So far, readers have sent along some excellent questions about the San Onofre Nuclear Generating Station (nicknamed SONGS), and I will do my best to answer them in this and upcoming posts. More questions are welcome, so don’t be shy.

Earlier today I was asked to compare San Onofre with California’s only other operating nuclear power plant — Diablo Canyon in San Luis Obispo. My focus of late has been on San Onofre because of its Southern California location, but I know enough about Diablo Canyon to offer a few comparisons.

The most striking difference at the moment is the relative performance of the two plants. While both facilities have spent much of the last few years in the Nuclear Regulatory Commission’s top category (meaning they do not require additional oversight), San Onofre slipped a notch a few months ago and has been the subject of three special inspections since June 2007.

The contrast is even more striking when it comes to the ratings from the Institute of Nuclear Power Operations, or INPO, an industry-sponsored organization that rates the performance of U.S. nuclear plants, relative to one another and according to industrywide standards of excellence. INPO has no regulatory authority and the voluntary INPO reviews are not made public — but the ratings are influential nonetheless, in part because the assessments are detailed and candid, and in part because they help determine how much a given nuclear plant has to pay for liability insurance.

INPO’s scale goes from one to five, with a so-called “INPO 1” rating being the best. David Lochbaum, formerly of the Union of Concerned Scientists and now a trainer at the NRC, says most plants are in one of the top two categories.

San Onofre dropped to an INPO 3 in 2006, and it stayed there after its 2008 review. By contrast, Diablo Canyon was an INPO 1 as recently as December 2007 — and we know that because a representative from the plant said so in a state legislative hearing. Since it would be unusual for a plant to drop two spots in the span of a year, it can be assumed that Diablo Canyon’s INPO rating is the better of the two — and perhaps quite a bit better.


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