Abstract:
An apparatus that harnesses the thermal energy of spent fuel rods in nuclear power plants to power the cooling system of the nuclear power plant particularly the cooling for the spent fuel rod storage ponds and the main reactors. The apparatus is comprised of a heat exchanger unit that accumulates the thermal energy of the spent fuel rods, a heat conveyance system that conveys the thermal energy of the spent fuel rods, and a heat engine that receives its thermal energy input from the spent fuel rods and produces mechanical power that runs an electrical generator which powers the cooling system of the nuclear power plant, particularly the controls and pumps that cool the spent fuel rod storage ponds and the main reactors. The apparatus provides a redundant power source and makes the cooling system of nuclear power plants independent of externally supplied electrical power and thereby resolves a key redundancy and safety concern with nuclear power generation. The apparatus also has application to other industries.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to industrial cooling systems, and more specifically to improvements thereto for powering such systems with a redundant power source that is not subject to outage. Specifically, the present invention harnesses the thermal energy of spent fuel rods in nuclear power plants to power the spent fuel rod storage ponds and reactors. The present invention may also be used in other industries to harness the thermal energy of process waste heat to power the process cooling system. 
       BACKGROUND OF THE INVENTION 
       [0002]    Cooling is the conveyance and disposal of the waste heat generated in any process where thermal energy is converted to useful work. It is a fundamental requirement without which the process cannot be sustained. Most processes used in everyday modern life, such as in power generation, manufacturing, petrochemicals, transportation, processing, construction, etc., rely on active cooling systems that require power to operate. Power is required for the operation and control of electrical motors in pumps, fans, valves, gates, etc., to convey the coolant from the low temperature source through the heat source within the process to the heat sink. Additional power is required in re-circulating cooling systems to operate the cooling towers or refrigeration units that provide the terminal cooling for the system. 
         [0003]    Failures or disruptions in the operation of cooling systems cannot be tolerated as it results in the stoppage of the main process with adverse and undesirable consequences. Therefore, cooling systems incorporate redundancies for key components, particularly for power, to maintain continued operation in the event of component failure or power outage. Power redundancy is usually provided in the form of standby generators, batteries, or both. The aim is to make the cooling system as fail-safe as possible. 
         [0004]    Nuclear power generation is unique in that waste heat generation does not cease once the plant is shut down. Heat generation continues owing to the natural decay of the fission products in the fuel rods. This is true even when the fuel rods are considered spent and transferred from the reactors to the spent fuel rod storage ponds where they are kept for several years. The fuel rods require continuous and uninterrupted cooling both in the reactors and the spent fuel storage ponds at all times, even when the plant is shut down. In the absence of adequate cooling, the fuel rods can heat up to extremely high temperatures and cause meltdown with catastrophic consequences. 
         [0005]    Therefore, redundant power for the cooling system of nuclear power plants is critically important because failure of the cooling system can have catastrophic consequences. Normally, the nuclear power plant cooling system is connected to both the power plant and the electrical grid for primary power supply, while backup generators provide emergency power in the event of power outage in the grid. In addition, batteries are provided to backup the generators in case of temporary disruption in power supply by the generators. 
         [0006]    However, the current power redundancy arrangement for nuclear power plants has proven to be fatally inadequate. This is a fact that was tragically demonstrated by the Fukushima Daiichi nuclear power plant cooling system failure in Japan following the 9.0 magnitude Tohoku earthquake and tsunami on 11 Mar. 2011. The earthquake prompted the automatic shut down of the nuclear power plant, which cut off the main power supply to the cooling system. This in turn prompted the startup of the emergency generators to run the cooling system water pumps and the control electronics. However, the Tsunami that followed caused the entire plant to flood, including the backup emergency generators and electrical switchgear. Also, the connection to the electrical grid was broken as the Tsunami destroyed the power lines. The backup batteries were only adequate for a few hours of cooling system operation. All power for cooling was lost and reactors started to overheat and meltdown owing to the natural decay of the fission products in the fuel rods. The water in the spent fuel storage pond started to overhead and to generate hydrogen which subsequently exploded with catastrophic consequences. The accident prompted a complete revision of the integrity and safety of nuclear power worldwide. The failure has been attributed to the inability to furnish a truly redundant and fail-safe power supply source for the cooling system. 
