WO2001039206A2

WO2001039206A2 - Cavitation nuclear reactor

Info

Publication number: WO2001039206A2
Application number: PCT/US2000/032247
Authority: WO
Inventors: Ross Tessien
Original assignee: Impulse Devices, Inc.
Priority date: 1999-11-24
Filing date: 2000-11-21
Publication date: 2001-05-31
Also published as: WO2001039204A3; WO2001039204A2; WO2001039205A3; WO2001039205A2; WO2001039206A3; AU2905801A; WO2001039206A9

Abstract

A composite nuclear reactor assembly, and a method for fabricating the same, is provided. The composite reactor assembly is designed for use as a solid cavitation nuclear reactor or CNR. The composite reactor assembly is comprised of an inner reactor core assembly and an outer spherical reactor portion. The inner core assembly includes a fuel portion and one or more extensions that are used to couple acoustic energy from the driver assemblies into the reactor. The core assembly is combined with the outer reactor portion such that the fuel portion is contained within the outer reactor portion while the extensions extend outwardly from the outer portion. In addition to providing a means for coupling acoustic energy into the reactor, preferably the extensions are also used as a means of supporting the reactor. A variety of techniques can be used to join the various elements of the composite reactor assembly, including electron beam welding and diffusion bonding.

Description

A COMPOSITE REACTOR ASSEMBLY FOR A CAVITATION

NUCLEAR REACTOR

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. Patent No. 09/512,517, filed February 23, 2000, which is a continuation-in-part of U.S. Patent Application Serial Nos. 09/448,402, filed November 24, 1999; 09/448,685, filed November 24, 1999; 09/448,141, filed November 24, 1999; 09/448,052, filed November 24, 1999; 09/448,753, filed

November 24, 1999; 09/448,142, filed November 24, 1999; 09/448,060, filed November 24, 1999; 09/448,309, filed November 24, 1999; 09/448,684, filed November 24, 1999; 09/444,716, filed November 24, 1999; 09/448,661, filed November 24, 1999; 09/448,686, filed November 24, 1999; 09/448,663, filed November 24, 1999; 09/448,981, filed November 24, 1999; 09/448,662, filed November 24, 1999; 09/448,401, filed November 24, 1999; and 09/444,717, filed November 24, 1999; all of which are incorporated herein by reference for all purposes. Additionally, this application is related to U.S. Patent Application Serial Nos. _/_, filed November 15, 2000 (Attorney Docket No. 22957-720, entitled A Driver Coupling Assembly for a Cavitation Nuclear Reactor) and _/_, filed November 15, 2000 (Attorney Docket No. 22957-721, entitled A Cavitation Nuclear Reactor Utilizing a Shaped Core Assembly), both of which are incorporated herein by reference for all purposes.

FIELD OF THE INVENTION The present invention relates generally to nuclear reactions and, more particularly, to a composite reactor assembly for use in an acoustically driven cavitation reactor system.

BACKGROUND OF THE INVENTION Cavitation is a well known phenomena in which small bubbles are formed and subsequently caused to expand and collapse through the application of acoustic energy. During the contraction phase of the cycle, the appropriately driven collapsing bubble causes a shock wave to be formed ahead of the collapsing bubble wall, resulting in a rapid increase in the temperature and the pressure within the bubble. If a sufficient temperature is reached, the bubble will briefly emit radiation, the spectrum of which is dependent upon the bubble temperature as well as the gas or gases within the bubble. The conversion of acoustic energy to optical energy is commonly referred to as sonoluminescence.

Numerous theories have been developed to explain the sonoluminescence phenomenon, although to date none of the theories appear adequate. Regardless of the theory, it is well agreed that extremely high bubble temperatures can be reached. Estimates place bubble temperatures between 10,000 and 1,000,000 degrees Kelvin.

Under appropriate conditions, the collapsing bubble can yield temperatures that are sufficient to drive fusion reactions. For example, U.S. Patent No. 4,333,796 discloses two different cavitation fusion reactors or CFRs. Each CFR is comprised of a reactor chamber and a plurality of acoustic horns coupled through the chamber walls.

Within the reactor chamber is a liquid host metal such as lithium or beryllium into which hydrogen isotopes are distributed either as dissolved gas, as hydrides, or as small bubbles. The acoustic horns are used to vary the ambient pressure in the liquid metal, creating small bubbles that are then caused to expand and collapse. The resultant high temperatures and pressures within the bubble and the host liquid are used to promote thermonuclear reactions of the hydrogen isotopes.

U.S. Patent No. 5,858,104 discloses a cavitation reactor chamber filled, in part, with a liquid. The chamber is coupled to a pressure source that allows the liquid to be pressurized to a static pressure different from the ambient atmospheric pressure. A pulsed acoustic shock wave is introduced into the liquid and reflected from a free surface of the liquid as a dilatation wave. The dilatation wave is focused on a desired location within the chamber, the desired location containing in at least one embodiment an object such as a biological cell, a pellet, or some other surface to be cleansed. The dilatation wave causes a bubble to form and expand while the static pressure causes the bubble to subsequently collapse and generate extremely high pressures.

U.S. Patent No. 5,659,173 discloses a technique for converting acoustic energy into other energy forms, the technique utilizing a feedback loop. The feedback loop monitors a characteristic of the emission and uses this characteristic to control the driving mechanism, thus allowing the process to be sustained for extended periods of time. Emission characteristics that may be monitored include the intensity of the produced energy as well as the repetition rate of the produced energy, assuming that the energy is in the form of pulses. In the disclosed system, the feedback loop may use the monitored information to alter the frequency or amplitude of the applied acoustic energy. What is needed in the art is a reactor assembly that is both economical and straightforward to fabricate and provides a simple means of controlling reactor composition. The present invention provides such a reactor assembly.

