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New Hope for Toxic Waste
| Article
# : |
13747 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
8 / 1988 |
3,099 Words |
| Author
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Douglas C. Comrie
Douglas C. Comrie is the president of D. Comrie Consulting
Ltd., a waste management and mine engineering company based in
Mississauga, Ontario, Canada. His work on geopolymers has
been carried out in conjunction with French chemical engineer
Joseph Davidovits. |
When nuclear plants began to dot the landscape of our planet, industry planners assumed that by the time the reactors' service lives were spent, in 25 to 35 years, the technology would exist to render them environmentally safe by disassembling or entombing them. Today, although a number of these service lives are drawing to a close, there is still debate about the selection of a suitable entombment technology. A permanent solution has yet to be accepted, and reactors remain extremely expensive and potentially dangerous to disassemble.
The entombment of a spent or damaged reactor poses severe problems, many of which are exemplified by the damaged Chernobyl reactor. After the disaster at Chernobyl, the reactor was entombed in concrete--a mixture of portland cement with sand and gravel. One of the dangers with this type of entombment involves the development of hydrothermal conditions--conditions that encourage the existence of warm, aqueous solutions. Hydrothermal solutions are created when rain, snow, or groundwater penetrate the concrete mass and are warmed by heat stored within the reactor. Over long periods of time, the reactor may actually act like a "heat engine," encouraging convection and circulation of such solutions.
Portland cement concrete does not readily tolerate hydrothermal conditions for an appreciable time; the Chernobyl concrete casing may crack and break apart in the coming years. Repeated seasonal cycles of freezing and thawing accelerate the decomposition of concrete. Of course, waterproofing compounds or waterproof barriers can be applied to prevent the penetration of water, but these will be subject to attack by chemical, solar (ultraviolet), and seasonal (freezing and thawing) conditions that will occur in the coming centuries. Unless constant surveillance and repairs are maintained for thousands of years, the leaching of irradiated concrete and the nuclear materials in the reactor may lead to sustained environmental contamination. The problems of Chernobyl are especially critical in view of the number of reactors existing around the world that must soon be decommissioned. In the United States alone, over 60 large reactors are due for decommissioning during the next decade.
The rate at which other environmental problems are mounting is also alarming. Toxic dumps are being filled at a rapid pace, with few new sites being developed. Vast acres of once-virgin land are being poisoned by abandoned mining wastes laden with heavy metals and acidic solutions. Rivers and ground water are widely threatened, and in many cases, contaminants already exceed water quality standards by several
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