A Study on dose control for Tokaimura criticality accident termination

Kanamori, Masashi; Suto, Toshiyuki ; Tanaka, Kenichi*; Takada, Jun*

It has been ten years since the Tokai-mura JCO criticality accident. Verification of dose control method and dose estimation for the termination of the accident was performed. At the time of the termination work, personal dose estimation and control was performed based on measurements of neutron and ray doses taken before the termination work. But the personal dose for workers as a result of termination work was found to be at least 50 times higher than the estimation made beforehand. We reevaluated doses based on the results of close range measurement from 40 m to 100 m, and based on theoretical reduction by distance. The results were found to match personal doses with a precision between 60-80%. Therefore, work can likely be done safely by taking into account three factors, (1) annual dose limits for workers, (2) dose to workers from sources other than the pertinent work, (3) measurement error, and adopting 10 mSv as a dose guideline for tasks such as dose evaluation.