Abstract:
An improved nuclear fission reactor of the liquid metal cooled type including a core configuration allowing for only two operational states, “On” or “Off”, therefore bi-stable. The flow of the primary cooling fluid suspends the core in the “On” state, with sufficient flow to remove the heat to an intermediate heat exchanger during normal operation. This invention utilizes the force of gravity to shut down the reactor after any loss of coolant flow, either a controlled reactor shut down or a “LOCA” event, as the core is controlled via dispersion of fuel elements. Electromagnetic pumps incorporating automatic safety electrical cut-offs are employed to shutdown the primary cooling system to disassemble the core to the “Off” configuration in a situation of a loss of secondary coolant. This design is a hybrid pool-loop unpressurized reactor unique in its use of a minimum number of components, utilizing no moving mechanical parts, no seals, optimized piping, and no control rods, defining an elegantly simple intrinsically safe nuclear reactor.

Description:
[0001]    This application claims benefit of Provisional Patent Application No. 61/319,608 filed on Mar. 31, 2010. 
     
    
     FEDERALLY SPONSORED RESEARCH 
       [0002]    Not Applicable 
       SEQUENCE LISTING OR PROGRAM 
       [0003]    Not Applicable 
         [0004]    Current U.S. Class: 376/381; 376/221; 376/339 
         [0005]    Current International Class: G21C 19/28 (20060101) 
         [0006]    Field of Search: 376/327, 381, 382, 383, 419, 447, 458, 355, 220, 221, 219 
       BACKGROUND 
       [0007]    1. Technical Field 
         [0008]    This invention relates to nuclear fission reactors in general and more specifically to nuclear fission reactors of the liquid metal cooled type. 
         [0009]    2. Description of Prior Art 
       References 
       [0010]      
         [0000]    
       
         
               
             
               
               
               
             
           
               
                   
               
               
                 U.S. Patent Documents 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 2,798,847 
                 July 1957 
                 Fermi et al. 
               
               
                 3,046,212 
                 July 1962 
                 Anderson 
               
               
                 4,293,380 
                 October 1981 
                 Robbins 
               
               
                 5,202,085 
                 April 1993 
                 Aoyama et al. 
               
               
                 7,403,585 
                 Jul. 1, 2004 
                 Ougouag, et al. 
               
               
                 7,139,352 
                 Nov. 21, 2006 
                 Nishiguchi, et al. 
               
               
                   
               
             
          
         
       
     
