by Clyde D. Watson, Oak Ridge Na tional Laboratory, Arnold J. Hoiberg, The Flintkote Co., and George A. West, Oak Ridge National Laboratory
I INDUSTRIES A
WASTES
W O R K B O O K
F E A T U R E
E
C
Asphalt Lining of Radiochemical Waste Storage Basins Application of asphaltic membranes appears practical as lin ing of earth storage pits for aqueous radiochemical w a s t e
• RODUCTioN of economical elec tric power with a nuclear reactor is dependent, among other things, on minimum fuel reprocessing costs and minimum storage costs of waste materials resulting from reprocessing operations. Waste solutions and coolants from atomic power and research reactors vary in their radio activity from 1 0 - 4 to 102 curies per liter or higher. Storage of such
liquids—because of their radio activity, corrosive chemical com position, and heat generated—pre sents special problems. Storage times may vary from a few years, as with cooling water, to many cen turies with high-activity-level wastes. Radioisotopes of long half life, such as strontium, cesium, and the transuranics, must decay to safe biological tolerance levels before release.
Use of a cheap asphaltic lining i n a gravel-filled earth basin to contain boiling self-concentrating radioactive wastes was suggested—gravel deentrains radioactive liquids and par ticles from the vapor phase. Asphalts of good membrane structure have softening points, which prohibit d i rect contact with boiling waste. I t was not possible to insulate an asphalt membrane from the heat of a boiling
Pertinent References
P r e f a b r i c a t e d asphalt plank shown was i r r a d i a t e d t o 10 1 0 r. G a s evolution produced a vesicular structure with discontinuous passages b e t w e e n cells. Final cokelike structure o f the binder a f t e r this exposure shows that i r r a d i a tion o f bituminous material can b e con tinued t o a high removal o f h y d r o g e n
Arnold, E. D., others, "Compilation and Analysis of Waste Disposal Information," Oak Ridge Natl. Lab., ORNL-CF-57-2-20, Feb. 11, 1957. Charpie, R. Α., others, " A Chemical Processing Plant for a Nuclear Power Economy," Oak Ridge Natl. Lab., ORNL-1638, Feb. 5, 1954. Coppinger, Ε. Α., Tomlinson, R. E., "Heat Problems in the Disposal of High Level Radioactive Wastes," Cfiem. Eng. Progr. 52, 417-21 (1956). Culler, F. L . , McClain, S., "Status Report on the Disposal of Radioactive Wastes," Oak Ridge Natl. Lab., ORNL-CF-57-3 114 (Revised), June 25, 1957. F-llsperman, M . , Proc. First Western Conf. on Asphalt in Hydraulics, University of Utah Bull. 47, No. 14, 12 (1956). Eng. News-Record, "Asphaltic Membrane Is Used to Leakproof a Lake," 157, 40-1 (Nov. 22, 1956). Jury, S. H . , "Heat-Conduction Losses in Reactor Waste Basins," A.I.Ch.E. Journal 3,143, 9 M (1957). Shearon, W. H . , Hoiberg, A. J., "Catalytic Asphalt," IND. ENG. CHEM. 45, 2122-32 (1956). Struxness, E. G., Morton, R. J., Straub, Ο P., "Disposal of High Level Radio active Liquid Wastes in Terrestrial Pits," Intern. Conf. Peaceful L^ses of Atomic Energy 9, 684-91 (1956). Wolman, Α., Gorman, A. E., "Management and Disposal of Radioactive Wastes," Chem. Eng. Progr. 51, 470-4 (1955). Zeitlin, H . R., "Economic Requirements for Radioactive Waste Disposal i n a Nuclear Power Economy," Oak Ridge Natl. Lab., ORNL-CF-55-6-152.
