POWER GENERATION SYSTEM AND POWER GENERATION METHOD

Abstract

A power generation system comprises: a muon-catalyzed nuclear fusion device configured to undergo muon-catalyzed nuclear fusion; and a nuclear-reactor power generation device configured such that a nuclear fuel therein is irradiated with neutrons generated as a result of muon-catalyzed nuclear fusion in the muon-catalyzed nuclear fusion device, thereby to carry out power generation, wherein a pressurized-water nuclear reaction vessel in the nuclear-reactor power generation device is arranged so as to surround a nuclear fusion reactor core in which muon-catalyzed nuclear fusion occurs via a structural partition separating the muon-catalyzed nuclear fusion device from the nuclear-reactor power generation device.

Claims

1. A power generation system comprising: a muon-catalyzed nuclear fusion device configured to undergo muon-catalyzed nuclear fusion; and a nuclear-reactor power generation device configured such that a nuclear fuel therein is irradiated with neutrons generated as a result of muon-catalyzed nuclear fusion in the muon-catalyzed nuclear fusion device, thereby to carry out power generation, wherein a pressurized-water nuclear reaction vessel in the nuclear-reactor power generation device is arranged so as to surround a nuclear fusion reactor core in which muon-catalyzed nuclear fusion occurs via a structural partition separating the muon-catalyzed nuclear fusion device from the nuclear-reactor power generation device.

2. The power generation system according to claim 1, wherein the nuclear fuel includes thorium 232 (.sup.232Th), thorium oxide (.sup.232ThO.sub.2), or a mixture of thorium 232 and thorium oxide.

3. The power generation system according to claim 1, wherein the nuclear-reactor power generation device includes a fuel-holding portion, arranged so as to surround the nuclear fusion reactor core, for holding the nuclear fuel irradiated with fast neutrons emitted as a result of muon-catalyzed nuclear fusion thereby to undergo a nuclear fission reaction.

4. The power generation system according to claim 3, wherein the fuel-holding portion includes an assembly of fuel fine pipes for sealing the nuclear fuel molded into a pellet.

5. The power generation system according to claim 1, further comprising: a long lived fission product (LLFP)-holding portion for arranging an LLFP in the pressurized-water nuclear reaction vessel.

6. The power generation system according to claim 1, wherein the muon-catalyzed nuclear fusion device includes: a muon generation unit configured to generate negative muons; a gas supply unit configured to circulate and supply deuterium gas or deuterium-tritium mixture gas as a raw material gas; and a Laval nozzle configured to accelerate the raw material gas supplied from the gas supply unit to supersonic velocity, wherein the Laval nozzle has a shock wave generator arranged thereinside to undergo collision with the raw material gas accelerated to supersonic velocity thereby to generate an oblique shock wave, the raw material gas is supplied from the gas supply unit into the Laval nozzle, then the supplied raw material gas is accelerated through the Laval nozzle to supersonic velocity, and then the accelerated raw material gas collides with the shock wave generator, and thereby the oblique shock wave is generated, the oblique shock wave is converged on a center axis of the Laval nozzle so as to retain a high-density gas target in a gas phase, and the negative muons are introduced from the muon generation unit into the high-density gas target thereby to cause a nuclear fusion reaction to occur.

7. A power generation method comprising the steps of: irradiating a nuclear fuel arranged inside a pressurized-water nuclear reaction vessel in a nuclear fission reactor with neutrons generated as a result of muon-catalyzed nuclear fusion; while causing a nuclear fission reaction within the nuclear fuel to occur, thereby to carry out power generation.

8. The power generation method according to claim 7, wherein the nuclear fission reaction within the nuclear fuel irradiated with neutrons is controlled by controlling the neutrons generated as a result of muon-catalyzed fusion.

Description

BRIEF DESCRIPTIONS OF THE DRAWINGS

[0040] FIG. 1 depicts a view showing nuclide transmutation pathways in fusion neutrons with thorium 233 in a .sup.232Th nuclear fission reactor;

[0041] FIG. 2 depicts a schematic view showing a configuration obtained by combining a thorium 232 nuclear fission reactor with a reactor core of muon-catalyzed nuclear fusion, where F1 represents a circulation reactor for deuterium or deuterium-tritium, and F2 represents a pressurized light-water pathway;

[0042] FIG. 3 depicts schematic views showing a configuration of a muon-catalyzed fusion system, of which (A) shows schematically a major system configuration, and (B) shows schematically a shock wave generator in an enlarged manner;

[0043] FIG. 4 depicts an explanatory view showing schematically internal and whole structures of a power generation system; and

[0044] FIG. 5 depicts a schematic view showing the A-A cross section in FIG. 4.

DESCRIPTIONS OF EMBODIMENTS OF THE INVENTION

[Configuration of Power Generation System]

[0045] A power generation system S according to an embodiment of the present invention will be described, hereinafter, with reference to FIGS. 2 to 5.