         [0011]    Intrinsically safe nuclear fission reactors differ from conventional nuclear fission reactors in that the design is more elegantly simple, affording ease of operation, eliminating the refueling cycle and attendant removal and transport of fuel, and elimination the potential for nuclear proliferation by the misappropriation of nuclear materials. 
         [0012]    Conventional reactor designs include many additional components required to control the reactor; control rods, proportional energy conversion components coupled to the output level of the reactor, and controlled to the demand for electrical energy. Quoting the directors of ten national laboratories in the paper,  A Sustainable Energy Future: The Essential Role of Nuclear Energy , published in August of 2008, “a myriad of pumps and valves, miles of piping and wiring . . . ”, conventional reactors are subject to many critical points of failures of both equipment and human errors. 
         [0013]    Even proposed pebble bed reactors comprise a core formed by spherically shaped fuel elements or pebbles. The pebbles comprising the core are typically contained in a graphite reflector. A coolant, typically gaseous Helium, flows through the pebble core and the graphite reflector. The coolant, a leak prone gas, is not very efficient in heat transfer, and current reactor designs utilizing graphite pebbles are envisioned in un-domed above ground buildings. In the event of an introduction of air to the bed, a catastrophic fire may occur. These commercial designs may not be better or safer than the current generation II or III reactors, and are prone with similar complicated, numerous control and operational issues as are current conventional nuclear power reactors. 
         [0014]    The current design embodiment described herein of an intrinsically safe nuclear reactor utilizes spherical fuel elements, yet they are never removed from the reactor, and with no moving parts, no seals to be compromised, multiple electromagnetic primary cooling pumps, and gravity assured safe automatic shutdown operation for any foreseeable loss of coolant conditions. These metallic clad fuel spheres can be designed to operate for many dozens of years and the spent fuel remains in the reactor vessel at the end of the reactor useful life. 
         [0015]    Additionally since this intrinsically safe reactor design has a minimal number of components or parts, analysis, critical design review, licensing, certification, manufacture, and operations are inherently simpler and rigorous review is best focused on safety, reliability, and non-technical factors to meet the national energy needs. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is made in view of the aforesaid problems in the related art. 
         [0017]    An improved nuclear fission reactor of the liquid metal cooled type according to one embodiment of the present invention comprising a system of simple components to support the “core”, transfer the heat of nuclear fission via an intermediate heat exchanger, while utilizing no moving parts, nor mechanical seals, by the principle of electromagnetic pumping, and utilizing the constant ever-present force of gravity to assure safe shutdown. 
         [0018]    A device for the conversion of nuclear energy to high value, high temperature heat, by an intrinsically safe means utilizing a novel collection of components. 
         [0019]    This invention utilizes a hybrid pool-loop design to minimize the piping required, minimizing the plumbing components and simplifying design to achieve a minimal number of components therefore facilitating design, construction, and operations. The advantages of a large pool of primary coolant mitigate thermal transients and inter-pool leakage. 
         [0020]    A novel means of initiating and controlling the nuclear reaction without the use of control rods, deploying the fuel spheres, (the “core”) to start the reaction without employing any moving parts, creating an operation with two steady states; “On” or “Off”, therefore creating a bi-stable reactor, either full power output or no power output and cooling down to “Off” state with minimum residual decay heat output, therefore, control is simplified. 
         [0021]    By its design an intrinsically safe nuclear reactor is automatically self-deactivating in the case of loss of coolant incidents, or accidents, as the “core” is supported by the upward flow of the primary coolant. Thus if sufficient flow ceases, the “core” is turned to “Off”. 
         [0022]    The fuel source of an intrinsically safe nuclear reactor comprises a collection of spherical elements or “Fuel Spheres,” each of which may be approximately the size of a tennis ball or golf ball. These fuel spheres are more dense than the liquid coolant, thus causing them to sink in the absence of upward coolant fluid flow. Each metallic sphere comprises of a plurality of much smaller fuel particles or kernels dispersed in a metallic matrix within the hollow spherical shell. These hollow spheres are wetted with NaK so as to provide good thermal conductivity from the inside of the shell to the formed fuel element. The fuel comprises a fissionable material that may include any of the known fissionable isotopes, such as, but not limited to, U-235, U-233, or Pu-239, or may also contain fertile isotopes, such as, for example, U-238 or Th-232, that convert to fissile materials upon residence in an operating reactor core. Additionally a small quantity of a burnable poison e.g. Gadolinium may be incorporated in the fuel spheres to control the rate of the reaction. 
         [0023]    The nuclear fuel remains in the reactor vessel for the life of the system, and when decommissioned are abandoned in place in the reactor vessel and may never need to be transported or removed from the vessel. 
         [0024]    By providing the reactor with a moderator-to-fuel ratio that is optimally moderated for the asymptotic equilibrium state of the reactor at start-up; allowing the nuclear fission reactor to be continuously operated in an optimally moderated long term state. The reactor essentially operates with an isobreeder ratio. 
         [0025]    Deep subterranean installation of the reactor primary containment vessel will minimize the exposure to accidental natural and or intentional terrorist events. 
         [0026]    Also disclosed are a plurality of seismically stabilized supports which isolate the primary containment vessel inside of a larger secondary containment structure. 
         [0027]    Also disclosed is a method for incorporating an intrinsically safe nuclear fission reactor in a pumped storage system that comprises: (a) specifying an initial reactor design with a pumping unit and desalination unit; (b) specifying an energy storage reservoir and (c) a hydro-electric plant, thus creating a “Hybrid Nuclear Power System” (see System Flow Chart,  FIG. 4 ) 
         [0028]    Combinations of multiple intrinsically safe nuclear reactors, pumping units, and conventional hydro-electric power stations all utilizing a common large energy storage reservoir, comprise a “Hybrid Nuclear Power System” is also disclosed and claimed. 
         [0029]    In summary, this novel elegantly simple bi-stable reactor design can be characterized as “Inherently Safe” because of the utilization of the dependable gravitational forces to cause the safe shutdown of the core for all unforeseen events. Such events may result with a loss of coolant accident “LOCA”, leakage, rupture, or accidental total loss of power to the electromagnetic (EM) pumps, that will shut the system “Off” (see  FIG. 5 ). Even the loss of secondary cooling, will cause the EM pump thermal-electric breakers to open the circuits to shut off power and thus cease to support the core. 
         [0030]    The pool-loop configuration provides a very large mass of coolant with which to mitigate the thermal transients in the event of a total stoppage of pumping forces. Inertia and convection will provide initial coolant flow to remove the early heat of decay and a steady state low flow of coolant will even dissipate longer term heat of decay by the natural thermal convection, inherent in such a design configuration. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]    Illustrative and presently preferred embodiments of the invention are shown in the accompanying drawings in which: 
           [0032]      FIG. 1  is a sectional view of a representation the components of an intrinsically safe nuclear fission reactor according to one embodiment of the present invention; 
           [0033]      FIG. 2A  is a sectional view of a reactor core chamber of said reactor showing the “On” state, coolant supported “core” by primary coolant; 
           [0034]      FIG. 2B  is a sectional view of a reactor core chamber of said reactor showing the “Off” state, no flow or minimal flow to remove heat of decay, of primary coolant; 
           [0035]      FIG. 3  is a sectional view of a design of an electromagnetic pump for the primary coolant according to one embodiment of the present invention; 
           [0036]      FIG. 4  is a diagram of the components, one of which is the intrinsically safe reactor, in relation to other major components utilized to generate electricity, desalinate seawater, or provide district heat, in a “Hybrid Nuclear Power System”, according to the teachings of the present invention. 
           [0037]      FIG. 5  is a state diagram of the core due to any “LOCA” event. 
       
