GB2046981A - Ultimate heat sink for nuclear power plant - Google Patents

Abstract

Ultimate, missile-proof heat sink for the "safety part" of a nuclear power plant, and method for dissipation of residual heat from said power plant by said sink, said sink comprising an enclosed dry cooling tower 19 having an air inlet and outlet, at least one heat exchange means 26, supported on beam 21, by at least one support member 20 mounted vertically in the base of said tower, so that air introduced through said inlet and directed through said heat exchange means must be deflected towards said outlet. <IMAGE>

Description

SPECIFICATION Ultimate heat sink for nuclear power plant.

The present invention relates to an ultimate heat sink or reservoir for power plants utilizing thermal nuclear reactors and more particularly relates to an ultimate heat sink or reservoir for use in nuclear power plants which utilize the most widely used form of thermal nuclear reactors, viz., "light water" reactors such as boiling water nuclear reactors or pressurized water nuclear reactors so as to provide a capability for safely handling the residual heat generated by such reactors through use of dry cooling.

With boiling water reactors, as is well known, heat energy in the form of steam is generated in the nuclear reactor core and is delivered directly to the steam turbine and used to drive it; while in the pressurized water reactors, on the other hand, heat energy generated in the core is removed by water, as a reactor coolant, circulating at high pressure through the primary circuit or system (which cools or moderates the reactor) and transferred from the primary system to a secondary system in a heat exchanger, or boiler, thereby generating steam in the secondary system which is at a lower pressure and temperature than the primary coolant and which is used to drive the steam turbine.

The present invention, however, is not concerned with the cooling requirements associated either with cooling the steam used to drive the steam turbine or with cooling the steam exhausted by or from the steam turbine; instead, it is concerned with what is known as the "safety" part of the nuclear power plant wherein the residual heat generated in the reactor is controlled and dissipated.Since the general public has developed fears of nuclear technology, however, which have extended to the carefully controlled nuclear reactions which proceeds within commercial or state-or federally-owned or operated nuclear power plants, safety considerations consequently have come to be of paramount importance in the design, construction, and operation of such plants, especialiy with respect to their ability to handle residual heat generated by the reactor, and such considerations, of necessity, have come to embrace a variety of safety factors in view of the requirements and regulations that have been prom ulgated by the various state and federal authorities concerned with the use and regulation of nuclear power.

For example, one major safety consideration is concerned with the dissipation of residual heat upon shut-down of the nuclear reactor, or after an accident (usually one not necessarily associated with the nuclear portion of the plant). Governmental regulations require in such cases that the nuclear plants in question be equipped with an ultimate heat sink or reservoir to meet such contingencies. The capacity of such sink must be sufficient to provide cooling both for the period of time needed to evaluate a contingency and for the period of time required to take remedial action, if required. Under present-day conditions, this can call for a 30-day supply of water being made available for prospective contingencies.

Another aspect of safety is concerned with requirements, such as those set forth by the Code of Federal Regulations, Part 50, Appendix A, relating to general design criteria for nuclear power plants, among which are included provisions that: "....structures, systems, and components important to safety shall be designed to withstand the effects of natural phenomena .... without loss of capability to perform their safety functions." Such natural phenomena include, but are not limited to, earthquakes, tornadoes, hurricanes, tsunami, seiches, floods, or droughts.When conventional ultimate heat sinks are used, as, for example, large bodies of water such as rivers, lakes, oceans, spray ponds, reservoirs, or combinations thereof, other site-related events that may be caused by natural phenomena must be considered such as blockage, diversion, or even depletion of the body of water in question that is used. In addition, other events, including transportation accidents such as ship collisions, airplane crashes, etc., or oil spills and fires, etc. must be considered in connection with the overall nuclear power plant design.

In order for the ultimate heat sink to have maximum reliability to provide the required safety functions without any loss in capability, it is essential that the ultimate heat sink comprise a cooling source which is totally resistant to, or not adversely affected by, natural phenomena, such as discussed above.

This requirement is fully met by the ultimate heat sink of this invention, through use of the dry cooling means it provides.

It is well known that thermal nuclear reactors generate enormous amounts of heat, derived from the fission or fusion reactions conducted therein, much of which is used to drive the steam turbines that power the generators from which much of the current needs for electric power are derived. While considerable attention has been centered on the heat transfer needs associated with the electrical production or generating ends or purposes of the nuclear power plant, relatively little heed by comparison has been paid to the means required to handle the residual heat developed and retained by nuclear power plants, notwithstanding the importance of such means in view of the statutorily imposed rules or regulations which govern the treatment of residual heat requirements, primarily for safety and other health-related reasons.

Thus, the only ultimate heat sinks or reservoirs that have ever been used in the past and which are used even now to handle the residual heat requirements of present-day nuclear power plants are natural or man-made bodies of water such as the above-mentioned rivers, lakes, oceans, spray ponds, etc.

However, such ultimate heat sinks are not deemed to be satisfactory, particularly in view of their becoming contaminated by radioactivity and the attendant hazards of pollution, etc., they pose to the environment.