SUMMARY OF THE INVENTION

The present invention provides a composite reactor assembly, and a method for fabricating the same, for use as a spherical cavitation nuclear reactor or CNR. In general, a CNR according to the invention is comprised of a solid material and, more particularly, comprised of a fuel material interspersed within a host material. According to the invention, the composite reactor assembly is comprised of an inner reactor core assembly and an outer spherical reactor portion. The inner core assembly includes a fuel portion and one or more extensions that are used to couple acoustic energy from the driver assemblies into the reactor. The core assembly is combined with the outer reactor portion such that the fuel portion is contained within the outer reactor portion while the extensions extend away from the outer portion. In addition to providing a means for coupling acoustic energy into the reactor, preferably the extensions are also used as a means of supporting the reactor. A variety of techniques can be used to join the various elements of the composite reactor assembly, including electron beam welding and diffusion bonding. The driver assemblies which are coupled to the reactor through the core assembly extensions use transducers, preferably piezo-electric crystals, to convert electrical energy into acoustic energy. Preferably each of the driver assemblies also utilizes an acoustic wave guide to couple energy into the reactor and an acoustic balancing mass to improve the driver's performance characteristics. The acoustic energy driven into the CNR with the drivers creates a pressure intensity pattern within the reactor. The exact characteristics of the pressure intensity pattern are dependent upon, among other factors, the size, shape, and material comprising the CNR; the number, design, and locations of the drivers; the amplitude, frequency, and waveform of the source coupled to the CNR through the drivers; and the mechanical and thermal history of the CNR. As a result of the pressure intensity pattern, at numerous locations within the reactor the energy is large enough to form small cavities or bubbles. Preferably the creation of the bubbles is accompanied by the formation of small melt zones that enclose the bubbles. Melt zone formation can be facilitated by preheating the reactor core prior to and/or during reactor operation. Due to the phenomena of cavitation, the applied energy causes the newly formed bubbles to oscillate, undergoing a period of expansion followed by a period of bubble collapse. The velocity of the spherically converging material associated with the cavitation cycle, often times reaching high Mach numbers, is sufficient to achieve a density and temperature in excess of that required to drive the desired nuclear reaction.

In at least one embodiment, the CNR is contained within a high pressure enclosure which is fabricated from a material capable of withstanding the desired reactor operating temperature. Preferably the high pressure enclosure is encased in one or more layers of thermal insulation, followed by an outer enclosure. Coolant, fed through one or more nozzles, impinge upon the outer surface of the reactor to provide heat removal, typically resulting in the generation of vapor or steam. The vapor or steam is, in turn, coupled to an energy conversion system such as a steam turbine, heater radiator, steam piston motor, heat exchanger, or other heat utilization device. Material selection for the CNR, and more particularly reactant selection, is primarily driven by the desired nuclear reaction. In general, a host material is selected which preferably exhibits high thermal conductivity, high density, and high sound speed, thus promoting high shock wave velocities and the attendant generation of high temperatures. In order to achieve the intended reaction, the reactants are loaded into the host material using any of a variety of well known metallurgical techniques. Preferably the CNR, once loaded, includes a reactant concentration gradient wherein the lowest reactant concentration is at the exterior surface and the highest reactant concentration is at the center of the reactor. A consequence of a reactant concentration gradient is that the majority of reactions will take place at a distance from the exterior surface of the reactor. Since the reaction sites can become mechanically weakened during reactor operation due to repetitive stress cycling, minimizing cavitation and reactions near the reactor surface results in a reactor with a relatively strong outer shell, thereby extending reactor operational life. Additionally, reactor life can be extended by operating the reactor above the re-crystallization temperature of the host material, thus allowing defects at the reaction sites to continuously heal.

A variety of different nuclear reactions can be driven within the cavitation sites of the CNR. The possible nuclear reactions include fusion, fission, spallation, and neutron stripping. For example, fusion reactions can be forced to occur within the solid CNR using deuterium, tritium, and/or lithium as reactants. Although the fusion reactants can be loaded into a variety of host materials, preferably the host material is a metal of high acoustic impedance. Alternately, the host material can be selected on the basis of sound speed, cost, and its ability to absorb hydrogen. In another embodiment, photo- dissociation fission reactions are forced to occur within heavy atoms such as uranium or plutonium. In another embodiment, neutron stripping reactions are forced to take place within the CNR between heavy isotopes, preferably those with a large thermal neutron capture cross-section, and light isotopes such as deuterium, tritium, and lithium. Examples of suitable heavy isotopes include gadolinium, cadmium, and europium. A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic illustration of a reactor system in accordance with the invention;

Fig. 2 is an illustration of a reactor core assembly; Fig. 3 is a cross-sectional view of the reactor core assembly shown in Fig. 2; Fig. 4 is an illustration of the reactor core assembly shown in Figs. 2 and 3 combined with a spherical reactor assembly;

Fig. 5 is an illustration of a reactor core assembly with a spherical fuel portion located at approximately the center of the assembly;

Fig. 6 is an illustration of the reactor core assembly shown in Fig. 5 combined with a spherical reactor assembly;

Fig. 7 is a cross-sectional view of the reactor assembly shown in Fig. 4; Fig. 8 is a cross-sectional view of the coupling between the driver assembly and the CNR; Fig. 9 is a cross-sectional view of an alternate means of coupling the driver assembly and the CNR; and

