The evacuated area around the crippled Fukushima No. 1 nuclear power plant will be divided into five zones along municipal borders under a staged government plan to return residents to their homes, sources said Feb. 10.

Priority will be placed on decontamination, infrastructure rebuilding and the early return of evacuees to the inland municipalities of Tamura and Kawauchi, where radiation levels are low.

But full-scale decontamination in the Futaba and Okuma municipalities, which contain the stricken plant and where radiation levels are relatively high, will be put off, with only pilot programs envisaged in the short term.

The zoning will be decided not only on the basis of radiation levels, but also the extent of damage from the March 11 tsunami. Rebuilding work in the easiest zones is expected to begin in earnest in the spring.

An estimated annual dose for each resident of 20 millisieverts of radiation or less will be used as an indicator of habitability, with areas below that threshold designated "zones being prepared for the lifting of the evacuation order."

Places with annual radiation between 20 and 50 millisieverts are referred to as "no-residence zones," while locations with radiation exceeding 50 millisieverts are labeled "no-return zones."

The first zone encompasses inland districts that were not hit by the tsunami. Tamura city contains no area in excess of the 20 millisieverts limit, and estimated annual doses are also below 20 millisieverts in most parts of Kawauchi.

The government plans to finish decontamination work by March 2014 and have evacuees settled in their homes in those areas at an early date.

In coastal parts of Minami-Soma and in Naraha, annual radiation doses are generally below 20 millisieverts, but the tsunami destroyed key roads and waterways. That means they will be zoned separately, as areas where significant infrastructure rebuilding will have to accompany decontamination.

The inland municipalities of Kawamata, Iitate and Katsurao were not hit by the tsunami, but they include areas of both low and relatively high radiation doses. The government plans to first reduce the radiation doses to 20 millisieverts or less across all those districts.

Namie and Tomioka both were severely affected by the tsunami, and contain radiation hotspots. The government, therefore, plans to proceed with decontamination and infrastructure rebuilding concurrently and to have evacuees return home in stages, starting with areas with low radiation.

The Okuma and Futaba municipalities constitute the fifth and most challenging zone, with estimated annual doses of radiation exceeding 50 millisieverts in many localities. In the immediate future, decontamination work in the area will be limited to research to find out the most effective approaches.

While the central government is planning to take a direct and leading role in the decontamination of the 20-kilometer "no-entry zone" around the nuclear plant and the "planned evacuation zone" encompassing some areas beyond 20 km, it will have to coordinate its efforts with local authorities.

That may result in different approaches in different areas. The government of Iitate village, for instance, has its own plan to start decontamination work areas at high elevations, and that may mean a unique approach on the ground.

(The Asahi Shimbun, 11/02/2012)