After many years of blogging, and consistent with my desire to move toward retirement, we have ended the Insights blog. Thanks to Doug Bedell for his years of blog support.

What Should We Curse?

Posted on March 14, 2011
Filed Under Technology | Leave a Comment

The details of the nuclear accidents underway in Japan as we write will take months, if not years, to analyze. But as someone with decades of nuclear industry experience (including working on the recovery of Three Mile Island Unit 2), when the results are in I expect to be angry not at the technology, but rather about how we implemented it.

I don’t know what the design basis seismic event was for the Fukushima Daiichi Nuclear Power Station, but it was certainly less than the unprecedented 9.0 earthquake that struck on Friday. Nonetheless, when the accident is investigated I suspect we may well find the reactor would have shut down normally, even during this beyond-design-basis event, had we done but a few things differently.

As best I can tell from news reports, it was the shot from the tsunami, not the earthquake, that hit Fukushima’s vulnerable Achille’s heel. We know the seismic sensors caused the reactor to “scram,” that is shut down automatically thereby stopping the nuclear chain reaction. (These sensors work amazingly well. I’ve seen a small test reactor in the U.S. scram when a crane operator set a large, heavy piece of equipment down a little too hard adjacent to the reactor.)

I believe we also know that Fukushima did not suffer the classic accident that has been the reactor design bugaboo since nuclear reactors were invented: an earthquake that causes the total fracture of one of the reactors main coolant pipes, dumping massive amounts of cooling water out of the reactor.

Preliminary reports suggest that whatever the structural damage was to the reactor and its cooling systems, it was not enough to cause what we are seeing develop in Japan. Instead what we are seeing apparently stems from the loss of the plant’s emergency diesel generators. Once the reactor (which of course produces steam to generate electricity) shuts down, the diesel generators automatically start to provide the juice needed to operate the pumps, valves, blowers, and other equipment necessary to keep the reactor cool. All reactors give these essential generators seismic protection, and at Fukushima they are also protected by a concrete wall to stop a tsunami.

Alas, it appears the walls were too low to deal with wave from the unexpected 9.0 earthquake. The resultant tsunami cleared the wall and somehow damaged the generators, knocking out the power needed to keep the safety systems functioning. It seems that if the engineers had made a small design change, such as a higher wall or placing the generator building on higher ground, we might well be marveling at how these amazing reactors survived the earthquake of the millenium.

All of this is so much speculation at this point. Months from now when the analysis is in we may be cursing the technology. But I suspect we will be marveling at the technology and cursing our shortsighted placement of a few key components. – Dennis Owen


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