US3110557A - Radioactive waste disposal - Google Patents

Description

United States Patent 3,110,557 RADEUAQTEVE WATE DlSPUSAL Marshall L Specter, Roselle, NJ assigner to The M W. Kellogg Company, Jersey titty, N.J., a corporation of Delaware No Drawing. Filed Sept. Ill 1959, Ser. No. 839,ti-67 18 Claims. (ill. 23-5ll) This invention relates to a process for the preparation of unleachable complex compounds. In another aspect this invention relates to radioactive waste disposal and more specifically to a process for the incorporation of radioactive waste materials in a water-unleachable solid.

The production and processing of radioactive materials has presented many problems, one of which is the ultimate disposal or storage of radioactive wastes produced as a by-product from a nuclear reactor. The chief Waste disposal problem associated with reactor fuel processing is concerned with the handling of liquid waste which has been processed for the removal of fertile and fissionable uranium.

Because of the potential value of mixed or individual fission products and also because of the radioactivity of these products in the waste, the reactor fuel wastes cannot be treated in the same manner as the waste products of other industries. Consequently, most waste solutions from fuel processing plants are stored in underground, stainless steel tanks or in concrete, which is deposited in the ocean.

Since the need for storage space is continuously increasing, the liquid waste solution has been subjected to evaporation and distillation in order to decrease the volume of liquid to be stored. There is also the constant threat of leakage in the storage tanks since the solutions stored in them are highly acidic, usually nitric acid solutions. If leakage should occur, the radioactive materials could find their way into drinking Water by way of underground rivers and streams and would, therefore, be a serious physiological hazard.

Obviously, as these methods of disposal are not very assuring, more infallible methods are urgently demanded. Processes for treating wastes before final storage in containers have been proposed. Some of the proposed processes involve ion exchange and others, solid fixation in clays. However, ion exchange is somewhat complicated with precipitations and evaporations. Moreover, because of its complexity, this process would be extremely dilfi cult, if not impossible, to operate by remote control.

The fixation on clay processes presently being employed require extremely high temperature furnaces to maintain the heat of reaction and also call for the preliminary removal of alumina, iron oxides and zirconium oxide prior to treatment with clay. Since the presence of these oxides or cladding agents severely reduces the fixation capacity of the clay in the process, the removal of these oxides is essential. This process also fails to incorporate ruthenium oxide in the product of the process.

Fission products may be incorporated into either high or low melting glass. However, the low temperature glass is water-leachab'le due to the llux inherent in this material and both the low and high temperature glass would require a remote controlled glass plant, which would present severe operational and maintenance problems. In either case, during the requisite storage period of about 500 years, the glass could pulverize due to weakening by gamma irradiation or the introduction of strains caused by decay of fission products into derivative elements of a diiferent valence state. it is obvious then, these methods of storage still leave much to be desired and a simplified and more permanent method of disposal having a tolerance for inactive metal oxide cladding agents is urgently needed.

EJ19 557. Patented Nov. 12, 1963 ice Therefore, it is an object of this invention to provide an improved method for disposing of radioactive waste materials.

Another object of this invention is to provide a process for the preparation of water-unleachable attrition resistant radioactive materials.

Another object of this invention is to provide a method for the permanent and safe disposal of radioactive wastes.

Still another object of this invention is to provide a commercially feasible and simple method for the production of a water-unleachable rock containing radioactive waste components.

Other objects and advantages of the present invention will become apparent to those skilled in the art from the following description and disclosure.

According to the process of the present invention, a radioactive Waste is reacted, in the presence of a solid metal oxide, with a base metal in the elemental state, which is characterized as being polyvalent in a combined state and having a higher exothermic heat of oxide formation per oxygen atom (AlI /#O), than that of the metal oxide. initiation of the reaction is effected at a tem erature of at least 30i5 C. and the exothermic reaction is allowed to proceed to completion whereupon a water-unleachable rock-like product is produced, preferably a crystalline, water-unleachable rock, wherein the constituents of the radioactive waste, the metal oxide and the oxide of the elemental metal, are chemically combined in a complex compound.

The metal oxides which react with the elemental metals to produce the water-unleachable products of the reaction include the oxides of chromium, vanadium, strontium, cesium, iron, copper, titanium, manganese, lead, tungsten, tantalum, antimony, bismuth, cerium, nickel, tin, cobalt, molybdenum, etc.

