WO2001039202A2

WO2001039202A2 - Cavitation nuclear reactor

Info

Publication number: WO2001039202A2
Application number: PCT/US2000/031769
Authority: WO
Inventors: Ross Tessien
Original assignee: Burst Laboratories Inc
Current assignee: Burst Laboratories Inc
Priority date: 1999-11-24
Filing date: 2000-11-17
Publication date: 2001-05-31
Anticipated expiration: 2002-05-24
Also published as: WO2001039202A3; AU3072901A

Abstract

A reactor core includes a host material with a fuel material interspersed therein. Preferably, the host material has a higher acoustic impedance than the fuel material so that acoustic energy applied to the reactor core at or near the resonance frequency of the core is refracted and concentrated in the fuel material thereby causing cavitation within the fuel material, and thereby preferentially forming microcavities in contact with the fuel material. Acoustic energy is applied to the core using various techniques, such as by coupling piezoelectric crystals to the solid core or by driving cavitation in a liquid medium surrounding the core. The temperatures attained within the collapsing microactivities in the core are sufficient to drive numerous reactions, including nuclear reactions, such as deuterium (D) + D reactions. The fuel material preferably includes a fuel component, such as D and/or tritium (T) or a compound including D and/or T. Neutron stripping reactions can also be driven by including a material having a high neutron cross section, e.g., gadolinium, as a component of the fuel and/or the host. Various powder metallurgy techniques are used for loading the host material with the fuel material. The density profile of the fuel material within the host material can be uniform or preferentially greater toward the center of the core.

Description

MATERIALS FOR ENHANCING NUCLEAR CAVITATION REACTIONS AND PROCESSES FOR MAKING THE SAME

BACKGROUND OF THE INVENTION The present invention relates generally to materials for enhancing cavitation reactions and, more particularly to materials for enhancing nuclear cavitation reactions and related nuclear reactions and to processes for making the materials.

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.

What is needed in the art are materials that enhance the reactions obtainable in electrolytic cavitation reactor systems. In particular, what is needed are materials that enhance chemical and nuclear cavitation reactions and processes for making the materials. SUMMARY OF THE INVENTION The present invention provides mateπals, and processes for making the materials, that can be used to enhance vaπous chemical and nuclear cavitation reactions According to the invention, a reactor core includes a host mateπal with a fuel matenal interspersed therein Preferably, the host material has a higher acoustic impedance than the fuel mateπal Acoustic energy applied to the reactor core at or near the resonance ficqucncy of the core is refracted and concentrated in the fuel material thereby causing cavitation withm the fuel mateπal, and thereby preferentially forming microcavities in contact with the fuel material Acoustic energy is applied to the core using various techniques, such as by coupling piezoelectπc crystals to the solid core or by driving cavitation m a liquid medium surrounding the core The temperatures attained withm the collapsing microcavities in the core are sufficient to dnve numerous reactions, including nuclear reactions, such as deutenum (D) + D reactions The fuel mateπal preferably includes a fuel component, such as D and/or tπtium (T) or a compound including D and/or T Neutron stπpping reactions can also be driven by including a mateπal having a high neutron cross section, e g , gadolinium, as a component of the fuel and/or the host Vaπous powder metallurgy techniques can be used for loading the host matenal with the fuel mateπal The density profile of the fuel mateπal within the host matenal can be uniform or preferentially greater toward the center of the core According to an aspect of the invention, a matenal arrangement is provided for enhancing cavitation reactions The mateπal arrangement typically compnses a core including a host mateπal having a first acoustic impedance, and a fuel mateπal interspersed withm the host matenal so as to form the core The fuel mateπal typically has an acoustic impedance that is different, e g , lower, than the acoustic impedance of the host mateπal The mateπal arrangement also typically includes a plurality of microcavities defined withm the core by applying acoustic energy to the core, wherein the microcavities are located in the vicinity of particles of the fuel mateπal In preferred aspects, a plurality of the microcavities are in contact with a plurality of the particles of the fuel mateπal According to another aspect of the invention, a method of making a mateπal arrangement for use in enhancing cavitation reactions is provided The method typically comprises the steps of mixing a first powder compπsing a host matenal with a second powder compπsing a fuel mateπal so as to form a composite powder, compressing the composite powder to form a compressed powder, and sinteπng the compressed powder to form a core mateπal Within the core, the fuel matenal is typically interspersed within the host matenal Furthermore, the fuel matenal typically has a different, e g , lower, acoustic impedance than the host mateπal The method also typically includes the step of applying acoustic energy to the core mateπal so as to form a plurality of microcavities in the vicinity of particles of the fuel material

Reference to the remaining portions of the specification, including the drawings and claims, will realize other features and advantages of the present invention Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are descnbed in detail below with respect to the accompanying drawings In the drawings, like reference numbers indicate identical or functionally similar elements

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic illustration of a nuclear reactor system in accordance with an embodiment of the present invention,

Figure 2 is a schematic illustration of a developing pressure wave intensity pattern within a CNR,

Figure 3 illustrates a reactor system including a chamber filled with a liquid host medium surrounding a reactor structure,

Figure 4 illustrates an example of a dπving circuit of Figure 3, Figure 5 illustrates several CNR configurations, Figure 6 is an illustration of an acoustic driver utilizing one or more streams of particles, Figure 7 is an illustration of an acoustic dnver similar to that shown m

Figure 6 except that the particles from the dπver impact a coupler which determines the impulse shape dπven into the reactor,

