Lessons in Nuclear Safety from Fukushima
Technology Review has a short article on what has been learned since the meltdowns last year – What We Learned About Nuclear Safety From Fukushima:
Reactors and radioactive materials at Fukushima Daiichi were destabilized by back-to-back beyond design-basis events. First was the magnitude 9.0 earthquake that felled the plant’s power lines, triggering diesel generators to maintain cooling of its reactor cores and spent fuel rods. Less than an hour later, the generators along with some of the plant’s last-resort battery power backup were gone, knocked out by a 14-meter tsunami wave that crested the plant’s seawall.
Human error and design limitations quickly compounded the impact of the loss of power. Operators mistakenly shut down battery-driven cooling on one reactor for three hours, for example. Within 24 hours of the tsunami, nuclear fuel in three reactors was melting down, and superheated fuel was generating hydrogen gas, whose ignition would blow open three reactor buildings in the days ahead, impeding response efforts and exposing elevated pools holding spent nuclear fuel.
So, that’s what we know happened. What’s surprising is that some of the obvious shortcomings of the plant’s design and operations weren’t recognized and dealt with well before the disaster.
What’s interesting and not surprising is that Fukushima is a textbook engineering failure, in that it wasn’t one flaw in design, execution, or operation that led to the meltdowns but a cascade of such failures, the absence of any one of which might have significantly limited the disaster or prevented it from happening altogether. Even with the beyond design-basis earthquake and the large tsunami following it, he plant might have remained under safe control had, for instance, the power lines not been knocked out for an extended period, or had the backup generators been out of reach of the tsunami.
The response from the US nuclear power industry has been to stage emergency equipment such as generators at strategically-located depots in anticipation of unanticipatable events. New nuclear power stations (yes, there are actually new ones under construction in the US) will use advanced passive safety features to safely shut down reactors in the event of an emergency and buy time for outside emergency response. Naturally such measures aren’t good enough for the Union of
Concerned Scientists Anti-Anything-Nuclear Activists, cited later in the article, for whom no degree of risk can ever be small enough.