Summary of Information on Americium Availability and Curium-242 Production

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This document consists of pages SUMMARY OF INFORMATION ON AMERICIUM AVAILABILITY AND 3. Contains no DOE classified info 6. Classified info bracketed

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This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency Portions of this document may be illegible in electronic image products. Images are produced from the best available

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This report has been prepared by Martin-Nuclear for the U.S. Atomic Energy Commission. It provides information on the availability of Americium and the

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II. Americium Availability 4 III. Curium Production 8 IV. Chemistry of Curium 24

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Figure Title Page 1 Schematic of Reactor Core Arrangement 9 2 Reactor Flux Distributions 10 3 Reactor Flux Distributions 11 4 Reactor Flux Distributions 12 5 Reactor Flux Distributions 13 6 Reactor Flux Distributions 14 7 Reactor Flux Distributions 15 8 Reactor Flux Distributions 16 9 Reactor Flux Distributions 17 10 Reactor Flux Distributions 18 11 Reactor Flux Distributions IV 12 Reactor Flux Distributions 20 13 Irradiation Products of Americium in the Materials Test Reactor 14 Two Hundred Fifty Milligrams Americium-241 and Fifty Grams

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This report contains a summary of the information on the availability of Americium-241 and the technology known for the pro duction of Curium-242. The information was collected by MartinNuclear at the request of the Aircraft Reactors Branch, U.S. Atomic Energy Commission. The report points out that there are 30 grams of Americium-241 available and a projection of isolating 30 grams each month in the next year. This quantity of Americium is sufficient to produce a 200-watt electrical power supply each three months using an efficiency of six per cent for the conversion of heat to electricity. It is possible, from the standpoint of Dow Chemical Company, for a high priority project to produce sufficient Americium for such isotopic power supplies at three times this rate if the Division of Military ap plication changes the age of the feed material at the Rocky Flats Plant. This material can be fabricated into suitable "slugs" for irradiation by any laboratory used to handling alpha active materials. Such facili ties exist at the University of California Radiation Laboratory and can be quite easily duplicated at The Martin Company. Quantities of Americium-241 up to 300 grams each 84 days can be irradiated at the ETR. A high priority is not required to obtain irradiation space for quantities up to 150 grams. At the present time there are no facilities that are available to process this amount of curium but by January 1, 1960 the proposed hot cell facility that is under design by the Nuclear Division of The Martin Company, under the SNAP programs, can quite easily and safely produce one unit in two months time. It is estimated that the first unit should cost about $3.06/curie or $80.00/watt while successive units should

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Curium, element 96, is the seventh member of the actinium series. This element is analgous to gadoli nium, element 64, in almost all of its chemical properties. Two isotopes of this element. Curium-242 and Curium-244, can be produced in macro quantities. Curium-242 is formed by neutron capture in Americium-241. This reaction takes place in the following manner. This equation states that when Americium-241 is irradiated with neutrons three products are formed; curium, plutonium and fission Curium-242 is an ideal source of energy for isotopic power plants since eight grams of this material gi^e off one kilowatt of thermal energy. Curium can be prepared as the metal which has a density greater than 7 g/cm and a melting point of over 1000°C. A Curium-242 pellet of one cubic centimeter, therefore, provides 875 watts of thermal power. If at some time in the future a higher temperature compound is of interest for thermionic conversion systems, the compound curium carbide can be easily synthesized. This substance will have a melting point in the region of 2000°C and a density of ^ 10 g/cm6, which indicates a power density Curium-242 decays by alpha emission with a half-life of 162 days and by spontaneous fission with a half-life of 7.2 x 10® years. The energy emitted by a curium disintegration is 6.21 Mev. In addition to its large decay energy and high specific power, this isotope is extremely valuable because of the lack of gamma emission associated with its disintegration.