    
    
     REFERENCE NUMERALS USED IN DRAWINGS 
       [0000]    
       
         
           
             A Electromagnetic Pumps 
             B Intermediate Heat Exchanger (IHX) 
             C Core Assembly 
               1  Core (Fuel Spheres) 
               2  Upper Chamber 
               3  Primary Reactor Containment Vessel 
               4  Lower Chamber 
               5  Outlet Screen 
               6  Inlet Screen 
               7  Pool Separation Bulkhead 
               8  Neutron Reflector 
               9  Outer Neutron Absorber 
               10  Inner Neutron Absorber 
               11  Seismic Supports 
               12  Electromagnetic Pump Coils 
               13  Secondary Containment Structure 
               14  Electromagnetic Pump Stators 
               15  Cool Pool 
               16  Pump Inlet Pipe 
               17  Primary Coolant Level 
               18  Magnetic Pipe to Shield Output 
               19  Coolant Flow 
               20  Pump Outlet Pipe 
               21  Hot Pool 
           
         
       
     
         [0062]    However, before proceeding with the description, it should be noted that the various embodiments shown and described herein are exemplary only and are not intended to represent the extent to which the present invention may be utilized. Indeed, the systems and methods described herein could be readily applied to any of a wide range of intrinsically safe nuclear fission reactor designs, as would be obvious to persons having ordinary skill in the art after having become familiar with the teachings provided herein. Consequently, the present invention should not be regarded as limited to the particular intrinsically safe reactor and example configurations shown and described herein. 
       DETAILED DESCRIPTION 
       [0063]    Referring now to  FIG. 1 , one embodiment of an intrinsically safe nuclear fission reactor may comprise an upper chamber  2  to hold the fuel spheres  1  in to a configuration that supports fission. 
         [0064]    When the pumps A are turned on, and sufficient pressure or flow  19  is achieved, the fuel spheres  1  are pushed up into the upper core chamber  2  and it is in the “On” state. The upper core is surrounded by a reflector  8  which, in one embodiment, comprises a generally cylindrically-shaped side reflector portion that encircles the core chamber. Additional reflectors may also be provided in certain reactor designs. As will be described in greater detail, an inverted cone shaped lower chamber  4  is positioned directly under the core chamber to hold the fuel spheres apart from each other in the “off” state, the walls of this chamber are surrounded by neutron moderating, or absorbing materials. 
         [0065]    One possible variant of application of the intrinsically safe reactor is in the Fast Reactor or breeder reactor configuration. A system can be provided with a suitable fuel sphere collection system (piping not shown) for collecting the fuel spheres as have become depleted to the extent where it is no longer desirable to operate with them. Partially depleted or enriched fuel may be recycled to a reprocessing unit of the reactor complex, whereas depleted fuel may also be removed from the reprocessing or refueling loop. 
         [0066]    Because continuous fueling reactor systems are well-known in the art and could be easily provided by persons having ordinary skill in the art after having become familiar with the teachings provided herein, the nuclear reactor system, as well as the various ancillary systems that may be desired or required for the operation of a fast breeder nuclear reactor system, will not be described in further detail herein. 
         [0067]    Fuel spheres having different overall diameters are possible and should be regarded as being within the scope of the present invention, provided suitable modifications are made to the reactor system to allow fuel spheres having different diameters to be used. 
       Core Description 
       [0068]    Utilizes hollow spheres of enriched uranium or other fissile fuel encased in such a way as to be more dense than the coolant medium, so as to sink in non-flowing hot primary coolant. 
         [0069]    In the coolant, the primary cooling fluid may be an eutectic alloy of Sodium and Potassium (NaK). One possible eutectic mix is liquid from −12.6 to 785° C., and has a density of 866 kg/m 3  at 21° C. and 855 kg/m 3  at 100° C., making it less dense than water. 
         [0070]    The envisioned reactor has only two power states: “On” or “Off”, therefore bi-stable. 
         [0071]    While in the “On” state, referring to  FIG. 2A , the core is formed in a “upper core chamber”  2  held in such a configuration, geometrically collected inside of such chamber surrounded by neutron reflective material  8  in such a way as to allow the core to reach criticality and begin the nuclear fission process, and as the primary cooling fluid  19  flows upwards through the core chambers supporting the “core” it also removes the heat of nuclear fission and transfers the heat up past an outlet screen like structure  5 , therefore the pressure of the primary coolant pushes upwards against the constant force of gravity and “holds” the core in the “On” state. 
