CA2211145A1 - Stabilized depleted uranium material - Google Patents

Abstract

The present invention is a radiation shielding composition devised to provide shielding for radioactive materials. The invention is a stabilized depleted uranium material having an air and/or water impermeable layer (28) at the surface (26) of a depleted uranium compound (24). The stabilized depleted uranium material is a stable form of at least one depleted uranium compound, which may be used for radiation shielding as a base component, aggregate or additive, in shielding materials such as concrete, ceramic, bituminous materials, metal, composite, polymercements, polymer, glass or water.

Description

STABILIZED DEPLETED URANIIIM MATERIAL
BACKGROUND

Related Application This application is a continuation-in-part of Quapp et al., filed January 23, 1995, entitled "Radiation Shielding Composition" assigned Attorney Docket No. PI-700 and United States Serial Number 08/378,161, the whole of which is hereby incorporated by reference.
Field of the Invention This invention relates to the field of radiation shielding for radioactive materials. More particularly, this invention relates to a stabilized depleted uranium material for attenuating gamma rays in radiation shielding materials.
Background of the Invention Two important characteristics of radiation shielding with respect to radioactive materials are: (1) gamma radiation absorption and (2) neutron absorption.
Gamma rays are quanta of electromagnetic wave energy similar to but of much higher energy than ordinary X-rays. Gamma rays are emitted by certain radioactive materials during the decay process and are highly penetrating, being absorbed- only by adequate thicknesses of substantially dense matter, such as lead, heavy metals, and various forms of cement. Neutrons, on the other hand, are uncharged elementary particles.
Neutrons interact with matter primarily through collisions and are absorbed by materials exhibiting substantially large thermal neutron capture cross-sections. The present invention goes to the absorption of gamma radiation absorption; however, it is to be understood that the present invention may be practiced in combination with neutron absorption techniques known in the art.
Substantial efforts have gone into developing economical ways to store and dispose of increasing amounts of radioactive materials, particularly radiative wastes produced from the processing of nuclear fuel, nuclear power plants, and other nuclear facilities. A
significant portion of this effort has been directed at radiation shielding means having improved radiation shielding compositions for containers, containment systems and the like, wherein the high-level radioactive material is contained over extended periods of time.
High-level radiative materials, including liquids from reprocessing and spent (used) nuclear fuel, typically have half-lives of hundreds of thousands of years. The reprocessing material is generally stored as liquids, then solidified, permanently stored, and disposed of as required. Spent nuclear fuel is stored initially in water-cooled pools at the reactor sites awaiting shipment to a permanent disposal site. After about ten years, the fuel may be moved to dry storage containers until such time that a permanent disposal facility becomes available.
Ideally, radiation shielding means, such as containers for storage and transport of radiative materials, should confine them safely for at least about 100 years, and preferably about 300 years.
Lead has often been used for gamma ray shielding in radiation shielding means because it is dense, easily worked and relatively inexpensive. A lead shield can often be thinner and more compact than a comparable radiation shield made of almost any other material except depleted uranium. This ability to take up less space and be more portable is highly desirable for radiation shielding systems since it is often necessary to move the shielding systems, such as to more remote locations for safety purposes. Additionally, it is often desirable to build shielding systems in locations where there is limited space and available real estate for radioactive storage purposes is at a premium.
One disadvantage of lead is it tends to accumulate in the body, similar to other heavy-metal poisons, and continues producing toxic effects for may years after exposure. Therefore, it is desirable to eliminate lead from many of its present uses, including radiation shielding, and define substitutes for lead. It has been recognized that it would be advantageous to develop radiation shielding systems utilizing depleted uranium (chiefly uranium-238). Although there have been efforts in the art to develop depleted uranium for radiation shielding, such as the use of depleted uranium rods or small balls in an iron cask as radiation shielding for shipping and storing spent nuclear fuel, Takeshima et al, U.S. Patent No. 4,868,400, such efforts have met with limited success.
These limitations are due in part to the radioactivity of uranium and depleted uranium metals, and in part to their high chemical reactivity (i.e. the tendency to corrode and readily oxidize).
One can find in the art a structure that includes depleted uranium covered by a non-radioactive, highly absorbent material, such as steel, e.g. Reese, U.S.
Patent No. Re. 29,876. In the prior art depleted uranium containers have been coated with stainless steel. Elsewhere in the prior art depleted uranium particles have been coated with metals and similar materials having high thermal conductivity, such as aluminum, copper, silver, magnesium, or the like, Takeshima et al., U.S. Patent No. 5,015,863. These efforts have met with limited success due to the complexity of the coating process, the expense of the coating materials, and the limited practical utility of depleted uranium having such coatings. Alternative shielding systems have employed a radiation shield having a depleted uranium core for absorbing gamma rays with a bismuth coating to attempt to prevent corrosion.
Alternatively, a gadolinium sheet has been positioned between the uranium core and the bismuth coating for absorbing neutrons, Kronberg, U.S. Patent No. 5,334,847.

