Thursday, March 03, 2011

Shaky Reasoning

In 2008, the Vermont Yankee nuclear power plant in Vernon, Vermont began storing high-level radioactive waste in 19-foot tall dry casks outdoors, on a concrete slab 254 feet away from the bank of the Connecticut River.

That's a foot and a half beyond what Dr. Leslie Kanat, a Geology Professor at Johnston State College, calls the "Probable Maximum Flood Level."

I am more than a bit concerned about those casks, but maybe I ought to feel relieved--even if a foot and a half doesn't sound like much. Maybe I also ought to feel relieved that Holtec International, the company supplying the casks, reports that their casks stay operational even when submerged at 50 feet for 8 hours. But while Holtec's tests have reassured me that river water would not be a problem for those dry casks, I'm not so sure about river mud.

Holtec's dry casks have vent holes at top and bottom. They are designed for air to enter at bottom, cool the waste, and exit at top.

What would happen if those vents were blocked? Did Holtec run tests for that?

It did not. But in 2002, Dr. Marvin Resnikoff, an international consultant on radioactive waste management, was asked by The Connecticut Yankee Decommissioning Advisory Committee how long it would take for a cask to overheat if vents were blocked. His answer: Maybe a week.

"Maybe." And, again, maybe I should feel relieved. After, all, there's a nice margin of safety in that hypothetical week. I can imagine fire engines arriving at the high-level radioactive waste storage slab right after helping little old ladies out of their collapsed homes, and taking care to hose down the casks after hosing down the fires decimating Main Street. But what about the fact that guesses are sometimes off the mark? What if there were not a week to spare but only two days or three? Would emergency workers even know to abandon their attempts to help survivors and begin to frantically deal with muddy dry casks?

And what about the fact that, during his testimony to the Connecticut Yankee Decommissioning Advisory Committee, Dr. Resnikoff explained that each dry cask contains a Cesium and Strontium inventory equal to 10 Hiroshima bombs?

Entergy, the plant's corporate owner, has never actually acknowledged that mud could reach the vents of the dry casks at Vermont Yankee. Their directors and administrators keep the conversation focused solely on water. But Ray Shadis, technical director for the anti-nuclear watchdog group New England Coalition, is concerned about the combination of Cesium, Strontium, and high temperatures due to a failed, mud-dependent cooling system. In a not-too-difficult-to-imagine scenario, Shadis suggests that the ground surrounding the concrete slab that holds the casks could become wet with river water. Consequently (he says), the slab could become unstable.

And then what?

Well, if you shake even relatively dry soil really, really hard, its strength and stiffness are reduced. That's called "liquefaction." It's responsible for much of the damage during earthquakes. If you actually add liquid to the mix, you create something like quicksand.

What if the Connecticut River Valley suffered a double whammy of flood plus even a minor earthquake? Could the ground around the slab holding the dry casks become like quicksand? Could an edge of the slab shift or, worse, tip?

Even Entergy has suggested that the ground around the concrete slab could get an occasional and maybe even regular soaking soaking from river water. What they haven't gone out of their way to point out is that Vermont is in a bit of an earthquake zone. We have been significantly rattled 15 times since 1900.

Most scientists agree that we are entering an unstable time weather-wise, with melting ice caps, rising waters, and the possibility of more frequent flooding. Given that, I can't help but question Entergy's foresight in trying to get a license extension allowing them to create another 20 years of radioactive waste, only to store it in an earthquake zone near a population center at river's edge.

This is adapted from a Vermont Public Radio commentary by the author.

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