The chemical that leaked at a uranium-processing plant in Oklahoma on Saturday, resulting in the death of one worker and injury to at least 32 others, breaks down on contact with moisture into a substance that is extremely dangerous even in small amounts, according to Federal officials.
The chemical, uranium hexafluoride, is a key material in the making of nuclear weapons and nuclear fuel. But company and Federal officials said the health dangers of uranium hexafluoride stem more from its chemical properties than from its radioactivity, which is slight.
The chemical leaked from a ruptured tank at the Sequoyah Fuels Corporation plant in Gore, Okla. Uranium hexafluoride is stored out of contact with moisture because the chemical reacts so strongly with it, even with minute amounts in the air.
On contact with moisture in the air, it breaks down into uranyl fluoride, a slightly radioactive uranium compound similar to the natural ore, and hydrofluoric acid, a highly corrosive chemical.
Acid Kills on Contact
The acid, which is used commercially to etch glass and clean metals, can kill almost immediately on contact and is so hazardous that a leak of as little as 9.5 ounces is dangerous at 200 feet, Federal officials say. It is one of 402 highly toxic chemicals on a list issued last month by the Environmental Protection Agency. The agency issued the list in the aftermath of the leak of methyl isocyanate in Bhopal, India, on Dec. 2, 1984, that killed more than 2,000 people and injured 200,000.
Agency data show that a leak of hydrofluoric acid is more dangerous in smaller amounts than methyl isocyanate, a pesticide component.
Ingestion of one-twentieth of an ounce of hydrofluoric acid can cause death. Contact can cause ”total destruction of the eyes,” the E.P.A. said. Inhalation causes extreme irritation of the respiratory tract. Vomiting, diarrhea and circulatory collapse are also associated with ingesting the acid.
Two Commercial Plants
About 536 million pounds of hydrofluoric acid are produced in the United States each year, but only two commercial plants make uranium hexafluoride. One is the Sequoyah plant, owned by the Kerr-McGee Corporation. The other is an Allied Chemical plant in Metropolis, Ill.
The slightly radioactive chemical formed when uranium hexafluoride breaks down, uranyl fluoride, is a white dust. Although it dispersed into and near the plant Saturday, its concentrations were too low to cause any health concern, the authorities said yesterday.
”This is a chemical processing plant, not a nuclear plant,” said Dr. Edwin T. Still, director of environment and health management for Kerr-McGee.
Questions About Operation
Yesterday, as they have after other chemical accidents, experts raised questions about the operation of the Gore plant and other facilities. The questions included whether the tank was overheated and thus overpressured, whether the chemical was contaminated, whether there were appropriate gauges and alarms, how skilled the workers were, whether the equipment was properly maintained and why the tank had been overfilled.
Failures in those areas were important factors both in the accident at Bhopal and in a leak in August at another Union Carbide pesticide plant in Institute, W.Va.
Saturday’s accident, like those incidents, occurred on a weekend. Some experts are concerned about safety on weekend and overnight shifts, when senior staff may not be on duty. The 1979 Three Mile Island accident, the most serious mishap at a commercial nuclear reactor, occurred at 4 A.M.
William J. Shelley, a chemical engineer who is a consultant to Kerr-McGee, said yesterday that plant workers had occasionally discovered contamination in shipping tanks like the one that ruptured Saturday. In such a case, he said, the tanks were heated and their contents were pumped back into the plant for reprocessing.
He said, however, that he did not know if that is what plant workers were doing Saturday.
The plant makes uranium hexafluoride, the nuclear fuel component, in a complicated chemical process. The process begins with refined uranium ore which the plant receives in 55-gallon drums in the form of a yellow powder called yellowcake.
The yellowcake is dissolved in nitric acid, which is also on the E.P.A.’s list of hazardous substances, and the solution is piped to tanks in which trace metals, sand and other impurities are extracted. It is then piped to another set of tanks where the solution is heated to remove the nitric acid and to reconcentrate the uranium in orange beads of uranium trioxide.
Several other chemical changes are still needed to create uranium hexafluoride, the nuclear fuel component. First, the beads are heated to form dark brown uranium dioxide powder. That is combined with hydrofluoric acid to form uranium tetrafluoride, a bright green solid.
That is piped to a tall column where fluorine, which is also on the E.P.A.’s list, is introduced, resulting in uranium hexafluoride gas.
The gas is cooled to a liquid and then piped into cylindrical tanks for shipping. In the tanks, the liquid turns to a solid as its temperature falls naturally to below 140 degrees Fahrenheit. The material is shipped to one of three nuclear fuel production plants owned by the Department of Energy: at Oak Ridge, Tenn.; Paducah, Ky., or Portsmouth, Ohio.
Fuel for Reactors or Bombs
There, the material is turned back to a gas and filtered again and again to remove the active uranium isotope, U-235, for use as reactor fuel. Further concentration results in uranium suitable for bombs. The inactive isotope, U-238, is discarded as waste.
The uranium hexafluoride is used because it is has been the most effective medium for concentrating the radioactive material, according to Emanuel Gordon, a fuel expert at the Atomic Industrial Forum, a trade association. But a new process, using lasers, is being developed. It would bypass the need for the uranium hexafluoride and would be a lot cheaper, because it would concentrate or enrich the uranium in one step, instead of hundreds, experts say.
The nuclear and chemical industries have been among the safest of all major industries. The chemical industry has the best worker safety record in manufacturing. Dr. Still, the Kerr-McGee official, said there has not been another fatality or serious injury in the 15 years that the Gore plant has operated.Its 140 employees annually produce about 650 cylinders of either 10 tons or 14 tons each, he added.
While a few workers have been killed in research reactors, no one has been killed at a commercial reactor or previously in nuclear fuel processing plants, experts said. The main danger of radiation from nuclear power is from waste products after the fuel burned in a reactor.
It has not been established that radiation from nuclear plants has caused health problems, although several suits are pending concerning the accident at Three Mile Island.