REPORTING FROM SEOUL -– In the latest sign that Japan's nuclear nightmare at the stricken Fukushima Daiichi power plant is not over, officials on Wednesday detected an ominous radioactive gas that suggested possible nuclear fission at one of the reactors.
Officials from the Tokyo Electric Power Co., or Tepco, acknowledged that they had detected signs of the gas xenon, which they said could be the byproduct of a nuclear reaction.
As a precaution, workers injected boric acid, a substance that neutralizes nuclear fission, through the facilities cooling pipes, the utility said.
The Fukushima Daiichi plant was damaged during a massive tsunami triggered by a March 11 earthquake that struck the coastal region several hundred miles northeast of Tokyo.
The rushing water sent three of the plant's reactors into meltdown, touching off fires and triggering several explosions –- prompting the evacuation of tens of thousands of nearby residents who have yet to return.
Officials on Wednesday downplayed the discovery, insisting that it had not led to a rise in the reactor's temperature, pressure or radiation levels, and that there were no radiation leaks outside the facility. They added that the presence of xenon would not delay ongoing efforts to cool the reactor.
"We have confirmed that the reactor is stable, and we don't believe this will have any impact on our future work," said Tepco spokesman Osamu Yokokura.
The latest setback is untimely for Tepco and Japanese central government officials. Prime Minister Yoshihiko Noda has in recent days lauded the nation's plan to build a nuclear power plant in Vietnam, insisting that Japan's safety standards are state of the art.
Critics have blasted the plan, citing Japan's new indecisiveness over its own future as a nuclear nation, but Noda's administration insists that the country has learned valuable lessons through its handling of the Fukushima crisis.
In recent months, Tepco claims to have made progress in stabilizing the plant. The utility says it has reached a "cold shutdown," meaning that temperatures at the reactors' cores are constant and under control. But officials warn that it might take three decades to safely decommission the facility, with plans calling for it to be encased in concrete.
Many nuclear critics insist that the disaster will continue to cause health hazards. An independent report released last month claimed that the plant had released twice as much radioactivity in the meltdown as Japanese authorities had estimated.
And utility officials raised eyebrows when they suggested a plan to build facilities in nearby towns to store radioactive waste from the cleanup effort.
There are also continued concerns about the level of radioactivity in Japan's air, water and ground. This week, the nation's forest agency tried to calm fears, announcing that levels of the toxic isotope cesium they expect to be found in cedar pollen next spring will be below the legal safety limit.
-- John M. Glionna
Photo: A girl plays at a temporary housing complex for evacuees who fled the town of Namie near the crippled nuclear plant. Credit: Kubota Yoko / Reuters