Daily Archives: June 23, 2011

Japan Nuclear Disaster Update 29: Indecent Exposure

Much of the current news is about exposure and fallout.

As a point of information, the Sievert is a unit of “dose equivliant” from exposure to ionizing radiation. It was designed to indicate relative levels of biological effects on living organisms. This measurement technique attempts to take into account the fact that radiation is absorbed differently by different tissues. Usually we speak in terms of humans unless otherwise specified. There are one thousand millisieverts in a sievert (mSv). Zero to 0.25 Sv in a day is considered to have no effect. At up to one Sv people feel sick and more susceptible tissues are damaged. 10 Sv in a day is deadly. As one goes from 1 to 10 Sv in a day things get worse. If a person is esposed to about 6 Sv in a day or more, they won’t die that day. But later, they probably will. Some of the numbers are given in microsieverts, one thousand times less than a millisievert.

In practice, it is common to measure the effects of radiation exposure accumulated over longer time periods. For example, one measures the maximum dose allowed for US radiation-related workers at 50 mSv per year. When mSv is being discussed in most of the text in Ana’s feed (below) you should assume “per year” is meant if not stated, unless otherwise indicated, although in some cases it seems that the measure being used is accumulated to date, which is closer to one fourth of a year.

The question has been raised; Are increased radiation levels across North America sufficient to explain a jump in infant mortality seen since Fukushima, or is that a coincidence? These deaths are concentrated in the region that would have a larger increase of exposure (the west coast). Probably not. Fukushima is so far away. Babies are so … tough and able to withstand toxic insults. And you can’t see radiation, so how bad can it be? Anyway, it ends up that this is probably some very creative data cooking.

One of the main problems at Fukushima at present is the highly radioactive water flooding the structures’ basements. As this water is being pumped around a certain unspecified (probably unknown) amount of radioactive material is being removed from it. In theory, it is possible to remove most of the raidioisotope from the water, but then one is stuck with a pile of radioactive carbon filtering material. An unknown amount of water is leaking from the plant before being contaminated. Efforts to decrease the amount of water being pumped into the plant, and thus becoming contaminated, were tried but resulted in increasing heat in a reactor core.

The other main, continuing story is the growing understanding of how poorly prepared TEPCO was for any sort of disaster at the plant, and how much sweeping under the rug was going on after the earthquake and tsunami.

Meanwhile, efforts continue to reinforce the Number 4 reactor spent fuel rod containment pool which is thought to be too weak to sustain a serious earthquake. Reinforcement is in fact being put in place but it will be several more weeks before that job is done. The water in the containment pool is still quite hot.

Enigmatically, even though the situation at Fukushima improves only very slowly and radiation continues to spew from the plant, the International Atomic Energy Agency no longer sees it as the top story, and it is now supplanted by various IAEA activities and an FAQ about nuclear safety, relegated to page two, as it were, of their web site. The latest update is still JUne 2nd.

Ana’s Feed

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