JP2023509097A - Fuel structure and shield structure of radioisotope thermoelectric generator - Google Patents

Abstract

Provided fuel structures have a thickness less than or equal to the mean free path of electrons emitted by the radioactive energy source to prevent electrons produced by the radioactive energy source from stopping within the fuel structure. , and thus configured to prevent control radiation from being generated within the fuel structure. Further provided is a system comprising a first shield formed of a first material having a thickness exceeding the mean free path of electrons emitted from the radioactive source material such that electrons pass through said first shield. and a second shield formed of a second material configured to prevent bremsstrahlung radiation generated by the electrons from passing through the second shield. A two-layer shield system comprising a shield.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application claims priority from U.S. Provisional Application No. 62/948,479, filed Dec. 16, 2019, the entire contents of which are incorporated by reference. incorporated herein by.

TECHNICAL FIELD This disclosure relates generally to fuel structures and shielded power sources, and more specifically to high energy beta sources.

A radioisotope thermoelectric generator (RTG) is a device that produces energy by converting heat generated from radioactive decay into electricity. RTG uses a high-energy beta ray source to promote radioactive decay. RTGs are well-known devices and are used in a variety of industries and applications, including military and space travel. Previous versions of RTG were used in low-maintenance scenarios (eg, space travel). These RTGs generally produced hundreds of watts or less of power for relatively short periods of time. A typical RTG design has included a fuel capsule containing a large disk of strontium titanate (SrTiO3) surrounded by large amounts of high density metal (eg, lead (Pb)) or concrete.

Strontium-90 ( ⁹⁰ Sr) has a known process of radioactive decay. Strontium-90 decays to yttrium-90 ( ⁹⁰ Y), itself a beta ray source with a maximum energy level of about 2.2 MeV and a half-life of about 64 hours. When yttrium-90 decays, it transforms into zirconium-90 ( ⁹⁰ Zr), a stable isotope of naturally occurring zirconium. Beta particles (such as electrons and positrons) can produce bremsstrahlung radiation (X-rays) when slowed down. This is especially noticeable for beta particles with energies above 2 MeV. Bremsstrahlung radiation generates electromagnetic waves (such as photons) by decelerating charged particles such as electrons. To satisfy the law of conservation of energy, the energy of the photon is equal to the energy of the charged particle before deceleration minus the energy of the charged particle after deceleration (e.g., Eγ=E(i) _e −E( f) _e- ). Higher atomic number materials may produce more x-rays when beta rays interact with (eg, impinge on) the material. This means that using a less dense material to shield these particles is preferable because it reduces the generation of x-rays. As with beta particles, the resulting bremsstrahlung x-rays technically have an energy range up to a maximum energy equal to that of the beta particle (assuming the beta particle is completely stopped in the material case).

Past designs of RTG performed well for the given task. However, past designs of RTGs have limited their transport modularity and output. These and/or other problems exist.

The following is a non-exhaustive listing of some aspects of the technology. These and other aspects are described in the subsequent disclosure.

In some embodiments, the fuel structure includes a radioactive source material that includes a high energy beta-emitter, and electrons emitted from the radioactive source material as a result of the beta decay process pass through the fuel structure without stopping. It is thereby configured to have a thickness less than or equal to the mean free path of electrons emitted from the radioactive source material so as to prevent bremsstrahlung radiation from being generated within the fuel structure.

In some other aspects, the system for shielding the radioactive source material is a first shield formed of a first material having a thickness exceeding the mean free path of electrons emitted from the radioactive source material. and a second shield formed of a second material, wherein bremsstrahlung radiation generated by the electrons passes through the second shield by having a second shield configured to prevent

These and other aspects of the present technology will be better understood upon reading the present application with reference to the following figures. In these figures, identical numbers indicate similar or identical elements.

FIG. 3 illustrates an example of a historical fuel structure configuration for a radioisotope thermoelectric generator (RTG) and an optimized fuel structure configuration for the RTG, according to various embodiments.

FIG. 10 illustrates an example of a two-phase shield for RTG, according to various embodiments.

1 illustrates an example distributed fuel structure for an RTG, according to various embodiments; FIG.

FIG. 3 illustrates an example concentric fuel structure for an RTG, according to various embodiments;

FIG. 4 illustrates another example concentric fuel structure for an RTG, according to various embodiments;

FIG. 4 illustrates another example distributed fuel structure for an RTG, according to various embodiments;

7 is a perspective view of a distributed fuel structure for the RTG of FIG. 6, according to various embodiments; FIG.

While the techniques of the present invention are susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. Drawings may not be to scale. However, the drawings and detailed description based thereon are not intended to limit the technology to the particular forms disclosed, but rather within the spirit and scope of the technology as defined by the appended claims. It should be understood that it is intended to cover all possible modifications, equivalents and alternatives.

To alleviate the problems described herein, the inventors have devised solutions and, possibly equally importantly, those skilled in the field of radioisotope thermoelectric generators (RTG) I needed to recognize problems that I had overlooked (or didn't foresee). Indeed, we would like to emphasize that these problems are difficult to recognize. Further, since there are multiple problems to address, some embodiments are specific to one problem and all embodiments address all of the problems of conventional systems described herein. It should be understood that it does not provide all of the advantages described herein. In short, improvements that solve one or more permutations of these and/or other problems are described below.

A power source containing a high-energy beta-emitting source may be used to design a radioisotope thermoelectric generator (RTG). The RTG converts heat into electricity, which is output from the RTG and can power various devices. Such devices may include, for example, satellites, unmanned facilities, solar panels, communication devices, and the like. Heat can be produced by the decay of radioactive source material. A decay process can include, for example, a radioactive element decaying into another element while outputting one or more particles. As used herein, a radioactive element refers to an element containing an unstable nucleus in which the number of protons and neutrons contained in the nucleus is out of proportion. One type of radioactive decay is beta decay, in which an initially unstable atom decays into another element (stable or unstable), outputting an electron or positron. The half-life (τ) of a radioactive element indicates the time it takes for an unstable atom to decay to half its initial value. Each radioactive element may have different half-lives, and these half-lives are generally well known in the scientific community.

