Thursday, March 17, 2011

Fukushima follow-up

I wrote, the other day, about the coverage of the ongoing events at the Fukushima nuclear plant in Japan, and I was ... not complimentary of the media. I linked a couple of pieces indicating that, as bad as the situation was, it's unlikely to be catastrophic (in life or death terms - it's obviously catastrophic financially). And I sent that piece, and those links, off to a friend of mine who is a nuclear scientist, a very smart guy who knows all about this stuff, to ask whether those assessments were correct. I need to leave out his name, but he gave me permission to post this response.
You are absolutely right about the confusion and misinformation coming from the media… In fact, I did not know if I should laugh out loud or cry when I was watching the garbage coming from media over the weekend. Later on Sunday I got an e-mail from American Nuclear Society which gave exactly the information that you found in the first link. This was the first time I could piece together what happened and I used this together with information on this particular plant design to prepare a presentation on this event for my colleagues. This link contains more factual information that you could obtain from all US journalists combined. The journalists do not know what they are talking about…

Regarding the development at Fukushima, the situation is serious and still developing. The description given in ANS link is about Unit 1. Unit 3 had similar developments. Explosion of hydrogen/steam mixture released from reactor vessel damaged the roof of the reactor building. This is a relatively weak structure, which serves as a secondary containment. The reactor vessel and the main leak-tight containment that surrounds the reactor vessel were not damaged. However, fuel in both units was damaged and probably partially melted, as indicated by presence of hydrogen that is generated by steam/zirconium reaction if temperatures go above 1200C. TEPCO claims that both units are now under cold shutdown, i.e. being cooled, so they should not be releasing any significant radiation.

Unit 2 is of larger concern because the loud noise that was heard at the bottom of the plan was likely steam or H2 explosion that damaged the suppression pool. The suppression pool has connections to the main containment, so radioactivity can leak out of the containment. But if they keep the core under water, I would not expect very large releases.

Unit 4 is of even bigger concern because, although it was shut down and did not have any fuel in the reactor vessel, it has a lot of spent fuel in the reactor cooling pool and it looks like they must have lost cooling there and boiled off enough water to uncover the fuel rods to generate hydrogen that caused the explosion that took out the roof. So it is critical that they keep cooling this pool, because it has an open path to the environment.

So this is roughly the story as I see it now based on information I could gather. Situation is developing and there is a lack of information to be able to piece together a more accurate picture or any predictions. But clearly, this is not a Chernobyl type and radiation levels are much, much smaller than at Chernobyl. For example, at one point they claimed 400microSievert/hr. To put this number in some perspective, I had a radioactive stress test done at Boston with technicium 99m, and I went after the test to the MIT reactor to measure the levels and every inch of my body was shooting out 500microSievert/hour.

It is a complex situation and it would require whole lecture, but I hope this brief description will help out...
He also sent me another link, to a blog by another nuclear engineer, walking through the events at Fukushima in plain English. It is both fascinating and reassuring. I recommend reading it all, but here's his takeaway:
The reactors were designed 40 years ago, and in 2008 were certified for ground motion corresponding to about a magnitude 6.7 earthquake right under the plant.[11] The reason this ground motion was selected was that Japan’s regulatory agency expected (rightly so!) that a ground motion stronger than that had a chance of happening only once in 10,000 years. We lost the statistical gamble on that one. But here’s the amazing thing: the reactors did exactly what they were designed to do: and so did the other nuclear units all over Japan. Only 7 of the 55 units in Japan [7] had any trouble shutting down, and they were the ones closest to the epicenter. And the trouble wasn’t even in the reactor, or the containment structure, or the piping – all of these things performed exactly as designed! The trouble was the tsunami that took out the fuel supply for the backup diesel generators. Let’s recap with a statement from Steve at Neutron Economy: “What this proves is that in the very worst scenario - a once-in-a-lifetime earthquake beyond the design basis - that the systems can safely contain the integrity of the reactor, particularly with well-trained personnel”. [5]

...

Damage from the earthquake and tsunami includes a fire at an oil refinery that is still burning; breaks in a hydroelectric dam, explosions in natural gas systems, and tons and tons of battery and gasoline spills. There is damage to the environment and danger to people from every form of energy that we use today.

So nuclear’s looking pretty good, right now. Fear aside, I think we’re going to end up with the least damage to life, health, and the environment out of all the energy sources in use in Japan. (Except solar.)

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