Fig. 10 is a cross-sectional view of another alternate means of coupling the driver assembly and the CNR.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS Fig. 1 is a schematic illustration of a nuclear reactor system 100 in accordance with at least one embodiment of the invention. At the core of system 100 is a cavitation nuclear reactor (hereafter, CNR) 101 within which the desired reaction, e.g., fusion reaction, takes place. As shown, extensions 103, integral to CNR 101, are used to couple acoustic energy from a pair of driver assemblies 105 into the reactor. It is understood that although two driver assemblies 105 are shown, both fewer and greater numbers of drivers can be coupled to the CNR, the principal benefit of increasing the number of drivers being the amount of additional energy that can be coupled into the reactor. The use of multiple drivers also enables the excitement of more complete resonance modes, thereby taking advantage of the constructive interference as well as beating of the resonant energy. Driver assemblies 105 also provide a convenient method for supporting CNR 101 while providing minimal damping of the acoustic characteristics of the CNR thus insuring that the CNR acts as an under-damped resonator. According to the invention, acoustic energy is coupled to CNR 101 through driver assemblies 105. As a result of the coupled acoustic energy, a pressure intensity pattern develops within CNR 101. The exact characteristics of the intensity pattern are dependent upon, among other factors, the size, shape, and material comprising CNR 101; the number, design, and locations of driver assemblies 105; the amplitude, frequency, and waveform of the coupled energy; and the mechanical and thermal history of CNR 101 (e.g., how long CNR 101 has been in operation, the locations of previously formed cavities, etc.). An example of a pressure intensity pattern that can be created within the reactor is one in which pressure intensity anti-nodes exist throughout the reactor. These anti-nodes occur where there is a convergence of acoustic energy (i.e., basically the phenomena of three-dimensional constructive interference). Alternately, the pressure intensity pattern formed within the reactor can be such that the strongest pressure anti-node will exist at the center of the CNR with the intensity of the pressure anti -nodes decreasing with increasing distance from the center of the reactor. As a result of the intensity pattern, at numerous locations within CNR 101 the energy is high enough to form small cavities or bubbles within the solid material, the bubbles typically being between about 0.1 and about 100 micrometers in diameter. Preferably the intensity pattern also causes localized heating and the creation of small melt zones, the bubbles being formed within the melt zones, thus taking advantage of the differences between liquids and solids in their respective abilities to support shear stress. Due to the cavitation phenomena, the applied acoustic energy causes the newly formed bubbles to oscillate. During oscillation the bubbles first expand and then collapse. In the preferred embodiment of the invention, the spherically converging material associated with the cavitation process attains high Mach number velocities, thus leading to a density and temperature in excess of that required to drive the desired nuclear reaction. Furthermore, in the preferred embodiment the bubbles or cavities undergo repetitive cavitation cycles. It should be understood, however, that under the appropriate conditions, e.g., sufficient input energy, appropriate fuel, etc., a single bubble cavitation cycle is sufficient to cause the desired nuclear reaction to take place within that bubble.

Vapor Generation System

As shown in Fig. 1, CNR 101 is held within a high pressure enclosure 107. At least one nozzle 109, and preferably a plurality of nozzles 109, spray coolant 111, preferably in the form of a mist, onto CNR 101. Nozzle or nozzles 109 can be replaced by any means suitable for directing coolant 111 onto CNR 101. Preferably water is used as the coolant. The coolant impinging upon the outer surface of CNR 101 serves two purposes. First, coolant 111 maintains the reactor at the desired operating temperature. The rate of cooling primarily depends upon the number of nozzles 109, the heat capacity of coolant 111, and the flow rate of coolant 111 from each nozzle 109. Second, as coolant 111 impinges upon the hot outer surface of CNR 101, a high pressure fluid (e.g., vapor or liquid) is generated, for example through the vaporization of the coolant. This high pressure fluid is contained within enclosure 107. If coolant 111 is water, as in the preferred embodiment, steam is generated by the vaporization of the coolant. Nozzles 109 are coupled to a coolant source 113 via high pressure lines

115. Preferably surrounding enclosure 107 is thermal insulation 117 and a second, outer enclosure 119. One or more high pressure fluid transport pipes 121, preferably thermally insulated, penetrate enclosures 107 and 119 and thermal insulation 117. transport pipes 121 being used to transport the high pressure and high temperature fluid (e.g., liquid, vapor, or steam) to the intended energy conversion system 123. Suitable energy conversion systems include, but are not limited to, steam turbines, heater radiators, steam piston motors, or other heat exchangers. The material used for thermal insulation 117 as well as the materials used for high pressure enclosure 107 and outer enclosure 119 are primarily driven by the desired reactor operating temperature. The desired reactor operating temperature is, in turn, primarily driven by the type of energy conversion system 123 to be coupled to the vapor generation system as well as the melting temperature of the reactor host material. In a typical application, CNR 101 operates at an extremely high temperature, thus requiring enclosure 107 to be fabricated from a high melting point material such as tungsten; thermal insulation 117 to be fabricated from a refractory material; and outer enclosure 119 to be fabricated from a suitably high melting point material such as titanium. It is understood that other material combinations can also be used with the present invention.

At the bottom of enclosure 107 are one or more detectors 124 which monitor the accumulation of liquid coolant within the enclosure. If the liquid level surpasses a predetermined level, a portion of the liquid can be removed via one or more exit ports 125. Preferably the predetermined level is calculated to prevent the accumulated coolant from rising to the level of CNR 101 as such contact would alter the resonance characteristics of the reactor. In the preferred embodiment of the invention, a solenoid controlled valve 126 is coupled to exit port 125, thus allowing a system controller 127 to automatically monitor liquid build-up with detector 124 and drain liquid via port 125 as necessary.