Commercial systems using concrete as the shielding material have developed due to the comparatively low cost of concrete in the manufacture of systems, as compared to the cost of materials such as steel and 5 lead. Additionally, cement is relatively easy and inexpensive to cast into a desired form in order to assure a concrete having the structural stability necessary for radiation shielding. Advances in concrete technology have provided composite systems with a metal liner and a thick concrete outer shell for shielding gamma and neutron radiation. Due to these advantages concrete shielding systems now completely dominate the market for shielding of radiative materials.
However, concrete systems require great thicknesses to obtain the necessary shielding properties for radioactive materials; thus, concrete systems generally lack portability due to their high mass and substantial bulk, and limit the volume of radiative material that may be stored due to the space required for an adequate thickness of concrete.
It has been suggested that shielding characteristics may be improved by merely admixing depleted uranium metal or uranium oxides in a concrete, Yoshihisa et al., Japanese Patent Application Pub. No.
61-091598. While such approaches do have some potential for reducing the thickness of the radiation shielding material required there are serious chemical reactivity problems with these systems and the admixed depleted uranium or uranium oxide does not achieve as high a density as is desired. Most notably, the admixed depleted uranium or uranium oxide undergoes reactions in the concrete that results in the degradation of the concrete that prevents the concrete from obtaining the desired system life of one hundred years, particularly at elevated temperatures.
In another attempt found in the prior art, a three layered structure has been employed to attempt to reduce the thickness concrete shielding, Suzuki et al., U.S.
Patent No. 4,687,614. The three layered structure comprises a metallic vessel with a concrete lining and inner layer which is reinforced with a reinforcing 5 material and strengthened with a polymeric impregnant, and a polymerized and cured impregnant layer as an intermediate layer between the metallic and concrete layers. However, this attempt, like others, has generally been unsuccessful in achieving the desired size reduction, while maintaining the cost advantages, desired strength and other properties of conventional concrete systems.
Summary of the Invention It is an object of the present invention to provide a radiation shielding concrete product for attenuating gamma rays and absorbing neutrons emitted from a radioactive material.
It is also an object of the invention to provide a depleted uranium material for use in a radiation shielding material wherein the depleted uranium material is chemically stable and does not degrade upon long-term storage.
It is another object of the invention to provide a method of shielding radiation comprising gamma rays and neutrons with a composition comprising gamma ray attenuating and neutron absorbing components.
It is still another object of the invention to provide a method of making a stabilized depleted uranium material for use in shielding radiation comprising gamma rays and neutrons.
These and other objects can be obtained by providing a radiation shielding concrete product comprising a stabilized depleted uranium material and a neutron absorbing component, the stabilized depleted uranium material and neutron absorbing component being present in the concrete product in sufficient amounts to provide a concrete having a density between about 4 and about 15 grams per cm3 and that will, at a predetermined thickness, attenuate gamma rays and absorb neutrons from a radioactive material of projected gamma ray and neutron emissions over a determined time period. The 5 stabilized depleted uranium material is stabilized such that degradation of the concrete is prevented at a temperature of 250 C for a period of at least one month when in an environment that would be saturated with water vapor at room temperature.
A method of shielding radioactive material generating nuclear radiation comprising neutrons and gamma rays with a container containing gamma attenuating and neutron absorbing components comprises:
(a) determining the mass volume of radioactive material and the projected amount of radioactivity to be emitted in the form of gamma rays and neutrons over a determined time by the radioactive material;
(b) preparing a container for storage of the radioactive materials comprising an enclosed storage space surrounded by a layer of a radiation shielding concrete product, having a predetermined thickness, the .concrete comprising a stabilized depleted uranium material and a neutron absorbing component, the stabilized depleted uranium material and neutron absorbing component being present in the concrete product in sufficient amounts to provide a concrete having a density of between about 4 and about 10 grams per cm3 and which will, at the predetermined thickness, attenuate and absorb gamma rays and neutrons projected to be emitted from the mass volume of neutrons projected to be emitted from the mass volume of radioactive material over the determined time period; and (c) placing and sealing the mass volume of radioactive material in the enclosed storage space of the container.
A stabilized depleted uranium material for use in a radiation shielding material comprises:

at least one particle of a depleted uranium compound, the particle having a surface; and a layer circumferentially disposed on the surface of the particle wherein the layer does not substantially degrade at a temperature of between about 90 C and 250 C
for a period of at least one month in an environment that would be saturated with water vapor at room temperature. The depleted uranium compound is preferably a member selected from the group consisting of uranium silicides, uranium borides, uranium nitrides, uranium phosphides, uranium sulfides, uranium arsenides, uranium selenides, uranium tellurides, uranium carbides, uranium bismuthides, uranium antimonides, and mixtures thereof.
In one illustrative embodiment, the layer is formed by the reaction of the depleted uranium compound with a stabilizing agent, preferably wherein the stabilizing agent is an oxidizing agent that reacts with the depleted uranium compound to result in a product that is substantially water and air impermeable. In another illustrative embodiment, the layer is formed by coating the particle with a coating material selected from the group consisting of cement, ceramic material, bituminous material, metal, composite, polymer cement, polymer, glass, and mixtures thereof. In still another illustrative embodiment, the stabilized depleted uranium material is formed into a densified aggregation of particles. Such a densified aggregate can be formed by binding a plurality of particles together with binding means to form an aggregate thereof. The binding means is preferably a member selected from the group consisting of glasses, polymers, cements, ceramics, bituminous materials, metals, composites, polymer cements, and mixtures thereof. A densified aggregate can also be formed by fusing a plurality of particles together. A densified aggregate can also be formed by sintering a plurality of said particles in a sintering material. Preferred sintering materials are selected from the group consisting of clay, soil, basalt, and mixtures thereof. The stabilized depleted uranium material also preferably comprises a neutron absorbing material selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.
A method of making a stabilized depleted uranium material for use in a radiation shielding material comprising the steps of:
(a) providing a particle of a depleted uranium compound, said particle having a surface; and (b) forming a layer circumferentially disposed on the surface of said particle wherein said layer does not substantially degrade at a temperature of between about 90 C and 250 C for a period of at least one month in an environment that would be saturated with water vapor at room temperature.
Description of the Preferred Embodiments Drawings The features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with the accompanying drawings in which:
FIG. 1 is an enlarged cross-sectional view of stabilized depleted uranium material made in accordance with the principles of the present invention, having an inherently stable surface layer.
FIG. 2 is a cross-sectional view of shielding material containing the invention of FIG. 1. FIG. 3 is an enlarged cross-sectional view of an alternative embodiment of the invention of FIG. 1, having a coating.
FIG. 4 is an enlarged cross-sectional view of an alternative embodiment of the invention of FIG. 1, having a coating.

