Fukushima redux - design basis Godzilla?

Fukushima redux - design basis Godzilla?

Barry Brook | 17 March 2011 at 12:05 PM URL: http://wp.me/piCIJ-144

I am currently compiling an update for the Fukishima Nuclear Accident as of March 17.  The situation is developing very quickly and commenters on this thread (March 16 updates) are doing an excellent job at posting regular updates.
Meanwhile, here is a guest post from Luke Weston.
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Looks like we need an update post on the situation with the Fukushima nuclear power reactors. The situation continues to change and develop, but good, sensible, detailed information is still hard to find.
In the wake of the Fukushima incident, it has really helped me to understand what happened in 1979 at Three Mile Island; with nonsense all throughout the media, and FUD, and panic spreading, with good information almost impossible to find, and with the over-abundance of bad information leading to hysteria.
But this is the first time it has happened to the Facebook and Twitter generation; I’ve yet to determine whether that’s a good thing or a bad thing. We need to keep working hard to make sure it’s a net benefit for the good information, not the dodgy information.

Design Basis Godzilla

Why wasn't the earthquake design basis set high enough?, some people ask. What if the next earthquake is magnitude 10? Magnitude 12? Magnitude 20? But where does it stop? Where do you set the design basis? What if the reactor is attacked by Godzilla?
No matter where you set the design basis, you will always exceed it one day, eventually. And when you do, the anti-nuclearists will complain that the design basis is not set high enough.
There is always some really extreme, really catastrophic situation that you can imagine, but what is its probability in any given year?
It's all about Probabilistic Risk Assessment.
You know what the average probability per year of a magnitude 8 earthquake in the area is, what the probability of a magnitude 9 earthquake is, what the probability of a large tsunami is, etc. I'm not sure what the probability of Godzilla attack is. Need to ask an expert. Somebody get Matthew Broderick in here; he's the guy to ask.
And you decide what the acceptable probability of a severe core damage ("meltdown") incident (which won't hurt anybody but will probably write off the reactor, like TMI) for the nuclear reactor is in any given year - let's suppose it is decided that one such failure per 50,000 reactor-years of operation is acceptable. Then, with that in mind, you design the degree of seismic hardening and safety engineering for the nuclear power plant so that you hit that target.
It is the safest way to do it which is actually realistic. You can't say that it's absolutely 100% resistant to any hypothetical scenario of destruction that you can imagine, because there is always something that you can imagine that is more destructive.

Seawater injection into the primary containment of Unit 1 - not into the reactor vessel itself

On 12 March, TEPCO announced that they planned to cool the Unit 1 reactor with seawater, adding boric acid to the water as a nuclear poison, to prevent any possibility of unintended criticality. The injection of fresh water and seawater into the primary containment vessel through a fire-extinguishing system line commenced on the 13th of March.
This is not an injection of seawater into any part of the nuclear reactor or the Nuclear Steam Supply System itself. It is an injection of seawater into the containment structure surrounding the reactor pressure vessel.
These reports confirm my earlier prediction that they were not talking about actually putting seawater into the nuclear steam supply system, despite the lack of any previous clear, sensible announcements in the press to this effect.
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