Figure 8 is an illustration of an acoustic dπver utilizing a jet of liquid droplets, Figure 9 is an illustration of a microwave dπver,

Figure 10 is an illustration of a CNR that includes an inner core region surrounded by an outer shell, and Figure 11 illustrates a cross section (spherical or cylindrical) of a reactor wherein the density of fuel particles decreases with increasing distance from the center of the reactor according to one embodiment of the present invention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS Figure 1 is a schematic illustration of a reactor system 100 in accordance with an embodiment of the present invention. At the core of system 100 is a solid cavitation reactor (hereinafter, CNR) 101 within which one or more desired reactions, e.g., fusion reactions, chemical reactions, etc., take place. Regardless of the reactor configuration, in this embodiment, CNR 101 is comprised principally of a solid material that may or may not include a means for heat removal (e.g., cooling jacket, heat pipes, etc.). Acoustic energy from a source 103 is coupled to CNR 101 via one or more drivers 105. CNR 101 is held by one or more support members 107 that are preferably designed to have minimal impact on the energy patterns within CNR 101.

According to one embodiment of the invention, acoustic energy is coupled to CNR 101 through drivers 105. As schematically illustrated in Figure 2, the acoustic energy from drivers 105 results in a pressure intensity pattern within CNR 101. The exact characteristics of the intensity pattern are dependent upon, among other factors, the size, shape, and material(s) comprising CNR 101; the number, design, and locations of drivers 105; the frequency of source 103; 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.). 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 solid material, the "bubbles" being between about 0.1 and about 100 micrometers in diameter depending on the material(s) used. 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 collapse process attains supersonic velocities, thus leading to a density and temperature in excess of that required to drive the desired reaction, e.g., the desired nuclear reaction(s) or desired chemical catalytic reaction(s). Temperatures attained are typically between about 10,000°K and about 1 ,000,000°K or greater. Furthermore, in the preferred embodiment, the bubbles or cavities repetitively undergo the expansion/collapse cycles. It should be understood, however, that under the appropriate conditions, e.g., sufficient input energy, appropriate fuel, etc., a single collapse cycle for a given bubble is sufficient to cause the desired reaction to take place within that bubble.

As previously noted, the pressure intensity pattern within the CNR is dependent upon a variety of geometrical, topographic, topological, material and driver characteristics. Accordingly, a variety of pressure intensity patterns can be created within the reactor. For example, in a CNR having a spherical geometry as illustrated in Figure 2, if CNR 201 is driven by a driver 203 at a frequency that is greater than the resonant frequency of the reactor, a pressure intensity pattern develops in which pressure anti- nodes exist throughout the reactor. These anti-nodes, two of which are shown in Figure 2 at a pair of locations 205, occur where there is a convergence of acoustic energy (i.e., basically the phenomena of constructive interference in three dimensions). Alternately, CNR 201 can be coupled to a driver 207 operating at the resonant frequency of the reactor or, at harmonics or sub-harmonics of the resonant frequency. Due to the resonance of the structure, the strongest pressure anti-node will exist at the center of CNR 201 at a location 209 with the intensity of the pressure anti-nodes decreasing with increasing distance from the center of the reactor. In an alternate embodiment, the CNR may be comprised of two or more individual structures such as an inner sphere 211 of one material composition surrounded by an outer shell 213 of another material composition. As in the single structure design previously described, driver 215 can either drive the reactor at the resonant frequency, or some integer multiple thereof, or it can .drive the reactor at a non-resonant frequency. Regardless of whether the reactor is comprised of a single structure or multiple structures, the reactor can be coupled to a single driver or to multiple drivers. Note that if multiple drivers are used they need not operate at the same frequency. For example, in a reactor configuration utilizing multiple structures, e.g., an inner core and one or more outer shells, each driver can be designed to operate at the resonant frequency of one of the individual structures. Further, it should be understood that although spherical reactors are shown in Figure 2, the invention is not so limited. The use of resonant and non-resonant frequencies in both single structure reactors and multi-structure reactors is applicable to both spherical and non-spherical reactors. According to an alternate embodiment of the present invention, the CNR includes a reactor structure 265 in a reactor chamber 255 which is filled, at least in part, with a liquid 260. As shown in Figure 3, nuclear reactor system 250 includes reactor chamber 255 filled with a liquid 260. In one embodiment, chamber 255 is a glass flask, but may be made of any material, such as a metal or ceramic composition, that allows the liquid 260 to be pressurized to a static pressure different from the ambient static pressure. At the center of chamber 255 is a reactor structure 265, within which the desired reactions take place. As shown, reactor structure 265 is a disk, but any other geometry can be used, e.g., spherical, cylindrical, planar, etc., as desired. In a preferred embodiment, liquid 260 is heavy water (including deuterium (D) and/or tritium (T)) and reactor structure 265 is a disk 265 comprised primarily of gadolinium loaded with deuterium, e.g., by electrolysis in a deuterium environment, by heating in a deuterium gas environment, etc. For example, in one embodiment, the gadolinium reactor structure is loaded with deuterium in a D₂0 environment using electrolysis run at 60V using a platinum anode 267. Alternatively, structure 265 can be loaded with fuel using electrolysis and cavitation. It will be apparent that other liquids, and other reactor structures including any other host material loaded with a fuel material, as desired for the desired reaction can be used as will be described in more detail below.