Reactor Design

As illustrated in Fig. 1, and shown more thoroughly in Figs. 2-4, the preferred embodiment of CNR 101 is comprised of an inner reactor core assembly 200 and an outer spherical reactor portion 401. Within core assembly 200, preferably the fuel is concentrated within a fuel portion 201 which is interposed between extension portions 103. In the preferred embodiment the overall length of assembly 200 is approximately 35 centimeters with each extension being approximately 15 centimeters in length and with fuel portion 201 being approximately 5 centimeters in length. The diameter of core assembly 200 is approximately 5 centimeters. Preferably fuel portion 201 is electron beam welded to extensions 103 at joint 203. If electron beam welding is used, preferably a machining operation such as a turning or grinding operation is performed after the welding operation in order to clean up the weld slag. It is understood that other techniques, such as diffusion bonding or spin welding, can be used to couple fuel portion 201 to extensions 103.

Core assembly 200 is inserted into a hole bored within the approximately 20 centimeter diameter spherical reactor portion 401. The hole can be bored by a drilling operation, preferably by a reaming operation, and more preferably by a honing operation in order to achieve a good surface finish on the bored hole. More preferably still, the interior surface of the hole and the exterior surface of core assembly 200 is polished prior to assembly.

As shown in Fig. 4, fuel portion 201 is located approximately at the center of spherical portion 401. Preferably joints 403 between assembly 200 and spherical reactor portion 401 are electron beam welded under vacuum conditions. The resultant welds are stress relieved. Additionally, preferably the welds provide a radial fillet thus reducing the tendency for fatigue failures at that juncture.

In the preferred embodiment of the invention, after the assembly of CNR 101, the various portions of the assembly are diffusion bonded together, for example using a hot isostatic press or HIP process. If diffusion bonding is used, preferably fuel portion 201 is diffusion bonded to extensions 103 prior to diffusion bonding core assembly 200 to spherical reactor portion 401. Prior to the HIP process, the surfaces to be bonded undergo a chemical cleaning process. As a result of the HIP process, the completed reactor is almost identical in terms of the mechanical characteristics to a reactor fabricated from a single piece of material.

The multi-component design of CNR 101 offers many advantages over other reactor manufacturing approaches. First, it is a very straightforward method of manufacturing. Second, it allows the fuel material to be easily concentrated within the center fuel portion of the reactor. Third, it provides a simple means of controlling and/or varying the acoustic impedance of the reactor. For example, reactor extensions 103 and spherical reactor portion 401 can be fabricated from a material with a different acoustic impedance, preferably a higher acoustic impedance, than the material used for the host material of the fuel portion of the reactor. Note that if different acoustic impedance materials are used, it is generally preferred to form the fuel portion into a sphere as shown in Figs. 5 and 6. As illustrated, in this embodiment reactor core assembly 500 is fabricated from an approximately spherical fuel portion 501 and cupped reactor extensions 503. Fig. 7 is a cross-sectional view of the preferred embodiment of the reactor assembly shown in Fig. 4. As shown, each reactor extension 103 includes a threaded hole 701, thus providing a simple means of coupling driver assemblies 105 to CNR 101. In addition, the use of threaded holes 701 allow driver assemblies 105 to communicate both tensile and compressive forces to the reactor. Extending axially towards the center of the reactor assembly from threaded holes 701 are a pair of small diameter holes 703. Holes 703 provide a controlled failure mechanism for CNR 101. Specifically, if the reactor begins to fail, for example due to the temperature of the reactor becoming too high, the reactor will fail along the reactor's axis, the failure occurring in a relatively controlled fashion. In the preferred embodiment of the invention, the reactor is operated in a mode designed to achieve a gradient in the intensity of the pressure anti-nodes with the intensity of the pressure anti-nodes decreasing with increasing distance from the center of the reactor. Given that the material around individual cavities becomes mechanically weakened due to repetitive stress cycling, a benefit of this approach is to provide a relatively strong outer shell in which the mechanical stresses are at a minimum, thereby keeping the reactor intact for an extended period of time. In contrast, a reactor that is not operated in this mode will form cavities at or near the surface of the reactor, leading to relatively rapid reactor failure primarily due to material fatigue fractures similar to those observed in materials subjected to ultrasonic radiation for extended periods of time. There are several different ways to achieve a gradient reactor configuration. For example, in the preferred embodiment the reactor is driven at a resonant frequency, or an integer multiple thereof, resulting in a gradient in the intensity of the pressure anti-nodes. Therefore in a spherical reactor driven with a single resonant frequency that is much higher than the fundamental frequency, the maximum pressure anti-node intensity is at the center of the reactor and decreases with increasing distance from the center of the reactor. In an alternate embodiment, the gradient can be achieved in the number, rather than the intensity, of the pressure anti-nodes. In this type of gradient reactor the highest density of pressure anti-nodes is located at the center of the reactor, with the density decreasing with increasing distance from the center of the reactor. In another alternate embodiment, the composition of the reactor can be varied in such a manner as to achieve a radial gradient in cavity formation density. For example, a fuel material having a low acoustic impedance can be loaded into a host material with a high acoustic impedance such that the fuel material particle density is highest at the center of the reactor, decreasing with increasing distance from the center of the reactor. In the preferred embodiment, it is relatively straightforward to achieve this effect as fuel portion 201 can easily be fabricated using fuel particles with a lower acoustic impedance material than the host material comprising extensions 103 and spherical portion 401. Although the material selected for CNR 101 depends upon the desired nuclear reaction, preferably the host material has a high thermal conductivity, a high sound speed, and a high density, thus promoting high shock wave velocities and the attendant generation of high temperatures. In addition, preferably the host material has a higher melting temperature than the fuel material, and more preferably that the melting temperature of the host material is greater than the vaporization temperature of the fuel material. As a consequence of these requirements, preferably the host material is a metal although other materials, such as ceramics, can also be used as the host material. More preferably, the host material is comprised of tungsten, thus allowing the reactor to run at extremely high temperatures. Other suitable host materials for CNR 101 include titanium, gadolinium, cadmium, molybdenum, rhenium, osmium, hafnium, iridium, niobium, ruthenium, uranium, or tantalum.

