.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., “Re-
covery 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 an 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.The 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 an 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.
ELUTION. The product is removed with dilute nitric acid (0.3M). To keep the volume of the product at a minimum, a displacement fraction is recycled to the feed tank. Only after the concentrated product solution starts to come o f fis the eluent diverted to the product tank. Prior to load-out and shipment as V A L E N C E AYJUSTMENT. the nitrate, the neptunium is adjusted to the stable V valence state by heating to 98' to looo C. for 1 to 2 minutes. The waaste streams from the loading WASTETREATMENT. and washing- steps are treated with nitrite to destroy the hydrazine and aluminum nitratr to complex the fluoride before returning them to the backcycle waste system of the Purex plant. T h e flowsheet is designed to allow 10% neptunium recycle within the purification unit with a lass to the backcycle system of the P u r a Plant of only 0.2%. Essentially, no direct loss of neptunium occurs in the purification unit. Gassing in the ion exchange column is controlled by operaring all cycles a t 35 f 5 p.s.i.g. and periodically degassing, using a steam jet as a vacuum source. Auxiliary features for backcycling, reworking, and resin addition and removal are incorporated in the design of this facility.
Figure 1. Arrangement layout of the two-story neptunium purification facility
New Neptunium Purification FacilitierSpace Limitations Early design scoping studies indicated that the most suitable location for installation of a new purification facility was a space 20 X GO X 25 feet high, located in the bottom level of the Purex plant. T h e design challenge, therefore, in implementation of the neptunium purification process was to install a Control Room, Chemical Make-up Room, Hot Cell, Maintenance Room, Load-Out Room, air locks, and a multitude of vessels within this very limited space. Design Philosophy
The design philosophy adapted for this facility extends Hanford practices for remote operation and contact maintenance of chemical separation plants. Operations are conducted remotely from a graphic panel board located in the Control Room. The Control Roam is separated from the processing equipment by sufficient shielding to provide personnel with adequate protection from radiation. Equipment is arranged so that or.'inary maintenance functions can be performed through the use of shielding barriers and confinement hoods for protection against radiation and contamination, respectively. All-welded vcssels are employed. Mechanical equipment subject to maintenance is excluded from the shielded rquipment area. Nuclear safety had to he considered in the design philosophy. Neptunium-237 does not constitute a critical mass hazard, hut unsafe concentrations of plutonium-239 can accumulate. This restriction complicated the design objective of a compact equipment layout, as it limited the shape, size, and location of the processing equipment.
Figure 2. Size and relationship of the neptunium purification equipment
Description of the Neptunium Purification Facilities nnd Other Design Fenturer
new facility. T h e Maintenance Room is entered only for repair and replacement of minor equipment. l h e Hot Cell is entered only for inspection and inirequent maintenance. When such entries are necessary, the process equipment is emptied and decontaminated to safe radiation levels. Radiation protection for operating and maintenance personnel is provided by various types ofshielding. Personnel in the Control Room are protected from the radioactivity emanating from the Hot Cell by the structural walls, which are made of high-density concrete. Operations and maintenance personnel, while working in the Maintenance Hood, are also shielded from the Hat Cell equipment by a shielding wall. Lead glass windows and a thick stainless steel hood front protect from radiation within the Maintenance Hood. Most of the piping and equipment is fabricated of stainless steel 304-L for corrosion resistance and for ease ofdecontamination. The concentrator is fabricated of titanium.
Fig-ure 1 shows salient features including the Control Room, Hot Cell, Maintenance Room, Load-Out Room, and Chemical Make-up Room. Operations are performed remotely from the graphic control board in the Control Room, except for load-out of product, which is performed manually. Operating personnel are normally stationed only in the Control Room and in the Chemical Make-up Room. which is an the second level of the
Hot Cell. The Hot Cell houses all of the neptunium purification equipment (Figure 2) including- a feed receiver, stripperconcentrator, column feed tank, ion exchange column, waste tank, condenser, two sump tanks, several seal pots, and the associated piping. All of this equipment is installed within a stainless steel hood with transparent plastic panels. The remaining area in the Hot Cell is for access and equipment removal operations. Entry into the Hot Cell will he for emergency work only. A minimum number of equipment items suh,iect to maintenance were installed in the Hot Cell, VOt. 3
NO. 4
OCTOBER
1964
307
Figure
3.
