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JCO Criticality Accident:

STA Lowers Evaluation Levels of Exposure Dose

On Jan. 31, 2000, the Science and Technology Agency (STA) released the exposure levels of the local residents and the workers who carried out various tasks, such as the extraction of coolant water, during efforts to contain the criticality accident at Tokai-mura, Ibaraki Prefecture in September last year. These levels are drastically lower than the previous dose level evaluations. STA explains that in the case of residents, lower dose levels are the result of considering the shielding effects of buildings, and for the workers, a result of revising sensitivity of the pocket dosimeters and neutron Rem counters.
According to the report, there were 119 residents who were exposed to more than 1mSv, the annual dose limit for the public, and the highest exposure rate is estimated as low as 21mSv. As for exposed workers, the worker who was measured to have received 120mSv during the extraction of coolant water is estimated in the latest report to have been exposed to less than 50mSv. However, this is just one evaluation result which itself contains margins of error, and could easily be several times larger or smaller depending on methods of evaluation.
On Feb. 16, CNIC, acting with the "Criticality Accident Victims' Group," submitted a proposal to the STA and the Nuclear Regulatory Commission regarding the details of the exposure dose evaluation for this accident and the ways these agencies have been treating the local residents.
The proposal contained the following four demands; 1) The withdrawal of, and an apology for propagandizing to the public the false argument that doses less than 200mSv or 50msv are safe, thereby implying that there is a threshold level of safety. 2) A scientific reevaluation of the latest dose level estimates. 3) A repeat of the dose evaluation for the JCO accident on the basis of the 1990 recommendations of the International Commission on Radiological Protection. 4) Exposed residents must be guaranteed health examinations in accordance with those for nuclear-workers, including blood tests, and that they should be issued with health management cards.

by Chihiro Kamisawa


Citizens' Nuclear Information Center
Akebonobashi Co-op 2F-B, 8-5 Sumiyoshi-cho,
Shinjuku-ku, Tokyo, 162-0065, Japan