Experts Say Lapses Led to Japan's A-Plant Failure


By MATTHEW L. WALD 23 Oct 1999, © New York Times

The Japanese nuclear accident three weeks ago occurred largely because managers counted on workers to follow rules but never explained why the rules were important, three Energy Department experts said today, after touring the plant this week.

The experts told a news conference here that managers should have concentrated on providing equipment designed to make such accidents impossible.


Skeptical reports in Japan contest this view of the accident, suggesting that the plant's workers routinely took dangerous shortcuts that violated rules and were encouraged to do so by plant managers in an effort to increase productivity.

At the Japanese Embassy here, a spokesman said officials were trying to obtain a transcript of the experts' remarks and would not comment until then.

At the news conference, Frank McCoy, deputy manager of the Energy Department's Savannah River Operations Office, said that Japanese officials had performed a safety evaluation of the plant, at Tokaimura, and concluded that an accidental reaction was impossible. Based on that, the plant had no emergency plan, he said. The plant processes nuclear fuel.

Mr. McCoy said the technicians were trying to carry out a task with incorrect equipment. ''Using the system in the right way was more difficult than anyone would have desired,'' he said. Mr. McCoy and his colleagues gave a description that made the job sound like trying to bake a cake in a frying pan.

The experts, an official delegation invited by the Japanese Government, gave a detailed explanation of the accident, on Sept. 30, in which technicians brought too much uranium together in one spot and created an unintended chain reaction that continued for 17 hours. They were dissolving a powdered form of uranium with an acid and had planned to ship it to another plant for baking into solid fuel.

The workers should have stored the material in a tall column-shaped cylinder, a shape that would have prevented a critical mass from forming, said Dr. Leroy Lewis, a chemist at the Idaho National Engineering and Environmental Laboratory. But, he added, the spigot to draw liquids out of that container was about four inches off the ground, suitable for filling a low, flat pan, which is used in the normal process that involves the tank. In this case, the workers wanted to fill a taller container.

So the workers put the dissolved uranium in a second vessel, intended for another purpose entirely, the experts said. It had a spigot that was easier to use. But the vessel was circular, a shape that encourages a chain reaction. Worse, it was surrounded with a shell filled with cooling water, and the water functioned as a reflector, bouncing neutrons from the uranium back into the tank, improving the conditions for a reaction. The workers did not understand the reason behind the rules that limit the sizes of batches and containers, the experts said.

Emergency workers stopped the reaction by smashing a pipe connected to the water shell, letting the water drain.

The American approach would be to assure that there were no containers present in which material could form a critical mass, the experts said. The size and shape of such a container would vary according to the material. For the uranium that the Japanese were processing, which was 19 percent of the type that can sustain a chain reaction, the containers would have to be smaller or would have to be flat or columnlike.

The Energy Department experts said that the Tokaimura accident let out a huge shower of radiation in the form of gamma rays and neutrons, but that those emissions ended when the reaction stopped. The radioactive materials were almost entirely contained in the vessel where the reaction occurred.