Work to restore electricity and crucial cooling systems at the crippled Fukushima No. 1 nuclear power plant resumed Tuesday, a day after workers were forced to evacuate when unidentified smoke spewed from reactors No. 2 and No. 3.

Firefighters sprayed a massive amount of water onto the spent nuclear fuel pool at the No. 3 reactor, while restarting similar efforts at the No. 4 reactor, according to Tokyo Electric Power Co.

Although white smoke — possibly steam — billowed continuously from the buildings housing the No. 2 and No. 3 reactors, Tepco said work could proceed as radiation levels didn’t surge at the site.

Defense Minister Toshimi Kitazawa said he believes the smoke rising from the No. 2 reactor was vapor given off by the water that has been sprayed, while the blackish smoke briefly detected Tuesday at the No. 3 reactor was likely rubble that caught fire following a rise in temperature.

Work to restore electricity resumed at 8 a.m. Tuesday.

With power restored to the No. 3 reactor, all of the plant’s six reactors have now been hooked up so that key equipment can be restarted, including ventilation systems to filter radioactive substances from the air and gauges in the control room.

Workers still need to check the condition of each piece of equipment before feeding the power in, the nuclear safety agency said.

Tepco hopes to restore power to key equipment, including data measuring devices, and functions by Wednesday for the No. 1 and 2 reactors and by Thursday for the No. 3 and 4 reactors, Hidehiko Nishiyama, a spokesman for the Nuclear and Industrial Safety Agency, said.

The March 11 quake and ensuing tsunami knocked out power at the plant, causing cooling system failures at the No. 1, 2 and 3 reactors, resulting in their apparent partial core meltdowns.

The pools storing spent nuclear fuel outside the reactors at the No. 2, 3 and 4 units have all lost their cooling functions, requiring coolant water to be pumped in, while hydrogen explosions have blown off the roofs and upper walls of the buildings housing the No. 1, 3 and 4 units.

Tepco said access to electricity has been confirmed at reactor No. 2, and workers were checking the soundness of its utilities, including cooling pumps and other key safety equipment. However, the electrical connection from reactor No. 2 to the adjacent No. 1 had not been confirmed.

The No. 2 reactor was the first of the six to have its power center re-connected Sunday from cables Tepco laid outside the plant.

Reactor No. 4 had electricity access restored at 10:35 a.m. Tuesday, and was also undergoing utility checks. Work was also being done to connect electricity between reactors 4 and 3, Tepco said.

Regarding reactors 5 and 6, Tepco said work was ongoing to connect pipes to outside electrical supplies to pump in seawater to its circulation system, and that the operation should be completed Wednesday.

Information from Kyodo added

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