NRC: loss of offsite power at Catawba Unit 1 last April was potentially of substantial significance to safety
The U.S. Nuclear Regulatory Commission (NRC) has just announced that on Sept. 11th, it will conduct a post-incident review with Duke Nuclear to discuss an April 2012 loss of off-site power at Catawba Unit 1 atomic reactor in South Carolina (picture, left). NRC's preliminary review has determined that the incident may be designated a "yellow finding" (in NRC's green, white, yellow, red system of increasingly significant incidents), meaning "of substantial significance to safety." Off-site power is the primary power source for running safety and cooling systems.
While General Electric Mark Is (such as the Fukushima Daiichi Units 1 to 4) and IIs are Boiling Water Reactors with too small, too weak "pressure suppression" containments, ice condenser containments, as at Catawba Unit 1, are a form of "pressure suppression" containment -- again too small and too weak -- at a Pressurized Water Reactor design. The ice condeners in the U.S. include two units at Catawba in SC, two units at McGuire in NC, two units at Sequoyah in TN, one unit at Watts Bar in TN, and two units at Cook in MI.
Ice condensers were originally desiged for floating atomic reactors on barges, where the containment, of necessity, would have to be smaller and lighter, so it wouldn't sink under its own weight. Once licensed by NRC or its predecessor, the Atomic Energy Commission, however, nuclear utilities took advantage of the certified reactor design, by building them on land, in order to save money on the containment structure.
Thanks to revelations by Tennessee Valley Authority whistleblower Curtis Overall, and nuclear safety advocacy by David Lochbaum at Union of Concerned Scientists, the Cook ice condensers in southwest Michigan were shutdown from 1997 to 2000 for major safety violations, resulting in one of the biggest fines in NRC history up to that point.