Japanese earthquake, tsunami, and nuclear safety: ‘NDR’ revisited

Go to the main UK and international news websites and you will find, almost without exception, the same story right at the top of the page: the potential meltdown at Japan’s Fukushima I Nuclear Power Plant.

So what’s the current state of play? Very broadly, this is my understanding: a full blown ‘nuclear’ explosion is impossible (control rods were inserted into the reactors at the time of the earthquake which immediately ceased the nuclear chain reaction— all the current difficulties are down to excess heat); it seems a Chernobyl-style explosion (ie one that scatters radioactive material over a wide area) is extremely unlikely, due to improvements in reactor design; but some kind of a ‘Three Mile Island’-style meltdown is possible, as a worse-case scenario. Some mildly-radioactive steam was vented to release pressure within the reactor cores, and emergency flooding of the reactors for cooling means that there will be a volume of radioactive sea water to be disposed of afterwards, when the situation is under control. Unfortunately there were a number of injuries on the site, and one worker died operating a crane.

So: one death to date in the immediate aftermath of the nuclear emergency, from a crane accident. Of course, some radiation has been released, possibly with further releases to come: what about delayed fatalities from cancer in the local population? This is a complex issue that I’m not going to address here, other than to say that current descriptive epidemiological methods struggle to find unequivocal evidence for definite excess mortality in populations previously exposed to similar accidents: any effect is likely to be small. For example Hatch et al’s follow-up of cancer incidence of the population around Three Mile Island following the 1979 meltdown showed no effect, while Wing et al’s re-analysis which included dose estimates showed a tiny effect: an all-cancer percent increase per dose unit of 0.034 +/- 0.013, for the years 1981-1985. Of course longer follow up might show more cases and increase these estimates, but the absolute numbers are never going to be big (and these are incident cases, not deaths).

The Fukushima emergency, of course, is a direct consequence of the magnitude 8.9 (or greater?) earthquake which occurred about 100 miles off the east coast of Honshu Island two days ago. For clear, amateur-friendly geological explanations and nice diagrams, see here.

Another direct, and more immediate, consequence of the earthquake was the tsunami. It’s likely that the tsunami caused the majority of the 688 (and rising) confirmed death toll. Japan is a world-leader in earthquake-proofing buildings, but there’s only so much that can be done to protect against 6 metre-high walls of water rushing inland. Most fatality estimates on the news sites go much higher than 688, but in this case the wikipedia figure seems to be the most conservative, so we’ll stick with that for— yes, you guessed it— our news/death ratio calculation.

We have our fatalities: 1, and 688, for the Japanese nuclear emergency and for the tsunami, respectively (subject to the uncertainties above). Just now Google News UK generated 15,900 and 29,572 hits for ‘Japan earthquake nuclear’ and ‘Japan earthquake tsunami’ respectively.

NDR for earthquake-related nuclear emergency = 15,900
and for earthquake-related tsunami = 29,572/688 = 42.9

For NDRs, big numbers means hype. See here and here for context.

Excellent summaries of Fukushima nuclear situation here.


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