CA1000426

Atomic Energy of Canada Limited

PHILOSOPHY AND PRACTICE

OF WASTE MANAGEMENT AT CRNL

by

C. A. MAWSON

Chalk River, Ontario

June, 1967

AECL-2710

AECL-2710

T l i é u j . it: el ^ r o U g u e Je la gestion des aêcnets radioact i is à Chalk River

par C-A. Mawson K ê s u m ê - t^e rapport donne u n aperçu de l 'h i s to i re du développement des pratiques de gestion des déchets r a ­dioact i fs à Chalk R iver . L ' ob jec t i f était d e mettre a u point u n s ys tème pouvant fonctionner e n toute sécur i té sur un site avoisinant une région habitée et de s ' assurer que des installations appropr iées pourraient être f a b r i ­quées et ut i l i sées à un coût raisonnable. Les installations ainsi r éa l i s ées à Chalk River pour l ' en fouissement des déchets radioact i fs sont déc r i t e s . Un compte rendu est donné d ' expér iences ayant p e r m i s de vér i f i e r le c o m p o r ­tement des produits de f i ss ion qui se déplacent dans l a nappe aquifère . Des indications sont fournies e n c e qui concerne l a d i spers ion des radionucl ides dans l ' e n v i r o n ­nement. La base uti l isée pour f ixer les l imites de s e r v i c e de certains types d 'enfouissement est indiquée. Le r a p ­port existant entre l e s niveaux maximaux de d é c h a r g R d a n s

la r i v i è r e e t l es concentrat ions maximales admiss ib l e s r e c o m m a n d é e s par l a C o m m i s s i o n Internationale d e P r o ­tection Radiologique (CIPR) est u n é lément important d e cette base . On d é m n n t r p q n p I P ? H ^ r V i p f c r ^ r l i o a c t î f c a c ­

tuellement pompés dans la fosse d e réacteur N° 2 p o u r ­raient être déchargées dans la r i v i è re sans que soient atteintes les concentrations maximales admiss ib l e s de la r . I P R m ;» i c o n f a i t } c o p o n d a n t ( r c m . a. r q u e r cjvto c c l » p r o - v c _

querait une forte augmentation des niveaux mesurés d e Sr-90 et d e Cs-137 dans l»eau d e l a r i v i è re .

C K a l U R i v e r , Ott . to.i - io

F é v r i e r 1967

PHILOSOPHY AND PRACTICE OF WASTE MANAGEMENT AT CRNL

by

C.A. Mawson

S Y N O P S I S

The h i s Lui y uP d e v e l o p m e n t of w a s t e m a n a g e m e n t practices at CRNL is outlined. The policy has been to develop a system that could be operated safely at a site c l o s e to a b u i l t - u p area anrl tn d e m o n s t r a t e the (-.(instruction and use of facilities that can be made and operated at a reasonable cost. The waste facilities are described and an account is given of experiments designed to test the be­haviour of fission products moving through the ground water zone. Other experiments on dispersion of radionuclides through the environment are outlined. The basis for setting working lim i L s fur c e r t a i n types u£ d i s p o s a l s is g i v e n , especially the connection between maximum discharge levels to the river and the MPC W recommendations of the ICRP. It is s h o w n that w a s t e at p r e s e n t pumper! tn R e a c t n r Pit 2 roui d be discharged to the river without approaching the ICRP limits, but it is pointed out that this would cause a large increase in the measured levels of Sr-90 and Cs-137 in the river water.

Environmental Research Branch, B i o l o g y and H e a l t h P h y s i c s D i v i s i o n ,

Chalk River Nuclear Laboratories, Chalk River, Ontario.

February, 1967.

AECL-2710

C O N T E N T S Page

MAP SHOWING DISPOSAL AREAS Facing 1

I N T R O D U C T I O N 1

GENERAL POLICY 2

DISPOSAL FACILITIES 3

Disposal of Solids (a) Low Level Wastes 3 (b) High Level Wastes 4

(i) Asphalt trenches 4 (ii) Concrete trenches 4

(iii) Tile holes 4 (iv) Irradiated fuel holes 5 (v) Bottle Crib 5

(vi) Concrete monoliths 6 (vii) E m e r g e n c y p i t s G

(viii) Experimental incinerator 6

(r) FittpTisinns nf Disposal Areas f\

Disposal of Liquids (a) E m e r g e n c y B a s i n 7 (b) Reactor Pit No. 2 7 (c) Chemical Pit 7 fdl Caustic Crib 8 (e) Other Liquid Wastes 8 (f) High Level Tanks 9

E X P E R I M E N T S

1. Movement of High-Ionic Wastes Through Soil 10 2. L e a c h i n g of N c p h c l i n c S y e n i t e Gla33 11 3. Surface Disposals 11 4. Tracing of Water Movement 12 5. Airborne Contamination 12 6. Meteorology 12 7. Ion Transport in Aquatic Communities 12

D I S P O S A L P O L I C I E S

Setting of River Discharge Levels 13 S e t t i n g o£ Solid W a s t e D i s p o s a l L i m i t s 14

ii

C O N T E N T S (Cont'd)

Page

OPERATING POLICIES

1. Solid Wastes 15 2. Liquid Wastes 16

TABLE I - Disposal of Soluble Wastes to Area A 17 II - Disposals to Reactor Pit 2, 1966 18 TTT - D a i l y D i s c h a r g e s for CRNL to O t t a w a

River 18

B I B L I O G R A P H Y 21

Portion of Perch Lake Basin Containing Waste Management Areas

(Dotted line Indicates rock rim of the basin exposed in many places.)

INTRODUCTION

The h i s t o r y of w a s t e m a n a g e m e n t at CRNL can be divided conveniently into two periods by the date of the 1952 accident at the NRX reactor.

Before December 1952 solid disposals were made in the A Disposal Area, which consists of sand underlain by lenses of silt, succeeded by glacial till and granite bed­rock. The glacial till is almost impermeable to water, and where silt horizons occur they also are impermeable. The water table lies at about 2 m below the surface, and the d e p l h ul sand Lu Lhe Lill is about 15 m. W a s t e s w e r e bui'ied directly in the sand, except for bottled liquids and high-level material such as Co-60 sources, and wastes arising from e x a m i n a t i o n of i r r a d i a t e d fuel - The h o t t l e s w e r e placer] in a concrete tank sunk in the ground and the high-level solids were dropped into a concrete-1ined hole. Low-level liquid wastes were bled into the Ottawa river, diluted by the cooling water of the NRX reactor, and high-level liquids were stored in stainless steel tanks situated near to the river bank.