         [0072]    In the event of a loss of primary coolant flow incident or accident, the core will “fall” or “sink” back into the lower chamber  4  due to gravitational forces into the “Off”, referring to  FIG. 2B , chamber and cease to support fission, thus intrinsically safe in all operational conditions. Normal shutdown is achieved by operations turning off the electromagnetic pumps, ceasing the primary coolant flow and shutting down the core. Natural convection can be assisted and nominal low flow rate of primary coolant can be maintained with low power to the EM pumps ( FIG. 1 . A), to provide cooling of the “off” core to remove decay heat. 
         [0073]    While in the “Off” state (referring to  FIG. 2B ), the core is not formed as the primary coolant flow is off, but rather has fallen, sunken down via gravitational forces into a geometrically dispersed, separated configuration surrounded by neutron absorbing materials  9  and  10 , the “Off” chamber  4 , thus intrinsically safe as gravity holds the fuel spheres separated and in the absence of the neutron reflector cannot possibly react with each other so as to be unable to support nuclear fission, in the stable “Off” state, 
         [0074]    In the event of a fuel sphere failure, the hollow core of the fuel sphere will fill with coolant and “sink” back into the “Off” chamber, not contributing to the reaction. 
         [0075]    An additional embodiment of the present invention (not shown in the attached drawings) is to utilize multiple lower core chambers as optional sources of fuel spheres supplied by a plurality of flow chambers from a plurality of electromagnetic pumps and pumping power levels. Each lower chamber holding a sufficient quantity of fuel spheres to fill the upper chamber to support fission. 
       Pump Description 
       [0076]    Multiple electromagnetic pumps (EMPs) ( FIG. 1  A), refer to  FIG. 3 , utilizing pump coil and stator assemblies  12  &amp;  14  separated from the pumped fluid, are included to provide redundant unit capacity in the event of partial pump failures, with extra capacity held in reserve, 
         [0077]    The primary coolant flows from the upper collection plenum (cool pool  15  above IHX B in  FIG. 1 ) after being cooled (heat energy removed via the IHX) and the pumping forces are applied to the cool side of the working fluid (primary coolant), 
         [0078]    Inlet of fluid to the EMP is accomplished by an annulus opening to a pipe  16  where the electromagnetic forces push the liquid metal upwards to the top of the concentric pipes. The return magnetic flux is carried by the concentric magnetic pipe  18  completing the pumping flux. 
         [0079]    Output from the electromagnetic pumps is via a relatively short straight pipe  20  thru the center of the pump, shielded from electromagnetic forces via a thick martinetic pipe shield  18 . The output pipe  20  is only connected to the top of the distribution chamber, at one end, and thus is allowed to expand in length to minimize stresses inside the pump. 
         [0080]    Electromagnetic pumping forces are applied in the outer coaxial space outside of the magnetic shield material  18 , with the pump output of coolant reversed in flow down the center space of the pump assembly, 
         [0081]    An additional design feature herein claimed is the incorporation of an additional length of concentric pipe(s)  16  &amp;  18  which extends above the zone of electromagnetic pumping forces, a “stand-pipe”, to prevent reverse flow in the event of pump shutdown or failure, due to the remaining EMPs pumping pressure, 
         [0082]    An additional design benefit to such an arraignment of coaxial flow is the ease of manufacture of the pumps as the EMP coil assemblies can be easily installed over the pipe assembly. 
         [0083]    A bimetallic thermal-electrical breaker switch (not shown) may be utilized to assure shutdown of the pumping electrical current in the event of an unplanned loss of secondary coolant flow, as when the pumping upper chamber temperature rises above a predetermined point the electricity will be automatically shut off and the pumping forces stopped, therefore the primary coolant flow will stop and the “core” returned to the “Off” state. 
       Intermediate Heat Exchanger (IHX) Description 
       [0084]    To assure the intrinsic safety of the whole system, the primary cooling fluid that is in “contact” with the nuclear fuel in the “core” of the reactor is not allowed to leave the primary reactor vessel, 
         [0085]    The primary coolant is “pooled”, in two plenums separated by a bulkhead where the outer “pool” is the cool side of the system and the inner “pool” is the hot side of the primary cooling system, 
