Patent Number: 039376524
Section: description

In the embodiment of the invention shown in FIG. 1, a nuclear reactor core 11 is housed in a reactor chamber 12 within a prestressed concrete pressure vessel 13. Extending vertically within the wall thickness of the vessel 13 are provided chambers or cavities 14 and 15 which are sealed at their ends and are connected through ducts 16 to the reactor chamber 12. Within each of a plurality of the chambers 14 (say, four in number) is disposed a respective main boiler unit 17 and a respective main circulator unit 18 arranged to draw heated coolant fluid, say helium under pressure, from the reactor core 11 and thence through the respective main boiler unit 17 before returning it to the reactor chamber 12 for passage once more through the core 11. Similarly, a plurality of auxiliary boiler units 19 (which may also be four in number) are disposed each in a respective one of the chambers 15 which also accommodates a respective auxiliary circulator unit 20 which similarly draws heated coolant fluid from the reactor core 11 and thence through the respective auxiliary boiler unit 19 before returning it to the reactor chamber 12 for passage once more through the core 11. The detailed arrangement, including ducting to effect the desired circulation paths for the reactor coolant fluid, are described and shown in greater detail in our said co-pending application. The main boiler units 17 are supplied with water through water feed lines 21, and their high-pressure steam outputs are supplied through steam lines 22 to one or more turbines of main steam turbogenerators 22' of the installation. Each chamber 14 which houses a main boiler unit 17 may also accommodate a respective steam reheater unit (not shown) for intermediate reheating of the steam supplied to the main turbogenerator turbines. The auxiliary boiler units 19 are supplied with feed water through water feed lines 23, and their steam output is supplied through steam lines 24 to, eventually, the turbines 25 of one or more auxiliary steam turbogenerators which provide essential power for the operation of the installation. In accordance with the present invention, however, the steam from the auxiliary boiler units 19 is also employed to drive steam turbines 26 which drive the main coolant circulator units 18. The power requirements for the units 18 are only some 3% of the gross station output. In the embodiment of the invention shown in Fig. 1, this steam from the auxiliary boilers is fed by the steam lines 24 to a header 27, and thence to the turbines 26 from which it is exhausted to a further header 28 whence in turn it is fed to the auxiliary turbogenerator turbines 25. Each of the circulator-drive turbines 26 is provided with a respective steam bypass line shown as including pressure reducing valves 29 and an attemperator 30; and this provision, in conjunction with the normal throttle control (not shown) enables the flexible power requirements of the main circulators 18 to be met, including the provision of safety margins. Each turbine 26 may be directly coupled to the respective circulator 18, and, typically, may be a single-stage machine which runs at approximately 6000 revolutions per minute with inlet steam conditions 1500 psig/1000.degree.F and exhaust conditions 650 psig/800.degree.F. A safety valve 31 may be provided at the header 28 as protection for the auxiliary steam system in the event of a trip of the main circulators 18, and a feed heater system 32 may be interposed between the exhausts from the turbines 25 of the auxiliary turbogenerators and the water feed lines 23. The auxiliary circulator units 20 may be driven by steam turbines supplied from the auxiliary boiler units 19, or (as shown) each may be driven by a respective electric motor 33 supplied by the auxiliary generator driven by the auxiliary turbines 25. The embodiment of the invention shown in FIG. 2 is almost identical with that shown in FIG. 1, and corresponding parts are indicated by the same references in the two cases (except that no auxiliary turbine 25 is actually shown in FIG. 2). The difference between the two embodiments is that, in that shown in FIG. 2, the steam from the header 28 is reheated before being supplied to the auxiliary turbines 25, and for that purpose there is associated with each auxiliary boiler 19, in the same chamber 15, a respective reheater unit 34 through which steam passes on its way from the header 28 to the auxiliary turbines 25. This reheating provides a small increase in overall station efficiency. The two embodiments of the invention described above are conceived as applied to a helium-cooled high-temperature gas-cooled reactor, but it will be understood that the invention may also find application in connection with the coolant circulators of other types of fluid-cooled reactors.