M y 1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
a broad program planned for improving waste-handling facilities; the prime feature is the installation of a waste collection and monitoring system. I n the new buildings special drain lines for radioactive waste are being provided for every laboratory. Special hot sinks of a new design, which should provide more utility and safety with less chance of use for nonradioactive waste, are being installed to drain to these lines. The radioactive drain system of each building, new and old, in the processing area is to terminate in a collection tank, which is to be provided with a level recorder, a sampling device, a n agitator, and a means of discharging to the large surge tank for the evaporator. A similar collection and monitoring system for metal waste is being installed. Figure 4 is a schematic flow sheet illustrating these monitoring systems. The monitoring systems should afford the Operations Division, which manages the Oak Ridge Yational Laboratory waste facilities, a measure of control over the waste flows by tending to minimize the volumes of radiochemical waste in making the contributors aware of their waste quantities, and by revealing the sources of dilution of the radiochemical waste. If the monitoring system is successful in reducing the volume of radiochemical waste to be concentrated, it might be possible to evaporate the large volumes of low activity waste from all cell and equipment decontaminations. At the present time, it is necessary to discharge a part of this waste to the settling basin. X o additional storage space is being provided during this period of construction, because the performance of the waste evaporator during its f i s t year has indicated that storage space for concentrated waste in existing tanks will last for several years. By the time this space is filled, processes now in the development stage should provide more storage space in existing facilities now used for other purposes.
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The over-all picture of the future of Oak Ridge National Laboratory’s waste disposal looks bright. Progress is being made toward solving present difficulties, in the belief that discharges of radioactivity to the natural drainage system can be further minimized and the laboratory can a t all times operate within the limits imposed by public safety.
Definition of Terms The roentgen, r, is that quantity of x- or gamma-radiation such that the associated corpuscular emission per 0.0001293 gram of air produces in air ions carrying 1 electrostatic unit quantity of electricity of either sign. The roentgen equivalent physical, rep, is that quantity of ionizing radiation which is capable of producing 1.615 X 10’2 ion pairs per gram of tissue or that will suffer an absorption in tissue of 83 ergs per gram. One mrep is 1/1000 rep. The curie is the unit of mass of radioactivity emanation, being derived from the amount in equilibrium with 1 gram of radium. One curie is 3.7 X 10’0 disintegrations per second
Acknowledgment The author expresses grateful appreciation to the folloming coworkers at Oak Ridge National Laboratory for information supplied and for assistance rendered in the preparation of this paper: Harris Blauer, P. B. Orr, E. J. Witkowski, K. Z. Morgan, 0. W. Kochtitzky, F. L. Steahlg, E. L. Sicholson, and E. 31. Shank. RECEIVED November 24, 1950. Work performed a t the Oak Ridge National Laboratory under Contract No. IT-7406-eng-26 for the htoinic Energy Cominismon.
Concentration of Radioactive Liquid Waste by Evaporation Evaporation was selected as the method for concentrating dilute radioactive wastes at the Knolls Atomic Power Laboratory because it was the simplest and most certain method of complying with the policy that no detectable amounts of radioactive material be discharged into the Mohawk River. A forced circulation type of evaporator system having a rated capacity of 500 gallons per hour was provided. It has
produced decontamination factors of 107 from evaporator heel to condensate. Miscellaneous , dilute radioactive wastes may be highly concentrated in a safe and effective manner at a direct cost of approximately 3 cents per gallon. Indirect and amortization costs in this installation were about 8 cents per gallon additional.
G . E.McCulloughl KNOLLS ATOMIC POWER LABORATORY, SCHENECTADY, N. Y.