According to this embodiment of the invention, a pulsed acoustic shock wave is introduced into liquid 260 using acoustic hom 270. Driving elements 275 couple acoustic energy to the hom 270. In a prefeπed embodiment, driving _elements_275 include piezoelectric crystals coupled to a driving circuit 280 that applies a voltage waveform to the piezoelectric crystals. The voltage level and driving frequency is set with a waveform generator 285. RF amplifier 290 provides amplification for the generated waveform. In one embodiment, waveform generator 285 is an ETC model M321 waveform generator, and RF amplifier 290 is a ENI model 2100L RF amplifier. An example of a useful driving circuit is shown in Figure 4. Oscilloscope 295 is provided to measure the voltage and current applied to the piezocrystals. Horn 270 is preferably made of titanium, but any other rigid material can be used. Additionally, as shown, thin steel plates 277 can be used to make the connection between the piezocrystal 275 and horn 270. Copper wires 282 support the system while minimizing acoustic damping. When the voltage and current are in phase, the hom will be in resonance. By adjusting the voltage and current, it is possible to fine tune the acoustic horn so that the resonant frequency of the hom matches the resonance of liquid- filled chamber 255.

In the case of a spherical structure, the resonant frequency can be found by dividing the speed of sound in the material by the diameter of the sphere as follows:

where f_r is the resonant frequency, c_m is the speed of sound in the material and d is the diameter of the spherical structure (e.g., spherical chamber, spherical reactor). For a liquid-filled spherical glass chamber, c is the speed of sound in the liquid and d is the diameter of the chamber. Glass will generally cause the actual resonant frequency to be about 10% higher. If the chamber isn't perfectly spherical, the resonance can be measured empirically by fixing a piezocrystal to the side of the chamber to act as a microphone. Observing the voltage across this piezocrystal while driving different frequencies with the driver horn will yield the chamber's resonant frequency. The resonant frequency for a solid sphere can be calculated in the same manner by dividing the speed of sound in the material by the diameter of the sphere. For example, for a two inch diameter titanium sphere, the resonant frequency is about lOOKHz. It will be apparent to one skilled in the art that other geometries and topologies may be used, with appropriate changes in the formulas for determining resonance frequencies as are well known. In the embodiment shown in Figure 3, by applying acoustic energy at the resonant frequency of the liquid-filled chamber, antinodes are preferentially focused in the vicinity of reactor structure 265 so that bubbles in liquid 260 will cavitate and collapse on reactor structure 265. The cavitation and collapse of bubbles on reactor structure 265 will drive acoustic energy into reactor structure 265. It is therefore possible to drive secondary cavitation reactions within reactor structure 265 with the appropriate selection of materials and dimensions of the reactor structure 265 relative to chamber 255, with an antinode distribution dependent upon the material(s) and geometry of reactor structure 265. The cavitating and collapsing bubbles, therefore, act as a driving mechanism for driving acoustic energy into reactor structure 265. As will be appreciated by one skilled in the art, a CNR (e.g., CNR 101,

CNR 201 or reactor structure 265 in a liquid-filled chamber 255) can utilize any of a variety of different shapes. For example, as illustrated in Figure 5, CNR 101 can have a spherical shape 301, a cylindrical shape 303, a conical shape 304, a rectangular shape 305, or an inegular shape 307 A CNR in accordance with the present invention can also utilize one or more hollow portions 309, which penetrate through the reactor core, preferably for use with a liquid coolant thus providing improved cooling and heat extraction Such a structure, with one hole is known in mathematics as a non-simple topology, or, a topology having one handle Examples of such configurations include a cylinder 31 1, a donut-shaped CNR 313, and a rectangular shape 315 It is understood, however, that the shapes shown in Figure 5 are intended to be illustrative only as there are limitless configurations that can be used with the present invention The size and shape of a CNR are primarily determined by the available acoustic energy, the number of drivers, and the type and intensity of the desired reaction

In one embodiment of the invention, the CNR (e g , solid CNR 101 or reactor structure 265) 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 matenal around individual cavities becomes mechanically weakened due to repetitive stress cycling, a benefit of a gradient CNR configuration (hereafter referred to as a GCNR) 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 penod of time In contrast, a reactor that is not operated utilizing the intensity gradient configuration, e g , CNR 201, will form cavities through the volume, including at or near the surface of the reactor, leading to relatively rapid reactor failure pπmaπly due to matenal fatigue fractures similar to those observed m materials subjected to ultrasonic radiation for extended peπods of time

Another benefit of the GCNR design is to provide nuclear radiation shielding Depending upon the type of nuclear reaction that is promoted within the CNR, one or more radioactive by-products can be formed Therefore by dnving nuclear reactions near the center of the reactor and minimizing or eliminating nuclear reactions from occurπng near the reactor's extenor surface, the outer layer of the reactor will provide radiation shielding, the efficiency of which depends upon the radioactive byproducts formed as well as the thickness and mateπal of the outer layer There are several different ways to achieve a gradient reactor configuration For example, and as previously descnbed, the reactor can be dπven (directly or via secondary cavitation effects) at the resonant frequency, or an integer multiple thereof, resulting in a gradient in the intensity of the pressure anti-nodes In this type of reactor, the maximum pressure anti-node intensity is at the center of the reactor and decreases with increasing distance from the center of the reactor. Alternately, the gradient can be achieved in the number, rather than the intensity, of the pressure anti- nodes. In this type of GCNR, the highest density of pressure anti-nodes is located near the center of the reactor, with the density decreasing with increasing distance from the center of the reactor. Alternately, the composition of the reactor can be varied in such a manner as to achieve a GCNR. For example, a fuel material having a low acoustic impedance can be loaded into a host material having a high acoustic impedance such that the fuel material density is highest at the center of the reactor, decreasing with increasing distance from the center of the reactor. For example, Figure 1 1 illustrates a cross section (spherical or cylindrical) of a reactor, according to one embodiment, wherein the density of fuel particles decreases as the distance from the center increases (i.e. increasing r). Alternatively, the density profile of fuel material can be uniform throughout or it can be increasing with increasing distance from the center of the reactor, as desired. Examples of suitable fuel and host material combinations include, but are not limited to, gadolinium deuteride (GdD2) and tungsten (W), lithium deuteride (LiD) and W, LiD and Gd, deuterium (D) and titanium (Ti), and D and lead(Pd).

