Patent Number: 039740293
Section: description

The reactor comprises a core 1 contained within a chamber 2 through which a gas such as helium is arranged to be circulated in normal use of the reactor, the gas passing around a closed circulatory system comprising a plurality of parallel loops 3, each incorporating a gas turbine, one of which is represented at 4, coupled to a main alternator 5. Each turbine unit 4 includes, in the usual way, a power turbine 6 coupled to the alternator 5, and a high pressure turbine 7 for driving low pressure and high pressure compressors 8 and 9, a precooler 10 and intercooler 11 being provided for cooling the gas passing to the low pressure and high pressure compressors respectively, and a recuperator 12 effecting an exchange of heat between the gas leaving the power turbine 6 and that fed from the high pressure compressor 9 to the reactor chamber 2. In accordance with the invention there is also provided an auxiliary circulatory system comprising a plurality of auxiliary cooling loops, one of which is represented at 13, connected to the chamber 2 in parallel with the main circulatory system. Each of these auxiliary cooling loops incorporates a motor driven circulator 15 producing a flow of gas around the loop, and a boiler 14 in which the hot gas leaving the reactor core 1 provides the heat for generating steam for an auxiliary steam-turbine 20 driving an auxiliary generator 16. The auxiliary boiler/steam turbine system is arranged to be run continuously and provides sufficient cooling to cover reactor start-up, shut-down and emergency conditions with the main gas turbine system inoperative. Power produced by the auxiliary generator 16 can be used to supply power for reactor services and ancillary equipment. The arrangement thus enables the reactor to be started-up separate from the gas turbine cycle start-up, and in addition long term heat removal, either after a reactor trip or under normal reactor shut-down is facilitated by shutting down the gas turbine units and removing heat from the core by the auxiliary circulatory system, as previously explained. The temperature of the gas fed to the auxiliary boilers 14 from the reactor core 1 is preferably reduced, by mixing the gas emerging from the core with gas at a lower temperature. For this purpose each cooling loop 13 may be associated with a by-pass pipe 17 which allows some of the cooled gas leaving the respective boiler 14 to by-pass the reactor core 1 as shown. However other means of cooling the gas between the reactor core and the boilers can alternatively be provided. Thus the gas leaving the reactor core may be mixed with cooler gas from another source, for example an appropriate part of the gas turbine system. Typically four gas turbine units and four auxiliary boilers will be associated with the reactor and these are conveniently located in chambers, commonly termed pods, in a concrete pressure vessel wall which surrounds and provides the chamber 2 for the reactor core 1. FIG. 2 shows one such arrangement, each gas turbine unit 4, including associated compressors, recuperator and the like, being housed in an adjacent pair of chambers or pods 21, 22 formed within and spaced around a pressure vessel wall 18 which surrounds the reactor core, each auxiliary boiler 14 being located in a pod 23 separating adjacent pairs of gas turbine pods as shown. In a modification, not illustrated, the reactor core is housed in a primary pressure vessel, surrounded by a secondary pressure vessel, the gas turbine units and auxiliary boilers being located in the space between the primary and secondary pressure vessels, for example in a manner similar to that described with reference to FIGS. 5 and 6 of co-pending U.S. patent application Ser. No. 222947. Although the invention is particularly applicable to nuclear reactors of the kind incorporating closed cycle gas turbines, it will be appreciated that it has application to reactors in which alternative forms of energy convertors are employed. Thus the invention may be used to advantage in gas cooled reactor systems in which the major portion of the reactor heat is used for process heating.