US2992889A - Method for separating plutonium and fission products employing an oxide as a carrierfor fission products - Google Patents

Description

United This invention relates to methods for processing of materials containing the element of atomic number 94, known as plutonium, and more particularly to processes for separating plutonium from extraneous matter present in neutron irradiated uranium as exemplified by fission products and the like radioactive contaminants. More particularly this invention concerns a separation and concentration procedure involving the use of scavengers whereby improved decontamination may be accomplished and certain specific activities isolated.

As described herein, the isotope of element 94 having a mass of 239 is referred to as 94 and is also called plutonium symbol Pu. In addition, the isotope of element 93 having a mass of 239 is referred to as 93 Reference herein to any of the elements is to be understood as denoting the element generically, whether in its free state or in the form of a compound, unless indicated otherwise by the context. That is, in general, any Pu isotope may be processed by the present invention.

Elements 93 and 94 may be obtained from uranium by various processes which do not form a part of the present invention including irradiation of uranium with neutrons from any suitable neutron source, but preferably the neutrons used are obtained from a chain reaction of neutrons with uranium.

Naturally occurring uranium contains a major portion of U a minor portion of g2U and small amounts of other substances such as UX and UX When a mass of such uranium is subjected to neutron irradiation, particularly with neutrons of resonance or thermal energies, U by capture of a neutron becomes U which has a half life of about 23 minutes and by beta decay becomes 93 The 93 has a half life of about 2.3 days and by beta decay becomes 94 Thus, neutron irradiated uranium contains both 93 and 94 but by storing such irradiated uranium for a suitable period of time, the 93 is converted almost entirely to 94 In addition to the above-mentioned reaction, the reaction of neutrons with fissionable nuclei such as the nucleus of U results in the production of a large number of radioactive fission products. As it is usually undesirable to produce a large concentration of these fission products which must, in view of their-high radioactivity, be separated from the 94 and 'further as the weight of radioactive fission products present in neutron irradiated uranium is proportional to the amount of 93 and 94 formed therein, it is generally preferable to discontinue the irradiation of the uranium by neutrons when the combined amount of 93 and 94 is equal to approximately 0.02 percent by weight of the uranium mass. At this concentration of these substances, the concentration of fission elements which must be removed is approximately the same percentage.

A number of processes have already been proposed for accomplishing decontamination and the separation and concentration of Pu. Certain of these processes are generically known as the bismuth phosphate type process and the wet fluoride type of process. These processes are the invention of others and the details of the processes are described in copending application as, for example, application Ser. No. 519,714, now US. Patent No. 2,785,951, issued March 19, 1 957, to Stanley G. Thomp- Patent Patented July 18, 1961.

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son and Glenn T. Seaborg, to be referred to hereinafter. Consequently all of the details of operation of the aforementioned processes are not described herein.

As indicated above, such irradiated materials contain a substantial content of radioactive materials as exemplified by fission products. For example a substantial amount of gamma activity may be present. As is known such activity presents hazards and unless removed difficulties may be encountered. The treatment with bismuth phosphate for extraction and decontamination or by means of other processes serves to eliminate a large amount of this radioactivity.

However, it has been noted that, for example, while processes as exemplified by the bismuth phosphate process when first employed are particularly effective in eliminating a large amount of activity, repetition thereof will not completely remove all of the activity. This presumably may bev due to the fact that certain activities are not sensitive to, do not have an afiinity for, or otherwise, are not afiected by the bismuth phosphate carrier. Hence, repetition of cycles using the bismuth phosphate carrier does not entirely eliminate these specific activities. The same condition apparently also prevails with other carriers which in their initial use will carry substantial amounts of activity but which. will notentirely eliminate the activity.

I have found that there are certain may be employed as, for example, in conjunction with. by-product carrier precipitate formation for improving decontamination. These added reagents not only increase the amount of fission product and the like activity carried down, but apparently also carry down certain specific activities which have heretofore been diflicult to remove. The use of these materials is referred to herein as scavenger additions. While the preceding description has been directed to the separation of activity in the recovery of Pu as this is a common situation in which the invention would be used, it may be used in other instances. For example, in some instances it may be desirable to isolate gamma activity for special purposes, or, it may be desired to isolate certain fission components. as Cb and Zr from materials containing no Pu and the present invention also. may be employed in these instances.