         [0007]    Therefore, there remains an urgent need to furnish a truly a truly independent and redundant power source for cooling system in nuclear power generation plants capable of continued operation to provide adequate cooling once all external power sources are disrupted. Such as system would also have application in other industries where continuous and uninterrupted cooling is needed to assure safety and prevent material damage or degradation. 
       SUMMARY OF THE INVENTION 
       [0008]    The present invention provides an answer to the above stated need by using the thermal energy of the spent fuel rods as the main source of power for the operation of the nuclear power plant cooling system, making it an internally powered cooling system that does not require any external source of electrical power for its intended operation, and therefore cannot be disrupted by external power outages. The cooling system operation will continue without interruption for as long as there is adequate thermal energy in the spent fuel rods, which is in the order of several years after removal from the reactors and transfer to the spent fuel rod storage ponds. The invention may also be used in other industries by using the thermal energy of the process waste heat as the main source of power for the operation of the plant cooling system. For such applications the cooling system is designed to continue operation until the reduction in the waste heat due to process shut down and continued cooling reaches a level where active cooling is no longer required to ensure safety or to prevent material damage. Therefore, the present invention makes the cooling systems in both nuclear power generation and in other industries immune from external power outage. 
         [0009]    The preferred embodiment of the invention uses a heat engine, such as the Sterling Engine, Steam Engine, Steam Turbine, or similar to convert the thermal energy of the fuel rods or the process waste heat to mechanical work that could either be used to generate electricity to operate the cooling system, and/or to directly power the cooling system pumps. The heat engine receives its thermal energy input from the spent fuel rods or process waste heat source(s) via appropriately designed heat exchange and heat transfer/conveyance systems. The invention may either be configured as a self contained packaged units installed in one location, or as separate components installed at various locations within the plant. 
         [0010]    The difference between the present invention and previous inventions that also work by recovery and conversion of process thermal energy and waste heat is the object of the present invention, which is to use the recovered thermal energy for powering the cooling system of the process itself i.e. to realize power redundancy for the process cooling system. This is fundamentally different from the recovery and conversion of process waste heat to improve process efficiency, for which there is ample precedence. The fact that the present invention uses the process waste heat for thermal energy input means that it also improves process efficiency, but that is not an object of this invention. 
         [0011]    It is an object of the invention to provide a redundant power source for the cooling system of nuclear power plants by apparatus described so as to make the cooling system independent of externally supplied electrical power. 
         [0012]    It is an object of the invention to provide a redundant power source for the cooling system of other industries in power generation, manufacturing, petrochemicals, transportation, processing, construction, etc., by apparatus described as to make the cooling system of those industries independent of externally supplied electrical power. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  is a schematic diagram of one embodiment of the invention in nuclear power generation application using conduction for heat transfer between the spent fuel rods and the heat engine. 
           [0014]      FIG. 2  is a schematic diagram of one embodiment of the invention in nuclear power generation application using a liquid medium in piping for heat transfer between the spent fuel rods and the heat engine. 
           [0015]      FIG. 3  is a schematic diagram of one embodiment of the invention in nuclear power generation application using steam for converting the thermal energy of the spent fuel rods to electricity. 
           [0016]      FIG. 4  is a schematic diagram of one embodiment of the invention in nuclear power generation application using submersible pumps for cooling the spent fuel pond. 
           [0017]      FIG. 5  is a schematic diagram of one embodiment of the invention in nuclear power generation application using submersible electrical generation units inside the spent fuel pond. 
