AN D M ETHOD OF TH E SAM E

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[00011 This appl ication claims the benefit of United States Provisional Patent Application No. 61 /476,624, filed April 18, 201 1 , the entirety of which is incorporated herein by reference.

FIELD OF THE INVENTION

| 0002 | The present invention relates generally to systems and methods of removing thermal energy from pools of liquid, and specifically to systems and methods of removing thermal energy from spent nuclear fuel pools that are self-powered and autonomous.

BACKGROUND OF THE INVENTION

[0003) The spent fuel pool (SFP) in a nuclear power plant serves to store used spent nuclear fuel discharged from the reactor in a deep pool (approximately 40 feet deep) of water. I n existing systems, the decay heat produced by the spent nuclear fuel is removed from the SFP by circulating the pool water through a heat exchanger (referred to as the Fuel Pool Cooler) using a hydraulic pump. In the Fuel Pool Cooler, the pool water rejects heat to a cool ing medium which is circulated using another set of pumps. Subsequent to it's cool ing in the Fuel Pool cooler, the pool water is also purified by passing it through a bed of demineralizers before returning it to the pool.

|0004| In existing systems, the satisfactory performance of the spent fuel cooling and clean up system described above is critically dependent on pumps which require electric energy to operate. As the events at the Fukushima Dai-ichi showed, even a redundant source of power such as Diesel generators cannot preclude the paralysis of the classical fuel pool cooling system.

|0005| In order to insure that the decay heat produced by the fuel stored in the SFP is unconditionally rejected to the environment, the present invention introduces a heat removal system and method that does not require an external source of electric energy or equipment that can be rendered ineffective by an extreme environmental phenomenon such as a tsunami, hurricane, earthquake and the like.

I BRI EF SUMMARY OF THE I NVENTION

[0006] These, and other drawbacks, are remedied by the present invention. An autonomous and self-powered system of cooling a pool of liquid in which radioactive materials are immersed is presented. The inventive system utilizes a closed-loop fluid circuit through which a low boil ing point working fluid flows. The closed-loop fluid circuil of the inventive system, in accordance with the Rankine Cycle: ( 1 ) extracts thermal energy from the liquid of the pool into the working fluid; (2) converts a first portion of the extracted thermal energy into electrical energy that is used to power one or more forced flow units that induce flow of the working fluid through the closed-loop fluid circuit; and (3) transfers a second portion of the extracted thermal energy to a secondary fluid, such as air. In this way, the inventive system operates without the need for any electrical energy other than that which is generates internally in accordance with the Rankine Cycle.

|0007| In one embodiment, the invention can be an autonomous sel f-powered system for cool ing radioactive materials, the system comprising: a pool of liquid, the radioactive materials immersed in the pool of liquid; a closed-loop fluid circuit comprising a working fluid having a boiling temperature that is less than a boiling temperature of the liquid of the pool, the closed-loop fluid circuit comprising, in operable fluid coupling, an evaporative heat exchanger at least partially immersed in the liquid of the pool, a turbogenerator, and a condenser; one or more forced flow units operably coupled to the closed-loop fluid circuit to induce flow of the working fluid through the closed-loop fluid circuit; and the closed-loop fluid circuit converting thermal energy extracted from the liquid of the pool into electrical energy in accordance with the Rankine Cycle, the electrical energy powering the one or more forced flow units.