The meaning of theterms decontamination, scavenging,

scavengers, product precipitate, by-product precipitate,

bismuth phosphate process, extraction and other similar terms will be further apparent as the description proceeds.

The invention has for one object to provide improvements in processes for the separation andrecovery of Pu.

Still another object is to provide a method of treating materials containing Pu whereby better decontamination may be accomplished.

Another object is to provide a process for the separation and recovery of Pu which includes scavenging.

Still another object is to provide a procedure in the separation and recovery of Pu whereby specific activities may be removed. h

Still another object is to provide a scavenging method which may be used in conjunction with known processes for extracting and decontaminating materials containing Pu A still further object is to provide a method of isolat ing certain fission activity, such as Cb and Zr activity.

Another object is to provide a scavenging process which may be carried out in existing equipment without change along with known processes or with a minimum of change.

Another object is to provide a method of removing certain activities involving the use of one or more of the scavengers comprising manganese, silicon and titanium compounds.

Other objectswill appear hereinafter.

I have found that by supplementing by-product deconadditions whichv tamination steps by means of Mn, Si, and Ti compounds as scavengers that decontamination and isolation of certain fission activity maybe obtained. In particular I have found that by means of the use of MnO SiO and TiO scavengers in accordance with the present invention that troublesome gamma activity present along with the Pu may to a large extent be eliminated. The scavengers of the present invention may be added in various forms and ways as will be described in detail hereinafter.

The type of irradiated materials such as materials containing Pu which may be treated are any of the usual mixtures or solutions thereof encountered generally. For example, such materials are described in app. Ser. No. 519,714 aforementioned. These materials would, for example, comprise an inorganic acid solution containing the Pu, the radioactive materials which it is desired to eliminate, and various other constituents. In general, the initial materials would have been subjected to conventional processing comprising extraction and concentration for the elimination of some of the extraneous substances. That is, a standard product precipitation would have been applied under (r) conditions and the carrier containing Pu together with that'radioactivity which had also been carried along would be redissolved and subjected to a conventional by-product precipitation under conditions for the elimination of radioactivity. The scavenging of the present invention would usually be applied in conjunction With such a by-product precipitation for increasing the decontamination obtainable thereby.

In the event it is desired to isolate only a certain activity without reference to Pu recovery, an ether extract, the water exchange therefrom or comparable liquid may be treated with the reagents of the present invention for carrying down certain activities to be isolated.

It has been found that plutonium present in a solution acidified with an acid such as nitric, sulphuric, or hydrochloric and in the absence of strong oxidizing agents, or preferably in the presence of a reducing agent such as sulphur dioxide or Fe++, oxalic acid, or formic acid, can be substantially carried out of solution by co-precipitation with some insoluble rare earth compound, such as lanthanum or cerium fluoride, or with certain insoluble phosphates, such as the phosphates of bismuth, lanthanum, and zirconium. Rare earth iodates and oxalates are also efl'icient materials for substantially carrying plutonium out of solution under these conditions. Thorium fluoride, iodate or oxalate also are efficient carriers for plutonium under these conditions. The plutonium when it is in this carriable condition, generally referred to as Pu probably is in the oxidation state of +4 and in some instances may be in a +3 state. The oxidation state of plutonium in this condition may be referred to as the fluoride insoluble or phosphate insoluble state.

In sharp contrast to this fluoride insoluble or phosphate insoluble state of plutonium, it has been found that the addition to the acid solution of a strong oxidizing agent, such as peroxydisulphate ion (8 0 plus silver ion (Ag++) as a catalyst, leads to the oxidation of the plutonium to an oxidation state or states in which it is not carried by rare earth or thorium fluoride, iodate or oxalate or by the phosphates of bismuth, zirconium, or lanthanum, when these are precipitated from the solution. Under these conditions, the plutonium is oxidized to state greater than +4, as the or {+6, oxidation states and may be generally referred to as Pu The particular valence state of the plutonium in this condition is not important in this invention, provided it is phosphate and fluoride soluble, and such plutonium in solution may be referred to as being in the fluoride soluble or phosphate soluble oxidation state. It has been found that a number of oxidizing agents are capable of oxidizing the plutonium from the fluoride insoluble or phosphate insoluble oxidation state to the fluoride soluble or phosphate soluble state, and the oxidizing potential required for this change is more negative than -1.0 to -l,.4 volts 4 on the Latimer scale of potentials. For example, it has been found that permanganate, periodate, dichromate and ceric ions in acid solutions can be used to efiiect this oxidation. According to the best evidence available, all of these oxidizing agents, when incorporated in aqueous acidic solutions containing plutonium in ionic form, result in the plutonium being oxidized to the hexavalent state, i.e., to the plutonyl ion. It has also been found that reducing agents more positive than the above-mentioned potential range can effect'reduction from the fluoride soluble or phosphate soluble oxidation state to the fluoride insoluble or phosphate insoluble state.

