On 11 March 2011, a massive earthquake hit Japan. The six reactors at Fukushima-Dai-ichi suffered ground accelerations somewhat in excess of design specification. It appears that all of the critical plant equipment survived the earthquake without serious damage, and safety systems performed as designed. The following tsunami, however, carried the fuel tanks for the emergency diesels out to sea, and compromised the battery backup systems. All off-site power was lost, and power sufficient operate the pumps that provide cooling of the reactors and the used-fuel pools remained unavailable for over a week. Heroic efforts by the TEPCo operators limited the radiological release. A massive recovery operation will begin as soon as they succeed in restoring the shutdown cooling systems.
It is important to put the consequences of this event in context. This was not a disaster (the earthquake and tsunami were disasters). This was not an accident; the plant experienced a natural event (“Act of God” in insurance parlance) far beyond what it was designed for. Based on the evidence available today, it can be stated with confidence that no one will have suffered any identifiable radiation-related heath effects from this event. A few of the operators may have received a high enough dose of radiation to have a slight statistical increase in their long term risk of developing cancer, but I would place the number at no more than 10 to 50. None of the reports suggest that any person will have received a dose approaching one Sievert, which would imply immediate health effects.
The major lesson to be learned is that for any water-cooled reactor there must be an absolutely secure supply of power sufficient to operate cooling pumps. Many other lessons are likely to be learned. At this early point, it appears that design criteria for fuel storage pools may need to be revised, and hydrogen control assessed.
Given the severity of the challenge faced by the operators at Fukushima, and their ability to manage the situation in such a way as to preclude any significant radiation related health consequences for workers or the public, this event should be a reassurance that properly designed and regulated nuclear power does not pose a catastrophic risk to the public—that, overall, nuclear power remains a safe and clean energy sources.
UPDATE: As the first comment on Bill Hannum’s guest post, Barry Brook quoted an important segment from Bernard Cohen’s text: “The Worst Possible Accident”. Prof. Cohen concludes with this paragraph:
(…) But this once-in-a-billion-year accident is practically the only nuclear reactor accident ever discussed in the media. When it is discussed, its probability is hardly ever mentioned, and many people, including Helen Caldicott, who wrote a book on the subject, imply that it’s the consequence of an average meltdown rather than of 1 out of 100,000 meltdowns. I have frequently been told that the probability doesn’t matter — the very fact that such an accident is possible makes nuclear power unacceptable. According to that way of thinking, we have shown that the use of gasoline is not acceptable, and almost any human activity can similarly be shown to be unacceptable. If probability didn’t matter, we would all die tomorrow from any one of thousands of dangers we live with constantly.