The reactor, which was taken off-line in September for refueling, was reported in May to have 11 cracks or "indications," with the most serious having boric acid leaking out and requiring immediate repair.
Most of the cracks, according to Dominion spokesman Rick Zuercher, were in the reactor's tubing but only penetrated through about one-seventh of the wall, so it still met the American Society of Mechanical Engineer's guidelines.
At the time, Dominion officials considered replacing the reactor heads at their two nuclear power plants - North Anna and the Surrey station - in Virginia. Since North Anna's reactor is down, Zuercher said that now is as good a time as any to do repairs.
"We just determined it would be more cost-effective to just replace it," Zuercher said. "We expect to get the new head in December and return the unit to service in January."
Dominion purchased a crack-resistant vessel head from a French company earlier in the month. Officials expect to replace North Anna's other head and the two at Surrey during the next few years.
"It can be expensive to fix, and since we were going to replace the heads on Surrey and Anna in 2004 and 2005, we figured that, with the opportunity to buy this head … that it would just make sense to go ahead and replace it now," Zuercher said.
Nuclear power stations nationwide came under scrutiny this year when investigators discovered a six-inch hole in the steel dome of a reactor at the Davis Besse plant in Ohio. The hole there also was caused by boric acid, and the discovery led to 12 nuclear plants - including the two in Virginia - being put on a Nuclear Regulatory Commission "close watch" list.
Zuercher reiterated Monday that the indications at the North Anna and Surrey plants were minor when compared to others across the nation.
"This is the phenomenon that Davis Besse in Ohio saw. However, at Davis Besse, they allowed this to continue for years," Zuercher said. "Ours is really not a safety issue so much as a technical issue."