Patent GB-886874-A (GB)
Title: Device and method for producing power
IPC: G21C15/26
Filed: 1956-06-11
Abstract: 886,874. Reactors. UNITED STATES ATOMIC ENERGY COMMISSION. June 11, 1956 [June 28, 1955], No. 18038/56. Class 39(4) In a water-cooled and moderated steam generating reactor, stabilisation is effected by bubble formation and neutron absorption in U<SP>238</SP> in the case of large reactors, and by bubble formation alone in the case of small sized reactors. Two embodiments of the large and one of the small type are described, in both types the core being formed of vertical fuel containers which contain fuel elements and through which the coolant flows vertically upwards. Each reactor has a vertical cylindrical pressure vessel enclosed in a concrete mass and vertically displaceable control rods. In the first embodiment of the large type, Fig. 2, the reactor core 95 is supported in the pressure vessel 82 beneath water surface 156. Each fuel element 116 is mounted in a channel 117 in the support 114. Each control rod 104 has a drive mechanism 106 in chamber 97. Steam leaves the vessel 82 through 158 and water is returned to the reactor through the ring 173. The steam generated at the reactor may be passed directly to a condenser when the load on the turbine is reduced. An external heater is provided to heat the water before withdrawal of the control rods. The concrete shield is cooled by water flowing through tubes 107. In the second embodiment, Fig. 16, heavy water is used as the coolant and moderator and the core 220 is mounted in pressure vessel 222 and surrounded by the thermal neutron shield 226. The fuel elements 252 are supported by grids 228, 230. Heavy water enters 220 through 240 and steam leaves at 246 after passing the steam separating baffle 244. The fuel elements 252 are placed in a triangular lattice pattern and are unloaded by a mechanism inserted at the unloading tubes 248. The control elements are manipulated from below the reactor. The concrete shield 330 is cooled by coils 331. In the third embodiment, Fig. 26, regulation is effected by neutron leakage due to bubble formation. The core 418 is mounted in the pressure vessel 402 beneath the water surface 480. Pneumatic control rod drive mechanism 414 is connected by rods 476 and 452 to the control plates 470 and control rod 450 respectively. To effect a rapid shut down, the water may be removed by opening valve 484 and rod 450 is moved by 414. The fuel elements 118, 119 of reactor 95, Figs. 5, 4, are formed of vertical fuel plates 128, 138 mounted on hollow stems 120 and upper orifices 133. The fuel plates 128 are held between side plates 124, and are formed of natural uranium with added zirconium and niobium. The cladding 130 is zirconium. The fuel plates of element 119 are similarly mounted but are formed in three sections, the upper and lower, 138 being of natural uranium containing U<SP>238</SP> and the centre section 139 containing uranium enriched with U<SP>235</SP>. The fuel element 252 of reactor 220, Figs. 18, 19, is formed of a zirconium tube 254 supported between tubes 256, 258 to permit the free flow of heavy water which enters at 256. The fuel is formed in twisted ribbons 268, supported at 270, and are of natural uranium mixed with niobium and zirconium and clad in zirconium. The steam issuing from 252 passes through the separator 277 where the water is swirled to the inner wall 282 by the wave 276 and passes through the perforated ring 288 and downwards between sleeves 280 and 282. The fuel elements 424 of reactor 418, Figs. 31, 32 has side plates 426 which support the fuel plates 430. The latter are curved, are supported at the centre with a rib 440, contain a mixture of U<SP>235</SP> and aluminium and are aluminium clad. A fuel unloading mechanism, Fig. 24, is provided with a gripper device 312 mounted on the arm 306 which is displaceable parallel to the vertical axis of frame 302 by translation of shaft 316. Device 312 is operated pneumatically from line 314 and the fuel elements are cooled during lifting by water from tube 324. In a power plant, not shown, steam from the reactor flows directly to a turbo-generator, the condensate from which passes through an ion exchange system before return to the reactor. The turbine throttle valve and a bypass valve are coupled to the overspeed governor in order that a fall in turbine load opens the by-pass valve to prevent a rise of pressure in the reactor and a consequent fall in steam voids. Specification 817,751 is referred to.