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A list of gammas associated with this disintegration process is as A spontaneous fission gamma A spontaneous fission neutron From these data it is quite easy to see that only a small amount of shielding is required for an isotopic power supply that has a maximum power density with a minimum of ground handling problems. The ad vantages gained by the minimum number of gammas are not limited to only ground handling. These extend through the life of the power supply by minimizing the radiation damage to electronic components in the circuitry and lessening the problems connected with film storage in the vehicle. In addition, it is possible to maintain animal life in the same vehicle with the power supply. The plutonium formed is a very special isotope, Plutonium-242, which is the ideal starting material for synthesizing all other trans uranium elements. To demonstrate the interest in this isotope an ad hoc committee has been formed by the Atomic Energy Commission Research Division, to sponsor a program to convert ten kilograms of Plutonium-239 to one kilogram of Plutonium-242. This expensive, but important, program involves the conversion of the ten kilograms of plutonium into plutoniumaluminum alloy, irradiating the alloy for one year in the Savannah River Reactor and then chemically reprocessing the Plutonium-242 and separating

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it from the nine kilograms of fission products. This program will then have Plutonium-242 with the following mass analysis. This material will be packaged and re-irradiated for several years in a reactor such as the Materials Test Reactor, (MTR), Idaho Falls, Idaho, to produce large amounts of Curium-244, Americium-243, berkelium and californium for research purposes. This same material can be supplied as a by-product from a large scale Curium-242 production at a large savings of manpower and

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II. AMERICIUM AVAILABILITY Americium-241 is produced by the beta decay of Plutonium-241 which is a 13-year isotope. This isotope is formed in the production facilities today as a by-product from the production of Plutonium-23 9. When Uranium-238 is irradiated in a pile the material goes through the Since most material which has been irradiated in production reactors waits three months from the time it is removed from the pile to proces sing, very little of the Plutonium-241 has decayed to americium before purification. After purification the plutonium is stored in a stockpile of materials and during this time the Plutonium-241 decays to Americium-241 at a constant rate. A typical isotopic composition of plutonium in the stockpiles today has the following mass per cent. The isotopic composition of plutonium stored for three years will contain 0.083 per cent by mass of Americium-241. Experimentally it has been shown by Dow Chemical Company at the Rocky Flats Plant, Denver, that it is possible to isolate 0. 07 per cent of the plutonium by weight as pure Americium-241 if the stockpile material has stood for The chemical process plant run by Dow Chemical Company has a capacity to process 200 kilograms of plutonium through its wet chemistry section each month on a three-shift basis. At the present time this plant operates on two shifts and is processing 100 kilograms of plutonium a month. In January 1959, this output will increase to 150 kilograms a month on a two-shift basis. At the present time, one third of this plutonium is three-year old stockpile material and the other two thirds is fresh from 1fhe Hanford Laboratories. From this mixture of new feed and old stockpile material americium is being recovered at a rate of 0. 02 per cent of the plutonium going through wet chemistry.

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A chemical process investigated by Robert Penneman and John Coleman, Los Alamos, New Mexico and developed into an excel lent process by I. B. Venable, John Pringle and his staff at the Rocky Flats Plant, has made the production of Americium-241 a routine pro duction. This process has been developed so well by the Dow Chemical Company that the total output of their wet chemical line can be purified and separated into pure Americium-241 by six technicians. This americium process line has been in operation only three months and during this time the following have been isolated. At the present time there are 30 grams of Americium-241 in its pure state and the present plans call for purifying 30 grams each month. The output of this plant can be increased to 100 grams a month instead of 30 by changing the plutonium feed to a rework program of three-year old material instead of the mixture of one-third old material and two-thirds fresh feed. This increase can be accomplished with no change in existing equipment or process techniques. The cost of americium was discussed with I. B. Venable and John Pringle, Dow Chemical Company. At the present time there are no exact cost figures available on this product but starting January 1, 1959 a cost system for americium is being instituted. Some time in March exact figures will be available. To obtain a working cost figure, it was agreed to use the month of November as an example. During this month, 20 grams of americium were produced using six man-months of labor. Using the costing system of the Rocky Flats Plant this amounts to $1,000 per gram. If the americium content of the feed is increased by increasing the average age of the feed material the cost should decrease to an even lower level. This decrease in cost would be based on the assumption that the time to handle a particular volume of solution is a constant. Thus increasing the americium concentration per liter should reflect directly in a reduction of the cost per gram of material. For these reasons it was agreed that $1,000 per gram was a conservative number to use for cost estimating purposes.