FIG. 5 is a cross-sectional view of shielding material containing the invention of FIGS. 3 and 4.
FIG. 6 is an enlarged cross-sectional view of an alternative embodiment of the invention of FIG. 1, having an aggregate formed by densification.
FIG. 7 is an enlarged cross-sectional view of an alternative embodiment of the invention of FIG. 1, having an aggregate formed by fusing.
FIG. 8 is an enlarged cross-sectional view of an alternative embodiment of the invention of FIG. 1, having an aggregate formed by sintering.
FIG. 9 is a cross-sectional view of shielding material containing stabilized depleted uranium material of FIGS. 6-8.
FIG. 10 is another cross-sectional view of shielding material containing stabilized depleted uranium material of FIGS. 6-8.
FIG. 11 is a cross-sectional view of shielding material containing stabilized depleted uranium material of FIGS. 1, 4, and 6-8.
Reference numbers are used consistently throughout the application to indicate like structures.
Structure The stable depleted uranium material of the present invention comprises at least one layer circumferentially disposed about the surface of a particle of depleted uranium compound 'which thereby causes the depleted uranium compound to be stable. The layer may be formed (a) due to the inherent properties of the product of the reaction of at least one stabilizing agent with at least one depleted uranium compound, (b) by coating at least one depleted uranium compound with at least one coating material, or (c) in the densification of at least one depleted uranium compound.
Depleted uranium, predominantly U-238, is a radioactive by-product produced in substantial quantities during the manufacture of fuel grade uranium i.e. enriched in U-235. To produce a workable and sufficiently solid form of depleted uranium material, depleted uranium compounds, known to those skilled in the art are used. These depleted uranium compounds 5 include: depleted uranium oxides, such as U02, U03 and U308; depleted uranium silicides, such as U3Si21 U3Si, USi, U2Si3, and Usi3; depleted uranium borides, such as UB2;
depleted uranium nitrides such as UN, UN2, and U2N3;
depleted uranium phosphides, such as UP, UP2, and U3P4;
10 depleted uranium sulfides, such as US, U2S31 U3S5, US2;
depleted uranium arsenides, such as UAs, U3As41 UasZ;
depleted uranium selenides, such as USe, U3Se51 U2Se31 USe2, and USe3; depleted uranium tellurides, such as UTe, U3Te4, U2Te31 UTe2, and UTe3; depleted uranium carbides, such as UC, UC2, and U2C3; depleted uranium bismuthides, such as UBi, U3Bi4, and UBi2; and depleted uranium antimonides, such as USb, U3Sb4 and USb2; and mixtures thereof.
Past efforts to utilize depleted uranium compounds have been largely unsuccessful, due in part to the expense in forming a shielding container and in part to the chemical reactivity of many of the depleted uranium compounds, which make it difficult, if not impossible, to obtain the desired long-life of the shielding container. The present invention employs depleted uranium compounds, but in a stable form, thereby providing a useful stabilized depleted uranium material for shielding containers, structures, walls and the like.
The stabilized radiation shielding composition of the present invention is a "stabilized depleted uranium material" for use in a "shielding material." The term "shielding material" designates a material, such as concrete, ceramic, bituminous material, metal, composite, polymer cement, polymer glass, or water, containing at least one stabilized depleted uranium material and used for shielding radioactive materials.

The shielding material may be for use in containers, structures and objects such as those indicated above.
Radiation shielding devices, such as containers, structures and objects are made from such shielding materials. Radiation shielding devices include:
floors, walls, ceilings, roofs, windows, doors, hatches, buildings, silos, pads, foundations, footings, vessels, vaults, transportation containers, storage containers, canisters, pipes, valves, vats, housings, concretes, slags, mats, sheets, wires, bricks, pellets, rods, slugs, bars, fibers, and the like.
Containers, structures, and objects having the stabilized depleted uranium material of the present invention have long-term durability, good handling properties, maximal internal capacity, good structural stability and minimal thickness. An especially desirable feature of this invention is the ability to utilize depleted uranium for. a useful purpose, thus solving a serious disposal problem that exists around the world for depleted uranium.
The term "stable" as applied herein refers to chemical stability and is preferably defined as stabilized depleted uranium material that does not substantially degrade at a temperature between approximately 90 C and 250 C, and more preferably at 250 C, for a period of at least one month in an environment that is saturated in water vapor at room temperature.
The term "stabilized depleted uranium material" is used to refer to:
(a) depleted uranium compound particles having at least a surface layer which is inherently stable;

(b) coated depleted uranium compound particles which are stable; or (c) stable densified aggregation of depleted uranium compound particles.

The present invention relates to the formation of stabilized depleted uranium material for use in a shielding material by forming a stable layer at the surface of particles of the depleted uranium compound.
Any stabilized depleted uranium material can be used in any shielding material for advantageously attenuating gamma rays. Additionally, the shielding materials, such as concrete, polymers, polymer cement, waxes and water, have inherent neutron attenuating qualities, an additional benefit when shielding radioactive materials.
It will be appreciated that the particles of the present invention are not necessarily of any particular shape, and that the cross-sectional diameters of particles can vary substantially from one particle to another. It will further be appreciated that the particles of the present invention can vary substantially from the illustrative particle sizes, and that such particles may be larger or smaller than such particle dimensions discussed in association with each embodiment.
An illustrative embodiment of the present invention shown in figure 1 is a stabilized depleted uranium material generally indicated at 20, which comprises a particle 24 of at least one depleted uranium compound having a stable surface layer 28 circumferentially disposed thereon. The stable surface layer 28 is the product of a reaction of depleted uranium compound and a stabilizing agent. This stable reaction product is disposed at least at the surface 26, and possibly deeper into and including the entire particle 24, to form at least an inherently stable layer 28.
Illustratively, consider the particle 24 of finely divided depleted uranium compound shown in figure 1.
The size of the depleted uranium compound particle 24 of the embodiment of figure 1 is generally in the range from approximately 5x10-7m (meters) to 5x10-2m, with preferred particle 24 size in the range from approximately 1x10'3m to ix10-2ta.
The stabilizing agent can comprise any material that can be reacted with or impregnated into the surface 26 of the particle 24, thereby causing at least the surface 26 of the particle 24 to be stable. For example, depleted uranium silicides can be used for the formation of an,inherently stable surface layer 28 on the particle 24 because the depleted uranium silicides can be combined with an oxygen based oxidizer (such as air, oxygen, or water) to form a stable layer 28 of amorphous silicon oxide (Si.02). Thus, reacting a depleted uranium compound, such as uranium silicide, with a stabilizing agent, such as an oxidizing agent, can produce the desired stable layer 28.
A particle 24 of depleted uranium sulfides or selenides can be oxidized to form at least a stable oxide surface layer 28 having good resistance to water and oxidation up to 300 C. Also, a particle 24 of depleted uranium bismuthide can also be oxidized to form a stable surface layer 28. Thus, stabilizing agents that form oxides from sulfides, selenides and bismuthides can comprise appropriate stabilizing agents.
Other depleted uranium compounds that can form a stable surface layer 28 include depleted uranium nitrides, carbides, phosphides and arsenides as well as borides, tellurides and antimonides. Thus, stabilizing agents can include those agents that form oxides from nitrides, carbides, phosphides, and arsenides, borides, tellurides and antimonides may also be appropriate stabilizing agents.
However, the various forms of depleted uranium oxide appear to disadvantageously swell and the depleted uranium nitrides and carbides seem to react with water vapor at the surface. The depleted uranium phosphide and arsenide compounds appear to be somewhat more stable than the nitrides and carbides, and therefore may be preferable.
The reaction forming at least a stable surface layer 28 on the particle 24 can occur before, at the time of, or after the inclusion of the depleted uranium compound in a shielding material 32 as shown in figure 2; provided that in those cases where the reaction forming the stable surface layer 28 occurs at the time of or after the inclusion of the depleted uranium compound particle 24 in the shielding material does not substantially reduce the structural integrity of the shielding material.
In one embodiment, depleted uranium silicide compounds can be reacted with oxygen, water or a similar oxidizing reagent to form at least a layer 28 of silicon oxide (Si02) on the particle 24. Such reactions as may be carried out by those skilled in the art illustratively include the following:

UxSiy + 02 =;~ U,,Siy-1 + Si021 or UxSiY + 2H20 ~ U,~SiY_1 + Si02 + 2H2;

where x and y represent the atom ratio in the molecule of depleted uranium and silicon, respectively. Those skilled in the art will appreciate that the above formulae are merely illustrative of the formation of at least a stable surface layer 28, and one skilled in the art will recognize additional methods for forming a stabilized surface layer 28 for a particle 24 of depleted uranium compound.
An alternative embodiment of the present invention shown in figure 3 is a stabilized depleted uranium material indicated generally at 40 which comprises a particle 44 of at least one depleted uranium compound, the surface 46 of which is coated with a coating material 48 which is stable and may further be substantially water and/or air impermeable material. By coating it is understood that either the surface 46 is directly covered at least partially, but preferably entirely, by the coating material 48, or that the surface 46 is covered by one or more layers of an 5 additional material; where the additional material is covered at least partially, but preferably entirely, by the coating material 48. Thus, it will be appreciated that the coating material 48 does not necessarily contact the surface 46 of the depleted uranium compound 10 particle 44, but at least partially covers the particle 44 even though at least one layer of additional material is disposed between the surface 46 of the particle 44 and the coating material 48.
In this embodiment a particle 44 of depleted 15 uranium compound is coated with a coating material 48, which is a member selection from the group consisting of glasses, polymers, cements, ceramics, bituminous materials, metals, composites, polymer cements, and mixtures thereof. Suitable glasses include silicon dioxide glass, clay glass and mixtures thereof.
Suitable polymers can include thermoplastic polymers, casting resins and polymers, and thermosetting resins and polymers, such as: ABS copolymers, allyl resins, amino resins, acetal resins, cellulose acetates, celluloses, epoxy resins, melamines, phenol-formaldehyde resins, phenolic resins, phenoxy resins, polyphenylenes, polypropylenes, polyacrylonitrile, polybutylenes, polycarbonate, polyethylene terephthalate, polyethylene (including cross-linked polyethylene), polyimides polymethacrylonitrile, polymethyl methacrylate, polymethylpentenes, polyolefins, polyphosphates, polystyrenes, polysulfones, polytetrafluoroethylene, polyurethane, polyvinyl butyrals, polyvinyl chloride, polyvinyl acetates, thermosetting resins, and ureas.
Care must be taken to avoid a coating material 48 which will be readily destroyed by corrosion, chemical reaction or degradation by the depleted uranium compound WO 96/23310 PCTlUS96/00903 or the surrounding environment. For this reason the ceramic and glass coatings are especially preferred.
With respect to the embodiment shown in figure 3, the particle 44 is coated with a coating material 48 is shown in figure 3. The particle 44 of depleted uranium compound 48 can be formed from finely divided depleted uranium compound, comprising single crystal of depleted uranium compound. Similarly, as shown in figure 4, the stabilized depleted uranium material 50 of this alternative embodiment may comprise a particle 52 of depleted uranium material which comprises more than one crystal 54-57 of at least one depleted uranium compound, bounded together with narrow disorganized regions of common atoms at grain boundaries 58 between the crystals 54-57; the surface 59 of the particle 52 being coated with material 60 as discussed with respect to the embodiment of figure 3.
In the alternative embodiments of the present invention shown in figures 3-4, the size of the depleted uranium compound particles 44 and 52 generally range from approximately 5x10-6n to 5x10'2m, with preferred particle size in the range from approximately 1x10-3m to 1x10'Zm.
As shown in figure 4, additional advantages may arise where the coating material 60 comprises neutron absorbing means, indicated at 64, thus having the additional advantage of absorbing neutrons as well as shielding gamma radiation. Neutron absorbing components of the coating material 60 (as well as the shielding material) include hydrogen and oxygen. Additives to the coating material 60 that can further enhance neutron absorption include: beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium.
Now referring back to figure 3, there is shown the coating material 48 applied to the depleted uranium compound particle 44 by methods well known in the art of coating; which include forming at least one layer by at least one: bath, spray, extruder, die, mold, blower, roller, solution, emulsion, electrodeposition; and includes such techniques as: bathing, spraying, extruding, casting, molding (including use of injection and vacuum techniques), blowing, rolling, electroplating, fusing, mixing, hot powder coating, precipitating, laminating, calendaring, pressing, rolling, drop forming (where a droplet is formed about the particle), dry spinning (process of forcing a solution through holes in a spinneret and evaporating the solvent), dipping, melt spinning (process of forcing molten material through holes in a spinneret and cooling), pultrusion (process of dipping, passed through die, and curing), wet spinning (process of precipitation from solutions), thermoforming (process of formation using hot thermoplastic sheets), and similar coating processes. It is to be understood the coating material 48 may vary in thickness from a substantially thin film to a relatively thick layer as compared to the particle 44 size, and the coating material 48 may further vary from a substantially uniformly thick layer to a relatively non-uniformly thick layer. Finally, it is to be understood that the coating material 48 comprises at least one layer, and may comprise more than one layer, formed about the particle 44.
As shown in figure 5, the stabilized depleted uranium material 40 or 50 of this embodiment may be disposed in a shielding material 62.
In another alternative embodiment of the present invention, the depleted uranium compound comprises at least two particles disposed substantially close together such that at least one stable aggregate of depleted uranium compound which is "substantially dense"
is formed. By "substantially dense" it is meant that the density of aggregate can range from approximately 4 to 15 grams per cm3 (cubic centimeter) , yet the preferred density range for the aggregate is in the range from approximately 5 to 11 grams per cm3.
Other alternative embodiments of the present invention include densifying particles of depleted uranium compound having an inherently stable layer or a coating within a binding means to form an aggregate;
fusing the coatings of depleted uranium compound particles to form an aggregate; and, sintering particles of depleted uranium compound in a sintering material so as to form an aggregate. In addition to stability, such aggregates provide increased density of the depleted uranium, which is employed advantageously in shielding material.
