Patent Number: 050376012
Section: description

DESCRIPTION OF THE PREFERRED EMBODIMENTS The glass-pool, air-cycle nuclear power plant of this invention is shown in the exploded view of FIG. 1 and is designated generally by the reference numeral 10. The power plant includes an outer containment structure 12 which houses an internal pressure vessel 14 that contains the reactor capsule 16 and heat exchange casing 18. The outer containment structure 12 is of sufficient size to control any escape of cycled gas that is under compression in the pressure vessel. It is to be understood that since the gas does not go through a phase change the size of the containment structure need only be of sufficient size to adequately contain at moderately low pressure, expanded gases from the volume of space between the pressure vessel 14 and the heat exchange casing. The pressure vessel and the heat exchange casing 18 form a heat exchange unit 20 which is coupled to a turbine 22 such that compressed and heated gases expand though one or more nozzles 24 to drive a rotor 26. The air cycle path is schematically shown in FIG. 1 and comprises a closed cycle with a compressor 28 that receives expanded gases from the turbine 22 and compresses them to an operating pressure of approximately 150 psi. The discharge from the compressor 28 is split into two different paths 30 and 32. One path 30 delivers a portion of the discharge from the compressor to the heat exchange unit 20 and then to the turbine nozzle 24. The other path delivers the remaining portion of the discharge from the compressor to an intercooler 34. After cooling, the compressed and chilled air is past to a nozzle 36 for expansion though the turbine rotor 26. Although the nozzles 24 and 36 are shown schematically in FIG. 1 it is to be understood that more sophisticated designs can be incorporated such as a circumferential housing having alternate hot and cold discharge nozzles that discharge into the rotor thereby maintaining the temperature of the rotor blades relatively low. Because of the temperature differential between the high temperature and low temperature gases, the violent mixing in an expansion chamber 40, subsequent to the expansion though the turbine 26, will result in cooling of the hot gases to a temperature that approaches ambient temperatures with a concomitant loss in velocity of the gases. The gases then can be returned as a homogenous low pressure, low temperature gas to the compressor via a common return path 38. Referring now to FIG. 3, a portion of the pressure vessel 14 is shown with the reactor capsule 16 and the heat exchange casing 18. The thick heat exchange casing 18 is a shell of a high temperature, highly conductive alloy material such as Inconel, which not only performs the function of a heat sink, but has radiating fins 19 for the transmission of thermal energy from the core 27, to the air passage between the heat exchange casing 18 and the outer wall of the pressure vessel 14. The heat exchange casing also provides a final shield to absorb any neutrons penetrating the reflective carbon inner shell 17 of the reactor capsule. Because of the low pressures involved, the outer wall of the pressure vessel 14 can be constructed from reinforced concrete with or without any shielding material. The reactor capsule 16 comprises a glass matrix heat sink 29 having a staged silica and thorium oxide mix which diminishes from a central 50/50 mixture around the core 27 to a 25/75, 15/85 and finally all silica composition as shown in FIG. 3 by the notations a, b, c, and d respectively. In the central core 27, originally protected by a glass flask 31 is a cavity into which fuel balls 33 are deposited. Two alternatives are provided for initiating the fission reaction to convert the thorium to uranium and cause the U.sup.233 to fission. As shown in FIG. 3 fuel balls 33 are introduce by an external vehicle 46 on start-up and commissioning of the plant. The fuel balls may include fissionable U.sup.235 material which on deposit of a critical mass of fuel balls will start a chain reaction and initiate fission in other fertile thorium balls. The fuel balls 42 are deposited though a feed pipe 44 that is coupled to the vehicle 46 by a retractable coupling pipe 48. A carbon plug 50 in a vertical tube 52 is retracted allowing the fuel ball 42 to drop to the glass flask 54. Upon deposit of the predetermined number of thorium and U.sup.235 fuel balls to initiate a chain reaction, the moderator plug 50 is lowered into a blocking position to contain the thermal reaction and reflect emitted neutrons. The fissionable fuel balls melt the glass flask 54 and commence emitting neutrons to initiate the transformation of the thorium in the glass/thorium matrix to a fissile material. The matrix eventually melts such that the core and sink glass become a molten mass. Alternately, a safer means may be used to initiate a reaction. Relatively pure fuel balls of thorium.sup.232 and a noncritical quantity of U.sup.235 may be deposited through the feed pipe 44 with the plug 50 retracted. A photo neutron generating gun 56 with a magnetic deflector 58 at its end is inserted as a probe into the feed pipe 44 wherein an accelerator in the vehicle directs a photoneutron beam down the gun 56 to the deflector where the beam is deflected and directed at the uranium and thorium fuel in the flask. The gun activated neutron emissions to augment the uranium emitted neutrons to initiate fission and the breeding of fissionable U.sup.233 from the thorium in the fuel balls and in the surrounding glass matrix. A accelerator with a beam energy of 40 Me V would be required for the startup. The accelerator of this power level can be constructed for mounting in a trailer that can be moved from site to site for start-up of multiple nuclear plants of the type described. Use of non-uranium target materials that will emit neutrons upon bombardment