26 April 2011—Twenty-five years ago, the day the commentary of the Chernobyl catastrophe reached the West, I was in Washington, D.C., covering one of the annual meetings of the American Physical Society. A leading nuclear physicist was dragooned to speculate in front of a hushed audience about what could have gone so terribly wrong. His tentative explanation had to do with an obscure phenomenon called ”Wigner energy,” which I had never heard of and which I found hard to understand. Evidently it was an undesirable energy release that can occur in reactors containing a lot of graphite.
That night, sitting at the bar of the funky little hotel I like to stay at when I’m in D.C., I discovered that the man sitting next to me was none other than Walter S. Sullivan, at that time the most eminent science journalist in the United States—considered by some to be the ”Dean” of science journalism. Sullivan, a charming fellow, was able to explain to me what Wigner energy was all about.
What makes this memory interesting today is that Wigner energy turned out to have nothing whatsoever to do with the Chernobyl accident. Everything the eminent American physicist had said was irrelevant, and so was Sullivan’s elegant explanation.
The major lesson of Chernobyl—and the lesson of the 1979 Three Mile Island disaster before it, and very likely that of the still unfolding Fukushima disaster—is to expect the unexpected.
After a detailed analysis of the Chernobyl incident, it turned out that the graphite-moderated reactor in use there had a peculiar design defect: When it was operating at certain power levels, if there was a loss of coolant, the reactivity of the plant would escalate abruptly and sharply. In addition, the inner containment structure of the reactor, instead of being a steel pressure vessel as is the case with most other reactors, was essentially a box with a weakly attached lid. All the fuel and control rods penetrated that lid, so if there was a sudden increase in pressure, the lid would lift and rupture all the rods.
Of course it was hard to fathom how Soviet engineers could have designed a reactor with such singular defects, and even harder to fathom why the Chernobyl operators had deliberately put the reactor into the precise state where it would be most likely to explode. But hardest of all to accept was the possibility that everything could go dreadfully wrong all at once, partly because of some underlying single cause.
”Focusing on individual components” in risk analysis can be profoundly misleading, as the Princeton University researcher M.V. Ramana pointed out in a recent commentary. The seductive but misleading reasoning was that ”a severe accident [couldn’t] happen unless multiple safety systems [failed] simultaneously,” and that ”therefore, a severe accident is exceedingly unlikely.”
The recent Fukushima disaster in Japan once again brought home the real risk of common-cause failures: A single event led to ”the loss of off-site electrical power to the reactor complex, the loss of oil tanks and replacement fuel for diesel generators, the flooding of the electrical switchyard, and perhaps damage to the inlets that brought in cooling water from the ocean,” as Ramana enumerates. ”Fukushima also demonstrated one of the perverse impacts of using multiple systems to ensure greater levels of safety: Redundancy can sometimes make things worse.”
Another outcome of Chernobyl, now to be tragically repeated at Fukushima: Long term, the invisible results of the accident will be even worse than the visible ones. It will take decades to restore the immediate physical environment of the Fukushima plants—an exercise that has not gone well in the region around Chernobyl. Meanwhile, there will be an ongoing death toll over the years from radiation-induced cancers. But these victims will be unidentifiable, not only because it will be impossible to determine if a particular cancer is caused by radiation from Fukushima or by something else, but because the total expected increases in cancer and cancer death rates will be undectable among the extremely large numbers of cancers that will occur in any case.