E
VAPORATION was selected for concentrathg laboratory, laundry, and other dilute radioactive wastes a t the Knolls Atomic Power Laboratory because it was the simplest and most certain method of complying with the policy that no detectable amounts of radioactive material be discharged to the Xohawk River. The allowable limit for “no detectable radioactivity” has been arbitrarily established as 300 disintegrations per minute per liter of alpha activity and 4000 disintegrations per minute per liter of beta-gamma activity. The dilute wastes contain up to 1.2 X lo4disintegrations per minute per liter of alpha activity and 1.4 X lo8 disintegrations per minute per liter of beta-gamma 1 Present address. Sucleonics Department, General Electric Co., Richland, Wash.
radioactivity. Some wastes contain higher specific activities, but these are, in general, blended with other wastes to obtain the specific activity figures mentioned. As shown in Figure 1, the combined wastes are accumulated in 10,000-gallon tanks. When a given tank is full, its contents are recirculated, sampled, and fed to one of two evaporator systems. After these wastes are metered, they are adjusted to a pH range of 7.5 to 8.5 by the continuous addition of 5% sodium hvdroxide as they pass through a mixing tee. Evaporation is effected in a forced-circulation system consisting of a flash pan, circulating pump, heat exchanger, separating tower, and condenser. The flash pan is 6 feet in diameter and 12 feet high, and contains, together with the circulating
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Vol. 43, No. 7
Figure 2. Evaporator Storage Tank# pan. This vaporization produces a spray that knocks dowu foaming. The designed operation rate is 500 gallons per hour, but experience has shown that tthe equipment may be operated satisfactorily a t from 300 to 700 gallons per hour. The overhead is passed through baffles to the separating tower, which is 6 feet in diameter and 20 feet high. The vapor enters this tower tangentially a t the bottom, and passes through a
I
I
I
Figure 1. Flow Diagram
system, approximately 300 gallons of liquid. This material is recirculated by the centrifugal pump a t the rate of 650 gallons per minute through the heat exchanger and back into the flash pan. The heat exchanger, with an over-all heat transfer coefficient of approximately 600, operates a t a pressure slightly higher than atmospheric, and the flash pan is maintained a t a vacuum of 26 inches of mercury. This effectively prevents evaporation and consequent scaling on the heat transfer surfaces. About 1% of the recirculating stream flashes upon entering the flash
~i~~~~ 3.
West Evaporator Recirculation pump and Heat Exchanger
July 1951
Figure 4.
IN D U S T R I A L A N D E N G IN E E R IN G C H E M I S T R Y
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Lower Sections of West Evaporator Flash Column and Separating Column
12-foot de-entrainment section and then through four bubble trays The vapor is condensed and received in one of two 5000gallon tanks. Samples are taken from these receivers to determine the activity level in the condensate. If the activity is sufficiently low, the material is discharged to the storm sewer; insufficiently decontaminated material may be returned to the evaporator storage tanks. Activity in the condensate has been 0 to 2 (*4) disintegrations per minute per liter of alpha activity and 2 to 35 (*20) disintegrations per minute per liter of betagamma activity, The heel in the flash pan contains approximately lo6 disintegrations per minute per liter of alpha activity and 108 disintegrations per minute per liter of beta-gamma activity when the 300-gallon heel contains 20% solids. De-
.
Figure 5. Large Vacuum Drum Dryer Discharge Mechanism
contamination factors of lo7 are achieved in the evaporator system from evaporator heel to condensate. The maximum decontamination factor which may be obtained has not yet been determined.
Figure 6. Upper Sections of West Evaporator Flash Column and Separating Column
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Figure 7 . Upper Level of East Evaporator Bay
Figure 8.