Although the material selection for the CNR (e.g., CNR 101 or reactor structure 265) depends upon the desired reaction, preferably the host material has a high thermal conductivity and a high sound speed thus promoting high shock wave velocities and the attendant generation of high temperatures. As a consequence of these requirements, preferably the host material is a metal. In the preferred embodiment of the invention, the CNR is fabricated from titanium, tungsten, or gadolinium, although a variety of other host materials can be used such as cadmium, molybdenum, rhenium, and osmium. Additional host materials include europium, tantalum, uranium, boron, iridium, Plutonium, Samarium, Platinum, Thorium, chromium, niobium, ruthenium, dysprosium, mercury, cobalt and gold.

In order to accomplish the desired nuclear reaction, the proper reactants, e.g., nuclear fuels, must be loaded into the CNR (e.g., CNR 101 or reactor structure 265). 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 are loaded into the host lattice structure material comprising the CNR. For example, a powder of a fuel reactant (e.g., LiD, LiT, CdD, CdT, GdD2 or GdT2) can be mixed with a powder of the host material (e.g., Ti, W, Os, Mo, Gd) to form a mixture which can then be pressed into the desired reactor shape, e.g., a sphere, cylinder, disk, etc., using a hot isostatic press, cold isostatic press, or other means. Preferably the powders include particles having diameters in the range of about 1 to about 100 micrometers, more preferably in the range of about .1 to about 1 micrometers, and even more preferably in the range of about 1 to about 100 nanometers, or even smaller. Host material particles are preferably as small as possible, e.g., nanophase powders, but commercially available sizes are adequate and will reduce costs. Among other advantages, powder metallurgy provides an easy technique for controlling both the concentration and placement of the reactants within the host material 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 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. Once loaded, the host material is machined into the desired reactor shape. Preferably 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 rrietal lattice. Yet other techniques for loading reactants include 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. For example, using the arrangement shown in Figure 3, a reactor structure can be loaded with deuterium through electrolysis in a deuterium environment such as heavy water.

Alternatively, or additionally, secondary cavitation effects as described above provide a technique for creating microcavities and loading deuterium into a reactor structure in heavy water. Regardless of the technique used to load the reactant into the host material of the reactor, in one embodiment the loaded reactor is placed in a vacuum oven or in an oven utilizing a high pressure inert gas such as argon. Inert gases, e.g., argon, do not readily penetrate into the interior of the reactor. The purpose of this heating step is to allow the reactant atoms (e.g., D and or T) to diffuse out of the exterior 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 GCNR is formed as previously described, thus providing a reactor in which the mechanical integrity of the exterior surface has been improved, leading to increased reactor life.

As mentioned briefly above, to promote the formation of microcavities within the reactor structure, it is advantageous to use a host material having a high sound speed and a high thermal conductivity. Also, it is advantageous to use. a fuel material having a high sound speed to promote the formation of microcavities in the vicinity of fuel particles and to promote high shock wave velocities in the collapsing cavities. Furthermore, it is advantageous to use a host material having a high acoustic impedance relative to the acoustic impedance of the loaded fuel material. In general, acoustic energy tends to be refracted and concentrated upon crossing a boundary from a high acoustic impedance area to a lower acoustic impedance area.

Acoustic impedance, Z, is defined as follows: Z = v_c * p, where v_c is the speed of, sound in the material and p the density of the material. Thus, it is preferable to use host and fuel materials having high sound speeds, wherein the fuel material has a lower density relative to the host material. In general, the following table illustrates the basic criteria for selecting host and fuel materials based on acoustic impedance and temperature properties as will be discussed in more detail below. Host Material Fuel Material high Z ( high v_c) low Z (high v_c) t melt — 1 vap

Tmeit ^>> Tmeit T vap » ^-^ T J- vap

It is advantageous to have a host material with a melting temperature (Tmeit) that is greater than or substantially equal to the temperature at which the fuel material vaporizes (T_vap) because the cavitation reactions are sensitive to vapor pressure, hence, as the fuel temperature approaches it's vapoπzation temperature (T_vap), the amount of energy released is dramatically reduced. Therefore, if the melting temperature of the host material is higher than the temperature of vapoπzation of the fuel material, the host material will not melt as a result of the released energy. Furthermore, it is advantageous to have a host material with a melting temperature (T_meit) that is much greater than the melting temperature of the fuel material (T_mei_t) to promote the formation of cavities at the locations of the fuel material.

