Monday, March 14, 2011

Thoughts on Fukushima, 14th Mar.

Comments on “Why I am not worried about Japan’s nuclear reactors”

re-blogged at

This very well written account of the possible causes and consequences of the nuclear accidents in Japan at fukushima has stormed to the top of Google search and has already garnered over 220,000 readers. The author is not a nuclear engineer, although he is clearly quite familiar with the technology involved and seems to have a very pragmatic approach to the risks involved.

The arguments and reassurances put forward are based in general on sound science, and do not need the backing of an appropriately qualified authority to back them up. The science is straight forward and is in general un-contentious.

There are a number of points in the account which I would like to comment on.

1) Fukushima reactor 1 does not have a core catcher assembly. This issue has come up in the comments to the post and means that if the core did melt the result would be less controlled than as described in the post. Having said that, this scenario seems unlikely as the core is cooling and is being moderated effectively by boron containing seawater.

2) It has been reported that radioactive Iodine and Caesium are contained in the released products. This is worrying as it may imply that the cladding on some of the fuel elements has been breached. Radioactive Iodine is taken up by the thyroid gland and can lead to cancer of the thyroid. Prompt Administration of Iodine to the affected population is an effective preventative measure at the levels which one would expect given current information. I don’t know about the health consequences of Caesium.

3) Some of the terminology used in the article is not standard. Thus as described in the article there are four levels of containment. It is more normal to describe the “stainless steel kettle” with its concrete surround as the primary containment.

Events have moved on, and we have seen what appears to be a further hydrogen explosion in Fukushima 3. Fukushima 3 is a later version of the same boiling water design and this version seems to have a “suppression pool” underneath the main reactor vessel.

My conclusion is be cautiously optimistic. The picture changes if it turns out that either of the reactors is leaking cooling water, or if significant amounts of the core becomes exposed and heat up in either reactor. One issue which has not been discussed extensively is the status of any spent or irradiated fuel which may be stored on site. Issues surround this have to potential to cause more widespread site contamination, jeopardising continuing operation of the other reactors present.

Selected references:

A trailmeme with some more technical documents is here


  1. I found your blog when I tried to find out if Fukushima had a core-catcher after reading Morgsatlarge's interesting blogpost. Thank you for your additional thoughts, it is hard to find more information in this difficult time. Lois

  2. Finding information, does not appear to be the problem, finding reliable information is harder.
    The Wikepedia entry,
    is now a good jumping off point for well referenced hard data.