A nuclear advisor to the Cabinet has resigned in protest against government stopgap measures that deal with the ongoing nuclear crisis in Fukushima Prefecture.
Toshiso Kosako, 61, a University of Tokyo professor specializing in radiation safety, submitted a letter of resignation to the Prime Minister's Office on April 29.
In particular, Kosako protested against the government's decision to revise the maximum permissible level of radiation exposure among children up to 20 millisieverts per year, saying, "Should I approve that decision, I would no longer be a researcher. I would not want my children to be exposed to that amount of radiation."
Kosako revealed the Cabinet did not accept his advice that outdoor school activities for elementary and junior high school students near the crippled power station be restricted to prevent them from being exposed to over 1 millisievert of radiation per year.
"It is quite rare for nuclear power plant workers dealing with radioactive materials to be exposed to 20 millisieverts of radiation per year. I cannot allow infants and children to be exposed to such high levels of radiation from an academic as well as humanitarian point of view."
In a tearful news conference, Kosako said he could not stay and allow the government to set what he called improper radiation limits of 20 millisieverts an hour for elementary schools in areas near the plant.
"I cannot allow this as a scholar," he said. "I feel the government response has been merely to bide time."
I am not a health physicist (i.e. radiation expert), but I think Professor Kosako is correct. 20 mSv/year (which is also the evacuation threshold) is not a dose to be subjected to without good cause. It is ten times background radiation; it is comparbale to a CT scan every year. Based on ICRP recommendations, 20 mSv (1 year) should be estimated to cause an excess fatal-cancer risk of 0.1% (general population -- for children this should be higher?):
Admittedly there is signficiant uncertainty about such a prediction, as 20 mSv is a sufficiently low dose that emprical data does not exist (you can only extrapolate from known effects at much higher doses). The Health Physics Society, for instance, recommends against quantiative estimation below 50 mSv (5 rem). But 20 mSv is pretty close to 50 mSv; I should think there's a good chance there are substantial health risks at this dose rate, even if the linear extrapolation is an overestimate.
As a related issue (one I've been repeatedly bringing up), some people in yet-to-be-evacuated areas have already received doses of up to 20 mSv (in Namie, measured), or maybe 50 mSv (extrapolated). Actually these are outdoors doses, so actual exposures are attenuated (by maybe a half).