Patent GB-1162641-A (GB)
Title: Improvements in or relating to Nuclear Reactors
Inventor: STAMFORD STANLEY
IPC: G21C15/18
Filed: 1965-12-13
Abstract: 1,162,641. Cooling reactors. UNITED KINGDOM ATOMIC ENERGY AUTHORITY. 12 Dec., 1966 [13 Dec., 1965], No. 52902/65. Heading G6C. A nuclear reactor has an emergency coolant spray system for cooling the core in the event of failure of the reactor coolant, the pressure of which system is approximately equal to the reactor operating pressure during normal running of the reactor whereby the reactor pressure restricts the flow of coolant into the reactor core to an insignificant amount so that either a decrease of reactor pressure or an increase of system pressure is effective to increase the rate of flow of coolant into the reactor core. In the embodiment described, a fast reactor cooled by a downward flow of supercritical steam as illustrated in Fig. 1 comprises a reactor vessel 2 having an outer wall 5 and an inner wall 6, the latter being divided into an inlet plenum 8 and an outlet plenum 9 by the core 1. The space 10 between the inner and outer walls forms part of an auxiliary cooling circuit communicating with the coolant inlet plenum 8 through a cooler 11 so that a continuous stream of cool fluid flows through the space 10 cooling the inner and outer walls. A pressure equalizing frangible diaphragm D is provided in the inner wall 6 as a safety measure. Liquid reactivity control means 18, as described in Specification 1,162,642 and an emergency spray cooling reservoir 19 are disposed within the space 10. The reservoir 19 is toroidal and connected to an emergency supply system comprising a condensate tank connected by pumps to an accumulator from which a pipe line with a predetermined restriction and solenoidoperated valves leads to the reservoir 19. The valves are operable to by-pass the restriction out of the pipe line if there is a sudden loss of coolant pressure or during reactor shut-down or that the pressure in the accumulator is applied to the reservoir 19 without throttling by the restriction. As shown in Fig. 4, risers 43 lead from the reservoir 19 through the inner wall 6 to a support plate 44 on which the core 1 rests, each being connected via a manifold 46 within the support plate to flow paths inside fuel element sub-assemblies. A stub pipe 50 is supported in each hole 49 in the support plate by a spider 51 and joined by a bore 52 to a riser 43; the stub pipes and the bores joining them to the risers from the manifolds 46. Central stainless steel tubular members 53 seat on these stub pipes 50 and each fuel element sub-assembly, as shown in Fig. 6, comprises a hexagonal wrapper 60 with three internal partitions 61 each joined to the central tubular member 53. The fuel is in the form of oval-shaped pins assembled together in the form of fuel plates 56, three stacks 57, 58, 59 of these plates each forming a fuel element subassembly. Each partition 61 is in contact on one side with one plate 56 of one of the stacks and on the other side with the edges of the plates of another stack. The partitions 61 are double-walled and divided by baffles 62 into rectangular section passageways 63 which extend longitudinally of the fuel element subassembly. Apertures leading from these passageways 63 spray emergency coolant into the spaces between adjacent plates 56 in a stack at spaced intervals along the length of the fuel element sub-assembly. These passageways 63 are connected at the ends of the fuel element subassembly to the central tubular member 53 by plenums 65. The plenums 65 also connect to sprays 66 carried by comb-like lateral support members 67 whose teeth 68 engage between each pair of adjacent plates 56. In normal reactor operation, a steady small flow of emergency coolant is pumped into the reactor at a rate set by the above-mentioned restriction. On failure of the main coolant supply, emergency coolant is driven from the reservoir 19 through the fuel element subassemblies at an increased rate. The pressure in the reservoir 19 will now tend to fall but by this time the solenoid-operated valves in the pipe line from the accumulator will have had time to open so restoring the pressure in the reservoir 19. In normal reactor shut-down, the pressure in the reservoir 19 is increased by bypassing the restriction and the emergency coolant flow rate into the fuel element subassemblies thus increased.