I think it is short lived.  Preliminary damage reports say it was one unit under scheduled maintenance.  It will prolong the shutdown, but the other 75% of the plant will likely be online by morning.

http://www.cmegroup.com/education/market-commentary/energy/2013/04/...

The Nat Gas futures market has been firm throughout the entire session today on news of Southern Companies largest utility unit… Georgia Power experiencing an explosion and subsequent shut down of its 3,166 megawatt coal fired power unit. The explosion occurred late Thursday afternoon and will likely result in an increase in Nat Gas power related consumption until this unit is fixed and back on stream.

With inventories now slightly below normal (compared to the five year average for the current week) the market is now exposed to unscheduled interruptions in any part of the power grid that will ultimately result in an increased usage level of Nat Gas for generating power. The Georgia Power issue would probably not have even resulted in a blink had it occurred last year at this time when end of winter inventory levels were at a record high. However, with the overhang gone and the summer cooling season yet to come the market will react to any of these type of situations with a quick rally in prices… if for nothing other than short covering.