NEW NEPTUNIUM RECOVERY FACILITY A T THE HANFORD PUREX PLANT J.
P. D U C K W O R T H A N D
L. R . M I C H E L S
Huriford .l/ornic Piuducis Oprintzun, General Electric Co . Rickland, 11'ush
A complete solvent extraction battery was a d d e d to the Hanford Purex Plant for the continuous recovery of neptunium-237 as a third product.
The adoption of a compatible flowsheet and the design and application
of new recovery equipment are outlined.
The solvent extraction battery i s installed in a space formerly
occupied b y a single extraction column, illustrating the use of the "package" concept to extend the scope of the Hanford remote maintenance philosophy for more effective use of canyon or shielded space.
\cas recently Purex Plant for the continuous recovery of a third product from irradiated reactor fuels. T h e third product is the transuranic isotope neptunium-237. which is the starting material for the production of PuY33now orbiting the earth in the Transit I\' Satellite as the heat source for the power supply. T h e Purex plant. part of the huge reactor and chemical processing complex a t Hanford: LYash.. separates and decontaminates plutonium from irradiated natural uranium for its subsequent use in weapons components. 'The irradiated uranium is also recovered and decontaminated from fission products for subsequent enrichment in diffusion cascades. More recently, the Purex plant has been employed for the recovery of special by-product materials including the fission products. strontium-90, cesium-137. and cerium-144, and the transuranic. neptunium-237. Development of the process and equipment for recovering neptunium started in 1958, with the first of a series of special campaign tests made during scheduled shutdo;cn of normal plant operations. I n 1960, a recovery and decontamination flo\csheet \$'as developed by Benedict. McKenzie. and Richardson ( 7 ) which was compatible with the Hanford Purex process and existing equipment. This paper describes new equipment suitable for continuous operation on a neptunium recovery cycle. T h e solvent extraction equipment was installed in space formerly occupied by a single column, illustrating the use of the equipment package concept for more effective use of canyon space and extending the scope of the Hanford remote maintenance philosophy (3. 5).
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ADDITIOSAL
S O L V E N T E X T R A C T I O S BATTERY
A' installed . in the Hanford
Source and Chemistry of Neptunium
Neptunium-237 is produced in the atomic reactors as a result of tivo n, y reactions \.rith L-zs5 or by n. 2n reactions Xvith U-238. I n the Purex process. neptunium exists as a nitrate in three oxidation states. The neptunium(I\.) and neptunium(V1) states are extractable in the Purex solvent (30 vol. yc TBP in kerosine diluent) and neptunium(Y). the most stable state. is not. .The oxidation-reduction potentials for the various neptunium species are close enough to those of plutonium that the same chemicals Lvhich are used to separate plutonium from the uranium in the Purex process can be used to separate neptunium from uranium and from plutonium. I n fact. since 302.
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PROCESS D E S I G N A N D DEVELOPMENT
both the (I\-) and states have about equal solubilities and extractabilities, both an oxidizing and a reducing floxssheet Ivere developed to separate the neptunium. Because of existing equipment limitations. the reducing flo\vsheet ;cas the first developed and. therefore. was the flo\csheet adopted for this project. 'l'he oxidizing flolcsheet. although not plant-proved, has specific advantages and \\-as given consideration in the design of the equipment to permit eventual application.
