Nuclear reaction brought under control at Japanese uranium plant

Residents who live within a 10-kilometer radius of the plant were advised to stay in doors

October 1, 1999
Web posted at: 10:48 a.m. HKT (0248 GMT)

In this story: U.S. working with Japan on response Earlier accident in same area RELATED STORIES, SITES

TOKAIMURA, Japan (CNN) -- Radiation levels dropped back to normal as Japanese engineers stopped a chain reaction inside a uranium processing plant on Friday, raising hope that Japan's worst-ever nuclear disaster could be on the verge of ending.

Before dawn, workers drained coolant water from a highly-radioactive tank at the JCO Co. plant in Tokaimura, about 120 kilometers (70 miles) northeast of Tokyo. They hoped that by removing the water -- which magnifies a nuclear reaction when it comes in contact with uranium -- they could hamper or even stop the reaction.

Radiation containment levels immediately plummeted to a quarter of what they measured before the water was drained and soon reached what officials said were near-normal levels.

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Sato Kazao, the chairman of the security committee, announced the end to the reaction around 9:30 a.m. Friday (8:30 p.m. ET Thursday).

"For now, the nuclear chain reaction has ended," he told reporters. "This is a very important first step in the process of clearing up this accident."

The reaction started when workers mixed too much uranium with nitric acid in a storage tank on Thursday, officials for the JCO Co. plant said.

The officials said 16 kilograms (35 pounds), instead of 2.4 kilograms (5 pounds), were used.

Rescue officials said at least 39 people were suffering from radiation exposure in Tokaimura, including two workers who were in critical condition. Three paramedics who treated the workers were also found to be contaminated and were hospitalized.

Local officials told residents within a 10-kilometer (six-mile) radius of the plant to stay in their homes with windows and vents closed for a second day Friday. Schools and transportation services in the region were shut down.

More than 300,000 people have been affected by the order. About 150 people were evacuated from the immediate vicinity of the plant, one of 15 nuclear-related plants in Tokaimura.

The governor of the local Ibaraki Prefecture, Masaru Hashimoto, said Friday that authorities were considering enlarging the evacuation area from a 350-meter (380-yard) radius around the plant to a 500-meter (550-yard) radius.

Local officials said radiation levels had been as high as 10,000 times above normal shortly after the accident.

Transportation services and schools in the region were shut down due to the nuclear accident

U.S. officials told CNN that the State Department and Department of Energy are working closely with the government of Japan on the response to the accident.

Nuclear experts from the Energy Department are in contact with Japanese energy and emergency response officials, and U.S. Embassy officials in Japan are helping to coordinate any additional U.S. assistance.

Japanese Chief Cabinet Secretary Hiromu Nonaka said late Thursday that there was "strong possibility" of a "criticality incident" -- meaning the point at which a nuclear chain reaction becomes self-sustaining.

Nonaka said that the accident could be the worst in Japan's history.

The workers at the plant reported seeing a blue light, and then they became ill. They were first taken to a local hospital, and later flown to a hospital that specializes in radiation sickness.

Hisashi Ouchi, 35, and Masato Shinohara, 39, were listed in critical condition, hospital officials said. The two were in a state of shock with fever and diarrhea.

Hashimoto said Friday that authorities were considering enlarging the evacuation area around the stricken plant

The accident was not the first in Tokaimura. A "very serious" fire and explosion occurred on March 11, 1997. Officials said the fire was extinguished within 16 minutes, but that some radiation escaped.

Thirty-seven workers suffered radiation poisoning in that accident.

The village of Tokaimura has a population of around 34,000 people.

The 1997 accident prompted Japanese nuclear industry trade unions to call for closer supervision of the industry.

The world's worst nuclear accident occurred April 26, 1986, when an explosion and fire at the Chernobyl power plant in Ukraine spewed radiation over much of Europe. Thirty-one people died in the immediate aftermath of the accident and hundreds of thousands were evacuated from area.

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