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The only other economical source of Americium-241 will be from the high burnup plutonium formed by civilian power reactors. Much of this material will have an isotopic composition such as: After this material has stood for three years it produces 3.75 grams of americium for each kilogram of plutonium processed. The only ma terial of this type being prepared today is ten kilograms that are being readied for the University of California Livermore Laboratory. This material will be used for critical experiments and will not be available for separation for many years. Many other civilian reactors produce this type of plutonium but there are no facilities available that can process the various type power reactor fuel elements and at the same time recover the plutonium produced. A letter dated November 17, 1958 from F. K. Pittman, Director, Division of Reactor Development to E. J. Block, Director, Division of "In many cases the plutonium from nuclear power reactors, returned to the Atomic Energy Commission for chemical processing, will contain relatively high percentages of Plutonium-241. This material, therefore, presents a good potential source of Americium-241. From the data available to this office, it has been established that 0.6 kilogram of Americium-241 could possibly be available at the end of FY 63 and another 0.7 kilogram at the end of FY 64. These figures have been derived on the basis that the plutonium returned in FY 62 and FY 63 be stored for one year in each case to allow the decay of Plutonium-241 and growth of Americium-241. If the plutonium delivered in FY 62 is stored two years and the plutonium delivered in FY 63 is stored one year, the total Americium-241 theoretically available at the end of FY 64 would

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This plutonium which is produced in civilian reactors must have its americium content removed if it is allowed to stand for long periods of time. If this americium content is not removed before this material is re-inserted in a reactor, the americium will form large quantities of Curium-242 which is an alpha emitter. These alphas will be many times greater than those of plutonium and will make the already difficult alpha-gamma handling problem much more serious and expensive.

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III. CURIUM PRODUCTION Curium-242 at the present time has been produced in quantities The starting material, Americium-241, was prepared for irradiation by cold processing americium oxide and aluminum powder into pellets at pressures of 45,000 psi. These pellets were then placed in an aluminum sleeve with 1/16 inch walls and repressed to a pressure of 70,000 psi. On each end of these tubes of americium and aluminum mixture, there was a 1/2 inch pure aluminum pellet. This technique provided a method for keeping the americium cool during irradiation in the pile and also made a safe container for the Curium-242 formed. At the present time 28 such slugs have been irradiated in the MTR with no sign of activity in the water. The best method of packaging americium for curium production was discussed with Fred L. McMillan of Phillips Petroleum at the Engineer ing Test Reactor (ETR) in Idaho. At this time he pointed out that there are 30 irradiation positions in the ETR that have neutron fluxes equal to or greater than L-55 in the MTR. (Most of Curium-242 to date has been produced in L-55 of the MTR.) It is possible to use the center 15 inches of these positions to irradiate five slugs each five inches long and with a one-inch outside diameter. It is recommended that the same americium concentration per cubic centimeter used in previous slugs be maintained. This will mean that each slug will contain 4.2 grams of americium. Eight such reactor positions can safely irradiate 100 grams of Americium-241. An optimum time for these irradiations is four cycles of 21 days each or 84 days to produce a maximum of Curium-242 from the Americium-241 used. Since there are more than 24 such positions in the reactor, 300 grams of Americium-241 could be irradiated at any one time. A reactor core arrangement schematic (Fig. 1) and flux maps of many of these positions in the ETR (Fig. 2 through 12) are attached for examination. The Curium-242 produced as a function of time may be seen in Fig. 13. The flux used in this calculation is based on many …