In some embodiments, an RTG may be formed that includes strontium-90 as the radioactive element. Strontium-90 contains 38 protons and 52 neutrons (eg, 38+52=90). Strontium-90 is an isotope of strontium (Sr) and has a half-life of 28.9 years. Strontium-90 changes to yttrium-90 by beta decay and emits electrons of 546 keV. Yttrium-90 contains 39 protons and 51 neutrons (eg, 39+51=90). Yttrium-90 is an isotope of yttrium (Y) and has a half-life of 64.1 hours. Yttrium-90 changes to zirconium-90 by beta decay and emits electrons of 2,280.1 keV or 2.2801 MeV. Although the foregoing description generally relates to radioactive source materials containing Strontium-90, in some embodiments RTGs containing other radioactive elements that produce high-energy beta rays (e.g., beta rays greater than 2 MeV) may be formed. For example, instead of strontium-90, plutonium-238, polonium-210, or americium-241 may alternatively be used.

RTGs require some form of shielding for safety, as the materials they use are radioactive. A general goal of shield design, regardless of its application, is to reduce bremsstrahlung radiation. Past shield designs have resulted in bremsstrahlung radiation occurring before the beta rays can escape from the fuel (such as radioactive material) itself. However, fuel structures that reduce/eliminate bremsstrahlung radiation generated within the fuel itself have not yet been fabricated, especially for highly radioactive energy sources. Past fuel constructions that generate bremsstrahlung radiation within the fuel itself have previously been a solution only for small amounts of strontium-90. For example, current strontium-90 radioactive power source designs employ large radius fuel structures, even though it has been known since at least 1968 that virtually all bremsstrahlung x-rays originate inside the fuel. are doing. In highly active beta sources, all bremsstrahlung radiation is generated within the fuel, so the use of shield structures to reduce bremsstrahlung generation has not been attempted. Therefore, in order to shield the high-energy beta-ray source and the accompanying generation of bremsstrahlung X-rays, it was necessary to use a large amount of heavy metal or concrete.

It is not possible to reduce the weight of high-energy beta-ray source shields due to the large masses of heavy metals and concrete that must be used in the shields, and attempts have yet to be made to make shields that are portable and intended for terrestrial use. not Generally, high-energy beta sources are only used in remote locations, so passive safety design elements have been given less importance. Shielded structures intended for transportable use in non-remote locations require inherent safety features provided by large masses of heavy metals and concrete, while at the same time preventing or mitigating hazards under unusual conditions. In order to do so, it must also be lightweight enough to be transported.

FIG. 1 shows an example of a historical fuel structure configuration 100 for a radioisotope thermoelectric generator (RTG) and an optimized fuel structure configuration 150 for an RTG, according to various embodiments. . In some embodiments, the morphology 150 for the RTG optimized fuel structure may be formed such that bremsstrahlung emission may be reduced compared to the morphology 100 for the historical fuel structure. . For example, an optimized fuel structure configuration 150 may reduce the generation of bremsstrahlung X-rays by allowing high-energy beta rays to escape from the fuel source. The fuel source of the optimized fuel structure can be, for example, a high energy beta emitter such as Strontium-90.

As can be seen in FIG. 1, past fuel structure configurations 100 may have radii that are greater than the mean free path of the beta rays of the fuel source. In this example, electrons produced via beta decay of the radioactive source material are converted to bremsstrahlung radiation (eg, x-rays) within the fuel source (eg, the fuel source of past fuel structures). However, in some embodiments, the optimized fuel structure configuration 150 may have a radius that is smaller than the mean free path of beta rays, whereby the beta rays are initially bremsstrahlung x-rays. can escape from the fuel source (eg, the fuel source of the optimized fuel structure) without being converted to . After escaping from the fuel source (e.g., the fuel source of an optimized fuel structure), the beta rays may be slowed down in a low density material such as part of the shield, thereby suppressing the generation of bremsstrahlung radiation. can be

FIG. 2 shows an example of a two-phase shield 220 for RTG, according to various embodiments. In some embodiments, the RTG 200 includes a fuel 202, also referred to interchangeably herein as a fuel source 202, a fuel container 204, and interchangeably herein a two-phase shield 220, shield 220, and/or A two-phase shield system 220, also referred to as system 220, may be included. Two-phase shield system 220 may include first shield 206 and second shield 208 . In some embodiments, the first shield 206 may be interchangeably referred to herein as the primary shield 206 and the second shield 208 may be interchangeably referred to herein as the secondary shield 208. may be

In some embodiments, the dual-phase shield 220 may be designed to reduce bremsstrahlung radiation generation, prevent line leakage from the RTG 200, and provide structural stability for the RTG 200. In some embodiments, first shield 206 may be formed of a material having a low effective atomic number. First shield 206 may be configured to attenuate at least a portion of bremsstrahlung radiation leaking from fuel 202 and fuel container 204 (eg, as seen in configuration 150 of FIG. 1). In some embodiments, second shield 208 may be formed of a material having a high effective atomic number. The second shield 208 may be configured to absorb bremsstrahlung radiation that escapes from and/or originates within the first shield 206 . The second shield 208 may also be configured to provide structural stability and robustness to the two-phase shield 220 and thus to the RTG 200 as well. In some embodiments, the RTG 200 may be configured to operate at approximately 700° C. or higher.

In some embodiments, the first shield 206 may serve to attenuate as much of the bremsstrahlung radiation escaping from the fuel 202 and fuel container 204 as possible. Additionally, the first shield 206 may be designed to generate a minimal amount of bremsstrahlung radiation. In some embodiments, first shield 206 may be configured to act as a heat transfer medium to transfer heat between a heat source and a heat sink. For example, in RTG 200 , fuel particles (eg, strontium titanate particles), fuel reservoir 204 , and/or first shield 206 are configured such that the fuel particles decelerate within fuel 202 , fuel reservoir 204 , and/or first shield 206 . Therefore, it can function as a heat source. Since heat is generated by the slowing action of the strontium titanate particles in the medium, the medium can be the heat source where the slowing occurs. A heat sink for the RTG 200 may be, for example, the outer surface of the second shield 208 . The outer surface of the second shield 208 can serve as a hot side for one or more thermoelectric converters operatively coupled thereto. In some embodiments, the materials used to form the first shield 206 and the second shield 208 are good thermal conductors, thereby improving heat transfer efficiency to the thermoelectric converter and Reduce hot spots that can cause decomposition. First shield 206 may be formed of one or more materials. For example, the first shield 206 may be made of graphite, lithium hydride, hydrogen-based oil or resin, molten salt, or the like. The one or more materials used to form the first shield 206 may additionally or alternatively include materials with low density, low atomic number, high thermal conductivity, and/or high material decomposition temperature. Additionally, it may be a material that is compatible with the material (eg, strontium titanate) containing the radiation source (eg, strontium-90) used.

