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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.
Terasaka, Yuta; Watanabe, Kenichi*; Uritani, Akira*
Nuclear Instruments and Methods in Physics Research A, 1034, p.166793_1 - 166793_6, 2022/07
Times Cited Count：2 Percentile：53.91(Instruments & Instrumentation)Sanada, Yukihisa
Hokeikyo Nyusu, (68), p.2 - 6, 2021/10
Due to the impact of the Fukushima Daiichi Nuclear Power Station accident (hereinafter referred to as the power station accident) of Tokyo Electric Power Company Holdings, Inc., the surrounding environment was contaminated with radioactive substances such as radioactive cesium. After the nuclear power plant accident, plastic scintillation fiber is one of the applied wire and surface radiation measurement techniques. This paper summarizes the development process from a series of development to the introduction of the actual machine.
Yamamoto, Takahiro; Ito, Chikara; Maeda, Shigetaka; Ito, Hideaki; Sekine, Takashi
JAEA-Technology 2017-036, 41 Pages, 2018/02
JAEA-Technology-2017-036.pdf:7.86MB
In the experimental fast reactor Joyo, the damaged upper core structure (UCS) was retrieved into the cask in May 2014 The dose rate on UCS surface was quite high due to the activation for over 30 years operation. In order to attain the optimum safety design, manufacture and operation of equipment for UCS replacement, the method to evaluate UCS surface dose rate was developed on the basis of C/E obtained by the in-vessel dose rate measurement in Joyo. In order to verify the evaluation method, the axial gamma-ray distribution measurement on the surface of the cask, which contained UCS, was conducted using a plastic scintillating optical fiber (PSF) detector. This paper describes the comparison results between calculation and measurement as follows. (1) The measured axial gamma-ray distribution on the cask surface had a peak on proper location with considering the cask shielding structure and agree well with the calculated distribution. (2) The C/E of axial gamma-ray distribution on the cask surface was ranged from 1.1 to 1.7. It was confirmed that the calculation for UCS replacement equipment design had a margin conservatively. Then, the results showed that the developed evaluation method for UCS replacement equipment design was sufficiently reliable.
Sanada, Yukihisa; Yamada, Tsutomu*; Sato, Yoshiharu; Nishizawa, Yukiyasu; Ishibashi, Satoshi*; Watanabe, Masahisa; Torii, Tatsuo
JAEA-Research 2016-011, 52 Pages, 2016/09
JAEA-Research-2016-011.pdf:10.54MB
In the Tokyo Electric Power Co.,Inc. the Fukushima Dai-ichi Nuclear Power Station, management of the contaminated water becomes the social problem, and the situation that severe correspondence is necessary continues to prevent an outflow to the ocean. Plastic scintillation fiber (PSF) can apply as technique to direct measure the concentration of radioactive material in the water at a tank and drainage. In this paper, the results of fundamental test was summarized to apply for monitoring of leakage to the tank and monitoring of drainage in the Fukushima Dai-ichi Nuclear Power Station.
Sanada, Yukihisa; Urabe, Yoshimi; Orita, Tadashi; Takamura, Yoshihide; Torii, Tatsuo
Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 5 Pages, 2015/05
There are approximately 3,700 irrigation ponds in the Fukushima prefecture. Contamination by radiocesium at the bottom of these ponds has been a concern since the accident at the TEPCO's Fukushima Daiichi Nuclear Power Station (FDNPS). Among them, there are some reservoirs which contain radioactive materials in the bottom sediment. Three years have passed since the accident of the Fukushima Daiichi Nuclear Power Station. In relation to the restoration of agriculture in the disaster-stricken area, there are concerns over the migration of radioactive cesium in the environment. We developed 20 meter-length a plastic scintillation fiber (PSF) for measurement in water. We have conducted tests at dozens of irrigation ponds in Fukushima pref. using PSF to confirm the performance of the devices and to standardize measurement techniques and analytical procedures.
