Patent GB-1474938-A (GB)
Title: Nuclear reactors
IPC: G21C15/02
Filed: 1974-04-29
Abstract: 1474938 Cooling nuclear reactors NUCLEAR POWER CO (WHETSTONE) Ltd 25 April 1975 [29 April 1974] 18619/74 Heading G6C The invention provides a nuclear reactor cooling-water supply header assembly, and its embodiment in a reactor cooling circuit, constructed to minimize the effects of, for example, pipe ruptures or loss of forced coolant circulation. Reactor; reactor cooling circuit.-The reactor, which is described as a SGHWR, comprises a core (Fig. 1) divided into four quadrants A, B, C, D for cooling purposes. Each quadrant has an associated cooling circuit 12A-12D and each circuit comprises in addition to its group of core pressure tubes, a bottom, coolant supply header assembly 14A-14D, respectively, (see below), circulation pumps 13A-13D, a steam drum 21A-21D (Fig. 2), and associated components and arrangements as described below with reference to one such circuit, namely circuit 12D. The water/steam mixture leaving upper ends of each group of core pressure tubes 18 passes to the associated steam drum 21D in which steam and water separate, the water being recirculated via downcomers 23D and the circulation pumps 13D to the bottom supply header 14D and thence to the lower ends of the pressure tubes 18. Make-up feedwater is supplied from a reservoir by an electrically operated pump 24 and conduit 25 to the steam drum 21D. As a safeguard in the event of mains failure, an auxiliary pump 26 driven by a steam turbine 27 is provided to circulate feedwater to the steam drum; the turbine 27 receives steam supply from its associated steam drum 21D or from one of the other steam drums, for example, steam drum 21C associated with the cooling circuit 12C. In addition to receiving its principal coolant flow from its associated steam drum and bottom header, each group of pressure tubes 18 receives an auxiliary coolant flow derived from a steam drum associated with a different coolant circuit. For example, steam drum 21D supplies between 4 and 6% of the total coolant flow through pressure tubes in core quadrant C via a continuously operable pump 45D and supply conduit 46D. This auxiliary flow, which is sprayed into the interior of each fuel assembly contained within each given pressure tube in the core quadrant in question, constitutes, in event of emergencies, a flow of emergency coolant to those assemblies. Detailed arrangements for conducting this auxiliary flow into the interior of a fuel assembly are described (Fig. 4, not shown).  Coolant escaping into the interior of the containment structure 10 is collected in a sump 30 from whence it may be re-supplied to the pressure tubes via a pump 31 and cooler 32. Bottom supply header assembly.-Each such assembly 14A, 14B, 14C, 14D may be constructed as a separate entity; however, as shown with reference to Fig. 3, these assemblies are preferably interconnected in pairs. Each assembly is of identical construction and, as shown with reference to assembly 14D, comprises a plurality of sub-header pipes 29D running parallel with each other and each having a plurality of water outlets 15D for connection each to a respective reactor pressure-tube feedpipe. A water inlet 26D, for connection to a respective one of the pumps 13D conducts water to an associated header pipe 27D having branch pipes 28D connected to the sub-header pipes 29D. Ends of the sub-header pipes 29D at both ends of the assembly 14D are connected by pipes 30D; or, in the case described, in which the assemblies 14C, 14D are interconnected, the adjacent ends of the sub-header pipes 29C, 29D are connected together. Within the header assembly 14D pipe sizes and dispositions are such that, in the event of a pipe rupture, each pressure tube feed outlet continues to receive coolant flow.