           [0018]      FIG. 6  is a schematic diagram of one embodiment of the invention in other industries application using the process waste heat to generate electricity for the cooling system. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]    Referring first to  FIG. 1 , there is shown an apparatus  100  that harnesses the thermal energy  120  of the spent fuel rod  114  to power the nuclear power plant cooling system  140 , according to one embodiment of the invention. Heat exchanger unit  115  is accumulates the thermal energy  120  of the spent fuel rods  114  held by support  113  inside the spent fuel rod storage pond  111  by controlled shielding of the spent fuel rods  114  from the surrounding cooling water  112  so as to achieve a pre-determined elevated temperature inside the heat exchanger  115 . Internal element  116  transfers the thermal energy  120  to heat conductors  117  which convey it to the electrical power generation unit  131  by heat conduction. The latter consists of a heat engine such as a Sterling Engine  133 , which receives the thermal energy  120  via element  132  and converts it to mechanical energy that drives the electrical generator  135  via transmission system  134 . Electricity generated by unit  131  is transmitted via electrical cables  136  to power all controls and pumps associated with the nuclear power plant cooling system  140 , which is shown as a once-through system in this embodiment. Pump  142  supplies cold water from open water body  141  via cold water pipe  143  to spent fuel pond  111 , while pump  145  returns the hot water from the spent fuel pond  111  via hot water pipe  144  back to the open water body. Although not shown, the electricity generated could equally be used to power a re-circulating cooling system that uses cooling towers in lieu of the once through system  140  shown. The apparatus  100  is preferably sized in sufficient numbers and equipment capacity to provide adequate electrical power for the cooling system  140  such that there is no need for any externally supplied electrical power for normal operation. Alternatively, the apparatus  100  may be sized to only provide sufficient power for emergency level cooling to prevent excessive overheating of the spent fuel storage ponds during external power outage. 
         [0020]      FIG. 2  is another embodiment of the invention showing an apparatus  200  that is almost identical in its principal of operation to apparatus  100  shown in  FIG. 1 , but uses liquid communication for thermal energy transfer instead of conduction. The heat exchanger unit  215  accumulates the thermal energy  220  of the spent fuel rods  214  held by support  213  inside the spent fuel rod storage pond  211  by controlled shielding of the spent fuel rods  214  from the surrounding cooling water  212  so as to achieve a pre-determined elevated temperature inside the heat exchanger  215 . Plate or tube heat exchangers  216  and  232  are connected by conveyance piping  218  and recirculation pump  217  to convey the thermal energy  220  to the electrical power generation unit  231 . The latter consists of a heat engine such as a Sterling Engine  233  that converts the thermal energy  220  to mechanical energy that drives the electrical generator  235  via transmission system  234 . Electricity generated by unit  231  is transmitted via electrical cables  236  to power all controls and pumps associated with the nuclear power plant cooling system  240 , which is shown as a once-through system in this embodiment. Pump  242  supplies cold water from open water body  241  via cold water pipe  243  to spent fuel pond  211 , while pump  245  returns the hot water from the spent fuel pond  211  via hot water pipe  244  back to the open water body. Although not shown, the electricity generated could equally be used to power a re-circulating cooling system that uses cooling towers in lieu of the once through system  240  shown. As with apparatus  100  shown in  FIG. 1 , apparatus  200  is preferably sized in sufficient numbers and equipment capacity to provide adequate electrical power for the normal operation of cooling system  240  without the need for any externally supplied electrical power. Alternatively, apparatus  200  may be sized to only provide sufficient power for emergency level cooling to prevent excessive overheating of the spent fuel storage ponds during external power outage. Given that pump  217  must operate before generator  235  can start operation, pump  217  must be connected to a source such as a battery unit that enables the operation of the pump without the generator  235  being in operation but maintains its charge by connecting to generator  235  via electrical cables  236 . 
