Grid damage from tornadoes that tore through Arkansas Sunday forced two reactors at the state's only nuclear plant to power down.At 7:32 p.m., a grid operator ordered units 1 and 2 at Entergy's Arkansas Nuclear One to go offline as soon as possible. According to a report filed with the Nuclear Regulatory Commission, unit 2 tripped automatically from 51 percent power 40 minutes later as it was reducing its output. Backup power remained available, and safety systems responded as designed. An axial shape index trip caused the core protection calculator system to shut the unit down automatically.At the same time, operators at unit 1 began a rapid plant shutdown, reducing power by 5 to 7 percent per minute. After unit 2 tripped, they stabilized the reactor at 19 percent power and then kept the unit under a 200 megawatt limit in coordination with the grid operator. The storms killed at least 15 people in Arkansas, according to the governor's office, with fatalities also reported in Oklahoma and Iowa. As of 2 p.m., Monday, Entergy Arkansas reported power outages for 10,500 customers, down from 35,722 the previous evening.Photo: The tornado wrecked this substation control house and bucket truck in Mayflower, Ark., about 60 miles from the plant. Source: Entergy
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