FUKUSHIMA--Despite clean-up efforts, relatively high levels of radiation remain at some locations around the crippled Fukushima No. 1 nuclear power plant, according to data from government pilot decontamination programs.
Interim results show that readings of 4-5 millisieverts per hour were detected at three locations at a height of 1 meter above the ground near the plant.
The levels exceed the 3.8-microsieverts-per-hour threshold, or the equivalent of a 20-millisieverts-per-year dose, which is used by the government as a measure for issuing evacuation orders.
The pilot programs, which started in November, cover 15 locations in 11 municipalities.
The Japan Atomic Energy Agency on March 26 held a briefing in Fukushima, the capital of Fukushima Prefecture, to release results obtained so far at 10 locations in eight municipalities.
The JAEA said the three locations around the plant originally had higher radiation levels of around 10 microsieverts per hour.
Officials of the government and the JAEA said the high residual radiation readings are partly due to the insufficient removal of radioactive substances and partly due to high radiation levels in the surroundings.
In regards to standards for the realignment of evacuation zones that are expected to be set soon, the reduced levels correspond to the category of "no-residence zones," where the residents will have to wait years to return.
The interim report also showed that decontamination reduced the air radiation levels to 1-2 microsieverts per hour at the remaining seven locations, where they used to be around 5 microsieverts or less per hour before decontamination started.
According to the standards for the revised evacuation zoning, those locations will be categorized in the "zones being prepared for the lifting of the evacuation order," where the residents can expect to return soon.
The government also evaluated the various decontamination techniques, tested during the pilot programs, on the basis of their efficiencies, dose reduction rates and other factors.
The government said high-pressure spraying of housing roofs cannot be recommended, partly because splashed water can contaminate the surroundings. Brushing and wiping with a cloth were recommended instead.
The report also said that the most effective decontamination methods in athletic fields include overturning the surface soil; in forests, the removal of fallen leaves, humus and surface soil; and on asphalt-paved roads, cleaning under extremely high pressure, more than 10 times the typical levels, and shaving off the surface.
The government plans to reflect the latest findings in its guidelines on basic decontamination techniques.
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