A military tank that will be used to clear rubble from the Fukushima nuclear… (Takehiko Kobayashi / Yomiuri…)
Although officials of the U.S. Nuclear Regulatory Commission said Monday that conditions at the Fukushima Daiichi nuclear power plant appear to have stabilized and that the containment vessels at three reactors had not been seriously breached, smoke was reported rising from two reactors Monday evening.
The cause of the smoke was unknown, however, and it did not appear to be associated with a radiation spike.
The executive director of the NRC, Bill Borchardt, said Monday 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 have suffered some core damage but do not appear to be leaking significant quantities of radiation.
Photos: Japan grapples with crisis
"I say optimistically that things appear to be on the verge of stabilizing," he said.
Workers on site have been pouring massive amounts of seawater onto the reactors and spent fuel pools in an effort to keep them cool, but Monday evening white smoke was seen rising from reactor building No. 2 and gray smoke from reactor building No. 3. In the latter case, the smoke was thought to be coming from the building's southeastern side, where the reactor's spent fuel pool is located.
Reactors No. 2 and No. 3 have been particular concerns. 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.
Times wire services contributed to this story.