|0008| In another embodiment, the invention can be an autonomous self-powered system for cooling a pool of liquid comprising: a closed-loop fluid circuit comprising a working fluid having a boiling temperature that is less than a boiling temperature of the liquid of the pool, the closed-loop fluid circuit comprising, in operable fluid coupling, an evaporative heat exchanger at least partially immersed in the liquid of the pool, a turbogenerator, and a condenser; one or more forced flow units operably coupled to the closed-loop fluid circuit to induce flow of the working fluid through the closed-loop fluid circuit; and the closed-loop fluid circuit converting thermal energy extracted from the liquid of the pool into electrical energy in accordance with the Rankine Cycle, the electrical energy powering the one or more forced flow units. [0009| In yet another embodiment, the invention can be a method of cooling a pool of liquid comprising: flowing the working fluid having a boiling temperature that is less than a boiling temperature of the liquid of the pool through a closed-loop fluid circuit that, in accordance with a Rank ine Cycle: ( 1 ) extracts thermal energy from the l iquid of the pool into the working fluid; (2) converts a first portion of the extracted thermal energy into electrical energy that is used to power one or more forced flow units that induce flow of the working fluid through the closed-loop fluid circuit; and (3) transfers a second portion of the extracted thermal energy to a secondary fluid.

(0010) In a yet further aspect, the invention can be a vertical evaporative heat exchanger for immersion in a heated fluid comprising: a tubeside fluid circuit comprising: a top header; a bottom header; a core tube forming a downcomer passageway between the top header and the bottom header, the core tube having a first effecti ve coefficient of thermal conductivity; a plurality of heat exchange tubes forming passageways between the bottom header and the top header, the plural ity of the heat exchange tubes having a second effective coefficient of thermal conductivity that is greater than the first effective coefficient of thermal conductivity; a working fluid in the tubeside fluid circuit: an inlet for introducing a liquid phase of the working fluid into the tubeside fluid circuit; an outlet for allowing a vapor phase of the working fluid to exit the top header; and wherein transfer of heal from the heated fluid to the working fluid induces a thermosiphon flow of the liquid phase of the working fluid within the tubeside fluid circuit.

(001 11 Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

BRI EF DESCRI PTION OF TH E DRAWINGS

(0012 | The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:

|00 13| Figure 1 is a schematic of an autonomous self-powered cooling system according to one embodiment of the present invention;

100141 Figure 2 is a schematic of an evaporative heat exchanger for use in the autonomous self-powered cooling system of FIG. 1 ; |0015| Figure 3 is an induced air-flow air cooled condenser for use in the autonomous self- powered cooling system of FIG. 1 ;

|0016| Figure 4 is a natural draft air cooled condenser for use in the autonomous self- powered cooling system of FIG. 1 ;

|0017| Figure 5A is perspective view of the heat exchange tube bundle of the natural draft air cooled condenser of FIG. 4;

|0018| Figure 5B is a close-up view of area V-V of FIG. 5A; and

|0019] Figure 6 is a transverse cross-section of tinned heat exchange tube for use in the evaporative heal exchanger of FIG. 2 and/or the air cooled condensers of FIGS. 3and 4.

DETAILED DESCRIPTION OF TH E DRAWINGS

[0020] The following description of the preferred embodiment s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. While the invention is exemplified in FIGS. 1 -6 as being used to cool pools of liquid in which radioactive materials are immersed (such as spent nuclear fuel, high level radioactive waste or low level radioactive waste), the invention is not so limited and can be used to cool any body of liquid in need of cooling.

|002 l | Referring first to FIG. 1 , an autonomous self-powered cooling system 1000 according to an embodiment of (he present invention is schematically illustrated. The autonomous self- powered cooling system 1000 generally comprises a closed-loop fluid circuit 100, an electrical circuit 200, and a pool of liquid 50. Radioactive materials 20 are immersed in the pool of liquid 50, which in the exemplified embodiment is a spent fuel pool. Radioactive materials 20, such as spent nuclear fuel, generate a substantial amount of heat for a considerable amount of time after completion of a useful cycle in a nuclear reactor. Thus, the radioactive materials 20 are immersed in the pool of liquid 50 to cool the radioactive materials 20 to temperatures suitable for dry storage. In embodiments where the radioactive materials 20 are spent nuclear fuel rods, said spent nuclear fuel rods will be supported in the pool of liquid 50 in fuel racks located at the bottom of the pool of liquid 50 and resting on the floor. Examples of suitable fuel racks are disclosed in United States Patent Application Publication No. 2008/0260088, entitled Apparatus and Method for Supporting Fuel Assemblies in an Underwater Environment Having Lateral Access Loading, published on October 23, 2008, and United States Patent Application Publication No. 2009/01 75404, entitled Apparatus or Supporting Radioactive Fuel Assemblies and Methods of Manufcturing the Same, published on July 9, 2009, the entireties of which are hereby incorporated by reference.

