Saturday, May 28, 2011

Protests by Fukushima parents pay off - Radiation limits for students will be revised lower, and topsoil will be removed from Fukushima schools

If you recall what transpired last month, education board officials overseeing schools in the Fukushima Prefecture jacked up permissible doses for school children from the standard 1 milliSievert/year to a very difficult to accept 20 milliSievert/year.  Angry parents have been protesting ever since, and have succeeded in forcing the Ministry of Education to acquiesce to their demands.  From the NYT:
"The education minister, Yoshiaki Takaki, said Friday that the government would, for the time being, revert to the original limit of 1 millisievert a year. Mr. Takaki said the government would pay for local schools with radiation levels above that limit to remove contaminated topsoil from their grounds.

“We will provide financial support to schools for measures to deal with soil in schoolyards as a way to lower radiation levels for children,” Mr. Takaki said at a news conference."
It was a tough call.  Education officials - weighing radiation safety vs Japan's high educational expectations - facilely cited a 2009 recommendation from the International Commission on Radiological Protection (ICRP) that addresses this sort of scenario.  During emergencies, the ICRP Publication 109 states that populations can be exposed to 20 to 100 mSv per year for short periods of time. The education ministry calculated that children could spend 8 hours a day in a schoolyard exposed to as much as 3.8 microsieverts per hour, and 16 hours a day indoors exposed to 1.52 microsieverts per hour.  Under these circumstances, annual doses would come in just under the 20-mSv limit.

Mext had recently conducted measurements at 58 public schools, and said none of them exceeded 3.8 microSeiverts per hour.  After the removal of topsoil, municipality officials are stating that doses in some areas will be reduced to just 0.6 microSievert/hour.

Here's a note of concern: ICRP recommendations, along with official exposure measurements are taken "in air", and are likely read with the equipment some distance from the ground.  If activity is as high as 600,000 becquerels per square metre in some areas like the IRSN recently reported, foot and ankle doses could be higher than official numbers by a factor of 2-4 due to beta contribution and principles of inverse square law.

If you measure the distance from ground to gonads for younger children (Kinder through Grade 6), you begin to appreciate why they should make the distinction.  In addition to the generic 'in air' reading, it's helpful to see the exposure numbers taken at 5cm, 20 cm and 1 meter levels from the soil.


  1. Robbie001 sez:

    Another note of concern is dust the kids raise during play will become an inhalation hazard. Never mind any local dust storms or even something as simple as plowing a dry field could be hazardous.

  2. You can find a live stream geiger counter reading from Iitate, Fukushima by scrolling a few posts down or going to the 'live geiger counter readings in Japan' page on this blog. I find this particular stream is invaluable. It gives us access to outdoor readings in the non-exclusion zone area, and it's typical of the exposures Fukushima residents face on a daily basis.

    I watch it regularly. Readings during the day are usually a solid 3-4 micro Sievert/hr. At night it seems to go indoors, where it drops into the 0.5-.075 range.

    The parents are expecting the ministry of education to create an environment where kids won't exceed 1 milliSv/yr. How is that possible? Any rates that average over just 0.114 microSv/hr, and they go above the limit.