The failure of the NRX cooling system on Dec. 12, 1952 led to the accumulation of about 4.5 x 10 3 m 3 of water c o n t a i n i n g ahmit I D 3 Ci of Sr-9fl + Y-90, w i t h other associated fission products, in the basement of the reactor. This water was pumped into a network of shallow trenches in the A Disposal Area. Owing to the sandy nature of the soil the water sank rapidly into the ground, but investigation soon revealed that the fission products were held near to the point of entry into the ground, and moved very slowly through the sand. T h e s e u L i c i v a l i o n s s u g g e s t e d that i n s t e a d of running low-level liquid wastes into the river it might be better to put them into the ground. The slow movement of f i s s i o n p r o d u c t s t h r o u g h the soil would p r o v i d e time for decay, and the danger of an accident or an operational error causing unforeseen contamination of the river would be avoided. The system of trenches used for the NRX disposals had reduced available space in the A Area to such an extent that it was clear that another disposal area for solids would have to be developed quite soon.

With these circumstances in mind, a "five-year experiment" was started in the summer of 1953. Near to the A Disposal Area we found a "lcettle", w h i c h is e s s e n t i a l l y a sand hill with a hollow top. A pipeline from the kettle ("Reactor Pit 1") to the Active Area carried 250 - 500 m 3

of water per day, mainly from the Fuel Storage Bays. The water sank treeiy into the sand, and there was never any danger of the pit filling up. However, a mound formed in the

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water table and a small spring appeared within the A Area fence. The overflow from the spring quickly drained back into the sand, and never carried more total activity than 2 mCi/day (mainly Ru-106 and S-35). Use of Reactor Pit 1 continued until October 1956, when it was abandoned and c o v e r e d w i t h sand. F r o m that t i m e o n w a r d s l o w - l e v e l l i q u i d wastes have been pumped into a gravel-filled pit (Reactor Pit 2) or into a smaller but similar Chemical Pit which is used for solutions containing such materials as acids, alkalis, detergents, salts and complexing agents.

When A Area was full a new disposal area, B, was developed for solid wates. It was Intended from the beginning that the B Area should be used as a trial ground for disposal techniques aimed at prevention of contamination of the e n v i r o n m e n t . T h i s w a s also the o b j e c t i v e of the u s e of g r o u n d disposal for low-level liquids.

GENERAL POLICY

At the time when future waste management policies were being actively considered at C R N L ( 1 9 5 2 - 5 4 ) it was becoming clear that AECL would be involved in the development of nuclear power. At the same time it was also clear that v e r y l i t t l e w a s r e a l l y k n o w n about r a d i o a c t i v e w a s t e m a n a g e ­ment. Designers of nuclear reactors did not devote much thought to this subject and wastes were disposed of on an ad hoc basis by people of varied professional background who Teamed their work "on the job". The literature was scanty, and not of high quality, and the methods used were crude. The safety of many of these operations was problematical, and there was a growing feeling that there was a " W a s t e D i s p u t a i Problem" that might be a serious restriction upon the develop­ment of nuclear power. Alarm on this subject was spreading from h e a l t h p h y s i c i s t s to the g e n e r a l p u b l i c , w i t h p e s s i m i s t i c articles in the press and doubting statements on the radio.

The realisation that the transportation of radio­active wastes from power reactor sites to Chalk River would be impracticable led us to the conclusion that we should develop techniques that would be acceptable in places less isolated than C R N L . uur isolation, the great e x t e n t uf the p r o t e c t e d area under our control, and the large flow of the Ottawa River made it possible for us to engage in bolder experiments t h a n s e e m e d p o s s i b l e at most o t h e r e s t a b l i s h m e n t s .

There were several other places where such experi­ments could have been carried out safely, but other circum­stances (such as the very great depth to the water table at Hanford and the climate of public opinion in Europe) made the

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work impracticable or unattractive at those sites. We were s t a r t i n g n e w d i s p o s a l f a c i l i t i e s , so w e w e r e not inhihiterl by preconceived notions or rigid codes of practice. We also had the advantage of a very large involuntary experiment under way - namely the 1000 Ci of Sr-90 + Y-90 already in the ground resulting from the NRX accident.

With this background we decided to develop f a c i l i t i e s fur the d i s p o s a l of solid r a d i o a c t i v e w a s t e s that would be so good that they could be installed in almost any location without fear of the escape of radionuclides to the e n v i r o n m e n t , and at the same time to subject the gronnrl to a severe test of its capacity for delaying the movement of radionuclides that were free to move through the ground, and particularly in the ground water. This was a two-pronged attack - on the one hand to learn how we could confine wastes, and on the other hand to learn how they behaved when they were not confined.

DISPOSAL FACILITIES

The original scheme was set up as a five-year experiment. Dr. A.J. Cipriani was firmly convinced (largely as a result of preliminary observations which showed minimal movement of the 1952 NRX wastes) that ground disposal was so safe that it could be continued indefinitely on the scale foreseen for CRNL. Others were more sceptical, but eventually Dr. Cipriani proved to he right. The practices developed during the 5-year experiment are still being operated ten years later.

Disposal of Solids

fa) Low Level Wastes

The low level wastes consist mainly of paper, packing material, broken glassware, protective clothing and cleaning materials. They are buried directly in the sand in trenches, compressed by a crane-operated weight, and covered with sand when full. Records are kept of the position of e a c h t r e n c h . T h i s p r a c t i c e is w a s t e f u l of s p a c e but is cheap and easy to operate. It would not, however, be practi­cable in a place where ground is very valuable.

The original definition of "low level" stated that no single "package" should contain more than 1 mCi of fission products, or its equivalent, and that it should not contain any plutonium. This was modified later to permit disposal of up to 5 nominal millicuries per package, and the proviso concerning plutonium was dropped. The changes were due to an

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alteration of the "mix" of fission products normally occurring in the waste, and tu the u b s e r v a t i u u that piiituiiium d o e s not move appreciably through the ground. A rough estimate of the amount of radioactive material in each package is made by m e a s u r i n g the b e t a - g a m m a d o s e r a t e at "50 cm from the s u r f a c e by means of an instrument standardised by readings taken from bags containing paper contaminated with a known amount of mixed fission products.

