Introduction of external drift kriging into the program for estimating radioactivity distribution ESRAD code for supporting final survey of site release

Shimada, Taro ; Nabekura, Nobuhide*; Takeda, Seiji 

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.