Patent GB-1484093-A (GB)
Title: Liquid cooled nuclear reactor
IPC: G21D1/04
Filed: 1975-04-25
Abstract: 1484093 Cooling nuclear reactors WESTNGHOUSE ELECTRIC CORP 25 April 1975 0 May 1974] 17233/75 Heading G6C In a nuclear reactor, for example a fast, liquid sodium-cooled breeder reactor, the coolant circuit and associated cover gas system are arranged such as to ensure continued immersion of the reactor core in a pool of coolant in the event of a coolant pipe rupture. In one embodiment (Fig. 1) hot coolant passes from the reactor vessel 10 via a pipe 24 to a heat exchanger 26; thence through a circulating pump 28 and is returned to an inlet of the reactor vessel via a pipe 48. Coolant fills the reactor vessel 10 to a level 18, a cover gas space 20 being provided above this level. Similarly, an enclosure 30 of the pump is filled with coolant to a level 34, above which is a cover gas space 32. A coolant reservoir tank 42 is also provided; this is filled with coolant to a level 46 slightly below the level 18 in the reactor vessel 10 and a cover gas space 44 in the tank 42 is connected by way of equalizing pressure pipes 60 to both the cover gas spaces 20, 32 in the reactor vessel and pump enclosure. A coolant outlet of the reservoir tank 42 is connected to the pump 28 inlet, for example by way of a pipe including a check valve 64. Within the reactor vessel 10, a flow-restricting barrier 50 above the coolant outlet nozzle 16 restricts the amount of coolant which can pass to an upper part of the reactor vessel. A drainage line 62 extending between the upper part of the reactor vessel and the reservoir tank 42 acts to drain off coolant above the level 18 in the reactor vessel into the reservoir tank. The drainage line 62 may include an auxiliary heat exchanger for cooling the drainage coolant prior to its entry into the reservoir tank 42; alternatively means are provided to ensure adequate mixing of the drainage coolant with that in the reservoir tank 42. The arrangement enables pressure of the cover gas in the reactor vessel 10 to be maintained at a relatively low level; thus, in the event of a major break in one of the coolant pipes, reactor coolant pressure will be reduced immediately to that of the cover gas, and escaping coolant will be discharged at the pressure of the cover gas. Since cover gas pressure is relatively low, the amount of coolant discharged per unit time will be relatively small. In a modification (Fig. 5, not shown) the need for an auxiliary heat exchanger in the drainage line (as described above) is eliminated. This is achieved by provision of a second flow-restricting barrier (51) in the reactor vessel and above the first such barrier. A space between the two barriers is connected via a pipe (68) to the return line (48) from the pump (28) to the reactor vessel. Thus relatively cool coolant admitted to this space passes through the second barrier to the upper region of the reactor vessel and hence drainage coolant from said upper region via the drainage line is relatively cool. In a second embodiment (Fig. 2), the separate coolant reservoir tank previously described is dispensed with; instead, coolant discharging from the heat exchanger 26 passes into a pump enclosure 72 and thence to the pump inlet. The enclosure 72 thus provides a reservoir of coolant. As in the previous embodiment, a pressure equalizing line 60 extends between the cover gas spaces 20 and 76 in the reactor vessel 10 and pump enclosure 72, respectively. Also, the drainage line 62 from the reactor vessel 10 extends into the pump enclosure 72. An arrangement as described above in relation to the modification of the previous embodiment may also be provided. In both embodiments certain reactor assemblies pass through one or both carriers in the reactor vessel and the Specification describes in some detail arrangements for sealing between these assemblies and the barriers.