Consistency required for Fukushima return

24 January 2014

Decontamination near the Fukushima Daiichi plant is progressing more efficiently, with convergence on measures that will support a return to evacuated areas. An IAEA team encouraged experts to communicate that radiation dose rates below 20 mSv per year are acceptable.

A group organised by the International Atomic Energy Agency (IAEA) spend a week touring the area in October last year. Today it released its final report on the efforts made by Japanese authorities in handling the clean-up and social impacts of the accident.

"In remediation situations, any level of individual radiation dose in the range of 1 to 20 mSv per year is acceptable and in line with the international standards" 
IAEA International Mission Report

Successful engagement with people affected by the accident was noted at the national, prefectural and municipal levels. Intermediaries such as doctors, local leaders and independent scientists have been effective, said the IAEA team, in fostering confidence in data coming from the area and its interpretation.

Realistic doses, realistic plans

During the accident in March 2011 some 160,000 people were evacuated from an area within 20 kilometres of Fukushima Daiichi as well as zone to the northwest. The majority are yet to return to their home towns, although most have been able to make daylight visits to maintain property. The government has surveyed each evacuated municipality, estimating the dose rates resulting from the contamination and characterising their readiness for return to normality.

Several evacuated municipalities near Fukushima Daiichi have already been classified as 'ready to return' - meaning they have a calculated doses rate of 20 mSv per year or less. However, this is based on a generic formula that assumes a person spends 8 hours outside with no protection, and the rest of the time inside. In fact, the formula has been shown to significantly overestimate individual doses, due to different amounts of time spent outdoors and because people will readily modify their daily routines when given advice on how to reduce their radiation dose. In 22 towns across Fukushima prefecture a study of 77,400 people recorded individual doses some three to seven times less than those predicted by the generic formula.

"There needs to be a continued movement towards the use of individual doses, as measured by personal dosimeters," said the IAEA. This would support planning for resettlement, and can also reassure people in the wider prefecture - particularly parents of small children.

IAEA on food and farming
"Comprehensive implementation of food safety measures has protected consumers and improved consumer confidence in farm produce, reflected in an increase in economic value of the crops."
"Intensive monitoring of foodstuffs has shown that much of the land can produce food below the reference level for permissible radioactivity, and that remediation measures, such as the application of potassium fertilizer, are effective."

At the same time, IAEA welcomed that clean-up teams in the wider prefecture are focusing their work on reducing air dose rate - typically measured 1 metre above the ground - rather than measurements taken at the surface itself. These are more reflective of the doses actually received by people in normal life. "This is leading some municipalities to conclude that an additional 1 mSv per year is more applicable to a long-term dose reduction goal" that cannot be achieved solely by decontamination. This is turn leads to better informed decisions a more efficient allocation of resources.

The IAEA team encouraged Japanese institutions to "increase efforts to communicate that in remediation situations, any level of individual radiation dose in the range of 1 to 20 mSv per year is acceptable and in line with the international standards and with the recommendations from the relevant international organisations." Here they refer to studies from the International Committee on Radiological Protection (ICRP), the United Nations Scientific Committee on the Effects of Atomic Radiation, the World Health Organisation (WHO) and the IAEA itself.

Researched and written
by World Nuclear News