Abstract:
A reactor cooling system for cooling a nuclear reactor using nitrogen comprising a refrigeration unit for cooling and compressing nitrogen gas into liquid nitrogen, a liquids storage tank to store liquid nitrogen, the tank in fluid communication with the refrigeration unit, a heat exchanger drop system in fluid communication with the liquids storage tank, adjacent to the nuclear reactor, wherein the nitrogen absorbs heat by becoming gaseous, a tank for receiving and holding nitrogen gas in fluid communication with the heat exchanger and in fluid communication with the refrigeration unit, and where the system is a closed-loop drop system.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a continuation-in-part of U.S. Nonprovisional patent application Ser. No. 13/694,431 filed on Dec. 3, 2012, entitled “Liquid Nitrogen Emergency Cooling System for Nuclear Plants”, which claims benefit of U.S. Provisional Patent Application No. 61/630,321 filed on Dec. 9, 2011, entitled “Liquid Nitrogen Emergency Cooling System for Nuclear Power Plants”, the entire disclosures of which are incorporated by reference herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to a reactor cooling system for cooling a nuclear reactor using nitrogen in a closed-loop system. 
       BACKGROUND 
       [0003]    Current emergency cooling systems rely heavily on a mass storage of water, and a comparatively small temperature difference for cooling. Further, current systems are large scale and massive in size, and rely on generated power, gravity feed and/or pressurized systems and manual activation of several components to secure the shutdown of a nuclear plant in the event of natural disaster, damage or attack, etc. 
         [0004]    Therefore, there is a need for emergency cooling system that can be activated automatically, and passively, to immediately, by means of the application of liquid Nitrogen in a closed loop system, cool overheated equipment to a safe working temperature. Further, there is a need for an emergency cooling system that eliminates the production of Hydrogen or other hazardous gases caused by the overheating of equipment, and the subsequent danger of explosion, by using liquid Nitrogen in a closed loop system. Further, there is also a need for a system that provides for a differential of over a greater range from coolant to “boil off” temperatures, providing a more efficiency in cooling, while producing no explosive gasses (such as hydrogen, etc.) which can be produced by current cooling systems. 
       SUMMARY OF THE INVENTION 
       [0005]    In the present invention a reactor cooling system for cooling a nuclear reactor using nitrogen is presented comprising a refrigeration unit for cooling and compressing nitrogen gas into liquid nitrogen, a liquids storage tank to store liquid nitrogen, the tank in fluid communication with the refrigeration unit, a heat exchanger drop system in fluid communication with the liquids storage tank, adjacent to the nuclear reactor, wherein the nitrogen absorbs heat by becoming gaseous, a tank for receiving and holding nitrogen gas in fluid communication with the heat exchanger and in fluid communication with the refrigeration unit; and wherein the system is a closed-loop system. 
         [0006]    In an embodiment of the invention, the system includes a gas-powered generating unit, for generating electricity from the nitrogen gas as it expands. 
         [0007]    In another embodiment, the system further includes a hydraulic system for using the power of the expanding gas from an outlet of the heat exchanger drop. In this embodiment, the hydraulic system can either be used to restart the nuclear power plant or to provide hydraulic power. Moreover, the hydraulic system opens and shuts valves as needed for the safe continued operation of under normal circumstances, in the event of a near failure, and for emergency shut down. 
         [0008]    In yet another embodiment, the system can include an overpressure relief valve system for bypassing the refrigeration unit. 
         [0009]    In yet another embodiment, the system can include a relief valve to relieve excess pressure in the system. In an embodiment, the relief valve may be evacuated to an expansion tank. 
         [0010]    The foregoing, and other features and advantages of the invention, will be apparent from the following, more particular description of the preferred embodiments of the invention, the accompanying drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    For a more complete understanding of the present invention, the objects and advantages thereof, reference is now made to the ensuing descriptions taken in connection with the accompanying drawings briefly described as follows. 
           [0012]      FIG. 1  shows the operation of the Liquid Nitrogen Emergency Cooling System for Nuclear Power Plants, according to an embodiment of the present invention; 
           [0013]      FIG. 2A  shows the emergency drop system for the system&#39;s heat exchanger, according to an embodiment of the present invention; 
           [0014]      FIG. 2B  shows the emergency drop system for the system&#39;s heat exchanger, according to an embodiment of the present invention; 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0015]    In its current form, the system will utilize current “waste energy” and/or engineered energy, produced by an electrical generation plant to continuously collect, condense, cool, store and recycle nitrogen gas (N 2 ) from the atmosphere for use in the system. The waste energy is that energy which is normally produced as a stand-by amount, and which must be continually produced “in case” a demand is placed on the power grid. This is an unavoidable energy, which represents drag, and therefore loss, on the generation system, without being used for practical purposes. 