The setting of the level at which wastes must be put into concrete facilities is arbitrary. If it is set too low, the concrete f a c i l i t i e s aie used w a s t e f u l l y . If it is set too high, the radiation field from the packages may cause inconvenience during disposal operations or give rise to u n a c c e p t a b l e r a d i a t i o n l e v e l s in the v i c i n i t y of the trench

while this is still in use.

(b) High Level Wastes Items containing more than 5 nominal m C i of activity

are placed in leak-tight containment facilities under the ground, surface. These are of various types.

(i) Asphalt trenches. For the first two years, dis­p o s a l s w e r e m a d e into t r e n c h e s lined w i t h a s p h a l t w h i c h w e r e sealed with asphalt when full. When cracking was noticed in an exposed asphalt covering surface this technique was abandoned. Very small leaks have been detected from an asphalt trench which contained unusually high-level dis­posals resulting from a clean-up operation. This has led to minor contamination of a small intermittent stream running within two or three metres from the trench.

(ii) Concrete trenches. The asphalt trenches were r e p l a c e d w i t h r e i n f o r c e d c o n c r e t e s t r u c t u r e s , u s u a l l y about 60 m long, divided into 12 m bays by cross-walls. When full, the contents are covered with sand and a concrete roof is p o u r e d , w h i c h is then covered to ground level with 0.5 to 1 m of sand. One bay at a time is used. While in use it is covered with a temporary plywood roof. Recent practice has been to build double concrete trenches, thus saving one wall but requiring a more expensive type of roof.

(iii) Tile holes. It is inconvenient to place intensely r a d i o a c t i v e s o u r c e s in c o n c r e t e t r e n c h e s b e c a u s e r a d i a t i o n fields from an open trench cause operational problems in protection of workers. At first we covered such disposals w i t h sand as soon as they were made, but this was wasteful of space. Facilities constructed from concrete drain pipe of various sizes have been very successful. A concrete slab is poured at the bottom of a trench. Before this has set

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concrete drain pipes, painted on the outside with asphalt, are pushed into the slab. About 5 cm of asphalt is poured inside the pipe. More pipe is then fitter! nn top of the first section, with the joints sealed with asphalt, until ground surface is reached. Back-filling progresses as the pipes are fitted. The ground is then compacted around the mouth of the top pipe, and a waterproof cover is put on.

The kind of disposal destined for a "tile holes" dnlves at the dispusal area in a heavy shipping flask, the bottom of which is closed by a sliding gate, operated like a drawer by a crank. A concrete "pad" with a hole in the middle, and fitted with steel dowel pins for alignment of the flask, is positioned over the hole while it is in use. The hole in the pad is closed with a heavy shielding plug. The plug is removed by a mobile crane, which then places the flask on the pad. An operator cranks open the gate and the object in the flask (usually pieces of irradiated fuel or source material from radiotherapy units) falls down the hole. After removal of Lhe flask a few shuvels-full uf sand are put inLu the hole and the shielding plug is replaced.

(iv) Irradiated fuel holes. These are similar to the tile holes except that they are constructed with a steel pipe inside the concrete pipe, and the annulus is filled with concrete. The holes are located on 1.23 m centres and the space between the tops of the pipes is covered with concrete. The spacing is calculated to be sufficient to dissipate the decay-heat from holes filled with six-month-old fuel suffi­ciently well to prevent a temperature rise that would cause deterioration of the concrete. Representative holes have been fitted with temperature recorders and an experiment is in progress to chock the calculations.

Fuel is placed in the holes inside a steel can holding up to six NRX fuel elements. The can of fuel is recoverable, but some holes are designed for reception of waste material from the caves, in which case the holes are sealed with concrete. Criticality approval is obtained before any disposal of fissionable material is carried out.

(v) Bottle crib. Bottles of miscellaneous waste are placed on the floor of a concrete bunker constructed like a house basement. The walls and floor are coated with asphalt about 1 cm thick and the floor is covered with sand. When full, the bottles are covered with sand and about 5 cm of asphalt is poured over the sand to form a new floor for the next layer of bottles. It is realised that some of the bottles will rupture, but it is considered unlikely that the sLrucLure itself will leak. The contents of these bottles could sometimes be discharged into the Chemical Pit in Area A,

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but transfer to the liquid waste system would be operationally inconvenient.

(vi) Concrete monoliths. This was a one-shot operation designed to dispose of "medium-active" waste from the old fuel p r o c e s s i n g p l a n L . W a s t e uf lliis n a t u i e dues not a r i s e in current operations. It was a nitric acid solution, which was mixed with cement powder containing 21 bentonite and allowed to s o l i d i f y in s t e e l d r u m s . T h e d r u m s w e r e placed nn c o n c r è t e pads poured at the bottom of a large trench. The pads were surrounded with forms and filled with concrete so that the drums were enclosed within solid blocks of concrete. These structures were not reinforced and might be expected to crack, but drilling and ground water sampling around and beneath the monoliths has shown that escape of radionuclides into the ground has b e e n n e g l i g i b l e . The m o n o l i t h s are entirely below ground.

(vii) E m e r g e n c y p i t s . T h r e e l a r g e c o n c r e t e - 1 i n ed p i t s were constructed for reception of the products of accidents. One of these was used for a burned NRU fuel element, but the other two are still available.

(viii) Experimental incinerator. Since it seemed likely that nuclear power stations situated near to cities would not have sufficient ground available for burial of c o m b u s l i b i e low-level waste we wished to gain experience in the operation of an incinerator fitted with the necessary devices for p r e v e n t i o n of c o n t a m i n a t i o n of the a t m o s p h e r e and of the operators. The incinerator was designed at CRNL and was operated for a period sufficient to obtain the required infor­mation. Costs of disposal by incineration were so much greater than those for ground burial that it was shut down at this stage.