A standard bismuth phosphate by-product precipitation alone may eliminate one-half or more of the gamma activity dependent on the initial intensity and related factors. On the other hand, a comparable by-product precipitation cycle conducted in the same manner but supplemented by a scavenger and otherwise carried out in accordance with the present invention may permit the elimination of 10% to or a greater amount more of the gamma activity. In addition, by means of the scavenger action the substantially complete elimination of certain activity as for example that due to Cb and Zr contaminants which are carried along with the Pu may be accomplished.

A still further understanding of my invention may be had by a consideration of the examples which follow. I have found that by supplementing the action of a byproduct precipitation as for example BiPO precipitation under oxidizing conditions, with Mn, Si, and Ti compounds as scavengers that decontamination may be improved.

The scavenger may be added in various forms and ways as will be indicated to some extent in the following examples, also the scavenger may be made up as a preformed precipitate and added as a slurry.

EXAMPLE I In accordance with this example a conventional acid solution of irradiated U materials, such as described in Ser. No. 519,714 was treated by the usual BiPO, cycles. At the conclusion of a by-product precipitation cycle, prior to applying the scavenging treatment of the present invention, studies were made relative to the gamma activity.

The standard bismuth phosphate by-product precipitation alone brought down approximately 50-55% of the original gamma activity. On the other hand, it was found, in this example, that a comparable by-product precipitation cycle employing a comparable bismuth phosphate carrier supplemented by the use of a manganese dioxide scavenger permitted the bringing down of 60% to 87% of the gamma activity. Also, the manganese dioxide scavenger, substantially completely carried all activity due to columbium as well as large amounts of activity due to active zirconium and tellurium fission products.

The formation of the manganese dioxide scavenger was accomplished in the nitric acid solution in which the standard bismuth phosphate precipitation was carried out. That is, manganese dioxide was precipitated from the nitric acid solution containing fission products by the oxidation of about mg. per liter of manganous nitrate in boiling solution with KClO Precipitation also may be accomplished by the treatment of the manganous ni trate with potassium permanganate or divalent silver ion and persulfate. In another method of carrying out this invention an externally formed manganese dioxide slurry may be made up and added. While in this example the scavenger Was precipitated supplemental to the lay-product precipitate it will be noted that the scavenger formation may be carried out either before, simultaneously, or subsequently to the primary bismuth phosphate or other byproduct precipitation cycle.

EXAMPLE H In this example a number of runs were carried out for studying the gross scavenging effect as compared with carrying accomplished by bismuth phosphate alone. The solutions treated comprised those resulting from diluting 5 milliliters of a stock solution of bismuth phosphate product precipitate in N HNO (contained 35 mgs. of Bi+++/ml.) to 50 milliliters. The stock solutions were prepared by dissolving in nitric acid a bismuth phosphate product precipitate obtained in a process such as described above in Ser. No. 519,714. Dependent upon the particular cycle that the bismuth phosphate was obtained in, there would be varying amounts of fission products, Pu, and the other components. The various decontamin'aiing-precipitates to be described in the table which follows were thrown down by procedures already described. The precipitates were digested at 75 C. for about 1 /2 hours, washed with 10 milliliters of a usual wash solution, centrifuged, mounted, and counted. In the following table appears the gamma activity obtained for the indicated precipitates brought down from solutions with initial gamma activity of about 7,000 counts per minute.

l MuOi brought down 30 minutes after BiPO4, but centrifuged 011 with it.

The '7 activity of Bi-PO; reduced (product) precipitates obtained after MnO scavenging was found in the two cases investigated to be about one-half that of the control- BiPO reduced precipitate.