         [0021]      FIG. 3  is another embodiment of the invention showing an apparatus  300  that is similar in its principal of operation to apparatus  100  shown in  FIG. 1 , but uses steam for conversion of thermal energy to mechanical work. The steam generator unit  315  encapsulates the spent fuel rods  314  held by support  313  inside the spent fuel rod storage pond  311 , either in part or in their entirety so as to achieve and maintain a pre-determined temperature and pressure inside the steam generator unit  315 . Although not shown, a separate and dedicated facility from the spent fuel rod storage pond may be used for the steam generator  315  in lieu of housing it inside the spent fuel pond. Alternatively, heat transfer arrangements shown in  FIGS. 1 and 2  could be used to convey the heat to the steam generator outside the spent fuel pond instead of the steam generator encapsulating the spent fuel rods inside the pond. Piping  321  conveys the steam  320  to condensing steam turbine unit  330 . Steam turbine  331  produces mechanical energy to drive the electrical generator  333  via transmission system  332 . Condensate  335  is pumped by pump  323  and returned to steam generator  315  via piping  322 . Cooling for the condensing steam turbine may be provided by cooling system  350  comprised of cooling tower  351 , fans  352 , basin  353 , piping  354 , and recirculating pump  355 . Although not shown, a non-condensing steam turbine could also be used in addition to a condensing steam turbine if that achieves better heat conversion efficiency or has other advantages. Also, cooling for the condensing steam turbine may alternatively be provided by the nuclear power plant once through system  340  instead of a separate system  350 . Electricity generated by unit  333  is transmitted via electrical cables  334  to power all controls and pumps associated with the nuclear power plant cooling systems  340  and  350 , which are shown as once-through and recirculating systems respectively in this embodiment, but may be any combination and type of viable cooling systems. Pump  342  supplies cold water from open water body  341  via cold water pipe  343  to spent fuel pond  311 , while pump  345  returns the hot water from the spent fuel pond  311  via hot water pipe  344  back to the open water body. Although not shown, the electricity generated could equally be used to power a re-circulating cooling system that uses cooling towers in lieu of the once through system  340  shown. As with apparatus  100  shown in  FIG. 1 , apparatus  300  is preferably sized in sufficient numbers and equipment capacity to provide adequate electrical power for the normal operation of cooling systems  340  and  350  without the need for any externally supplied electrical power. Alternatively, apparatus  300  may be sized to only provide sufficient power for emergency level cooling to prevent excessive overheating of the spent fuel storage ponds during external power outage. Given that pumps  323  and  355  must operate before generator  333  can start operation, they must be connected a source such as a battery unit that enables the operation of the these pumps without the generator  333  in operation but maintains its charge by connecting to generator  333  via electrical cables  334 . 
         [0022]      FIG. 4  is another embodiment of the invention showing an apparatus  400  that harnesses the thermal energy of the spent fuel rods to directly power a submersible pump to recirculate the water in the spent fuel rod pond of a nuclear power plant. Heat exchanger unit  415  accumulates the thermal energy  420  of the spent fuel rods  414  held by support  413  inside the spent fuel rod storage pond  411  by controlled shielding of the spent fuel rods  414  from the surrounding cooling water  412  so as to achieve a pre-determined elevated temperature inside the heat exchanger  415 . Internal element  423  transfers the thermal energy  420  to heat engine  422 , which converts it to mechanical energy that directly drives the submersible pump  431  via transmission  424 . Pump  431  pumps the spent fuel rod pond water  412  to cooling system  450 , which is comprised of piping  451 , natural draft cooling tower  451 , basin  453 , and gravity return piping  454 . The embodiment of the invention shown in  FIG. 4  does not require electricity to operate the cooling system pumps, while the use of natural draft cooling tower  452  means that no electricity is required to achieve cooling at the cooling tower. Also, the cold water basin  453  of the cooling tower is located at an elevation above the elevation of the spent fuel rod storage pond water level  412 , such that cold water returns to the storage pond by gravity. However, electricity is still required for the cooling system control electronics and may be required for the supply of makeup water to the cooling tower. Although not shown, the electricity required could be provided by incorporating an electrical generator within apparatus  400  to drive off of the transmission system  424 , or it could be independently generated by an appropriately sized apparatus shown in  FIG. 1 , or by other independent means such as solar power. 