The preferred metal oxide reactants of the present process are those having a -Al-l /#O at or below about kcaL/rnole. These oxides include iron oxide, lead oxide, stannic oxide, titanium oxide, manganese oxide, nickel oxide, cobalt oxide, chromium oxide, copper oxide, molybdenum oxide, and zinc oxide. Most preferred of this group are the higher oxides of iron, lead, titanium, manganese, copper and nickel.

The metal oxides of the reaction discussed above can be employed alone or in admixtures of any combination of the above-mentioned oxides such as mixtures found in haematite, magnetite, ilmenite, etc. The metal oxide may be present as a component of the radioactive waste and when present in sufficient amount, can be reacted with the elemental metal without the addition of a metal oxide reactant to the reaction mixture. However, when the components of the radioactive waste are not present as oxide reactants, or when such oxide reactants are not present in an amount suificient to initiate the reaction with the elemental metal, a metal oxide reactant is added to the mixture of waste and elemental metal. Also, compounds may be employed in the reaction which produce the reactant oxides in situ when heating the reaction mixture to the initiation temperature. Such compounds are the organic oxygen-containing salts of the above metals, for example, the oxylates and the acetates and inorganic oxygen-containing salts of these metals such as the carbonates and the nitrates.

Metal halides, sulfides, carbides or other more stable metal oxides which are inert, insofar as the initiation reaction is concerned, i.e., those which have a higher heat of monoxide formation than the monoxide of the elemental metal, may also be present in the reaction mixture with the reactant metal oxide and the elemental metal. These stable oxides, however, are incorporated in the final product since the temperatures generated by the reactants after the initiation temperature is reached, is sufiicient to I" I W F cause the stable oxides to react. Thus, aluminum oxide, which is inert with respect to silicon at ordinary temperatures, is incorporated into the product of the reaction between ferric oxide and silicon after initiation, since the temperatures chemically generated in this reaction, for example, up to 2500 C., are sufficient to cause incorpo ration of the alumina.

Any of the metal oxides of the aforementioned preferred group can be added to a reactive system to lower the initiation temperature and to hasten the initiation, if desired. For example, when silicon is reacted with ferric oxide, the initiation temperature can be considerably lowered by adding a minor amount of CuO, although, the reaction would occur without the addition of CuO under more severe conditions. However, when radioactive materials are present as stable halides, sulfides, carbides, or more stable oxides, the use of a reactive metal oxide, preferably one of those having a AH,-/#O below 100 kcaL/mole, is mandatory to the success of the reaction.

According to the process of the present invention and as stated above, the reactant metal oxide can be present in a mixture of oxides and/or salts, such as a mixture found in a radioactive waste from a nuclear reactor, or can be supplied to a system comprising a radioactive waste and the elemental metal. Generally, the radioactive wastes contain small amounts of strontium, cesium, and ruthenium oxides together with larger amounts of zirconium, iron and aluminum oxides from the cladding agents. The waste may also contain infinitesimal, trace amounts of uranium and/ or thorium since these elements are usually extracted from the waste as completely as possible before leaving the reactor. In some cases, the Waste mixture is treated with nitric acid and the components of the waste are thereby converted to their corresponding nitrate salts. These salts, upon being heated, are converted to the corresponding oxides and react with the elemental metal either before, or during the course of reaction. For example, when it is desirable to initiate the reaction at a temperature below which the nitrate salts are converted to their corresponding oxides, a metal oxide reactant is chosen which reacts with the elemental metal at the desired temperature. The reaction between the elemental metal and the selected metal oxide reactant is initiated in the presence of the waste material and the heat generated by the reaction is sufiicient to bring about the conversion to oxides of the components in the waste. The elemental metal then additionally reacts with these converted oxides.

Alternatively, the radioactive waste containing nitrates may be heated with the elemental metal to a temperature at which the conversion to oxides takes place and the spontaneous reaction between the oxides and the elemental metal occurs. When the radioactive waste material is dissolved in a liquid, it can be dried either before or after mixing with the elemental metal. However, for ease of handling, the reaction mixture is dried prior to initiation.

Of the salts which decompose to oxides upon heating, those which are capable of reacting exothermically with the elemental metal can be included as part of the oxidant portion of the system; whereas those which are incapable of exothermic reaction, are incorporated into the reaction product endothermically by the heat energy generated within the system. In some cases, the radioactive waste may contain a metal halide and, in these cases, where the metal halide reacts exothermically with the elemental metal as, for example, TiF reacts with Al, it is not necessary to convert the metal salt to the oxide for initiating and sustaining the reaction.