In some embodiments, graphite may be selected as the material to use for the first shield 206 as it has good thermal conductivity and a low effective atomic number of 6. Additionally, graphite is highly compatible with other materials and has been used as a material compatibility buffer in previous RTG designs. The melting point of graphite is higher (eg, 3,600° C.) than that of strontium titanate (eg, 2,080° C.) and is thermally stable. Graphite is also non-toxic, relatively inexpensive, and is used in many existing nuclear applications.

In some embodiments, lithium hydride or hydrogen-based oils may be selected as materials used for first shield 206 due to their low density, acceptable thermal conductivity, and low effective atomic number. . For example, lithium hydride has an effective atomic number of 1.5, while hydrogen-based oils are generally higher and will depend on the particular oil used. Both materials are compatible with other materials in fuel structures, but lithium hydride's toxicity can increase manufacturing costs and the risk of containment loss. Hydrogen-based oils are relatively inexpensive, but lithium hydride is not. The maximum temperature before decomposition or boiling of both lithium hydride and hydrogen-based oil limits the operating temperature of the fuel structure to less than 700° C., which is the desired operating temperature for the RTG 200.

In some embodiments, molten salt options such as FLiBe (Li2BeF4) may be selected as the material used for first shield 206. FIG. The molten salt option has an effective atomic number of 3.3, which represents a reduction in bremsstrahlung intensity of approximately 87%. The molten salt option has a density of about 1.9 g/cm ³ . The molten salt option has acceptable thermal conductivity and is relatively inexpensive to manufacture. Furthermore, the material compatibility of the molten salt option with other materials of fuel structures is believed to be satisfactory, and the molten salt option is already used in many nuclear applications.

In some embodiments, the second shield 208 may function to stop remaining beta rays escaping from the first shield 206 from exiting the RTG 200 . Secondary shield 208 is designed to block or absorb any small amount of bremsstrahlung radiation produced by fuel 202, fuel container 204, and/or primary shield 206 and not attenuated by fuel container 204 or primary shield 206. may be configured. Second shield 208 may be formed of one or more materials that may be different than the one or more materials of first shield 206 . For example, the one or more materials used to form the second shield 208 have a high density, high effective atomic number, high thermal conductivity, high material decomposition temperature, and are compatible with other materials in the RTG 200. may contain materials that By way of example, second shield 208 may be formed of tungsten, lead, depleted uranium, combinations thereof, or other materials. In some embodiments, a combination of tungsten, lead, and/or depleted uranium may be used to control heat transfer.

In some embodiments, electrons 210 produced as a result of radioactive decay (eg, beta decay) of radioactive material (eg, strontium-90) within fuel 202 escape fuel 202 and decay within fuel container 204. can be For example, the radius of fuel 202 may be smaller than the mean free path of electrons 210, thereby allowing electrons 210 to escape fuel 202 without being converted to bremsstrahlung radiation. In some embodiments, electrons 212 produced as a result of radioactive decay (eg, beta decay) of radioactive material (eg, strontium-90) within fuel 202 escape fuel 202 and pass through fuel container 204. , can be attenuated in the first shield 206 . In some embodiments, electrons 214 produced as a result of radioactive decay (eg, beta decay) of radioactive material (eg, strontium-90) within fuel 202 do not escape fuel 202, and bremsstrahlung (eg, bremsstrahlung) x-rays) 216. Bremsstrahlung radiation 216 may escape from fuel 202 , pass through fuel container 204 and first shield 206 and be attenuated by second shield 208 . In some embodiments, electrons 218 produced as a result of radioactive decay (e.g., beta decay) of radioactive material (e.g., strontium-90) within fuel 202 escape fuel 202 and enter fuel container 204 and first It can pass through shield 206 and be attenuated by a second shield 208 . Alternatively, electrons produced as a result of radioactive decay (e.g., beta decay) of radioactive material (e.g., strontium-90) within fuel 202 escape fuel 202 and exit fuel container 204, first shield 206, or second shield 206. It can be converted into bremsstrahlung within the shield 208 . Regardless of whether the bremsstrahlung radiation is generated in the fuel container 204, the first shield 206, or the second shield 208, the bremsstrahlung radiation is prevented from escaping from the RTG 200 before reaching the second shield 208 or there. can be attenuated by

Most nuclear fuel structures can be housed in multi-level containment structures as an inherent safety element. However, some past designs for Strontium 90 fuel capsules have included a single layer containment vessel. Some embodiments improve fuel structure safety by reducing radiation exposure and fuel containment loss if the shield is punctured or the containment is lost in some other way. including a graduated containment structure to increase Additionally, the graduated containment structure can provide a lightweight attenuation scheme for any generated bremsstrahlung radiation. In some embodiments, the graduated shield uses a morphological combination that utilizes self-shielding, compartmentalizing the fuel into separate compartments, and dispersing the fuel so that spread of the fuel is limited if the shield is impacted. and morphological designs that reduce radiation exposure under unusual circumstances. In some embodiments, abnormal operating conditions may refer to events other than "normal" operation of the RTG. For example, an unusual operating condition may exist when the fuel container 204 has a hole. As another example, abnormal operating conditions may exist when there is thermal decomposition in the first shield 206 and/or the second shield 208 .

In some embodiments, fuel structures for high-energy beta-emitters such as strontium-90 are described herein. As an example, the range (eg, mean free path) of electrons in strontium titanate (SrTiO3) can be about 2 mm. Therefore, electrons generated within the strontium titanate source will stop within about 2 mm of the strontium titanate source material.