Description of Previous Recovery Process and Equipment
l ' h e previous method of recovering and separating neptunium from the Purex process as summarized by Harmon ( 2 ) required t\\-o major operations. First, during the normal uranium and plutonium recovery operations. neptunium \vas extracted and recycled through the backcycle \vaste system by causing it to folio\\- the uranium through the plant. T h e second operation required the separation of neptunium from uranium and plutonium and the decontamination from fission products. 'To carry out the second operation, the equipment in the final plutonium cycle was used. \\.'hen the main portion of the plant \\'as shut do\vn. the neptunium \vas recovered from a concentrated solution of backcycle Lvaste. hlthough these operations \cere fairly successful. they had t\co major dra\cbacks. First. during the normal operating period. the bulk of the neptunium inventory in the backcycle \vaste system could be lost to the final \caste evaporatorJvithin an eight-hour period if a n upset occurred in the first cycle extraction column. Second. the use of the final plutonium cycle equipment during plant shutdowm necessitated the loss of an appreciable amount of normal processing time. T h e correction or elimination of these two drawbacks motivated the study to install a continuous recover)- s p t e m . Xn evaluation of the knoicn neptunium separations methods on all possible neptunium-containing streams in the Purex plant resulted in three primary conclusions. The concentrated backcycle Tvaste stream ivould be the most adaptable source of feed for neptunium separation. A minimum of t\io solvent extraction columns \could be required o\ving to the limiting height of the canyon cells. T h e columns and associated equipment ivould have to be nuclear geometrically favorably designed because of the presence of plutonium in the backc>-cletvaste stream. \Vith these parameters. the plant-proved reducing floivsheet was adapted for the proposed project. In the interest of economy. the recovery and decontarnina-
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Final Waste Evaporator
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tindergmund
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Column 2nd Cycle
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Figure 1 . Path of neptunium through the Purex process and the relationship of the continuous neptunium recovery system
tion of neptunium were to be carried out stepwise in the same equipment rather than to provide equipment for additional solvent extraction cycles. N e w Recovery Process
T h e new continuous recovery process and equipment, with relation to the parent Purex process, are shown in Figure 1. To recover neptunium from the Purex process, three steps or phases are used. P h a s e I. .4portion of the backcycle waste stream is routed to the recovery equipment where the neptunium is separated from the uranium and plutonium and recycled internally while the plutonium is returned in the reduced form to the backcycle waste evaporator; the uranium remaining in the 5olvent is routed to the first cycle partition column. Only a portion of the backcycle waste is processed. because the capacity of the equipment is limited by the geometrically favorable design. P h a s e 11. After sufficient neptunium is accumulated in the equipment for a batch purification run, the backcycle waste feed to the equipment is stopped and Phase I1 is started. A "cold" synthetic feed is substituted for the "hot" feed, and the neptunium continues to be recycled through the equipment until the fission products, uranium and plutonium, are removed. P h a s e 111. After sufficient decontamination and purification have been achieved. the product stream from the stripping column is diverted to a batch ,ion exchange purification unit for concentration and final purification. After the equipment is pbrged of the decontaminated neptunium, the backcycle waste stream is again routed to the neptunium columns and the accumulation flowsheet (Phase I) is reinstatcd. N e w Neptunium Recovery Facilities
Early design scoping studies indicated that the only canyon position suitable for installation was a space 14 X 14 X 39 feet. Originally. at the Purex plant start-up, this position was occupied solely by a single pulse column and pulse generator. With the conversion of Purex from a three-cycle to a two-cycle process in 1958, the column and pulse generator were removed and a standard 10-foot 0.d. X 10-foot tank was installed in the position. Any new facilities designed for this canyon position were to include a replacement tank.
