After notching a rare victory by stopping highly radioactive water from flowing into the Pacific, workers at Japan's flooded nuclear power complex on April 7 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 on March 11, 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 (kilometers) 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 Thursday, 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, AP reports.