from an external photo neutron generating source is a preferred consideration for a safe start-up regime. A pure thorium start-up is discussed hereafter. Power is extracted from the system as schematically shown in FIG. 3. The compressor 28 compresses air in a closed cycle. Cooled air is received through a return conduit 38 from a collector 40. The air is compressed to approximately 150 p.s.i. by the compressor 28. Part of the compressed air, approximately 80%, is cooled an intercooler 34 and the remaining portion is heated in the reactor or heat exchange unit 20. The hot stream and cold stream drive a turbine 22, which in turn drives the compressor 28 and the power take-off 58. The expanded gases discharged from the turbine 22 are collected in the expander-collector 40 and thermally equalized for return to the compressor. The equalization of temperature in the mixed air and further minor heat loss by radiation from the return conduit 38 returns the mixed air to the compressor at substantially ambient temperature. Alternately, an active heat exchanger can be incorporated to further cool high temperature gases after expansion whether before or after mixture in the collector. The core 27 is permitted to operate at maximum temperature in excess of 4500.degree. F. The temperature declines as the distance from the core increases with the outer portions of glass pool sink 29 reaching 3000.degree. F. and the graphite shell 17 averaging 2800.degree. F. The system is sized and charged with fissionable material to generate and maintain a surface temperature at the heat exchange casing of 2700.degree. F., with an exit air flow temperature of 1700.degree. F. The combined expansion of the compressed and heated air and the compressed and cooled air will result in a mixed air in the collector 40 having an temperature approximating ambient temperature. Although the cycle efficiency is only about 3-4 percent, once commissioned the relatively inexpensive charge of fuel should continue producing thermal energy for years. An alternate embodiment of the invention is shown in FIGS. 4 and 5. Referring to FIG. 4, a modified pressure vessel for the nuclear power plant is shown. The pressure vessel 60 has an air intake flange 62 and a hot air outlet flange 64 for connecting to a compressor and turbine circuit as shown in FIG. 5. The pressure vessel 60 is generally spherical in shape to house a spherical reactor capsule 66 that is eccentrically situated in the vessel to enable inlet air to be heated by radial fins 68 of increasing surface area as the air passes from inlet to outlet. The spherical reactor capsule is designed to most efficiently radiate thermal energy from the fuel core 70 to the alloy heat exchange casing 72. The fission is preferably initiated by deposit of pure thorium fuel balls 74 in a glass container 76 having an impact cushion 78 to prevent breakage during fueling. The glass container 76 is coupled to the end of a high temperature ceramic feed pipe 80 which remains after the glass container has melted on initiation of the reaction. The container 76 is encompassed by a thorium-glass matrix of diminishing thorium content. For example, the inner packing 82 has a 50-50, thorium/glass content, the next layer 84, a 25-75, thorium/glass content, and the outer packing 86 an all glass content. A graphite shell 88 provides a reflecting neutron shield. The fuel balls 74 rest on a ceramic pedestal 90 having a secondary dish 92 to receive any fuel balls or heavy fissionables that overflow the top cradle 94 during operation. Fission is preferably initiated by depositing a quantity of high-grade thorium fuel balls through a feed tube 96 with a control rod 98 retracted. The control rod 98 may be fabricated from a neutron absorbing composition such as a boron in a ceramic or Inconel matrix. The control rod 98 is designed to be irreversibly positioned in the reactor if dropped down the feed pipe 80 and into the molten glass matrix to poison the reaction. Ordinarily it is positioned in the upper portion of the feed pipe 80 unless further withdrawn to allow for feeding of additional fuel balls through the feed tube 96. The control rod 98 is also withdrawn on initiating reaction by clearing photoneutron path shown in broken line. A horizontal probe (99) from a LINAC photoneutron generator connects with the guide conduit 100 and directs a photoneutron generating beam at an electromagnetic deflector 102 which is moved into position shown in dotted line, to deflect the beam at the fuel balls in the cone. The photoneutron generating beam stimulates the fuel balls to generate neutron emissions to initiate a fission reaction. The fertile thorium transforms to a fissile U.sup.233 under bombardment by the photoneutron generating beam and the released neutrons of the stimulated mass. As shown schematically in FIG. 5, an alternate closed air flow circuit cycles air from a collector or mixing chamber 104 to a multistage compressor 106 having an intercooler 107 between each stage for compression of air to the turbine operating pressure of 150 psig. A separate compressor 109 without intercooling also compresses a portion of the air from the collector via a bleed path 108 for delivery to the reactor heat exchanger 110 where the air is heated to at least 1700.degree. F. before delivery to the turbine 112, which is the embodiment disclosed, accepts both the cold air from the intercooled compressor and the hot air from the reactor. The expanded air is mixed in the collector 104 where temperature and velocity are reduced for return to the cycle. While, in the foregoing, embodiments of the present invention have been set forth in considerable detail for the purposes of making a complete disclosure of the invention, it may be apparent to those of skill in the art that numerous changes may be made in such detail without departing from the spirit and principles of the invention.