ENGINEERING RESEARCH INSTITUTE THE UNIVERS I T Y OF MICH I GAN ANN ARBOR Report On PREPARATION OF RADIATION SOURCES FROM FISSION PRODUCTS BY THE CLAY PROCESS by J. E. Schoolmeester and Jo Jo Martin, Project Supervisor UoSo Atomic Energy Commission Contract No. AT (11-1)-162 Chicago 80, Illinois August, 1957

The University of Michigan * Engineering Research Institute ABSTRACT This study was made to determine the feasibility of producing usable radiation sources by the montmorillonite clay processo The clay.process was developed at Brookhaven National Laboratory primarily to solve the problem of ultimately disposing of waste fission productso After reviewing the process in detail, it is shown that radiation sources may be prepared with specific activity as high as 405 curies of cesium-137 per gram of clayo Sources of this strength would be entirely suitable for such processing applications as promotion of chemical reactions,, preservation of foods, or steriliza'ion of drugso Furthermore, the operations involved in the clay process are simpler and more straightforward than those of any other process for making radiation sources from fission productso It is concluded from this study that some clay sources should be prepared to demonstrate the actual processo ii

The University of Michigan * Engineering Research Institute INTRODUCTION The future of atomic energy as a primary source of power is becoming brighter with more power reactors being planned or constructed. With the growth of an atomic power industry will come an associated growth of chemical plants devoted to the reprocessing of spent reactor fuel elementso One of the more serious problems to be encountered by these reprocessing plants is the storage and disposition of the radioactive fission products which are separated from the unburnt fuel The disposal of the so-called waste fission products has been the subject of several research programs during the past few yearso As the number of curies of fission products produced per year increases9 the concept of utilizing these wastes as radiation sources becomes increasingly attractiveo The construction at Oak Ridge National Laboratory of a multimillion dollar pilot plant for the production of Cs 37Cl is evidence of this trend in thinkingo This study has been undertaken along similar lines of reasoning to determine the feasibility of preparing a usable, safe, and relatively inexpensive source of radiation from fission products by a process different from that employed at Oak Ridgeo The process considered is basically that of adsorbing Csl37 on montmorillonite clayo This report contains a brief discussion of the principles of the clay process and a description of the type of source producedo A proposed laboratory procedure for preparation of a small source is includedo Conclusions regarding the 1

The University of Michigan * Engineering Research Institute advantages and disadvantages of the clay process based on the findings of this study are giveno Appended to the report are complete and detailed calculations on which the conclusions are basedo PRINCIPLES OF THE CLAY PROCESS The essential principles underlying the clay process are taken from a series of studies made at Brookhaven National Laboratory (3,4,7). The fundamental paper of this series (7) is. concerned with the adsorption phenomenon of montmorillonite clayo This clay possesses the property of being able to adsorb large numbers of cations from extremely dilute solutions through an ion exchange type of mechanism. There appears to be a high degree of selectivity exhibited by the clay for the fission product cationso Howeverg trivalent cations such as Al+++ are also quite strongly adsorbed and present difficulty when present as interfering ions in the adsorbtion of Cs 3 It is, therefore, imperative to get as good a separation of Cs137 and Al+++ as possible for this process, if the ion sites in the clay are to be filled largely with fission product cationso Another unique property of montmorillonite clay is that it can be ground and mixed with water, and extruded into a "spaghetti-like" material that is ideal as a column packing. The spaghetti-formed clay is a stable aggregation and is physically unaffected by passing through it dilute solutionso Thus, it is a simple operation to remove fission product cations from a dilute solution by running it; through a column packed with the spaghetti-formed clayo 2

The University of Michigan * Engineering Research Institute The fission product wastes which are considered here for preparation of radiation sources have large amounts of aluminum ion presento The best method of separating out the aluminum for this process appears to be by calcining the waste at high temperature followed by leachingo The calcination converts all the cationic materials to the oxide The oxide of aluminum is extremely insoluble while those of the fission products do dissolve0 The leaching agent which gives the highest ratio of the fission product, Cs137, to Al1+++ is distilled water (4) This solution will produce the best radiation source after adsorption of the cesium in clayo Thus, the calcined wastes are leached with a large volume of distilled watero The dilute leaching solution is then passed through the columns of clayo Here the cations of the fission products, notably Csl37 are removed by ion exchange. Following adsorption of the cations the clay is fired at 1000~Co This fixes the adsorbed ions in the clay lattice so that they cannot be leached out except by the most drastic means, such as by using strong acidso This makes the clay comparatively safe to handle, for it will not release the radioactive cationso If the clay is used as a radiation source for a while and then disposed of by burying in the ground, one can be sure that the radioactivity will not get awayo This is extremely important in considering any ultimate disposal of the fission productso The principles of the clay process make it adaptable to more uses than preparation of a radiation sourceo In fact, the process was originally developed as purely a disposal methodo 3