Process flow sketch of the Purex neptunium purification facility
including resin level detector, resin screens, and thermowells. The stripper-concentrator is shown in Figure 2, and consists of two sections, a stainless steel, twin-barreled stripper and a titanium, thermosyphon concentrator, joined together by one of the few Ranges utilized in the Hot Cell. Since the concentrator is fabricated of titanium, Range extensions have been extended through the concrete shielding wall into the Maintenance Hood, where the Range connections to stainless steel piping are made. The ion exchange column feed tank (Figure 2) is a 3-inch annular tank with a &foot aver-all diameter and 5-foot height. An 8-inch ring of concrete and a cadmium liner inside the tank serve as a neutron moderator and poison, respectively. Mixing is achieved by recirculating the solution by means of an in-line pump located within the Maintenance Hood. The lank has a volume of 120 gallons and has all the normal services for operational control. The ion exchange column is fabricated of 6-inch stainless steel pipe, 101/2 feet long, with a 1-inch annular heatingcooling jacket surrounding the pipe. Screens have been Ranged into the top and the hottam of the column to provide a resin section approximately 9l/%feet long. A sonic probe, to indicate the resin level inside the column, is inserted into the top of the column with a Range connection. Temperature and pressure control systems are installed for normal operational control of the equipment. A 100-p.s.i.g. rupture disk provides pressure relief for the system. A degassing system composed of a steam jet connected to the top of the column removes gas formed within the resin during operations. BackRushing and back-Raw systems have been installed to facilitate remote removal of the resin from the column. Maintenance Hood. The Maintenance Hood, located in the Maintenance Room, is a shielded enclosure faced with 1inch thic.k stainless steel containing lead glass viewing ports and lead-covered glove ports. This hood contains the replaceable mechanical, electrical, and operating equipment which handles radioactive solutions between major equipment pieces in the Hot Cell. Equipment installed in this hood includes: electric and manual valves, steam traps, temperature elements, transmitters, pumps, filters, and miscellaneous instruments. The Maintenance Hood is designed for contact maintenance, and all of the equipment within it is flanged with standard stainless steel flanges. Product Load-Out Hood. The purified neptunium nitrate is prepared for off-site shipment in the Product Load-Out Hood. This hood is of standard fabrication, stainless steel and safety glass, and is equipped with glove and bagout ports far manual loading, operations. Standard I-gallon polyethylene bottles are filled by gravity feed from a small, calibrated head tank. The filled bottles are loaded into a lightly shielded cask for off-site shipment. 308
I & E C PROCESS D E S I G N A N D D E V E L O P M E N T
Types of Liquid Transfer. To eliminate installation of mechanical pumps inside the Hot Cell, various types of liquid transfer were utilized (Figure 3). Recirculation pumps used to agitate the two feed tanks are "in-line" pumps installed in the Maintenance Hood. The ion exchange column feed pump is a positive displacement proportioning pump located in the Maintenance Room with a remote head installed "in-line" in the Maintenance Hood. Thus, by locating these pumps in the hood, the process solutions are confined to the Hot Cell and the Maintenance Hood, and the pumps are so located that they can be readily maintained. Spent resin solution is transferred by water jets from the sump and waste tanks as water is necessary to fluidize the resin. All other liquid transfers in the Hot Cell are made with steam jets, which are proved to he reliable in remote service. Types of Agitation. As highlighted in Figure 3, various types of agitation are utilized in the Hot Cell equipment to provide fluid mixing, as a substitute for rotating mechanical agitators. I n the concentrator feed tank, mixing is achieved by returning 90% of the solution pumped from this slender 7inch i.d. tank back into the tank by means of a restricting orifice. Mixing is also accomplished by a pump recirculation technique in the annular ion exchange column feed tank. The waste tank and the produce receiver tank are air sparged from the bottom spray rings. The sump tank has a novel water swirler, similar to a dentist's fountain, for agitation to aid in the removal of bath resin and solids which may accumulate in the tank. Process Solution Samplers. To control operation of the vessels, sampling of various process streams is required. I n the sample stations installed for this facility, a new design was utilized to reduce sampler maintenance. The equipment and piping inside the sample station were installed in remote-type canyon jumpers to standardize sampler piping, reduce radiation exposure to maintenance personnel, and minimize outage time of failed equipment. Literoture Cited
(1) Buckinyham, J. S., General Electric Co., Richland, Wash.;
tion HW-59193 REV.,Se;t:
3, 1959
R ~ c ~ i v efor o review March 2, 1964 ACCEPTED July 30, 1964 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 No. AT(45-1)-1350.