EXAMPLE III In this example still further studies were made respecting the use of Mn0 as a scavenger. The usefulness of a scavenger does not necessarily always depend upon the gross activity removed. In some decontamination processes, a scavenger with a predilection for particular activities might'be used to great advantage. Accordingly, tests to determine the specificity of MnO action were undertaken as follows: MnO was precipitated from a 10 N HNO solution containing fission products by oxidation of about 0.2 gm. Mn(NO in boiling solution with NaClO The precipitate in each case was washed with 10 ml. of 6 N HNO mounted and a 7 count taken. The sample was then dissolved in about ml. 10 N HNO plus several drops 30% H 0 and the MnO reprecipitated by addition of NaClO under the same conditions. This mode of preparation of MnO was selected to prevent increase of MnO with the use of KMnO as oxidizing agent. The effect of the reprecipitation on 7 activity (without correction for small losses) is shown in Table B.

Table B ACTIVITY IN SUCOESSIVE REPRECIPITATIONS OF M110:

7 c./m. (151: Series) 1 Considerable amounts of MnO were lost in this run due to sticking on the sides of the lusteroid tube.

It appeared from these runs that the activity brought down each time is practically constant, the decrease being ascribable to manipulative losses. It was noted that there was some decrease in gross carrying power when MnO is precipitated by oxidizing Mn++ with C10 rather than Mno In the 2nd series, Al absorption curves of small fractions of the various Mn0 precipitates were made. The character of the curve does not change appreciably with reprecipitation. A rough breakdown of the curve shows that 70% of the activity at zero added absorber is due to 35 d. Cb B and 'y and the remaining activity due to a harder 8 radiation with a half thickness of 70 mg./cm. in Al. The activity of the Cb from the three times precipitated MnO of the 2nd series was found to have a 715 gm. half-thickness in Pb. Hard ,8 was about 3 times greater than Cb 7 activity in the rather large precipitates counted. The third MnO precipitate of the 1st series was analyzed for Cb. The 7 activity of the Cb O fraction accounted for 93% of total activity in the precipitate before solution. The ,8 absorption curve of the Cb O indicates pure 35 d. Cb.

Therefore, it may be seen that precipitation of MnO in accordance with the procedure of the present invention from fission product solutions presents a simple method for removing Cb in the BiPO process. Also, MnO precipitations are useful in the preparation or purification of carrier-free Cb tracers.

EXAMPLE IV In accordance with this example, an ether extract of irradiated uranium, which has been dissolved in nitric acid, was treated with the manganese oxide scavenger of the present invention. The manganese dioxide was precipitated in this solution by the Volhard reaction, i.e.

A slight excess of Mn++ is employed. The precipitation is made in the absence of excess phosphate to avoid the formation of dirty red brown trivalent inorganic complexes which precipitate MnO over a period of days.

It was found that the manganese dioxide carried over 50% of the activity and caused the separation of substantial amounts of the zirconium and columbium activity.

EXAMPLE V In the preceding examples the use of manganese dioxide has been described in some detail both for scavenging in conjunction with oxidizing conditions and the use of a by-product bismuth phosphate precipitate, especially for scavenging specific activities. It has further been found that silicon dioxide and titanium dioxide may be employed in a manner similar to the foregoing as scavengers in which any Pu in the liquid treated is in the plutonyl oxidation state. In this example a series of runs were carried out on employing manganese dioxide, silicon dioxide and titanium dioxide scavengers on aliquot parts of the same type of bismuth phosphate solution. That is, a series of 5 cc. aliquot parts of a bismuth phosphate product precipitate solution 5 N in nitric acid and containing .0625 gram of bismuth were segregated. Each aliquot part contained fission activity of a known character thoroughly mixed therewith. That is, each 5 cc. aliquot part showed about an 810 gamma count as counted in a 2 cc. sample bottle.

Precipitation was made from each aliquot part of this bismuth phosphate liquid containing fission activity by diluting to 1 N in nitric acid and at the same time in certain of the aliquot parts carrying out precipitation of manganese dioxide, titanium dioxide and silicon dioxide respectively in these various samples.

That is, manganese dioxide was precipitated in one sample by adding approximately 20 milliliters of a solution containing 16 milligrams of potassium permanganate and phosphoric acid, the temperature of the reaction be- "7 ing maintained approximately 50 C. As indicated, this particular aliquot part was N in nitric acid and there had previously been incorporated therein milligrams of a source of manganous ion. The manganese dioxide precipitate thrown down was separated, dried, and counted in a conventional manner for comparative purposes.

