Decontamination : How long still ?

Decontamination needed even after residents return

The Yomiuri Shimbun

http://www.yomiuri.co.jp/dy/national/T120409003637.htm

If decontamination work does not continue for a certain period in areas highly contaminated by radioactive substances from the Fukushima No. 1 nuclear power plant, returning residents will be exposed to at least 100 millisieverts of accumulated radiation over 30 years, the Science Council of Japan said Monday.

An accumulated radiation level of over 100 millisieverts increases the mortality risk from cancer by 0.5 percent.

The council estimated how radiation exposure would change over 30 years, looking at the level before residents were evacuated, the annual level when they return and the existence or lack of decontamination work.

It found residents would likely be exposed to nearly 250 millisieverts of radiation over 30 years if they return home when the annual radiation exposure level drops to 20 millisieverts and decontamination work does not continue, even if radioactive decay is taken into account.

If residents return home when the annual radiation exposure level drops to 10 millisieverts and decontamination work does not continue, they likely would be exposed to more than 100 millisieverts over 30 years.

However, if decontamination work continues for five years after residents return home following a drop to 10 millisieverts, the likely radiation exposure level drops to 80 millisieverts.

"It's necessary to make plans to continue decontamination and to sufficiently control radiation exposure after residents return home," said Fumiko Kasuga, a vice president of the council.

Also Monday, the council compiled a proposal that the density of radioactive substances in debris created by the Great East Japan Earthquake in Iwate and Miyagi prefectures is quite small and it is possible to dispose of debris in a wide range of areas.

Many municipalities have refused to accept the debris for disposal.