Abstract:
This invention describes an innovative miniaturized decay-heat engine formed by a closed-loop system powered by the spontaneous decay of radioisotopes emitting alpha particles. Said alpha particles are emitted inside a sealed and reinforced capsule or rod whose surfaces reach a relatively high temperature as a result of the capture of the alpha particles in the inner shell of said capsule. Radiation shielding is not a significant problem since alpha radiation is stopped by the materials encasing the capsule. The cladding material covering the alpha capsule or rod acts as the thermal interface and the radiation shield at the same time. This invention provides a power source for time duration significantly longer than any power system powered by fossil fuels with minimum weight. The unit is assembled in an ultra-compact package providing power from a few months to several years without need for refueling.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Thermionic Generators have been widely and effectively utilized as devices able to convert nuclear decay heat into electricity. The principles governing these technologies relay on thermocouple effects between junctions exposed to a temperature differential. Several patents on these devices have been developed over the last few decades. In order to produce significant power these devices are quite heavy and bulky. Miniaturized devices produce extremely low power level which might be all it is necessary for certain applications. For example, Power Chip™ is a solid-state device that uses small sandwich-like wafers to generate electricity from a temperature differential. The technology is closely related to Borealis proprietary Cool Chips™ technology. Borealis patent, titled “Process for Stampable Photoelectric Generator”, U.S. Pat. No. 6,239,356, was issued by the United States patent and Trademark Office on May 29th, 2001. A basic data search produced countless methods and apparatus for thermionic converters. For example, “Method and Apparatus for a Vacuum Thermionic converter” with thin film carbonaceous field emission, U.S. Pat. No. 6,064,137, and several other patents developed to decrease the work function of the materials forming the thermocouple junction to increase the electron efficiency. Most of these patents are centered on the utilization of decay heat to create a temperature differential between exotic junctions to produce electricity as efficiently as possible. All of these technologies, although very sophisticated, produce relatively bulky and relatively inefficient electric generators especially when the energy demand at their output is relatively high. The main objective of the present invention is to entirely by-pass the conversion of decay heat into electricity via thermocouple technologies. To achieve this objective a special heat exchanger in conjunction with a vapor cycle and a novel automatic cooling system for condensation is utilized to convert decay heat-to-fluid energy-to-electricity or mechanical work. This high-density power source is scaleable and can produce significant power output even when the unit is miniaturized.  
         SUMMARY OF THE INVENTION  
         [0002]    One or more sealed reinforced alpha decay-heated capsules or rods assembled inside a heat transfer mechanism formed by extended surfaces separated by a clearance become the heat source and the radiation shield of a closed-loop vapor cycle. An organic fluid, or any fluid with the proper thermal physical properties, is utilized as the expanding fluid inside said clearance. Once pressurized inside the clearance said fluid undergoes heat transfer with said extended surfaces in thermal contact with the decay-heated capsule or rod. The level of pressurization inside said clearance is proportional to the amount of decay heat available from the decaying isotopes. At this point high-pressure super-heated fluid is allowed to expand inside a vapor turbine, thereby converting the vapor energy into mechanical energy. Said vapor turbine is mechanically linked to a forced air/gas or liquid cooling system in thermal contact with compact condensers designed to condense said fluid once expanded through said vapor turbine. When the electric or mechanical load applied to the HDPS is minimum the decay-heated capsule(s) or rods are automatically cooled by an increased coolant flow forced by an air/gas compressor or liquid pump by means of an impeller driven by said vapor turbine. The output of this engine is shaft-work and electrical power scaleable in a manner proportional to the amount of alpha emitting isotopes, and for a duration proportional to the half-life of said alpha emitting isotopes. Isotopes can be generated as a result of neutron or ion bombardment, or they can be chemically extracted from spent nuclear fuel. If the alpha emitting isotope is also emitting other undesired forms of radiation such as gamma-rays or beta-rays, or a combination of said beta and gamma-rays, the unit can be equipped with additional shielding. Therefore, the unit is designed to safely operate with pure or almost pure alpha emitters, but can also be operated with isotopes having large probability of emission in the form of alpha particles and small probability of gamma or beta emission. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0003]    [0003]FIG. 1 Is a schematic representation of a cylindrical HDPS showing a preferential but not limiting disposition of one or more decay heated capsules or rods integrated inside a thermal-hydraulic closed loop wherein a fluid executes a vapor cycle.  
         [0004]    [0004]FIG. 2 Is a simplified representation of the basic steps necessary to manufacture one capsule or rods containing a selected isotope with a desired half-life and radiation decay mode (i.e. alpha, beta, etc.).  