The particles of depleted uranium compound range generally from approximately 5x10-7m to 5x10'2n, with preferred particle size in the range from approximately 1x10'3m to ix10-2a. Additionally, the aggregate may have a cross-sectional diameter ranging generally from approximately 5x10-4e to ix10'lm, and the preferred aggregate diameter is in the range from approximately 5x10'3m to 35x10'3n.
Consider first the alternative embodiment of the present invention shown in figure 6, wherein an aggregate, depicted generally as 80, comprises at least two particles 84 of at least one depleted uranium compound having a surface 86 which comprises an inherently stable layer or stable coating, wherein the particles 84 are densified within a binding means 88.
The binding means 88 can comprise a number of different materials useful for binding the particles 84 together in a substantially dense aggregate 80. The bindings means comprises those coating materials and a shielding materials such as those previously discussed above.
The binding means 88 forms what may be considered as a cementitious phase of atoms between the particles 84 of depleted uranium compound, the cementitious phase of the binding means 88 containing some atoms of elements dissimilar to the atoins of the depleted uranium compound and binding the particles 84 together, forming a substantially dense aggregate 80 which can be employed advantageously in a shielding material.
Additional advantages may arise where the binding material 88 further comprises neutron absorbing means, indicated at 90, such as those previously discussed.
Consider next the alternative embodiment of the present invention shown in figure 7, wherein an aggregate, depicted generally as 100, comprises at least two particles 104 of at least one depleted uranium compound, the surfaces (including a surface layers or coatings) 108 of the at least two depleted uranium compound particles being fused to form an aggregate 100.
As will be appreciated, the fusing of the surfaces 108 may form regions where material is melded together, as shown at 112, but may also form regions containing voids 116. While the melded and void regions may exist within one aggregate 100, it is preferable to avoid formation of voids 116 in order to obtain substantially dense material.
The fused surfaces 108 in this embodiment of the invention can comprise the inherently stable surface layers formed on depleted uranium compound particles, as well as including coatings, as have been previously discussed in other embodiments herein. In any event, the fusing of the surfaces 108 forms a stable aggregate 100 of at least two particles 104 which is preferably substantially dense and can be employed advantageously in a shielding material.
Additional advantages may arise where the coatings 108 further comprises neutron absorbing means, indicated at 110, such as those previously discussed.
Now, consider the alternative embodiment of the present invention shown in figure 8, wherein an aggregate, depicted generally as 120, comprises particles 124 having a surface 126, the particles 124 comprising at least one depleted uranium compound. In this embodiment the particles 124 are sintered in a sintering material 128 so as to form the stable 5 aggregate 120. Sintering forms a substantially dense aggregate 120 which can be employed advantageously in a shielding material, shown in figures 9-10.
Referring back to figure 8, the sintering process for producing the desired densification of particles 124 10 to form the aggregate 120 can include: (a) solid state sintering, (b) sintering aided by a liquid phase, also called liquid phase sintering; and (c) pressure aided sintering, also called hot pressing or hot isostatic pressing, where the solid or liquid phase sintering is 15 aided by the concurrent application of pressure.
Additionally, pressing the mixture of depleted uranium compound particles 124 and sintering material prior to sintering or after sintering, may be employed.
All sintering takes place at temperatures lower 20 than the melting point of the depleted uranium compound, even if a molten phase, or cementitious phase, of the sintering material is utilized. Also during sintering, one may expect some amount of grain growth in the depleted uranium compound.
As can be appreciated, in addition to the stability which arises due to the sintering, the aggregate 120 is also substantially dense and can be employed advantageously in a shielding material.
An especially preferred uranium aggregate 120 according to this alternative embodiment of the invention, due to its hardness, strength, stability, resistance to leaching and low cost is a finely divided depleted uranium compound which has been liquid phase sintered; where the sintering material comprises a material from the group which includes: clay, soil, and basalt. The aggregate 120 according to this embodiment comprises a sintered mixture of depleted uranium compound and one or more phases derived from a reactive liquid of the sintering material.
The depleted uranium compound particles 124 are contained within the aggregate 120 of this embodiment in one or more of the following physical forms: (1) chemically bound in an amorphous or glass phase, (2) chemically bound in crystalline mineral phases; and, (3) at least one oxide phase physically surrounded by a crystalline and amorphous phase. In addition to being stable, the aggregate 120 has been found to resist water, steam, oxygen, chemical phases in Portland cement, and weak acids and bases.
The sintering process for producing the aggregate 120 of this embodiment may additionally benefit from the application of pressure concurrent with the heating.
The application of pressure in the sintering process has the advantage of eliminating the need for very fine particles 124 of depleted uranium compound material and/or sintering material, and also removes voids and pores which may arise due to nonuniform admixing of the depleted uranium compound particles 124 and sintering material.
Additional advantages may arise where the sintering material 128 further comprises neutron absorbing means, indicated at 130, such as those previously discussed.
One preferred illustrative embodiment of a liquid phase sintering process employs natural or synthetic basalt. Preferably the basalt is finely ground prior to heating to form the reactive liquid phase of the sintering material. The finely ground basalt generally has a size ranging generally from approximately 1x10-6m to 5x10'sm, with preferred particle 124 size in the range from approximately 5x10-6m to 2x10'Sm. Additionally, a preferred basalt would comprise a material comprising:
(a) silicon oxide (e.g. Si Z) in an amount between approximately 25 and 60 weight percent; (b) aluminum oxide (e.g. A1203) in an amount between approximately 3 and 20 weight percent; (c) iron oxide (e.g. Fe203 and/or Fe/0) in an amount between approximately 10 and 30 weight percent; (d) titanium oxide (e.g. Ti02) in an amount between approximately 0 and 30 weight percent;
