Aug. 9 (Bloomberg) -- Four workers were killed by a steam leak at a nuclear-powered generating plant operated by Kansai Electric Power Co. in central Japan's Fukui prefecture, local officials and the company said. No radiation leaked from the facility, according to the central government.

The accident at the No. 3 reactor at Kansai Electric's Mihama plant happened at around 3:28 p.m. local time, said Youichi Kuroha, a spokesman at Osaka-based Kansai Electric. Fukui prefecture spokesman Akihiro Yamamoto said four workers had died, with as many as seven others injured. The four dead suffered severe burns, the Associated Press reported, citing Takanori Amimoto, an official from the Fukui state government office.

``Monitors inside and outside the reactor have registered no change,'' Japan's Ministry of Economy, Trade and Industry, which oversees the nation's nuclear industry, said in a statement. ``There is no risk of radiation in the area.''

Japanese power companies, whose reactors provide a third of the electricity in the world's second-largest economy, are trying to win back public support for nuclear energy after scandals over a lethal radiation leak, falsified safety documents and unreported cracks in nuclear plants in the past few years.

In the U.S., nuclear plants generate about a fifth of all electricity.

Maintenance Crew

The four workers killed in the Japanese accident were part of a sub-contracting crew preparing for maintenance on pipes next week. Steam escaped through a hole in the pipes that had been used in the reactor since it began operations 28 years ago. The pipes were designed to work for 30 years, Japan's NHK Television reported, citing Kansai Electric officials. The pipes carried steam heated to 140 degrees Celsius (284 degrees Fahrenheit).

The deaths were the first in Japan while a reactor was in operation, NHK reported. If researchers identify the problem as wear and tear, the accident is likely to affect maintenance of other nuclear plants, NHK said.

Prime Minister Junichiro Koizumi said a full investigation is needed to find out what happened.

Scheduled Shutdown

The leak occurred as workers were preparing to shut the reactor for scheduled maintenance, Keiji Matsueda, chief manager of operations at Kansai Electric, told reporters in Tokyo. The company, which earlier planned to close the unit for 90 days from Aug. 14, may have to extend the shutdown, he said. The reactor was last checked on July 15, 2003, Matsueda said.

Tokyo Electric Power Co., the nation's largest utility, said separately it shut down the Number 2 reactor at its Fukushima Daini nuclear power station Sunday because of a water leak.

In 1999, Japan suffered the world's worst nuclear accident since the 1986 Chernobyl disaster, when workers at a uranium processing plant northeast of Tokyo mixed a uranium solution in an open bucket, releasing radiation.

Two employees of the plant in Tokaimura, Ibaraki prefecture, run by a unit of Sumitomo Metal Mining Co., were killed and others were exposed to radiation.

Japan's government ordered Tokyo Electric to shut all its nuclear reactors and mandated safety checks at nuclear plants owned by Kansai Electric and other rivals after Tokyo Electric said in September 2002 it falsified nuclear safety documents to hide cracks.

The nuclear shutdowns forced utilities to restart oil and gas- fired plants, boosting Japan's oil imports in 2003 for the first time in six years.

Kansai Electric has three reactors, which can generate a total 1,666 megawatts of electricity, at its Mihama nuclear plant near the central Japan Sea coast. The No. 3 reactor was supplied by Mitsubishi Heavy Industries Ltd.

The No. 3 reactor was stopped automatically, while the other two reactors are still operating, the company said.

To contact the reporters on this story: Hector Forster in Tokyo at hforster@bloomberg.net; Fumishige Asano in Tokyo at fasano@bloomberg.net.

Last Updated: August 9, 2004 10:17 EDT