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Collaborative Laboratories for Advanced Decommissioning Science; Nagoya University*
JAEA-Review 2022-033, 80 Pages, 2022/12
JAEA-Review-2022-033.pdf:4.08MB
The Collaborative Laboratories for Advanced Decommissioning Science (CLADS), Japan Atomic Energy Agency (JAEA), had been conducting the Nuclear Energy Science & Technology and Human Resource Development Project (hereafter referred to "the Project") in FY2021. The Project aims to contribute to solving problems in the nuclear energy field represented by the decommissioning of the Fukushima Daiichi Nuclear Power Station (1F), Tokyo Electric Power Company Holdings, Inc. (TEPCO). For this purpose, intelligence was collected from all over the world, and basic research and human resource development were promoted by closely integrating/collaborating knowledge and experiences in various fields beyond the barrier of conventional organizations and research fields. The sponsor of the Project was moved from the Ministry of Education, Culture, Sports, Science and Technology to JAEA since the newly adopted proposals in FY2018. On this occasion, JAEA constructed a new research system where JAEA-academia collaboration is reinforced and medium-to-long term research/development and human resource development contributing to the decommissioning are stably and consecutively implemented. Among the adopted proposals in FY2019, this report summarizes the research results of the "Measurement methods for the radioactive source distribution inside reactor buildings using a one-dimensional optical fiber radiation sensor" conducted from FY2019 to FY2021. Since the final year of this proposal was FY2021, the results for three fiscal years were summarized. The present study aims to develop an optical fiber type radiation sensor that can measure the radiation distribution one-dimensionally along the fiber under a high radiation field for the decommissioning of 1F. Based on the conventional time-of-flight method, we found several promising sensor candidates for the radiation distribution measurement under high dose rate and many scattered gamma-rays.
Aoyagi, Kazuhei; Sakurai, Akitaka; Miyara, Nobukatsu; Sugita, Yutaka
JAEA-Research 2020-004, 68 Pages, 2020/06
JAEA-Research-2020-004.pdf:6.4MB
JAEA-Research-2020-004-appendix1(DVD-ROM).zip:636.84MBJAEA-Research-2020-004-appendix2(DVD-ROM).zip:457.72MBJAEA-Research-2020-004-appendix3(DVD-ROM).zip:595.19MB
In construction and operational phase of a high-level radioactive waste disposal project, it is necessary to monitor on mechanical stability of underground facility for long term. In this research, we measured the displacement of the rock around the gallery and the stress acting on support materials. Furthermore, we investigated the durability of measurement sensor installed in the rock mass and the support material such as concreate lining and steel support. As a result, optical fiber sensor is appropriate for measurement of the displacement of rock mass around the gallery, while it is enough to apply the conventional electric sensor for the measurement of stress acting on the support material in the geological environment (soft rock and low inflow). The result of the measurement in the fault zone in 350 m gallery, show that the stresses acting on both shotcrete and steel arch lib exceeded the value which will cause the instability of the gallery. However, as, we found no crack on the surface of the shotcrete. By observation on the surface of shotcrete, thus, it was concluded that careful observation of shotcrete around that section in addition to the monitoring the measured stress was necessary to continue. In other measurement sections, there was no risk for the instability of the gallery as a result of the investigation of the measurement result.
Aoki, Tomoyuki*; Tani, Takuya*; Sakai, Kazuo*; Koga, Yoshihisa*; Aoyagi, Kazuhei; Ishii, Eiichi
JAEA-Research 2020-002, 83 Pages, 2020/06
JAEA-Research-2020-002.pdf:8.25MBJAEA-Research-2020-002-appendix(CD-ROM).zip:6.63MB
The Japan Atomic Energy Agency (JAEA) has conducted with the Horonobe Underground Research Project in Horonobe, Teshio-gun, Hokkaido for the purpose of research and development related to geological disposal technology for high-level radioactive wastes in sedimentary soft rocks. The geology around the Horonobe Underground Research Laboratory (HURL) is composed of the Koetoi diatomaceous mudstone layer and the Wakkanai siliceous layer, both of which contain a large amount of diatom fossils. Since these rocks exhibit relatively high porosity but low permeability, it is important to investigate the poro-elastic characteristics of the rock mass. For this objective, it is necessary to measure parameters based on the poro-elastic theory. However, there are few measurement results of the poro-elastic parameters for the geology around HURL, and the characteristics such as dependence on confining pressure are not clearly understood. One of the reasons is that the rocks show low permeability and the pressure control during testing is difficult. Therefore, a poro-elastic parameter measurement test was conducted on the siliceous mudstone of the Wakkanai formation to accumulate measurement results on the poro-elastic parameters and to examine the dependence of the parameters on confining pressure. As a result, some dependency of the poro-elastic parameters on confining pressure was observed. Among the measured or calculated poro-elastic parameters, the drained bulk modulus increased, while the Skempton's pressure coefficient, and the Biot-Wills coefficient in the elastic region decreased with the increase in confining pressure. The measurement results also inferred that the foliation observed in the rock specimens might impact a degree of dependency of those parameters on confining pressure.