It is understood that the present reactor system can be used to drive fusion reactions, fission reactions, spallation reactions, and neutron stripping reactions. In order to accomplish the desired nuclear reactions, the proper reactants must be loaded into the host material of CNR 101, preferably loaded only into fuel portion 201. In the preferred embodiment, deuterium, lithium, and tritium reactants are loaded into the host material, typically in the form of lithium and deuterium or lithium and tritium. Other combinations such as deuterium and tritium or deuterium alone can also be used. Alternately, if the reactor is used for neutron stripping reactions, preferably the reactants are selected from light isotopes such as deuterium, tritium, and lithium and heavy isotopes with a large thermal neutron capture cross-section such as gadolinium, cadmium, and europium. Other suitable high neutron cross-section isotopes include boron, samarium, dysprosium, iridium, and mercury. In selecting materials for the reactor of the present invention, it is understood that the cavitation phenomenon benefits from the use of heavy ions. Specifically, during the period of bubble collapse within the cavitation cycle, the walls of the bubble are inwardly accelerating at approximately the same rate regardless of whether the bubble walls are comprised of heavy ions, light ions, or both. This is the result of the heavy ions, e.g., tungsten, and the light ions, e.g., deuterium, having approximately the same charge to mass ratio and therefore approximately the same acceleration profiles. At the end of the collapse period, the material comprising the opposing bubble walls collides with approximately the same velocity, resulting in the formation of a plasma in which the temperature is the average kinetic energy of the colliding material. Since kinetic energy scales linearly with mass, the effective temperature of a heavy ion is much higher than that of a light ion, and therefore the temperature of a plasma comprised of heavy ions will be much higher than that of a plasma comprised of light ions. Accordingly, by using a host material comprised of a high mass material such as gadolinium, tungsten, osmium, iridium, or uranium, the temperature of the plasma formed within the collapsing bubbles is higher than would otherwise be achievable, leading to improved nuclear reaction capabilities.

Given that the kinetic energy of an atom is proportional to the square of its velocity, the sound speed of the host material is even more important than its mass. Thus while doubling the mass of the host can lead to up to twice the plasma temperature, doubling the terminal collapse velocity can lead to up to four times the plasma temperature. Therefore high sound speed host materials such as beryllium, titanium, tungsten, and uranium are desirable. Of these, tungsten and uranium are ideal candidates as they have both a high mass and a high sound speed. Additionally, and in accordance with the invention, both the surface tension and the vapor pressure of the host material are considered during the host material selection process. A large surface tension leads to an improvement in the sphericity of the collapsing bubble and hence improved bubble wall acceleration. A reduction in the vapor pressure helps to achieve a smaller diameter in the final, collapsed bubble. Since the collapsing bubble walls are undergoing acceleration, the further a cavity collapses, the greater the peak velocity achieved by the atoms. Hence a reduced vapor pressure leads to a higher plasma temperature in the collapsed cavity. Typically, materials that exhibit a low vapor pressure also exhibit a high surface tension thus providing dual benefits to the present invention.

A variety of well known metallurgical techniques can be used to load the reactants, thus only brief descriptions are provided herein. Powder metallurgy is one technique by which the desired reactants can be loaded into the host material comprising the CNR. For example, a powder of a reactant (e.g., TiD, LiD, LiDT, TiDT, GdDT, or GdD₂) can be mixed with a powder of the parent lattice (e.g., Ti, W, Gd, Os, or Mo) to form a mixture of the desired concentration which can then be pressed into the desired shape, e.g., fuel portion 201. The compressed structure is then sintered. Preferably the fuel powders have diameters in the range of 1 to 100 micrometers, and more preferably in the range of 1 to 10 micrometers. The host powders have diameters as small as economically feasible with nanophase powders being prefeπed. Among other advantages, powder metallurgy provides an easy technique for controlling both the concentration and placement of the reactants within the parent lattice of the CNR. Another technique for loading reactants is to bubble the desired reactant, for example deuterium, into the melted host material. After the host material is loaded with the reactant, it is either cast or drawn into the desired shape. If necessary, the cast or drawn material can be further shaped by machining.

Yet another technique for loading reactants is to expose the host material to a high pressure gas of the desired reactant in a furnace, e.g., a deuterium furnace. For example, a titanium or tungsten host material can be exposed to high pressure deuterium using this technique. Alternately, a source of a high pressure gas of deuterium or other reactant can be attached to a host material which is then placed within a furnace. The reactant, e.g., deuterium, will flow through the metal lattice, particularly if the host material is in the form of a drawn bar. The host material can be machined into the desired reactor shape before or after loading. Preferably gas reactant loading is improved by loading at a high temperature or by using a glow discharge to ionize the reactant and break-up the molecules into free atoms that can more easily penetrate into the metal lattice. Yet other techniques for loading reactants are electrolysis and cavitation.

By performing electrolysis and/or cavitation on the exterior surface of the host material, the reactants can be driven into the interior. Migration of the reactants through the host material typically follows imperfections in the grain structure. Although the preferred embodiment of the invention concentrates the fuel into the center of the spherical reactor by placing the fuel within fuel portion 201, other techniques for achieving a gradient can be used. For example, once the reactant is loaded into the host material, the loaded reactor can be placed in a vacuum oven or in an oven utilizing a high pressure inert gas such as argon. Inert gases do not readily penetrate into the interior of the reactor. The purpose of this heating step is to allow certain reactant atoms, e.g., deuterium and tritium, to diffuse out of the reactor. Since the reactant atoms will diffuse first from the outermost layer of the reactor and last from the center of the reactor, the reactor will develop a reactant concentration gradient wherein the lowest reactant concentration is at the exterior surface and the highest reactant concentration is at the center of the reactor. As a consequence of this additional step, a gradient reactor is formed.