The University of Michigan * Engineering Research Institute If applied to the treatment of large urban water supplies contaminated by radioactive fallout, the clay process could be used to purify the water In this study, of course, the emphasis is on preparation of radiation sourceso After the clay is fired and the radioactivity locked in the lattice structure, the radiation source is made by simply packaging the clay in aluminum containerso As will be shown, the specific activity of the clay is such that sources of hundreds and thousands of curies can easily be madeo Because of the container walls, it is only the gamma radiation which can penetrate and be usedo The beta radiation will be absorbed and will serve simply to heat up the sourceo THE MONTMORILLONITE CLAY SOURCE This study indicates, according to the calculations given in the Appendix, that a gamma radiation source can be prepared with a specific activity as high as 4~5 curies of Cs137 per gram of clay and a density of 2o2 grams per cco A one kilo-curie source of this type will weigh 222 grams and have a volume of approximately 100 cco This is sufficiently concentrated to make it a useful radiation source for processing applicationso Because of the simplicity of the process, a clay source should be comparatively inexpensive to fabricate. Also the low density of the clay reduces the self absorption of gamma radiation to a small amounto The safety of a clay source should be emphasized, especially when comparing it with cesium chloride. The chloride is extremely soluble and is therefore especially hazardous if 4

The University of Michigan * Engineering Research Institute used near watero The clay source is extremely insoluble and wet conditions are of little concern. The clay source is directly ready for safe disposal when it is no longer usefulo This certainly is not the case with cesium chloride. For its ultimate disposal it must either be fixed in clay or it must be perfectly sealed in a corrosion-proof container0 A montmorillonite clay radiation source sealed in an aluminum container evidently possesses several advantages Its biggest disadvantage probably occurs in connection with its specific activity. It is possible to make cesium chloride sources with several times the specific activity of the clayo However, for many processing applications, such high specific activity is not required, so that the clay source should be entirely satisfactory~ PROPOSED LABORATORY PROCEDURE FOR PREPARATION OF A CLAY SOURCE This study indicates the worthwhileness of making some small clay sources0 Consequently9 it is proposed that a sample of the Arco, Idaho, high level waste be solidified and calcined at 550~C in a porcelain crucible0 The vapors should be carefully de-entrained to remove all condensables that might contain radioactivity0 All gases or vapors should be monitored to determine activity before venting them to the stack0 A schematic diagram of this procedure is shown in Figure 1 of the Appendix0 The calcined oxide is to be leached in the same crucible to avoid unnecessary handling0 This is accomplished by recirculating the leach water through the crucible containing the oxide from a leach reservoir of a larger volume0 A small 5

The University of Michigan * Engineering Research Institute jet or other type of sealed pump is used for recirculation ~ Approximately one month is required to remove the maximum percent of Cs from the oxide (4) The recirculating lines are so connected (see Figure 2) that the solution, after leaching operation is complete, is jetted from the reservoir to the clay columns. By using several columns in series, decontamination is high so that the exit solution can be run to the sewero As each column of clay becomes saturated, it is replaced with a fresh columno The solution contacts the fresh column last to give the desired decontaminationo Saturation of the clay is easily determined by counters at the inlet and outlet of each columns When the clay in a given column is saturated, the column is drained and fired using an induction furnace (Figaure 3)o After firing, a piston, fitting inside of the quartz column wall, forces the "spaghetti" out of the column and into the aluminum tube, The tube is supported in a close-fitting steel case, allowing the clay to be pulverized and compressed in the tubeo This supporting case is shifted remotely when the tube is filled and the tube is raised and welded shuto The tube is finally transferred to a lead pig for shipping0 CONCLUSIONS AND RECOMMENDATIONS It is the primary conclusion of this study that the preparation of powerful fission product radiation sources by the montmorillonite clay process is both possiLle and desirableo Specific activities up to 4~5 curies of Cs-137 per gram of clay can be obtained0 Sources made of the clay are sufficiently _ --