FIG. 3 illustrates an example distributed fuel structure 300 for RTG, according to various embodiments. In some embodiments, fuel structure 300 may include dispersed spherical structures formed of high-energy beta-emitters. The spherical structures may (i) have substantially the same size and (ii) be substantially spherical. For example, the volume V of each sphere may be equal to 4/3πr ³ , where “r” corresponds to the radius of a given spherical structure. The volume of each spherical structure may be within a predetermined tolerance level. For example, each spherical structure may have a volume V that is within N standard deviations σ of the volume of the average spherical structure. Spherical structures with volumes greater than V+Nσ or less than V−Nσ may be excluded from fuel structure 300 . Additionally, each spherical structure may have a radius r that is substantially constant throughout its volume.

In some embodiments, each spherical structure may have a radius of 2 mm or less, corresponding to the range of electrons produced by beta decay of strontium-90. In some embodiments, each spherical structure may be formed of strontium titanate and coated with graphite. In some embodiments, the spherical structures may be dispersed in a primary shield (eg, first shield 206) and sintered or hot pressed to form a secondary shield (eg, second shield 208). ).

FIG. 4 illustrates an example concentric fuel structure 400 for RTG, according to various embodiments. In some embodiments, the concentric fuel structure 400 may include concentric cylinders of high energy beta emitters having a thickness less than the mean free path of the high energy beta emitters. For example, the concentric fuel structure 400 may include concentric cylinders of strontium titanate having a thickness of 2 mm. In some embodiments, the concentric fuel structure 400 may further include concentric cylinders of a first shield material such as graphite. For example, the concentric fuel structure 400 includes a first cylinder of strontium titanate having a radius (e.g., mean free path of electrons emitted by strontium titanate) of 2 mm or less, which is graphite with a thickness of 7 mm or less. may be wrapped by a cylinder of strontium titanate, wrapped by another cylinder of graphite, and so on. In some embodiments, the maximum radial thickness of each cylinder of strontium titanate is 2 mm. Since the emitted radiation has an energy that is contained within the energy distribution of strontium titanate, the specific energy of a given photon is not constant, instead the energy of the photon can be a value obtained from the energy distribution. highly sexual. The number of cylinders of radioactive source material and the number of cylinders of first shield material may vary and may depend on the power a given fuel structure is to produce. For example, the number of cylinders is 6 or more (for example, 3 cylinders of strontium titanate and 3 cylinders of graphite), 10 or more (for example, 5 cylinders of strontium titanate and 5 cylinders of graphite), etc. good. In some embodiments, concentric cylinders of a high energy beta emitter (eg, strontium titanate) and a first shield material (eg, graphite) may be wrapped with a second shield material such as tungsten. . The thickness of the first shield material may be 0.1-1 mm, 0.5-1.5 mm, 1.0-2.0 mm, 1.5-2.5 mm, 2.0-3.0 mm, etc. you can The thickness of the second shield material may be 1-5 cm, 1-10 cm, 5-10 cm, 5-15 cm, and so on. This thickness is selected such that the radiation dose from the RTG is below the radiation dose threshold. For example, the thickness of the second shield material may be selected such that the radiation dose is less than 10 mrem/hr at a distance of 1 m.

FIG. 5 shows another example of a concentric fuel structure 500 for RTG, according to various embodiments. In some embodiments, concentric fuel structure 500 may be similar to concentric fuel structure 400 of FIG. 4, and the foregoing description may apply. The concentric fuel structure 500 may include a plurality of first concentric cylinders 502 of high energy beta emitter such as Strontium-90. For example, first concentric cylinder 502 may be formed of strontium titanate. A plurality of second concentric cylinders 504 may be interposed between the first concentric cylinders 502 . A second concentric cylinder 504 may form a first or primary shield in some embodiments. For example, second concentric cylinder 504 may be similar to first shield 206 of FIG. In some embodiments, the second concentric cylinder 504 has a low density, low atomic number, high thermal conductivity, high material decomposition temperature, and is compatible with the radiation source used (eg, Strontium 90). It may be made of any material. For example, the second concentric cylinder 504 may be made of graphite.

In some embodiments, a central cylinder of first concentric cylinders 502 may be surrounded by a first instance of second concentric cylinders 504 . A first instance of the second concentric cylinder 504 may be sandwiched between a first instance of the first concentric cylinder 502 . This alternating pattern of first concentric cylinders 502 and second concentric cylinders 504 may be repeated several times depending on the power requirements of the RTG. However, the outer cylinder of fuel structure 500 would be formed with a second concentric cylinder 504 . In some embodiments, the thickness of each of concentric cylinders 502 and 504 may be substantially similar. For example, concentric cylinders 502 and 504 may both have thicknesses equal to or less than 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, and the like. As another example, concentric cylinders 502 and 504 may have the same thickness in the range of 1-10 mm. In some embodiments, the thickness of each concentric cylinder 502 may be substantially similar to each other, and the thickness of each concentric cylinder 504 may be substantially similar to each other, although the thickness of the concentric cylinders 502 may be substantially similar to each other. can be different. For example, concentric cylinders 502 and 504 may each have a thickness equal to or less than one of 1 mm, 1.5 mm, 2 mm, 2.5 mm, 3 mm, and so on. As another example, concentric cylinders 502 and 504 may each have a thickness in the range of 1-10 mm. In some embodiments, the radius of each concentric cylinder 502 and each concentric cylinder 504 may increase as the number of cylinders increases (eg, inner cylinders may have smaller radii than outer cylinders). . For example, a first concentric cylinder 502 may have a first radius, and a first concentric cylinder 502 may have a second radius larger than the first concentric cylinder 504. may be surrounded by A first concentric cylinder 504 may be surrounded by a second concentric cylinder 502 having a third radius greater than the second radius. The same applies hereinafter. The radius may be, for example, 2 mm and gradually increase. The second radius may be selected in the range of 2-4 mm, 2.5-4.5 mm, 2-6 mm, etc., and the third radius may be selected in the range of 4-6 mm, 4.5-6 mm, etc. .5 mm, 4 to 7 mm, etc., may be selected.

