Threats not contemplated by designers
The inspections highlight a distinction between safety measures that are required and routinely inspected, based on anticipated risks -- the "design basis" events -- and threats that are considered too unlikely to require the same level of safety ruggedness, or "beyond design basis" events.
"I am really bothered by this separation between design basis and beyond-design basis," NRC Commissioner George Apostolakis said at a commission meeting last week.
"I appreciate the need for a design basis. Licensees know what they have to have to do. We impose all sorts of conditions. This particular pump must deliver this flow rate under these conditions. And then we are going to inspect. We asking them to test it and tell us what they find, all that."
The plant owners' responses to beyond design basis threats are usually voluntary. "We keep saying, 'Oh, these are beyond basis events therefore we don't' get involved.' We are happy that the industry responded. We look at it once. That's it. In the future it's up to them. I am really bothered by that."
"It is a constant challenge we have to deal with," NRC director of operations Bill Borchardt responded. "There is a balance."
Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500