Patent GB-972901-A (GB)
Title: Steam generating nuclear reactor systems
Inventor: JOHNSON FRANK GEOFFREY
IPC: G21C1/20
Filed: 1963-03-08
Abstract: 972, 901. Nuclear power plant. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. Feb. 27, 1964 [March 8, 1963], No. 9272/63. Heading G6C. A nuclear power plant utilizing a water cooled reactor includes a first containment structure  -  spaced from and housing the reactor, a second containment structure spaced from and containing the first structure, a pond of water in the space between the first and second structures, a duct leading from the first structure to below the surface of the water pool, and a pressure sensitive non-return relief valve for venting the second containment structure to atmosphere. The reactor 1 has an aluminium calandria tank containing heavy water moderator and a lattice of pressure tubes 2, each containing a fuel assembly of sheathed UO 2  pellets; most of the fuel assemblies use zirconium-tin alloy sheaths, but the fuel assemblies used in the centre pressure tubes are of stainless steel,and are used to superheat a small fraction of the steam from the remaining pressure tubes. The saturated and superheated steams are mixed before being fed to a turbine 15. A charge/discharge machine 17 is mounted on a rotatable shield 18 which is in turn mounted in an outer rotatable shield 19. A storage facility 25 is provided in the water pool 6 for irradiated fuel. The calandria tank is surrounded by neutron shielding in the form of steel tanks 20 filled with light water. Reactor power level is controlled by varying the level of the moderator, and is shut down by dropping shut-off rods into the core. If coolant circulating pumps fail, shut-down decay heat is removed from fuel in the boiling tubes by natural circulation and the resulting steam is sufficient to cool the superheating fuel, flow therethrough being induced .by auxiliary condensors 21. Power plant. The entire plant is housed in a turbine hall 5, capable of withstanding an internal pressure of 0.1 p.s.i.g., at which pressure the vent 12 opens. Air extraction ducts 26 are connected to fans outside the hall, and pass extracted air through filters and charcoal beds before venting to atmosphere. All structural parts are concrete. Pressure vessel failure. The first rush of steam, resulting in the main from pressurised water flashing, will not be contaminated to any great extent; this will probably be followed however by a smaller quantity of steam accompanied by significant quantities of radio-active material as by this time removal of primary coolant will have caused overheating and bursting of the fuel rods. The first rush of steam will pass through conduit 8, before entering the water pool 6 through grid supported pipes 28. A pressure censor in the conduit 8 causes the turbine hall extractor fans to be started. A bubble of displaced air will pass through the pool 6 and into the turbine hall, but most of the steam will be condensed by the water pool. Turbine hall pressure rises until the relief valve 12 opens, thus releasing first the large volume of air in the turbine hall before any steam reaches it from the opposite end of the hall. The relief valve 12 will have shut prior to the release of radio-active matter, and any which reaches the turbine hall through the water pool will eventually be drawn off through the extraction system.