[0046] As shown in FIG. 2, the power generation system S includes a muon-catalyzed nuclear fusion system S1 (muon-catalyzed nuclear fusion device) and a nuclear-reactor power generation system S2 (nuclear-reactor power generation device). The muon-catalyzed nuclear fusion system S1 is formed integrally with the nuclear-reactor power generation system S2 so as to separate traffic between a nuclear fusion reactor structure of the muon-catalyzed nuclear fusion system S1 and a nuclear fission reactor structure of the nuclear-reactor power generation system S2 via a structural partition 20 as a pipe wall of a gas pathway as well as so as to enable the nuclear-reactor power generation system S2 to be irradiated with fusion neutrons generated from the muon-catalyzed nuclear fusion system S1 to permeate through the structural partition 20.

[0047] As for the muon-catalyzed nuclear fusion system S1, a configuration described in WO 2019/168030 (Patent Document 1) having been proposed by the applicant may be adopted. As shown in FIG. 3, the muon-catalyzed nuclear fusion system S1 includes a muon generation unit 1, a gas supply unit, a Laval nozzle 2, a shock wave generator 3, a muon inlet window 4, and a unit for generating a nuclear fusion reactor core G.

[0048] The muon generation unit 1 is configured to generate negative muons needed as a catalyst for the muon-catalyzed nuclear fusion reaction, and to introduce the generated negative muons into the nuclear fusion reactor core G.

[0049] The muon generation unit 1 includes a proton accelerator and a muon generator (not illustrated) configured such that a target such as Be (beryllium) is irradiated with protons so as to generate pions, and then the negative muons are generated as a result of spontaneous decay of the generated pions. As for the proton accelerator, a well-known configuration may be adopted.

[0050] The muon inlet window 4 is arranged at a position where muon beam N1 is allowed to enter the nuclear fusion reactor core G having a high-density gas target generated so as to be retained in a gas phase by the shock wave generator 3, to be described later, in the Laval nozzle 2.

[0051] The gas supply unit is configured to circulate and supply deuterium gas or deuterium-tritium mixture gas, which is a raw material gas to serve as the target of the nuclear fusion reaction. As for the gas supply unit, a well-known configuration for circulating and supplying gas may be adopted. The gas supply unit according to an embodiment of the present invention includes a circulation-gas heat exchanger 5, a circulation-gas loop 6, a high-pressure compressor 7, and auxiliary equipment such as tanks and pipes.

[0052] The Laval nozzle 2 accelerates the raw material gas supplied from the gas supply unit to supersonic velocity. The Laval nozzle 2 is connected with the high-pressure compressor 7 at an upstream side, and formed with a tubular rectification portion 2a configured to allow the raw material gas to pass therethrough at subsonic velocity, a throat portion 2b reduced in diameter in comparison with the rectification portion 2a, and a tubular reaction portion 2c connected with the throat portion 2b. The tubular reaction portion 2c larger in diameter than the throat portion 2b is formed such that the raw material gas passing therethrough at supersonic velocity undergo the nuclear fusion reaction. The Laval nozzle 2 is a part of the structural partition 20 between the nuclear-reactor power generation system S2 and the muon-catalyzed nuclear fusion system S1.

[0053] The shock wave generator 3, arranged in the reaction portion 2c of the Laval nozzle 2, is configured to collide with the raw material gas accelerated to supersonic velocity so as to generate oblique shock wave. Further, the shock wave generator 3 is arranged so as to face the supersonic gas flow. The shock wave generator 3 can generate the oblique shock wave as a result of the collision with the supersonic gas flow so as to converge the generated oblique shock wave on a center axis of the Laval nozzle 2, thereby to retain the high-density gas target of the nuclear fusion reactor core G in a gas phase. The nuclear fusion reactor core G is in an ultrahigh-density gas having 10.sup.22 particles.Math.cm.sup.3, preferably having 410.sup.22 particles.Math.cm.sup.3, at a temperature of 300 to 900 K.

[0054] The shock wave generator 3 may be configured at least such that an aerodynamic balance can be maintained with respect to a dynamic pressure, oblique shock wave, Mach shock wave, and reflective wave of the gas flow at an upstream side therefrom. The shock wave generator 3 may be formed as, e.g., a pair of plate members having their respective oblique surfaces toward a downstream side while facing each other, or a plurality of small projections circularly arranged as shown in FIG. 3, etc. When the shock wave generator 3 is formed as such a plurality of small projections, a downstream end of the shock wave generator 3 can be protected from a large intensity of neutron beam and thermal flux because the downstream end can be distanced from the nuclear fusion generation region (nuclear fusion reactor core G).

