liquid sodium above which is an argon atmosphere. The tank 1 is mounted on a support 10 inside a safety vessel 11 intended to collect molten metal and fissile and fertile products in case of breaking of the tank 1 or of the assemblies 2. The liquid sodium coolant enters the reactor through pipe 12 and is divided by an annular diaphragm 14a into two flows, one of which under a higher pressure passes inside a vessel 14 whereas the other passes round this vessel. At the top of the vessel 11, an annular plug 25 is rotatably mounted in a fixed annular plug 23, a small plug 30 being rotatably mounted within the plug 25 with its axis of rotation offset with respect to that of the larger plug. By this means, loading and unloading of the fuel assemblies 2 through a channel 34a is possible since this channel can be brought into line with any of the assemblies. A cover 32 which applies assemblies 2 against a support plate 5 and carries thermocouples 32a is controlled by an arm 33 also passing through plug 30, as do the channels 34 through which the control rods are operated. The plugs 23, 25 and 30 consist of alternate layers of a neutron absorbing substance (e.g. heavy concrete) and a gamma-ray absorbing substance (e.g. lithium or bismuth).