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Sanada, Yukihisa; Abe, Tomohisa; Sasaki, Miyuki; Kanno, Marina*; Yamada, Tsutomu*; Nakasone, Takamasa*; Miyazaki, Nobuyuki*; Oshikiri, Keisuke*; Watabe, Hiroshi*
Journal of Nuclear Science and Technology, 61(5), p.693 - 702, 2024/05
Times Cited Count：5 Percentile：83.63(Nuclear Science & Technology)The "treated water" from which the main radioactive materials were removed contains tritium, and stakeholders in Japan have been debating how to treat it. The amount of treated water stored in the facility has reached its limit, and the Japanese government has decided that the treatment method will be to discharge the water into the ocean by FY 2023 (FY: Fiscal Year). The present research developed a simple and practical tritium monitor for the Fukushima Daiichi Nuclear Power Station (FDNPS) tritiated water release. A simple and practical tritium monitor was developed for FDNPS tritiated water release based on thin plastic scintillator sheets. The developed devices were calibrated using standard tritium solutions and a method for calculating the minimum detectable activity. Fifteen 0.25 mm-thick scintillators can be placed in the 0.26 L flow cell where the sample water is fed, yielding an active surface area of 3,200 mm
. The efficiency of tritiated water with full water is 0.000035 cps Bq
. The minimum detectable activity under simple shielding conditions was 7,800 Bq L (Measurement time was 3,600 s).
Sanada, Yukihisa; Oshikiri, Keisuke*; Kanno, Marina*; Abe, Tomohisa
Nuclear Instruments and Methods in Physics Research A, 1062, p.169208_1 - 169208_7, 2024/05
Times Cited Count：4 Percentile：96.65(Instruments & Instrumentation)As part of the decommissioning work at the Fukushima Daiichi Nuclear Power Plant (FDNPP), the release of stored treated water began in 2023. In this study, we developed a practical tritium monitor to continuously monitor the concentration of tritiated water, as confirmed by batch sampling measurements at the FDNPP. The monitor is arranged with a flow cell detector comprising inexpensive plastic scintillator pellets and incorporating simultaneous measurements by three detectors, a veto detector, and lead shielding to reduce the influence of environmental 
-rays. The system reached a detection limit of 911 Bq L-1 with a measurement time of 30 min, which is lower than the discharge standard for tritiated water of 1,500 Bq L-1. The system can also qualitatively distinguish the presence of disturbances due to interfering radionuclides other than tritium or background radiation using the 
-ray spectrum.
Hagiwara, Hiroki; Funaki, Hironori; Shiribiki, Natsu*; Kanno, Marina*; Sanada, Yukihisa
Journal of Radioanalytical and Nuclear Chemistry, 331(1), p.415 - 426, 2022/01
Times Cited Count：7 Percentile：66.91(Chemistry, Analytical)Morishita, Yuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
no journal, ,
We have tried to create a novel compact alpha/beta detector capable of direct insertion into piping for the immediate assessment of alpha and beta contamination. The detector, a phoswich detector, comprises scintillators for alpha and beta particles. For alpha particles, a ZnS(Ag) scintillator with a thickness of 3.25 mg/cm was used as the initial layer, while a cerium-doped Gd
GaAl
O
(GGAG) scintillator measuring 6 mm 
6 mm 6 mm served as the scintillator for the secondary layer for beta particles. The bottom of the GAGG scintillator was coupled with optical grease to a compact photomultiplier tube (H14603, Hamamatsu Photonics K.K.), with an effective diameter of 8 mm
. The signal was amplified by a preamplifier embedded in the compact photomultiplier tube and then the signal was input to a digitizer (DT5730S, CAEN). to confirm the alpha/beta discrimination performance. Subsequently, a thorium source emitting alpha and beta particles concurrently conducted measurement. A charge integration (CI) method was employed to distinguish the alpha and beta waveforms. A 2-dimensional Pulse Shape Discrimination (PSD) map showed the distribution of two clusters of alpha and beta particles, both of which were effectively discriminated. The detector has outer dimensions of 22.0 mm 22.0 mm 30.0 mm, facilitating direct insertion into a pipe for measurement purposes. As a future endeavor, we aim to optimize the discrimination between alpha and beta particles by modifying the combination of scintillators.
Abe, Tomohisa; Sanada, Yukihisa; Oshikiri, Keisuke*; Kanno, Marina*
no journal, ,
As part of the decommissioning work at the Fukushima Daiichi Nuclear Power Plant (FDNPP), the release of stored treated water began in 2023. In this study, we developed a practical tritium monitor to continuously monitor the concentration of tritiated water, as confirmed by batch sampling measurements at the FDNPP. This presentation will introduce the features of the developed monitor.
Morishita, Yuki; Yamada, Tsutomu*; Nakasone, Takamasa*; Kanno, Marina*; Sasaki, Miyuki; Sanada, Yukihisa; Torii, Tatsuo*
no journal, ,
The Fukushima Daiichi Nuclear Power Station's decommissioning requires thorough inspection of piping for contamination, including alpha nuclides. External alpha particle measurements are impossible, necessitating gamma-ray detection methods. A phoswich detector for low-energy gamma-ray detection was developed and validated experimentally at a nuclear fuel facility. The detector was designed considering energy deposition characteristics. The detector comprises YAlO:Ce and Bi
GeO scintillators with a photomultiplier tube for signal amplification. Measurement and simulation results show correlation between scintillator energy depositions for different gamma-ray energies. Pulse Shape Discrimination (PSD) plots distinguish alpha particles and gamma-rays, confirming simulation predictions. Nuclear fuel facility measurements exhibit higher energy deposition in the first scintillator layer. This suggests potential for developing a sensitive low-energy gamma-ray detector using scintillator combinations. Future work aims to optimize detector design and conduct field tests for validation.
