Japan’s Nuclear Regulation Authority has decided to increase the maximum annual radiation exposure limit for nuclear workers in emergencies to 250 millisieverts (mSv) per year from the current 100, starting from April 2016, a statement said.
The standard worker dose limit for Japanese workers is 50 mSv per year and 100 mSv over five years. Before the 2011 Fukushima-Daiichi accident, the emergency dose limit was set at 100 mSv per year, but was raised to 250 mSv per year to allow workers to respond to the accident. It was returned to 100 mSv per year in December 2011.
According to recommendations by the International Commission on Radiological Protection, the annual dose limit for controlled nuclear workers or medical personnel is 20 mSv per year, but can reach 50 mSv per year in an exceptional year when the five-year average is not higher than 20 mSv per year.
In light of the situation at Fukushima-Daiichi, the NRA had been considering increasing the limit in the event of another nuclear incident or emergency.
NRA chairman Shunichi Tanaka said the current limit could be an obstacle in containing a crisis and the revision, which will entail a legal amendment, is “a step forward” in addressing the issue.
The NRA said it believes increasing the limit to 250 mSv per year is appropriate based on overseas standards and scientific studies.
The International Atomic Energy Agency recommends 500 mSv per year as the maximum annual acceptable exposure limit for workers in emergencies.
It says the 500 mSv per year limit applies to those involved in ‘Type 1’ tasks such as saving lives and preventing core damage or a large radioactive release. The IAEA sets a limit of 100 mSv per year for those involved in ‘Type 2’ tasks, such as preventing serious injury, averting a large collective dose or preventing the development of catastrophic conditions.
The NRA said on its website that it would begin a consultation exercise on its decision to increase the limits. The consultation will end on 19 June 2015.