         [0016]    The N 2  is extracted from the atmosphere by a separation system, which is already widely available. The N 2  is compressed to pressure, and cooled to liquid, and then stored in liquid form for use in the system, which is passively activated. Part of the N 2  is continuously cycled to produce electricity for on-site usage, and to recharge an electrical storage unit. This N 2  is recovered in a closed system. 
         [0017]    Once activated, the liquid N 2  that is stored is applied to cool overheated equipment, and is recovered in an “operating pressure” safety system, which is more efficient than current systems which merely exhaust the containment heat by water cooling through heat exchange. Operating pressure, is a low pressure system used to recycle the N 2  back to the liquefaction unit to be reused in the system. 
         [0018]    N 2  is a natural component of the atmosphere, comprising approximately 80% of the air, non-reactive and is non-explosive. The N 2  will, upon expansion be held in a closed low, medium or high-pressure system. Even if that closed system were to be breached, the N 2  would be released at atmospheric pressure with no pollution generated. 
         [0019]    Finally, N 2  is safe to use in the system, and even if exposed to nuclear material, it has no long-lasting residual effects, and does not pose any significant danger to people, soil, air, animals or plants. There are no long-lasing radioactive isotopes which would result in contamination or pose health risks. Natural Nitrogen (N) consists of two stable isotopes, 14N, which makes up the vast majority of naturally occurring nitrogen, and 15N. Fourteen radioactive isotopes have also been identified, with atomic masses ranging from 10N to 25N, and 1 nuclear isomer, 11 mN. All are short-lived, the longest-lived being 13N with a half-life of 9.965 minutes. All others have half-lives under 7.15 seconds, with most under five-eighths of a second. Most of the isotopes with mass below 14 decay to isotopes of carbon, while most of the isotopes with mass above 15 decay to isotopes of oxygen. The shortest-lived isotope is 10N, with a half-life of 2.3 MeV. (Source available.) 
         [0020]      FIG. 1  shows the operation of the Liquid Nitrogen Emergency Cooling System for Nuclear Power Plants, designated generally as  100 , according to an embodiment of the present invention. 
         [0021]    Atmospheric nitrogen (N 2 ), which exists naturally as a diatomic molecule (i.e., a 2 atom molecule) in a gaseous state, is filtered from the atmosphere, compressed and cooled to a liquid state using readily available equipment, for example the cooler compressor refrigeration unit  118 . 
         [0022]    The liquefied gas is delivered to the liquid N 2  storage tank  102 . Storage tank  102  operates as a buffer or bellows, storing a sufficient amount of liquid nitrogen to provide cooling when necessary. 
         [0023]    Under non-emergency operation conditions, the liquid nitrogen continuously expands within the storage tank  102  and is diverted by means of a liquid N 2  boil-off overpressure line  122 , which is fitted with an overpressure relief valve system  124 , to a N 2  gas powered generating unit  110 , which generates electrical and/or hydraulic power, which is used to power a cooling, compressor, refrigeration unit  118 , making the closed-loop operation efficient. 
         [0024]    Under non-emergency operation conditions, the “spent” gaseous N 2 , from N 2  gas powered generating unit  110  is cycled back to cooling, compressor, refrigeration unit  118 , through a loop including a accumulator tank for N 2  gas  116 , which increases efficiency by reducing the amount of atmospheric filtering required by cooling, compressor, refrigeration unit  118  to deliver liquid nitrogen (N 2 ) to liquid N 2  storage tank  102 . In addition, the N 2  can be used to decontaminate equipment on site without removal of said equipment. 
         [0025]    Under non-emergency operation conditions, N 2  gas powered generating unit  110  also supplies electrical energy to an electrical energy storage system  114  for use during emergency operation conditions. 
         [0026]    In an embodiment, under non-emergency operation conditions, N 2  gas powered generating unit  110  also supplies electrical energy to a hydraulic system  112  for use during emergency operation conditions (e.g., to operate valves, and other equipment independently of electrical mechanisms). This assists to keep hydraulic psi of the N 2  at a workable state when at rest. 