The University of Michigan * Engineering Research Institute concentrated so that many curies of activity may be assembled in reasonably small volumes for processing applicationso The clay process, which involves calcining, leeching and absorption of the fission products, and firing and packaging of the clay, is comparatively simple and should be operable behind thick shieldingo The permanence of clay sources and their readiness for ultimate disposal after use give them advantages not possessed by other sources prepared from fission productso Because of the feasibility of the clay process, it is recommended that some small sources be prepared in a bench-scale operationo It is believed that most of the operations could be carried out in conventional laboratory equipmento Special devices would be required to prepare the clay and to load and seal the clay in aluminum capsuleso Preparation of these small sources would demonstrate the complete workability and simplicity of the processo Following the bench-scale operations larger pilot plant equipment should be constructed to prepare sources that would compete with cobalt-60o When sufficient fission products are available, it might no longer be necessary to use up valuable nuclear reactor time to make cobalt-60 sources, since fission products would serve in their steado Production of cheap radiation sources is necessary if a radiation processing industry is to be developedo It is doubtful that nuclear reactors can ever be operated to make artificial isotopes, such as cobalt-60, very cheaplyo Fission products being a true waste by-product of the nuclear power industry, have the potential, at least, of being made available at comparatively low costo 7

The University of Michigan * Engineering Research Institute APPENDIX Calculation of Clay Source Activity The composition of Arco high-level wastes before evaporation is as follows [for first raffinate (1AR)].(1) Al(N03)3 = 1o58 M NH3 = 0.25 N FoPo (Fission Products) = 0.31 gram/liter SPo GR. - 1.247 After concentrating to 2.2 M Al(N03)3 before storing (2), che concentration of fission products becomes 2.2 15- xO0.31. 0432 gram/liter For normal fission products, cooled 100 days, the amount of radioactive cesium-137 is 602 % (3) while 6 -% of the FoPo is Cs135 (11)o The total amount of Cs in the waste is.122 g -Cs x 0.432 FP. = 000525, Cs g,F.oP liter liter Upon solidifying and calcining the aqueous waste at 550~C, the amount of Cs in the calcined oxides may be determined as follows: A(N03)3 = 2o2 molar therefore Al+++ = 2.2 molar Al+++ = 22 moles x 26o97 am = 59.2. A+++ liter mole liter mole wto 2&97 1/2 x 101,94 Al+++ 2 1/2 A1203 heat 59o2 grams x grams 59A2 gAAl++ + |59o2 a. 59o2 x 1/2 x 101o94 = 112 gs A1203 l liter 26097 liter There was also 0o0525 go Cs /liter, therefore, 8

The University of Michigan * Engineering Research Institute.0525 g0 Cs in 112 go A1203 or o0525 = 407 x 10-4 g~ Cs 112 go oxides Note: In this calculation the oxides were considered to be pure A1203 since the amount of other oxides adds a negligible amount to the weight of A12030 Using distilled H20 to leach the Cs from the calcined Al203 the Al+ concentration in the leach solution is 10-5 normal (4) The amount of Cs leached in 25 days is 75 % (5) The concentration of Cs in the leach using 100 cc distilled H20 per gram of oxides (6) is g Cs o75 x 4 e7 x l0"4 1.00. leach 137 mol —mole 58 x mole 2o58 x lQO5 lite- M N Since both trivalent AL.+++ and Cs are strongly adsorbed by montmorillonite clay by an ion exchange mechanism, it is logical to assume that these ions will be adsorbed in proportion to their concentration in equivalents, or normalities. The capacity of the clay is lo12 milliequivalents per gram (7)o The amount of Cs adsorbed by the clay is equivalents of Cs capacity total equivalents (Al + Cs) x capacity 2o58 x 10'5 milliequivo Cs 1"5 +. 0 5' x 1 12 = 0 81 milliequiv Cs 10 + 2o58 x 10 x gram clay converting milliequivalents to grams o81 millieqo = -11 x 137 ram = Oolll go Cs 1000 eqo gram clay but, only 51 % (11) is Cs137 ----------------------— 9 —-----------