|0022| As a result of being immersed in the pool of liquid 50, thermal energy from the radioactive materials 20 is transferred to the pool of liquid 50, thereby heating the pool of liquid 50 and cooling the radioactive materials. However, as the pool of liquid 50 heats up over time, thermal energy must be removed from the pool of liquid 50 to maintain the temperature of the pool of liquid 50 within an acceptable range so that adequate cooling of the radioactive materials 20 can be continued.

|0023| As discussed in greater detail below, the closed-loop fluid circuit 100 extends through the pool of liquid 50. A working fluid 75 is flowed through the closed-loop fluid circuit 100. The closed-loop fluid circuit 100 extracts thermal energy from the pool of liquid 50 (into the working fluid 75) and converts the extracted thermal energy into electrical energy. The electrical energy generated by said conversion powers the electrical circuit 200, which in turn powers forced flow units 1 0, 15 1 (described below) that induce flow of the working fluid 75 (FIG. 2) through the closed-loop circuit 100. The aforementioned extraction and conversion of thermal energy into electrical energy is accomplished by the closed-loop fluid circuit 100 in accordance with the Rankine Cycle. In certain specific embodiments, and depending on the identity of the liquid 50 to be cooled and the working fluid 75 being used, the closed-loop fluid circuit 100 can accomplish the extraction and conversion of thermal energy into electrical energy in accordance with, the Organic Rankine Cycle.

|0024| In order to cool the pool of liquid 50 prior to the liqu id 50 of the pool evaporating/boiling, the working fluid 75 is preferably a low boiling-point fluid (relative to the liquid 50 of the pool). More specifically, the working fluid 75 is selected so that it has a boiling temperature that is less than the boiling temperature of the liquid 50 of the pool. It is appreciated that the temperature at which a liquid boils/evaporates is dependent on pressure and that the liquid 50 of the pool and the working fluid 75 may be subject to different pressures in certain embodiments of the invention. Furthermore, as discussed in greater detai l below, the working fluid 75 is evaporated/boi led in an evaporative heat exchanger 1 10 that is immersed in the pool of liquid 50. In certain such embodi ments, the liquid 50 of the pool will be under a fu st pressure and the working fluid 75 in the evaporative heat exchanger 1 1 0 will be under a second pressure that is greater than first pressure. Thus, in such an embodiment, the working fluid 75 is selected so that the boiling temperature of the working fluid 75 at the second pressure is less than the boiling temperature of the liquid 50 of the pool at the first pressure. In one specific embodiment, the first pressure wil l be atmospheric pressure and the second pressure wil l be in a range of 250 psia to 400 psia.

|0025] In one embodiment, the liquid 50 of the pool is water. As used herein, the term "water" includes borated water, demineralized water and other forms of treated water or water with additives. Suitable working fluids 75 include, without limitation, refrigerants. Suitable refrigerants may include, without limitation, ammonia, sulfur dioxide, chlorofluorocarbons, hydrochlorofluorocarbons, hydrofluorocarbons, haloalkanes, and hydrocarbons. One particularly suitable refrigerant that can be used as the working fluid 75 is tetraflouroethane, commonly known as HFC- 134a.