For throwing down a silicon dioxide precipitate, one of the samples aforementioned 5 N in nitric acid and containing about 2.8 grams of Bi+++ per liter was treated in the following manner. Approximately 20 milliliters of water and about the same amount of phosphoric acid were added. contemporaneously there was added about 1 milliliter of a saturated water glass solution (sodium silicate solution), with stirring. The temperature as in the other instances was maintained at about 50 C. The silicon dioxide scavenger precipitate thrown down was separated, dried, and counted in routine manner for comparative purposes to determine whether greater activity has been removed than by bismuth phosphate alone.

Another aliquot sample was treated for throwing down titanium dioxide. There was added contemporaneously with the water and phosphoric additions already described, about milligrams of a milky suspension of titanium dioxide. This was incorporated with stirring and the temperature was maintained at about 50 C. The titanium dioxide precipitate was separated, dried, and counted in routine manner.

In all of the runs described the stirring at 50 C. was

fairly vigorous and the precipitation operations, including digestion, required about two hours for each sample. Also the resultant slurries were cooled prior to separating the scavenger precipitates by centrifugation, and the precipitates were Washed in the usual manner with water, then ethyl alcohol and ether for drying. As a result of these various runs and observations made thereon, it was noted that in each instance where a scavenger precipitate comprising one of the materials manganese oxide, silicon dioxide and titanium dioxide was precipitated in addition to bismuth phosphate the amount of gamma activity carried down was greater than that carried down by bismuth phosphate alone. For example in the instances of manganese dioxide the gamma activity carried down as determined by counting in electronic equipment of usual type indicated that more than twice as much gamma activity was carried down. Also, considerably more than half the initial 810 c./m. of the starting solution has been carried down. Therefore it is apparent from the preceding examples and description that I have shown that gamma activity and certain fission activities may be removed by means of scavenger additions comprising one or more of the compounds manganese, silicon, and titanium. The solutions which are especially suitable for treatment result from dissolving irridated uranium in nitric acid and applying the usual bismuth phosphate cycles thereto with the scavenger treatment of the present invention applied at about the time of a by-product precipitation under (0) conditions. Or the ether extract or aqueous exchange liquid from such nitric acid solutions of the irradiated material may be treated. However, the exact type of solution treated is not a limitation upon the present invention. It has been found that in instances where plutonium is present, plutonium recovery is as efiicient where the scavengers of the present invention are used as where a carrier, such as bismuth phosphate, is used alone.

In addition as indicated in certain of the examples, activity due to colurnbium, zirconium, and certain other fission components may be specifically isolated by certain of the carriers of the present invention. For example, by throwing down an externally formed MnO carrier in a 1 N HNO solution containing Zr and Ch activity, all of the Cb and some of the Zr (about 50%) will be carried down. By throwing down an externally formed MnO- carrier in 10-16 N HNO all of the Cb activity would be carried and the Zr would be left in solution. An externally formed M'nO may be prepared as follows: Manganese dioxide was prepared by oxidation of manganous nitrate with potassium chlorate inlO M nitric acid. Twenty ml. of 50% manganous nitrate solution (reagent grade) were added to 3 liters of IO M nitric acid and the solution heated nearly to boiling. Forty grams of potassium chlorate were then added in small batches and'the resulting manganese dioxide suspension digested until most of the chlorine dioxide hade been expelled. The manganese dioxide suspension was filtered through a fine sintered glass filtering funnel and the precipitate was washed with water, alcohol, and ether. The final preparation was stored in a vacuum desiccator. e

The formation of the manganese dioxide scavenger has been described as accomplishable in a number of different ways. Likewise the formation of scavengers comprising silicon dioxide and titanium dioxide may be accomplished in a number of ways. For example, silicon dioxide may be formed by adding sodium silicate solution to the nitric acid solution in which the BiPO by-product precipitation is carried out. Titanium dioxide may be prepared by hydrolyzing titanium tetrachloride, washing and adding the resultant slurry. Usually a fraction of a gram of scavenger per liter of liquid treated is suilicient. However, up to 5 grams per liter may be used. The foregoing are merely illustrative methods. By the term scavenger I embrace any of the various compounds of Mn, Si and Ti which function to remove activity either in the presence or absence of Pu as described. The exact details respecting forming BiPO, or other carrier precipitates, oxidizing or reducing solutions of irradiated materials and similar de{ tails are not a limitation on the present invention and are the invention of others. As already indicated, my scavengers and scavenging treatment may be employed in conjunction with various carriers of which BiPO has merely been described as a typical example.

