Despite the passing of 13.5 years since the TEPCO’s Fukushima Daiichi Nuclear Power Station (FDNPS) accident, the areas inside the FDNPS buildings remain high-dose rate making it difficult for workers to enter and work for extended periods. Understanding the distribution of radioactive contamination in these work sites is crucial for reducing worker exposure and planning work strategies.
 To address this problem, the Japan Atomic Energy Agency has developed the integrated Radiation Imaging System (iRIS) to visualize the three-dimensional (3D) distribution of radioactive contamination in the work environment and conduct demonstration tests *.
 Figure 1 shows the results of a demonstration test conducted inside the Unit 1 reactor building in collaboration with TEPCO HD. Since the building contains high-dose rate areas making entry of workers difficult, the iRIS was mounted on a mecanum wheel robot to conduct the survey remotely. This system comprises a Compton camera, SLAM device, and survey meter. The results show a sharp increase in dose rates directly below the high-concentration radioactive contamination on the ceiling pipes (Red region of panel Fig. 1b). Through the iRIS based-remote survey of high-dose rate areas inside buildings in FDNPS that were previously not surveyed, we can contribute to improving the environment inside the FDNPS buildings.
 

* Japan Atomic Energy Agency, "Visualization" of Radioactive Contamination at the Decommissioning Site on a 3D Map−Understanding Invisible Radioactive Contamination in a Virtual Space and Reducing Worker Exposure−, May 14, 2021, Press release.

This research was conducted as a joint research project with the Tokyo Electric Power Company Holdings, Inc., entitled “Research on Performance Verification of Analytical Instruments in Decommissioning Site Environments.”