After completion of the loading of the reactant into the host material, preferably CNR 101 is conditioned, thereby making it easier to initiate the cavitation process during full-scale operation of the reactor without the use of an external heat source. To condition the reactor, cavities are formed near the fuel or reactant particles within fuel portion 201 of core assembly 200, the cavities remaining in place after completion of the cavity forming step. Once the cavities are formed, acoustic energy applied to the reactor during normal reactor operation will be preferentially focused at the cavity sites, thus leading to a more efficient cavitation process.

One approach for forming the desired conditioning cavities within the reactor is to heat the reactor to a temperature above the melting temperature of the reactants, but below the melting temperature of the host material, and then inject acoustic energy into the reactor. Once the cavities are formed, they remain in place even though the application of acoustic energy and heat to the reactor is discontinued. Although during the heating step the reactor is preferably heated to a temperature above the melting temperature of the reactants, it is understood that the reactor can be heated to a lower temperature if sufficient acoustic energy is injected into the reactor.

Another approach to form the conditioning cavities is to heat the material to a temperature above the vaporization or dissociation temperature of the fuel. As a result of this heating step, the gas evolves and forms cavities. Driver Design

As previously noted, the cavitation phenomenon is the result of energy, preferably in the form of acoustic energy, being driven into the reactor and forming a pressure intensity pattern. The pressure intensity pattern creates bubbles within the reactor, the bubbles undergoing alternating periods of expansion and collapse. It is during the period of collapse that the spherically converging material achieves the density and temperatures required to drive the desired reactions.

In essence the pressure intensity pattern is due to the interference pattern set up within the reactor between the acoustic energy transmitted into the reactor from each of the driver assemblies and from the acoustic energy reflected from the various reactor free surfaces, e.g., exterior surfaces. Therefore the pattern is dependent upon the number, type, acoustic frequency, and coupling location of the driver assemblies as well as the composition, size, and shape of the CNR.

Regardless of the design of the CNR, the reactor will have one or more resonant frequencies. The fundamental resonant frequency characteristics of the reactor can be estimated using the sound speed of the material comprising the CNR as well as the dimensions of the CNR. Thus, for example, a reactor designed in accordance with the preferred embodiment of the present invention and comprised of titanium will have a fundamental resonant frequency of about 13 kHz. After a fundamental resonant frequency is estimated, an initial driver frequency is selected on the basis of this estimate, utilizing either a fundamental resonant frequency or some integer multiple thereof, assuming resonant excitation is desired as in the preferred embodiment. The driving frequency can then be fine tuned by monitoring some aspect of the reactor, such as the amount of acoustic or white noise generated by the collapsing cavities within the reactor, and adjusting the driving frequency to maximize the selected characteristic. Alternately, the fundamental frequency or frequencies of the reactor can be experimentally determined using techniques well known by those of skill in the art.

Although the desired frequency of the driver assemblies is given by the resonance of the reactor, assuming a resonant reactor design as in the prefeπed embodiment, the waveform of the incident driver acoustic energy is less limited. For example, the waveform of the incident energy can be sinusoidal in nature, matching the essentially sinusoidal nature of the reactor's response to the injected acoustic energy. Preferably, however, the acoustic energy injected into the reactor by the driver assemblies is in the form of a series of impulses timed to coincide with the sinusoidal waveform of the reactor, thus leading to higher bubble implosion velocities. More preferably, the injected acoustic energy utilizes a square waveform, thereby providing the benefits of a sharp rising edge, such as with an impulse, while allowing a wider range of commercial drivers to be used.

The present invention can utilize any of a variety of acoustic drivers. Additionally, although in the prefeπed embodiment a pair of opposed ultrasonic drivers is used, either fewer or greater numbers of drivers can be used. For example in the present system, two more drivers can be coupled to the reactor, the new drivers mounted orthogonally to, and within the same plane as, the present drivers. The benefit of additional drivers is that it is easier to increase the total injected power, and thus the intensity and numbers of collapsing bubbles. Additionally, by coupling more drivers to the reactor, it is easier to maintain the uniformity of the pressure driving the bubbles, thus helping to maintain the sphericity of the collapsing bubble. By improving both the sphericity of the collapse and the intensity of the collapse, the plasma temperature within the collapsing bubble is increased, thereby aiding the reaction process.

In the prefeπed embodiment of the invention, driver assemblies 105 utilize transducers to convert electrical energy into acoustic energy. Preferably piezo-electric crystals 129 are used although a magnetostrictive device can also be used within the driver assembly. As magnetostrictive drivers deliver a greater amount of energy but at a lower frequency than piezo-electric crystals, they are ideally suited for larger reactors which have a lower resonant frequency but require greater driver energy.

Driver assemblies 105 can utilize a single piezo-electric crystal per assembly. In the prefeπed embodiment, however, each assembly uses a pair of crystals as shown. By utilizing a pair of piezo-electric crystals, the adjacent surfaces of the two crystals can be of the same polarity, thereby minimizing potential grounding problems. Each driver assembly 105 includes an acoustic wave guide 131 and an acoustic balancing mass 133.

As previously noted, preferably resonant excitation is used. Accordingly, in order to achieve strong resonance, the lengths of acoustic wave guide 131 and acoustic balancing mass 133 are selected to be a harmonic of the desired drive frequency. Thus, for example, assuming a titanium host material with a resonant frequency of approximately 13 kHz, in the prefeπed embodiment piezo-electric crystals 129 are designed to operate at approximately 13 kHz, or an integer multiple thereof, and the lengths of guide 131 and mass 133 are multiples of the fundamental resonance frequency.

