US3320175A - Processing of radioactive liquids - Google Patents

Description

y 16, 1 s. A. PoDBEREsKY ETAL 3,320,175

PROCESSING OF RADIOACTIVE LIQUIDS Filed July 5, 1961 2 Sheets-Sheet 1 s R O T N E V N BERNARD A. PODBERESKY HARRISON T. LOESER THEIR ATTORNEYS May 16, 1967 B. A. PODBERESKY ETAL 3,329,175

PROCESSING OF RADIOACTIVE LIQUIDS 2 Sheets-Sheet 2 Filed July 5, 1961 wiozumwum 02m JOEFZOU U2 awwuoma INVENTORS BERNARD APODBERESKY HARRISON T. LOESER BY @AMW, JQW M THEIR ATTORNEYS United States Patent 3,320,175 PROCESSHNG OF RADIOACTIVE LIQUIDS Bernard A. Porlbereslry, Norwich, and Harrison T. Loeser,

Waterford, Conn, assignors to General Dynamics Corporation, New York, N.Y., a corporation of Delaware Filed July 5, 1961, Ser. No. 122,012 3 Claims. (Cl. 252-301.1)

(a) evaporation (b) crystalliaztion (c) demineralization (d) fixation (e) 'centrifugation These methods suffer from the disadvantage that the highly radioactive residues remaining after processing are in a form which is difficult for handling and storage. Furthermore, the methods are costly since they utilize relatively expensive material and equipment.

Demineralization with ion exchange resins is somewhat limited in its application to radioactive liquid wastes since the regeneration of the exhausted resin produces highly radioactive liquids which themselves must be processed or stored in shielded tanks. In addition, replacement of the resin involves elaborate and expensive packaging of the exhausted resin for burial. Still another advantage in using ion exchange resin for processing radioactive liquid wastes is the direct effects of radiation on the resin resulting in a decrease in the exchange capacity and degradation of the physical and chemical characteristics of the resin.

Thus, a demand exists in the nuclear industry for a more efficient and economical method of removing radioactive ions from liquid wastes.

It is an object of this invention to provide an economical and efiicient method for decontaminating batch quantities or flowing streams of radioactive liquid wastes.

It is another object to provide a novel means for placing certain radioactive isotopes in a form for use as radiation sources.

A further object of this invention is to provide means for removing radioactive ions from a liquid and placing them in a convenient form for handling and storage.

Still another object is to provide a means for augmenting demineralization of radioactive liquid Wastes and increasing the operating life of ion exchange demineralizers.

These and other objects and advantages are realized by the application of an electric field to liquid wastes containing radioactive ions to remove the ions from the solution.

This invention may be better understood from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a perspective view of a unit for processing a batch of radioactive liquid wastes;

FIG. 2 is a diagrammatic sketch of asystem for processing a continuous flow of radioactive liquid waste materials;

FIG. 3 represents an end view of an electrode found suitable for use in either a batch or flow-type processing unit of this invention;

FIG. 4 is a side view of the housing designed for use with a flow-type processing unit of this invention; and

3,3Z,i?5 Patented May 16, 1967 FIG. 5 is a view of a section taken on a plane represented by the line 5-5 of FIG. 4 looking in the direction of the arrows.

An illustrative embodiment of the present invention includes a container with electrodes to provide a potential gradient therebetween. When a solution containing radioactive ions is brought into contact with the electrodes, the radioactive metallic ions present are deposited on the electrodes and thus etficiently and quickly removed from the solution.

One embodiment of this invention involves the use of sacrificial anodes which go into solution during the period in which a potential is applied across the electrodes. This feature provides additional ions in the solution to replace the radioactive metallic ions being removed and enables the process to proceed at a more efiicient rate.

A further advantage in the use of sacrificial anodes lies in the removal of non-metallic radioactive isotopes from liquid wastes by combination of the non-metallic radioactive ions with the ions of the sacrificial anodes to form an insoluble precipitate. An example of this particular embodiment is the removal of radioactive sulphur in the form of a copper sulfate precipitate when the solubility product of the latter is exceeded.