         [0005]    [0005]FIG. 3 Is a schematic with a detailed description of the rotating components forming the power plant of the HDPS unit along with the cooling system.  
         [0006]    [0006]FIG. 4 Is a schematic representation of a miniaturized configuration of the HDPS scaleable down to the size of a “fat” cigarette wherein all sub-components are self-contained.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0007]    The working principles of the HDPS system are now described by utilizing the schematics and representations shown in FIGS.  1 - 4 .  
         [0008]    In FIG. 1, one or more decay-heating fuel elements  1 , formed by sealed and reinforced pellets or capsules  1   a  (FIG. 2), containing a desired amount of nuclear decaying isotopes If (FIG. 2), are positioned inside a thermal hydraulic circuit  2 . These fuel elements can be manufactured in any shape or dimension. Said fuel element(s)  1  are positioned inside said thermal-hydraulic circuit  2  such that between the surfaces of said fuel elements  1  and said thermal-hydraulic circuit  2  there is enough clearance to allow a fluid to expand while transiting inside said clearance. Said fluid is stored inside the storage tank  3  and inside the hydraulic path of the high efficiency condenser  4 . Said fluid is compressed by pump  5 , which can be submerged inside tank  3 , or positioned anywhere in the unit as long as the suction of pump  5  is hydraulically connected with the hydraulic path indicated by number  4  in FIG. 1. Pump  5  is mechanically driven by a gear system  9  coupled with shaft  10 . Once said fluid is pressurized at relatively high-pressure check valve  6  allows said fluid to flow inside hydraulic path  7  until it reaches one or more fluid injector(s)  8 . At this point relatively cold fluid is forced to an intimate thermal contact with the outer surfaces of fuel element(s)  1  since said clearance, formed along hydraulic path  2 , does not allow blankets of rapidly expanding vapor to shield the cold fluid. In other words, all of the cold fluid injected from injector  8  is exposed to a high heat transfer rate inside said clearance so as that all of said cold fluid is converted into superheated vapor. At the exit  11  of said thermal-hydraulic circuit  2  said superheated vapor is throttled via nozzle  12  so that it can expand through vapor turbine  13 . The expanded vapor is now vented inside the closed-loop high efficiency condenser  4  where said vapor releases the remaining enthalpy of vaporization to the cooled surfaces of said high efficiency condensers  4 . Once enough heat has been released said vapor condenses back to liquid fluid, thereby resetting the condition for a new vapor cycle. The heat rejection from the surfaces of said high efficiency condensers to the environment is accomplished mainly by convective heat transfer inside the coolant hydraulic path  14 . This coolant indicated by arrows  15  can be air or any fluid provided that the blades of impeller  16  are proportionally shaped so as to add kinetic energy and pressure to a cooling fluid whether this is in a liquid or gaseous form. Another cooling mechanism of said high efficiency condensers is accomplished via conduction from the inner surfaces of path  4  to cooling fins  17  positioned along the circumference of the HDPS unit.  
         [0009]    In FIG. 2 a decay-heated rod  1  formed by one or more alpha decaying capsule  1   a  is shown. A preferential but not limiting manufacturing method of the decay-heated capsule is achieved by considering a sealed capsule  1   e  containing an inert stable chemical such as the element “Bismuth”  1   f  in a desired amount. The sealed capsule  1   e  is formed by Aluminum or other materials able to withstand the high pressure developed inside the capsule once the materials in its inside become activated, and having extremely short half-life once exposed to a radiation field (i.e. neutron flux). This sealed capsule  1   e  is then exposed to a neutron flux  1   g  inside a nuclear reactor  1   h  for a an amount of time proportional to the amount of chemical  1   f  inside capsule  1   e . The reactor  1   h  can be substituted with an accelerator in which case neutrons can be obtained through ion bombardment. After a certain time of exposure inside a radiation field the chemical  1   f  is transformed into a radioactive isotope which will decay via alpha radiation, thereby heating the capsule  1   e . At this point isotope  1   ff  is liquid due to its much higher temperature. If the capsule  1   e  is formed by Aluminum it will take approximately 2 days for the Aluminum to become stable again. If the chemical  1   f , once exposed to a neutron flux, becomes a pure alpha emitter the capsule will remain at high temperature for a time depending to the half-life of the activated chemicals. As an example if Bismuth- 209  is utilized, the consequent alpha emitter is Polonium- 210  which will decay into lead with a half-life of approximately 140 days. The thermal output of this isotope is approximately 140 W/g making it a remarkably compact heat source. Once the capsule  1   e  made of Aluminum, or any other material, becomes stable after the exposure inside a neutron field it is sintered inside a reinforced metal capsule  1   a . The mechanical properties of this multi-shell capsule (or pellet) have to be able to withstand any kind of reasonable disruptive scenario (i.e. puncture, collision, explosion, high-temperatures etc.), since the alpha emitting isotope is extremely toxic. All manufacturing process must be executed by licensed operators and through the use of robotic equipment. One or more capsule  1   a  can now be inserted inside a rod  1  filled with an oil solution containing lead  1   j , and weld shut at both ends  1   k . The combination of multiple capsules  1   a , scaleable in all dimensions, with the mechanical and radiation shield formed by the rod  1  cladding, forms a multiple barrier to rupture. The lead-oil solution  1   j  provides an optimum convective heat transfer mechanism, and a radiation shield for any gamma emitting impurities present in the chemical  1   f  prior irradiation. The pressure inside this system can reach elevated levels without jeopardizing the integrity of rod  1 .  
