1 in the Chemical laboratory Edited by NORMAN V. STEERE, 140 Melbourne Ave., S.E. Minneapolis, Minn. 554 14
Two
S. G. PEARSALL and W. WILSHUSEN Brookhaven National Loboratory Health Physics Division Upton, New York
Radioactive Waste In order to simplify the problem, let us consider that two problems exist in the handling of radioactive materials, namely external exposure in whieh all or part of the body is exposed to a. source of radiation, and internal exposme in whieh the source of the radiation is taken into the body by ingestion, inhalation, puncture wound, or absorption through theskin. External exposures can be controlled by the use of time, distance and shielding. While three forms of radiation (alpha, beta and gamma) are normally encounteredin a wastedisposaleffort, only gamma radiation requires the extensive use of shielding and because of this, gamma emitters are the most difficult and expensive to dispose of. Normally, high level radioactive wastes will not be produced a t smaller installations unless a nuclear facility such as a reactor or accelerator is present. However, many of our colleges and universities now have the capability of producing "large quantities" of radioaetive waste as defined by the Atomic Energy Commission and the Department of Transportation. I n some eases, even wastes which are not considered to be large quantities but which fall under the classification of "low specific activity" produce radiation levels high enough to present shipping problems, and containers must be provided which will reduce radiation levels to permissible limits. In t,he BNL operation, three thicknesses of concrete shields, 6, 12, and 17 inches, have been routinely used. In addition, lead inserts have been made which can be placed within the t,hickest shield and thus make possible the rout,ine shipment of quantities of cobalt. as high a3 twenty curies. Special containers have been made whieh have held as much as 2,500 cnries, and higher quantities could be packaged by the addition of more shielding. Beta aud alpha radiation do not present niguificant shielding problems, nor do they pmsent as great n problem of whole body exposure. They do, however, offer problems of internal eexposnre so they must be treated with ca1.e and must be packaged tightly. Normdly, exposue to these beta and gamma emitters can be cont~~olledby adequate protective equipment, prohibition of eat,ing and smoking while radioactive material is being handled, and good honsekeeping. Two additional considerations must, be taken into account when handling
Table 3.
feature
use to which it is put and such other factors before local disposal can be utilized safely. With a knowledge of these factors iL is possible to establish a solid waste disposal program for the disposal of small amounts of material. Thus, Brook-
1. The Disposal of Chemical and Radioactive Waste-Part
I
Effect of Decay Along with Rate o f Movement of O n e Foot Der Day Distance to Reduce to 1%
Isotope Bismuth 210 Yttrium 91 Zirconium 96 Calcium 45 Cerium 144 Iron 5.5 Strontium 90
.5 days 67 days 65 davs 180 dn$s 275 days 4 yr 25 vr
radioactive waste whieh are not fact,ors when handling "on-radioactive chemicals. These are the use of shielding and the phenomenon of radioactive decay.
