After notching a rare victory by stopping highly radioactive water from flowing into the Pacific, workers at Japan’s flooded nuclear power complex turned to their next task: injecting nitrogen to prevent more hydrogen explosions.
Nuclear officials said there was no immediate threat of explosions like the three that rocked the Fukushima Dai-ichi plant not long after the tsunami hit on March 11, but their plans are a reminder of how much work remains to stabilise the complex.
Workers are racing to cool down the plant’s reactors, which have been overheating since power was knocked out by the 9.0 magnitude earthquake and tsunami that killed as many as 25,000 people and destroyed hundreds of miles of coastline.
Unable to restore normal cooling systems because water has damaged them and radioactivity has made conditions dangerous, workers have resorted to pumping water into the reactors and letting it gush wherever it can.
Superheated or damaged fuel rods can pull explosive hydrogen from the cooling water. If the gas were to combine with oxygen, there could be a blast, but nitrogen reduces that possibility.
Technicians began pumping nitrogen into an area around one of the plant’s six reactors early today, said Makoto Watanabe, a spokesman for Japan’s Nuclear and Industrial Safety Agency. They want to prevent hydrogen explosions that could spew radiation and damage the reactors.
An internal report from March 26 by the US Nuclear Regulatory Commission warned such explosions could occur.
The nitrogen pumping also has risks, but Japan’s nuclear agency approved it as a necessary measure to avoid danger, spokesman Hidehiko Nishiyama said. The injection will take six days and could release radioactive vapour into the environment, but residents within 12 miles of the plant have been evacuated.
The government said it might consider expanding that zone, though not because of the nitrogen injection.
An expansion might not necessarily mean the radiation that has been spewing into the air and water from the plant is getting worse.
The effects of radiation are determined by both the strength of the dose and the length of exposure, so the concern is that people farther away might start being affected as the crisis drags on.
“I would imagine residents in areas facing a possibility of long-term exposure are extremely worried,” chief cabinet secretary Yukio Edano said. “We are currently consulting with experts so that we can come up with a clear safety standard.”
Edano did not say how far the zone might be expanded or how many people might be affected. Tens of thousands have been living in shelters since the tsunami, either because they lost their homes or are in the evacuation zone or both.
Police in hard-hit Fukushima prefecture prepared to launch a full-scale search for bodies in the evacuation zone. Nearly 250 agents from the Tokyo Metropolitan Police will join local police searching for 4,200 people still missing there.
At the plant, 225km north east of Tokyo, workers finally halted a leak of highly contaminated water that raised worry about the safety of seafood caught off the coast.
But even that rare good news came with a caveat. Highly contaminated water pooling around the plant has often made it difficult or impossible for workers to access some areas because of concerns about radiation exposure.
Now that the leak has stopped, the pooling could actually get worse because water that had been going into the ocean could back up onto the grounds of the complex.