The use of properly designed sacrificial anodes will not reduce the operating life of the processing unit. By preliminary testing and evaluation, anodes can be properly sized in thickness to operate efiiciently in a processing unit for lengthy periods before being exhausted.

In the processing of liquids containing radioactive cobalt, there is a tendency toward the formation of insoluble cobaltic hydroxide by virtue of the oxidation of cobaltous ion to cobaltic ion, and subsequent combination with hydroxyl ion present in the liquid. This formation of a precipitate supplements the removal of cobalt by deposition on the cathode and serves to increase the etficiency of the method. Other radioactive ions which form insoluble precipitates in a manner similar to that of cobalt may likewise be removed from waste liquids.

The present invention may be made to operate even more efiiciently in many instances by the addition of certain chemicals to the liquid being :processed. The use of such additives to control conditions such as pH and ion concentration forms an important subsidiary feature of the invention. Thus, the addition of a chemical which supplies non-radioactive ions of the radioactive isotope being removed will increase the rate of deposition and permit more rapid removal of a greater percentage of the radioactive ions A very important advantage of theinvention is its adaptation to a continuous or batch operation. A flowing stream or a single batch of radioactive waste can be quickly and efficiently decontaminated by the present method. FIG. 1 shows apparatus suitable for processing a batch of waste material, which includes a container 10, adapted to hold a liquid 11 to be processed. The anodes 12 are made of inert material such as carbon and cathodes 13 are in the form of conductive metal plates. The anodes 12 and cathodes 13 are suspended from mental bars 14 attached to the rim 15 of the container 10. In the particular embodiment depicted in FIG. 1, two cathodes 13 are positioned directly opposite each anode 12.

In FIG. 2 there is depicted a system which has been efiiciently used in processing a continuous flow of material. The initial reservoir 16 contains the liquid waste to be processed. The pump 17 pumps the liquid through processing units 18 and 19 connected in series for greater efficiency and then ultimately to the final reservoir 20. The filters shown at 21 and 22 act to remove precipitates formed during the processing. In this embodiment the control unit 23 for the operation is removed from the immediate vicinity of the actual processing equipment to eliminate radiation danger to operating personnel. If desired, the liquid may be recycled by returning it to the initial reservoir from the final reservoir and the process repeated. The sampling line 24 permits removal of portions of the processed liquid for determination of the radioactive isotope content.

Processing units may be connected in series for greater operating efliciency. Furthermore, the control unit for operating the continuous system does not require radiation shielding to protect operating personnel, since the control unit can be separated from the processing unit or units, as shown in FIG. 2. The most eificient use of the method of the invention requires testing a sample of the liquid waste initially to determine optimum operating conditions and selection of proper electrode material.

The present invention not only provides an economical and efiicient means for decontaminating radioactive liquid wastes, but the compact form of the deposited radioactive material facilitates handling and storage of the material. Since the radioactive isotopes are concentrated within a relatively small area, the protective shielding normally required can be substantially reduced. Furthermore, the processing equipment is not subjected to degradation by the effects of radiation to the extent noted in other processing operations such as where ion exchange resins have been utilized.

Another important advantage of the invention is the fact that under certain easily-determined operating conditions, the radioactive material is in the form of finegrained adherent deposits which can be utilized as a source of radiation. Thus, the radioactive isotopes are recovered from liquid wastes and made to serve a useful purpose. Other operating conditions will result in the production of non-adherent deposits of radioactive materil which are swept away from the electrode and trapped in a filter thus extending the operating life of the unit.

It should be realized that instead of replacing a demineralized with the processing unit of this invention, the operating life of the ion exchange resin can be extended by positioning a processing unit of this invention in front of the resin in the purification loop. In this manner, the unit will supplement the resin by electro-deposition of ions which ordinarily occupy ion exchange resin sites in the demineralizer.

The design of the elect-rode is important if optimum operating conditions are to be attained. FIG. 3 shows a wrap-around type electrode consisting of alternate layers of fiberglass insulation 25 and brass sheeting 26 rolled into a cylinder 27 to fit the particular housing of the processing unit. This design offers a large electrode surface area with relatively close spacing.