When hydrates of the metal oxides or salts are present, the mixture is preferably heated to drive ofi the water and/or to convert the salts to oxides before initiating the reaction. Thereafter, the elemental metal is contacted as the temperature is generally raised to initiate the re- Cir action, whereupon heating is discontinued and the reaction proceeds to completion with the formation of rock-like material or mineral material. This product is the corresponding complex oxide in which the metal oxide reactant, oxides in the original mixture and the elemental metal are chemically bonded by the oxygen atoms. After initiation of the reaction, all of the resulting oxides are incorporated into the crystalline, water-unleachable rock which is produced by the process of this invention.

TABLE I ACCUMULATION AND DECAY OF FISSION PRODUCTS Half-life Accumula- Residual b 0.1 MP0 a Nuclide Present (yr.) tion a/ml.) e/ml.)

(um/ml.)

0.148 21.1X10 0.1 MPC 7X10" 28 3. 0X10 2. 3X10 8X1 0- 0.159 26. 4X10 0. 1 IWPC 2X10" 0.178 30.0 10 01 MPC 0.096 30. 0X10 0.1 IVIPC 4X10 0.110 13. 0X10 0. 1 MPC l. 0 1. 4x10 14 10 0. 000 1. 6X10 01 IHIC 10 3O 2. 5x10 2.0X10 1. 5X10- 0. 035 30. 0X10 0. 1 MPG 2X10- 0.088 28.2Xl0 O.1 M PC O. 038 28. 2x10 0. 1 IVIPC 4X10 0. 780 24. 7X10 35 4X10 0. 032 12. 2X10 0. 1 MPG 2. 6 6. 9X10 4. 8x10 0. 1 O. 005 10 49 0. 02 2X10 3 3. 0 1. 5X10 7X10 5. 3X10 5X10 7X10- 1* Accumulation in ten years by power program starting at 2,000 mw. and increasing to 30,000 mw. Expressed as microcuries per milliliter assuming a waste volume 1.5)(10 gallons.

b Microcuries per milliliter after an additional tcn-year decay of the ten-year accumulation.

Ten percent of Handbook 52 maximum-permissible values for mincentration in water.

d Assuming 1 percent losses for arbitrary operating conditions.

The elemental metal hereinabove described, is preferably a metal having a AH /#O of a crystalline monoxide greater than kcal/mole and capable of having a valence greater than two in the combined state. Examples of metals included in this preferred group are aluminum, phosphorus, plutonium, silicon, tantalum, throium, zirconium and vanadium; and, most preferred for the process of the present invention are zirconium, aluminum and silicon. Although, it is to be understood that any polyvalent base metal in the elemental state such as, for example, magnesium and calcium, which is characterized by having a higher monoxide AH /#O kcaL/mole than the monoxide of the metal oxide reactant, is a suitable elemental metal reactant in the present process and also that mixtures of these metals may be employed in the present process. It is also to be understood that other metals, which are desirable to incorporate into the product of the reaction, can be added to the reaction mixture as an elemental metal to produce the corresponding complex metal oxide product.

In certain instances, it is desirable to incorporate silica or alumina into the product produced by the process of this invention to improve its unleachable characteristics. When such is the case, silica, alumina and/or other stable metal oxides can the incorporated into the product by the exothermic reaction of an alkali or alkaline earth elemental metal, such as, for example, calcium or magnesium with a reactive metal oxide, such as, for example, Fe O TiO etc., to provide the thermal enengy necessary for the endothermic incorporation of these generally inert metal oxides into the product.

The solid radioactive waste, the elemental metal which initially reacts with the metal oxide and the metal oxide reactant in the process, have a particle size not in excess of 10 mm. diameter. Preferably, the metal, elemental metal and the metal oxide reactants, are ground to pass at least about 70 percent through a 100 mesh Tyler screen, and most preferably at least about 90 percent through a mesh Tyler screen. In the present invention, it has been found that the initiation temperature varies directly with the particle size of the elemental metal and the metal oxide reactants, so that with a sufficiently clean fine powder of these reactants, eig. below 0.005 mm. in diameter, the reaction may be initiated at room temperature (30 C.i5 C.) or even below.

The particle size of the metal can be reduced by any one of a number of methods. For example, the metal can be ground to the desired size or the metal can be treated with a hydrogen halide such as hydrogen fluoride to reduce the size of the particles. It is to be understood, of course, that a combination of these procedures may also be employed, if desired.

