Integration of Mobile Robotics and Radiation Measurement for Decommissioning of Fukushima Daiichi Nuclear Power Plant and other applications (JK Joint Workshop 2019)

Integration of Mobile Robotics and Radiation Measurement for Decommissioning of Fukushima Daiichi Nuclear Power Plant and other applications Yusuke TAMURA, Hajime ASAMA The University of Tokyo [email protected] 2019 Japan-Korea Joint Workshop on Next Generation Robotics, Dec. 21, 2019.

Accident of Fukushima Daiichi NPP Tsunami caused meltdown & explosion Meltdown (Unit 1, 2, 3) Hydrogen explosion (Unit 1, 3, 4) A large amount of radioactive material was scattered. March 2011 Unit 1 Unit 3 Unit 2 Unit 4 August 2019 The dose rate inside/outside the site has decreased, but the dose rate inside the reactor building is still high. Decontamination is required to reduce the radiation exposure risk of workers. 2

Nuclear Security Possible nuclear security incidents - Dirty-bomb Dispersal of radioactive materials using conventional explosives or any other type of radiological dispersion device. - Silent-source attack Hidden radioactive material placed in a public space such as a stadium, station, airport, shopping mall, etc. Manual searching for radioactive materials Courtesy by Dr. Tsuchiya (National Research Institute of Police Science) Detection method of radioactive materials is required. 3

Objective 3D mapping of radiation sources Requirements - Unmanned radiation source mapping - Localization of concealed/invisible radiation sources 4

Related works (1) Survey of radioactive contamination in the reactor building of Unit 1 (Dec. 2013) Warrior (iRobot) Gamma camera with collimator http://photo.tepco.co.jp/date/2014/201401-j/ 140117-01j.html Gamma camera with collimator … Collimator is very heavy for small robots 5

• http://photo.tepco.co.jp/date/2014/201401-j/

Related works (2) Using a Compton camera that does not require a collimator Radioactive source localization and mapping with UAV [Vetter2019] Assumption that radiation source is on a visible surface … Gamma-rays have high penetrating power 6

Our approach Gamma-ray CT by using mobile robot with Compton camera Radiation detector Radiation source? Mobile robot Observation Move 7

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Gamma-ray Gamma-rays are the photons emitted from the atomic nuclear decay of radioactive isotopes. 137 55 （e.g.）137 55 Cs Cs 30.17y β- decay 137 55Cs γ decay 137m ! 56Ba + e +⌫ β-, 94.6%, 512 keV 2.55m γ, 662 keV 137m 56Ba 137 ! 56Ba + β-, 5.4%, 1.17MeV Gamma-rays can pass through many kinds of materials. paper aluminum lead 137 56 Ba water, concrete alpha beta gamma/X neutron 8

Compton camera Gamma-rays are scattered on the first layer (Compton scattering) and absorbed on the second layer (photoelectric effect). Radiation source scattered photon 0 Gamma-ray (photon) θ ✓ incident photon scatterer ✓ absorber ◆ 2 ✓ recoil electron 1 E2 1 E1 + E2 ◆ cos ✓ = 1 me c 1 1 ✓ ◆ = 1 me c 2 E2 2 E11 :+deposited E2 1 energy on scatterer c : light speed m : electron mass e cos ✓ = 1 me c on absorber E2 : absorbed E1 + Eenergy 2 <latexit sha1_base64="lu/Cf4S7fI2pX3rx5Qu1Ikpy69Q=">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</latexit> <latexit <latexit sha1_base64="Wg2vZ/PqrDYR6SWLo2vnPQc6cEQ=">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</latexit> Incident angle and nuclide can be estimated. 9

Gamma-ray CT Single-Photon Emission Computed Tomography (SPECT) Gamma camera Collimator Gamma-ray radiation source https://www.innervision.co.jp/var/ezwebin_site/storage/ images/ad/suite/siemens/technical_notes/1407pr/ intevo/91359-1-jpn-JP/intevo.jpg Position and orientation of the detector is required for tomography. SLAM technique is used for localization of a Compton camera mounted on a mobile robot. 10

• https://www.innervision.co.jp/var/ezwebin_site/storage/

Gamma-ray CT with mobile robot SLAM Compton Camera LOAM (Lidar Odometry And Mapping) Gamma-ray ✓ Scatterer Pose Absorber Compton cone MLEM (Maximum Likelihood-Expectation Maximization) Estimate the most likely tomographic image from the projected image by iterative calculation 3D radiation map 11

Use of map information Radiation sources are NOT on the LiDAR side from the observed objects BUT on the surface of objects or behind them. unknown Invisible radiation source free obstacle Reconstruction area can be limited only to the obstacle/unknown area of the map. for fast and accurate source localization 12

Experimental setting Robot & sensors Environment Velodyne VLP-16 Compton camera Source 2 Pioneer 3DX Source 1 Radiation source: 137Cs 2.2MBq # of measurement locations: 10 13

Result Radiation source localization Previous study [Kim2017] Proposed method Error (m) [Kim2017] Proposed method Source 1 N/A N/A Source 2 0.40 0.09 14

4π Compton camera Three-dimensional arrangement of detector elements Radiation source Normal Compton camera 4π Compton camera 15

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Summary Objective: 3D mapping of invisible radiation sources Approach: Gamma-ray CT by using a mobile robot equipped with a Compton camera Ongoing & Future work: Online 3D mapping of radiation sources using a 4π Compton gamma-ray imager mounted on a mobile robot 17