haven has been able to establish a policy which permits the local disposal of the fallowing amounts:
Radioactive intensity can be reduced by surrounding the radioactive material with an absorbing material. In general, the more dense t,he absorbing material or the greater thc thickness of a given material, the mare the intensity will he reduced. If the energy of t,he radiation as well as the curie content is known, the required shielding can be calculated. However, many limes in waste disposal operations isotopes become mixed and curie contents are unknown, so that a. scientific cak:olation may have to give way to an edueat,ed estimate of theshielding needed. Radioactive decay is the term used to describe the reduced rate of radioaetive disintegrations with time. The period of time in which a given isot,ope reduces its disirrteeration rale to one'half of its original value is known w the "half life." Since all radioactive materials have a measurable and predictable half life, varying from fractions of a second to billions of years, this may be a primary consideration in the select,ion of disposal method, or in the determination of qnantities which may be disposed of by any method. As an example, the following is taken from L)eLagunas to show the combined effect of a known rate of movement of the water table and half life. These figures do not in fact represent a true rate of migration through the soil, as adsorption and ion exchange make the actual rate somewhat less. Also, unless the material was introduced directly into t,he water table, solubility and other factors would affect the rate of movement downward to the water table. All of these factors plus the environmentsl factors mentioned previously must be taken into consideration. Thus it is important to confiider how far ground water will move before i t has left the site, the area into whieh it moves, the
100 days to B yr
Holf-Life Leas tllan 100 days
Over 5 yr
Ra or Pu
Total annual limit:
Amou"l/Yeor 10 curies 1 curie 100 mi11iouries 10 milliouries 10 curies'
I t was stated previously that three methods were available for the disposal of chemical waste. I n disposing of radioaet,ive waste this mieht be reduced to two-dilotiou and utilizing radioactive decay. Methods and techniques far accomplishing these are more varied than for chemicals, but such techniques as shielding, burying, solidifying, etc., are usually aids to make it possible to store the waste until it has decayed. At times it is contemplated that while material is stored same release to the environment will take place, but dilution is considered to be s~fficientto minimize the hazard. Thus it is often difficult to separate methods of radioactive waste disposal. No detailed discussion is eontemplsted here of the origin of wsstes in the United States. Such a discussion would, however, necessarily include the production of high level liquid wsstes a t the fuel reprocessing plants. At these sites the liquid process wastes are stored in steel tanks which in many cases must be water-cooled to carry off the heat produced by radioactive decay. Storing this process waste for decay is the most widely used method in this country today. Large research effortsare being devoted to improve upon the disposal methods available for process wastes, one of the most intriguing of which is the fusing of the waste into glass. This has two advantages. First, it results in greatly decreased volume, and two it provides an end product which is almost unleachable when it is buried. Other methods, too numerous to mention here, are being investigated hut ctt the present time the number of tanks in use is steadily in~
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(Continued a page A678)
Volume 45, Number
9, September 1968
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A677
that the dilution possibilities in the event of package failure are great, and the British have availed themselves of this method to a considerable extent for radioDilution active waste disposal. Even though At Brookhaven a stack 310 ft. high there is great prejudice against conpasses all of the cooling air from an air- taminsting the oceans with radioactive cooled, graphite-moderated reactor. This materid, the British have excellent docw air contains ahout 17,000 Ci of Argon mentation that their ~ractices are not 41 per day, yet the exposure to personnel causing appreciable increases in the ina t ground level, both on and off site, ventory of radioactive nuclides in the is well below the MPC levels specified ocean. in Handbook 69. Thus we are able to For economic reasons as well as practidispose of quite large quantities of radio- cal considerations, sea disposal was dmactive gas for which any other disposal continued ctt BNL about 1959, and all method a l d d be irqrrnv! icai. packaged wastes are now shipped to land Similarly, i~ ic nrrcptnhir for IiKl. to burial sites. These sites, located adrelee-c rsdiua~tivel>il>11d4 into the s8t.itnr). vantageously around the country, bury sewer system and ufiimately into a smail wastes under oarefully controlled condistresm if the quantity is not sufficient tions. A flat fee per cubic foot of waste to raise the activity levels of the effluent is charged, of which a percentage is set at the site perimeter to higher than the aside in a. trust fund for perpetual care published acceptable levels. I t is there- of the burial ground. fore possible to advantageously use the Intermediate level liquid wastes, which volume of sewage as well as the volume of will here be defined as those too radiowater in the small stream to dilute the active for sewage disposal hut less active low level wastes. Such disposal of soluble than process wastes, are produced at wastes is authorized, with limitations, almost every insts.ll.llation handling radiofor licenses hy Part 20.303° and offers active material. Specification containers relief from more complicated and expensive do exist for the shipping of radioactive disposal methods. liquids, but inasmuch as the capacity of At one time, sea disposal played a these is small and the fabrication is exlarge psrt in the waste disposal aperrttion pensive, they are not practical for waste of sites located near both seahoerds. shipments unless a very small quantity Waste material in 55 aallon drums was is involved. I t is frequently found, taken to specified sites & the ocem where therefore, t,hat it is advantageous to the depth exceeded 1000 fathoms and solidify these liquids so that they can he rolled overboard. Inasmuch as the oceans shipped as solid waste, and in many cases of the world are estimated to contain (Continued on page AS831 3.27 X 108 cu mi of water, it is obvious
creasing, indicating that this is still the best method available.
