Hairline cracks in the reactor heads are developing, or are highly susceptible to developing, at 13 of the United States' 69 operating PWRs, according to the Nuclear Regulatory Commission (NRC). Of the 13 units, cracks were found and repairs were made at four units, two have yet to be inspected (Davis Besse 1 and Donald C Cook 2), and seven did not show cracks.
Last August the NRC published a bulletin asking PWR operators to justify continued operation beyond 2001, due to concerns over the circular vessel head penetration nozzle cracking. In the past cracks have appeared along the length of the nozzles, but the NRC believed that the problem was not serious enough to require any further attention beyond inspections and repairs during routine outages. However, the NRC said the circular cracks around the nozzle width were a "potentially significant" safety concern.
The NRC has allowed FirstEnergy Nuclear Operating Company, operators of Davis Besse, to continue operating the reactor until its refuelling outage, brought forward by six weeks from the originally planned date to February 16. FirstEnergy said it would carry out a 100% qualified visual inspection and non-destructive examination of the control rod drive mechanism nozzles. Donald C Cook 2 is due to shut for repairs in mid-January.
Davis Besse is a Babcock & Wilcox designed PWR, as are the three Oconee units where circumferential cracking in vessel head penetration nozzles was found in all three units. FirstEnergy has announced it will replace the vessel head at Davis-Besse, probably during a refuelling outage in spring 2004. Earlier in 2001 Duke Power announced it would replace the vessel heads at all three Oconee units.
Cracks were also found and repairs made at Crystal River 3. The seven units that were inspected and found to have no cracks were: Three Mile Island 1, H B Robinson 2, North Anna 1 and 2, Surry 1 and 2 and Arkansas Nuclear One unit 1.