Preferably the frequency of crystals 129 is adjustable over a relatively large range, thus allowing the frequency to be fine tuned. Furthermore, preferably the frequency of crystals 129 can be periodically altered to at least a small degree, e.g., ± 10 percent of the driving frequency, as required to change the acoustic interference pattern and to insure that the cavities within the reactor are formed at varying locations. By varying the locations within the reactor where cavitation occurs, the reactor will operate for a longer period of time prior to the occuπence of a mechanically induced failure. Varying the cavity locations also allows regions in the reactor core containing unused fuel to be excited, thereby providing efficient fuel usage. It should be noted, however, that due to the continual formation and collapse of cavities within the reactor, the frequency characteristics of the reactor are continually changing on microscopic levels, thus automatically varying the locations of cavitation within the reactor and reducing the need to vary the driver frequency.

In order to achieve the desired high reactor temperatures without overheating piezo-electric crystals 129, preferably driver assemblies 105 are actively cooled. In the prefeπed embodiment, each driver assembly 105 includes at least one, and preferably a plurality, of nozzles 135. Nozzles 135 are coupled via lines 137 to a driver coolant system 139. Each driver assembly 105 can utilize a separate coolant system 139, or a single coolant system can be used for all of the drivers. Driver coolant systems 139 typically are separate from coolant system 113 which is used to produce vapor. System 139 can, however, be used to preheat coolant for system 113. Depending upon the desired transducer operating temperature, nozzles 135 can either direct cooled gas, liquid coolant, or a mist of gas and coolant at acoustic wave guide 131. Preferably drivers 105 also include a liquid temperature monitor 141 and a drain system 143. The temperature of the coolant, for example as determined by monitor 141, can provide a feedback signal to a processor 145 which allows the coolant flow rate to be modulated in order to achieve the optimum transducer operating temperature. It is understood that liquid temperature monitor 141 can be replaced with other sensing means that provide a similar feedback signal. For example, as opposed to monitoring the temperature of the coolant, one or more IR sensors can be used to directly monitor the temperature of acoustic wave guide 131. Driver assemblies 105 can be coupled to CNR 101 using any of a variety of techniques. There are several design constraints, however, placed on the driver coupling. First, the coupling must be sealed to enclosure 107 in such a manner as to maintain the high pressure characteristics of the enclosure. Second, the coupling must allow the efficient coupling of energy from acoustic wave guide 131 to reactor extensions 103. Third, to the extent possible, it is beneficial to thermally separate the high temperature reactor environment from the lower temperature driver assembly.

Fig. 8 is a cross-sectional view of one technique of coupling driver assembly 105 to CNR 101. A coupling member 801 is threadably coupled to threaded hole 701 in reactor extension 103. A flanged surface of coupling member 801 is bolted to enclosure 107. A seal, such as a copper seal (not shown), maintains the pressure integrity of enclosure 107. If required, a portion 803 of coupling member 801 can be fabricated to be thin enough to provide additional flexure, thus insuring a relatively efficient means of coupling the acoustic energy from the driver into the reactor. A rod 805 with a flanged surface 807 mates to the flanged surface of coupling member 801, the two flanged portions being bolted together. Preferably interposed between the two flanged surfaces is a disk 809 that is fabricated from a suitable low thermal conductivity material, such as a ceramic. Disk 809 helps to thermally isolate the driver from the reactor. Alternately, rod 805 can be fabricated from a machineable ceramic. For some applications, the use of a thermally insulating material (e.g., disk 809) eliminates the need for a driver coolant system.

In this embodiment, acoustic wave guide 131, piezo-electric crystals 129, and acoustic balancing mass 133 are coupled together using rod 805. Specifically, rod 805 extends through each of these driver components, the assembly being held together with a nut 811. In this embodiment additional low thermal conductivity washers can be used to further isolate piezo-electric crystals 129 from the high temperature reactor. For example, another ceramic washer can be interposed between the pair of piezo-electric crystals and the end surface of acoustic wave guide 131 at a location 813. Alternately, additional ceramic washers can be located at one or more positions 815 along the length ofacoustic wave guide 131.

Fig. 9 is a cross-sectional view of an alternate technique of coupling driver assembly 105 to CNR 101. As in the prior embodiment, coupling member 801 is threadably coupled to hole 701 and bolted to enclosure 107. In this embodiment, however, a threaded rod 901 is directly threaded into coupling member 801. Preferably disk 809 and/or ceramic washers 903 are used to isolate piezo-electric crystals 129 from the high temperature reactor.

Fig. 10 is a cross-sectional view of another alternate technique of coupling driver assembly 105 to CNR 101. In contrast to the prior embodiments, no coupling member is attached to enclosure 107 and interposed between the driver assembly and the reactor. Rather, a threaded rod 1001 is directly threaded into hole 701 of reactor extension 103. Preferably a pressure sealing member 1003 is interposed between extension 103 and enclosure 107. More preferably a second pressure sealing member 1005, in addition to pressure sealing member 1003, is interposed between the driver assembly and enclosure 107. As in the prior embodiments, preferably disk 809 and/or ceramic washers 903 are used to isolate piezo-electric crystals 129 from the high temperature reactor.

As will be understood by those familiar with the art, the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For example, it is understood that the present composite reactor assembly can be used in a CNR that does not utilize a high pressure enclosure and a vapor generation system. Similarly, the present invention is not limited to CNR systems utilizing driver assemblies as shown. Accordingly, the disclosures and descriptions herein are intended to be illustrative, but not limiting, of the scope of the invention which is set forth in the following claims.