|0026| The exemplified embodiment of the closed-loop fluid circuit 100 generally comprise an evaporative heat exchanger 1 10, a turbogenerator 1 30, a condenser 1 50, a working fluid reservoir 1 70, and a hydraulic pump 190. The aforementioned components 1 1 0, 1 30. 1 50, 1 70, 190 of the closed-loop fluid circuit 100 are operably and fluidly coupled together using appropriate piping, joints and fittings as is well-known in the art to form a fluid-tight closed- loop through which the working fluid 75 can flow through in both a liquid phase 75A and a vapor phase 75B. The working fluid 75 is in the liquid phase 75A between a working fluid outlet 153 of the condenser 1 50 and a working fluid inlet 1 1 1 of the evaporative heat exchanger 1 10. The working fluid 75 is in the vapor phase 7513 between a working fluid outlet I 12 of the evaporative heat exchanger 1 1 0 and a working fluid inlet 1 52 of the condenser 1 50. As discussed in greater detail below, the evaporative heat exchanger 1 10, which is immersed in the liquid 50 of the pool, converts the working fluid 75 from the liquid phase 75A to the vapor phase 75B by transferring thermal energy from the liquid 50 of the pool into the working fluid 75. Conversely, the condenser 150 converts the working fluid 75 from the vapor phase 75B to the liquid phase 75A by transferring thermal energy from the working fluid 75 into a secondary fluid (which can be air that is rejected to the environment in certain embodiments).

[00271 In the exempli fied embodiment, the autonomous self-powered system 1 000 further comprises two forced flow units that induce flow of the working fluid 75 through the closed- loop fluid circuit 100, namely the hydraulic pump 190 (which is considered part of the closed-loop fluid circuit 100) and a blower 1 51 which, when operated, forces cool ing air to flow over heat exchange tubes 154 (as shown in Figure 6) of the condenser 150. The hydraulic pump 190 directly induces flow of the working fluid 75 through the closed-loop fluid circuit 100 by drawing the liquid-phase 75A of the working fluid 75 from the working fluid reservoir 1 70 and forcing the liquid-phase 75A of the working fluid 75 into the evaporative heat exchanger 1 10. The blower 1 5 1 indirectly induces flow of the working fluid 75 through the closed-loop fluid circuit 100 by increasing air flow over the heat exchange tubes 154 of the condenser 150 (the working fluid 75 being the tubeside fluid in the condenser 1 50), thereby increasing the extraction of thermal energy from the working fluid 75 in the condenser 1 50 and promoting increased condensation and a thermo-siphon flow effect of the working fluid 75. In certain embodiments of the invention, more or less forced flow units can be incorporated into the autonomous self-powered system 1000 as desired.

[0028] For example, in certain embodiments, the blower 151 may be omitted while, in certain other embodiments, the hydraulic pump 90 may be omitted. For example, if the condenser 50 were a natural draft air-cooled condenser (see FIGS. 4-5B), the blower 15 1 may be omitted. Furthermore, in certain embodiments where the condenser 50 is not an air cooled condenser, but is for example a shell and tube heat exchanger, a hydraulic pump that is used to force flow of the secondary fluid through the condenser 50 can be a forced flow unit.

|0029| Irrespective of the exact number and identity of the forced flow units that are used to induce flow of the of the working fluid 75 through the closed-loop fluid circuit 1 00, all of said forced flow units are powered only by electrical energy generated through the conversion of the thermal energy that is extracted from the l iquid 50 of the pool. More specifically, in the exemplified embodiment, both the hydraulic pump 190 and the blower 15 1 are operably and electrically coupled to the electrical circuit 200, which is powered solely by the electrical energy generated by the turbogenerator 130 (discussed in greater detail belo ). Thus, the autonomous self-powered system 1000 can operate to cool the liquid 50 of the pool for an indefinite period of time and completely independent of any outside sources of electrical energy, other than that electrical energy that is generated through the conversion of the thermal energy extracted from the liquid 50 of the pool. Stated simply, the thermal energy of the liquid 50 of the pool is the sole source of energy required to drive the cooling system 1000.

