A steam leak at a Japanese nuclear power plant killed at least four workers today, but officials said no radiation had escaped in the accident, the worst ever in terms of deaths at a Japanese nuclear facility.
Several others were injured, some seriously, officials said.
The incident, which took place on the anniversary of the 1945 atomic bombing of the city of Nagasaki, is certain to increase distrust of the nuclear industry among ordinary people in Japan, which depends on nuclear power for a third of its energy needs.
"Radioactive materials weren't contained in the steam that leaked out ... We've received a report that there is no impact from radiation on the surrounding environment," an official for the Nuclear and Industrial Safety Agency told a news conference.
Police said earlier that five workers had died.
The accident occurred in a building housing turbines for the Number 3 reactor at the Mihama nuclear plant in Fukui prefecture, 200 miles west of Tokyo.
Kansai Electric Power Co. Inc., which runs the plant, said it had shut the 826,000 kilowatt nuclear generation unit at the facility. The company said it was unsure when it would restart.
The accident occurred at around 3:30 p.m. (0630 GMT) just after some workers had entered the facility to take measurements ahead of a scheduled shutdown for maintenance, national broadcaster NHK reported.
The temperature of the steam that filled the room was probably about 200 degrees Celsius (390 Fahrenheit), media reports said.
The Fukui prefectural government said the cause of the accident was under investigation, but a trade ministry spokesman briefing reporters said there was no technical problem with the core nuclear reactor at the plant.
Japan's worst previous accident at a nuclear facility took place at a uranium processing plant in Tokaimura, a town north of Tokyo, on September 30th, 1999, when an uncontrolled nuclear chain reaction was triggered after three poorly trained workers were using buckets to mix nuclear fuel in a tub.
The resulting release of radiation killed two workers and forced the evacuation of thousands of nearby residents.
In a separate incident involving a nuclear facility, Tokyo Electric Power Co. (TEPCO), Japan's biggest power producer, said today that it had shut a nuclear power generation unit at its Fukushima-Daini plant due to a water leak.
TEPCO was forced to close all its 17 nuclear power plants temporarily by April 2003 after admitting that it had falsified safety documents for more than a decade, revelations that severely undermined public confidence in the nuclear industry.