Japan has been advised not to be overly conservative in its decontamination of areas affected by the Fukushima accident. Its work so far has been good but it should focus squarely on effective reduction of public radiation dose.
The advice comes from a team of 12 experts assembled by the International Atomic Energy Agency (IAEA) that has spent time with Japanese authorities over in the area marked for 'deliberate evacuation', northwest of the Fukushima Daiichi plant.
This is the area where most of the released radioisotopes came to ground, settling on the surfaces of buildings and into the first five centimetres of topsoil. Virtually everyone has left this 500 square kilometre area on advice from government, and they will not return until radiation doses from contaminants are assured to be less than 20 millisieverts per year.
The Japan Atomic Energy Agency (JAEA) has been leading the decontamination effort, sometimes organising teams of volunteers. For example, parents have now successfully decontaminated around 400 school playgrounds. Areas frequented by children are being dealt with first, and JAEA is working to build up a "practical catalogue" of decontamination techniques to ease the work in wider areas that will follow.
According to the IAEA team, JAEA's mapping has given "a good basis for a successful remediation program" and real-time radiation monitoring will be publicly available. These are "important measures to reassure the public and the international community." Authorities will need to move from building to building, systematically cleaning areas where radioactive elements have accumulated.
The IAEA team praised JAEA and its partners for moving quickly with the work, and the government for supplying the necessary resources. JAEA's public information was acknowledged by the team, which said support from local agencies in Fukushima was "an effective self-help mechanism."
The principle advice for the Japanese government was that it should "cautiously balance" the different factors that affect the net benefit of clean-up to ensure the actual reduction of radiation doses to the public. "They are advised to avoid over-conservatism which could not effectively contribute to the reduction of exposure rates."
In practical terms this translates to focusing on the quickest dose reduction, without unwanted side effects like classifying millions of tonnes of very lightly contaminated topsoil as 'radioactive waste'. It may be desirable to remove this soil from childrens' playgrounds, for example, but some of the material may pose no realistic threat to health and could be recycled or used in construction work, said the IAEA team.
Another point of consideration is the handling of large open areas like forests. "The investment of time and effort in removing contamination beyond certain levels... where the additional exposure is relatively low, does not automatically lead to a reduction of doses for the public." Japanese authorities have already noted that removing some contaminated leaf mold could have a greater harmful effect on some parts of the ecosystem.
Achieving the right classification for this kind of clean-up is vital, and the IAEA offered to support Japan in considering "new and appropriate" criteria.
At the same time, Japan will need properly designated end points for contaminated soil and debris that does indeed require long-term management - and plans for this must include local people and agencies as much as possible.
In urban areas "it is obvious that most of the [waste] material contains very low levels of radioactivity," in the opinion of the team. The right place for most of this to be managed would be existing facilities for industrial waste facilities, rather than specialist radioactive waste.
The team was cautiously positive towards agriculture, saying "for the next cropping season there is room for reducing some of the conservatism." One factor here could be that ploughing at some farms has already moved the contaminated upper part of the topsoil to levels not reached by crop roots. Agriculture is another area that IAEA stands ready to support Japan in considering a new strategy, based on results from experimental areas.
Researched and written
by World Nuclear News