Although power cables have been "restored," only the pump in reactor #5 is running on power from grid. I believe #6 is being cooled from a generator. #2 is cracked. Reactor #3 appears to be at risk. Spent fuel pool in #4 is cracked and may only be cooled via water bombardment.
Here is what Reuters reports:
Firefighters postponed spraying Japan's badly damaged nuclear reactor No. 3 with seawater on Monday after a plume of grey smoke was seen over the structure, the government says.
- Engineers have re-established power cables to all six reactors. Electricity restored at No. 2 reactor and a pump in reactor No. 5 is now running on power from grid.
- If engineers are unable to cool the reactor, the last option would be entombing the plant with concrete and sand to prevent a catastrophic radiation leak, the method used at Chernobyl in Ukraine in 1986.
Kyodo news offers more details
The smoke stopped after 6 p.m. [at reactor #3], 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....
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....
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.