Sanada, Yukihisa; Torii, Tatsuo
Nihon Genshiryoku Gakkai-Shi ATOMO
, 57(2), p.94 - 98, 2015/02
In Fukushima, quick and direct technique to measure a wide area of bottom of water is needed. We developed the plastic scintillation fiber (PSF) since accident at 1F. Therefore, the PSF was applied to measurement of irrigation pond. Here, the measuring method and the monitoring result are reported.
Sanada, Yukihisa; Yamada, Tsutomu; Takamura, Yoshihide; Torii, Tatsuo
no journal, ,
no abstracts in English
Takamura, Yoshihide; Urabe, Yoshimi; Yamada, Tsutomu; Sanada, Yukihisa
no journal, ,
no abstracts in English
Shimada, Taro; Takai, Shizuka; Takeda, Seiji
no journal, ,
In order to recycle contaminated debris of which concentration is relatively lower in Fukushima Daiichi Nuclear Power Station, it is necessary to confirm that the mean radioactive concentration is lower than a reference value with consideration of the distribution by measurement and evaluation. We studied a method combining radiation measurement and inverse analysis to obtain the distribution of radioactivity concentration of recycled material. Plastic scintillation fiber will be applied to radiation measurement to obtain dose rates outside the container containing recycled material at many measurement points. As a result of application of 7 inverse analysis methods to typical two types of distribution, GVSPM and ML-EL methods can evaluate true values in the trials.
Terasaka, Yuta; Sato, Yuki; Torii, Tatsuo
no journal, ,
no abstracts in English
dose rate distribution in JoyoYamamoto, Takahiro; Maeda, Shigetaka; Ito, Chikara
no journal, ,
In the experimental fast reactor Joyo, the damaged upper core structure (UCS) was retrieved into the cask in May 2014 for its replacement as a part of the restoration work of the incident concerning with the irradiation test sub-assembly named MARICO-2. The dose rate on UCS surface was quite high due to the activation for over 30 years operation. In order to attain the optimum safety design, manufacture and operation of equipment for UCS replacement, the method to evaluate UCS surface dose rate was developed on the basis of C/E obtained by the in-vessel dose rate measurement in Joyo. In order to verify the evaluation method, the axial -ray distribution measurement on the surface of the cask, which contained UCS, was conducted using a plastic scintillating optical fiber (PSF) detector. As a result, the measured axial -ray distribution on the cask surface had a peak on proper location with considering the cask shielding structure and agree well with the calculated distribution and the C/E of axial -ray distribution on the cask surface was ranged from 1.1 to 1.7. It was confirmed that the calculation for UCS replacement equipment design had a margin of conservatively. Then, the results showed that the applied evaluation method for UCS replacement equipment design was sufficiently reliable. In the in-vessel repair work for sodium cooled fast reactors (SFRs), the design and work condition estimation are important. The accumulated experience provides valuable insights into further improvements for in-vessel repair techniques in SFRs.
Terasaka, Yuta; Sato, Yuki; Torii, Tatsuo
no journal, ,
no abstracts in English
Terasaka, Yuta; Sato, Yuki; Watanabe, Kenichi*; Uritani, Akira*; Torii, Tatsuo
no journal, ,
no abstracts in English
Terasaka, Yuta
no journal, ,
no abstracts in English
Katengeza, E.*; Sanada, Yukihisa; Ochi, Kotaro; Iimoto, Takeshi*
no journal, ,
Since 2013, plastic scintillation fiber (PSF) is calibrated from counting rate to radiocesium concentration by comparing with the average concentration of the top 10 cm of sediment core sample. The purpose of this study is to clarify influence of radiocesium depth distribution on PSF calibration factor and measurement uncertainty. The radiocesium concentration was estimated by varying the calibration depth of PSF from 5 to 30 cm at 5 cm intervals. The estimated radiocesium concentration was compared with the radiocesium concentration in the bottom sediment collected at the PSF measurement point. The normalized mean squared error values were the smallest at the calibration depth of 15-20 cm, suggesting that the measurement can be optimized by changing the calibration depth.
Terasaka, Yuta
no journal, ,
