Work to restore power and key cooling functions to the troubled reactors at the quake-hit Fukushima Daiichi nuclear power plant was marred Monday by smoke that rose from the buildings housing the No. 2 and No. 3 reactors, the plant operator said.
Tokyo Electric Power Co. and the government's nuclear safety agency said operations to revive power systems and spray massive coolant water onto overheating spent nuclear fuel pools will likely resume Tuesday after the utility observes the situation at the site.
TEPCO said it had briefly evacuated its workers after grayish and blackish smoke was seen at the southeast of the No. 3 reactor building around 3:55 p.m. above a pool storing spent nuclear fuel, though a blast was not heard.
The smoke stopped after 6 p.m., but TEPCO subsequently found that white smoke was rising through a crack in the roof of the building that houses the No. 2 reactor at around 6:20 p.m. The utility said later the smoke was believed to be steam, not from the reactor's core or spent fuel pool.
Firefighters and the Self-Defense Forces will prepare for the resumption of water-dousing operations Tuesday morning, the agency said. Three trucks with a concrete squeeze pump and a 50-meter arm provided by private firms will join the mission to pour water from a higher point.
The Nuclear and Industrial Safety Agency said no injuries were confirmed in the incidents. Radiation levels at the plant briefly increased after white smoke was detected from the No. 2 reactor, but later fell.
Chief Cabinet Secretary Yukio Edano told a press conference that ''no problems had arisen'' with regard to the reactors and radiation levels after the smoke was detected.
Hidehiko Nishiyama, a spokesman for the nuclear safety agency, said the causes of the smoke billowing from the No. 2 and No. 3 reactor buildings remain unknown and that the originally scheduled work to revive power and cooling systems at the troubled reactors will be delayed by one day.
As the No. 3 reactor remains without power, smoke was not apparently triggered by an electricity leak or short-circuiting, Nishiyama said.
Following a magnitude 9.0 quake and ensuing tsunami on March 11, the cooling functions failed at the No. 1, No. 2 and No. 3 reactors and their cores are believed to have partially melted.
At present, coolant water is being pumped into the three reactors and the pools for spent nuclear fuel rods at the No. 2, No. 3 and No. 4 units. The roofs and upper walls of the buildings that house the No. 1, No. 3 and No. 4 reactors have been blown away by hydrogen explosions.
Before the smoke was detected, external power had reached the power-receiving facilities of the No. 2 and No. 5 reactors on Sunday, clearing the way for the plant operator to restore systems to monitor radiation levels and other data, light the control rooms and cool down the reactors and their spent-fuel storage pools.
On Monday, TEPCO finished laying cables to transmit electricity to the No. 4 reactor, as a step toward resuscitating the power systems at the No. 3 and No. 4 reactors, according to the utility and the nuclear agency.
The plant operator was also trying to restore a ventilation system to filter radioactive substances from the air and some measuring equipment at the control room of the No. 2 reactor, but this mission remained uncompleted due to the temporary evacuation.
The restoration of some functions at the control room would help improve working conditions, according to the nuclear agency.
It may take more time before the vital cooling system is restored at the No. 2 reactor, the containment vessel of which suffered damage to its pressure-suppression chamber, as some replacement parts are needed for the electrical system, the agency added.
In Vienna on Monday, International Atomic Energy Agency Director General Yukiya Amano told a special meeting of its board of governors that the situation at the Fukushima plant ''remains serious, but we are starting to see some positive developments.''
Amano, who made an emergency trip to Japan last week, said the IAEA will ''continue to do everything in its power to help Japan to overcome'' the crisis at the power station on the Pacific coast of Fukushima Prefecture, around 220 kilometers northeast of Tokyo.
To facilitate the water-spraying operations at the plant, the government is also preparing SDF tanks to remove rubble emitting high-level radiation from around the reactors.
Japan's nuclear agency, meanwhile, said one of seven workers who were injured following a March 14 hydrogen explosion at the No. 3 reactor was found to have been exposed to radiation amounting to over 150 millisievert per hour.
The level is lower than the maximum limit of 250 millisievert per hour set by the health ministry for workers tackling the emergency at the Fukushima plant.
TEPCO and the nuclear agency said the height of a tsunami that submerged key functions at the Fukushima plant is believed to have reached 14 meters, much higher than the 5.7 meters that the utility had factored in before the disaster struck the power station.