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Takai, Shizuka; Namekawa, Masakazu*; Shimada, Taro; Takeda, Seiji
IEEE Transactions on Nuclear Science, 69(7), p.1789 - 1798, 2022/07
Times Cited Count：0 Percentile：0.01(Engineering, Electrical & Electronic)To reduce a large amount of contaminated concrete rubble stored in the Fukushima Daiichi Nuclear Power Station site, recycling low-radioactivity rubble within the site is a possible remedy. To promote recycling while ensuring safety, not only the average radioactivity but also the radioactivity distribution of concrete rubble should be efficiently evaluated because the details of rubble contamination caused by the accident remain unclear and likely include hotspots. However, evaluating inhomogeneous contamination of thick and/or dense materials is difficult using previous measurement systems, such as clearance monitors. This study experimentally confirmed the potential applicability of image reconstruction algorithms for radioactivity distribution evaluation in concrete rubble filled in a chamber. Radiation was measured using plastic scintillation fiber around the chamber (50 
50 40 cm
). Localized hotspots were simulated using standard sources of 
Cs, which is one of the main nuclides of contaminated rubble. The radioactivity distribution was calculated for 100 or 50 voxels (voxel size: (10 cm) or 10 10 20 cm) constituting the chamber. For 100 voxels, inner hotspots were undetected, whereas, for 50 voxels, both inner and surface hotspots were reconstructible. The distribution evaluated using the maximum likelihood expectation maximization algorithm was the most accurate; the average radioactivity was estimated within 70% accuracy in all seven cases.
Sudo, Makoto; Takai, Masakazu; Sasaki, Toshiki; Nakazawa, Osamu; Fukumoto, Masahiro
Proceedings of International Waste Management Symposium 2005 (WM 2005), 0 Pages, 2005/03
None
Sudo, Makoto; Takai, Masakazu; Sasaki, Toshiki; Nakazawa, Osamu; Fukumoto, Masahiro
Waste Management 2005 Proceeding, CD-ROM, 6p., 6 Pages, 2005/00
Focusing on the cover layer materials (as the Radon Barrier Materials), which could have the effect to restrain the radon from scattering into the air and the effect of the radiation shielding, we produced the radon barrier materials with crude bentonite on an experimental basis, using the rotary type comprehensive unit for grinding and mixing, through which we carried out the evaluation of the characteristics thereof.
Takai, Masakazu; Sudo, Makoto; Nakazawa, Osamu; Fukumoto, Masahiro; Suto, Osamu
Journal of Physics and Chemistry of Solids, 66, p.694 - 696, 2004/00
Times Cited Count：7 Percentile：30.12(Chemistry, Multidisciplinary)None
Takai, Masakazu; Aoyama, Makoto; Nakazawa, Osamu; Suto, Osamu
Proceedings of 11th International IUPAC Conference on High Temperature Materials Chemistry (HTMC-11), P. 215, 2003/00
None
Takai, Masakazu; Sudo, Makoto; Nakazawa, Osamu; Suto, Osamu
Proceedings of 11th International IUPAC Conference on High Temperature Materials Chemistry (HTMC-11), (pb77), 215 Pages, 2003/00
None
Shimada, Taro; Namekawa, Masakazu*; Takai, Shizuka; Takeda, Seiji
no journal, ,
It is necessary to confirm the radioactive concentration of recycling contaminated rubbles which is less than the reference concentration for restricted use in the site of Fukushima Daiichi NPS. In order to develop measurement and evaluation methods in the combination of plastic scintillation fiber and inverse analysis for confirmation survey in the 1F site, we studied the measurement methods and geometrical system. We carried out the radiation measurement for simulated recycling rubbles using sealed radiation sources and analyzed gamma radiation fluxes on the PSF. The measurement result was almost agreed with the analytic result by means of correction of position resolution and detecting efficiency for the 
-ray energy of the PSF. It suggested that it was possible to estimate the radioactive concentration of recycling rubbles.