I/EC
W
O R K B O O K
FEATURES
87 A
I/EC
INDUSTRIAL WASTES
During irradiation o f carbon d i o x i d e , a 2 4 % expansion only 1 2 % at 1 X
•
Feature
all asphalts evolved h y d r o g e n and minor amounts and increased in volume. Sample to the left showed at 5 X 1 0 s r, while sample to the right e x p a n d e d 1 0 9 r. Level before irradiation is indicated b y a r r o w
basin by covering it with earth or similar inorganic material. Consequently, the idea of filling a basin with gravel and allowing it to boil from its own fission product heat has been abandoned for asphalt. A n extensive study on the application of low cost asphaltic membranes in this service indicates they could be used, provided certain conditions are met. Liquid wastes should first be neutralized and decayed sufficiently so that the self-
Table I.
A Workbook
heating temperature does not exceed 150° F. Another factor to be considered is time required for the asphalt to acquire a dose of 109 roentgens (r)—more than 25 years. Asphaltic membranes resist flow at high temperatures and, at temperatures below boiling, they remain flexible and have high durability. They also have the ability to relieve internal stresses which might be imposed without failure i n tension. Since
G a m m a Irradiation Changes Penetration and Softening Point of Asphalts and Tars with G a m m a Irradiation of up to 5 X 1 0 s r Decrease i n Penetration Increase, at 77° F., °F./10»r» Mm./10/10»ra 1.4 0.4 2.0 1.9 3.0 0.9 2.0 2.7 1.7 2.9 1.9 2.1
S.P.
No. of Samples Tars 6 , av. 4 AsphallsS av. 9 Below 45 pen (av. 34) 4 Above 45 pen (av. 57) 5 Above 200° F. S.P. (av. 246° F.) 4 Below 200° F. S.P. (av. 184° F.) 5 Materia]
Blends : 10 and 2 0 % microwax 1 % GRS rubber 2 5 % mineral filler
Exposure Level, Roentgen
4 1 2
3.1 3.6 6.7
1.1 3.3 5.3
Effect of Irradiation Dose Crude Sovirce Arkansas (membrane A)
1 0-5X10» 5.8 2.2 1 5 X 10» - 1 X 10» 11.6 3.7 " After irradiation up to 5 X 10» r. ° I n i t i a l l y from 192° to 237° F . softening point (ring & ball) and 0 to 15 penetration at 77° F. c I n i t i a l l y from 177° to 278° F. softening point (ring & ball) and 38 to 71 penetration at 77° F.
88 A
INDUSTRIAL AND ENGINEERING CHEMISTRY
1947, over 9,000,000 square yards of such membranes have been used. Possible extensive use of waste storage basins for liquid is likely to increase this figure tremendously. Extensive laboratory irradiation and chemical immersion tests were made on asphalts and tars. Investigation to a limited extent was made of the effect of irradiation on prefabricated asphalt plank and sheet membrane lining used in seepage control. One-year field tests determined the effect of irradiation on asphaltic membrane i n neutralized waste. Ability of asphalt plank to resist minor earth movements without rupturing was also considered. T i m e required for an asphalt or tar to acquire a destructive dose of radiation from a fuel with burnup of 1000 to 10,000 megawatt days per ton can be estimated from observed data. Decay time for wastes in this burnup range necessary to extend service life to 100 to 300 years, based on effect of irradiation alone, is then calculated. Level or total dose of gamma irradiation is the primary variable. Dosage in 20 exposures varied from 107 to 1010 r. Twelve exposures determined variation of physical and compositional changes of asphalts with total dose (irradiation). Character of asphalts was varied by air-blowing with and without additions of phosphorus pentoxide catalyst and by varying the crude source : Two Arkansas and one Wyoming crudes were irradiated. Initial properties of the asphalts were changed by the amount of processing and oil content of the base. Effect of several additives—wax, GR-S rubber, and mineral fillers—was determined. The degree of attack on bitumens by nitric acid content of the waste solutions was studied in the chemical tests phase. Results of Irradiation Tests
Gamma irradiation of asphalts causes: evolution of hydrogen and carbon dioxide, resulting i n 14 to 30% volume increase i n honeycomb structure; increase in softening point, slight increase in ductility, and decrease i n penetration; decrease i n flash point, but no increase i n "loss on heating" or solubility i n carbon tetrachloride; and increase in asphaltenes and resins and decrease in oils. Asphalts hardened with an average
A Workbook
Average Composition of a Radio chemical Waste Solution Stored in an Earth Basin
Solution: Sp. gr. pH Na NO,
NH3 α SO, PO 4
co 3
= = = =
Feature
•
INDUSTRIAL WASTES
I / E C
The increasing use of atomic power in industry wilt intensify the problem of long-term storage of liquid radioactive wastes. This flowsheet shows the reprocessing and storage pattern which may become an integral part of a plant in the not-too-distant future.