More often, the reactions of the present invention are initiated at a temperature in excess of about 200 C., preferably between about 700 C. and about 1200 C. Once the reaction is initiated, it is not necessary to continue supplying heat to the system since it goes to completion exothermically. Temperatures up to 2800 C. or higher are generated chemically by the reaction after the reaction is initiated.

The pressure selected for :a given reaction is in accordance with the particular requirements of the reaction. Thus, when reacting a radioactive waste containing volatile material such as ruthenium oxide with an elemental metal and reactive metal oxide, the reaction is preferably conducted at atmospheric pressure, reduced pressure or in vacuo and in a closed reactor wherein the volatile radioactive metal compounds are trapped and incorporated into the solid product produced. Other reactions, which present no hazard in regard to volatile materials, can be conducted at reduced pressure but are usually carried out under atmospheric pressure in an open or closed system; whichever is preferred. It is to be understood, however, that pressures up to about 100 atmospheres can be imposed on the reaction if it is desirable to do so.

According to the process of the present invention, the reactant metal oxide and the elemental metal are mixed in a mole ratio of between about .01:1 and about 20:1, preferably between about 01:1 and about 5:1. When inactive materials, such as metal halides, carbides, sulfides, or inactive metal oxides, are also present in the reaction mixture, the active ingredients should not be diluted to the point where the exothermic reaction of the elemental metal and reactive metal oxide is prevented from occurring. The degree of dilution varies with the specific metal and reactive metal oxide employed.

Obviously, equipment must be used which will withstand the extreme temperature generated by the reaction. Therefore, metal, ceramic or ceramic lined and insulated reactors, are preferred since they are readily available and relatively inexpensive. When reactors composed of steel or other materials having temperature resistance below the temperature generated by the reaction are employed, a coolant or diluent must be present in the reaction mixture to carry off excess heat. Such coolants are materials which generally do not react exothermically; for example, magnesium oxide or aluminum oxide or any of the other materials known to be useful for this purpose. Thus, when reacting a radioactive waste which usually contains a large amount of A1 0 the aluminum oxide may serve a beneficial purpose in the reaction as a coolant. In any event, the presence of A1 0 does not have the deleterious effect on the reaction herein disclosed, as it has on processes of the prior art. Thickwalled vessels are not necessary unless employing pressures substantially above atmospheric.

In the process of the present reaction, the product produced is a water-unleachable solid which is suitable for permanent and safe disposal in the ceramic or other container, which, if not sealed during the reaction, is sealed upon completion of the reaction and the container and contents deposited for storage.

A preferred embodiment of the process for fixing radioactive waste in an unleachable solid by remote control comprises: drying the waste at a temperature at or above C.; depositing the dried waste in a ceramiclined reactor wherein it is admixed with a reactant metal oxide, for example ferric oxide, and a suitable elemental metal, for example silicon, of at least 0.104 mm. particle diameter; sealing the mixture in the reactor; initiating the reaction at a temperature of between about 700 C. and about 1200 C. by lowering a portable furnace over the sealed reactor; and allowing the reaction to run to completion after which the sealed reactor is allowed to cool and the immobile, water-unleachable product in the sealed reactor is removed for storage. From the foregoing description, it is evident that by the process of the present invention, fixing radioactive waste materials in unleachable form is accomplished in a novel manner and at significantly lower initiation temperatures than heretofore believed possible.

Processes formely employed for fixing radioactive wastes have used furnaces to maintain the heat necessary for the reaction at the required temperatures, i.e., in the order of 1500 C. and preferably higher. Externally heating reactants to temperatures in this range demands expensive equipment of high heat output and requires a great deal of time in attaining the temperature and maintaining it constant. During the period of gradual heating, volatile radioactive materials escape, thus extensive shielding equipment must be employed. One of the advantages of the present process is that after the reaction is initiated in a sealed container at a comparatively low temperature, an instantaneous release of heat, up to 2000 C. or 2800 C. is obtained, thus eliminating the escape of volatile materials by incorporation into the product and reducing expense by avoiding the necessity of treating large gas volumes and employing extensive shielding equipment. All of these advantages of tthe present process are obtained while providing a greatly simplified procedure with greatly reduced external heating requirements.

For a better understanding of the present invention, reference is now had to the accompanying examples, which are not to be construed as unnecessarily limiting to the invention hereinabove described.

Of the following examples, Examples 1 through 3 were carried out to illustrate some of the various reaction systems which can be employed with elemental aluminum or silicon in the presence of a radioactive waste material to produce a crystalline water-unleachable solid product wherein the components of the radioactive waste, elemental metal, and the metal oxide, are chemically bonded together by oxygen atoms. In the presence of a dried radioactive waste, the procedure employed in these examples for obtaining the crystalline product would be unchanged. The drying of the waste material can be accomplished by gentle heating at or above 100 C.

