Waterford — The Millstone Power Station violated safety requirements by not having adequate documentation in place for the steps that plant staff would follow during an emergency to test the radioactivity level of coolant water.

The Nuclear Regulatory Commission issued notice of the safety violation on Monday. It was categorized as a "green" finding, the lowest level of safety significance, and is being corrected by the plant, according to the NRC notice.

Josephine Ambrosini, senior resident inspector for the NRC at Millstone, said the safety violation was found during an Aug. 20 emergency preparedness exercise that involved the nuclear power plant and 10 communities in its Emergency Planning Zone. The readings of the coolant water, used to keep the reactor from overheating, are supposed to be taken within 15 minutes of an emergency being declared at the plant, she said. During the exercise, plant staff was able to obtain readings at other locations in the plant to assess radioactivity levels, but did not have the written procedures in place to get the coolant readings. The violation pertained mainly to the Unit 3 reactor, she added.

"The exercise wasn't disrupted by it," she said.

Ken Holt, spokesman for Millstone owner Dominion, said there are interim measures now in place so that if an emergency were to occur, staff has written procedures available to follow to take the coolant readings.

"We are also making permanent changes in the procedures," he said.

The coolant readings, he explained, are used to verify radiation readings taken elsewhere in the plant during an emergency.

Millstone has had one other "green" finding this year. In August, the NRC cited the Unit 3 for inadequate documentation of a design weakness in valves that would shut off water flow during an emergency.

Safety violations are ranked on a four-tiered scale — green, white, yellow and red, with red being the most serious. "Green" findings are those that "are not willful or have no immediate safety consequences" and do not result in fines, Ambrosini said.

j.benson@theday.com