T h i s paper originated as an engineering report of a survey of waste handling at the Oak Ridge National Laboratory, made i n preparation for expanding a n d reorganizing the industrial waste disposal facilities in line with the general expansion of the laboratory during 1950 a n d 1951. As a result of the report, a centralized system of collecting a n d treating liquid wastes was planned a n d construction started. Improved methods were developed for monitoring the waste streams to detect radioactivity before discharge of wastes into the river. Although much of the construction work on the waste collection facilities i s still i n progress, the
first completed stages of the program have resulted in a considerable improvement i n the handling of radioactive waste. Discharge of radioactivity to the natural environment has been greatly reduced. It i s expected that even greater reductions will result when the program is completed. This report demonstrates how careful precautions are being taken to prevent contamination of this country's rivers a n d streams by atomic energy installations. T h e adaptation of second-hand equipment a n d of normal separation processes, such as precipitation a n d evaporation, to the new technique of handling radioactive waste will be of chemical interest.
Frank N. Browder OAK RIDGE NATIONAL LABORATORY, OAK RIDGE, TENN.
Liquid Waste Disposal at Oak Ridge National Laboratory 0
NE of the startling factors in dealing with radioactivity is t h a t it cannot be destroyed. No degree of heat or cold,
no chemical reaction, can speed u p or slow down the emanation of particles and rays from radioactive atoms. Time is the only agency capable of destroying radioactivity. This fact presents the large quantity producer of radioactive waste with two alternatives for disposing of it: 1. He can render the radioactive waste harmless by diluting i t and dispersing it until the concentration of the radioactive components is too low to damage animal tissue. 2. He can separate the radioactive components from the waste, concentrate them to a convenient volume, and store them until time can destroy them by natural decay. Oak Ridge National Laboratory is a large quantity producer of radioactive waste as a result of the production of radioisotopes and of investigations in the fields of research and development, in which the laboratory engages as part of the Atomic Energy Commission's program. The present size of the laboratory and the scope of its work have been reached by a series of expansions, which are still continuing. The means of handling the considerable quantities of waste produced by the processes performed a t the laboratory have had to be changed from time to time in order to keep pace with the expanding program. The types of liquid industrial wastes produced a t the laboratory are classified and handled according to their composition. 1. Metal waste is so named because it contains dissolved compounds of uranium, the metal of the atomic project. This waste must be collected, concentrated, and stored for recovery processes. It is nearly always very radioactive, requiring special prccautions in handling and storing. 2. Radiochemical waste is composed of highly radioactive fission products and various chemical by-products from the production and developmental processes of the laboratory. The methods employed in treating the 50,000 gallons per week flow of this stream are described in this paper. 3. Process waste is the large volume waste composed mostly of cooling water and nonradioactive chemical by-products. The process waste flow averages about 5,000,000 gallons per week. b
The first facilities of Oak Ridge National Laboratory, a pile and a chemical separations plant, were constructed in 1943 to serve as a pilot plant for the Hanford, Wash., works. ilt t h a t time, a number of very large underground concrete tanks were constructed to hold the entire anticipated accumulation of metal
and radiochemical waste for t'he life of the laboratory, which was expected to be one year. Before the storage tanks were completed, however, a change in the process under investigation made it evident t h a t their capacity would not be great enough. Expansion of the scope of the work further increased the quantities of radiochemical waste, so that it became necessary to devise a method of disposing of it. It was decided to precipitate as much activity as possible in the storage tanks and t o decant the activity remaining in solution from the tanks, dilute i t with the laboratory's h r g e volume of process waste, and disperse it in a natwal stream. A dam was built 1.7 miles below the laboratory in the autuinn of 1943 to create a controlled area for the discharge of activity. This dam impounds the waters of White Oak Creek, a stream which passes through the laboratory site and empties into the Clinch River within the Oak Ridge restricted area. A settling basin of 1,600,000-gallon capacit,y was put, into operat,ion in July 1944 to serve as the dilutiou and sampling facility and to capture radioact,ive solids formed by calcium in the dilution mater. Figure 1 shows the controlled area which was constructed. The block in the upper right corner represents the settling basin. The numbers represent miles above the mouth of the stream. Additional decontamination of the radiochemical supernatant was gained by collecting and holding waste in one of the large storage tanks for as long a time as possible, while decanting to the settling basin from another tank containing aged waste. This procedure allowed sufficient time for much short-life (and hence more intense) activity to decay before discharge to the creek. The isotopes removed by this procedure were %day 1131, 5.3-day Xe133, 28-day Celdl, 33-hour Ce143,41-day Rulo3, 12.8day Ba140, and 40-hour These maneuvers afforded the laboratory's 50,000 gallons of radiodctive waste per week a precipit.ation step, about one month holdup for decay, triple settling (in the tanks, the settling basin, and in the lake behind the dam), and about 500,000 to 1 average dilution in bhe Clinch River. It was calculated t h a t 5 curies per day of mixed fission products could be discharged safely into this lake system; a n average activity discharge considerably below this level has been maintained by constant measurements with various types of instruments. Three criteria of safe operation of the liquid waste disposal system a t Oak Ridge National Laboratory were established: 1502
INDUSTRIAL AND ENGINEERING CHEMISTRY
July 1951
