Concern continues after tsunami

Kevin has been ‘spot on’ so far in his informed speculation about events at the Fukushima I plant in the aftermath of the tsunami (previous post here), so I thought I’d share a bit more.   First, we just wanted to say that our thoughts are with the Japanese people, and with the plant staff working to avert further disaster despite the considerable risks.

Here are graphics from NOAA of the tsunami wave propagation:

NOAA Environmental Visualization Laboratory - Tsunami Wave Height Model Shows Pacific-Wide Impact.

UK Channel 4 news this evening reported concerns over the Onegawa and Tokai plants in addition problems with several reactors at Fukushima I and II (as mentioned by Boballab).  Here’s a reminder that the plants now reporting problems were those most affected by the tsunami.  They were built to withstand earthquakes, but suffered from lack of power –  inundation resulting in failed back up diesel generators / limited battery life.

Location of the earthquake epicentre in relation to tsunami wave height, and the four nuclear plants (N=>S: Onagawa, Daiichi, Daini, and Tokai) now reporting problems.

Current evacuations are 20 and 10km for the two Fukushima plants respectively. Google maps has an overlay (link here) showing 10km, 20km, 100km and 200km evacuation zones around the Daiichi and Daini plants, a reminder that the problems are far from over yet.

From Kevin [10:38 am Saturday 12th March]:

Those images of the reactor containment building post the explosion say it all. I think it’s eventually going to turn out to be the case that they’ve had a partial core melt.

[From Yahoo News: Chief Cabinet Secretary Yukio Edano said [earlier today] there might have been a partial meltdown of the fuel rods at the No. 1 reactor at Fukushima. Engineers were pumping in seawater, trying to prevent the same happening at the No. 3 reactor…]

If they are injecting sewater and boric acid then they clearly have concerns about the integrity of the fuel matrix.  One thing that hasn’t been mentioning so far it seems is the possibility of ‘clad ballooning’.   I need to check, but if they use zirconium for the fuel cladding (which is highly likely), then if, the fuel gets too hot the gaseous fission products within the fuel pellet matrix can be released and the internal pressure within the fuel pin cause the zirconium cladding to ‘balloon’. The ‘ballooning’ of the fuel pin causes the spacing between the fuel pins to be restricted, which in turn causes the fuel to increase temperature still further and acts as a positive feedback.  In some cases it is possible for the configuration if the fuel pellets achieve a limit geometry which can become re-critical.  The best way to mitigate that possibility is to add something that absorbs as many thermalised neutrons as possible, hence the boric acid mixed in with the coolant.  You also definitely want to avoid repeated ‘quenching’ of the fuel i.e. allowing it to be uncovered and recovered repeatedly.  I think this is most likely what has been going on but not a Dicky bird about this from the official sources.
Post Three Mile Island this is pretty much what happened, and thanks to the secondary containment building there was very little release of gaseous fission products into the environment, but obvious and clear damage to the reactor core.
If you lose integrity to your secondary containment then you’ve had it IMO; you can expect significant radiological releases.  It would take quite a lot of core integrity disruption though to get anywhere close to the levels of releases at Chernobyl.

Reuters reports that the Japanese Nuclear safety agency rates the incident a 4 on the 1 to 7 International Nuclear and Radiological Event Scale, less serious than Three Mile Island, which was a 5, and Chernobyl at 7.   Meanwhile the FT (at 20:50 GMT) has a good analysis of the presently known facts of the now admitted partial meltdown.

Pierre Gosselin’s NoTricksZone has a summary from Der Speigel and other sources of the amount of energy released by the quake that is worth reading: http://notrickszone.com/2011/03/13/600-million-hiroshima-bombs-80-years-of-global-energy-usage-in-just-minutes/

Thanks to commenters on E.M.Smith’s site I just found another summary “Fukushima a simple explanation”, which is the best I’ve read.