[0055] The nuclear-reactor power generation system S2 includes a pressurized-water reaction vessel 10, the above-described structural partition 20, a fuel-holding portion 30, and a power generation unit 40.

[0056] The Laval nozzle 2 is arranged along a center axis inside the pressured-water reaction vessel 10. The pressurized-water reaction vessel 10 is separated from the muon-catalyzed nuclear fusion system S1 (Laval nozzle 2) via the structural partition 20, and more specifically, arranged so as to surround the nuclear fusion reactor core.

[0057] The structural partition 20 is configured to separate the above-described circulation flow tunnel system allowing the deuterium-tritium gas to flow therethrough at supersonic velocity from the below-described nuclear fission reactor filled with light water or heavy water. For such a structural partition 20 according to an embodiment of the present invention, special steel having reduced deterioration due to neutrons and reduced embrittlement due to hydrogen may be used. Such special steel has been developed for the nuclear fusion (e.g., reduced activation ferric steel).

[0058] The fuel-holding portion 30 formed in a cylindrical shape as the entire appearance is arranged coaxially with respect to the Laval nozzle 2 so as to surround the nuclear fusion reactor core G undergoing the muon-catalyzed fusion in the Laval nozzle 2.

[0059] It is preferred that thorium 232 (.sup.232Th) in the fuel-holding portion (blanket module) be irradiated directly with fast neutrons generated by the nuclear fusion in order to proceed efficiently nuclide transmutation from thorium 232 as a nuclear fuel to uranium 233. The fuel-holding portion 30 is the blanket module, arranged so as to surround the structural partition 20, configured to hold the nuclear fuel undergoing the fission reaction while being irradiated with the fast neutrons emitted through the muon-catalyzed nuclear fusion. The fuel-holding portion 30 has both of a function as a moderation and shielding material against neutrons and a function as a converter from the neutron energy to heat.

[0060] In an embodiment according to the present invention, the fuel-holding portion 30 is configured as an assembly of fuel fine pipes (fuel rods) 31, and a large number of the fuel fine pipes 31 are arrayed concentrically as a whole. Each fuel fine pipe 31 has the nuclear fuel containing thorium 232 as a parent nuclide sealed therein, where each of a plurality of pieces of the nuclear fuel is molded in e.g. a pellet shape. The fuel fine pipes 31 are surrounded by a pressurized-water jacket 41 filled with pressurized light water. The pressurized-water jacket 41 recovers the energy emitted by the nuclear fission. Each of the fuel fine pipes 31 is preferably made of stainless steel or reduced activation ferric steel of high resistance against neutron irradiation.

[0061] The energy of neutrons is reduced proportionally to a distance from the center in a radial direction. The energy of neutrons in the fuel-holding portion 30 closer to an outer circumference is attenuated to an energy region of thermal neutrons. Since uranium 233 (233U) undergoes nuclear fission efficiently due to thermal neutrons, the outer circumferential portion becomes hotter.

[0062] Thorium 232 is transmuted to uranium 233 according to the reaction chain in FIG. 1. A level of neutron multiplication with respect to uranium 233 is obtained theoretically as being 2.38. Such a level is higher than levels for uranium 235 (.sup.235U) and plutonium 239 (.sup.239Pu) within the energy region of thermal neutrons. According to the data of the pressurized light-water breeder reactor at Shippingport, a breeding level of 1.02 was reported. For the deviation from the theoretical level, the absorption of neutrons (neutron poisoning) due to light water is the most influential. In an embodiment according to the present invention, a diameter of the fuel fine pipe 31 is set to be large enough to reduce a ratio of surface area/volume of the fuel rod, which further results in increase in consumption rate inside fuel pellet and decrease in neutron poisoning due to light water for the generated neutrons. Further, a temperature of cooling water can be raised to improve Rankine cycle efficiency of the nuclear fission reactor.

[0063] For the above-described objectives, thorium oxide (ThO.sub.2) powder is molded and sintered to produce the pellets for the nuclear fuel. ThO.sub.2 has a high melting point, and the sintering temperature is 2000 C. or higher. It is difficult to sinter ceramic as thick as 25 mm or more in diameter at a high temperature; nevertheless, the difficulty is solved by applying a micro-wave sintering technique as proposed in Japanese Unexamined Patent Application Publication No. 2003-277157.

[0064] As the nuclear fuel, .sup.232Th (thorium 232) pellets or pellets having thorium 232 and thorium oxide are mixed may also be used.

[0065] The power generation unit 40 includes a well-known configuration of a pressurized light-water nuclear fission reactor. The power generation unit 40 includes a power generation apparatus 44 having the pressurized-water jacket 41, a pressurizer 42, a steam generator 43, a steam turbine, a power generator, a condenser, and the like, and a water-supply pump 45, or the like.