         [0086]    The coolant is forced by pressure differential up through the “core” and is heated by the thermal radiation from the nuclear reaction from the inlet temperature of approximately 200 degrees F. to the output temperature of approximately 1000 degrees F. before flowing upwards through the IHX tubes. 
         [0087]    The secondary working fluid, NaK or alternately Pb/Bi, flows from the inlet pipe down to the upper portion of the IHX and into an annular distribution header where a plurality of cooling tubes are connected to the distribution header. 
         [0088]    Flow of secondary coolant proceeds down to the lower annular collection header and thereby absorbs heat energy from the primary coolant via conduction and thermal radiation from the “Hot pool  21 ” directly above the “core” chamber, into the secondary working fluid inside the IHX tubes, 
         [0089]    The IHX tubes are manifold, of equal overall length, and are in a spiral shape to mitigate the effects of differential expansion due to the possible differential temperatures in adjacent tubes, this allows the stresses to be spread along the entire tube based on a spiral, spring-like geometry of the individual tubes. 
         [0090]    The secondary coolant flows from the reactor to a vaporizer, i.e., steam generator or Brighton Cycle system, to convert the heat to work via conventional evaporation condensation cycles, and thus transferring the energy flows back to the reactor to “cool” the “Hot Pool” once again. 
         [0091]    This invention utilizes a plurality of seismic supports  11  which isolate the Primary Reactor Vessel  3  from the secondary containment structure in the event of an earthquake. Said secondary containment structure  13  is constructed on-site and the reactor vessel is delivered to the site as a fully fueled sealed module, then installed, covered and buried. 
         [0092]    As a component of a “Hybrid Nuclear Power System”, the Intrinsically Safe Nuclear Reactor, (ISNR), provides high value, high temperature heat to an other energy conversion component (water/steam/water or other vapor cycle thermal to mechanical energy system; the VaporDyne Unit) which converts the high value heat output from the Intermediate Heat Exchanger IHX portion of the reactor, to mechanical energy to pump lower level reservoir water up to a high potential energy reservoir to provide water with high hydrostatic head, to a conventional hydro-electric plant to create electricity and distribute the electricity to the community, and waste heat from the energy conversion component also utilizes low value heat to provide district heating and cooling, and to desalinated seawater. 
         [0093]    Additionally as the total “Hybrid Nuclear Power System” is modular in nature, multiple ISNRs could provide heat energy to multiple VaporDyne units that could utilize the same reservoir with multiple ISNR/VaporDyne reactor-pumps and hydro-electric plants to increase overall performance and operational redundancy of the total system. 
         [0094]    An additional embodiment of the present invention is to utilize the ISNR as a source of high temperature heat for industrial process, e.g. Steel Processing, or Hydrogen Generation. 
         [0095]    An additional embodiment of the present invention is to utilize the ISNR as a source of high temperature heat to augment existing generation II and III nuclear power plants as the end-of-life-cycle of the older technology units are decommissioned, thereby utilizing the existing site and steam powered electrical generation equipment. 
         [0096]    An additional embodiment of the present invention is to utilize the ISNR as a source of high temperature heat to offset the use of coal, natural gas, or other fossil fuels in existing power plants thereby shifting the source of power to non-carbon dioxide emitting sources, and also utilizing the existing site and steam powered electrical generation equipment. 
         [0097]    In summation, then, because persons having ordinary skill in the art could readily select from one or several component configurations of the design described herein, after having become familiar with the teachings of the present invention, the present invention should not be regarded as limited to varying any one or combination of the reactor components described herein. 
         [0098]    Present invention should not be regarded as limited to any kind of cooling fluid. 
         [0099]    Present invention should not be regarded as limited to any scale of power output. 
         [0100]    Present invention should not be regarded as limited to any particular fuel source or combination of fuel sources. 
         [0101]    Having herein set forth preferred embodiments of the present invention, it is anticipated that suitable modifications can be made thereto which will nonetheless remain within the scope of the invention. The invention shall therefore only be construed in accordance with the specific included claims.