Study on application of kriging to evaluation of radioactivity concentration for ensuring compliance with the criterion of site release

Ishigami, Tsutomu; Shimada, Taro 

In the field of decommissioning of nuclear facilities, a reliable method for ensuring compliance with the criterion of site release is an important technical issue to be resolved in Japan. Considering that kriging can consider the spatial correlation of radioactivity concentrations, we propose a method of applying kriging to ensure compliance with the site release criterion. Estimated radioactivity concentrations exhibit uncertainty, which results in a certain probability of the occurrence of decision errors regarding site release. We describe a method for calculating the uncertainty and establish a minimum number of measurement points required. We applied the proposed method and a conventional statistical method to two sample cases. It was observed that the proposed method appropriately estimated the mean radioactivity concentration and led to an efficient measurement requiring fewer measurement points relative to the conventional method when spatial correlation existed.