[0066] The fuel fine pipe 31 having an oxide of LLFP etc. mixed and sealed or having only LLFP sealed may also be used in addition to the nuclear fuel. In such a case, the fuel fine pipe 31 corresponds to an LLFP-holding portion. According to the configuration, LLFP can be irradiated with neutrons so that the lifetime thereof can be shortened and the amount thereof can be reduced concurrently with each other. The fuel-holding portion 30 (breeder block) may be arranged such that the breeding of neutrons and the breeding of nuclear fission substance can be maximized through the nuclear fission reactor.

[0067] The fuel fine pipes 31 having LLFP sealed therein are preferably arranged within a radius of 2/3 on an outside of several stages from an inner circumference of the fuel-holding portion 30. A ratio between the number of the fuel fine pipes 31 having the LLFP sealed therein and the number of the fuel fine pipes 31 having thorium sealed therein has a trade-off relationship with the power generation quantity (Non-Patent Document 5).

[Power Generation Method]

[0068] Next, the power generation method implemented through the power generation system S will be described hereinafter.

[0069] In the muon-catalyzed nuclear fusion system S1, isotropically-emitted fast neutrons having 14.1 MeV generated in the nuclear fusion reactor core G stimulate the nuclear fission reaction in the fuel-holding portion 30.

[0070] The fuel fine pipes 31 of the fuel-holding portion 30 is heated to 600 C. or higher, and cooled with circulated and pressurized primary water in the pressurized-water jacket 41. This hot thermal source heats the pressurized water in the pressurized-water jacket 41 to 500 C. or higher, and introduces this hot primary water into the steam generator 43 so as to generate hot steam. The steam is supplied from the steam generator 43 through a steam-supply pipe 43a to the power generation apparatus 44, and the power generation apparatus 44 can perform the turbine power generation. A water pipe 43b is added to this configuration so as to form a secondary loop. The circulated and pressurized primary water is circulated with the water-supply pump 45.

[0071] With the circulation-gas heat exchanger 5, helium gas is heated to be usable for direct hydrogen production at high temperature.

Effects of Embodiment

[0072] According to the power generation system S and the power generation method in an embodiment of the present invention, neutrons generated in the muon-catalyzed nuclear fusion system S1 can be used to operate the nuclear-reactor power generation system S2. The fusion neutrons having 14.1 MeV generated in the muon-catalyzed nuclear fusion system S1 is radiated to thorium 232 as the nuclear raw material in the nuclear-reactor power generation system S2, and there can be achieved the nuclear fission reactor capable of initiating the decay chain of thorium 232 through the (n, 2n) and (n, 3n) reactions therein. This can result in establishing a composite power generation system obtained by combining nuclear fusion and fission capable of generating a nuclear reactor output beyond that of fusion neutrons, and thereby, a highly-efficient, safe, and small-sized sub-critical nuclear fission reactor without causing any radioactive wastes can be achieved.

[0073] The nuclear fission reactor can be electrically controlled through the muon-catalyzed nuclear fusion output, instead of mechanically controlling of a control rod or other mechanical control structures. The muon-catalyzed fusion is instantly terminated upon necessary termination of the muon-catalyzed fusion, and for this reason, there is no need to insert a control rod. The power generation method with high reliability as fail-safe can, therefore, be achieved.

[0074] The fuel fine pipes having LLFP sealed therein are appropriately arranged between the thorium-sealed pipes to perform power generation due to the (n, 2n) reaction etc. concurrently with the LLFP's lifetime-shortening and LLFP's amount-reduction. The reduction in amount and volume of LLFP having been accumulated due to the nuclear fission reactors up to the present time can also be proceeded.

OTHER EMBODIMENTS

[0075] Through the muon-catalyzed nuclear fusion system S1, a DD-fusion reaction using deuterium gas as a raw material gas can also be handled.

REFERENCE NUMERALS

[0076] 1 Muon generation unit [0077] 2 Laval nozzle [0078] 2a Rectification portion [0079] 2b Throat portion [0080] 2c Reaction portion [0081] 3 Shock wave generator [0082] 4 Muon inlet window [0083] 5 Circulation-gas heat exchanger [0084] 6 Circulation-gas loop [0085] 7 High-pressure compressor [0086] 10 Reaction vessel [0087] 20 Structural partition [0088] 30 Fuel-holding portion (Blanket module) [0089] 31 Fuel fine pipe [0090] 40 Power generation unit [0091] 41 Pressurized-water jacket [0092] 42 Pressurizer [0093] 43 Steam generator [0094] 43a Steam-supply pipe [0095] 43b Water pipe [0096] 44 Power generation apparatus [0097] 45 Water-supply pump [0098] S Power generation system [0099] G Nuclear fusion reactor core [0100] N1 Muon beam [0101] S1 Muon-catalyzed nuclear fusion system (device) [0102] S2 Nuclear-reactor power generation system (device)