http://www.reuters.com/article/2011/03/12/us-japan-quake-nuclear-us-analysis-idUSTRE72B04C20110312By Scott DiSavino
NEW YORK | Fri Mar 11, 2011 8:18pm EST
(Reuters) - Japanese officials may only have hours to cool reactors that have been disabled by Friday's massive earthquake and tsunami or face a nuclear meltdown.
Tokyo Electric Power Co (TEPCO) (9501.T) is racing to cool down the reactor core after a highly unusual "station blackout" -- the total loss of power necessary to keep water circulating through the plant to prevent overheating.
Daiichi Units 1, 2 and 3 reactors shut down automatically at 2:46 p.m. local time due to the earthquake. But about an hour later, the on-site diesel back-up generators also shut, leaving the reactors without alternating current (AC) power.
That caused Tepco to declare an emergency and the government to evacuate thousands of people from near the plant. Such a blackout is "one of the most serious conditions that can affect a nuclear plant," according to experts at the Union of Concerned Scientists, a U.S. based nuclear watchdog group.