NEWS OF THE WEEK
NUCLEAR POWER: Extent of Soviet accident uncertain Detailed, official information about the Chernobyl nuclear power-plant disaster as of late last week remained wrapped in the Soviet Union's usual shroud of secrecy. But there seems to be no doubt that it is the worst accident in the 43-year history of nuclear power. However, the long-term health and environmental effects of the disaster, not to mention the political, economic, and nuclear industry repercussions, still are uncertain. The accident, which U.S. officials said may have begun as early as Friday, April 25, was not disclosed by the Soviet Union until the following Monday, after higher-thannormal levels of radiation were detected in the atmosphere over four Scandinavian countries. Health officials in those countries said they considered those levels to be harmless. Experts around the world trying to assess the magnitude of the accident last week were confronted with tight-lipped Soviet officials and conflicting reports of deaths, radioactive contamination, and a possible meltdown of the reactor core. The Soviets were saying that only two persons had died and 197 had been hospitalized, with 49 of them being discharged from the hospital after a medical examination. But unofficial reports claimed the death toll was much higher. Soviet officials said repeatedly that western news reports exaggerated the seriousness of the disaster. At press time, the Soviet Union said the graphite fire at the nuclear plant had been extinguished, but that could not be confirmed independently. Earlier, satellite photos of the plant showed two hot spots, suggesting that a second unit might be overheating. Speculation on the cause and course of the accident flourished in 4
May 5, 1986C&EN
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fmm? the near-absence of reliable information. But some basic facts were available. For example, the accident occurred at the Chernobyl plant's unit No. 4, which began operating in 1983. The 1000-MW reactor, like the plant's other three operating units, uses uranium dioxide as the fuel, light water as the coolant, and graphite as the moderator. The reactor consists of a 1000-ton pile of graphite bricks with 1693 narrow channels running throughout. Those channels house the fuel rods and allow coolant to flow past them. The fuel pellets, which consist of uranium-238 enriched with about 2% uranium-235, are encased inside tubes made of zircaloy, a zirconiumniobium alloy. From interviews with various sources, C&EN has pieced together a scenario of what might have happened, although uncertainties abound. The initiating event could have been a loss of coolant. With no water to carry away the tremendous heat produced by the fissioning uranium atoms, the fuel rods would have heated up, melting the zircaloy
cladding and releasing volatile fission products. At higher temperatures, the uranium dioxide would begin to melt. According to Lawrence M. Grossman, a nuclear engineer at the University of California, Berkeley, the molten zirconium alloy could react explosively with residual water or steam to form hydrogen gas. Such an explosion could rupture the metallic skin around the graphite, exposing it to air. The heat from the molten fuel could ignite the graphite, starting a fire. It would be "just like a charcoal burner/' comments another nuclear engineer. Some experts also speculated that the graphite, heated by the melting fuel rods, could react with water (steam) to produce explosive gases such as hydrogen. But Grossman believes that reaction requires much higher temperatures than the zircaloy-water reaction. Satellite photos obtained by the U.S. and a photo shown on Soviet television indicated that an explosion apparently destroyed the roof of the reactor building. Experts were divided over whether a meltdown of the reactor's core actually had occurred. Some claimed that a graphite fire could have started without a meltdown. They speculated that the accident might have been sparked during a procedure that must be performed periodically with graphite-moderated reactors. That procedure involves allowing the graphite to heat up beyond its normal temperature to release energy accumulated as a result of distortions to its crystal lattice caused by high-energy neutrons. According to nuclear physicist D. Allan Bromley of Yale University, the Soviet technicians might have been caught in a "runaway situation" with the graphite temperature rising too quickly to control.
