Four workers were killed and seven others were injured Monday when steam leaked from a nuclear reactor in Mihama, Fukui Prefecture, in Japan’s worst nuclear plant accident, rescue officials said.

According to information received by the Nuclear and Industrial Safety Agency in Tokyo, the leak took place at around 3:28 p.m. at a facility housing the turbines for the No. 3 reactor at Kansai Electric Power Co.’s Mihama Nuclear Power Plant.

Local authorities and Kepco officials said the deaths and injuries were probably due to exposure to high-temperature steam. Of the seven listed as injured, two were in serious condition, according to the Fukui Prefectural Police.

The 826,000-kilowatt reactor automatically shut down after the incident, officials at the nation’s second-largest utility said, adding they believe a lack of cooling water in the plant led to the accident.

No radiation is believed to have leaked outside the facility, and sources at the Defense Facilities Administration Agency said Fukui Prefecture officials did not see a need for Self-Defense Forces elements to be dispatched to the town to assist in disaster relief.

The accident occurred during regular maintenance in a facility housing the reactor turbines, according to Kepco. The dead and injured were all employees of Kiuchi Keisoku, a Kepco subcontractor based in Tennoji Ward, Osaka. Kepco said there were about 200 people in the facility.

The four dead were identified as Hiroya Takatori, 29, Kazutoshi Nakagawa, 41, Tomoki Iseki, 30 and Eiji Taoka, 46.

Kiuchi Keisoku officials said Kepco had asked for a regular inspection of the turbines and workers had been moving the necessary equipment into the facility when the accident occurred. Kiuchi Keisoku conducts turbine inspections at the Mihama plant once a year.

A 65-old woman who works in a cafeteria in the plant said: “Staff rushed (into the cafeteria), screaming. I put in a container all the ice I could find and gave it to them.

“I don’t know exactly what happened. This is the first time an incident like this has happened in my 14 years of work here.”

The building is where steam heated to some 200 degrees moves turbines to generate electricity. The steam is produced from secondary cooling water and is not radioactive, Kepco officials said.

The accident apparently occurred when steam leaked as a result of damage to the turbines or some other problem, the officials added. Kepco said it has found a hole in a 50-cm diameter pipe that feeds steam in the turbine facility.

Kepco President Yosaku Fuji apologized for the accident at an evening news conference, saying, “We are deeply sorry for those who have died and their families, and for causing the accident.”

He did not comment on how he would take responsibility, saying he cannot answer until the exact cause of the accident is known.

The Nuclear and Industrial Safety Agency said it would dispatch a six-member expert team to look into the accident.

Speaking to reporters at the Prime Minister’s Official Residence, Prime Minister Junichiro Koizumi said it was regrettable the accident led to many fatalities and injuries.

“I would like those concerned to fully grasp the facts and act accordingly,” he said.

The No. 3 reactor where Monday’s accident took place began commercial operations in December 1976.

In February 1991, a tube inside a steam generator at the No. 2 reactor in the same plant broke, resulting in 55 tons of radioactive water leaking from the main cooling system into the secondary system that powers the reactor’s turbines.

That accident was the first time in Japan that an emergency reactor core cooling system was activated.

Until Monday, the nation’s worst nuclear accident occurred Sept. 30, 1999, at a nuclear plant in Tokaimura, Ibaraki Prefecture. Two employees who were exposed to extremely high doses of radiation died, and 663 others were exposed to lower amounts of radiation.

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