         [0023]      FIG. 5  is another embodiment of the invention showing an apparatus  500  that harnesses the thermal energy of the spent fuel rods to power a submersible electricity generating unit(s) which provides the electricity for the nuclear power plant cooling system. Heat exchanger unit  515  accumulates the thermal energy  520  of the spent fuel rods  514  held by support  513  inside the spent fuel rod storage pond  511  by controlled shielding of the spent fuel rods  514  from the surrounding cooling water  512  so as to achieve a pre-determined elevated temperature inside the heat exchanger  515 . Internal element  516  transfers the thermal energy  4520  to heat engine  532  which converts it to mechanical energy that drives the electrical power generation unit  535  via transmission system  534 . Electricity generated by unit  531  is transmitted via electrical cables  536  to power all controls and pumps associated with the nuclear power plant cooling system  540 , which is shown as a once-through system in this embodiment. Pump  542  supplies cold water from open water body  541  via cold water pipe  543  to spent fuel pond  511 , while pump  545  returns the hot water from the spent fuel pond  511  via hot water pipe  544  back to the open water body  541 . Although not shown, the electricity generated could equally be used to power a re-circulating cooling system that uses cooling towers in lieu of the once through system  540  shown. The apparatus  500  is preferably sized in sufficient numbers and equipment capacity to provide adequate electrical power for the cooling system  540  such that there is no need for any externally supplied electrical power for normal operation. Alternatively, the apparatus  500  may be sized to only provide sufficient power for emergency level cooling to prevent excessive overheating of the spent fuel storage ponds during external power outage. 
         [0024]      FIG. 6  is another embodiment of the invention showing an apparatus  600  that harnesses the process waste heat  650  in industries such as power generation, manufacturing, petrochemicals, transportation, processing, construction, etc., to generate electricity to power the process cooling system. Cooling pump  614  circulates coolant through process  651  to collect and convey waste heat  650  from within process  651  via high-temperature piping  611 , heat exchanger  613 , and low temperature piping  612 . Part of the waste heat  650  is harnessed upstream of the cooling system heat exchangers  631  at single or multiple locations as necessary by heat exchanger  621 . Internal element  622  transfers the harnessed waste heat  620  to heat engine  632 , which converts it to mechanical energy that drives the electrical power generation unit  633  via transmission system  635 . Electricity generated is transmitted via electrical cables  634  to power all controls and pumps of cooling system  640 , which is shown as a once-through system in this embodiment, as well as pump(s)  614  and its controls. Pump  642  pumps cold water from open water body  641  via cold water pipe  643  to heat exchanger  613 , and returns the hot water from the heat exchanger  613  via hot water pipe  644  back to the open water body  641 . Although not shown, the electricity generated could equally be used to power a re-circulating cooling system that uses cooling towers in lieu of the once through system  640 . The apparatus  600  is preferably sized in sufficient numbers and equipment capacity to provide adequate electrical power for the cooling system  640  such that there is no need for any externally supplied electrical power for normal operation. Alternatively, the apparatus  600  may be sized to only provide sufficient power for emergency level cooling to prevent excessive overheating of the spent fuel storage ponds during external power outage. Given that pump  614  must operate before generator  633  can start operation, pump  614  must be connected to a source such as a battery unit that enables the operation of the pump without the generator  634  being in operation but maintains its charge by connecting to generator  634  via electrical cables  634 . 
         [0025]    The present invention is susceptible to modifications and variations which may be introduced thereto without departing from the inventive concepts and the object of the invention. Mechanisms other than heat conduction, liquid communication, and steam may be used for heat transfer, and other types of heat engines may be employed to convert the waste heat energy to suitable forms that may be used in a variety of configurations to power the cooling system. For example, the waste heat may be directly used to power an adsorption cooling system to furnish part or all of the process cooling needed to accomplish redundancy. Such modifications and variations are within the invention concepts. 
         [0026]    Although presented in terms of cooling systems in nuclear power plant generation and in other industries, the present invention is obviously adaptable to other situations where process waste heat may be used to power the cooling system of the process. For example, the waste heat generated at an electronic component may be used to drive a local cooling system for that component, or the exhaust heat from an engine could be used to power a cooling system for the engine and/or the exhaust. The essence of the present invention is the harnessing of the heat generated by or in a given process for the cooling of the process and/or removal of the heat. 
         [0027]    While the present invention has been described in connection with what is considered the most practical and preferred embodiment, it is to be understood that the present invention is not to be limited to the disclosed arrangements, but is intended to cover various arrangements which are included within the spirit and scope of the broadest possible interpretation of the appended claims so as to encompass all modifications and equivalent arrangements which are possible.