FIG. 4 shows the construction of a container designed to house either a wrap-around or cell-type electrode in a continuous operation. The container 28 is preferably constructed from a sturdy material such as cast iron. The electrical connections are made with the aid of an insulated electrical penetration fitting 29. The waste material enters the housing through the inflow conduit 30 and is removed by way of the outflow conduit 31 after coming into contact with the electrodes contained within housing 28.

A cell-type electrode in cross-section is shown in FIG. 5. The electrode 32 allows close electrode spacing and presents a large electrode area per unit volume of liquid passing through the cell. It is constructed of brass plates 33 about 0.032 inch thick, with plastic strips 34 about inch thick used as insulators. The electrical connections are such that each alternate electrode is of the same electrical polarity.

If desired, the electrode may be placed within a suitable container (not shown) which is then inserted into the housing structure depicted in FIG. 5. Of course, the inner container would be perforated to enable the radioactive eiiluent to contact the electrode.

The following examples further illustrate the invention. In these examples, the electrodes were chemically cleaned prior to the operation. Cleanliness of the electrodes is an important factor in obtaining good adherent deposits.

Example 1 In this example, a solution containing metallic ions was tested in order to determine the feasibility of quickly and economically removing radioactive ions from solution. Initial tests were run using reactor grade water containing very small concentrations of radioctive cobalt. The concentration of cobalt was too dilute for accurate quantitative determination. By counting the gamma radioaction, it was determined that approximately of the Co in solution was removed in 15 minutes of operation. For convenience, the remaining tests were conducted with non-radioactive ions.

Example 2 The cathodes of the processing unit were various metal plates such as copper while the anodes were inert carbon plates. The electrodes were suspended from copper bars in a tank as shown in FIG. 1. Each carbon anode was positioned directly opposite two metal cathodes with the distance between the anodes and cathodes being approximately three inches.

A batch of solution was prepared containing ions of cobalt and iron and was processed utilizing the batch unit. Both cobalt and iron were deposited from the solution on the cathodes when a current of 400 milliamperes was applied. This mixed ion solution contained the following components:

CoSO -7H O 252 NaCl 7 H 30 28 Feclg' KCl Example 3 The following solution was processed using a batch type unit as shown in FIG. 1:

Cobaltous sulfate-7161 0 g./l 2 Sodium chloride mg./l Boric acid mg./l 200 The boric acid additive acted as a buffering agent. A receptacle was filled with this cobalt solution and a wrap around type electrode constructed as shown in FIG. 3 was introduced into the container. A current of about 300 milliamperes was supplied to the electrodes (1.29 rna./cm. After about 30 seconds of operation, the characteristic pink color of the cobalt solution disappeared indicating that a large percentage of the cobalt ions in the solution had been removed. After the electrode was withdrawn, a brownish-colored precipitate was discovered suspended in the treated solution. This suspended precipitate, identified as cobaltic hydroxide, was removed from the treated solution by filtration. The filtered solution was analyzed to determine the amount of cobalt remaining in the solution after processing. The result of the analysis is as follows:

00 Content Before Processing (p.p.m.)

00 Content After Processing (p.p.m.)

Percent Removed 1 This series of experiments in the second line utilized a double fiberglass screening rather than a single layer as insulation.

The extraordinary efficiency of the method of the present invention is clearly illustrated by this example. A thirty second operation resulted in almost complete removal of the cobalt isotope.

Example 4 In this example, a flow model processing unit as de scribed in FIG. 4 was used to process a continuous stream of material. A five-micron filter was installed in the processing loop downstream from the unit to remove the hydroxide precipitate. Other components in the processing loop included a 4.5 gallon/minute pump, a flowrneter, a twenty-micron pre-filter, the processing unit itself and the necessary control equipment. Initial tests were conducted using a wrap-around type electrode installed in the processing unit housing. With both the pre-filter and post-filter in the test loop, the maximum flow rate obtained was one gallon per minute. The unit performed well for several minutes using a current of 800 milliamperes (0.14 ma./cm. and a current of 500 milliamperes (0.09 ma./cm. After several minutes operation, however, the unit removal effectiveness decreased. It was noted that the fiberglass screening used as the insulation on the electrode had retained a considerable amount of fluid. The water-filled insulation apparently acted as a physical barrier tending to prevent the migration of the ions to the electrodes and decreasing the electrodeposition process. After the fiberglass insulation had been allowed to dry, the electrode again operated effectively.