In some embodiments, a third cylinder 506 may surround concentric cylinders 502 and 504 . The third cylinder 506 may be substantially similar to the second shield 208 of FIG. 2 and the discussion above may apply. In some embodiments, third cylinder 506 is made of one or more materials that have high density, high effective atomic number, high thermal conductivity, high material decomposition temperature, and are compatible with other materials in the RTG. may be formed. For example, third cylinder 506 may be formed of tungsten. In some embodiments, the thickness of the third cylinder 506 may depend on RTG design requirements (eg, power requirements, number of instances of the first shield, material composition, etc.). In some embodiments, the third cylinder 506 may be enclosed by a layer of air 508 or exposed to the natural environment.

FIG. 6 is a diagram illustrating another example distributed fuel structure for RTG, according to various embodiments. RTG 600 may include dispersed spherical structures formed of high-energy beta-emitters. The spherical structures may (i) have substantially the same size and (ii) be substantially spherical. For example, the spherical structures may be the same or similar to the spherical structures described above with reference to FIG. In some embodiments, each spherical structure may have a radius of 2 mm or less, corresponding to the range of electrons produced by beta decay of strontium-90. In some embodiments, each spherical structure may be formed of strontium titanate and coated with graphite. In some embodiments, spherical structures may be dispersed within the first shield 604 . For example, first shield 604 may be formed of one or more materials having low density, low atomic number, high thermal conductivity, and/or high material decomposition temperature, and additionally or alternatively, the radiation used may It may be a material that is compatible with the material (eg, strontium-90) containing the source (eg, strontium titanate). As an example, first shield 604 may be formed of graphite. In some embodiments, first shield 604 may include a buffer layer between the portion containing spherical structure 602 and second shields 606 and 608 .

Second shields 606 and 608 are each formed from one or more materials that have high density, high effective atomic number, high thermal conductivity, high material decomposition temperature, and are compatible with other materials in RTG 200 . good too. As an example, the second shields 606 and 608 may be made of tungsten. In some embodiments, second shield 606 may have a first thickness and second shield 608 may have a second thickness. For example, the thickness of the second shield 606 may be 5 mm and the thickness of the second shield 608 may be 10 mm. Each of the second shields 606 and 608 may have a thickness selected from within a thickness range including 1-5 cm, 1-10 cm, 5-10 cm, 5-15 cm, and the like. This thickness is selected such that the radiation dose from the RTG is below the radiation dose threshold. For example, the thickness of the second shield may be selected such that at a distance of 1 m the radiation dose is less than 10 mrem/hr. In some embodiments, the second shield 606 may have a substantially constant thickness. For example, the second shield 606 may be a sidewall of the RTG 600 having a substantially constant thickness (eg, selected at a value within the range of 5-10 cm). In some embodiments, the second shield 608 may vary in thickness, such that the thickness proximate the perimeter of the RTG 600 is the same as the thickness along the central axis of the RTG 600 (eg, between 5 and 500). (selected values within the range of 10 cm).

7 is a perspective view of a distributed fuel structure for the RTG of FIG. 6, according to various embodiments; FIG. As can be seen from FIG. 7, the RTG 600 described in detail in FIG. 6 above is shown. In FIG. 7, a perspective view of RTG 600 is depicted.

In some embodiments, the fuel structures described herein are used as space environment heater units, cold environment heater units, thermal power sources for energy conversion, medical radioisotope storage shields, spent It can be used in a variety of applications, including nuclear fuel transport shields, medical radioisotope transport shields, spent nuclear fuel shields, emergency radiation containment, bioradiation protection for space environments, and bioradiation protection for emergency radiation environments. is not limited to

The reader should understand that this application describes several separately useful techniques. Applicants have grouped these technologies into one document rather than separating them into multiple independent patent applications, which leads to economy of the filing process because the subject matter of the technologies is related. It is from. However, separate advantages and aspects of such technology should not be confused. In some cases, although the embodiments address all of the deficiencies noted herein, the techniques are useful independently and some embodiments address only a subset of such problems. or provide other unmentioned advantages that would be apparent to one of ordinary skill in the art reading this disclosure. Due to cost constraints, some of the technology disclosed in this specification may not currently be claimed and may be filed in a later application, such as a continuation application, or amending the present claims. Doing so may result in a claim for ownership. Similarly, for the sake of space, the "Abstract" and "Summary of the Invention" sections of this application are deemed to be a comprehensive description of all such techniques or all aspects of such techniques. shouldn't.

The detailed description and drawings are not intended to limit the technology to the particular forms disclosed, but rather all modifications that come within the spirit and scope of the technology as defined by the appended claims. , equivalents, and alternatives are intended to be covered. Further modifications and alternative embodiments of various aspects of the technology will be apparent to those skilled in the art upon reading this description. Accordingly, the description and drawings are to be construed as illustrative only and are intended to teach those skilled in the art the general manner of practicing the technology. It is to be understood that the forms of the technology shown and described herein are to be considered as example embodiments. Various elements and materials may be substituted for those shown and described herein, parts and processes may be reversed or omitted, and certain features of the technology may be Although they may be utilized independently, all of these will become apparent to those skilled in the art after having the benefit of this description of the technology. Changes may be made in the elements described herein without departing from the spirit and scope of the technology as described in the following claims. The headings used herein are for organizational purposes and are not intended to be used to limit the scope of the description.

