Patent Number: 041621913
Section: summary

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to steam generators and particularly to such steam generators for use in nuclear power plants. 2. Description of the Prior Art Steam generators for use in power plants, and particularly for use in nuclear power plants are well known, such as the type of steam generator manufactured by Westinghouse. One such typical prior art steam generator is shown in FIG. 1 of the drawings. These prior art steam generators utilized in nuclear power plants are normally contained in a containment building, such as one made of concrete. Moreover, these prior art steam generators known to applicant are unitary structures comprising a housing having an upper shell and lower shell portion with a moisture separator, including a swirl vane moisture separator, normally being located in the upper shell portion and with a tube bundle normally being located in the lower shell portion. In such prior art steam generators presently employed in nuclear power plants, the steam generator is completely enclosed and is placed in the containment building prior to the concrete being poured. As a result, once the containment building is sealed there is no way to replace this steam generator without breaking or destroying the containment building. Accordingly, if there is a failure in the tube bundle, it has heretofore been necessary to break the containment building in order to repair the steam generator as that is the only manner in which access can be had to various portions of the steam generator. Moreover, failure in the tube bundle of this prior art unitary type of steam generator has required replacement of the entire steam generator in order to allow for such repair, which complete replacement is quite costly in that such a steam generator costs approximately $15,000,000 by 1976 standards. With the widespread acceptance and use of nuclear power plants, there have been more and more such tube failures in the tube bundles of such steam generators which have required the power plant to be shut down. This, of course, can be extremely costly inasmuch as the steam generators are a vital component in the operation of the nuclear power plant. Moreover, since such nuclear power plants normally include three or four such steam generators in operation, the cost of replacement and/or repair can become quite prohibitive. Although the use of modular housing in various types of heat exchangers has been well known, such as disclosed in U.S. Pat. Nos. 1,372,010; 2,228,549; 2,241,209; 1,564,446; 1,790,897; 973,610; 514,338 and 784,192, such techniques, to applicant's knowledge, have not been used with respect to steam generators and particularly steam generators for use in nuclear power plants, despite the serious problems encountered with respect to repair and/or replacement of these steam generators in situ. These disavantages of the prior art are overcome by the present invention. SUMMARY OF THE INVENTION An improved steam generator for use in a nuclear power plant of the pressurized water type in which a turbine generator is driven by the steam output of the steam generator to provide electrical power therefrom and the steam generator is powered by a nuclear energy heat source, comprises a vertically assemblable modular structure for the steam generator. The modular structure comprises a base module, a tube bundle module removably mountable on the base module in sealing relationship therewith and an uppermost dryer module removably mountable on the tube bundle module in sealing relationship therewith for providing the vertically assemblable modular structure. The vertically assembled base module and tube bundle module comprise the lower housing portion of the steam generator and the dryer module comprises the upper housing portion of the steam generator. The dryer module has a steam outlet at one end thereof which is communicable with the turbine for providing steam generated within the steam generator to the turbine and a mositure separator means within the interior thereof in communication with the steam outlet for drying the generated steam provided to the steam outlet. The other end of the dryer module has a closure flange. The tube bundle module has a closure means, such as a closure flange, at the upper end thereof and a closure flange at the lower end thereof and contains a vertically extending tube bundle therein through which heat exchange fluid flows for enabling the provision of the steam. The tube handle has a tube sheet at one end thereof for supporting the tube bundle with the tubes comprising the tube bundle extending through the tube sheet in flow through communication with heat exchange fluid provided thereto. The tube bundle module also contains a feedwater inlet through which feedwater is provided for conversion into steam. The tube sheet comprises the lower end closure flange of the tube bundle module. The dryer module closure flange and the tube bundle module upper closure means effectuate the aforementioned sealing relationship between the tube bundle module and the dryer module. The base module uppermost portion has an outer shell having a tapered interior wall with the base module having the heat exchange fluid inlet therein which is in flow through communication with the vertically assembled tube module tube bundle. The exterior surface of the tube sheet closure flange is tapered complementary to the base module outer shell interior wall tapered portion and removably receivable therein for forming the aforementioned sealing relationship between the tube bundle module and the base module, with the associated weight of the vertically assembled dryer module and tube bundle module on the tube sheet closure flange effectuating the sealing relationship between the base module and the tube bundle module for facilitating closure by the tube sheet closure flange, whereby ready access to and removal of the tube bundle module in situ from the nuclear power plant steam generator is facilitated. Thus, the entire associated weight of the vertically assembled dryer and tube bundle modules is supported on the base module. Removable locking means are provided for lockably retaining the modules comprising the steam generator in vertically assembled relation. The vertically assembled modular nuclear steam generator is contained within a containment building structure therefor and may be disassembled for enabling repair of the steam generator without breaking or destroying the containment building structure.