Claims

WHAT IS CLAIMED IS:

1. A cavitation nuclear reactor, comprising: a reactor core assembly, wherein during operation said reactor core assembly is comprised of a solid material interspersed by a plurality of cavitation bubbles, said reactor core assembly further comprising: a first reactor portion; and a second reactor portion, wherein a first segment of said second reactor portion is within said first reactor portion and a second segment of said second reactor portion extends outwardly from said first reactor portion; and an acoustic driver coupled to said second segment of said second reactor portion for injecting acoustic energy into said reactor core assembly.

2. The cavitation nuclear reactor of claim 1 , wherein said injected acoustic energy forms a pressure density pattern comprising a plurality of pressure intensity anti -nodes, wherein said plurality of cavitation bubbles form at a portion of said plurality of pressure intensity anti-nodes, and wherein said plurality of cavitation bubbles undergo at least one complete cavitation cycle comprising a period of bubble expansion and a period of bubble collapse.

3. The cavitation nuclear reactor of claim 2, wherein a plurality of nuclear reactions occur within a portion of said plurality of cavitation bubbles during said cavitation cycle.

4. The cavitation nuclear reactor of claim 1 , wherein said first reactor portion is substantially spherical.

5. The cavitation nuclear reactor of claim 1, wherein said second reactor portion is substantially cylindrical.

6. The cavitation nuclear reactor of claim 1 , wherein said first reactor portion is comprised of a host material, said first segment of said second reactor portion is comprised of a fuel material interspersed within said host material, and said second segment of said second reactor portion is comprised of said host material.

7. The cavitation nuclear reactor of claim 6, wherein a first melting temperature associated with said host material is greater than a second melting temperature associated with said fuel material.

8. The cavitation nuclear reactor of claim 6, wherein a melting temperature associated with said host material is greater than a vaporization temperature associated with said fuel material.

9. The cavitation nuclear reactor of claim 6, wherein said host material is selected from the group of materials consisting of titanium, tungsten, gadolinium, cadmium, molybdenum, rhenium, osmium, hafnium, iridium, niobium, ruthenium, and tantalum.

10. The cavitation nuclear reactor of claim 6, wherein said fuel material is selected from the group of materials consisting of deuterium, tritium, and lithium.

11. The cavitation nuclear reactor of claim 1 , wherein said first segment of said second reactor portion is electron beam welded to said second segment of said second reactor portion.

12. The cavitation nuclear reactor of claim 1 , wherein said first segment of said second reactor portion is diffusion bonded to said second segment of said second reactor portion.

13. The cavitation nuclear reactor of claim 1 , wherein said first reactor portion is electron beam welded to said second reactor portion.

14. The cavitation nuclear reactor of claim 1 , wherein said first reactor portion is diffusion bonded to said second reactor portion.

15. The cavitation nuclear reactor of claim 1 , wherein said first reactor portion is diffusion bonded to said second reactor portion using a HIP process.

16. The cavitation nuclear reactor of claim 1, wherein an interface between said first segment of said second reactor portion and said second segment of said second reactor portion is substantially planar.

17. The cavitation nuclear reactor of claim 1 , said second reactor portion further comprising a third segment extending outwardly from said first reactor portion.

18. The cavitation nuclear reactor of claim 17, wherein said first segment of said second reactor portion is substantially spherical.

19. The cavitation nuclear reactor of claim 18, wherein an end surface of said second segment of said second reactor portion is concave, said second segment concave surface cupping said substantially spherical first segment of said second reactor portion, and wherein an end surface of said third segment of said second reactor portion is concave, said third segment concave surface cupping said substantially spherical first segment of said second reactor portion.

20. The cavitation nuclear reactor of claim 1 , wherein said acoustic driver is threadably coupled to said second segment of said second reactor portion.

21. The cavitation nuclear reactor of claim 1 , wherein a first acoustic impedance coπesponding to said first reactor portion and to said second segment of said second reactor portion is different from a second acoustic impedance coπesponding to said first segment of said second reactor portion.

22. The cavitation nuclear reactor of claim 21 , wherein said first acoustic impedance is higher than said second acoustic impedance.

23. A method of fabricating a cavitation nuclear reactor core assembly, said method comprising the steps of: mating a first segment of a first reactor portion to a second segment of said first reactor portion; inserting at least a section of said first reactor portion into a second reactor portion; and joining said first reactor portion to said second reactor portion.

24. The method of claim 23, further comprising the step of welding said first segment of said first reactor portion to said second segment of said first reactor portion, said welding step being performed prior to said inserting step.

25. The method of claim 24, wherein said welding step utilizes electron beam welding.

26. The method of claim 24, further comprising the step of grinding a weld joint produced by said welding step.

27. The method of claim 24, further comprising the step of turning a weld joint produced by said welding step.

28. The method of claim 23, further comprising the step of diffusion bonding said first segment of said first reactor portion to said second segment of said first reactor portion, said diffusion bonding step being performed prior to said inserting step.

29. The method of claim 28, wherein said diffusion bonding is performed with a HIP process.

30. The method of claim 23, further comprising the step of boring a hole within said second reactor portion, said boring step being performed prior to said inserting step.

31. The method of claim 30, wherein said boring step utilizes a drilling operation.

32. The method of claim 30, wherein said boring step utilizes a reaming operation.

33. The method of claim 30, further comprising the steps of polishing an exterior surface of said first reactor portion and an interior surface of said hole within said second reactor portion, said polishing steps being performed prior to said inserting step.

34. The method of claim 23, wherein said joining step utilizes welding.

35. The method of claim 23, wherein said joining step utilizes electron beam welding.

36. The method of claim 23, wherein said joining step utilizes diffusion bonding.

37. The method of claim 36, wherein said diffusion bonding is performed with a HIP process.

38. The method of claim 23, further comprising the step of loading a fuel material into said first segment of said first reactor portion prior to mating said first segment of said first reactor portion to said second segment of said first reactor portion.