(e) zirconium oxide (e.g. ZrO2) in an amount between approximately 0 and 15 weight percent; (f) calcium oxide (e.g. CaO) in an amount between approximately 0 and 15 weight percent; (g) magnesium oxide (e.g. MgO) in an amount between approximately 0 and 5 weight percent; (h) sodium oxide (e.g. Na20) in an amount between approximately 0 and 5 weight percent; (i) potassium oxide ( e. g. KZO ) in an amount between approximately 0 and 5 weight percent; and wherein the weight percents are those of the sintering material based on the total weight of the composition thereof prior to the addition of any depleted uranium compound.
The preferred liquid phase sintering process for a depleted uranium compound according to this embodiment is carried out at a temperature between approximately 1000 C and 1500 C in an oxidizing or reducing atmosphere; which is starkly different from normal solid state sintering of uranium dioxide powder which is carried out at about 1700 C in a vacuum or reducing atmosphere in the production of nuclear fuel.
Another embodiment of the present invention employs clay as the sintering material for liquid phase sintering. Clay is advantageous because it provides plasticity and binding properties to a mixture containing a finely divided depleted uranium compound, thus greatly aiding the "green" forming of the mixture prior to the firing application of heat in the furnace for sintering.
Solid state sintering includes dry pressing and extrusion processes. With solid state sintering organic binders must be added to the depleted uranium compound particles in order to provide sufficient plasticity to form a green having sufficient density and strength to be handled prior to sintering.
In one illustrative example of the practice of the present invention, depleted uranium hexafluoride is hydrolyzed with water and precipitated as ammonium diuranate or ammonium uranyl carbonate, by addition of ammonia or ammonium carbonate respectively. The precipitate is dried and then calcined and reduced at 800 C in hydrogen to produce the depleted uranium compound, depleted uranium oxide as a powder.
Once the depleted uranium oxide is produced, a coarse aggregate if formed by cold pressing a mixture of depleted uranium oxide and basalt to approximately 60%
density. This is followed by sintering the mixture under pressure, the sintering being carried out at a temperature between approximately 1000 C and 1500 C in an oxidizing atmosphere such as air, the pressure being sufficient to produce an aggregate 120 having a density of approximately 5 to 11 grams per cm3.
Another illustrative example of the practice of the present invention would be to mix the depleted uranium oxide powder and basalt with a small amount of polyvinyl alcohol and allow it to form into roughly spherical clumps under agitation by the "flying disk" process, and then sintering the clumps under pressure, the sintering being carried out at a temperature between approximately 1000 C and 1500 C in an oxidizing atmosphere of air, the pressure being sufficient to produce an aggregate 120 having a density of approximately 5 to 11 grams per cm3.
As is shown in figure 9, an aggregate 80, 100, 120 such as those discussed in figures 6, 7, and 8, can be included in a shielding material 140, such as concrete, ceramic, bituminous materials, metal, composite, polymer cements, polymer, glass or water. As indicated in figure 9, the aggregate 80, 100, 120 may be admixed throughout the shielding material 140, or as indicated in figure 10, the aggregate 80, 100, 120 may be placed in a compact configuration within the shielding material 140.
As indicated in figure 9, additional advantages may arise where the shielding material 140 further comprises neutron absorbing means, indicated at 150, such as those previously discussed.
As shown in figure 11, it is to be appreciated that the shielding material 160 may include more than one form of stabilized depleted uranium material 20, 40, 50, 80, 100, 120.
Shielding materials may comprise at least one of the following: concrete, ceramic, bituminous materials, metal, composite, polymer cements, polymer, glass, water, and other such substances known by those skilled in the art. It is preferred that the shielding material further comprise a substance useful in attenuating and absorbing neutrons, such as those neutron absorption means discussed above. Specific illustrative examples of shielding materials useful in the practice of the present invention include: portland cement, polymers, sulfur polymer cement, waxes, water, bituminous materials, and metal.
Additional advantages may arise where the shielding material comprises neutron absorbing means, such as those previously discussed.
By way of further example, a stabilized depleted uranium material incorporated into a concrete shielding material is illustrated.
Concrete incorporating depleted uranium oxide aggregate is produced by conventional means. Mix proportions for conventional heavy aggregate concretes are similar to those used for construction concretes.
Such mix proportions are also suitable for use with the depleted uranium oxide aggregates. Mix proportions are 1 part cement, 2 parts sand, and 4 parts coarse aggregate by weight, with about 5.5 to 6 gallons of water per 94-lb bag of cement. Ordinary Portland cement WO 96/23310 PCTlUS96/00903 (Portland Type I-II cement) is used. The water/cement ratio (which could affect neutron absorption) is selected to maximize the concrete strength. Uranium oxide aggregates are coated with a water and air 5 impermeable coating to provide desired stability at elevated temperatures. Heavy mineral fines (e.g., barite or magnetite sands) are used as a replacement for sand if further increases in concrete density are desired. Neutron absorbing additives, such as boron 10 compounds, e.g. boron carbide, boron frits, baron-containing glass, or B203; hafnium compounds, e. g. Hf02;
or gadolinium compounds, e.g. Gd203, are also added as needed.
The concrete shielding composition of this 15 invention preferably contains reinforcing materials, such as steel bars, necessary to meet structural requirements for accidents and seismic events, reinforcing fillers and/or strengthening impregnants.
These materials include steel fiber, glass fiber, 20 polymer fiber, lath and reinforcing steel mesh.
A U02 aggregate concrete, using typical standard mix proportions, has a density of between about 6.8 and about 8.0 g/m3 (20 to 500 lb/ft3), depending upon the density of the U02 aggregate and whether silica sand or 25 barite sand is used.
Depleted uranium oxide concrete has a much higher density than conventional heavy aggregate concretes or construction concretes (Table (1). Since the shielding advantage for gamma radiation is approximately proportional to the density of the concrete, a unit thickness of depleted U02 concrete provides an average of 1.8 times the shielding of conventional heavy aggregate concrete (contains barite, magnetite or limonite as a replacement for conventional gravel aggregate) and 3.2 times that for construction concrete.
The improved shielding performance of U02 aggregate concrete provides significant container weight savings.

