Radiation imaging of a highly contaminated filter train inside Fukushima Daiichi Nuclear Power Station unit 2 using an integrated Radiation Imaging System based on a Compton camera

The Fukushima Daiichi Nuclear Power Station (FDNPS) suffered a meltdown in the aftermath of the large tsunami caused by the Great East Japan Earthquake that occurred on 11 March 2011. A massive amount of radioactive substance was spread over a wide area both inside and outside the FDNPS site. In this study, we present an approach for visualizing a radioactive hotspot on a standby gas-treatment system filter train, a highly contaminated piece of equipment in the air-conditioning room of the Unit 2 reactor building of FDNPS, using radiation imaging based on a Compton camera. In addition to fixed-point measurements using only the Compton camera, data acquisition while moving using an integrated Radiation Imaging System (iRIS), which combines a Compton camera with a simultaneous localization and mapping device and a survey meter, enabled the three-dimensional visualization of the hotspot location on the filter train. In addition, we visualized the hotspot and quantitatively evaluated its radioactivity. Notably, the visualized hotspot location and estimated radioactivity value are consistent with the accident investigation report of the FDNPS. Finally, the extent to which the radioactivity increased the ambient dose equivalent rate in the surrounding environment was explored.

Automated summary

In this study, a radioactive hotspot on a highly contaminated standby gas-treatment system filter train in the air-conditioning room of the Unit 2 reactor building of the Fukushima Daiichi Nuclear Power Station was visualized using radiation imaging based on a Compton camera. The hotspot location was visualized and its radioactivity was quantitatively evaluated using an integrated Radiation Imaging System. The increase in ambient dose equivalent rate in the surrounding environment due to the radioactivity was also explored.