1.04 ~12 16 mg./ml.\ = 70% of 24 mg./ml.J total solids
=1 =· = 45 mg./ml. =I =j
Activity: Gross beta = 6.6 X 10e curies/min./ ml., approx, 10^ s curie/liter Cs137 = 75% of count Ru'»« = 15% of count
increase in softening point for nine samples of 2.68 F. per 108 r and a de crease i n penetration at 77° F. of 1.9 m m . per 108 r exposure (Table I ) . Addition of 25% mineral filler more than doubled these changes, as might be expected with a higher density compound with a higher irradiation absorption coefficient. Change in ductility was insignifi cant insofar as the ability of the mem brane to conform to subgrade move ment without cracking was con cerned. Extrapolation of data to 1010 r seems to indicate that mem brane asphalts are excessively hard ened at this level. Apparent selective destruction of ductility effect of 1 % rubber on an exposure to 5 Χ 108 r was of par ticular interest. Prefabricated asphaltic membranes appear to be al tered similarly in physical properties to sprayable asphalts. More harden ing as a result of filler content was noted. Plank types withstood ir radiation to 109 r without change. However, when the dose is increased to 10'° r, severe embrittlement oc curs. Pitch and coal tar enamels show little change i n penetration or softening point on irradiation, as might be expected from the lower i n itial values. Evolution of gas from ir radiated tars does not produce ve sicular structure as i n membrane as phalts. Cold-flow properties of the pitches are such that bubbles formed are released rapidly. Results of Chemical I m m e r s i o n Tests
A l l asphaltic membranes and tars are attacked by nitric acid solutions at temperatures from 150° to 225° F.
•5
«
Prefabricated membranes are also attacked by caustic solutions—action appears to decrease the strength of the felt filler. When the acid is neu tralized to less than 1 % , rate of at tack decreases rapidly. I n solutions where attack is slight, asphalts having softening points of 270° F. or above show no appreciable deformation on storage at 200° F. for 6 days. When bubbles are formed by severe attack, asphalts of at least 280° F. initial softening point may be required be fore distortion can be minimized, be cause of the buoyancy effect of the bubbles formed on the asphalt film. Table II.
.«s·*·
< 0
Costs a n d Construction Factors
Cost of constructing a 1,000,000gallon, lined earth basin for the re tention of radiochemical waste solu tions has been estimated to be $0.03 per gallon when sprayed lining or prefabricated asphalt plank is used. This cost includes excavation, grad ing, ditching, seeding, perimeter fence, lights, liquid level indicator, asphalt lining, and compaction. I t does not include roofing (Table I I ) . I n areas where rainfall is such that a roof is required, the estimated cost would be increased to $0.07 per gal lon.
Breakdown of Cost Items in Construction of Asphalt-Lined Storage Basins
Number
1
Excavation, $ Grading Ditching Seeding Fencing Lights Level indicator Subtotal, $ Asphalt 6 Shadow field Subtotal, $ Engineering @ 10% Total, $ Concrete footing Flat roof Roof supports Subtotal, $ Engineering @ 10% Subtotal, $ Grand total, $ $/gallon
2
3"
4
1 X 106 gal.
Basin Size Item 4,276 2,881 3,604 500 4,200 6,800 1,000 23,261 2,603 1,948 27,812 2,781 30,593
30,593 0.031
5 5 _ X 10« gal.