Large Vacuum Double-Drum Dryer
July
1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
The feed to the evaporator contains about 0.270 solids that are mostly dissolved. Feed is added until the total solids content of the evaporator heel is approximately 2070, after which the volume of the heel is halved to produce 150 gallons of 40% solids material. This material is transferred in a batch operation to a dryer feed tank. Wastes containing over 30% solids and the concentrated diluted wastes are dried on specially designed doubledrum vacuum dryers built by the Buflovak Equipment Division of the Blaw-Knox Construction Co. These drums have 32 and 6 square feet of drying surface, respectively, and operate at 25 inches of mercury vacuum. The dryers are of stainless steel construction, designed to present smooth interior surfaces in order to minimize holdup of dried material, and are steamjacketed to prevent condensate from wetting the dried product. The dryers are fed by material recirculating through a feed pan beneath the twin dryer rolls. Pickers splash the material onto the steam-jacketed rotating drums, and Stellite knives strip the material from the drums and guide it into the hoppers. In order to dry materials of different physical properties, the steam pressure, rate of rotation of the drums, picker speed, and vacuum may be varied to produce the desired free-flowing product. The dry material is flaky and free-flowing and contains from 5 to 10% moisture. The hopper legs are equipped with special discharge valves to provide dust-free transfer of dried materials into storage containers. This operation is performed under vacuum. After transfer of the dried material, the interior of the valve is sprayed with water a t a nozzle pressure of 85 pounds per square inch. This effectively cleans the interior of the discharge valve and
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settles any dust rising from the container. The valve is then dried by jacketed steam. The waste drums are moved into the dryer cells, filled, and removed by remote control. Seventygallon unshielded stainless drums receive low-level wastes from the large dryer, and 5-gallon stainless drums shielded with 4 inches of high-density cast iron receive the more active material from the smaller dryer. Each major item of equipment exposed t o radioactive contamination may be decontaminated independently from a central system for supplying water, acid, sodium hydroxide, steam, and other materials a t high pressure. Figures 2 to 8 show the major components of the evaporation and drying systems.
Cost of Operation After the plant had been operated at the rate of over 100,000 gallons per month, which is the design rate for two-shift singleevaporator operation, the cost of evaporating a gallon of dilute liquid waste was computed. The direct labor and material cost, including steam, power, maintenance, and laboratory analyses is $0.029 per gallon. The indirect laboratory expense amounts to $0.037 per gallon. Amortization of the building over a period of 40 years and the equipment plus installation costs over a period of 10 years comes to $0.072 per gallon, a total of W.138 per gallon, when the plant is operated a t the rate of 1,500,000gallons per year. If the plant were operated on a threeshift single-evaporator basis, the amortization cost would be reduced to $0.048 per gallon, making a total of $0.114 per gallon when processing at the rate of 2,250,000 gallons per year. RECEIVEDNovember 24. 1950.
Removal of Plutonium from Laboratory Wastes A
.
study of the removal of plutonium from laboratory wastes was undertaken in order to secure information upon which to base pilot plant design. The methods investigated included: coprecipitation with iron, aluminum, and other metal ions; adsorption by various agents such as activated carbon, celite, kaolin, etc.; and removal. by living biological floc (activated sludges). The activated sludge process required a three-stage countercurrent plant with the addition of organic food sources ahead of each stage in order to reduce the plutonium content of the effluent to the desired level. Activated carbon was the best of the adsorption agents studied. Split treatment with long
periods of mechanical agitation was necessary in order to prevent the creating of a large amount of contaminated adsorption agent. When substantial amounts of organic complexing agents were absent from the wastes, the coprecipitation treatment appeared to be the simplest, cheapest, and most efficient method. An iron floc was preferable to an alum floc. The amount of iron required for the treatment was nominal, 10 p.p.m. of ferric chloride with sufficient lime added to bring the pH above 7 was adequate to produce the desired plutonium removal. This study should permit design of an adequate unit for decontaminating laboratory wastes containing plutonium.
C. W. Christenson, M. B. Ettinger', Gordon G. Robeckl, E. R. Hermann, K. C. Kohr, and J. F. Newell ATOMIC ENERGY COMMISSION, LOS ALAMOS, N. M.
T
HE toxicology of plutonium comprises a new field and while this subject is being diligently pursued, final clarification cannot be expected for many years. At the time this work was initiated, safe tolerance levels for the plutonium content of drinking water were still undetermined. Members of the Los Alamos scientific laboratory staff suggested t h a t the goal for.plutonium content of any effluent discharged should be tentatively set a t 70 1 Present address, U. S. Public Health Service, Environmental Health Center, Cincinnati, Ohio.
counts per minute per liter. These authorities believed that this goal should satisfy the final requirements which will be developed for permissible plutonium content in drinking water. Since a waste may contain other toxic, noxious, or objectionable materials, an important secondary objective is the reduction of these materials to satisfactory limits. I n the case of these nonradioactive contaminants present in the various wastes t o he dealt with, the standards prescribed by ordinary public health practice may be taken as adequate.