[0030| Referring still to FIG. 1 , the general operation cycle of the autonomous self-powered system 1000 will be described. The working fluid reservoir 170 stores an amount of the liquid phase 75a of the working fluid 75 to charge and control the quantity of the working fluid 75 in the thermal cycle at start up. The working fluid reservoir 170 also provides the means to evacuate the closed-loop fluid circuit 100 of air and to fill the closed-loop fluid circuit 100 with the required amount of the working fluid 75. In certain embodiments, the working fluid reservoir 1 70 is needed only at the beginning of the system operation (start up) to insure that the proper quantity of the working fluid 75 is injected into the thermal cycle. |0031 | The hydraulic pump 190 is located downstream of the working fluid reservoir 170 in the exempli fied embodiment. However, in alternate embodiments, the hydraulic pump 190 can be located upstream of the working fluid reservoir 1 70. Once started, the hydraulic pump 190 draws the liquid phase 75 A of the working fluid 75 from the working fluid reservoir 1 70, thereby drawing the liquid phase 75A of the working fluid 75 into the working fluid inlet 1 91 of the hydraulic pump 190. As the hydraulic pump 190 operates, the l iquid phase 75A of the working fluid 75 is expelled from the working fluid outlet 192 of the hydraul ic pump under pressure. The expelled liquid phase 75A of the working fluid 75 is forced into the evaporative heat exchanger 1 10 via the working fluid inlet 1 1 1 of the evaporative heat exchanger 1 10.

|0032| The evaporative heat exchanger 1 10 is at least partially immersed in the liquid 50 of the pool so that thermal energy from liquid 50 can be transferred to the working fluid 70 while in the evaporative heat exchanger 1 10. In the exemplified embodiment, the evaporative heat exchanger 1 10 is ful l immersed in the liquid 50 of the pool . Furthermore, the evaporative heat exchanger 1 10 is located at a top of the pool of liquid 50, which tends to be hotter than the bottom of the poo, of liquid 50 due to temperature differentials in the l iquid 50 ( hot fluids rise). In one embodiment, the evaporative heat exchanger 1 10 is mounted to one of the sidewal ls 55 of the pool of liquid 50 so that the evaporative heat exchanger 1 1 0 does not interfere with loading and unloading operations that take place within the pool of liquid 50 for the radioactive materials 20.

[0033] The details of one embodiment of the evaporative heat exchanger 1 10, including the operation thereof, wi l l now be described with reference to FIGS. 1 and 2 concurrently. Of course, the invention is not so limited, and the evaporative heat exchanger 1 10 can take on other structural embodiments in other embodiments of the invention. The evaporative heat exchanger 1 10 generally comprises a core tube 1 13 (which acts as a downcomer tube in the exemplified embodiment), a plurality of heat exchange tubes 1 14, a working fluid bottom header 1 15, and a working fluid top header 1 16, which collectively define a tubeside fluid circuit. The working fluid bottom header 1 15 comprises a bottom tube sheet 1 1 7 while the working fluid top header 1 16 comprises a top tube sheet 1 1 8.

|0034| In one embodiment, the bottom and top headers 1 15, 1 16 and the core pipe 1 1 3 are constructed of a corrosion resistant alloy, such as stainless steel. The bottom and top tube sheets are constructed of an aluminum clad stainless steel. The heat exchange tubes I 14 are constructed of aluminum (as used herein the term "aluminum" includes aluminum alloys) and are welded to the aluminum cladding of the bottom and top tube sheets 1 1 7, 1 1 S to make leak tight joints. The core pipe 1 13 will be welded to the stainless steel base metal of the bottom and top tube sheets 1 1 7, 1 18. Of course, other materials and construction methodologies can be used as would be known to those of skill in the art.