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Journal of Chemical Education
this is necessary before a disposal site will accept them. At Brookhaven the solidification of liquid wastes is carried out in modified fuel oil tanks which are dry filled with four parts of vermiculite to one part of portland cement. The contaminated liquid, a slurry produced as the end product of an evaporator, is pumped into the tank via a tube whieh ext,ends to the bottom. The liquid level is raised until t,he vermiculite becomes wet on the top surface and then the mixture is allowed to harden for 72 hr. If the liquid is pumped onto the top surface of the vermiculite and cement and dlllowed to percolate downward, a stratification of the ingredients would occur, and separate layers of cement, vermiculite and water will appear and never solidify. This method produces an end product with a density of about 1.2 with sufficient strength to be self-supporting. I t might be pointed out that this same technique could be carried out in a container as small arts a five gallon pail and conld thus he applied on a. laboratory scale. The British, on t,he other hand, have built facilities to mix such liquids with bitumen or asphalt. This has the advantage of reducing volume, and the final product is almost unleachable. This method does offer some advantage over the use of vermiculite, but the initial plant cost can not be justified unless the quantity of liquid far disposal is large. All reactors, secelerators, and laboratories produce solid wastes in many different forms. Ordinarily, these present no difficult disposal problems, as the
radiation levels are normally low and arrangements can he made with a licensed disposal agent to transport them in almost any farm. However, for the large producer of waste materials, disposal techniques must usually he worked out for each operation. Packaging of radioactive waste is necessarily mare complex than that required for chemicals, both because of the nature of the material and because of the number of regulatory agencies that can dictate how it can be carried out. I n general, but not without exception, state regulations follow those of the Office of Transportation (formerly Interstate Commerce Commission) and the Atomic Energy Commission. The AEC serves in an advisory capacity for all shipments whieh are classified as "large quantity,'! leaving to the Department of Tranaportatian all other shipments of radioactive material.
Volume Reduction Inasmuch as all methods of radioactive waste disposal represent substantial expense, s. great deal of effort is applied to reduce the volume of waste produced. Several techniques for accomplishing this are worthy of beingmentioned. In any discussion of the disposal of radioactive waste, the question of incineration inevitably arises. The obvious advantage of this method is the great reduction of volume, and the method has been investigated by almost every large installation in this country and
(Continued on page A684)
sbrbroad. The results have not been encouraging, and few sites are attempting to reduce waste volume by this method today. The clean-up of the smoke effluent is difficult. The degree of cleanliness of stack wastes which are discharged to the atmosphere requires extensive filtering to meet present rules and regulation. These filtering casts are very high so most places have found that it is more economical to bale and transport combustibles than it is to burn them. I t has also been found that for s n incinerator to operate economically, it must operate for extended periods. Very few sites in the United States produce enough combustible wastes for sustained operation, and those that might produce sufficient quantity have access to cheaper disposal methods such as on-site burial. At the Harwell laboratory in England, an incinerator is operated with some success, but in order to obtain sufficient volume for sustained operation waste is accepted from other sites. As a result of the difficulties encountered with incinerstion, compaction has more widespread use a t the present. BNL is using a small commercially available hydraulic baler such as is used in many plants for baling paper waste products. This provides a volume reduction of as much as five to one, and makes bales weighing up to 200 lbs. These in turn are packed in large sheet steel boxes and eventually transported to a. burial site. These are shipped as "low specific activity waste" and no specification container is required. Large quantities of liquid wastes are produced which are too active to he dumped into s sanitary sewer system, but which are uneconomical to process for dispossl in the original form. I n some cases this problem is solved by filtration, passing through ion exchange columns, by evaporation of the dilute waste, or by some combination of these. I t is the product of such evaporation which is solidified into vermiculite a t BNL. The volume reduction here is almost 100:l a t the evaporation stage alone, and the volume reduction on other stages of treatment is unknown, although substantial. One very substantial method of volume reduction is by decontamination. Many items are found which can be reused if decontaminated, and the combined cost of disposal and the replacement value of the item may be significantly higher than the cost of decontamination. A specialized form of this decontamination technique is used a t BNL. Large items, such as tanks, duct work, etc., are opened up with high explosives (Fig. 4) so that the interior contaminated surfaces are
Figure 4. A one thoumnd gallon fuel oil tank which was opened with high explosives and then shot blasted.
