Catastrophie may have been averted, Does anyone know how long...

Catastrophie may have been averted, Does anyone know how long the rods can be exposed before they have a critical meltdown?

http://www.marketwatch.com/story/water-flow-restored-to-striken-japan-reactor-2011-03-14

HONG KONG (MarketWatch) - Japanese authorities said late Monday technicians battling to prevent a meltdown at the No. 2 reactor at the Fukushima Daiichi Nuclear Power Station were able to restore injection of seawater into the reactor around 8.00 p.m. local time (7.00 a.m. Eastern Standard). Fuel rods inside the reactor were almost fully exposed for nearly two hours before water flow was restored, with the odds being a partial melting of the rods during that time, according to national broadcaster NHK. Japanese government officials said they were optimistic the reactor could be stabilized if seawater flow to the overheating reactor continues uninterrupted.