|0035| The core tube 1 13 extends from the working fluid outlet header 1 16 to the working fluid inlet header 1 15, thereby forming a fluid-tight path between the two through which the liquid phase 75A of the working fluid 75 will flow. More specifically, the core tube 1 1 3 is connected to the lower and upper tube sheets 1 1 7, 1 1 8 of the working fluid headers 1 1 5, 1 1 6. The working fluid inlet 1 1 1 extends into the core tube 1 13 and introduces cool liquid phase 75A of the working fluid 75 i nto a top portion of the core tube 1 13. The core tube 1 13 is formed of a material that has a low coefficient of thermal conductivity (as compared to the material of which the heat exchange tubes 1 14 are constructed), such as steel. The core tube 1 1 3 may also comprise a thermal insulating layer, which can be an insulating shroud tube, to minimize heating of the liquid phase 75A of the working fluid 75 in the core tube 1 1 3 by the liquid 50 of the pool. Irrespective of the materials and/or construction of the core tube 1 13, the core tube 1 13 has an effective coefficient of thermal conductivity (measured from an inner surface that is contact with the working fluid 75 to an outer surface that is in contact with the liquid 50 of the pool) that is less than the effective coefficient of thermal conductivity of the heat exchange tubes 1 14 (measured from an inner surface that is contact with the working fluid 75 to an outer surface that is in contact with the liquid 50 of the pool) in certain embodiments of the invention. As discussed in detail below, this helps achieve an internal thermosiphon recirculation flow of the liquid phase 75A of the working fluid 75 within the evaporative heat exchanger 1 10 itself (indicated by the flow arrows in FIG. 2).

[0036| The plurality of heat exchange tubes 1 14 form a tube bundle that circumferentially surrounds the core tube 1 13. The plurality of heat exchange lubes 1 14 are arranged in a substantially vertical orientation. The heat exchange tubes 1 14 are constructed of a material having a high coefficient of thermal conductivity to effectively transfer thermal energy from the liquid 50 of the pool to the working fluid 75. Suitable materials include, without limitation, aluminum, copper, or materials of similar thermal conductivity. In one embodiment, the heat exchange tubes 1 14 are (Inned tubes comprising a tube portion 1 1 and a plurality of fins 1 20 extending from an outer surface of the rube portion 1 1 (shown in FIG. 6). In the exempli fied embodiment, each heat exchange tube 1 14 comprises four fins 120 extending from the tube portion 1 1 9 at points of 90 degree circumferential separation.

[0037] During operation of the autonomous self-powered system 1000, cool liquid phase 75 A of the working fluid 75 enters the evaporative heat exchanger 1 10 via the working fluid inlet 1 1 1 as discussed above. The liquid phase 75A of the working fluid 75 is considered "cool" at this time because it had been previously cooled in the condenser 50. As the cool liquid phase 75 A of the working fluid 75 enters the evaporative heat exchanger 1 10, it is introduced into the core tube 1 13. The cool liquid phase 75A of the working fluid 75 flows downward through the core tube and into the bottom header 1 15, thereby fill ing the bottom header 1 15 and flowing upward into the plurality of heat exchange tubes 1 14. As the liquid phase 75 A of the working fluid 75 flows upward in the plurality of heat exchange tubes 1 14, thermal energy from the liquid 50 of the pool that surrounds the plurality of heat exchange tubes 1 14 is conducted through the plural ity of heat exchange tubes 1 14 and into the liquid phase 75Λ of the working fluid 75, thereby heating the liquid phase 75A of the working fluid 75. The warmed liquid phase 75A of the working fluid 75 then enters the top header 1 16 where it is drawn back into the core tube 1 1 3 by a thermosiphon effect. As a result, the liquid phase 75A of the working fluid 75 is recirculated back through the aforementioned cycle until the liquid phase 75A of the working fluid 75 achieves the boiling temperature of the working fluid 75, thereby being converted into the vapor phase 75B of the working fluid 75. The vapor phase 75B of the working fluid 75 rises within the evaporative heat exchanger 1 10 and gather within a top portion of the top header 1 16 where it then exits the evaporative heat exchanger 1 1 0 via the working fluid outlet(s) 1 12. The internal design of the evaporative heat exchanger 1 10 promotes recirculation of the working fluid 1 17 and separation of the vapor phase 75B from the liquid phase 75 A in the top header 1 16 (as shown in Figure 2). |0038| As mentioned above, the evaporative heat exchanger 1 10 is pressurized to a supra- atmospheric pressure. In one embodiment, the pressure within the evaporative heat exchanger 1 10 is between 250 psia to 400 psia, with a more preferred range being between 280 psia and 320 psia, with approximately 300 psia being most preferred. Pressurization of the evaporative heat exchanger 1 10 is achieved through properly positioned valves as would be known to those of skill in the art. In one embodiment, the working fluid 75 and the pressure within the evaporative heat exchanger 1 10 are selected so that the working fluid evaporates at a temperature between 145 °F and 1 75 °F, and more preferably between 1 55 °F and 165 °F.