An example of a preferred selection of materials for use in a CNR is a sintered mixture of tungsten as a host material and GdD2 (having a low acoustic impedance relative to tungsten) as a fuel material. Application of acoustic energy will result in the formation of localized regions of fuel particles of low acoustic impedance into which applied acoustic energy is preferentially refracted and concentrated thereby creating pressure antinodes in the vicinity of the fuel particles. Thus, the regions containing GdD2 are typically the first to melt, both due to the concentration of energy in these regions as well as the lower melting temperature of GdD2 as compared to tungsten. The concentration of acoustic energy in the fuel material will cause cavitation within the fuel material. As the cavitation "bubbles" collapse, the materials in the perimeter of the "bubble" are slammed together at supersonic velocities creating enough heat to ignite any fuel particle in the vicinity of the collapse (i.e., within about .1 micrometer to about 10 micrometers of the "bubble" or microcavity). The present invention can utilize any of a variety of acoustic driver arrangements for applying acoustic energy to reactor structures. It is understood, however, that these drivers are not limited to use with the solid core CNRs of the present invention, but can also be used with a conventional CNR utilizing a liquid host medium. Typically the acoustic driver is coupled to a frequency source. The desired frequency depends upon the characteristics of the host material and the desired pressure intensity pattern, although for a metal host preferably the frequency is in the range of 1 kHz to 1 GHz, and more preferably in the range of 100 kHz to 10 MHz. In the preferred embodiment the output frequency of source 103 is adjustable over a relatively large range, thus allowing the frequency to be fine tuned to the characteristics of a specific CNR. Additionally, in the preferred embodiment the frequency output of source 103 is periodically altered to at least a small degree, e.g., ± 10%, thereby changing the acoustic interference pattern and insuring that the locations of the cavities formed within the reactor vary. By varying the locations within the reactor where cavitation occurs, the reactor will operate for a longer period of time prior to the occurrence 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, thus automatically varying the locations of cavitation within the reactor and reducing the need to vary the frequency output of source 103.

As previously noted, a CNR (e.g., CNR 101 or reactor structure 265 in a liquid-filled chamber) has well defined frequency characteristics, e.g., fundamental frequency, that are dependenfupon not only the material(s) comprising the CNR but also the size and shape of the CNR. As above, the fundamental frequency can be estimated using the sound speed of the material(s) comprising the CNR as well as the dimensions of the CNR. An initial driver frequency can then be selected on the basis of this estimate, using either the fundamental or resonant frequency of the CNR or some integer multiple thereof, assuming resonant excitation is desired. Solid metal or ceramic structures are preferred when resonance is desired. 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 of the reactor can be experimentally determined using techniques well known by those of skill in the art. In accordance with the present invention, preferably resonant standing waves are generated within the reactor, thus leading to the formation of large numbers of cavities, e g , on the order of 10⁶/cm³ to 10^I2/cm³ As a consequence, a frequency greater than the fundamental frequency of the CNR is coupled through the dπvers into the CNR A CNR in accordance with the present invention can use one or more drivers It is understood, however, that preferably more than one driver, and typically more than two drivers, are used to generate piessure intensity patterns with a large number of pressure anti-nodes The resonance pattern (l e , pressure intensity pattern) generated within the reactor is dependent on the number of dπvers and, as previously noted, the input frequency or frequencies as well as the frequency characteπstics of the reactor In addition, the resonance pattern is also controlled by the dπver locations and the manner in which the dπvers are coupled to the reactor It has been found that the mounting locations are virtually limitless (e g , opposed dπvers, multiple adjacent dnvers, etc ) although some locations are preferable in order to minimize generating an exceedingly large number of cavitation sites withm a relatively small area of the reactor, thus potentially leading to premature reactor failure If multiple dπvers are used they can be of either the same or different type and of either the same or different frequency In addition, the presently disclosed dπvers can be coupled to solid core reactors other than the sphencal CNR shown in Figure 1 or the cubic CNR shown in Figure 9 Furthermore, the disclosed dπvers can be used to apply acoustic energy to the liquid-filled chamber reactor as shown m Figure 3

In a preferred embodiment, piezoelectnc crystals are used to couple acoustic energy to a CNR For example, as shown in Figure 3, piezoelectπc elements are used to couple acoustic energy to horns, which in turn dπve acoustic waves within chamber 255 For a solid CNR as shown for example Figure 1, piezoelectnc crystals are preferably used to dπve acoustic energy into the reactor Figures 6-9 illustrate alternate embodiments for coupling acoustic energy to a solid CNR (It is understood that these techniques are equally applicable to applying acoustic energy to the liquid-filled chamber reactor of Figure 3 ) Figure 6 illustrates an acoustic driver system 600 based on a shot peening technique System 600 utilizes one or more particle discharge systems 601, each directing a stream of individual particles 603 at CNR 101 As each particle 603 collides with the surface of CNR 101 , an acoustic wave impulse is generated Dπver system 600 may also implement laser peening in which a pulsed laser source is directed at CNR 101, resulting in the generation of acoustic pulses

In a slight vaπation of the previous dπver system, dnver system 700 shown in Figure 7 includes a coupler 701 mounted to CNR 101 The stream of particles 603 impact coupler 701 rather than the outer surface of CNR 101 Coupler 701 controls the shape of the impulse generated by particles 603 within CNR 101 as well as providing a wear surface that can be designed to be easily replaceable

