Nuclear Accident Avoided at Japanese Uranium Plant

A team of Japanese engineers successfully halted a fission chain-reaction inside a uranium processing plant on Friday, a sign that Japan's worst nuclear disaster was on the verge of coming to an end.

Hundreds of residents were still being warned to remain inside their homes for the remainder of the day, to avoid any possibility of exposure to harmful radiation in the environment. Dozens, mostly workers from the plant, were treated for contamination.

Just before dawn, engineers ordered workers to drain coolant water from a highly radioactive tank at the JCO Co. plant in Tokaimura, approximately 120 km.(70 miles) northeast of Tokyo. The water magnifies a nuclear reaction when it comes in contact with uranium. Engineers hoped that removing the water would slow down or even suffocate the reaction.

Radiation containment levels immediately fell to a quarter of what they were before the draining of the coolant water and were soon at a level officails said were near normal.

Kazuo Sato, chairman of the Nuclear Power Safety Committee, announced that the reaction had ended at abot 9:30 a.m. Friday (0030 GMT). "For now, the nuclear chain reaction has ended," he claimed in an interview with reporters. "This is a very important first step in the process of clearing up this accident."

The fission reaction started when a worker skipped an integral step and mixed too much uranium with nitric acid in a storage tank on Thursday, JCO Co. officials stated Friday. They also stated that 16 kilograms (35 pounds) instead of 2.4 kilograms (5 pounds), were used.

Nuclear fission occurs when neutrons collide with uranium, causing atoms to split and release huge amounts of energy and is the principle behind the atomic bomb. Water stimulates the neutrons, spurring along the reaction.

According to rescue workers, 55 people were suffering from radiation exposure, including two workers who were in critical condition. Three paramedics who treated the workers were hospitalized after they were contaminated.

Government officials stated that Thursday's accident released a gas containing alpha, beta, and gamma radiation into the atmosphere. Levels of radiation reached 10,000 times the normal level shortly after the accident, officials said. Resident within a 10-kilometer (6-mile) radius of the plant were told to remain in their homes with windows and vents closed again on Friday. Schools and transportation services were in the region were also halted, affecting more than 300,000 people. Approximately 150 people were evacuated from the plant's immediate vicinity.

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