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Shimada, Taro; Nabekura, Nobuhide*; Takeda, Seiji
no journal, ,
It is necessary to confirm that the public radiation exposure dose by residual radioactivity is less than the criteria after site release at the completion of decommissioning of nuclear facilities. In order to obtain the radioactivity distribution in the site to evaluate the public dose, we have been developing a computer code, ESRAD, which estimates the radioactivity distribution from limited measurement data of radioactivity of soil in the site using the kriging. In this study, we improved the code by introducing the external drift kriging where dose rate distribution obtained before final survey was used as supplement information. Some calculations were carried out supposing hypothetical radioactivity distribution. As a result, the external drift kriging using dose rate distribution may improve the estimation results rather than the ordinary kriging.
Shimada, Taro; Nabekura, Nobuhide*; Miwa, Kazuji; Takeda, Seiji
no journal, ,
It is required to confirm that dose of public using the land after site release for is less than the criteria by dose evaluation based on the contamination distribution obtained by site survey before the completion of the decommissioning of nuclear facilities. Therefore JAEA is developing the methodology to evaluate public dose. We studied estimating methods for contamination distribution based on the data from the scoping survey and the final sampling measurement with errors using external drift kriging. As a result, it is indicated that estimated distribution by external drift kriging using scoping survey results with measurement errors is the same as that without measurement error. Estimation variance was increased with measurement errors. Therefore the evaluation method will be applied to determine the radioactivity distribution with uncertainty.
Shimada, Taro; Nabekura, Nobuhide*; Miwa, Kazuji; Takeda, Seiji
no journal, ,
It is necessary for confirmation of completion of decommissioning of nuclear facilities to comply with dose criteria for public using the land after site release, based on the radioactivity distribution at the land of the site. We are developing a methodology of public dose evaluation based on the survey results of evaluation of the radioactivity distribution. In this report, the external drift kriging method combined with scoping survey and sampling measurement were applied to 1km square area, and a cross validation method was applied to validate the evaluated distribution. Index of Mean Absolute Error is appropriate to evaluate the difference between evaluation and measurement. In addition, upper limit of 95% single side confidence interval for the evaluation of non-measured point was suggested to input for dose evaluation.