ENVIRONMENTAL RESTORATION AT CHALK RIVER LABORATORIES 1 Background

4.

Disposal in New LLRW Facility - mined caverns

- open pit with pervious surround - engineered burial mound

Manage in Place - in situ soil mixing - cap and cover

Treat and Manage on Site - fixation/stabilization

3. ENVIRONMENTAL RESTORATION AT CHALK RIVER LABORATORIES 3.1 Background

Atomic Energy of Canada Limited (AECL) is the federal Crown Corporation responsible for research and development for the uses of nuclear energy in Canada. AECL develops and markets CANDU reactors, supplies CANDU and light water reactors (LWR) support services, develops and applies radioactive waste management and site remediation technology, and provides associated products such as research reactors and industrial accelerators.

AECL has two major research sites - Chalk River Laboratories in Ontario where

operations started in the mid-1940s, and Whiteshell Laboratories in Manitoba where operations started in the mid-1960s. The current focus of AECL's LLRW program is to make the

transition from interim storage to permanent disposal at the CRL site [16]. A complementary

program is directed as assessing the need for remedial action at old CRL storage sites dating back to the 1940s and 1950s, and implementing the required remedial activities.

Waste management practices evolved over the years of operation of nuclear facilities at CRL. Initially there were no established practices and various approaches were taken with both liquid and solid wastes. In some cases these practices, which were acceptable at the time, have led to radionuclide discharges to soil and the formation of groundwater contaminant plumes. Some specific trials were also conducted to determine the rate and extent of subsurface and ground water contamination that might result from inadvertent spills and to gain specific knowledge from wastes placed purposely in the ground. There is no danger to the general public as the specific waste sites are well within the boundaries of the laboratory, nor is there any risk to employees since the sites are well delineated with signed fences.

A strong and active hydrogeological program is in place at CRL to observe and to model radionuclide releases and to develop a thorough understanding of contaminant transport in saturated and unsaturated media. Recently, a remediation program was initiated to set priorities on the cleanup and restoration of the contaminated sites on the CRL property, to meet the environmental standards of stewardship outlined by the Federal Government. Part of the remediation program is to develop a suite of technologies that can be applied to the

removal of contaminants from soils and ground water in an efficient and cost-effective manner.

The radioisotope and fission product wastes, and associated contaminated soils, at these old sites are of relatively short half-life compared to the natural radionuclides in the Port Hope area, and other, historic wastes. Consequently, thee will be some differences in the

approaches to remedial action.

3.2 Ground water Remediation by Selective Contaminant Removal

Remediation technology for the removal of low concentrations of radionuclides, heavy metals and organics from ground water began several years ago by applying novel technology developed for radionuclide removal from waste waters. The process involved adding water soluble polymers to create macromolecules by attaching dissolved ions to the polymers. The macromolecules were then removed from solution by using cross-flow ultrafiltration. The process provided high removal efficiencies, it was highly selective in the removal of hazardous substances, and generated a minimal volume of secondary waste. Unfortunately, the

technology is generally applicable to low ionic strength waters and the presence of large concentrations of iron caused the membranes to foul rapidly.

Building on the experience gained in laboratory and field investigations, the technology to selectively remove contaminants was improved by switching to a more porous membrane and by altering the chemical treatment. By inducing precipitation and adding fine sorption materials, similar removal efficiencies were achieved without the membranes being fouled by the presence of iron while attaining low volumes of secondary waste requiring immobilization and eventual disposal. The effluent quality achievable with the process can be made to comply with drinking water standards.

The technology has been successfully demonstrated on a contaminated site at CRL and is now in routine operation. Over the past two years, more than 2 million litres of water have been treated to reduce Sr-90 concentrations from about 2,500 Bq/L to < 1 Bq/L, with typical effluent values at 3 Bq/L, well below the Canadian drinking water standard set at 10 Bq/L.

The process in place involves the sequential addition of chemicals and adsorption/ion exchange materials to remove contaminants. The combination of chemical conditioning, cross-flow microfiltration and dewatering by filter pressing is effective for treating various ground waters containing mixed wastes having diverse physical and chemical properties. The filtrate water is discharged once it meets the specified water quality. To achieve high quality water, up to three steps of chemical treatment and microfiltration may be employed to remove contaminants. The secondary waste volume is typically 1/500 the volume of the feed.

The chemical conditioning and microfiltration process has significant technical

advantages and economic benefits for site remediation. The combined action of precipitation, co-precipitation, adsorption and ion-exchange coupled with cross-flow microfiltration

effectively removes dissolved contaminants into a concentrated suspension. The direct contact of contaminants with iron and other metal precipitates provides high contaminant removal efficiencies and fast kinetics. Low cost ion exchange/adsorbent materials are utilized in a continuous operation. Less space is required than conventional systems and the use of modular construction permits flexibility and adaptability to different flow requirements as well as providing portability and ease of movement to a contaminated site. One of the features of the process is that it is sufficiently generic to permit treatment of waste solutions containing a variety of radioactive and hazardous substances.

3.3 Recent Advances

Further progress in site remediation has taken place with acidic soil leachates, generally created by oxidation and dissolution of sulfide-bearing wastes which in turn dissolve heavy metal contaminants. The application of ultrasonics after the addition of pH adjustment

chemicals, oxidants and precipitants leads to the removal of contaminants more rapidly. With subsequent separation of solids by cross-flow microfiltration and filter pressing, the overall time for processing is generally reduced by an order of magnitude. Ultrasonic mixing hi place of mechanical agitation in large tanks increases the conversion of contaminants to precipitates and affects the rate by which oxidation and ion exchange takes place. Without large tanks required for sufficient time to allow processes to take place, the use of ultrasonics permits the system to be more compact, more portable, more energy efficient and requires less capital for construction. The technology generates minimal fugitive emissions and also produces a treated effluent that meets applicable discharge limits. The technology has also been able to treat waste containing small quantities of dissolved or suspended organics.

Soil washing has been evaluated to speed up the removal of contaminants from ground water, by applying chemicals in solution directly to the soil. By stripping the contaminants from the soil, the leachate can then be treated to extract the contaminants. Application of in situ soil stripping could reduce the time required for treating contaminated ground water by eliminating the source.

Studies are underway at CRL to develop injection and recovery methods that will allow soil treatment without having to disturb the soil. A key factor is having a good understanding of the hydrogeological properties of the contaminated site to properly situate the injection and recovery wells. One of the successful materials for injection and removal of radioactivity from CRL soils is dilute ferric chloride. Other dilute solvents can also be employed and are

dependent on the contaminant to be extracted. Soil leaching tests established that the passage of five to six pore volumes of leachant solution removed close to 100% of all leachable Sr-90.

This leachate was then passed through the chemical treatment/microfiltration system to extract the leached Sr-90. Further tests are planned at other CRL contaminated sites to improve the removal of contaminants including uranium, cobalt, cesium, lead and other radionuclides and heavy metals.

There appears to be potential for application of these technologies to LLRWMO projects. An initial laboratory scale test for removal of arsenic and uranium from groundwater from historic sites in Port Hope has produced good results.

4. DECOMMISSIONING AND WASTE MANAGEMENT AT URANIUM MINE