Figure 8 is an illustration of an acoustic dnver system 800 including one or more pulsed liquid jet generators 801 Each liquid jet generator 801 directs a liquid jet, for example comprised of water, at CNR 101 A vaπety of techniques can be used to pulse liquid jet generators 801 in order to form a stream of liquid droplets 803 that generate acoustic impulses withm the reactor upon impact against CNR 101 or a suitable coupler 805 For example, an ultrasonically excited needle restπction can be placed within the jet causing modulation of the fluid flowing through the jet, and thus the formation of droplets 803 Alternately, the fluid can be ultrasonically driven, resulting in modulation of the pressure at the tip of the jet as well as modulation of the fluid flow rate Alternately, jet generator assemblies 801 can be acoustically modulated, thereby alteπng the mass flow rate of the fluid exiting the jets

In another embodiment, one or more magnetostnctive devices (not shown) are used to supply acoustic energy when it is desired to apply high power acoustic energy at low frequencies

The previously descnbed dπvers are based on the coupling of acoustic energy to a CNR In an alternate approach shown in Figure 9, microwave energy is coupled into the matenal compnsing the CNR As shown, CNR 901 is constructed of powders, thus providing a matenal that efficiently absorbs microwave energy

For the purposes of the present example, CNR 901 is compπsed of two powders, a powder consisting of 5 micrometer particles of GdD2 (fuel composition) and a second powder consisting of 5 micrometer particles of tungsten (host mateπal) It is understood that other matenals as well as combinations of more than two powders can also be used in the present invention as descnbed above The ratio of tungsten to GdD2 is selected to be about 1000 to 1 , thus providing an average spacing of approximately 50 micrometers between adjacent GdD2 particles It will be apparent to one skilled in the art that other ratios may be selected depending on the selected materials, the desired densities and the desired reactions. Depending on the materials selected, the desired microwave frequencies will be anywhere in the range from about 20GHZ to about 1MHz.

The use of multiple powders, e.g., the two powders used in the present example, result in the formation of localized regions of low acoustic impedance into which the acoustic energy is preferentially refracted and concentrated. Thus in the present example the regions containing GdD2 are the first to melt, both due to the concentration of energy in these regions as well as the lower melting temperature of GdD2 compared to tungsten.

The frequency of microwave source 903 is determined by the particle size. Therefore for a 5 micrometer particle as in the present example, microwave frequencies on the order of 1 GHz are preferred since, assuming a sound speed of 5 kilometers per second in the metal, a 1 GHz frequency corresponds to an acoustic wavelength of 5 micrometers. Matching the frequency of the incident microwave energy to the particle size insures that the energy will be efficiently absorbed by the particle, setting the particle structures into resonance. It will be understood that other frequencies can cause the particles to resonate, although not as efficiently as a matching frequency. Alternately, the excitation frequency of microwave source 903 can be designed to match the average fuel particle spacing. In this example with a spacing of 50 micrometers between fuel particles, an excitation frequency of 100 MHz will achieve the desired frequency match. One advantage of this driver is that it provides added flexibility in the design of the CNR since virtually any convenient geometry can be used that will allow penetration of the microwave energy. For example, CNR 901 has a cubic geometry. In order to aid the penetration and focusing of the incident microwave radiation from source 903 into the CNR, surface 905 adjacent, to source 903 includes one or more conical depressions 907.

In another embodiment, the frequency of microwave source 903 is swept from a high frequency to a low frequency. As a particle begins to resonate, its size begins to increase, thereby lowering its resonant frequency. By sweeping the applied frequency from a high frequency to a low frequency, the system is able to track the change in resonant frequency of the excited particles to a degree so as to enhance the amount of microwave energy absorbed over time. The range of frequencies applied is preferably swept from about 20GHz down to about 500MHz, more preferably from about 1GHz down to about 500 MHz, and even more preferably down to about 1MHz. As previously noted, it is advantageous to utilize an intensity interference pattern in which the intensity of the pressure anti-nodes varies from low near the reactor surface to high at the reactor center. This configuration, previously termed a GCNR, extends the life of the reactor by minimizing the mechanical stresses placed on the outer shell, thereby providing a strong outer shell that encloses the primary reaction sites.

The CNR embodiment illustrated in Figure 10 improves upon this concept by utilizing a layered design. Although CNR 1200 shown in Figure 10 surrounds an inner core region 1203 with a single layer 1205, it is understood that the core can be surrounded by more than a single layer. The acoustic energy is delivered to inner core 1203 through the outer layer or layers utilizing any of the acoustic drivers that have previously been described. It should also be understood that although a spherical configuration is shown, the invention is not so limited. For example, a layered cube, a layered cylinder, a layered rectangular shape, and a layered random shape are also envisioned. The unifying aspect of this embodiment is the confinement of the desired fuel material within one or more exterior layers of a different, preferably non-fuel material. The inner confined region can be spherical, cubic, or otherwise shaped. It should also be understood that CNR 1200 can be used in the liquid-filled chamber 255 as shown in Figure 3 (i.e., as reactor structure 265).

