Workers at Japan's stricken Fukushima Daiichi nuclear power complex continued efforts to restore power to its most troubled reactors, while authorities said they would probe higher-than-permitted levels of radioactivity in nearby seawater.
White smoke continued to rise from the buildings of two of the most troubled reactors, No. 2 and No. 3, said Hidehiko Nishiyama, an official with Japan's Nuclear and Industrial Safety Agency. But he said that radioactivity levels remain stable around the plant and that work resumed on Tuesday morning to restore power to reactor Nos. 1-4.
Reports of smoke temporarily halted work Monday after recovery efforts made slow but significant progress over the weekend. Workers returned after officials found radioactivity at the site remained near lowered levels.
Restoring power could significantly help efforts to keep radioactive fuel on the site from overheating. Government officials and workers for utility Tokyo Electric Power Co. on Monday connected the No. 1 and No. 2 reactors to the grid, and efforts on Tuesday included connecting No. 3 and No. 4.
Meanwhile, the agency said it detected higher-than-permitted levels of radioactive materials in seawater near the complex, raising the possibility that contamination from the plant could spread to marine life.
The agency said there is no immediate health risk to humans, as the area around the plant had already been evacuated.
The agency, known as NISA, said that sampling conducted in waters about 100 meters south of the plant on Monday afternoon showed that the amount of iodine-131 exceeded the allowable limit by more than 126 times.
NISA said it has alerted the agriculture ministry about possible ramifications for the seafood industry.
Many steps remain before the company can turn on the all-important cooling systems at the other reactors and declare full control over the plant damaged after the March 11 earthquake.
"We aren't out of the crisis situation yet, but we are seeing a light at the end," said Prime Minister Naoto Kan on Monday.
Overall, officials expressed confidence that Japan was on the right track in putting a lid on the nuclear disaster triggered by the March 11 earthquake and tsunami that left more than 21,000 people dead or missing.
The tsunami knocked out regular backup power systems at the Fukushima Daiichi plant, which rendered the plant's cooling systems unusable. Fuel rods in use as well as spent rods in cooling pools began to heat up, triggering fires and explosions.
It took several days for the government to take effective control of the disaster, meaning that the full power of Japan's military and big-city fire departments wasn't engaged in the fight until a week after the quake.