The Great East Japan Earthquake occurred on March 11, 2011, and the accident at TEPCO's Fukushima Daiichi Nuclear Power Station caused widespread contamination in Fukushima Prefecture and elsewhere. JAEA started its activities on the day of March 11 when it was dispatched by a Self-Defense Forces helicopter from Hyakuri Air Base in Ibaraki Prefecture to the Okuma Town Off-Site Center. The activities included physical survey, health consultation telephone counter, temporary return home response for residents, whole body measurement of TEPCO employees and Fukushima Prefecture residents, environmental radiation monitoring, and others. The lecture reviewed the various events that took place during the first year after the disaster and introduced the dilemma under which JAEA has been working through simulated experiences.

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At Fukushima Daiichi Nuclear Power Site (Hereafter, it will be referred to as “1F”), which experienced a severe nuclear accident, new radiation measurement technologies were introduced to cope with changing situations and harsh environments. This has led to improvements in the quality of radiation measurements and a reduction in the burden on the site. On the other hand, it showed that there are needs that cannot be met with current technology. While efforts within our company are a prerequisite, we have asked external experts for cooperation on new technologies that our company cannot create.

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National Institute of Technology, Fukushima College (Fukushima KOSEN) is a national engineering higher education institution located closest to the Fukushima Daiichi Nuclear Power Plant. Fukushima KOSEN regards the contribution to the reconstruction of Fukushima as an important issue for social contribution. In order to achieve the decommissioning of the Fukushima Daiichi Nuclear Power Plant, the training of young people to take up this challenge is an urgent task. The recovery of the local environment from radioactive contamination and the treatment and disposal of radioactive waste are also important issues. Furthermore, robot development in collaboration with local companies will be described.

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Water radiolysis induces oxidative dissolution of uranium oxides. Understanding of this process is a chemical basis for safety assessment of the deep geological repository of spent fuel and would serve as knowledge for retrieval and storage of fuel debris after a severe accident of nuclear power reactors. In order to evaluate the release rate of radioactive elements from the UO2 matrix of spent nuclear fuel, several chemical kinetic models have been developed. However, the conventional reaction models were found out to be simplistic based on new insights obtained recent experimental studies. Therefore, the reaction mechanism of surface oxidation and dissolution of uranium is now a subject of revisit. Here, a few recent studies regarding the reaction mechanism are introduced.

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Real-time dose-rate monitoring system under the high dose-rate situation is required for the decommissioning of the Fukushima Daiichi Nuclear Plants to remove the debris remaining inside the plants. We have proposed a dose-rate monitor consisting of a scintillator, over 100-m long optical fiber and CCD spectrometer. Some noises with a dominant-emission wavelength band of below 550 nm originating from the optical fiber itself must be separated from the scintillator emission light in 650-1000 nm, which is used as signal data, up to now. In this paper, we investigated if the noise region defined as below 550 nm is available for the position estimation of the hot spot through the fiber. The intensities of the noise emission or absorption band of such fiber-emission spectra are expected to depend on the hot-spot position through the fiber, and we demonstrated such dependence, “one-dimensional dose-rate distribution”, with a 20 m-long optical fiber and CCD spectrometer. Two types of optical fibers (High OH and Low OH) were tested under several length conditions of the fiber from the CCD spectrometer to 60Co source. The results of the emission spectra showed the intensity ratio of absorption to maximum intensity peak decreased as such length condition increased. We found that fiber noise is available for the position estimation for the hotspots (debris).

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A gamma detector/camera will receive both direct gamma radiation from a gamma source and scattered or shielded radiation from objects around the source. To consider the effects of scattering and shielding, it is useful to acquire an environment map around the detector using Simultaneous Localization and Mapping (SLAM), and to construct a 3D shape model for radiation transport Monte Carlo simulation from the 3D point cloud data of SLAM. This paper gives an overview of the 3D voxel modelling method and its application in the finding of 137Cs point sources using 4π gamma imaging.

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