Fukushima and Neoguri: is the rain a pain?

Typhoon (now a transitioning tropical storm) Neoguri is moving north off the east coast of Japan, dumping a lot of rain, over 30 cm (1 foot) in places).  There have been landslides and flooding, but at least the winds have died down a lot.  One of the concerns is for the tsunami damaged reactors at the Fukushima Daiichi Nuclear Power Station, and in particular the hundreds of storage tanks of contaminated water on site.  Here’s a recent satellite view of the plant:
fuku_tanks_march

They shouldn’t experience severe wind or waves.  One question is how much of a problem the rain itself will be.  In looking at the data, it doesn’t seem like that much unless something breaks that shouldn’t (which, given the track record for the site, isn’t really comforting).  Let’s take a look at the “data”.  I have “data” in quotes, because this comes from Tokyo Electric Power Company (TEPCO), and I’m honestly not sure I trust it very far.  For one thing, they keep shifting sample locations, techniques, and intervals, and to top it off the English vs. Japanese sites seem to have different data sets.  This is using the data file from the Japanese site, for a location in front of the “impermeable wall” (which is obviously at least somewhat permeable) near the Unit1 water intact channel.  This plot is looking at one of the by-products of fission, Cesium-137.  Cs-137 is a serious health concern because it is water soluble and concentrates in soft tissues.  The WHO guidance for “drinking water” quality is 10 Bq/L, USA EPA limits are 7.41 Bq/L, the Japanese regulators apparently allow 90 Bq/L.  Here are the numbers for the last year:
raw_counts

So is there a relation between rainfall and the Cs137 levels?  There doesn’t seem to be much of one.  The raw correlation for changes peaks on day one after the rain event, and where there was more than 5mm of rain is about 0.2.  That means at best only 4 percent of the variation is explainable by rainfall alone.  If all observations are included, there is essentially no correlation.  Here is a plot of the change is Cs137 readings vs. rainfall:
cs137_plot1

Lots of “gotcha’s” to this quick look analysis.  Note the biggest rainfall events in the last year were only in the 6-8cm range.  Since the tsunami, the peak rainfall event seems to have been 9.18 cm.  Neoguri could dump two or three times that amount.

I’m still looking at other measurement locations, as well as trying to make sense of their hashwork of measurements.  To paraphrase Mr. Scott, analysis is easy; reading Japanese, now that’s difficult.

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