20,936 7,149 5,848 1,000 5,928 9,600 1,000
30,593 2,425 36,504 280 39,209 3,921 43,130 73,723 0.074
23,261 3,150 2,281 28,692" 2,869 31,561 2,425 36,504 280 39,209 3,921 43,130 74,691 0.075
51,461 9,829 9,884 71,174 7,117 78,291
78,291 0.0157
78,291 4,575 135,000 1,120 140,695 14,069 154,764 233,055 0.049
• As basin does not have 1 foot of compacted earth cover on top of lining basin, volume is 1,151,501 instead of 1,000,000 gallons. 6 1, 2, 4, 5, sprayed asphalt, contains 10% wax. 3, prefabricated asphalt plank.
VOL. 50, NO. 8
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89 A
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INDUSTRIAL WASTES
Table III.
•
A Workbook
Feature
Basin Specifications Used in Determining Suitability of Asphalt Linings in Waste Storage
Number
1
Shape Length of side at top, ft. Length of side at bottom, ft. Depth, ft. Slope of sides Compacted earth added to asphalt, ft. Volume to be excavated, cubic yards Surface area to be lined, square yards Storage capacity, gallons * Correspond to numbers in Table I I .
A 5,000,000-gallon capacity basin can be constructed for m u c h less per u n i t v o l u m e stored; w i t h o u t roofing the figure w o u l d be $0.02 a n d w i t h roofing $0.05. A l t h o u g h a flat r o o f of prestrcsscd concrete increases storage cost b y a factor o f 2.5, concrete was selected over w o o d o r m e t a l construction because i t w o u l d give m a n y more years o f maintenance-free service. U n a t t e n d e d w o o d structures have l i t t l e likelihood o f lasting for 100 years or m o r e under these conditions w i t h o u t frequent repairs. Cost data m a y be o n the h i g h side b u t should be fairly representative o f
2
3
4
average n a t i o n a l costs for this type of construction. I n m a n y sections o f the c o u n t r y where excavation is aided byideal conditions o f soil a n d t e r r a i n , earth basins can be constructed m u c h cheaper. I n 1956, a n asphalt m e m b r a n e - l i n e d basin o f 300,000,000g a l l o n capacity was constructed, w i t h o u t a roof, for about 1.5 mils per gallon. T h i s basin contains n o n radioactive l i q u i d waste f r o m t h e R o c k y M o u n t a i n arsenal. Cost of basins m i g h t be further reduced b y m o r e economical design. T h e design estimated is n o t necessarily the most p r a c t i c a l for a l l
BROOKSEAL* . . . a new and better sealing concept D E A D - E N D for corrosion and plugging t r o u b l e s in p r e s s u r e i n s t r u m e n t s Live, fully-responsive pres- sion resistant materials for sure transmission with a posi- body and diaphragm. tive block to corrosion and Clean-out types permit replugging. Pressure elements moval without disturbing l i completely filled with I N - quid fill; flushing connection ERT L I Q U I D held by ISOL A T I N G D I A P H R A G M . optional. Withstands overN o gaskets or O-rings . . . range up to 2500 psig. Pipe, instead H O N E D M E T A L - flange or saddle mounted. T O - M E T A L sealing sur- Single wrench handles assemfaces. Wide choice of corro- bly, disassembly. Write for Bulletin 250. *Tradename
BROOKS ROTAMETER COMPANY 858 G S T R E E T , LANSDALE, PENNSYLVANIA
90 A
5
Frustrum of right pyramid ; square base ISO 294 84 228 11 • 3 / 1 (33.3%) 1 1 0 1 — 1 5702 27915 2603 9829 1 million 5 million
INDUSTRIAL AND ENGINEERING CHEMISTRY
S.A. IO»4
applications, as a l l the storage capacity was below g r o u n d level. Spoil was merely piled a r o u n d the basin t o provide freeboard a n d shadow shieldi n g . Some was placed o n the asphalt m e m b r a n e to protect i t from the sun a n d from w a v e a c t i o n . T o p p i n g i n this m a n n e r also prevents the asphalt from floating. I n the case o f a basin only p a r t i a l l y u n d e r g r o u n d , w i t h walls b u i l t u p f r o m the d i r t used t o f o r m the undersurface, some economies m i g h t be realized—excavation cost w o u l d be o n l y a fraction o f the total. H o w e v e r , o p t i m u m economical design o f a storage basin w i l l always be a function of v o l u m e , excavation cost, l i n i n g cost, a n