         [0027]    Under emergency operation conditions, an activation mechanism  120  operates in a “fail-safe” manner, automatically applying liquid nitrogen to a heat exchanger-drop system  106 . When the heat in the reactor rises above a pre-determined threshold, the nitrogen cooling system is descended into the reactor by the drop system. 
         [0028]    With further reference to  FIGS. 2A and 2B , under emergency operation conditions, an emergency drop system  105  is triggered to bring heat exchanger  106  into proper position to cause cooling of the nuclear power plant. The drop system operates with one or more nested sections of piping  104  on either side of the heat exchanger  106 . As the heat exchanger  106  lowers, the piping  104  expands such that the lip  103  of the inner pipe catches against the narrowing  103   b  of the outer pipe. This may be extended to several pipes  104  in a telescopic fashion, and O-rings or gaskets are present wherever the pipes  104  extend and the lips  103   a  meet the narrowing  103   b,  to seal the joints. The piping is held in place by mounts  109  connected to the structure by heat activated fusible links  107  or by other, computer-controlled mechanisms that operate by excessive heat. Once the heat fusible links  107  heat up enough to collapse and release the piping  104 , the piping  104  extends downwardly to lower the heat exchanger  106  into the reactor. In an alternative embodiment, the heat causes the N 2  to boil and differential pressure causes a burst disc (rupture disc)  108  to open, pushing the drop system and pipe  104  rapidly downward to minimize loss of the N 2  through the pipe junctions. The burst disc  108  is designed to burst at a precise differential pressure to release N 2  as required to achieve cooling as needed, depending on the size of the system. The piping seals once the system has dropped into the reactor and prevents the escape of N 2  gas. In an embodiment, the dropped heat exchanger  106  is held in place by a locking mechanism  111  having a counterweight holding the dropped pipe in place, with facility to raise the heat exchanger  106  when it is no longer needed. 
         [0029]    In order to reduce pipe hammer from liquefied N 2  in the pipes, the pipes may contain a heat exchanger which enables the N 2  to be converted into a gaseous form, reducing pipe hammer. Alternatively, the pipes may be made thicker and stronger to withstand pipe hammer. 
         [0030]    Liquid nitrogen from liquid N 2  storage tank  102  flows through heat exchanger-drop system  106  and removes heat by becoming gaseous. The expanded, gaseous nitrogen from exhaust of N 2  gas  108 , which acts as a receiver for gaseous N 2 , is delivered to the N 2  gas powered generating unit  110  to supply both electrical and hydraulic power. 
         [0031]    In an embodiment, stored power, held in hydraulic system  112  and electrical energy storage system  114  is used to restart the nuclear power plant. 
         [0032]    During emergency operation conditions, the “spent” gaseous N 2 , from N 2  gas powered generating unit  110  is cycled back to cooling, compressor, refrigeration unit  118 , through a loop including accumulator tank for N 2  gas  116 , which allows system  100  to be recharged in real time for continuous operation in cooling the nuclear power plant. The condensers may in effect be used as a battery pack. 
         [0033]    Under all conditions, in the event of overpressure of system  100 , nitrogen gas is released into the atmosphere by means of overpressure relief valve system  124  after it is vented to an evacuated expansion tank. 
         [0034]    System  100  is efficient, affordable and readily available to retrofit to existing nuclear power generation plants, and can be incorporated into new facilities. System  100  is needed to accomplish the automatic operation and safe application of liquid N 2  coolant, extraction and storage of liquid N 2  for use as coolant, and the recapture system for the N 2 , and the reduction of radiation danger potential. 
         [0035]    Regarding applications, in addition to large-scale nuclear generation units, system  100  can be applied to other systems, for example: (1) Small-scale applications for nuclear generation units—further research will be needed to determine how the system can best be adapted for use in small-scale nuclear generators; (2) Small-scale application for portable nuclear generation units—further research will be conducted to determine how the system can best be adapted for use in small-scale nuclear generators on board aircraft, shipping, spacecraft, rural and residential applications; and (3) heavy and light manufacturing process power supply configurations—further research will be conducted to determine how the system can best be adapted for use in small-scale, medium-scale and large-scale applications suited for power-grid-independent nuclear generators, which can operate in as stand-alone configuration for such operations. With all of these applications in mind, system  100  achieves the basic goal of providing safety for emergency shut down and cooling of power generation plants.