|0039| Referring solely now to FIG. 1 , the pressurized vapor phase 75B of the working fluid 75 exits the working fluid outlet 1 1 2 of the evaporative heat exchanger 1 10 and enters the working fluid inlet 13 1 of the turbogenerator 130. The pressurized vapor phase 75 B of the working fluid 75 produced in the evaporative heat exchanger 1 10 then serves to energize a suitably sized turbogenerator 1 30. In other words, the turbogenerator 130 converts a first portion of the thermal energy extracted from the liquid 50 of the pool (which is now in the form of kinetic energy (velocity head) and/or potential energy (pressure head) of the vapor flow) to electrical power, as would be understood by those of skill in the art. As used herein, the term "turbogenerator" includes a device and/or subsystem that includes a turbine and electrical generator either in directed or indirect connection. The term "turbogenerator" is intended to include any device and/or subsystem that can convert the pressurized vapor phase 75B of the working fluid 75 into electrical energy. As the vapor phase 75B of the working fluid 75 passes through the turbogenerator 1 30 it is partially depressurized as it exits the working fluid outlet 132 of the turbogenertaor stil l in the vapor phase 75B. At this point, the vapor phase 75B of the working fluid 75 may be at a pressure between 200 psia and 270 psia. |0040| As mentioned above, the forced flow units (which in the exemplified embodiment are the hydraulic pump 190 and the blower 151) are operably and electrically coupled to the turbogenerator 130 by the electrical circuit 130 via electrical lines 201 . All of the forced flow units are powered solely by the electrical energy generated by the turbogenerator 130 as discussed above. Moreover, in many instances, the turbogenerator 130 wil l generate surplus electrical energy. Thus, the autonomous self-powered system 1000 may further comprise a rechargeable electrical energy source 202, such as a battery, operably and electrically coupled to the turbogenerator 1 30 by the electrical circuit 200. In certain embodiments, the rechargeable electrical energy source 202 will be operably coupled to a controller so that certain valves, sensors, and other electrical components can be operated even when the turbogenerator 130 is not running.

{00411 Referring still to FIG. 1 , the partially depressurized vapor phase 75B of the working fluid 75 that exits the turbogenerator 130 enters the working fluid inlet 1 52 of the condenser 150. ' The condenser 1 50 transfers a sufficient amount of thermal energy from the partial ly depressurized vapor phase 75B of the working fluid 75 to a secondary fluid so that the depressurized vapor phase 75B of the working fluid 75 is converted back into the liquid phase 75A of the working fluid 75. The condensed liquid phase 75A of the working fluid 75 exits the condenser 1 50 via the working fluid outlet 1 53 of the condenser where it flows back into the working fluid reservoir 1 70 for recirculation through the closed-loop fluid circuit 100. In one embodiment, the condenser 1 50 is an air-cooled condenser and, thus, the secondary fluid is air that is expelled to the environment. In other embodiments, the condenser 1 50 can be any type of heat exchanger than can remove thermal energy from the partially depressurized vapor phase 75B of the working fluid 75, including without limitation, a shell and tube heat exchanger, a plate heat exchanger, a plate and shell heat exchanger, an adiabatic heat exchanger, a plate fin heat exchanger, and a pillow plate heat exchanger.

|0042| Referring to FIGS. 1 and 3 concurrently, an example of induced flow air cooled- condenser 1 50 that can be used in the system 1000 is exemplified. The induced flow air cooled-condenser 150 comprises a plurality of heat exchange tubes 1 54 (FIG. 6) positioned within an internal cavity formed by a housing 159. The working fluid 75 is the tubeside fluid and flows through the plurality of heat exchange tubes 1 54. The plurality of heat exchange tubes 1 54 are arranged in a substantially vertical orientation and are finned as discussed above with respect to the heat exchange tubes 1 14 of the evaporative heat exchanger 1 10, and as shown in FIG. 6.