(cJ Extensions of Disposal Areas

The rate of consumption of ground by open trench d i s p o s a l of low l e v e l w a s t e s h a s c a u s e d c o n c e r n from time to time. Exploration by P.J. Parsons, using drilling equipment, soil sampling and water-table measurement techniques, identified a considerable area suitable for extension of the B Disposal site, and an entirely new area just outside the Perch Lake Basin which was considered suitable for low-level disposals. The latter site has been partially cleared and is in use at the present time, l e a v i n g the B A r e a free lor high-level disposal facilities. It is designated "C Area" and is so extensive that it will be available for a great m a n y y e a r s .

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Disposal of Liquids

(a) Eiueigency B a s i n

The problem faced in 1952 of how to dispose of the l a r g e v o l u m e of c o n t a m i n a t e d c o o l i n g w a t e r in the NRX base­ment was solved by pumping it into trenches in the A Disposal Area. This operation could not be repeated because the A Area is full, and the B Area could not be used economically for such a purpose. The C Area is too distant, and is out­side the Perch Lake Basin. A sand dune was therefore selected for construction of a large basin by excavation of the top of the d u n e . The hole w a s lined w i t h p o l y e t h y l e n e , which was covered with a layer of gravel and sand. A pipe­line was laid between the reactors and the emergency basin. R a i n w a t e r c o l l e c t s in the b a s i n , but the capacity is maintained at a minimum of 5 x 10 3 m 3. The basin is emptied each year before freeze-up. So far as can be ascertained the basin is leak-free, and there has been very little denudation or channelling of the banks. Active water collected in this basin could be decontaminated by ion exchange.

(b) Reactor Pit No. 2

The spent fuel s t o r a g e h a y s h a v e a c i r c u l a t i o n system which includes filters and deionisers, but build-up of tritium, collidal material and poorly-adsorbed elements make it necessary to bleed off a fraction of the contents and replace it with clean water. This water is pumped to the A Disposal Area, where it enters a large, pebble filled pit, and seeps into the ground. The pebbles serve as a radiation s h i e l d and prevent. c o n t a m i n a t i o n o f w i l d - l i f e or s c a t t e r i n g of air-borne contaminants.

U p to J u n e 1966 this pit had r e c e i v e d 1? ^Dfl c u r i e s of soluble fission products (total B), of which 10-20? was Sr-90. During the period 1956-62, when there was no re­circulation system in the storage bays, about 12 000 m 3/month, containing an average of 17 Ci soluble total (3, was pumped to the pit. During the past two years this has been reduced to 2000 m 3, containing about 1.3 Ci total (?, per month.

Very little movement of this active material has been detected - it is estimated that over 901 of the whole amount has r e m a i n e d w i t h i n a few m e t r e s from the h o t t o m of the pit.

(c) Chemical Pit

It is undesirable that solutions containing acids, alkalis, complexing agents and other chemicals should be added

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to water pumped to Reactor Pit No. 2, since they might leach the fission products adsorbed on the soil. A pit similar in design to the reactor pit, but considerably smaller, was constructed in Disposal Area A in such a location that its drainage would not pass through the reactor pit. Active waste lines terminate in holding tanks in the laboratory area, which are connected to the pipeline to the Disposal Area. When a sufficient volume has accumulated the chemical waste is p u m p e d v i a a v a l v e h o u s e to the a p p r o p r i a t e p i t .

Since this pit was put into operation it has received about 800 Ci of soluble fission products ("total B) . It is at present receiving about 6000 m 3, containing about 8 Ci of soluble fission products, per month.

As would be expected, there is movement of radio­active material from the Chemical Pit. There are several active seeps in a near-by swamp, but they have never caused a n y d i f f i c u l t y b e c a u s e the r a d i o n u c l i d e s arc a d s o r b e d on the decaying vegetation and very little penetrates as far as Perch Lake. The principal source of contamination of the swamp is Co-60. Compared with the amount of radioactive material known to have entered the pit, the seepage has been remarkably small.

Monitoring of both disposal pits is carried out by sampling of wells, determining radiation fields at the surface and at various depths in dry wells, and sampling of surface w a t e r s b e t w e e n the d i s p o s a l p i t s , P o r c h L a k e and the O t t a w a River. Activity derived from the disposal areas is included in the list of discharges to the Ottawa River shown in T a b l e III (p. i g ) .

(d) Caustic Crib

Small volumes of caustic soda solution used for dissolution of aluminum arise periodically. The main contami­nant is Co-60. Steel drums (200 litre) containing the liquid are p l a c e d in a c o n c r e t e b o x . W h e n full (.12 d r u m s ) the b o x is filled with asphalt or concrete and capped with concrete. A similar facility is used for organic liquids.

(e) Other Liquid Wastes

The very large volume of reactor cooling water carried by the Process bewer is used for dilution of certain wastes that would be difficult to handle by the liquid dis­posal system just described. For a short period a Laundry Pit w a s o p e r a t e d at the d i s p o s a l a r e a , but o w i n g to the presence of lint and soaps it plugged repeatedly and could not be used during the winter. Owing to the fact that it had

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to be raked at frequent intervals to maintain permeability-fan unpleasant and possibly hazardous task} it could not be filled with rock, so it froze.

When it was realised that the laundry wastes, together with those from the decontamination centre, seldom contained more than one curie of total $ activity per month, both these wastes were bled into the Process Sewer. This p r o c e d u r e is also u s e d for c e r t a i n low v o l u m e w a s t e s containing high concentrations of chemicals which would be incompatible with the contents of the active waste storage tanks or would cause unusual leaching p r o b l e m s in the Chemical Waste Pit. Controlled discharge by a metering pump ensures an acceptable concentration of radioactive and chemical pollutants in the Process Sewer.

(f) High-Level Tanks

T h e acid c o n c e n t r a t e of h i g h level w a s t e s a r i s i n g mainly from the old fuel-processing plant is stored in a small tank-farm located near the northeast border of the Perch Lake Basin. The tanks are buried in a d e e p bank of sand which runs under muskeg to the floor of the valley, which is lined with glacial till. Leak detecting instruments are installed and a spare tank and pump are available if a leak develops. The tanks are constructed on a cup-and-saucer principle so that contamination of the ground is very unlikely.

EXPERIMENTS

No attempt will be made to give a detailed account of the extensive experimental work done in the Perch Lake Basin since 1953. A bibliography is appended that gives key references, from which the most significant reports can be identified.