As used throughout this patent application, the word "may" is used in a permissive (i.e., likely to) sense rather than in a mandatory (i.e., must) sense. used in The words "include," "including," "includes," and the like mean including but not limited to. In this application, the singular forms "a," "an," and "the" include plural referents unless the content clearly dictates otherwise. Thus, for example, reference to "an element" or "a element" may be used to refer to one or more elements, such as "one or more". Regardless of the use of terms and phrases, they include combinations of two or more elements. The term "or" is non-exclusive, ie, includes both "and" and "or," unless specified otherwise. Conditional terms such as "in response to X, Y", "on X, Y", "if X, Y )”, “when X, Y (when X, Y)”, etc., if the antecedent is a necessary causal condition, if the antecedent is a sufficient causal condition, the antecedent is the dominant causal condition of the result. It includes causal relationships such as cases. For example, "state X occurs when condition Y is obtained" is generic to "X occurs only when Y" and "X occurs when Y and Z". Such a conditional relationship is not limited to those in which results are obtained immediately after the preceding conditions are obtained, but there are also cases in which results are delayed. A conditional statement also associates an antecedent with an outcome, eg, the antecedent relates to the likelihood of the outcome occurring. Descriptions in which multiple attributes or functions are mapped to multiple objects (e.g., one or more processors performing steps A, B, C, and D) will not be described unless otherwise indicated. It includes both mapping to all of those objects and having a subset of their attributes or functions mapped to a subset of those attributes or functions (e.g. all processors performing steps A-D respectively). processor 1 performs step A, processor 2 performs step B and part of step C, and processor 3 performs part of step C and step D). Further, a statement that a value or action is “based on” another term or value, unless otherwise indicated, includes both when that term or value is the sole factor and when that term or value is among more than one factor. is one factor of . A statement that "each" instance of a collection has a property is read to exclude instances where the same or similar members in other properties of a larger collection do not have that property, unless otherwise indicated. shouldn't. That is, "each" does not necessarily mean all. No limitation as to the order of the recited steps should be read into the claims unless explicitly specified, for example, "do X and then do Y." In contrast, a statement that could be inappropriately claimed to imply an order constraint, such as "do X on item, do Y on item X", does not imply order. It is used for the purpose of making the claim easier to read, rather than specifying it. Also, statements such as "at least Z of A, B, and C" (such as "at least Z of A, B, or C") refer to each category listed (A, B, and C). It refers to at least Z of which, and does not require at least Z units in each category. It should be clear from the discussion that, in this specification, discussions using terms such as "processing", "computing", "computing", "determining", etc., do not refer to a special purpose computer or similar special purpose computer, unless otherwise specified. It is understood to refer to the operation or process of a particular device, such as an electronic processing/computing device of interest. Features described with reference to geometric structures such as "parallel", "perpendicular/perpendicular", "square", "cylindrical" substantially embody the properties of that geometry It should be construed to include items, for example, reference to "parallel" surfaces would include substantially parallel surfaces. Allowable deviations from the Platonic notion of these geometrical structures should be determined with reference to the ranges in the specification and, if no such range is stated, the field of use. Reference should be made to industry norms in the field of manufacture of the specified features, and if no such range is defined, reference should be made to industry norms in the field of manufacture of the specified features, and if such a range is defined. If not, features that substantially embody a geometrical structure should be construed to include features that are within 15% of the defining attributes of that geometrical structure. Terms such as “first,” “second,” “third,” “predetermined,” etc., used in the claims are used to distinguish or identify, and may be used consecutively or It does not imply numerical limitations.