[0043] The induced flow air cooled-condenser 1 50 comprises a cool air inlet 155 and a warmed air outlet 1 6. The warmed air outlet 1 56 is at a higher elevation than the cool air inlet 155. The plurality of heat exchange tubes 1 54 are located in the cavity of the housing at an elevation between the elevation of the cool air inlet 155 and an elevation of the warmed air outlet 156. As such, in addition to the air flow within the housing 159 being forced by operation of the blower 1 51 , which is located within the warmed air outlet 156, additional air flow will be achieved by the natural convective flow of the air as il is heated (i.e., the chimney effect). As warmed air exists the condenser 150 via the warmed air outlet 156, additional cool air is drawn into the cool air inlet 155. The induced flow air cooled- condenser 150, in certain embodiments, is located outside of the containment building in which the pool of liquid 50 is located.

|0044| Referring now to FIGS. 4-5B concurrently, an example of natural draft air cooled- condenser 250 that can be used in the system 1000 is exemplified. Of note, the flow of air over the heat exchanger tubes 154 (which are also vertically oriented) is accomplished solely by natural convection (i.e., the chimney effect) and, thus, the blower 151 is not required. However, in certain embodiments, the blower 1 51 can be incorporated into the natural draft air cooled-condenser 250 as desired to accommodate for situations where the ambient air may reach elevated temperatures, that could negatively affect adequate heat removal from the working fluid 75. Of further note, the natural draft air cooled-condenser 250 comprises a working fluid in let header 260 comprising a plural ity concentrically arranged toroidal tubes. Simi larly, the natural draft air cooled-condenser 250 also comprises a working fluid outlet header 261 comprising a plurality concentrically arranged toroidal tubes. The plurality of heat exchange tubes 1 4 form a tube bundle that extends from the toroidal tubes of the working fluid inlet header 260 to the toroidal tubes of the working fluid outlet header 261. |0045| As with the air-cooled condenser 150, the natural draft air cooled-condenser 250 comprises a cool air inlet 255 and a warmed air outlet 256. The warmed air outlet 256 is at a higher elevation than the cool air inlet 255. The plurality of heat exchange tubes 254 are located in the cavity of the housing 259 at an elevation between the elevation of the cool air inlet 255 and an elevation of the warmed air outlet 256.

|0046| The system 1000 of the present invention can be used to remove heat from any pool of water. In particular, it can be used to reject the decay heat from a spent fuel pool. Because the inventive system 1000 does not require any external active components such as pumps, motors, or electric actuators/controllers, it can engineered as an autonomous system that is not reliant on an external energy source to function. Thus, the inventive system 1000 is safe from an extreme environmental event such as a tsunami. It is evident that several of the systems 1000 can be deployed in a single pool of liquid i f desired.

|0047| The inventive system 1000 can be retrofit to existing plants for use both as an emergency cooling system under station blackout scenarios and as an auxiliary system to provide operational flexibility during corrective and elective maintenance (particularly during outages). The inventive system 1000 can also be incorporated into the plant design for new build projects to operate as the primary cooling system, thereby removing station blackout as a possible threat to spent fuel pool safety.

|0048| As used throughout, ranges are used as shorthand for describing each and every value that is within the range. Any value within the range can be selected as the terminus of the range. In addition, all references cited herein are hereby incorporated by referenced in their entireties. In the event of a confl ict in a definition in the present disclosure and that of a cited reference, the present disclosure controls.

|0049| While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques. It is to be understood that other embodiments may be uti lized and structural and functional modifications may be made without departing from the scope of the present invention. Thus, the spirit and scope of the invention should be construed broadly as set forth in the appended claims.