In a s e n s e , the w h o l e B a s i n is one big tsApei iiueiiL . Over the years a large number of test holes have been installed, some of which are suitable for taking samples of ground water. Others are dry holes s u i t a b l e for r n d i o l n g g i n g . The test holes are located in and through places where experimental disposals have been made, and along the projected tracks of movement of radionuclides carried by ground water. Drilling and soil sampling equipment and a trained drilling crew are available, and are used extensively for sub-surface investigation. Movement of radioactive wastes through the g r o u n d is a v e r y s l o w p r o c e s s , and e x p e r i m e n t s of this n a t u r e require observations extended over many years.

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Sampling of surface waters and vegetation are also i n c l u d e d in the experimental programme. Although most of the radioactive material associated with a well-planned experi­ment will remain below ground for an extended period, our water table is very near the surface and in some places it reaches the surface to iorm swamps. if the ground w a t e r is contaminated some of the upper part of the profile will emerge into the swamp water. This occurs at two or three p l a c e s a d j a c e n t to the A A r e a and the l o w - l e v e l l i q u i d disposal pits. The roots of vegetation growing in places where the water table is at or near the surface can also pick up r a d i o a c t i v i t y .

The geology of the Perch Lake Basin has been explored in great detail by N.R. Gadd of the Geological Survey of Canada, and P.J. Parsons has m a d e e x t e n s i v e s t u d i e s of the hydrology and soil structure of the basin.

S p e c i f i c E x p e r i m e n t s

1. Movement of High-Ionic Wastes Through Soil

In 1954 and 1955 large disposals of "medium-active" fuel processing wastes were made directly into the sand in the A Disposal Area. The object was to find out what would happen if a high-level waste tanK, hurled in sand, w e r e to leak into the ground. The wastes used were in nitric acid + ammonium nitrate, and in strong nitric acid respectively. Drilling, l u g g i n g and s a m p l i n g h a v e r e v e a l e d the d i r e c t i o n and rate of movement of the radioactive material, and these observations are continuing. A series of reports, particu­l a r l y by P.J. P a r s o n s , has been published.

Some of the results of this experiment can be summarised :

(a) When "high-ionic" wastes enter the sand they sink rapidly to the water table and then penetrate below its surface.

(b) Neutralisation of the acid and disappearance of n i t r a t e w a s u n e x p e c t e d l y r a p i d .

(c) While free acid and salts are present some of the radionuclides move rather rapidly with the ground water, but after neutralisation the rate of m o v e m e n t q u i c k l y slows d o w n to that expected for material dissolved in plain water. Even in our acidic sandy soil, with its very low cation e x c h a n g e c a p a c i t y , w a s t e s d i s s o l v e d in acid r e m a i n e d Close to the disposal site. When ammonium nitrate was present movement was more rapid and most of the Sr-90 left the d i spnsa1 p i t .

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(dj The only fission products that move appreciably are Ru-106, Sr-90 and Cs-137. Several years after the disposals were made Ce-144 and Sb-124 began to appear beyond the i m m e d i a t e n e i g h b o u r h o o d of the d i s p o s a l p i t s , but their rate of movement is very slow.

Ce) S r - 9 0 m o v e s at 1/10 tn 1/Fifl nf the r a t e of m o v e m e n t of the ground water through sand, but much more slowly through silt and silty clay. Cs-137 moves more slowly in our "soil" than Sr-90. On sloping ground the sub-surface water may move as much as cm per day. In level areas the rate may be as low as 2 or 3 cm/day.

(f) The t r a c k o£ m o v e m e n t o£ r a d i o n u c l i d e s in g r o u n d water can be forecast with considerable accuracy from hydro-logical investigations, but forecasts of rate of movement are less reliable. This is not s u r p r i s i n g b e c a u s e of p e r i o d i c differences in head of the water table and different types and structures of soil penetrated from time to time. However, we do know how to calculate rates provided sufficient infor­mation is obtainable.

(g) There are at least two distinct masses of ground w a t e r in the v i c i n i t y of the A A r e a . The lower une is muviiig very slowly, if at all.

(h) When r a d i o a c t i v e c a t i o n s m o v e in the s u r f a c e w a t e r s of a swamp they do not go far before they are trapped and held by the humus.

2. Leaching of Nepheline Syenite Glass

Two disposals of fission products fixed in nepheline s y e n i t e g l a s s b l o c k s h a v e b e e n m a d e b e n e a t h the gruuild water table in a swamp. Careful sampling of soil and water for several years has revealed that the leaching rate decreased rapidly until it w a s well h e l o w the v a l u e c a l c u l a t e d from laboratory experiments. Recent investigations show a further decrease in rate, by a factor of fifty below the original rate. It is quite clear that this glass is so resistant to leaching that it is a good medium for disposal of high-level wastes; the leaching rate in the soil is actually below the value originally specified as suitable for disposal of major q u a n t i t i e s of w a s t e , fixed in g l a s s , d i r e c t l y hiLu g r u u n d water.

3. Surface Disposals

Although the NRX basement water disposal was not a deliberate experiment, it provided a large deposit of fission products located near to the ground surface and well above the water table. This material is exposed to leaching only

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by natural precipitation. The downward movement of water in the unsaturated layer is now known to be slower than had previously been supposed. M o v e m e n t uf this active m a t e r i a l is, in fact, so slow that it is unlikely that detectable amounts will ever be carried by ground water much beyond the l i m i t s o £ the D i s p o s a l A r e a .

4. Tracing of Water Movement

Techniques have been developed for tracing the movement of water both under the ground and in lakes and rivers. Surprisingly little seems to be known about the dilution regimes of o p e n wateia and this w o r k is c o n t r i b u t i n g useful information in this field.

5. A i r b o r n e C o n t a m i n a t i o n

Experimental burning of low-level wastes in the C Area has shown that such operations do not cause distant dispersion of hazardous amounts of radionuclides, bailout is only detectable in the immediate vicinity of the burning refuse. Only people working in the smoke plume would be exposed to credible hazard.

6. Meteorology

The disposal of Ar-41 and H-3 from the CRNL stack has generated interest in micrometeorology and has provided means of measurement of dispersal phenomena. The presence of H-3 in the surface waters of the Perch Lake Basin has also enabled us to investigate evaporation rates from Perch Lake. Evaporation from large bodies of water is difficult to study and little is Known about it.