Inner core 1203 is preferably fabricated from the desired fuel material while outer layer 1205 is fabricated from a lower cost, high tensile strength host material, thereby lowering the overall manufacturing cost while simultaneously extending reactor life through the reduction of stress fatigue failures. Also preferably the acoustic impedance of core 1203 is lower than that of layer 1205 thus improving the shock tendencies of the reactor. In one embodiment, inner core 1203 is made of a fuel material including a fuel component mixed with the host material used to make outer layer 1205, so that acoustic impedance mismatches between core 1203 and outer layer 1205 are essentially eliminated. As an example of one embodiment, layer 1205 is made of tungsten and core 1203 is made of LiD or LiT mixed in tungsten. In general, any host and fuel materials as described above can be used. Alternatively, core 1203 is made of a fuel material mixed with a second (host) material different from the host material in layer 1205. In this case it is advantageous from resonance design considerations to minimize mismatches in acoustic impedance between core 1203 and layer 1205 through appropriate selection of the second mateπal Although more difficult to design for resonance, it is advantageous to use a second host matenal in core 1203 having a lower acoustic impedance than the first host material This results in steepening the πse time of incidental acoustic energy and augments shock formation in fuel material cavity collapses In one embodiment, core 1203 includes fuel matenal having a uniform density throughout, although the fuel matenal may have a non-uniform density profile within core 1203, for example, as shown in Figure 1 1

The desired fuel mateπal is selected depending on the desired reactιon(s) Desired reaction paths include Li + D reactions, D + D reactions, D + Gd reactions (e g , neutron stripping), D +Cd, etc It will also be appreciated that Tπtium (T) or T+D can be substituted for D in the listed and contemplated reactions, although T is less preferred for the sole reason that it is radioactive

Although the embodiment shown in Figure 10 can be used for any of the disclosed cavitation dπven nuclear reactions, the present embodiment is particularly useful for enhancing neutron stπpping reactions In neutron stπpping reactions, a heavy isotope with a large thermal neutron capture cross section is forced to react with a light isotope (e g , a hydrogen isotope such as deuteπum or tntium) According to the present invention, the neutron capture cross section of the heavy isotope is preferably greater than about 10 barns, more preferably greater than about 100 bams and even more preferably greater than about 1000 bams Generally, the higher the neutron capture cross section, the more likely a neutron stπpping reaction will occur The neutron stπpping reaction m a CNR can be enhanced through the use of high neutron cross section isotopes in the CNR For example, boron, cadmium, europium, gadolinium, samaπum, dysprosium, indium, and mercury all offer high neufron cross section isotopes Particularly, several isotopes of gadolinium offer extremely high neutron cross sections as does one isotope of cadmium The reaction occurs via quantum tunneling of neutrons from the bound states in the light nuclei to the heavier nuclei and is accompanied by an energy release on the order of approximately 4 MeV Typically the reaction requires a higher activation temperature than that required for a light isotope reaction Utilizing the present reactor arrangements, the plasma temperature achieved at the end of the collapse of the cavity is typically greater for heavier elements than for light elements This result is due to the fact that the temperature is the average kinetic energy of the particles in a material Thus for two particles of different mass traveling at the same velocity, the particle with the greater mass will have the higher kinetic temperature. As a consequence, the present reactor arrangements are ideally suited for neutron stripping reactions, for example where a deuteron is used to transfer a neutron to a second nucleus such as gadolinium. In a preferred embodiment, specific undesirable end products are avoided by removing isotopes with a mass number one less than that of the undesirable end product prior to initializing the neutron stripping reaction. Thus, for example, by removing ₆₄Gd and/or ₆₄Gd prior to the neutron stripping reaction, the formation rate for beta reactive isotopes ₆ Gd¹⁵⁹ and/or ₆ Gd¹⁶¹ can be greatly reduced. According to a preferred embodiment, core region 1203 is comprised of an enriched isotope of a material with a high neutron cross section, such as Gd^{l D7} (i.e., having a neutron cross section of approximately 254,000 barns) or other material having isotopes with high neutron capture cross sections as discussed above. Enriched material (e.g., gadolinium, cadmium, etc.) can be obtained using a variety of known enrichment techniques which will not be described in detail herein (e.g., atomic vapor laser isotope separation).

Layer 1205 is preferably comprised of a non-fuel material such as tungsten, titanium, or molybdenum that is capable of delivering the acoustic energy from the driver or drivers to core region 1203. An advantage of tungsten is its high sound speed, high density, and high acoustic impedance. Utilizing an exterior layer with a higher acoustic impedance than the central core region leads to an increase in_the velocity of the compression wave initiated by the driver as the compression wave passes the interface between the two materials. As a consequence, higher shock wave velocities and higher temperatures can be obtained vvifhin the collapsing cavities or bubbles. The use of tungsten, or a similar material, for layer 1205 offers other advantages. For example, it has a high mechanical operating temperature, thus allowing high temperature reactions to take place within the reactor without causing the ultimate failure of the reactor through melting.

While the invention has been described by way of example and in terms of the specific embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.

Claims

WHAT IS CLAIMED IS: 1. A material arrangement for use in enhancing cavitation reactions, comprising: a core including: a host material having a first acoustic impedance; and a fuel material interspersed within said host material so as to form the core, wherein the fuel material has a second acoustic impedance, said second acoustic impedance being different than the first acoustic impedance; and a plurality of microcavities defined within the core by applying acoustic energy to the core, wherein a plurality of the microcavities are in contact with at least a portion of said fuel material.

2. The material arrangement of claim 1 , wherein the host material includes Tungsten and wherein the fuel material includes Gadolinium Deuteride (GdD2).

3. The material arrangement of claim 1, wherein the core has a substantially spherical shape.

4. The material arrangement of claim 3, wherein said fuel material has a density within said core, and wherein the density of said fuel material is greater toward the center of the core.

5. The material arrangement of claim 1, wherein said fuel material has a density within said core, and wherein the density of said fuel material is substantially uniform throughout the core.