Example 1 REACTION OF RED FERRIC OXIDE-SILICON MIXTURE Into an open crucible was admixed 60 grams of P6 0, and 15 grams of silicon. The mixture, having an average particle size below 200 mesh (Tyler Standard Sieves), was heated to 900 C. to initiate the reaction. After about two minutes heating time, ignition occurred and a tremendous quantity of heat was generated, which was visually observed by emission of bright light. The material in the crucible was converted to a crystalline mass. The crystalline mass was analyzed for silica and iron content and was found to contain 29.3 weight percent silicon expressed as SiO and 70.5 weight percent iron expressed as FeO. The X-ray diffraction pattern of the powdered product was similar to the naturally occurring mineral fayalite, Fe SiO The powdered product was placed in boiling water at about 100 C. for one hour and was found to be substantially insoluble.

Example 2 REACTION OF RED FERRIC OXIDE, MAGNESIUM OXIDE Axi) sitirctm Into an open porcelain 90 cc. crucible was admixed 45 grams of ferric oxide, 3.8 grams of magnesium oxide and 15 grams of silicon. The admixture, having an average particle size of below about 200 mesh (Tyler Standard Sieves) was heated to 900 C. to initiate the reaction between the metal oxides and the elemental metal. After about two minutes heating time, ignition occurred and the mixture generated a tremendous quantity of heat, which was visually observed by a flash of white light. The materal in the porcelain crucible was converted to a rock-like mass containing a complex mixture of oxides of magnesium, iron and silicon. The powdered product after cooling was placed in boiling water for one hour and the product found to be insoluble. The X-ray diffraction pattern of the powdered reaction product was isomorphic to the mineral fayalite.

Example 3 REACTION or ALUMINFM-RED FERRIC OXIDE AiiXTURE One part by weight of aluminum powder was admixed with 4.45 parts by weight of Fe O Both reactants were finely divided powders which passed through a 200 mesh sieve. The reactants were transferred to an open porcelain crucible and after heating to 500 C. for one minute, an extremely exothermic reaction was observed to occur. The major portion of the product was a grey crystalline material. Chemical analysis of the crystalline portion of the product indicated that the aluminum content was 31.89 weight percent expressed as A1 and the iron content was 67.8 weight percent expressed as FeO. The analysis indicated a compound having the formula Fe Al O The powdered product was immersed in boiling water for one hour and was found to be substantially insoluble.

Examples 4 to 12 FIXATION OF STRONTIUIXI AND CESIUBi The examples reported in the following table (Table H) were carried out according to the procedure given below.

Powdered silicon or aluminum, ferric oxide, aluminum or hydrated aluminum nitrate, all of less than 0.07 In particle size, were mixed in porcelain crucibles in amounts indicated in Table II. Strontium or cesium was added in amounts as indicated in Table H as aqueous nitrate solutions to the mixtures. The resultant mixtures were 8 heated to between 100 C. and 150 C. in air to remove moisture and then to between 300 C. and 500 C. to remove oxides of nitrogen. The mixtures were then strongly heated to about 900 C., whereupon an exothermic reaction occurred and a rockdike product was produced, except in Examples 8 and 12 shown in Table II.

Each of the rock-like products of the above reactions was crushed, powdered, and transferred to a separate glass beaker containing 100 ml. of distilled water where the solids were extracted by boiling at about 100 C. for one hour. The water washings were then separately decanted through a filter and a second extraction was conducted in which each of the solid products was heated with 100 ml. of water for 16 hours at C. and boiled for one hour.

The purpose of the second leach was to determine whether traces of Sr or Cs when reported in the first leach were due to splashing or to extraction from the reaction mass. This precaution was unnecesssary in most silicon-containing runs since neither strontium nor cesium were detected in the first extraction.

The degree of fixation of strontium and cesium was determined by the following procedures:

The extraction water was analyzed directly for strontium and cesium by X-ray fiuorescene, and indirectly by pH measurement.

The limit of detection of strontium and cesium by X- ray fluorescene (XRF) was 10 ppm. This limit was extended to 2 ppm. in Examples 5 and 10 by concentrating the leach Water to /5 or more of the original volume, and reporting the X-ray fluorescene analyses based on the unconcentrated material.