T h e design challenge, therefore. in incorporating the neptunium recovery facility into the Purex plant \vas to fit t\co pulse columns. two pulse generators. tivo tanks. threc sample pots. and a forest of remote connectors or jumpers in a space originally intended for only a single column and pulse generator. without disrupting the basic Purex process. This resulted in the J Cell "Package" concept. Design Philosophy. The design philosophy adopted called for remote operation and maintenance of equipment wherever possible. T h e entire package \vas to be "remoted" into and out of the cell. All equipment subject to mechanical failure or process obsolescence \cas to be remotel)- removable from the package. such as pumps. agitators. jets. valves. fio\vmeters. and control instrumentation. .-\lrhough small pulse generators are essentially trouble-free. they \Yere to be remoted as an added precaution. Pulse column cartridges were designed for remote replacement to pro\ride added process flexibility since it was not practical to remote the entire column. T h e philosophy also required that maximum use be made of the very limited services from the operating gallery and limited r o u t i n g to and from the parent Purex vessels. In addition to the above limitations, nuclear safety had to br considered. Although neptunium-23? does not constitute a critical mass hazard. plutonium-239 is present in small quantities in the Purex backc)-cle waste and. therefore. a potential exists for plutonium to reflux throughout the neptunium recovery battery. Consequently. a nuclear geometrically favorable design \vas required. This restriction complicated the design ob,jective of a compact equipnirnt package since. not only did it limit the shape and size of the equipment. but it also necessitated the positioning of equipmrnt \vith a minimum spacing of 2' 2 feet. T h e nuclear safet!- philosophy finally adopted \cas to use favorable geometry \\herever possible coupled with administrative controls where an "al\cays-safe" geometry could not be provided. This resulted in the aelrction of 7-inch i.d. columns and 3-inch annular vrcsels. Description of the J Cell Package. A flow sketch of the integrated process equipment selected for the .l Crll Package i, shown in Figure 2. T h e feed tank and the two column. constitute the primary equipment for the recovery hattrry VOL.
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Annulor feed tank, geometrically favorable in Figure 4. the event of high plutonium contamination of the feed
Figure 4 shows that the feed tank is a n annular tank with a centrally located “stand-pipe” pump-hoot. The solution is confined within a 3-inch thick outer annulus to provide 320 gallons maximum capacity. An internal 7-inch thick annular concrete plug installed immediately adjacent to the solution annulus is provided for nuclear safety. A steam coil and an air sparge ring are installed at the bottom of the solution annulus far heating and agitation functions, respectively. Excellent agitation is achieved in a n annular tank of this size with only 1s.c.f.m. sparge air. T h e new columns employ standard Purex pulse generators, which have been used successfully on three other columns since the Purex plant start-up. The amplitude of these cam-driven piston pulsers is fixed. Speed variation is achieved thiough changing the frequency of current supplied to the gear motor. T h e other equipment required is incorporated in some 90 jumpers which were provided for the J-Cell package to connect the neptunium equipment with the other portions of the P u r e i plant using the nozzles on the package and the original nozzles on both adjacent cell walls. These may be seen in Figure 5 which is a drawing of the canyon position, looking down on the equipment and jumpers. These jumpers are installed a t varying elevations and, therefore, do not interfere unduly with one another. Jumpers for the J-Cell package contain
Figure 5. Overhead sketch of the removable jumper arrangement required forincorporating the neptunium recovery equipment with the Purex process VOL. 3
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.58 remotely replaceable instruments and flow control pieces. Five major headers are provided within the package framework in order to minimize the need for multiple individual routings. ’These serve for the handling of waste: feed, organic solvent. and general vents. However. for better process control and to reduce harmonic interference from the pulse generators. each column and its related equipment were vented separately. Despite the space limitations and the close tolerances: the equipment was installed without incident; and, by the end of the first six months of operations, the continuous neptunium facility met or exceeded every operational requirement.
literature Cited
Acknowledgment
Division of Nuclear Chemistry & Technology. 146th Meeting, ACS. Denver, Colo.. January 1964. Operated for the Atomic Energy Commission by the General Electric Co. under contract N ~ .i~(45-1)-1350. .
T h e authors thank J. C. Willi and M. E. Yates for assistance in the design of the package.
(1) Renedict. G. E., McKenzie, T. R., Richardson, G. L., “Recovery of Neptunium in Solvent Extraction Processes,” Division of Industrial and Engineering Chemistry, 138th Meeting, ACS, New York. September 1960. (2) Harmon. M. K., “Current Status of Solvent Extraction Procrssing of Irradiated Uranium Fuels,” Hanford Atomic Products Operation HW-SA-2458, April 6, 1962. (3) Harty. I V . M., Chem. Eng. Profr. Symp. Ser. 50, No. 13, 115-21 (1 35 4). (4) Richardson, G. I,., Platt. A. M.. “The Design and Operation of Industrial Scale Pulse Columns for Purex Service,” Hanford Atomic Products Operation HW-SA-2037, November 1, 1960. (5) Rohrmann, C . .4., .h‘ucleonics 14, No. 6, 66 (1956).
