Two scientists fear that buried radioactive fuel might explode
Two scientists fear that buried radioactive fuel might explode
Ever since the nuclear power industry was born during the late 1950s, scientists have debated the thorny question of how to get rid of the dangerous radioactive byproducts that the electrical-generating plants produce. Proposed solutions have included shooting nuclear waste into space or burying it under ocean floors. But most industrialized nations have concluded that deep underground storage is the answer. Over thousands of years, proponents of the idea claim, buried nuclear waste would gradually lose its radioactive sting while posing little risk to the environment. Now, physicists at the U.S. National Laboratory in Los Alamos, N.M., have challenged those comfortable assumptions by suggesting that in certain circumstances radioactive waste leaking from corroded containers could begin a fission process, which in turn might trigger small-scale nuclear explosions. The theory, which became public last week, ignited a bitter controversy inside the highly regarded Los Alamos laboratory—and provided anti-nuclear campaigners with new ammunition at a time when both Canada and the United States are considering proposals to begin storing nuclear waste in sub-surface vaults.
Some environmentalists speculated that the controversial theory could doom Washington’s plan—bitterly opposed by the state of Nevada—to start burying nuclear waste under Yucca Mountain, 160 km northwest of Las Vegas, by the year 2010. In Canada, where the federally run Atomic Energy of Canada Ltd. is currently trying to drum up support for a proposal to bury nuclear waste at a yet-to-bechosen site, officials insisted that in the proposed Canadian storage system there was virtually no risk of underground nuclear blasts. Declared Ken Dormuth, director of AECL’s waste management program: “Our scientists can’t see any way it could happen.”
But many environmentalists said that the nuclear blast theory only served to under-
score the many dangers associated with underground storage, including the risk of radioactive waste leaking into the water table and thus endangering the environment and human lives for generations to come. “Over a period of thousands of years,” said Steve Shallhorn, a Torontobased spokesman for Greenpeace Canada, “the risk of
leakage and catastrophe is far too high.”
The alarming notion that buried waste might be capable of causing underground nuclear blasts first was raised at Los Alamos last year. Charles Bowman and Francesco Venneri started with the assumption—shared by many experts—that after thousands of years of underground storage, metal corrosion could allow some radioactive plutonium to escape into surrounding rock formations. The scientists speculated that if enough waste collected in one spot, neutrons—their behavior altered by their passage through surrounding rock—could act as missiles, splitting other atoms and initiating fission. If that process continued long enough, a nuclear blast might result. To evaluate this alarming prospect, Los Alamos officials set up review teams involving about 30 scientists, who found flaws in the theory. But because uncertainty remained, laboratory officials decided to invite a wider scientific review by making public the scientific paper in which Bowman and Venneri set out their theory.
Despite a barrage of criticism from his fellow scientists, Bowman, the main proponent of the theory, stood his ground, arguing that an initial nuclear blast might set off explosions in other batches of stored waste. “I don’t know what all the consequences would be,” Bowman told Maclean’s. “But it could be pretty serious.” Some critics of Bowman’s theory noted that it was in his interest to find fault with the idea of underground storage. The reason: Bowman’s job at Los Alamos is to de-
sign an alternative system in which particle accelerators would be used to transform radioactive waste into safer materials. Other Los Alamos scientists insisted that the nuclear explosion theory was so seriously riddled with scientific errors that it simply could not be valid. “I feel personally embarrassed,” said Jas Mercer-Smith, leader of Los Alamos’s thermonuclear weapons design team, “because this theory is going to make people think we at Los Alamos are all idiots.”