The indirect determination by pH measurement is based on the fact that when all the strontium or cesium nitrate present in the system is converted to the oxide, the oxide hydrolyzes to the basic hydroxide in the leach water. Based on a concentration of one millimol of either strontium or cesium salt per this. of wash water used in this work, the pH of the water should be 12.0 and the presence of either 1320 ppm. (0.01 N) cesium or 870 ppm. (0.01 M) strontium, theoretically indicated. A pH value under 7.0 indicates less than 0.01 part per million (p.p.rn.) of either Sr or Cs.

A control test was devised based on the observation that a mixture containing fired alumina instead of aluminum nitrate would not ignite when heated to 900 C. for 30 minutes or longer. The pH of the leach water from such a control, Example 8, in the strontium series was 11.3 and about 300 ppm. Sr were detected by X- TABLE II FIXATION OF 0.001 1\L[OL STRONTIUM NITRATE Composition, g. First Extraction Second Extraction Example No.

Al(NO 9H2O Si F0203 A A1 pH p.p.m. S1 1111 13.13.11]. S1 by XRF by XRF 3 1 1 0 0 6. 9 6. 5 not analyzed. 3 2 2 0 0 6. 4 5. 0 not detected. 3 4 1 O 0 6. 3 6. 3 not analyzed. 3 0 1 0 1 8.5 0-- 8.5 Do. 0 1 l 1 0 11.3 ca. 300 p.p.m 8. 6 DO.

FLXATION OF 0.001 MOL CESIUM NITRATE First Extraction Second Extraction pH p.p.m. Cs pH ppm. Cs

3 1 1 O 0 6. 0 not detected 6. 0 3 2 2 0 0 5. 8 do 6.2 not detected. l1 3 0 1 0 1 8.8 80 p p m 8. 3 20 ppm. 12 2 (control) 0 1 1 1 O 10. 5 ca. 700 p.p.m 8.6

1 Reported on basis of original volume; sample analyzed was concentrated 6.4 fold. 2 Did not ignitecontrol. 3 Reported on basis 0! original volume; sample analyzed was concentrated 5 fold 2 p.p.m.).

ray fluorescence. In the cesium control, Example 12, the pH was 10.5 and about 700 ppm. Cs were detected by X-ray fluorescence. The importance of attaining ignition and subsequent high temperatures is thus illustrated by comparing Examples 8 and 12 with Examples 4-7 and 9-11.

In the other examples listed in Table II, ignition did occur and the feasibility of immobilizing or fixing strontium and cesium is clearly demonstrated.

Example 13 DISPOSAL OF RADIOACTIVE \VASTE Into a porcelain lined reactor is introduced, at room temperature, ferro-ferric oxide, Fe O and metallic silicon in a weight ratio of 4:1. The particle size of the solid mixture is between about 0.089 mm. and about 0.065 mm. diameter. The following procedure is carried out by remote control with the operation protected behind a lead-shielded wall.

The reactor is brought into a radioactive area wherein radioactive waste material from a nuclear reactor is dried and a granular waste comprised essentially of oxides of aluminum, iron, zirconium, strontium, cesium, ruthenium, and other nuclides listed in Table I is admixed with the contents of the porcelain reactor in a weight ratio of about 1:1 (wasteziron oxide and silicon).

The contents are then placed in the reactor and the temperature of the mixture is subsequently raised to about 900 C. by lowering a portable furnace over the reactor and heating the reactor and contents. In the course of heating, any nitrates present are converted to the corresponding oxides. At this point the reactor is sealed and the pressure lowered to 0.5 p.s.i.a. Heating is continued until 900 C. is attained within the reactor, whereupon the spontaneous chemical generation of heat causes rapid reaction of the iron oxide, silicon and the oxides of the radioactive waste to produce a Water unleachable silicate rock which is cemented to the walls of the sealed reactor.

The reactor and contents sealed therein is then placed in a shielded vehicle and transported to a site of ultimate storage.

Example 14 One millimol of strontium nitrate was admixed with 3 grams of aluminum nitrate, Al(NO -6H O, 1.5 grams of aluminum powder and 3 grams of titanium dioxide in an open porcelain crucible. The mixture was being heated to about 500 C. in order to drive off oxides of nitrogen, when ignition occurred before the metal nitrates were decomposed. Extremely high temperatures were generated as indicated by an intense white glow in the reaction mass. The reaction product was finely ground and boiled in water at about 100 C. for one hour. The presence of strontium in the leach water was not indicated as evidence by the pH of the water extract. The pH was 9.1, which was identical to the pH of a control run to which 1.5 grams of aluminum, 3 grams of titanium dioxide and no strontium were admixed, fired, ground, and leached as described above. Had strontium been available for water leaching, the pH would have been 11.3 as in Example 8, above.