(Continued on page A888)
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exposed. These are then put into s. special room having an unusually large and efficient air filtration system, and the item is shot-blasted.'O As a result, the waste is concentrated into a few pails of dust and the cleaned item may now be thrown onto the sanitary landfill operation. Occasionally disposals are called Ear which present both chemical and radioactive problems. For example, a, recent disposal called for handling 140 c~lries of tritium in benzene. Evaporation of t,he benzene would a t the same time release the tritium, yet the shipment of both liquids and chemical wsste is denied to us by our burial site regulations. This problem was solved by introducing the benzene a t 8 low temDerature into melted paraffin. This solidified quickly with no appreciable release of tritium, and thus made a n easily disposable solid waste. An average of ten gallons a week oi organic solvents are received which contain a radioactive isotope of some kind. The easiest method of disposal for these is slow evaporation to dryness in a fume hood, using paint pails as the vessel and hat plates as the source of heat. Several gallons per day can be evaporated in this manner, leaving only a gallon pail to be disposed of as solid waste. If the ternperatore is kept low, almost no activitv is released to the environment.
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Journal o f Chemicol Educofion
by the vel.mieulite process. This does not pose s problem other than the addition of extra cement to assure hardening.
Conclusions An organization charged with disposal responsibilities is necessary for t,he disposal of waste chemicals and radioactive materials a t any institution where these mitt,erials are used. The primary purpose of this group is to assure that these msi terials are removed from the paint of production and eventually removed safely from the plant. I n order to accomplish this, the person responsible must be familiar with the options for disposal which are open to him because of law, location, and hazard. He must also be completely familiar with the techniques for exercising these options. Any local disposal operator must think first in terms of safety to personnel. I n many cases the technique used will not be that which is necessarily either the least expensive or the easiest, but that which most safely will complete the disposal. At the same time, however, every effort should be made to eliminate the air and water pollution wherever possible, particdarly where repetitive operations of a routine nature are carried on. With this in mind, it is possible by careful planning and good techniques to dispose of most wastes safely and sensibly with s. minimum of pollution of the environment.
References (8) WALLANCE DELAGUN i, '*A Hydrologic Analysrs uf Postulated Liqnid Waste Release," Geological Survey Bulletin 1156-E,U S . Government Printing Office (1966). (9) Federal Register Title 10,Part 20. and L. GEMMELL, (10) S. G. PEAR~.ALL "Desien and Control Problems Associated- with the Radiological Protection of Workem Operating a Large Decontamination Facility," Proe. of the Society for Radiological Protection (1966). (11) HARWELL,It. H. BURNS, "Radioactive Waste Control a t the United Kingdom Atomic Research Establishment," (reprinted from "Disposal oi Radioactive Waste" IAEA, Vienna 1960). (12) W. G. BELTER, ((US. Operational Experience in Radioactive Waste Management (1958-1963)" U.S. Atomic Energy Commission (1964). (13) WALTER RADGER, "Safety Problems Associated with the Disposal of Radioactive Waste," Nuclear Safety, 5,4 (1964). (14) Reaelor Fuel Processing, 9, 3 (1966). "Conversion of High Level Activity Wastes to Solids" Pages 172-175P . Rineman (15) RICHARD DENNISand WILLIAMKYxrmrs, "An Evaluation Program for Radioactive Wmte Incineration," NDLTbI-8 Edeewood Arsenal. (16) C. M n w s o ~ , "Waste Management and Monitoring a t Chalk River," AECL 987 (1960).
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