7. Ion Transport in Aquatic Communities

The presence of low levels of radioactive contami­nation in Perch Lake and other surface waters has given an opportunity for study of the routes and rates of movement of ions (particularly Sr and Cs) through an aquatic ecosystem. This aspect of our work will be extended considerably in the near future.

DISPOSAL POLICIES

The Radiation Health Manual (1948) contained the statement that "The maximum permissible daily disposal in the river is 1.5 curies per million gallons Active material which cannot be disposed of through the drains should be placed in the disposal containers provided Contents of

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such containers will be collected as often as necessary and b u r i e d in the d i s p o s a i a r e a " . This w a s the o n l y r e g u l a t i o n limiting waste disposal, and the first sentence is ambiguous as it does not really define a daily permissible effluent, but a maximum permissible concentration (3.4 x 10" 7 nCi/ml of unspecified radionuclides).

The Radiation Hazards Control Manual, written in 1 9 5 4 , set a local working limit of 20 mci br-yu, plus 1U Ci of other radionuclides per day for discharge to the river. Discharge of plutonium was limited to 1 mg/day. Rules for d i s p o s a l o£ w a s t e s w o r e g r e a t l y e x p a n d e d and it w a s s p e c i f i e d that the disposal areas were under the supervision of the Building Maintenance and Construction Branch "who will be advised by the R.H.C.B." - i.e. Radiation Hazards Control Branch. Àt this time Dr. C.A. Mawson was unofficially in charge of this advisory service as a representative of the director of the Biology and Health Physics Division, although he was actually on the staff of the Biology Branch. He was chairman of the recently formed Waste Farm Disposal Panel, reporting directly to the President on waste management m a t t e r s , e s p e c i a l l y on p r o p o s a l s for n e w types of d i s p o s a l s .

A revised form of the RHC Manual appeared in 1959, placing responsibility for advice, and approval for certain types of disposal, on the Environmental Research Branch. Working limits were placed on the amount of activity permitted for burial in sand trenches (1 nominal mCi/package or 1 mg of Pu), except by permission of the branch Head ot Environmental Research. The working limit for discharge of Sr-90 to the river was raised to 50 mCi/day and the non- Sr-90 limit was d e c r e a s e d to 4 C i / d a y . D i s c h a r g e of Pu to the r i v e r w a s limited to the increased value of 20 mg/day.

Setting of River Discharge Levels

There is no record of the reason for setting the discharge level for Sr-90 at 1.5 Ci/10 6 gal in 1948. However this value (3.4 x iu 7 yCi/mlJ is sufficiently close to the 168 h occupational MPC in force in 1954 (8 x 10~ 7 yCi/ml) to suggest that it was a round-figure approximation of this v a l u e . H o w e v e r in 1054 the effect of d i l u t i o n into the rivei volume was considered in setting the total permissible dis­charge .

The average river flow was taken to be 1 0 1 0 Imperial gallons (4.55 x 10 1* ml) per day. A discharge of 20 mCi/day Sr-90 would give a concentration of about 4 x 1 0 " 1 0 yCi/ml a f t e r a d m i x t u r e with the whole river volume (i.e. a "factor of safety" of 2000) . We knew very little about the capacity of the river for dilution of effluent, but it was argued that

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even if the effluent was only diluted into 1/100 of the total volume of Llie liver b e f o r e it e n t e r e d a p u b l i c w a t e r s u p p l y the necessary factor of safety of 10 (for the general population) would be exceeded. It is now known that this was a c h a r a c t e r i s t i c a l l y " e n n s e r v a t i v e " hypothesis.

In 1959 the MPC for Sr-90 had become 10" 6 uCi/ml. Experience had shown that a limit of 20 mCi/day for Sr-90 was not always easy to attain, but we were advised that 50 mci/ day would be adequate. This would give a "safety factor" of 1000 after dilution into the river, using the new occupational M P C . By this Lime we X n e w that on days w h e n t h e r e w a s l o w river flow and a strong up-river wind, activity derived from the process sewer could be detected in the Plant water intake, but it w a s b e l i e v e d that a d i l u t i o n factor of at least 100 was involved and such contamination seldom lasted longer than a few hours. On this basis the 50 mCi/day figure was accepted.

The ICRP recommendations for MPC W of "Any fission mixture (3,y)"* dated 1954 give a figure for continuous e x p o s u r e u f 1 0 " 7 (jCi/ml. T h e 1 D S 4 d i s c h a r g e limit o£ 10 C i / day of "non- Sr-90" radionuclides gives a concentration after total dilution of 2 x 10" 7 uCi/ml. This seems rather high, and m a y h a v e b e e n an e r r o r , since it contains no "safety factor" for a population as distinct from occupational workers. However, by 1959 the MPC W for a mixture of radio­nuclides not including either Sr-90 or Ra-226 had been raised to 2 x 10" 5 uCi/ml. Using a working limit of 4 Ci/day the concentration after complete dilution would be 10" 7 uCi/ml, giving an adequate "safety factor" of 200. The combined permitted effluent uf 50 m C i Sr - 9 0 « 4 Ci " o t h e r long lived 3 emitters", after dilution into the whole river, gives 1/150 of the MPC for continuous use by occupational workers.

It should be noted that we have always believed that Sr-90 is the principal hazard to the environment. It is much more likely than most other radionuclides having signifi­cant hazard to man, to travel considerable distances, we have therefore provided much higher "safety factors" for Sr-90 than for other radionuclides.

Setting of Solid Waste Disposal Limits

The s e t t i n g of one nominal millicurie per package for sand burial in 1959 had no rational basis. It was a purely administrative decision which ad actually been in force since 1956 when CRNL began to make monthly reports to the Department of National Health and welfare on the a m o u n t , n a L u r e and location of all significant amounts of radioactive material put into the disposal areas. We had to decide what was a

T h e r e was no M P C W for M F P free from S r - 9 0 in 1 9 5 4 .

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"significant" amount, and, rightly or wrongly, we settled on 1 mCi mixed fission products or their equivalent. This was e s t i m a t e d by the r a d i a t i o n f i e l d m e a s u r e d b y a p a r t i c u l a r instrument, standardised by measurement of the field arising from a bag containing a known amount of 6-year-old mixed fission products. This amount was later amended to 5 mCi and the material used for standardisation was altered to 2-year-old fission products, because it was pointed out that the average age of fission products normally going to dis­putai had a l t e r e d .

