Wednesday night’s extreme winds in the southern U.S. cut power to the Tennessee Valley Authority’s Browns Ferry nuclear plant, causing all three units to shut down.Two units were operating at full power and another at reduced power when the outage tripped the plant’s safety systems at 4:36 p.m., according to a TVA release. Seven of eight backup diesel generators ensured cooling systems continued operation, and crews worked Thursday to bring online the eighth generator, which was down for maintenance.Unit 3 achieved cold shutdown at 2:43 a.m., Thursday, followed by unit 2 three hours later. Unit 1 was still being cooled as of late Thursday morning.At that time, a single 161-kilovolt offsite power line was available to the plant, but operators continued to use backup power until more reliable offsite power could be made available, according to TVA. Storms and tornados that caused major damage in several states and killed more than 245 people disabled 90 large TVA transmission lines, and took out power to 677,000 customers.TVA operates three roughly 1,100-megawatt reactors at Browns Ferry in Athens, Ala., about 32 miles west of Huntsville, according to the Nuclear Regulatory Commission. All are General Electric Type 4 boiling water reactors with Mark 1 containment.Station blackouts are among the safety topics currently under evaluation by the NRC in response to the ongoing Fukushima Daiichi accident in Japan. In a briefing on the NRC’s efforts, Chairman Gregory Jaczko said Thursday in a prepared statement:"Severe storms in the South last night provided a stark reminder that we are not immune to the effects of natural events. Last night, Browns Ferry nuclear power plant experienced a loss of nearly all offsite power to the three units, resulting in shutdown. All safety functions performed as designed. All available emergency diesel generators started and loaded and emergency core cooling systems are operating normally. Spent fuel pool cooling is currently in service. The plants’ conditions are stable and are being placed in a cooled-down condition."
Similar although less severe problems at the neighboring Sequoyah plant ; "BOTH OFFSITE POWER SOURCES DECLARED INOPERABLE DUE TO EFFECTS OF INCLEMENT WEATHER", "50.72(b)(3)(v)(A) - POT UNABLE TO SAFE SD"