The technology of the present invention may be better understood with reference to the embodiments enumerated below.
[Embodiment 1]
A fuel structure comprising a radioactive source material comprising a high-energy beta-emitter, wherein electrons emitted by said radioactive source material as a result of a beta decay process pass through said fuel structure without stopping. to have a thickness less than or equal to the mean free path of electrons emitted by said radioactive source material, so as to prevent bremsstrahlung radiation from being generated within said fuel structure.
[Embodiment 2]
3. The fuel structure of embodiment 1, wherein the radioactive source material comprises strontium titanate.
[Embodiment 3]
3. The fuel structure of any of embodiments 1-2, wherein the high energy beta emitter comprises Strontium-90.
[Embodiment 4]
4. The fuel structure of any of embodiments 1-3, wherein the mean free path of electrons emitted by the radioactive energy source is 2 millimeters (mm) and the thickness of the fuel structure is 2 mm or less. .
[Embodiment 5]
5. The fuel structure of any of embodiments 1-4, wherein the energy of electrons emitted by the radioactive source material as a result of the beta decay process is 2 MeV.
[Embodiment 6]
6. The fuel structure of any of embodiments 1-5, wherein the radioactive source material has a decay activity of 100 Curies (Ci) or greater.
[Embodiment 7]
7. The fuel structure of any of embodiments 1-6, wherein the radioactive source material is formed of spherical structures having the thickness, the spherical structures dispersed within a first material.
[Embodiment 8]
8. A fuel structure as recited in embodiment 7, wherein said first material has a low density, low atomic number, high thermal conductivity, high material decomposition temperature, and is compatible with said radioactive source material.
[Embodiment 9]
9. The fuel structure of any of embodiments 7-8, wherein the first material comprises graphite.
[Embodiment 10]
10. The fuel structure of any of embodiments 7-9, wherein the first material comprises lithium hydride, hydrogen-based oil or resin, or molten salt.
[Embodiment 11]
11. The fuel structure of any of embodiments 7-10, wherein the first material in which the spherical structures formed of the radioactive source material are dispersed is further encased in a second material.
[Embodiment 12]
12. A fuel structure as recited in embodiment 11, wherein said second material has a high density, high effective atomic number, high thermal conductivity, high material decomposition temperature, and is compatible with other materials associated with said fuel structure. thing.
[Embodiment 13]
13. The fuel structure of any of embodiments 11-12, wherein the second material comprises tungsten.
[Embodiment 14]
13. The fuel structure of any of embodiments 11-12, wherein the second material comprises lead or depleted uranium.
[Embodiment 15]
15. The fuel structure of any of embodiments 1-14, wherein the radioactive source material is formed from a first plurality of cylinders.
[Embodiment 16]
16. The fuel structure of embodiment 15, further comprising a second plurality of cylinders formed of a first material, wherein the first plurality of cylinders and the second plurality of cylinders are concentric cylinders.
[Embodiment 17]
17. The fuel structure of any of embodiments 15-16, wherein the first material comprises graphite, lithium hydride, hydrogen-based oil or resin, or molten salt.
[Embodiment 18]
18. The fuel of any of embodiments 15-17, further comprising a third cylinder formed of a second material and configured to enclose the first plurality of cylinders and the second plurality of cylinders. Structure.
[Embodiment 19]
19. The fuel structure of embodiment 18, wherein the second material comprises tungsten, lead, or depleted uranium.
[Embodiment 20]
Embodiment 18 wherein each of said first plurality of cylinders has said thickness, wherein said thickness is 2 mm or less, and each of said second plurality of cylinders has an additional thickness of 7 mm or less. 20. The fuel structure according to any one of 19 to 19.
[Embodiment 21]
Each of said first plurality of cylinders has said thickness, said thickness being 0.1-1 mm, 0.5-1.5 mm, 1.0-2.0 mm, 1.5-2. 5 mm; 20. A fuel structure according to any of embodiments 18-19, having an additional thickness selected from 5 mm, or one of the range of 4-7 mm.
[Embodiment 22]
22. Any of embodiments 18-21, wherein the third cylinder has a thickness selected from one of the ranges 1-5 cm, 1-10 cm, 5-10 cm, or 5-15 cm. fuel structure.
[Embodiment 23]
A system for shielding a radioactive source material, comprising: a first shield formed of a first material, having a thickness exceeding the mean free path of electrons emitted from the radioactive source material; a first shield that prevents electrons from passing through the first shield, and a second shield formed of a second material, wherein bremsstrahlung radiation generated by the electrons passes through the second shield. and a second shield configured to prevent
[Embodiment 24]
The first material has a low density, low atomic number, high thermal conductivity, high material decomposition temperature and is compatible with the radioactive source material, and the second material has a high density, high effective atomic number, high thermal 24. The system of embodiment 23, having conductivity, high material decomposition temperature, and being compatible with other materials associated with said system.
[Embodiment 25]
25. Any of embodiments 23-24, wherein the first material comprises graphite, lithium hydride, hydrogen-based oil or resin, or molten salt, and the second material comprises tungsten, lead, or depleted uranium. system.
[Embodiment 26]
The mean free path of electrons emitted from the radioactive source material is 2 millimeters (2 mm), the thickness of the first material is 2 mm or less, and the thickness of the second material is about 7 mm or less. 25. The system of any of embodiments 23-24.
[Embodiment 27]
27. Any of embodiments 23-26, wherein electrons emitted from the radioactive source material have an energy of about 2 MeV and the thickness is selected to prevent the electrons from passing through the first shield. System as described.
[Embodiment 28]
a fuel source containing the radioactive source material; and a fuel container configured to contain the fuel source, wherein the first shield is configured to enclose the fuel container, and the second shield is configured to enclose the first shield. 29. The system of any of embodiments 23-28, further comprising a fuel container configured to enclose a fuel container.
[Embodiment 29]
29. The system of embodiment 28, wherein the fuel source comprises strontium titanate and the radioactive source material comprises strontium-90.
[Embodiment 30]
30. The system of any of embodiments 28-29, wherein the radioactive source material comprises a high energy beta emitter.
[Embodiment 31]
Embodiments 23-30, wherein bremsstrahlung radiation produced by said electrons is produced within said first shield, and bremsstrahlung radiation produced within said first shield is attenuated within said first shield or said second shield A system according to any of the preceding claims.
[Embodiment 32]
The bremsstrahlung radiation generated by the electrons is generated within a fuel container configured to contain a fuel source containing the radioactive source material, and the bremsstrahlung radiation generated within the fuel container is generated by the first shield or the 32. The system of any of embodiments 23-31, wherein the system is attenuated within the second shield.
[Embodiment 33]
further comprising a fuel structure comprising a radioactive source material comprising high energy beta emitters, said fuel structure configured to have a thickness less than or equal to said mean free path, said radioactive source as a result of a beta decay process; 33. Any of embodiments 23-32, wherein electrons emitted by matter are able to pass through the fuel structure without stopping, thereby preventing bremsstrahlung radiation from being generated within the fuel structure. System as described.
[Embodiment 34]
said radioactive source material comprising strontium titanate, said high energy beta emitter comprising strontium 90, said electrons emitted by said radioactive energy source having a mean free path of 2 millimeters (mm), said fuel structure 34. The system of any of embodiments 23-33, wherein the thickness of the object is 2 mm or less and the thickness of the first shield is greater than 2 mm.
[Embodiment 35]
The radioactive source material is formed of spherical structures having the thickness, the spherical structures are dispersed within the first shield, and the second shield covers the first shield in which the spherical structures are dispersed. 35. The system of any of embodiments 23-34, configured to wrap.
[Embodiment 36]
Implementation wherein the fuel structure includes a first plurality of cylinders, the first shield includes a second plurality of cylinders, the first plurality of cylinders and the second plurality of cylinders are concentric. 36. The system of any of aspects 23-35.
[Embodiment 37]
37. The system of embodiment 36, wherein the second shield includes cylinders configured to enclose the first plurality of cylinders and the second plurality of cylinders.
[Embodiment 38]
Embodiment 36, wherein each of said first plurality of cylinders has said thickness, wherein said thickness is 2 mm or less, and each of said second plurality of cylinders has an additional thickness of 7 mm or less 38. The system according to any of 37.
[Embodiment 39]
Each of said first plurality of cylinders has said thickness, said thickness being 0.1-1 mm, 0.5-1.5 mm, 1.0-2.0 mm, 1.5-2. 5 mm; 38. The system of any of embodiments 36-37, having an additional thickness selected from 5 mm, or one of the range of 4-7 mm.
[Embodiment 40]
40. The system of any of embodiments 37-39, wherein the cylinder has a thickness selected from one of the ranges 1-5 cm, 1-10 cm, 5-10 cm, or 5-15 cm.
[Embodiment 41]
23. A method of forming a fuel structure according to any of embodiments 1-22, comprising the steps of selecting a radioactive source material for use; and forming the fuel structure based on the mean free path thickness of electrons emitted by the radioactive source material, wherein the electrons emitted by the beta decay process stop wherein said fuel structure has said thickness to prevent bremsstrahlung radiation from being generated within said fuel structure by allowing it to pass through said fuel structure without interference.
[Embodiment 42]
41. A method of forming a system according to any of embodiments 23-40, comprising the steps of selecting a radioactive source material for use and obtaining a predetermined amount of said radioactive source material to produce a predetermined amount of energy. and selecting a first material for use in forming a first shield for shielding the radioactive source material, wherein the thickness of the first material is the thickness of the radiation emitted from the radioactive source material. shielding the radioactive source material, wherein the thickness prevents the electrons from passing through the first shield by exceeding the electron mean free path; selecting a second material for use in forming a second shield for the second shield, said second shield preventing bremsstrahlung radiation generated by said electrons from passing through said second shield; and forming a two-phase shield against a radioactive source comprising said first shield and said second shield, wherein said radioactive source material is within a first material of said first shield said second shield being dispersed or formed within a cylinder concentric with said first shield, said second shield enveloping said first shield.