Thus, there is presently no commercially available alternative that wholly satisfies the cooling needs and safety requirements, of residual reactor generated heat with maximum freedom from radioactive contamination. This void is now filled by the present invention.

The present invention provides a maximum safety ultimate heat sink or reservoir for power plants having a thermal nuclear reactor of any of the usual types: "light water" reactors, e.g., boiling water or pressurized water reactors; "heavy water" reactors; high-temperature gas-cooled reactors; fast breeder reactors; gas-cooled fast breeder reactors; etc. More specifically, the present invention provides a maximum safety ultimate heat sink or reservoir for thermal nuclear power plants which includes dry cooling means, capable of withstanding all natural phenomena, comprising an exterior protective structure and heat exhanger means contained therein.

Such sink constitutes a closed system wherein the heat exchanger units are disposed, preferably horizontally, and arranged in modules, the wall and roof of the protective structure are missile-proof, and said walls contain openings to permit atmospheric air to enter and exit from the structure A more complete understanding of the ultimate heat sink of the present invention will be had by reference to the following description when taken with the accompanying drawings wherein like num erals designate like parts throughout and wherein: Figure lisa flow diagram essentially of the prior art reactor cooling water system that ordinarily is used in conventional nuclear power plants except for the inclusion therein of the ultimate heat sink of the present invention.The dotted lines in Figure 1 denote the fact that the component cooling water exchanger of the prior art design can be replaced by the present ultimate heat sink; Figure 2 is a plan view of a partial flow plan of a nuclear power plant showing two thermal nuclear reactors at opposite ends to which are linked, respectively the ultimate heat sinks of the present invention; Figure 3 shows a heat sink in which there are five heat exchanger modules.

Figure 4 is a side elevational view, partially in section of the heat exchangers and modules shown in Figure 3; Figure 5 is a side elevational view, partially in section of the present heat exchangers taken along the line 5-5 of Figure 3, illustrating the flow of atmospheric air entering the present sink and exiting from the present sink; Figures 5a and 5b illustrate equivalent exchanger configurations; and Figure 6is an enlarged side elevational view, partially in section taken along line 6-6 of Figure 3, showing how the heat exchanger members are secured to the protective structure in which they are housed.

As previously discussed, the ultimate heat sink for a thermal nuclear power plant is provided essentially for purposes of satisfying several safety functions such as dissipation of residual heat after reactor "shut-down" or an accident.

In addition, the ultimate heat sink must be totally resistant to natural phenomena and provide complete protection against missiles. Thus, the importance of the ultimate heat sink is such that, if during plant operation the capability of the ultimate heat sink is threatened for any reason, restrictions must be placed on plant operation.

The ultimate heat sink, moreover, as its name suggests, is the ultimate depository of heat, and this, as is well known in the art, is with reference to its being the ultimate depository of heat for the nuclear reactor cooling system.

Atypical nuclear reactor cooling system is shown in Figure 1. As will be noted, Figure 1 illustrates two duplicate reactor cooling systems, only one (at a time) of which is actually used in practice for purposes of cooling. The duplicate or second system depicted is required by state or federal regulation for safety reasons so that it can be used in the event of either emergency or when the other reactor cooling is shut-down or otherwise inoperative. With reference to this figure, there is shown a housing 10 for a thermal nuclear reactor vessel 11.Reactor coolant, most commonly water, is circulated through the nuclear core by means not shown, and such coolant moderates or helps cool the reactor by removing residual heat from part of the coolant that accumulates in sump 12 via circuiation by means of a circulating pump through the residual heat removal exchanger 13 and recirculation of the exchanger effluent to the nuclear core. The remainder of the accumulated coolant in the sump 12 is pumped to a containment spray exchanger from which much of the radioactive contamination is removed, whereby a radioactive-rich stream from exchanger 14 is returned to housing 10 and sprayed into its interior and a radioactive-poor stream is conveyed to a recycle stream from residual heat removal exchanger 13 for further residual heat removal downstream.

The combined streams are then pumped to a final cooling stage in the component cooling water exchanger 15 from which the major part of the resulting cool effluent is recirculated to the residual heat removal exchanger 13 to aid its cooling function. The balance of the effluent from exchanger 15 is passed to an auxiliary load exchanger 16 in which it is utilized to provide cooling for services not depicted and from which it is recirculated by pump to exchanger 15.

As shown in Figure 2, in which a partial floor plan of the reactor site is presented,the housing 10 for the thermal nuclear 11 is operatively connected via piping to the present ultimate heat sink 17, which comprises duplicate heat exchanger units 18 of the completely closed, extended-surface type, arranged in modules which are connected in parallel to provide the required cooling. Each exchanger can contain a multiplicity of series passes to optimize its design with respect to heat transfer. The exchanger, as indicated, operates under mechanical draft provided by axial flow fans, and the mechanical draft may be either forced or induced. Depicted by the drawings, however, is a forced draft arrangement.

Each of such units is a mechanical draft, water-to-air exchanger completely enclosed within a closed protective structure indicated generally as 19 (Figure 5).