The accountability to DNHW for quantities of radio­n u c l i d e s e n t e r i n g the w a s t e m a n a g e m e n t s y s t e m m a d e it necessary to devise some method of measurement that would give order-of-magnitude accuracy. It is realised that figures obtained with a 3-ratemeter are not precise, but this is the best way we have at present for estimating active material in anything from a garbage bag to a contaminated tank.

O p e r a t i n g P o l i c i e s

1. Solid Wastes

Policies for operating the disposal areas have arisen partly from ignorance of the consequences to be expected from liberation of radionuclides into various s e c t o r s nf the environment, but they have been changed as knowledge has replaced ignorance. However, another important influence has been the desire to operate, and to be able to demonstrate, a w a s t e management system that is safe, simple to run, reason­ably economical and suitable for use near to centres of population.

The factor of ignorance has tended to ensure con­servative practices, which, from purely practical considera­tions, were unnecessary. We did not know w h e n c o n c r e t e trenches were designed that the rate of movement of Sr-90 in the saturated zone of our soil was of the order of metres per annum, nor were we aware that complete mixing into the full v o l u m e of the river would occur within a few Kilometres of the mouth of the Process Sewer. Now that we do know this we could increase the amount of active material liberated into the r i v e r , and w e c o u l d b u r y m u c h m o r e a c t i v e m a t e r i a l directly in the soil, without significant hazard to the environment. The question is - would this be a good thing to do?

The practices we have adopted in the solid disposal areas are such that we are in a position to demonstrate to v i s i t o r s the u p e i a t i o n of facilities that could be used safely in a built-up area. The direct burial of low-level

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waste could not be done at such a site, but baling or inciner­ation would yield products that could be placed in engineered facilities. E c u n u m i c c o n s i d e r a t i o n s h a v e n e v e r limited our own waste management operations, but the trenches, tile-holes and other structures are not unduly costly. A concrete trench c o s t s C R N L about t w i c e as m u c h as an open trench. We believe that it would be wise to continue our present solid waste disposal practices even though we could not produce evidence that direct burial of all our solid wastes would be hazardous.

It is sometimes inconvenient or impracticable to use our normal concrete facilities for disposal. In such cases we have consulted the W a s t e M a n a g e m e n t P a n e l , w h i c h has a p p r o v e d of a "Special Disposal", specifying the method to be used and the location. The necessity for a Special Disposal is likely to a r i s e b e c a u s e some p a r t i c u l a r object raises specific problems. Because it is a single item (rather than a class of items with a range of characteristics) it is possible to obtain a good deal of information about it, and hence to assess hazards rather accurately. In these circumstances "safety factors", applied because of ignorance, are not so necessary.

This S i t u a t i o n can be i l l u s t r a t e d from the d i s p o s a l of a reactor calandria. To maintain our normal standards it would be necessary to use a very large concrete-lined pit (similar to our e m e r g e n c y pits). However it is possible to make an estimate of the amount and nature of the radionuclides likely to be in the structure of the calandria before it is removed from the reactor, and to visualise the corrosion processes that could release this material to the environment. It might be found on removal from the reactor that decontami­nation of the surfaces would be desirable, but this would not be an insurmountable p i u b l e m . With this k n o w l e d g e it can be seen that a calandria can be buried in the sand provided that it is above the level of the water table and the radiation f i e l d at the g r o u n d s u r f a c e a f t e r burial does not exceed a level specified by the Waste Management Panel.

2. Liquid Wastes

Liquid disposals consist mainly of water from the fuel storage bays, which is pumped into Reactor Pit 2, and "chemical" Wastes W h i c h go into the C h e m i c a l Pits (See p . 7 - 9 ) .

Before ion exchange units were installed to clean up the fuel b a y w a t e r the a m o u n t of active liquid pumped to the disposal area was usually 200-500 m 3 / d a y . The installation of ion exchangers in 1962 led to a decrease in volume and a very marked decrease in activity discharged (Table I).

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TABLE I

DISPOSAL OF SOLUBLE WASTES TO AREA A

Volume (m 3/month)

Soluble 3-emitters (Ci/month)

Mean Range Mean Range

1956-57

1966, Jan-June

1.1x10* 1.8xl0 3 - 4.5X101*

2.1xl0 3 1.8xl0 3 - 2.5xl0 3

80 25 - 220

1.6 1.1 - 2.6

The volume discharged was reduced by a factor of 5 and the amnnnt nf s o l u b l e a c t i v e m a t e r i a l fell by a f a c t o r of 50. The question arises - is it necessary or desirable to continue to use Reactor Pit 2 for such disposals?

More than 12 000 Ci of soluble 3-emitters have been discharged to the pit, most of which has either decayed or is still quite near to the pit, but leaching of this material w o u l d be d e c r e a s e d if w a t e r did not pour c o n t i n u a l l y L h i u u g h the system. However, if the effluent was not put into the pit it would have to go into the river unless a treatment p l a n t w a s i n s t a l l e d . Could the river take t h e s e w a s t e s w i t h ­out hazard?

It is apparent CTable II) that a sharp increase in solids-borne radionuclides occurred in June. This was due to the presence of a failed fuel element in the NRX storage bay. The pattern shown during 1966 is typical of the period since ion exchange started - O.b to 2 curies per month total Sr-90 and 1 to 3 curies per month of "total 3-emitters", with occasional sharp rises when unusual conditions existed. The m e a n v a l u e s for daily d i s c h a r g e s h o w n in T a b l e II give a fair picture of what can be expected on an annual basis.

The w o r k i n g l i m i t s for d i s c h a r g e s tn the r i v e r (Radiation Hazards Control Manual, 1954 Revision, Table II) are 50 mCi/day Sr-90, 4 Ci/day 3-emitters other than Sr-90, and 20 mg/day a as Pu-239. It is apparent that present average discharges to Reactor Pit 2 are at the "working limit" for Sr-90 but are well below the limit for "non- Sr-90 total 3-emitters". More "Pu" is being discharged to the pit than is cot by the w o r k i n g l i m i t s for river d i s c h a r g e imposed by the Manual, but most of the a-emitting material is actually uranium, not plutonium.

