TOKYO — After notching a rare victory by stopping highly radioactive water from flowing into the Pacific on Wednesday, 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 a massive tsunami hit last month, but their plans are a reminder of how much work remains to stabilize 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 on March 11.
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 fuel rods can pull explosive hydrogen from cooling water, so now that more water is going into the reactors to cool them down, the concern is that hydrogen levels are rising.
Technicians were expected to start pumping nitrogen into an area around one of the plant's six reactors early Thursday to counteract the hydrogen. They want to prevent hydrogen explosions at all costs because they could spew radiation and damage the reactors.
The nitrogen pumping has its risks too, but Japan's Nuclear and Industrial Safety Agency approved it as a necessary measure to avoid danger, spokesman Hidehiko Nishiyama said. The injection could release radioactive vapor into the environment, but no one is living in a 12-mile (20-kilometer) evacuation zone around the plant.
The government said Wednesday 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.