' It is to be understood that all matters contained in the above description and examples are illustrative only and do not limit the scope of this invention as it is intended to claim the invention as broadly as possible in view of the prior art.

I claim:

1. In a process for the decontamination of plutonium in an aqueous acidic solution containing plutonyl ions and ions of uranium fission products, the steps which comprise contacting said solution with a finely divided readily hydrated oxide of the class consisting of silicon dioxide and titanium dioxide, and thereafter separating the supernatant plutonyl solution from said oxide and its associated fission products.

2. The process of claim 1 in which the readily hydrated oxide is silicon dioxide.

3. The process of claim 1 in which the readily hydrated oxide is titanium dioxide.

4. In a process for the decontamination of plutonium in an aqueous mineral acid solution containing plutonium ions and ions of uranium fission products, in which finely divided bismuth phosphate is provided in said solution while maintaining the plutonium in the hexavalent state, and the bismuth phosphate together with its associated fission products is separated from the supernatant solution, the improvement which comprises also providing in the solution, while maintaining the plutonium in the hexavalent state, a finely divided readily hydrated oxide of the class consisting of silicon dioxide, and titanium dioxide, and separating said oxide and its associated fission products from the supernatant solution of hexavalent plutonium ions. 7

5. The process of claim 4 in which the readily hydrated oxide is silicon dioxide.

6. The process of claim 4 in which the readily hydrated oxide is titanium dioxide.

7. In a process for the decontamination of plutonium in an aqueous nitric acid solution containing plutonium ions and ions of uranium fission products, including columbium and zirconium ions, in which bismuth phosphate is precipitated in said solution, while maintaining the plutonium in the hexavalent state, and the bismuth phosphate precipitate together with its associated fission products is separated from the supernatant solution, the improvement which comprises also precipitating in the solution, While maintaining the plutonium in the hexavalent state, a readily hydrated oxide of the class consisting of silicon dioxide, and titanium dioxide, and separating said oxide and its associated fission products from the supernatant solution of hexavalent plutonium ions.

8. The process of claim 7 in which the readily hydrated oxide is silicon dioxide.

9. The process of claim 7 in which the readily hydrated oxide is titanium dioxide.

References Cited in the file of this patent UNITED STATES PATENTS 1,059,531 Ebler Apr. 22, 1913 1,142,153 Ebler June 8, 1915 2,785,951 Thompson et a1 Mar. 19, 1957 10 2,799,553 Thompson et al July 16, 1957 2,819,144 Seaborg et al. Ian. 7, 1958' 2,849,282 Boyd Aug. 26, 1958 2,855,269 Boyd et a1. Oct. 7, 1958 2,859,093 Russell et a1. Nov. 4, 1958 2,934,404 Olson Apr. 26, 1960 OTHER REFERENCES McMillan et al.: Radioactive Element, 93, Physical Review, vol. 57, pp. 1185 and 1186 .(1-940).

Gest et al.: Article in Radiochemical Studies the Fission Products, Book 1 by Coryell and Sugarman, pages 170-175 (1951), which reports on page 170 material referred to as reference (I), H. B. Weiser, Inorganic Colloid Chem., vol. II, Chap. XIH, John Wiley & Sons, N.Y. C., 1938; also A.V. Grosse et al., J.A.C.S., vol. 57, page 438' (1935), and (2) W. W. Scott, Standard Methods of Chemical Analysis, vol. 1, page 558, D. Van Nostrand Co., Inc., NY. (1939).

ABC Document *CN-728, Production and Extraction of Plutonium Report for month ending June 21, 1943, pages 50-57.

Claims (1)

1. IN A PROCESS FOR THE DECONTAMINATION OF PLUTONIUM IN AN AQUEOUS ACIDIC SOLUTION CONTAINING PLUTONYL IONS AND IONS OF URANIUM FISSION PRODUCTS, THE STEPS WHICH COMPRISE CONTACTING SAID SOLUTION WITH A FINELY DIVIDED READILY HYDRATED OXIDE OF THE CLASS CONSISTING OF SILICON DIOXIDE AND TITANIUM DIOXIDE, AND THEREAFTER SEPARATING THE SUPERNATANT PLUTONYL SOLUTION FROM SAID OXIDE AND ITS ASSOCIATED FISSION PRODUCTS.