Assessing the extent of railway contamination

摘要

Restoration of damaged railway lines is important to help returning residents resume normal living conditions. Preliminary investigation of contamination of the railway track and the radiation dose for workers during restoration works was conducted. Investigation points were located between 20 - 30 km from the accident site. Major issues in evaluating the dose are as follows. To date, fallout caesium has mostly been adsorbed in surface layer of the soil. However, there is no depth profile data of caesium in railway ballast (crushed stone). The second issue is whether radioactive hot spots exist near railroads, for example in cable trenches or side ditches. The third issue is whether an internal exposure due to radioactive dust generated by restoration work is significant or not. Typically four points along the railway were investigated: earth fill, cut earth, combination of earth fill and cut earth and bridge. Air dose of those points are 0.2～1.0 μSv/h.