A vendor of spent fuel storage casks uses a 29 inch thickness of conventional concrete (150 lb/ft3) as a radiation shield. Depleted U02 concrete with a density of 500 lb/ft3, requires slightly less than 9 inches to provide the same amount of gamma radiation shielding.
A container having length of 16 feet, excluding capped ends, inside diameter of 70.5 inches, and required wall thickness of 29 inches for conventional concrete and 9 inches for depleted UO2 concrete, the depleted uranium concrete containing (including capped ends) weight 27%
less than the conventional concrete container.
Table 1. Density and equivalent shielding for different concrete types.

Concrete Type Aggregate Concrete Equivalent Density, Densit~, Shielding g/cm g/cm Thickness Ration' Construction 2.7 2.2 to 2.4 3.2 Concrete Conventional 3.6 to 3.4 to 4.8 1.8 Heavy 7.8 Aggregate Concrete U02 Aggregate 9.9 to 11 6.8 to 8.0 1 Concrete a. Equivalent shielding thickness ratio for gamma radiation assuming average concrete type density.

In addition to potential weight advantages, as illustrated in the preceding paragraph, significant space savings are also obtained. In the above example, the 70.5 inch inside diameter concrete cask contains an inner metal container holding 24 PWR spent fuel elements has an outside diameter of 129 inches. A depleted U02 concrete cask, having the same 70.5 inch inside diameter has an outside diameter of about 90 inches. Thus, the increased shielding capability of the uranium aggregate containing concrete of this invention compared to that of conventional concrete can provide increased storage capacity and/or save space in a shielding container.
Also, the potential smaller size of the UOZ concrete cask makes it easier to manufacture (e.g., lower form costs, etc.) and transport, as compared to a cask made from conventional concrete.
Another cost benefit of this invention utilizing depleted uranium aggregate is the costs that are avoided by not having to continue to store depleted UF6 gas in pressurized containers. There are also costs associated with the potential for release to the environment and other possible safety issues that are avoided. In addition, the stored UF6 will eventually have to be processed for disposal or some other use.

Claims (45)

28What is claimed is:

1. A radiation shielding concrete product comprising a stabilized depleted uranium material and a neutron absorbing component said stabilized depleted uranium material and neutron absorbing component being present in said concrete product in sufficient amounts to provide a concrete having a density between about 4 and 15 grams per cm3 and which will, at a predetermined thickness, attenuate gamma rays and absorb neutrons from a radioactive material of projected gamma ray and neutron emissions over a determined time period.

2. The product as in claim 1 wherein said stabilized depleted uranium material is coated such that it is sufficiently stable as to prevent degradation of said concrete at a temperature of 250 C for a period of at least one month when in an environment which would be saturated with water vapor at room temperature.

3. The product as in claim 2 wherein said stabilized depleted uranium material comprises a depleted uranium compound selected from the group consisting of uranium oxides, uranium silicides, uranium borides, uranium nitrides, uranium phosphides, uranium sulfides, uranium arsenides, uranium selenides, uranium tellurides, uranium carbides, uranium bismuthides, uranium antimonides, and mixtures thereof.

4. The product as in claim 2 wherein said stabilized depleted uranium material comprises a sintered mixture of a finely divided depleted uranium compound and at least one phased derived from a reactive liquid.

5. The products as in claim 4 where in said sintered mixture is formed by a liquid phase sintering technique and said stabilized depleted uranium material comprises a depleted uranium compound comprising a uranium oxide.

6. The product as in claim 4 wherein said reactive liquid is produced by heating at least one member selected from the group consisting of clay, soil, basalt, and mixtures thereof.

7. A product as in claim 6 wherein said depleted uranium compound comprises a uranium oxide and said reactive liquid is produced by heating finely divided basalt wherein said basalt has a composition comprising;
(a) silicon oxide in an amount between about 25 and 60 weight percent, (b) aluminum oxide in an amount between about 3 and about 20 weight percent, (c) iron oxide in an amount between about 10 and about 30 weight percent, (d) titanium oxide in an amount between 0 and about 30 weight percent, (e) zirconium oxide in an amount between 0 and about 15 weight percent, (f) calcium oxide in an amount between 0 and about 15 weight percent, (g) magnesium oxide in an amount between 0 and about 5 weight percent, (h) sodium oxide in an amount between 0 and about weight percent, and (i) potassium oxide in an amount between 0 and about 5 weight percent.

8. The product as in claim 7 wherein said sintered material is produced by a liquid phase sintering process carried out at a temperature between about 1000° and about 1500°C.

9. The product as in claim 2 wherein said depleted uranium aggregate is coated with a protective coating.

10. The product as in claim 2 wherein said neutron absorbing component is a member selected from the group consisting of hydrogen and compounds of boron, hafnium, gadolinium, beryllium, cadmium, iridium, mercury, europium, samarium, dysprosium, erbium, and lutetium.

11. A method of shielding radioactive materials generating nuclear radiation comprising neutrons and gamma rays with a container containing gamma attenuating and neutron absorbing components, comprising:
(a) determining the mass volume of radioactive material and the projected amount of radioactivity to be emitted in the form of gamma rays and neutrons over a determined time by said radioactive material;
(b) preparing a container for storage of said radioactive materials comprising an enclosed storage space surrounded by a layer of radiation shielding concrete product, having a predetermined thickness, said concrete comprising a stabilized depleted uranium material and a neutron absorbing component said stabilized depleted uranium material and neutron absorbing component being present in said concrete product in sufficient amounts to provide a concrete having a density of between about 4 and about 10 grams per cm3 and which will, at said predetermined thickness, attenuate and absorb gamma rays and neutrons projected to be emitted from said mass volume of neutrons projected to be emitted from said mass volume radioactive material over said determined time period; and (c) placing and sealing said mass volume of radioactive material in said enclosed storage space of said container.

12. A stabilized depleted uranium material for use in a radiation shielding material comprising:
at least one particle of a depleted uranium compound, said particle having a surface; and a layer circumferentially disposed on the surface of said particle wherein said layer does not substantially degrade at a temperature of between about 90°C and 250°C for a period of at least one month in an environment that would be saturated with water vapor at room temperature.

13. The stabilized depleted uranium material of claim 12 wherein the depleted uranium compound is a member selected from the group consisting of uranium silicides, uranium borides, tiranium nitrides, uranium phosphides, uranium sulfides, uranium arsenides, uranium selenides, uranium tellurides, uranium carbides, uranium bismuthides, uranium antimonides, and mixtures thereof.

14. The stabilized depleted uranium material of claim 13 wherein said layer is formed by the reaction of said depleted uranium compound with a stabilizing agent.