d roofi n g cost. C o n s t r u c t i o n of a n asphalt-lined basin is a r e l a t i v e l y simple o p e r a t i o n . P r i n c i p a l steps i n the operation a r e : excavation a n d placement of the soil, subgrade p r e p a r a t i o n , sterilization o f the weeds i n t h e subgrade, a p p l i c a t i o n o f the l i n i n g , a p p l i c a t i o n o f earth cover, a n d erection o f a roof w h e n req u i r e d . Slope o f the sides o f t h e basin should n o t exceed 1.5 to 1, t o avoid sloughing o f the earth or m e m brane. Slopes o f 2.5 to 1 o r 3 t o 1 are m o r e c o m m o n l y used ( T a b l e I I I ) . E q u i p m e n t needed for this type o f construction is typical e a r t h - m o v i n g and compaction equipment. Conclusions
Phosphorus pentoxide a i r - b l o w n asphaltic membranes remained i n serviceable c o n d i t i o n after exposure to 109 r. I n general, m e m b r a n e asp h a l t appears t o offer the best l i n i n g protection for storage basins for l o n g - t e r m r e t e n t i o n o f neutralized, partially decayed radiochemical wastes a n d asphaltic p l a n k m a t e r i a l is o n l y slightly less desirable. Prefabricated p l a n k c o n t a i n i n g organic a n d m i n e r a l fillers severely hardens to a friable c o n d i t i o n o n exposure to 10 1 0 r. A c t i o n o n such compositions as mineral-filled asphalts m a y be expected to be m o r e severe because of the higher absorption o f g a m m a r a d i a t i o n . I r r a d i a t i o n o f 5 times 10 8 r embrittles b o t h p l a n k a n d asbestos prefabricated m e m b r a n e so that they break w h e n flexed. H o w e v e r , b o t h can be expected to r e m a i n serviceable after this dosage. A vesicular structure i n asphalts forms very r a p i d l y as a result o f bubbles formed b y i r r a d i a t i o n a n d
causes a 3 0 % expansion at o r d i n a r y temperatures. N o increase i n v o l u m e occurs above this value. I r radiated coal tars release gas rapidly, developing little volume increase. Because of limited flexibility at or dinary temperatures, coal tars a n d enamels are not considered feasible for use as buried membranes. T h e y could possibly be modified to the nec essary flexibility. A d d i t i o n a l plasticization w o u l d be expected to involve modification i n the direction of i n creased gas formation and increased retention of that formed. A honeycomb structure develops i n asphalt o n irradiation. T h e voids are not continuous, and membranes 0.5 inch thick w o u l d be expected to have self-healing properties. U n d e r hydrostatic pressure they could re m a i n leak-tight. Additional in stallations are required to study the effects of gas evolution on membrane seepage control. A suggested form w o u l d involve a two-layer construc tion—the layer i n contact w i t h the subgrade having o p t i m u m flexi bility and heat and radiation re sistance, and the inner layer of l o w viscosity asphalt capable of releasing gas r a p i d l y to provide self-healing properties. F l u x i n g of the t w o ma terials should be very slow, or can be prevented by a suitable intermediate barrier. Chemical attack of solutions con taining nitric acid is very severe at temperatures of 150 ° to 225 ° F. Use of membranes at these temperatures should be considered only for solu tions w h i c h contain less t h a n 1 % strong oxidizing acids. Salt solu tions or alkaline solutions are confinable at temperatures u p to 200° F. w i t h o u t undue attack or softening of the membrane when the i n i t i a l softening point is at least 270° F . W h e n earth barriers are used to re tard the flow of membrane l i n i n g , solution temperatures can be i n creased. L i m i t e d testing of pre fabricated membranes indicates poor resistance to both acids and alkalies.
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TITLE
Aqueous system
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Other
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VOL.
50, NO.
8
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AUGUST 1958
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