The protective structure 19 comprises a closed enclosure (e.g., a building) having vertical walls and an arched roof, and is adapted to set upon and be connected to a seismic pad 25 (partially shown) which contains appropnate means such as shear keys to affix such structure to the site terrain. The vertical walls of the structure contain openings to permit atmospheric air to enter, be circulated through, and exit from, such structure. Structure 19, as seen in Figure 5, contains interior walls 20 to which are mounted transverse beams indicated generally as 21 that extend between such walls and the outside wall of the plant to support the exchanger unit. The exchanger units 18 are mounted on the beam 21 above said openings to enable structure 19 to provide line of sight missile protection.While the orientation of the exchanger units 18 is shown as being horizontal, it is manifestly capable of being a variety of other forms well known in the art as being equivalent, e.g., A-frame, as indicated in Figure 5a, inclined as indicated in Figure 5b, vertical, etc. The arched roof too of structure 19 provides protection from missile for missile flight paths other than line of sight. In addition, exterior walls can also be employed to provide protection from missiles.

To ensure that the possibility of cooling recirculation, i.e., the cycling of heated cooling air returning to the cooling air inlet, is made as remote as possible, the cooling air inlet is located on one side of protective structure 18 and the heated air discharge is located on the opposite side (as shown in Figure 5). Therefore, the outlet is located a significant distance away from the inlet. In the event of a site wind oriented from the discharge side to the inlet side, this separation ensures adequate dispersion of the hot air plume.

Also shown in Figure 5 are crane means attached to and suspended from the interior of the arched roof of protective structure 19 and this means enables the placement of both heat exchanger units 18 and transverse beams 21 to be effected.

Since, in view of the operational problems associated with a seismic event, structural elements, which comprise and support the protective enclosure 19 and also heat exchanger units 18 mounted within it, must, by governmental regulation, be able to withstand the forces imposed by such a seismic event without incurring any damage whatsoever. This therefore engenders a plurality of design problems for which the preferred structure of the present invention, which is made of reinforced concrete or like masonry material, now provides satisfactory solution. As biit one example of this, resort may be had to Figure 6 in which a structural member 23, generally in the form of an H-configuration, is shown. Member 23, in a preferred embodiment, is made of reinforced concrete and supports both the transverse beams 21 and the exchanger units 18 fastened thereto with means, indicated generally by reference numeral 24.

As shown, e.g., in Figure 5, 5a, and 5b, a support member 20 is vertically mounted in the base of the cooling tower and is adapted to deflect toward the outlet of said tower, said cooling air that has passed or circulated through the heat exchanger. As may be appreciated, such support member(s) can assume a variety of sizes, shapes, and forms, and may also include additional air deflecting surfaces.

The invention above described is not limited to the embodiments shown, but may be varied in many ways within the scope of the appended claims.

Claims (14)

1. An ultimate heat sink for a nuclear power plant, comprising at least one enclosed cooling tower having an air inlet and an air outlet at the outer sides of said tower, at least one heat exchange means mounted at the interior end of one of said outer sides of said tower, and at least one support member vertically mounted on the base of said tower, whereby air introduced through said inlet and directed through said heat exchanger is deflected by said support member towards said outlet.

2. A method of withdrawing residual heat from a nuclear power plant, comprising feeding an ultimate heat sink comprising an enclosed dry cooling tower having an air inlet and an air outlet with hot contaminated water and cooling air, and withdrawing the heated air from said cooling tower.

3. A method according to Claim 2 wherein said heat contaminated water comprises radio active contamination.

4. A cooling arrangement for a nuclear power plant, the arrangement comprising a structure fabricated from masonry material and defining an enclosure having side walls and an arched roof, an air inlet and an air outlet being provided in said side walls, said outlet being isolated from said inlet by separator means, said separator means providing support for heat exchanger means located in a path for air flowing between said inlet and outlet.

5. An arrangement according to claim 4 wherein said structure comprises exterior wall means adjacent said inlet.

6. An arrangement according to claim 4 or 5 wherein said separator means comprises a beam and interior wall means adjacent said outlet, said beam being supported at respective ends by a side wall of said enclosure and by said interior wall means.

7. An arrangement according to claim 6 wherein said heat exchanger means comprises a plurality of heat exchanger modules extending horizontally along said beam.

8. An arrangement according to claim 6 wherein said heat exchanger means comprises a plurality of heat exchanger modules arranged with alternate opposite angles of inclination.

9. An arrangement according to claim 6 wherein said beam is inclined and said heat exchanger means extends along an inclined surface.

10. An arrangement according to any one of claims 6 to 9 wherein said beam includes at least one section of H-shaped cross-section.

11. A cooling arrangement substantially as herein described with reference to Figure 5a of the accompanying drawing.

12. A cooling arrangement substantially as herein described with reference to Figure 5b of the accompanying drawing.

13. A cooling arrangement substantially as herein described with reference to Figure Sc of the accompanying drawing.

14. A cooling arrangement substantially as herein described with reference to Figure 6 of the accompanying drawing.