15. The stabilized depleted uranium material of claim 14 wherein said depleted uranium compound comprises uranium silicide and said stabilized depleted uranium material is mixed in a radiation shielding material comprising concrete.

16. The stabilized depleted uranium material of claim 14 wherein said stabilizing agent is an oxidizing agent that reacts with said depleted uranium compound to result in a product that is substantially water and air impermeable.

17. The stabilized depleted uranium material of claim 12 wherein said layer is formed by coating said particle with a coating material selected from the group consisting of cement, ceramic material, bituminous material, metal, composite, polymer cement, polymer, glass, and mixtures thereof.

18. The stabilized depleted uranium material of claim 17 wherein said coating material comprises a neutron absorbing material selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium, lutetium, and mixtures thereof.

19. The stabilized depleted uranium material of claim 12 further comprising:
binding means for binding a plurality of said particles together to form an aggregate thereof.

20. The stabilized depleted uranium material of claim 19 wherein said binding means is a member selected from the group consisting of glasses, polymers, cements, ceramics, bituminous materials, 'metals, composites, polymer cements, and mixtures thereof.

21. The stabilized depleted uranium material of claim 20 wherein said binding means further comprises a neutron absorbing material is a member selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.

22. The stabilized depleted uranium material of claim 12 wherein at least two of said particles are fused together to form an aggregate thereof.

23. The stabilized depleted uranium material of claim 22 wherein said aggregate further comprises a neutron absorbing material is a member selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.

24. The stabilized depleted uranium material of claim 12 wherein a plurality of said particles is sintered in a sintering material to form a stable aggregate thereof.

25. The stabilized depleted uranium material of claim 24 wherein said plurality of particles is sintered at a temperature of between about 1000°C and 15000.

26. The stabilized depleted uranium material of claim 25 wherein said sintering material is selected from the group consisting of clay, soil, basalt, and mixtures thereof.

27. The stabilized depleted uranium material of claim 26 wherein said sintering material is basalt comprising:
(a) silicon oxide in an amount between approximately 25 and 60 weight percent; (b) aluminum oxide in an amount between approximately 3 and 20 weight percent; (c) iron oxide in an amount between approximately 10 and 30 weight percent; (d) titanium oxide in an amount between approximately 0 and 30 weight percent; (e) zirconium oxide in an amount between approximately 0 and 15 weight percent; (f) calcium oxide in an amount between approximately 0 and 15 weight percent; (g) magnesium oxide in an amount between approximately 0 and 5 weight percent; (h) sodium oxide in an amount between approximately 0 and 5 weight percent; (i) potassium oxide in an amount between approximately 0 and 5 weight percent; and wherein the weight percents are those of the sintering material based on total weight prior to addition of depleted uranium compound.

28. The stabilized depleted uranium material of claim 24 wherein said sintering material further comprises a neutron absorbing material is a member selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.

29. A method of making a stabilized depleted uranium material for use in a radiation shielding material comprising the steps of:
(a) providing a particle of a depleted uranium compound, said particle having a surface; and (b) forming a layer circumferentially disposed on the surface of said particle wherein said layer does not substantially degrade at a temperature of between about 90°C and 250°C for a period of at least one month in an environment that would be saturated with water vapor at room temperature.

30. The method of claim 28 wherein the depleted uranium compound is a member selected from the group consisting of uranium silicides, uranium borides, uranium nitrides, uranium phosphides, uranium sulfides, uranium arsenides, uranium selenides, uranium tellurides, uranium carbides, uranium bismuthides, uranium antimonides, and mixtures thereof.

31. The method of claim 29 wherein said layer is formed by reaction of said depleted uranium compound with a stabilizing agent.

32. The method of claim 30 wherein said depleted uranium compound comprises uranium silicide and said stabilized depleted uranium material is mixed in a radiation shielding material comprising concrete.

33. The method of claim 30 wherein said stabilizing agent is an oxidizing agent that reacts with said depleted uranium compound to result in a product that is substantially water and air impermeable.

34. The method of claim 28 wherein said layer is formed by coating said particle with a coating material selected from the group consisting of cement, ceramic material, bituminous material, metal, composite, polymer cement, polymer, glass, and mixtures thereof.

35. The method of claim 33 wherein said coating material comprises a neutron absorbing material selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium, lutetium, and mixtures thereof.

36. The method of claim 28 wherein said stabilized depleted uranium material further comprises:
binding means for binding a plurality of said particles together to form an aggregate thereof.

37. The method of claim 35 wherein said binding means is a member selected from the group consisting of glasses, polymers, cements, ceramics, bituminous materials, metals, composites, polymer cements, and mixtures thereof.

38. The method of claim 36 wherein said binding means further comprises a neutron absorbing material is a member selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.

39. The method of claim 28 wherein at least two of said particles are fused together to form an aggregate thereof.

40. The method of claim 38 wherein said aggregate further comprises a neutron absorbing material is a member selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.

41. The method of claim 28 wherein a plurality of said particles is sintered in a sintering material to form a stable aggregate thereof.

42. The method of claim 40 wherein said plurality of particles is sintered at a temperature of between about 1000°C and 1500°.

43. The method of claim 41 wherein said sintering material is selected from the group consisting of clay, soil, basalt, and mixtures thereof.

44. The method of claim 42 wherein said sintering material is basalt comprising: (a) silicon oxide in an amount between approximately 25and 60 weight percent;
(b) aluminum oxide in an amount between approximately 3 and 20 weight percent; (c) iron oxide in an amount between approximately 10 and 30 weight percent; (d) titanium oxide in an amount between approximately 0 and 30 weight percent; (e) zirconium oxide in an amount between approximately 0 and 15 weight percent; (f) calcium oxide in an amount between approximately 0 and 15 weight percent; (g) magnesium oxide in an amount between approximately 0 and 5 weight percent; (h) sodium oxide in an amount between approximately 0 and 5 weight percent; (i) potassium oxide in an amount between approximately 0 and 5 weight percent; and wherein the weight percents are those of the sintering material based on total weight prior to addition of depleted uranium compound.

45. The stabilized depleted uranium material of claim 40 wherein said sintering material further comprises a neutron absorbing material is a member selected from the group consisting of compounds of beryllium, boron, cadmium, hafnium, iridium, mercury, europium, gadolinium, samarium, dysprosium, erbium and lutetium and mixtures thereof.