The controversial theory was another blow to the Yucca Mountain storage plan, which is already under fierce attack by the state of Nevada. Public opinion polls have shown that about 80 per cent of Nevadans oppose the plan, and the state’s Democratic Party administration has vowed to take Washington to court rather than see nuclear waste stored under the mountain. “There are no nuclear reactors in Nevada,” says Robert Loux, executive director of the Nevada Agency for Nuclear Projects, “and we resent the idea of being used as a disposal site for an industry based elsewhere in the country.” Moreover, environmentalists and other critics point out that a history of volcanic and earthquake activity in the area makes Yucca Mountain a poor choice for a nuclear waste site. “Washington has consistently attempted to skew research results to make the site look suitable,” says Loux. “Nevada is simply not going to stand for this. There is no trust here in the federal government” Bowman’s theory could also add to public unease over the idea of burying nuclear waste
deep within the Canadian Shield—the mantle of ancient rock that covers most of the eastern and central Canadian landmass. A proposal to do precisely that was unveiled last November by AECL and Ontario Hydro, the publicly owned provincial utility that operates 20 of Canada’s 22 power-generating CANDU reactors. No sites have been proposed, but AECL officials are in the midst of a cross-country tour aimed at making Canadians aware of the underground storage plan that is based on 15 years of research. Scientists at AECL laboratories near Pinawa, Man., 100 km east of Winnipeg, have studied such matters as the action of radioactive material on rock and the corrosive characteristics of metals. As well, technicians working in underground chambers sunk
in the local granite about 15 km north of Pinawa are assessing drilling techniques and evaluating materials that can best protect stored radioactive waste.
According to Dormuth, the exhaustive research has enabled AECL to propose a storage system that would be one of the best—and safest—in the world. In the proposed system, a network of tunnels and storage chambers would be carved out of granite at depths that could extend to more than 3,000 feet below the Earth’s surface. Nuclear waste sealed in titanium or copper canisters would be surrounded by buffer materials such as a clayand-sand mixture. They then could be entombed in vertical boreholes sunk beneath the floor of the chambers. Once a section of
the underground depository was filled with canisters, concrete and earth backfill would be used to seal the chambers. Backers of the plan say that the Canadian system is superior to the U.S. plan because rock in the Canadian Shield is less fractured and less porous than the Yucca Mountain formations—making it harder for water to reach and corrode the storage canisters. Says Dormuth: “We’ve come to the conclusion that disposal of nuclear waste in the Canadian Shield would be safe. The risks are very small.”
A full-scale study of the Canadian plan, including public hearings, is expected to be launched later this year or early in 1996 by the federal Environmental Assessment Agency. Only if Ottawa approves would a search for likely sites in the Canadian Shield be launched—and that process, say AECL officials, could take another 20 years. Under that timetable, officials say that underground storage in Canada could not begin until the year 2025—at the earliest.
While the AECL plan is designed to deal only with nuclear waste generated by Canadian nuclear power plants—about 16,500 tons have been produced so far—some environmentalists suspect that Ottawa may have other material in mind. While the Yucca Mountain repository, too, is designed for the storage of commercially generated nuclear waste, Washington is faced with the problem of disposing of more than 55 tons of weapons-grade plutonium left over from the Cold War. Last year, AECL suggested that, for a fee, Canada’s CANDU reactors could safely dispose of the plutonium by burning it as fuel. That suggestion, which is being studied by the U.S. energy department, angered environmentalists who pointed to the hazards involved in transporting highly radioactive plutonium around the country. And some environmentalists fear that Ottawa might someday be pressured into storing U.S. nuclear waste in the Canadian Shield. Says Greenpeace’s Shallhom: “I think Canada might be a little bit of a naive boy scout in its willingness to take other people’s nuclear waste.”
While controversy swirled around Bowman’s theory, nuclear experts and geologists agreed that he had raised at least one valid point: in considering any plan for underground nuclear waste disposal, the issue of criticality—the point at which a fissile material sets off a chain reaction—must be considered. AECL officials insist that the issue has been studied intensively—and that the risk of nuclear reactions, or explosions, is remote in the Canadian plan. Said Les Shemilt, a professor emeritus of chemical engineering at McMaster University in Hamilton, who is chairman of AECL’s technical advisory committee on waste dispoal: “I find it impossible to think of processes by which anything approaching criticality could occur.” Yet the shock waves from Bowman’s disturbing theory are likely to reverberate for some time, adding to the difficulties faced by officials as they struggle to win public approval for the idea of sealing toxic and radioactive substances in the bosom of the planet. □
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