10/6/2011 Gov't panel mulls interim goals on radiation dose

Source: NHK World 
Date: Thursday, October 06, 2011 15:39 +0900 (JST)
by: Yuko Fukushima


A government panel is calling for Japan's one-millisievert annual radiation limit to be eased for the interim, saying it will be difficult to restrict exposure in some areas near the troubled Fukushima nuclear plant.

The environment is contaminated by radioactive substances in areas hit by fallout from the Fukushima Daiichi nuclear power plant, causing concern that residents may be exposed to radiation for long periods.

The panel on radiation believes it will be difficult to keep their dose below the one-millisievert limit set by the government for normal times and proposed on Thursday to set an interim exposure target.

It says the target should be set between one and 20 millisieverts in line with recommendations by the International Commission for Radiological Protection.

The panel says the target should be lowered in steps as decontamination progresses.

It adds that targets could differ by region and that residents should have a voice in setting the targets.

The panel will wrap up its proposal at its next meeting, but its plan to ease the radiation exposure limit is expected to arouse controversy.

Editor's Note: Although it is true that the ICRP (International Commission for Radiological Protection) does give discretion for setting the maximum yearly safe limit, it seems like common sense that instead of arbitrarily raising the safe dosage to match current conditions, it would be better to move people further away from hot spots so that they can meet the lowest yearly radiation dose limit possible. 

What they are actually doing is sending people back in to previously evacuated areas, rather than expanding the exclusion zone and evacuating more people from known hotspot areas. Excerpts from ICRP Publication 103 concerning the guidelines for yearly radiation exposure thresholds can be found here. Page 165 and 166 of the Full text PDF file which contains the excerpted pages from Publication 103 is where the 1 millisieverts/year and 20 millisieverts/year thresholds appear. Another useful reference is ICRP Publication 111 which gives guidelines for protection of people living in long-term contaminated areas. From skimming through this document 1 millisievert/year is a key exposure level. If I understand correctly, if you are getting over 1 millisievert/year you are under normal circumstances considered to be working in a "planned exposure" situation (e.g. you work with radiological materials in healthcare or as a nuclear plant worker etc.). 

Note that 20 millisieverts per year is the maximum allowable dosage for nuclear workers worldwide in most places (averaged over 5 years) as per World Nuclear Association. So basically what the Japanese government is proposing is to potentially up the maximum allowable dosage for an average Japanese citizen to the same level as for nuclear workers!