One answer to radioactive waste problem: melt it into glass
Melting hundred-ton chunks of earth into massive monoliths of obsidian glass -- this capability has been developed and demonstrated by scientists at Battelle's Pacific Northwest Laboratories here with Department of Energy (DOE) funding. The primary purpose of this raw application of power is to immobilize radioactive wastes, which until 1970 were somewhat cavalierly dumped into trenches and covered with dirt on federal reservations here and in other parts of the country.Skip to next paragraph
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The radioactive material involved is transuranic (TRU) waste, which is not highly radioactive but is contaminated with long-lived elements that must be isolated from the environment for thousands of years. At Hanford, there are 100,000 cubic meters of this material, and DOE is trying to figure out what to do with it.
The Battelle approach is simple, if somewhat mind-boggling. It is called in situ vitrification, or ISV. Project manager Vincent FitzPatrick explains, ``Essentially, we're producing obsidian the same way that Mother Nature does.''
First, long rods of molybdenum metal are inserted in four holes drilled in the ground. The rods are connected to a massive electrical power supply in a large trailer. Next, two shallow trenches are dug to form an ``X'' connecting the rods. These are filled with a mixture of glass fragments and graphite. A special stainless steel hood is placed over the area, and pipes leading from this hood are connected to a second trailer. Finally, someone turns the switch that begins pouring electrical power into the ground.
The glass frit and graphite in the ``X'' provide an electrical path for the current. This heats the soil, sand, gravel, and rocks to 1,100 to 1,600 degrees C. (2,000 to 2,900 degrees F.), at which point they melt. This man-made lava conducts electricity readily. So the molten area grows as long as power is applied.
The full-scale system now being tested consumes about the same amount of electricity as an average midtown hotel -- or 3,750 kilowatts. And in about 100 hours it can form a 350-ton glass block, which then takes six months to cool.
As the dirt and rock melt, organic material is turned to gas, which burns as it contacts the air. That is why the hood must be made of stainless steel. It collects the burning gases and pipes them through an elaborate air filtration system, removing the minute quantities of radioactive particles that also are released.
Since 1980, when the idea originated, the process has gone through 21 engineering-scale tests and seven pilot-scale tests. The first full-scale burn was made last December, and the researchers are still waiting for it to completely cool before examining the glass. Large tests using radio active material will take place in 1986 and 1987.
``After that we will be pretty certain of the technology,'' comments Jerry White, who directs the waste-management program for DOE at Hanford.
The tests that have been done so far have proven that the glass created in this fashion is two times stronger than reinforced concrete and as durable as granite. Tests with plutonium-contaminated soils have also demonstrated that over 99 percent of the radioactive material is captured by the glass, reports FitzPatrick. As a result, estimates of the potential radiological exposures to a human in the glassified-waste disposal areas would be a thousandth of the percent of those resulting from intrusion into untreated areas, Battelle calculates.
While Mr. White is optimistic that this technology will have an important place in DOE's waste-disposal program, he cautions that it is unlikely to be used wholesale. Rather, he sees it as ``a great hole card, something we will be able to use when we need additional assurance.''
While ISV would be less expensive and cause less radiation exposure than digging up old TRU wastes, casting them in glass, and shipping them to an underground repository, it isn't exactly cheap. Battelle estimates costs would range from $125 to $250 a cubic yard (in 1982 dollars), depending on electricity costs and soil conditions.
A lower-cost alternative is to cover the trenches with concrete slabs to prevent human, animal, and plant intrusions into the contaminated soils. The Department of Energy plans to issue an environmental impact statement next February, covering a range of alternatives. After that a decision will be made. Meanwhile, enthusiastic Battelle researchers are trying to figure out other ways they can employ their obsidian-making process. A natural extension would be to use it to clean up toxic chemical dumps. The lavalike conditions the process creates destroy most organic chemicals, but dangerous elemental substances like heavy metals are largely retained in the melt.
``It's certainly intriguing,'' comments Glen Sjoblom of the Office of Air and Radiation at the Environmental Protection Agency. But many landfills already have problems with underground fires, he points out, so applying large amounts of current might not be a good idea.
Another possible use, suggests FitzPatrick, is to provide footings for buildings, bridges, pipelines, and similar structures in remote areas like Alaska -- or even the moon. In Alaska, he notes, concrete can cost up to $600 a yard; a large portable generator, it is estimated, can make glass for less than half that cost.