It is to be understood that many modifications and alterations of the above technique may be employed in accordance with the present invention and that Example 13 is only one of many equally beneficial methods disclosed herein for handling and disposal of the radioactive material. For example, in place of metallic silicon, elemental aluminum, zirconium or any other of the elemental metals hereinabove described may be substituted in Example 13 as the reactant metal. In like manner, lead oxide, titanium oxide or any of the abovedescribed metal oxides may be substituted in Example 13 for reaction with a suitable elemental metal such as aluminum or zirconium, to produce the radioactive waterunleachable product wherein the radioactive waste material is chemically bound in a complex compound.

Having thus described my invention, I claim:

1. The process which comprises reacting a mixture of solids containing a radioactive component, a normally solid inorganic oxide of a metal, which metal is polyvalent in the oxide composition, and an elemental metal characterized by being polyvalent in the combined state and having a higherAH /#O than that of the metal oxide reactant, by heating the mixture to at least the temperature at which the exothermic reaction between the metal oxide and the elemental metal is initiated and chemically reacting the radioactive component, the metal oxide and the elemental metal to form a solid complex mass.

2. The process which comprises reacting a dehydrated particulate solid mixture containing a radioactive component, a normally solid inorganic oxide of a metal, which metal is polyvalent in the oxide composition, and an elemental metal characterized by being polyvalent in the combined state and having a higher Al-I /#O than that of the metal oxide reactant, by heating the mixture to at least the temperature at which the exothermic reacion between the metal oxide and the elemental metal is initiated and chemically reacting the radioactive component, the metal oxide and the elemental metal to form a solid, complex, water-unleachable product.

3. The process which comprises dehydrating a radio active waste containing a radioactive component, reacting the resulting particulate radioactive solid mixture with a normally solid inorganic oxide of a metal, which metal is polyvalent in the oxide composition, and an elemental metal characterized by being polyvalent in a combined state and having a higher AH /#O than that of the metal oxide reactant, by heating the mixture to a temperature in excess of about 25 C. at which temperature the exothermic reaction between the metal oxide and the elemental metal is initiated, employing the exothermic heat of reaction to chemically react the radioactive component and to combine the radioactive component, the elemental metal and the metal oxide in a solid, radioactive, water-unleachable, complex product.

4. The process of claim 3 wherein the radioactive component is strontium.

5. The process of claim 3 wherein the radioactive component is cesium.

6. The process of claim 3 wherein the elemental metal is aluminum.

7. The process of claim 3 wherein the elemental metal is silicon.

8. The process of claim 3 wherein the elemental metal is zirconium.

9. The process of claim 3 wherein the elemental metal is magnesium.

10. The process which comprises reacting a particulate solid mixture comprising a dry radioactive waste containing a radioactive component, a normally solid inorganic oxide of a metal, which metal is polyvalent in the oxide composition, and an elemental base metal characterized by being polyvalent in a combined state and having a higher AH /#O than that of the metal oxide reactant, by heating the mixture containing metal oxide: elemental base metal in a mole ratio of between about 0.01:1 and about 20:1, to at least the temperature at which the exothermic reaction between the metal oxide and the elemental base metal is initiated, and employing the exothermic heat of reaction to chemically react the radioactive waste and the radioactive component in the reaction between the metal oxide and the elemental metal to produce a solid, complex, oxide product which is resistant to leaching with water.

11. The process of claim 10 wherein the metal oxide comprises an oxide of magnesium.

12. The process of claim 10 wherein the metal oxide comprises an oxide of iron.

13. The process of claim 10 wherein the metal oxide is a mixture of oxides found in minerals selected from 3 l the group consisting of haematite, magnetite, ilmenite, and mixtures thereof.

14. The process which comprises admixing a dehydrated radioactive waste containing a radioactive component, a mixture of normally solid inorganic oxides of metals, which metals are polyvalent in their respective oxide compositions, and wherein at least one of the metal oxides is a reactant in the process and one of the metal oxides is selected from the group consisting of silica and alumina, and an elemental metal characterized by being polyvalent in the combined state and having a higher AH /#O than that of the metal oxide reactant, said mixture having a particle size not greater than 1-0 mm. diameter, reacting said mixture by heating to a temperature in excess of 200 C. at which temperature the exotherrnic reaction between the reactant metal oxide and the elemental metal is initiated and chemically reacting the radioactive component in the reaction between a metal oxide and the elemental metal to form a stable, solid, complex compound of the admixture which is resistant to leaching with water.