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TABLE II

DISPOSALS TO REACTOR PIT 2, 1966

Jan. Feb. Mar. Apr. May June Daily Discharge

Jan. Feb. Mar. Apr. May June Mean Range

Soluble 3 (Ci) 1.5 1.4 1.2 1.1 1.5 2.5

Solids, 0 (Ci) 1.0 2.3 0.5 0.3 0.2 10.2

133 mCi* 47-430

Sr-90 (total Ci) 1.0 1.1 1.0 0.6 0.6 4.8 50 mCi 20-160

a as Pu-239 (total,mg) 180 140 100 135 25 71 36 mg 8- 60

« This includes the S r - 9 0 .

The rate of discharge of radionuclides to the Ottawa River from all sources (including the Process Sewer and all drainage from the Disposal Areas) is shown m Table ill.

TABLE III

AVERAGE DAILY DISCHARGE OF RADIONUCLIDES FROM CRNL TO OTTAWA RIVER (ALL SOURCES) OCT. - DEC. 196E

M o n t h Total 3 Ci/day

* S r 9 0

mCi/day C s 1 3 7

mUi/day C e 1 4 "

mCi/day R u 1 0 6

mcl/day P u 2 3 9

nig/day

O c t . 6.1 5.3 3.3 2.0 2.0 2.6

NOV, 8.1 6.6 4.8 1.6 1.0 4.9

uec. 6. 0 6.8 3.2 Li • Lt 1. 0 1. S

# Corrected for decay to mid -point of 24 hr sampling period.

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The discharge of "total 3" is higher than the working level defined in the RHC Manual, hut the Sr-90 and P U - 2 3 9 figures are well within the permitted amounts. This situation has existed for some time, but has been accepted on the ground that most of the "total 3" is rather short­l i v e d m a t e r i a l o£ l o w t o x i c i t y . Thi3 c a n be s e e n to be true by adding the Sr-90, Cs-137, Ce-144 and Ru-106 figures, which come to a total of 12 to 15 mCi per day, or less than 2% of the "total 8". Nevertheless it is clear that the addition of the active material now being discharged to Reactor Pit 2 to the present direct discharge to the river would violate the existing "working limits". It must be remembered that these working limits are set by executive action and can be varied provided that they ensure compliance with the letter and spirit of the ICRP recommendations.

If we assume a 50% increase in present annual average discharges through the pipeline, and a similar increase in direct discharges, the d a i l y t o t a l s would he

Total Sr-90 - 56 mCi T o t a l e-emitters - 10 Ci

as Pu-239 - 39 mg

A s s u m i n g an a v e r a g e river f l o w of 4.55 x 1 0 1 3 m l / d a y and complete mixing before arrival at a town water supply in­take, the concentrations at the intake would be 2 x 10 " 9 uCi/ml for Sr-90. 2 x 1 0 - 7 uCi/ml for "total B" and 1 0 " 1 0 uCi*/ml for "Pu-239". The MPCiesh occ , divided by 10, for each of these is 4 x 10" 7, 2 x 1 0 - 6 and 5 x 10" 6. Such a level of discharge made directly to the river would therefore add up as follows:

2 x 10" 9 2 x 10" 7 1 0 " 1 0

4 x 10'' + 2 x 1 0 _ b + 5 x 10" 6 x M P Cw(population)

= 1 x 1 0 ' 1 x M P C W p

Thus, if all these wastes were discharged to the river, rather than putting part of them into the ground, the operation would still be within the ICRP maximum permissible l i m i t s by a f a c t o r of ten.

To determine the significance of this figure, several points require consideration:

S p e c i f i c a c t i v i t y n f P n _ ? 3 Q = <52 m f i / g .

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1. The ICRP recommendations for maximum permissible concentrations are set to ensure that no overt damage occurs - they are not "danger levels". However it is recommended that exposures be kept as far below the maximum as may be practicable.

2. Laws and codes of practice accept the ICRP recom­mendations as legal limits.

3. In calculating the concentrations of radionuclides in river water it is assumed that there is no removal between the point of discharge and the point of consumption. Particulate material would in fact be deposited and adsorp­tion would occur on sedimenting material. Adsorption would also occur on the river bottom, on water pipes and in filtration systems. It was a l s o a s s u m e d that a 50% i n c r e a s e in discharge would take place. This seems unlikely, and would be detected immediately by the monitoring system.

4. The major portion of the fraction of the MPC W comes from the "8-emitters other than Sr-90". Much of this material would decay between the point of discharge and the point of water usage. No quantitative estimate of these factors can be given.

b. Sampling Of the river by G o v e r n m e n t d e p a r t m e n t s has nearly always shown that the addition of radioactive material to the river at CRNL does not add significantly to the amount of a c t i v i t y a l r e a d y in the w a t e r . A m a r k e d i n c r e a s e in the discharge would change this situation. This would not be good for public relations, even though no hazard could be demonstrated. If weapons testing remains at a low level the decrease in fission product activity in river water due to fallout will tend to make the CRNL effluent more detectable.

If we continue to assume a 5 0 % i n c r e a s e in dis charge, (the effluent received at present by Reactor Pit 2 being assumed discharged to the river) the "total 6 without 3 r - 9 0 " w o u l d i n c r e a s e from 6.7 Ci to about ID H i / d a y , but Sr-90 would increase from 6 mCi to 80 mCi and the Cs-137 from 4 mCi to 50 mCi. It is the Sr-90 and Cs-137 that are m e a s u r e d hy DNHW, who would note a very large increase, although, as previously shown, it could not be said to be hazardous.

ACKNOWLEDGEMENTS

I w i s h to e x p r e s s m y t h a n k s to D. WatSOn, M.H. Thomas, L.C. Watson, I.L. Ophel, P.J. Barry, W.F. Merritt and A.E. Russell for comments, criticisms and data used in preparation of this report.

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BIBLIOGRAPHY

L. Ophel and C.D. Fraser. CRHP-709 (1957). The Chalk River Liquid Disposal Area, 1956.

J. Parsons. AECL-1038 (i960). Soil and Ground-Water Investigations in Lower Perch Lake Basin.

J. Parsons. AECL-1325 (1961). Investigating the Migration of Fission Products from High-Ionic Liquids Deposited in Soil.

J. Parsons. AECL-1561 (1962). The Liquid Dis­posal Area.