The average discharge of mixed fission products into White Oak Creek must not exceed 5 curies per day and in no case may it exceed 35 curies per week. The total radiation level in the water must not exceed 100 mrep per day, which is considered t o be the maximum permissible level of radiation exposure. The concentration of any one or any combination of radioisotopes in the lake water must not exceed the maximum permissible concentration, calculated on the basis of what could concentrate in any body organ during the lifetime of the fish (or of a man using water from White Oak Lake as his sole source of water) sufficient to produce damage. This is considered to be a concentration in the body organ that will give 100 mrep per day of beta and gamma or 10 mrep per day of alpha-radiation or equivalent amounts of mixed radiation. This method of disposal by dilution and careful dissipation in a controlled natural drainage basin entirely within the Oak Ridge restricted area was continued until June 1949. That this method of disposal was adequate as a temporary measure has been demonstrated by the fact that the calculated concentration of gross beta-activity in the Clinch River due to Oak Ridge Kational Laboratory operations has averaged about 1 X 10-7 microcurie per milliliter. During periods of flood when quantities of “radioactive mud” were washed out of White Oak Lake into the Clinch River, activity increased by a factor of 4 or 5 for a short distance downstream. The maximum water activity of 5 X 10-7 microcurie per milliliter in the Clinch River is comparable to the radon activity of some springs, the water of which is prized for human consumption. The activity from Oak Ridge National Laboratory is primarily beta and gamma, alpha being negligible. Radon is an alpha-emitter, and in general alpha-emitters are about 10 times more hazardous when taken into the body than beta-emitters. In June 1949, a waste evaporator was put into operation, which, with auxiliary equipment, is engaged in concentrating the radioactive components of the radiochemical waste and storing them. The facilities for diluting and dispersing waste are being maintained to handle the evaporator effluent and the chemical wastes of the laboratory. Since the waste evaporator has been in operation, the amount of radioactivity discharged to the creek each week has been reduced tenfold. The waste evaporator is housed in a shielded concrete building in the waste tank farm near one of the large underground storage tanks. Figure 2 shows the arrangement of the evaporator in the building, and Figure 3 is a schematic flow sheet of the evaporator system.
Figure 1.
White Oak Creek and Lake
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Waste is transferred by underground pipes from the process buildings t o the large tank. This scheme provides surge capacity to smooth out the evaporator operation and to provide a relatively constant supply of feed. A smaller feed tank of about 2000-gallon capacity, housed in the evaporator building, takes batches of waste from the surge tank by means of a steam jet siphon and feeds the waste by gravity to the bottom of the evaporator. The evaporator is a simple, pot-type unit heated
Figure 2.
Radiochemical Waste Evaporator Piping not shown
by six removable, internal steam coils. The feed rate is automatically controlled to maintain a constant weight of liquid in the pot. Water vapor rising from the boiling waste passes through a centrifugal or cyclone-type separator for entrainment removal and then through a manifold to four parallel tube condensers. The condensate flows to a catch tank, which is emptied to the settling basin b y an automatic, intermittent siphon each time it fills. Between the condensers and the condensate catch tank the condensate flows through a small monitoring tank, where a conductivity probe is installed to detect entrainment. A Geiger counter, originally installed to monitor the condensate for entrained activity, proved unsatisfactory because a high background of activity tended to build up on the surfaces of the monitoring tank. As salts of high electrical conductivity usually accompany activity in entrainment, the conductivity probe has proved t o be effective in detecting entrainment. This monitor actuates an alarm to warn the evaporator operator to reduce the steam pressure and lower the liquid level when entrainment is detected. At the end of an evaporator run the extremely radioactive concedrate, while still hot, is drained by gravity from the evaporator to A another large underground concrete tank for storage. The end of a run is determined by the specific gravity of the material in the evapowo.2 34 rator pot, which is allowed t o reach a point slightly below saturation (1.3). A slight vacuum for the off-gas system is provided by a water jet that uses the exit water from the condensers and discharges both condenser water and scrubbed gases to the settling basin. The waste evaporator was constructed of used equipment available from salvage and surplus stocks. The design evaporation capacity is 300 gallons of water per hour a t atmospheric pressure, although the evaporator is capable of about twice this rate, depending primarily on the specific gravity of the feed. During the f i s t year of operating the evaporator, every effort was made to gain storage space in the waste storage tanks, The need for storage space had become critical because of expanded development programs, involving work with considerably higher levels of radioactivity than had been encountered a t any time in the previ-
ing reduces the decontaniinat,ion factor by carrying unevaporated,
PROCESSES
I
PR@CEss 'wASTE
means of combating foaming. It is planned in the near future t o add automatic controls to the steam supply and the liquid
level regulator, these controls to be actuated by the condensate monitor. The addition of a bubble cap column to reduce entrainment is also planned. If results reported at Knowles Laboratory can be duplicated a t Oak Ridge, the bubble cap column will markedly improve evaporator performance. The change in waste disposal policy from dilution and dispersion to concentration and permanent storage has brought its
number of cuiics discharged to this stream by the building.. it serves. It iq also planned to mount continuous activity monitors in these manholes to xvarn of slugs of activity that sometimes pass through this system. IThrk is being carried on to develop a satisfactory continuous monitor capable of detecting 75 to 100 beta counts per minute per milliliter. Oak Ridge Pjational Laboratory is in the midst of a peiiod of large scale construction, expansion, and improvement. It has
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