The University of Michigan * Engineering Research Institute 1 37 or o51 x o111 go Cs._ 057. Cs gram clay gram. clay Calculating the activity of pure Cs137 tH = 33 yr. t o6935/ (8) activity = N (9) where tH is half life,' is the decay constant, and N is the 137 number of molecules of Cs per gram, tH - (33 yr) (365 y) (86400 eJ) Jyro, ( 4day l04 x 1,09 seco o693.693 -10 -l o 9 3 = o693 = 6o67 x 10-10 sec.-I tH 1o04 x 7109 = 1 go Cs x 6023 23 atom 4038X1021 atom N =x 602 x 1023 mo --- 4.8 gram 137 gram gram mole activity = N) 4o38 x 1021 x 6o67 x 10-10 = 2o92 x 1012 disintegrations/seco 2o92 x l012 d s 307 x. ds curie 137 -'9 curie per gram Cs3 Then, the activity of a clay source containing 0o087 go Cs137 per gram of clay is curie source activity - 79 grx o057 C ~gram Cs g source 45 curies gram The density of the clay source is estimated to be 202 go/cco This is based on the assumption that the pulverized and compressed clay will be slightly less than the natural density of 2o348 go/cc (10)o 1000 curies For a 1000 Weight uries/gram = 222 grams curie source 222 grams and Volume - 202 grams/cco e 100 cco 1.0

The University of Michigan * Engineering Research Institute BLOWER EXHAUST HOOD / COOLING WATER PORCELIN CRUCIBLE AQUEOUS HEATER WASTE CONDENSABLES RING STAND HOLDER Figure 1o Equipment for Solidifying and Calcining Aqueous Waste 11

The University of Michigan * Engineering Research Institute DISTILLED H20 SUPPLY RECYCLE LEACH WATER LEACH RESERVOIR XIDE~ (SEVERAL LITERS) TO CLAY COLUMNS JET PUMP Figure 2, Leaching Apparatus 12

The University of Michigan * Engineering Research Institute PISTON TO FORCE CLAY INTO SOURCE JACKET & PULVERIZER o]1 l" EXIT H20 o0 o TO NEXT o0 0 COLUMN OR Sg S SEWER 0 0 o I -QUARTZ TUBE FURNACE 0 o 0 | ~'o - -"S PAGHETTI" CLAY o 0 o 0 ENTER H20 >~0 / REMOVABLE PLATE FROM LEACH RESERVOIR CLOSE FITTING STEEL SUPPORTING CYLINDER ALUMINUM SOURCE JACKET PULVERIZED | i lCs137 CLAY SOURCE PISTON FOR REMOVING SOURCE FROM SUPPORTING CYLINDER Figure 3' Adsorption and Source Loading Equipment 13

The University of Michigan * Engineering Research Institute REFERENCES (1) Phillips Petroleum Coo, Atomic Energy Division, "Chemical Processing of Reactor Fuel Elements at the Idaho Chemical Processing Plant" Idaho Operations Office, UOSo Atomic Energy Commilssion, po 8o (2) Ibido po p12 (3) Bo Manowitz and Lo PO Hatch, "Processes for High-Level Waste Disposal", Chemo Engo ProgO Symp. Series, 50 no, 12, 1954, Po 145o (4) Ao Abriss, Jo Jo Reilly Eo Jo Tuthill, "Separation of Cesium and Strontium fr9m Calcined Metal Oxides as a Process in Disposal of High Level Wastes", Brookhaven National Laboratory, Upton, New Yor 1957, po 10o table lo (5) Ibido Figure 9o (6) Ibid Po 2o (7) Wo So Ginell, Jo Jo Martin, Lo P Hatch, "Ultimate Disposal of Radioactive Wastes", Nucleonics, December9 1954, 12, po150 (8) Ro Lo Murray, Introduction to Nuclear EngineerinL, PrenticeHall Inco New York, 1954o (9) Ibido (10) Ro Eo Grim9 Clay Minerolo2 McGraw and Hill, New York, 1953. (11) Mo Eo Weech, "Sources of Radiation for Industry", University of Michigan Ann Arbor,9 Michigan, August, 1956, po 77o i.14