The amount of radiation released by the devastated reactor is still unknown. By midweek, the cloud of radioactive debris had been detected in several European countries. At the same time, reports from Scandinavia indicated that radiation levels there were declining significantly. In Sweden, some 700 miles from the Soviet reactor, at least 20 radioisotopes were detected in the air, according to Ronny O. Bergman, who directs research at the Swedish National Defense Research Institute's radiobiology division. The isotopes included iodine-131 and other iodine isotopes (which formed the bulk of the fallout), and radioisotopes of cesium, xenon, krypton, molybdenum, and neptunium. Radiation levels in some parts of Sweden had climbed to 10 to 20 times higher than background, he says. From the quantity of radioactive debris that has been detected wafting across Europe and Scandinavia, nuclear specialists contacted by C&EN have inferred "a pretty massive release" at the reactor site. The Chernobyl reactor, unlike U.S. nuclear reactors used solely for commercial power production, is not shielded from the environment by containment structures. It is located about 80 miles from Kiev, a major urban center. U.S. officials have suggested that a containment dome might have stemmed the dispersal of radioactive debris into the environment. Grossman, for one, believes that building large power reactors in urban areas without containment is "very irresponsible." The Soviet Union, which has more than a dozen other power plants containing graphite-moderated, water-cooled reactors, seems to favor this design. Two of the reactor's selling points are that it uses lightly enriched uranium and can generate electricity and produce weapons-grade plutonium at the same time. But some analysts think the Soviet Union's dependence on those reactors may be at an end. "I can't see that there'll be much future for the graphite-moderated reactor in the Soviet Union," comments Grossman. "I think it's probably going to be kaput." D
Waste site problems probed, solutions offered A report on 10 hazardous waste facilities by an independent study group details differences in their quality and management that could d e t e r m i n e how effectively each might be handling wastes. The study by the Council on Economic Priorities concludes that hazardous waste generators should be careful about where they send their wastes. They should avoid using cost and the proximity of the site as the sole criteria in their decisions. CEP, a 16 year old, independent, nonprofit research organization based in New York City that emphasizes studies of environmental and corporate responsibility, chose the eight largest firms that operate hazardous waste sites around the U.S. and then chose 10 sites run by those firms for evaluation based on location and their ability to handle and dispose of wastes. Using its own criteria, CEP determined that most of the sites are poor places to send hazardous wastes. The worstrated site is in Williamsburg, Ohio, and the best-rated is in Clive, Utah. CEP concludes that a "toxic-waste
shell game" is being played, with the Environmental Protection Agency moving hazardous wastes from Superfund cleanup activities "to operating sites that use the same inadequate technology as the most dangerous toxic waste dumps in the country." That view is bolstered by Rep. James J. Florio (D.-N.J.), who spoke at a press conference held in conjunction with release of the CEP report. He says, "The long-term solution to the Superfund shell game is the permanent destruction or immobilization of toxic wastes to eliminate toxic hazards altogether." The technology for that solution, Florio says, is already available. The report, CEP says, does more than just complain about the quality of hazardous waste sites; it offers a number of recommendations for improving the management and technical quality of the sites for consideration by both EPA and the managers and owners of the sites. Copies of the report are available from the Council on Economic Priorities, 30 Irving Place, New York, N.Y. 10003, for $34.94 plus $2.50 for postage and handling. D
Bonner meets with U.S. scientists at NAS, AAAS The Soviets have taken steps against many dissidents, but in the past decade two cases—both i n v o l v i n g scientists—have aroused world concern such as no others: physicist and human rights activist Andrei Sakharov, and computer scientist and Jewish-emigration activist Anatoly Shcharansky. Now the plight of Soviet dissidents is again being brought strongly before U.S. scientific and political leaders by two visitors. Yelena Bonner, Sakharov's wife, last week visited Washington, D.C. She met leading scientists and officials of a number of scientific societies at the annual meeting of the National Academy of Sciences and at the American Association for the Advancement of Science. And Shcharansky, released from prison and permitted to go to Israel in February (C&EN, Feb. 17, page 7), will visit the U.S. next week to meet
Bonner: disinformation campaign May 5, 1986 C&EN
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