Four people were killed and seven injured Monday by sprays of superheated steam at a nuclear power plant 200 miles west of Tokyo, but officials familiar with the accident said there was no indication of a radiation leak.
A spokesman for the plant, which is located in the picturesque village of Mihama and run by Kansai Electric Power, told reporters that the accident occurred when steam spewed from a leak in a turbine building at one of the plant's reactors, with bursts of the steam reportedly reaching temperatures as high as 300 degrees Fahrenheit. The accident automatically shut the facility down.
The incident follows a number of attempted coverups, mishaps and other problems that have plagued Japanese nuclear power plants in recent years, raising concerns over the safety of the country's 52 nuclear power complexes. Japan, the world's second-largest economy, relies on nuclear power for 30 percent of its electricity.
The Japanese government launched an investigation as Prime Minister Junichiro Koizumi told reporters that "we must put all our effort into determining the cause of the accident and to ensuring safety." He added the government would respond "resolutely, after confirming the facts."
According to the Kyodo news service, the dead and injured reportedly were subcontractors preparing for a regular inspection. They were laboring under a 22-inch-wide pipe when it apparently burst.
The leak was caused by a lack of cooling water in the reactor's turbine and by metal erosion in a condenser pipe, according to Kansai Electric.
The company told reporters that the broken pipe, originally 10 millimeters thick, had eroded to a thickness of only 1.4 millimeters. The pipe had not been replaced since it was first installed 27 years ago.
"I'm sorry to have caused such trouble," Yosaku Fuji, Kansai Electric's president, said at a news conference. "I cannot find the words to say to the deceased and the bereaved family members."
In February 1991, a tube inside a steam generator at another one of the plant's reactors broke, causing 55 tons of radioactive water to leak from the main cooling system into the secondary system that powers the reactor's turbine.
During that accident, an emergency core-cooling system was activated in Japan for the first time.
The Mihama plant, located near popular beach resorts, was the first nuclear plant built by Kansai Electric. Its first reactor began service in November 1970.
The Japanese public has grown increasingly alarmed by flaws and failures at nuclear plants here. In 1999, a radiation leak caused by human error at a fuel-reprocessing plant in Tokaimura, northeast of Tokyo, killed two workers and forced the evacuation of thousands of nearby residents.
A string of safety problems and attempted coverups followed. In February, eight workers were exposed to low-level radiation at a power plant when they were accidentally sprayed with contaminated water, although the contamination levels were not considered dangerous.
[The Reuters news agency reported two other incidents at nuclear power plants in Japan on Monday. In one, Tokyo Electric Power -- Japan's biggest electricity producer -- said it had shut a nuclear power generation unit at its Fukushima-Daini plant because of a water leak. In the other, a garbage disposal site at a nuclear power plant in Shimane prefecture in western Japan caught fire, Chugoku Electric Power Co. said. The blaze was quickly extinguished.]
Special correspondent Sachiko Sakimaki contributed to this report.