Smoke rising from two of the reactors in the troubled Fukushima Daiichi nuclear plant in Japan caused alarm and abruptly halted efforts to restore power to reactors Monday afternoon.

Workers from the Tokyo Electric Power Company were evacuated midafternoon after dark-colored smoke was seen rising from reactor No. 3 above a pool storing spent nuclear rods, Kyodo News Agency reported. A few hours later, a white plume was also seen rising through a crack in the roof of the building containing reactor No. 2, according to reports.

The smoke had stopped by evening. Power company officials told local reporters that the plume from reactor No. 2 appeared to be steam.

The cause of the plumes was unknown, but they did not appear to be associated with a radiation spike.


Photos: Unrelenting crisis grips Japan

Still, officials said the interruption would delay the work to restore power to the cooling systems at the plant by a day. The smoke also caused fire officials to halt the spraying of water onto the reactors. The power company and government officials said the efforts to connect the reactors to a power source and cool them would likely resume Tuesday, according to Kyodo News Agency.

The activity came on a day when the executive director of the U.S. Nuclear Regulatory Commission, Bill Borchardt, said that the agency’s staff in Japan reported that the three reactors that had shut down following the magnitude 9.0 Tohoku earthquake 10 days ago probably had suffered some core damage but did not appear to be leaking significant quantities of radiation.

“I say optimistically that things appear to be on the verge of stabilizing,” Borchardt said.


Local officials have been struggling to restore power to the reactors to restore cooling systems and lower reactor temperatures. Power has been restored to some of the plant’s six reactors, while others remain without electricity.

Photos: Before and after earthquake satellite images

Reactors Nos. 2 and 3 have been of particular concern. The containment vessel at reactor No. 2 is thought to be cracked, while reactor No. 3 is powered by a mixed oxide fuel that contains significant quantities of highly carcinogenic plutonium.

Engineers from Tokyo Electric Power Co., which owns the plant 140 miles north of Tokyo, have brought a new power line from the nation’s electrical grid to the site and connected it to the reactor buildings. But only the cooling pumps in reactor buildings 5 and 6, which have only spent fuel pools, have been energized. The pumps have brought water temperatures in the cooling pools down to normal levels.


Company officials said damaged electrical parts in the other buildings have made it difficult to restore power in those units. The company is now bringing in replacement parts in an effort to restore power and bring cooling pumps in the other reactors back on line.

The company has also brought in a large construction device normally used to pump a cement mixture. Officials initially said they were going to use it to pump the cement mixture and water into the spent fuel pool of reactor No. 4, which is thought to have boiled dry, allowing damage to have been done to the fuel rods there. Officials later said, however, that they intended to use the device only to pump water into the pool.