6. The material arrangement of claim 1 , wherein the core is substantially cylindrical in shape.

7. The material arrangement of claim 6, wherein said fuel material has a density within said core, and wherein the density of said fuel material is greater toward a center axis of the core.

8 The material arrangement of claim 1, wherein the fuel mateπal includes fuel particles having a vapoπzation temperature lower than a melting temperature of the host mateπal.

9. The mateπal arrangement of claim 1, wherein the host material is selected from the group consisting of tungsten, Os, Ta, Mo, Re, and uranium

10 The mateπal arrangement of claim 1 , wherein the fuel material includes a first mateπal selected from the group consisting of Gd, Eu, Cd, and Dy

11 The material arrangement of claim 10, wherein the fuel material further includes at least one of deuteπum (D) and tritium (T)

12 The mateπal arrangement of claim 1, wherein the host material includes Gd and wherein the fuel matenal includes LiD

13. The matenal arrangement of claim 1, wherein the host material is selected from the group consisting of Gd, Cd, Hg, Eu and Dy

14 The mateπal arrangement of claim 13, wherein the fuel mateπal includes a first mateπal different from the host mateπal, wherein the first mateπal is selected from the group consisting of Gd, Cd, Eu, Li, and Dy

15 The matenal arrangement of claim 13, wherein the fuel mateπal includes at least one of deuteπum (D) and tntium (T)

16 The mateπal arrangement of claim 1 , nerem the fuel mateπal includes a mateπal selected from the group consisting of D, Li, LiD, LiT, GdD2 and GdT2

17 The mateπal arrangement of claim 1 , w nerem the fuel mateπal includes a mateπal having a neutron capture cross section of greater than about 100 bams

18. The material arrangement of claim 1, wherein the microcavities formed in the core material have a diameter in the range of from about .1 micrometers to about 100 micrometers.

19. The material arrangement of claim 1, wherein acoustic energy is applied to the core using one or more piezoelectric drivers coupled to the core.

20. The material arrangement of claim 1 , wherein acoustic energy is applied to the core using one or more magnetostrictive devices coupled to the core.

21. The material arrangement of claim 1, wherein acoustic energy is applied to the core using one or more pulsed lasers.

22. The material arrangement of claim 1, wherein acoustic energy is applied to the core using one or more particle beams.

23. The material arrangement of claim 1, wherein acoustic energy is applied to the core by applying microwave radiation to the core.

24. The material arrangement of claim 23, wherein the microwave radiation applied to the core has a frequency in the range of from about 10MHz to about 20GHz.

25. The material arrangement of claim 23, wherein the microwave radiation applied to the core is repeatedly swept from a first frequency to a second frequency lower than the first frequency.

26. The material arrangement of claim 25, wherein the first frequency is approximately 1GHz, and wherein the second frequency is greater than approximately 1MHz.

27. The material arrangement of claim 1 , wherein the core is formed by compressing and sintering a mixture of a first powder including the host material and a second powder including the fuel material.

28. The material arrangement of claim 27, wherein one of a cold isostatic press and a hot isostatic press is used to form the core.

29. A method of making a material arrangement for use in enhancing cavitation reactions, comprising the steps of: mixing a first powder comprising a host material with a second powder comprising a fuel material so as to form a composite powder; compressing said composite powder to form a compressed powder; sintering said compressed powder to form a core material, wherein within the core the fuel material is interspersed within the host material, wherein said fuel material has a different acoustic impedance than the host material; and applying acoustic energy to the core material so as to form a plurality of microcavities, wherein a plurality of the microcavities are in contact with at least a portion of said fuel material.

30. The method of claim 29, wherein the fuel material has substantially a uniform density within the core material.

31. The method of claim 29, wherein the fuel material has a density within the core material that is greater toward a center of the core material.

32. The method of claim 29, wherein the core material is substantially cylindrical in shape.

33. The method of claim 29, wherein the core material is substantially spherical in shape.

34. The method of claim 29, wherein the fuel material includes fuel particles having a vaporization temperature that is lower than the melting temperature of the host material.

35 The method of claim 29, wherein the microcavities formed within the core material have a diameter m the range of from about 1 micrometers to about 100 micrometers

36 The method of claim 29, wherein the step of applying acoustic energy includes the step of driving one or more piezoelectnc elements coupled to the core mateπal

37 The method of claim 29, wherein the step of applying acoustic energy includes the step of dπving one or more magnetostπctive elements coupled to the core mateπal

38 The method of claim 29, wherein the step of applying acoustic energy includes the step of applying one or more pulsed laser beams to the core mateπal

39 The method of claim 29, wherein the step of applying acoustic energy includes the step of applying one or more particle beams to the core mateπal

40 The method of claim 29, wherein the step of applying acoustic energy includes the step of applying microwave energy the core mateπal

41 The method of claim 40, wherein the microwave radiation applied to the core mateπal has a frequency in the range of about 10 MHz to about 20GHz

42 The method of claim 40, wherein the step of applying microwave energy to the core material includes the step of sweeping the microwave energy applied from a first frequency to a second frequency lower than the first frequency

43 The method of claim 42, wherein the first frequency is approximately 1GHz, and wherein the second frequency is approximately 10MHz

44 The method of claim 29, wherein the step of compressing includes the step of pressing the composite powder using one of a cold isostatic press and a hot isostatic press

45. The method of claim 29, wherein the fuel material has an acoustic impedance that is lower than the acoustic impedance of the host material.

46. The material arrangement of claim 1, wherein second acoustic impedance is lower than the first acoustic impedance.