Claims (36)

A fuel design,
comprising a radioactive source material comprising high-energy beta-emitters;
to prevent electrons emitted by the radioactive source material as a result of a beta decay process from passing through the fuel structure without stopping, thereby generating bremsstrahlung radiation within the fuel structure; A fuel structure configured to have a thickness less than or equal to the mean free path of electrons emitted by the radioactive source material. 3. The fuel structure of claim 1, wherein said radioactive source material comprises strontium titanate. 2. The fuel structure of claim 1, wherein said high energy beta emitter comprises Strontium-90. the mean free path of electrons emitted by the radioactive energy source is 2 millimeters (mm);
2. The fuel structure of claim 1, wherein the fuel structure has a thickness of 2 mm or less. 2. The fuel structure of claim 1, wherein the energy of electrons emitted by said radioactive source material as a result of said beta decay process is 2 MeV. 2. The fuel structure of claim 1, wherein said radioactive source material has a decay activity of 100 Curies (Ci) or greater. 2. The fuel structure of claim 1, wherein said radioactive source material is formed of spherical structures having said thickness, said spherical structures dispersed within a first material. 8. The fuel structure of claim 7, wherein said first material has a low density, low atomic number, high thermal conductivity, high material decomposition temperature, and is compatible with said radioactive source material. 8. The fuel structure of claim 7, wherein said first material comprises graphite. 8. The fuel structure of claim 7, wherein said first material comprises lithium hydride, hydrogen-based oil or resin, or molten salt. 8. The fuel structure of claim 7, wherein said first material in which said spherical structures formed of said radioactive source material are dispersed is further encased in a second material. 12. The fuel structure of claim 11, wherein said second material has a high density, high effective atomic number, high thermal conductivity, high material decomposition temperature, and is compatible with other materials associated with said fuel structure. thing. 12. The fuel structure of claim 11, wherein said second material comprises tungsten. 12. The fuel structure of claim 11, wherein said second material comprises lead or depleted uranium. 2. The fuel structure of claim 1, wherein said radioactive source material is formed from a first plurality of cylinders. 16. The fuel structure of claim 15, further comprising a second plurality of cylinders formed of a first material, wherein said first plurality of cylinders and said second plurality of cylinders are concentric cylinders. 17. The fuel structure of claim 16, wherein said first material comprises graphite, lithium hydride, hydrogen-based oil or resin, or molten salt. 16. The fuel structure of claim 15, further comprising a third cylinder formed of a second material and configured to enclose the first plurality of cylinders and the second plurality of cylinders. 19. The fuel structure of claim 18, wherein said second material comprises tungsten, lead, or depleted uranium. 19. Each of said first plurality of cylinders has said thickness, wherein said thickness is 2 mm or less, and wherein each of said second plurality of cylinders has an additional thickness of 7 mm or less. A fuel structure as described in . A system for shielding radioactive source material, comprising:
a first shield formed of a first material having a thickness exceeding the mean free path of electrons emitted from the radioactive source material to prevent the electrons from passing through the first shield; a first shield;
a second shield formed of a second material and configured to prevent bremsstrahlung radiation generated by the electrons from passing through the second shield. the first material has a low density, a low atomic number, a high thermal conductivity, a high material decomposition temperature, and is compatible with the radioactive source material;
22. The system of claim 21, wherein said second material has a high density, high effective atomic number, high thermal conductivity, high material decomposition temperature, and is compatible with other materials associated with said system. the first material comprises graphite, lithium hydride, hydrogen-based oil or resin, or molten salt;
23. The system of claim 22, wherein said second material comprises tungsten, lead, or depleted uranium. The mean free path of electrons emitted from the radioactive source material is 2 millimeters (2 mm), the thickness of the first material is 2 mm or less,
22. The system of claim 21, wherein the thickness of said second material is 7 mm or less. 22. The system of claim 21, wherein electrons emitted from said radioactive source material have an energy of about 2 MeV and said thickness is selected to prevent said electrons from passing through said first shield. a fuel source containing the radioactive source material;
a fuel container configured to contain the fuel source, wherein the first shield is configured to enclose the fuel container and the second shield is configured to enclose the first shield; and 22. The system of claim 21, further comprising: the fuel source comprises strontium titanate;
27. The system of claim 26, wherein the radioactive source material comprises Strontium-90. 27. The system of claim 26, wherein said radioactive source material comprises a high energy beta emitter. 22. The claim of claim 21, wherein bremsstrahlung radiation produced by said electrons is produced within said first shield and bremsstrahlung radiation produced within said first shield is attenuated within said first shield or said second shield. system. The bremsstrahlung radiation generated by the electrons is generated within a fuel container configured to contain a fuel source containing the radioactive source material, and the bremsstrahlung radiation generated within the fuel container is generated by the first shield or the 22. The system of claim 21, attenuated within the second shield. further comprising a fuel structure with a radioactive source material including high energy beta emitters;
wherein the fuel structure is configured to have a thickness less than or equal to the mean free path;
Electrons emitted by the radioactive source material as a result of beta decay processes can pass through the fuel structure without stopping, thereby preventing bremsstrahlung radiation from being generated within the fuel structure. 22. The system of claim 21. the radioactive source material comprises strontium titanate;
the high-energy beta-emitter comprises strontium-90;
the mean free path of electrons emitted by the radioactive energy source is 2 millimeters (mm);
The fuel structure has a thickness of 2 mm or less,
32. The system of claim 31, wherein the thickness of said first shield is greater than 2 mm. The radioactive source material is formed of spherical structures having the thickness, the spherical structures are dispersed within the first shield, and the second shield covers the first shield in which the spherical structures are dispersed. 32. The system of claim 31, configured to wrap. The fuel structure includes a first plurality of cylinders, the first shield includes a second plurality of cylinders, the first plurality of cylinders and the second plurality of cylinders being concentric. 32. The system of Clause 31. 35. The system of claim 34, wherein the second shield includes cylinders configured to enclose the first plurality of cylinders and the second plurality of cylinders. 35. The cylinder of claim 34, wherein each of said first plurality of cylinders has said thickness, said thickness is 2 mm, and each of said second plurality of cylinders has an additional thickness of at least 7 mm. System as described.

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