         [0010]    The power production system of the HDPS is described in FIG. 3. The vapor turbine  13  is mechanically linked to shaft  10  which is supported by the thrust bearings  18 . Impeller  16  and the alternator rotor  19  are also mechanically linked to shaft  10 . Rotor  19  contains compact magnets  19   a  magnetically coupled with stationary coils  20 . When high-pressure vapor expands through the blades of vapor turbine  13  rotor  19  is set in motion generating an alternating magnetic field controlled by power switching components  21  driven by a centralized computer  22 . This provides a controlled electric output utilized to charge one or more batteries  23 ,  24 , and  25  at different voltages. The electric output can also be extracted from the HDPS unit without electronic control and batteries since these components can be positioned outside the unit. A mechanical output for mechanical actuation executable by the unit is represented by the gear system  26   a ,  26   b , and  26   c . A reduced low-rpm output is available at the mechanical coupler  27  while an unreduced high-rpm output is available at mechanical coupler  28  connected to shaft  10  via shaft  10 a. Cooling of the HDPS unit is achieved as a function of load. When the electric or mechanical load is maximum, approximately 45% of the heat is converted into mechanical and electrical energy. The impeller  16  is designed with blades shaped so that at this maximum load condition the cooling fluid  15  (liquid or gaseous) provides enough mass flow rates to extract heat from the high-efficiency condensers  4  and reject it to the environment through concentric channel  14 . When load is absent the speed of impeller  16  increases since all of the heat generated in the decay heated elements  1  is converted into mechanical energy at the vapor turbine  13 . Automatically a larger mass flow of coolant  15  is forced into concentric channel  14  providing increased cooling for the excess heat. This mechanism assures automatic cooling of the decay heating elements  1  under all scenarios. If failures develop in any component of the cooling circuit a thermostatic valve  29  opens filling the environment surrounding the thermal-hydraulic circuit  2  with a highly conductive foam kept under pressure in pressurized tank  30 . Even if tank  30  fails the heat transfer between the thermal-hydraulic circuit  2  and the cooling fins  17  is such that the decay heated rods  1  will remain at an equilibrium temperature which will not jeopardize the integrity of rods  1 .  
         [0011]    In FIG. 4 a miniaturized version of the HDPS unit is shown. In this figure one decay heat capsule la is contained inside a cylindrical structure which can reach the dimension of a cigarette. In this case vapor turbine  13  has a diameter in the same range of turbine for dentist equipment. The vapor cycle operates with the same principles described in FIG. 1. Fluid pump  5  is driven by a gear system  9  and  9   a  which brings shaft power to said pump  5  via shaft  10   b . Pump  5  is submerged inside tank  3 . High-pressure fluid is pumped through fluid injector  8  inside clearance  2  heated by the surfaces of capsule  1   a . Superheated vapor flows through nozzle  12  and expands through vapor turbine  13  connected to shaft  10 . Alternator rotor  19  is also driven by shaft  10 . The permanent magnets (rare earth magnets) can also be embedded inside the impeller  16  so that an alternated magnetic path is formed by said magnets and stationary coils  20 . Cooling fluid  15  goes through a filter  16   a  and inside the high-efficiency condenser clearance  14  where said expanded vapor condenses back to liquid and accumulates inside tank  3  again. Battery  23  is now approximately the size of a watch battery kept charged by the alternator system driven by the vapor turbine  13 . The numbering utilized to indicate the same components consistently with FIG. 1. This terminates the description of the scaleable HDPS for high-density power production without need for re-fueling or recharging for several months up to several years depending on which isotope is selected as the fuel of the decay heated capsule.