RECEIVED for review March 2. 1964 .\CCEPTED .July 30. 1964
NEW N*EPTUNIUM PURIFICATION FACILITY A T T H E HANFORD PUREX PLANT J . P. D U C K W O R T H A N D J.
R. L A R I V I E R E
Hanford dtomic Products Operation, General Electrzc Go., Richland, M/ash.
A production-size, ion exchange unit for the purification of neptunium at Hanford’s Purex plant is described. Anion exchange technology was developed so that batch operation of the unit can b e carried out on a programmed basis. The main processing and operational steps-concentration, anion exchange purification, and product removal-are controlled remotely. Contact maintenance is achieved by several novel design features, The major process equipment is located in a shielded walk-in “hot” cell where piping is of welded construction. All vulnerable equipment-such as valves and pumps-is located outside the hot cell in an enclosed shielded maintenance hood. Maintenance is performed through glove ports in a stainless steel shielding wall.
~ ~ ~ u x 1 u h i - 2which 3 7 , is now continuously recovered from irradiated fuels in both the Purex and Redox plants at Hanford, contains contaminants that must be removed before the neptunium is converted to plutonium-238 by further irradiation. This paper describes new batch ion exchange facilities for neptunium purification which were installed in very limited space within the Hanford Purex plant operated by the General Electric Co. under contract to the United States .4tomic Energy Commission. Process Chemistry
T h e process chemistry employed in the neptunium purification unit is based on an ion exchange flo\\.sheet developed by Hanford personnel ( 7 . 2). A s in all batch ion exchange operations, the process features resin loading. impuritv removal. and product elution. Ho\$ever, the integration of the batch process into the parent Purex process presents many complications. All chemicals used must be compatible with the basic Purex process. and the volumes ofwaste generated must be held to a minimum. Sequence of Operations. FEEDCONCESTRATION \’olume reduction of the dilute stream from recovery operations increases the neptunium concentration to a strength which is 306
l&EC PROCESS DESIGN A N D DEVELOPMENT
suitable for loading onto a n ion exchange resin. This is done in a stripper-concentrator in the presence of nitric acid. Steam stripping of a residual solvent from the aqueous stream is necessary to remove any dissolved or entrained organic before concentration to eliminate nitrate-organic reaction. Nitric acid is necessary, however, to prevent polymerization of plutonium in the feed. PEEDMAKE-UP. The concentrated feed is adjusted to 6M nitric acid and ferrous sulfamate and hydrazine are added to reduce the neptunium to the absorbing I\. valence and the plutonium to the nonabsorbing 111-valence state for ion exchange loading. RESINPRETRE.~TMENT. The anion exchange resin, 50- to 100-mesh Dowex 21-K, is pretreated with strong nitric acid prior to loading. The resin is allowed to stand in dilute acid between batch operations to reduce chemical degradation. FEEDLOADING.T h e adjusted feed is loaded onto the resin under controlled conditions of rate, temperature, and pressure. PLmoNirrM WASH. Although plutonium is reduced to the nonabsorbable I11 valence in the feed, enough is absorbed with the neptunium to contaminate the product. Therefore, a wash of concentrated nitric acid containing ferrous sulfamate and hydrazine is carried out at a low temperature (20’ C.) which favors plutonium removal. FISSION PRODUCT WASH. Fission products and other metallic impurities such as zirconium-niobium, ruthenium, and thorium are removed by a n 8M nitric acid wash at 70” C. Decontamination is improved by adding sodium fluoride to help wash off the contaminants. FLUORIDEASH. T o keep fluoride ion out of the product, the resin is washed with strong acid a t room temperature.