15. The process which comprises heating a liquid radioactive waste containing a radioactive component to obtain a radioactive dehydrated mixture of oxides in granular form; reacting the resulting granular radioactive mixture, a normally solid inorganic oxide of a metal, which metal is polyvalent in the oxide composition, and an elemental base metal characterized by being polyvalent in the combined state and having a higher AH /#O than that of the metal oxide reactant by heating the mixture to at least the temperature at which the exothermic reaction between the metal oxide reactant and the elemental base metal is initiated; and reacting the radioactive component with the elemental metal and metal oxide at the temperature generated by the exothermic reaction to produce a solid, water-unleachable, product wherein the metal oxide, the elemental metal and the radioactive component are chemically combined.

16. The process which comprises admixing a granular radioactive waste material containing a normally solid inorganic oxide of a metal which is polyvalent in the oxide composition and a radioactive component with an elemental base metal which is characterized by being polyvalent in the combined state and having a higher AH /#O than that of the metal oxide reactant, in a mole ratio of waste materialzelemental base metal of between about 0.01:1 and about 20:1, said metal oxide End comprising at least 10 percent of the waste material; reacting the mixture having a particle size not larger than 10 mm. diameter by heating the mixture to a temperature in excess of 200 C. at which temperature the exothermic reaction between the metal oxide reactant and the elemental metal is initiated to produce a solid, water-unleachable product wherein the metal oxide, the radioactive component and the elemental base metal are chemically reacted and combined.

17. The process which comprises drying at liquid radioactive waste containing nitrates by heating the liquid to a granular solid, converting the nitrates to the corresponding oxides by additional heating to produce a radioactive mixture of oxides containing a radioactive component; reacting the resulting granular mixture, a reactant normally solid, inorganic oxide of a metal, which metal is polyvalent in the oxide composition, and an elemental base metal characterized by being polyvalent in a combined state and having a higher AH;/#O than that of the metal oxide reactant, by raising the temperature of the mixture having an average particle size not larger than 10 mm. diameter to between about 700 C. and about 1200 C. at which temperature the exothermic reaction between the metal oxide reactant and the elemental base metal is initiated to produce a solid, water-unleachable, complex compound wherein the metal oxides and the radioactive component of the dried radioactive waste, the metal oxide reactant and the elemental base metal are chemically reacted and combined.

18. The process of claim 17 wherein the AH /#O of the elemental metal is greater than 100 kg./cal./mole.

References Cited in the file of this patent UNITED STATES PATENTS 1,100,743 Keetman et al June 23, 1914 1,142,154 Ebler June 8, 1915 1,154,230 Bredt Sept. 21, 1915 2,066,044 Leverenz Dec. 29, 1936 2,892,680 Burgus June 30, 1959 2,937,932 Hahn May 24, 1960 3,018,161 Erlebach et a1. Jan. 23, 1962 OTHER REFERENCES Ginell et al. in Nucleonics, vol. 12, pages 1418, Deccmber 1954.

Chem. and Eng. News, June 8, 1959, page 38.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3, 110,557 November 12, 1963 Marshall L. Spector' It is hereby certified that error appears in the above numbered patent requiring correction and that th e said Letters Patent should read as corrected below.

Column 9, line 54, for "evidence" read evidenced Signed and sealed this 23rd day of June 1964,

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims (1)

1. THE PROCESS WHICH COMPRISES REACTING A MIXTURE OF SOLIDS CONTAINING A RADIOACTIVE COMPOUNENT, A NORMALLY SOLID INORGANIC OXIDE OF A METAL, WHICH METAL IS POLYVALENT IN THE OXIDE COMPOSITION, AND AN ELEMENTAL METAL CHARACTERIZED BY BEING POLYVALENT IN THE COMBINED STATE AND HAVING A HIGHER-$HF*/#O THAN OF HE METAL OXIDE REACTANT, BY HEATING THE MIXTURE TO AT LEAST THE TEMPERATURE AT WHICH THE EXOTHERMIC REACTION BETWEEN THE METAL OXIDE AND THE ELEMENTAL METAL IS INITIATED AND CHEMICALLY RECTING THE RADIOACTIVE COMPONENT, THE METAL OXIDE AND THE ELEMENTAL METAL TO FORM A SOLID COMPLEX MASS.