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High Tension at San Onofre

Tensions are running high around San Onofre.

This week the North County Times published a follow-up article about one aspect of the recent CPUC (California Public Utilities Commission) hearings, namely, worries about the de-tensioning of the steel cables within the walls of the containment dome, which ring the reactor and are encased on all sides with cement.

A typical containment dome under construction looks a lot like a super-sized wicker basket. Hundreds of cables are laid down in rings around the dome, and hundreds more form polar quarter-circles out from the top, or semicircles that run near the top, and/or they follow various ellipses around the dome.

The main cables are typically 2 to 3 inches thick with some even thicker, and they are cross-braced with thousands of shorter 1-inch-thick cables. The whole thing is filled in around all the cables with concrete, forming the infamous domes that you see from the highway.

This system is called “pre-stressed” because a portion of the cable is left outside the concrete and is pulled with tremendous pressure while the concrete is hardened around the cable, and it is only after the concrete has hardened that the device doing the pulling is relaxed. Sometimes the “device” is a tightened bolt on a threaded end of the cable, which is left on afterwards.

San Onofre’s containment domes, for all their apparent mass and heft when viewed from the outside, are surprisingly thin and eggshell-like when considered in proportion. Or when it is considered that the containment dome is believed by most people to be strong enough to survive the impact of a 747 or an A-380 Airbus, but it can’t. It can only survive the impact of much smaller planes — even smaller than the four 767s used by terrorists on 9-11.

Furthermore, that’s not really their purpose. The real purpose of the containment dome is to hold back explosions inside the dome during a meltdown or near-meltdown of the core. These are expected to generate forces less than about 3.5 atmospheres within the dome — otherwise, the containment dome will burst and once it does, “all hell breaks out.”


Ah, but 3.5 atmosphere is not really all that much. And what if the containment dome, with all its mass, were to fall apart during an earthquake?

Well, they worried a little about that and decided to make the wires a little thicker and put a few more of them in place and tension them a bit tighter and viola! Instant earthquake-proof!

Of course, it’s bogus too. Maybe they made what might survive a 6.8 earthquake into something that might survive a 7.4. And maybe they overstressed something and didn’t realize it and the containment dome can now only survive a 6.3. Or maybe some of the wires have rusted inside because nobody noticed a wet rag that was dropped into the cement as it was poured, or a tool, that formed a bimetallic contact point. These things most certainly DO happen, although the nuclear industry assumes they don’t when they calculate the “safety factor” of their containment domes.

We’re talking about a very serious disaster here, and calculations might be “off!” There are so many factors involved. Only a real “test” — ie, an earthquake — will tell for sure. But if some big chunk of concrete falls onto a major component of the reactor during a 7.5 or 7.6 earthquake or whatever, then guess what? As one former San Onofre employee put it to me once, “Katie, bar the door!” For 100,000 years.

No nuclear reactor like San Onofre has ever been required to somehow survive a major breakage in the coolant system, such as might be caused by a steam generator being knocked over or disconnected by a large chunk of concrete falling from the ceiling of the containment dome.

None of this is discussed in the North County Times article, however, which only wonders whether, after cracking Humpty Dumpty apart to squeeze in the new steam generators, he can be put back together again correctly.

The article tells us that engineers from San Onofre went up in Northern California to study the shuttered Rancho Seco reactors. But nobody is rebuilding Rancho Seco, and they are not attempting to shake it as if in an earthquake (which would be a Herculean task, and very expensive), so there is a limit to what the San Onofre engineers can learn. According to the article, a couple of other reactors with less earthquake protection have had similar cuts in them and were determined by the NRC to be adequately repaired. The NRC could require a retrofit to the outside of the containment dome to reinforce it, like what is done to bridges all the time around California. Thus, even this tension issue would not cause the reactors to be shut down. Only stopping the Price-Anderson act is likely to do that, since that act absolves the nuclear industry of 99.9% of the costs of a nuclear reactor accident and puts it on the people who are actually harmed by the accident to pay for it themselves.

Without Price-Anderson’s protection, San Onofre’s owners would never have opened the plant. Price-Anderson is a criminal piece of legislation which should never have been enacted. It is unAmerican to absolve someone of responsibility for their actions and yet time and again, we find that that is the only way the nuclear industry can function.

Yes, the tension around San Onofre is incredible.

Ronald D. Hoffman, a computer programmer in Carlsbad, California, has written extensively about nuclear power. His essays have been translated into several different languages and published in more than a dozen countries. He can be reached at: rhoffman@animatedsoftware.com