Because of the high pressure drops in the system, the five-micron post filter was removed from the loop and replaced with a twenty-micron filter. This larger post filter eliminated the need for a pre-filter. With the five micron filter removed, a two gallons per minute flow rate was realized. A cell-type electrode was then substituted for the wrap-around electrode. This electrode was positioned in the housing of the unit and the necessary electrical connection made by use of the fitting as shown in FIGURES 4 and 5. The pump was ultimately bypassed to decrease the flow rate even further and provide a gravity feed system. After several minutes of efficient processing under an applied current of 800 milliamperes (0.52 ma./ cm. a greenish foam developed which proved to be copper sulfate and which was removed by providing a hole in the housing cap. This outlet became the liquid and foam outlet to the filter and the former outlet tube was used as a sampling line. With the system reassembled and the unit operated at 800 milliamperes, a considerable amount of foam and precipitate was observed in the outlet line to the post filter.

The following cobalt solution was processed using this flow model unit:

CoSO -7H O g./l 2 NaCl mg./l 100 H3303 mg./l

The results are as follows: Co content original solution (p.p.rn.) 315 6 First pass (p.p.m.): Percent removed 71.5 Final pass (p.p.m.):

It can readily be seen that the present invention is extremely versatile in its application to the processing of wastes containing radioactive ions in solution.

While particular embodiments of the present invention are shown and described for purposes of illustration, it is apparent that changes and modification may be made Without departing from this invention in its broader aspects. Therefore, the invention described herein is not to be construed as limited to the specific embodiments described, but is intended to encompass all modifications thereof coming within the scope of the following claims.

We claim:

1. A method for processing radioactive liquid wastes which comprises contacting a liquid containing radioactive non-metallic ions with electrodes including at least one anode and one cathode, the anode being fabricated from a metal which is reduced and goes into solution thereby combining with the non-metallic ions to form an insoluble precipitate.

2. A method for processing radioactive liquid wastes containing radioactive cobalt which comprises contacting a liquid Waste material containing a radioactive isotope of cobalt with electrodes and simultaneously depositing the cobalt on the cathode and precipitating cobalt in the form of cobaltic hydroxide.

3. A method for processing radioactive liquid wastes containing radioactive sulphur which comprises contacting a liquid waste material containing a radioactive isotope of sulphur with electrodes including at least one anode and one cathode, the anode containing copper, thereby precipitating sulphur in the form of copper sulfate.

References Cited by the Examiner UNITED STATES PATENTS 2,116,138 5/1938 Boss 204 275 2,299,964 10/1942 Grouch 204-149 2,399,389 4/1946 Negus 204-275 2,737,298 3/1956 Handel 204-449 2,854,315 9/1958 Alteretal.

OTHER REFERENCES Messing et al.: ORNL-2532, An Electrolytic Procedure for the Removal of Ruthenium and Nitrate from Alkaline Waste Solutions, Oak Ridge National Laboratory, 1958, pp. I7 and 20-23.

L. DEWAYNERUTLEDGE, Primary Examiner.

JOSEPH REBOLD, LEON D. ROSDOL, BENJAMIN R. PADGETT, Examiners.

" T. TUNG, L. A. SEBASTIAN, Assistant Examiners.

Claims (1)

1. A METHOD FOR PROCESSING RADIOACTIVE LIQUID WASTES WHICH COMPRISES CONTACTING A LIQUID CONTAINING RADIOACTIVE NON-METALLIC IONS WITH ELECTRODES INCLUDING AT LEAST ONE ANODE AND ONE CATHODE, THE ANODE BEING FABRICATED FROM A METAL WHICH IS REDUCED AND GOES INTO SOLUTION THEREBY COMBINING WITH THE NON-METALLIC IONS TO FORM AND INSOLUBLE PRECIPITATE.

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