Sustainable thermoelectric materials; Utilizing Fukushima weathered biotite via molten salt treatment

Honda, Mitsunori; Kaneta, Yui; Muraguchi, Masakazu*; Hayakawa, Kosetsu*; Oda, Masato*; Iino, Chiaki*; Ishii, Hiroyuki*; Goto, Takuya*

AIP Advances (Internet), 14(5), p.055034_1 - 055034_6, 2024/05

https://doi.org/10.1063/5.0206317

This study examines the utilization of Fukushima weathered biotite(WB)as an alternative to conventional thermoelectric materials traditionally derived from rare and toxic substances. WB underwent milling, classification, and subsequent heat treatment via molten-salt treatment to produce crystals exhibiting conductivity akin to semiconductors within from 650C to 850C range. Evaluation of WB and the derived crystal's electrical conductivity and Seebeck coefficient showcased their viability for high-temperature thermoelectric applications. Consequently, WB attained a dimensionless figure of merit (ZT) of 0.015, signaling its potential as a thermoelectric material that surpasses 650C.

Rapid multi-nuclide identification method by simultaneous , , and X-ray spectrum analysis

Oshima, Masumi*; Goto, Jun*; Hayakawa, Takehito*; Asai, Masato; Kin, Tadahiro*; Shinohara, Hirofumi*

Isotope News, (790), p.19 - 23, 2023/12

When analyzing samples that contain many radionuclides at various concentrations, such as radioactive waste or fuel debris, it is difficult to apply general spectrum analysis methods and is necessary to chemically separate each nuclide before quantifying it. The chemical separation is especially essential for analysis using a liquid scintillation counter (LSC). In this report, the authors explain the newly developed spectral determination method (SDM) in which the entire spectrum is fitted to quantify radioactivity of nuclides mixed in a sample. By applying the SDM to - and X-ray spectrum measured by LSC and -ray spectrum measured by Ge detector simultaneously, the authors demonstrated that radioactivity of 40 radionuclides mixed in a sample at concentrations varying by two orders could be quantified, which is useful to simplify chemical separation process in radionuclide quantification.

Experience and technology consolidation related to dismantling sodium equipment; Technology to reduce sodium remaining in 100m grade large tanks

Hayakawa, Masato; Shimoyama, Kazuhito; Miyakoshi, Hiroyuki; Suzuki, Shigeaki*

JAEA-Technology 2021-027, 33 Pages, 2022/01

JAEA-Technology-2021-027.pdf:3.64MB

At the Oarai Research and Development Institute of the Japan Atomic Energy Agency, experimental studies in various sodium environments are being conducted in connection with the research and development of sodium-cooled fast reactors such as the experimental fast reactor Joyo and the prototype fast reactor Monju. The dismantling of sodium test facilities and equipment that have achieved their purpose has been carried out sequentially, and a wealth of experience and technology has been accumulated. On the other hand, a large amount of metallic sodium used for research and testing is being reused for new testing facilities, and the large sodium tanks that contained the metallic sodium are being dismantled. In order to dismantle these tanks safely and efficiently, it is important to reduce the residual sodium inside the tanks (especially at the bottom) as much as possible before dismantling. Therefore, we have been working on the reduction of residual sodium at the bottom of several large sodium tanks of 100 m class. This report describes the technologies and experiences related to the reduction of residual sodium that have been carried out so far.

Analysis of the activities of the website "Question and Answer about radiation in Daily Life" after the accident at the Fukushima Daiichi Nuclear Power Station and some lessons learned from it; To pass on this experience to the future

Kono, Takahiko; Shimo, Michikuni*; Hayakawa, Hironobu*; Taniguchi, Kazufumi*; Tanaka, Masato*; Tanaka, Hitomi*; Onoue, Yosuke*; Nagaya, Hiroshi*; Torii, Hiroyuki*; Uno, Kazuko*

Hoken Butsuri (Internet), 55(4), p.226 - 238, 2020/12

https://doi.org/10.5453/jhps.55.226

After the accident at the Fukushima Daiichi Nuclear Power Station, artificial radionuclides such as radioactive cesium and iodine were released into the environment. It caused great anxiety not only in the vicinity of the Fukushima Daiichi Nuclear Power Station but also in other regions of Japan. Some members of the Japan Health Physics Society (JHPS) which is a leading academic society in Japan in the field of radiation protection volunteered to establish the website called "Question and Answer about radiation in Daily Life" just after the accident to reduce the anxiety of the residents about the health effects of radiation. After that, Committee of "Question and Answer about radiation in Daily Life" was established in August 2011 in JHPS, and this activity had been carried out under the responsibility of the society that answered with sincerity against questions from the public as specialists until February 2013. The number of questions on the website had gradually decreased as time passed; therefore, the Committee members decided to end these activities in February 2013. In this paper, following contents were shown; the activities of the Q&A website for about two years, the issues of the stance on our activities, the information related to the website activities and the analysis of Twitter data. Based on the experience and the knowledge obtained from these activities, the issues and experiences that can be utilized in the initial response to emergencies for radiation protection experts as well as other fields are presented.

Analytical data on contaminated water, rubble and other collected at the Fukushima Daiichi Nuclear Power Station

Asami, Makoto*; Takahatake, Yoko; Myodo, Masato; Tobita, Takeshi; Kobayashi, Kiwami; Hayakawa, Misa; Usui, Yuka; Watahiki, Hiromi; Shibata, Atsuhiro; Nomura, Kazunori; et al.

JAEA-Data/Code 2017-001, 78 Pages, 2017/03

JAEA-Data-Code-2017-001.pdf:4.92MB
JAEA-Data-Code-2017-001-appendix(DVD-ROM).zip:818.06MB

At Fukushima Daiichi Nuclear Power Station owned by Tokyo Electric Power Company Holdings, Incorporated (TEPCO), contaminated water (accumulated, treated) secondary waste from water treatment, rubble and soil were collected and analyzed. The data already opened to public was collected as this report. The analytical data reported by TEPCO, Japan Atomic Energy Agency and International Research Institute for Nuclear Decommissioning until the end of March, 2016, was collected. Information on the samples and values of radioactive nuclide concentration and others were tabulated, besides figures, which show change in radioactive nuclide concentration for major nuclides, are contained. And, English translation and the collected data are provided as electric data.

Development of basic NDA technologies of nuclear material accountancy of debris of melted fuel formed in severe accidents

Seya, Michio; Harada, Hideo; Kitatani, Fumito; Koizumi, Mitsuo; Tsuchiya, Harufumi; Iimura, Hideki; Kureta, Masatoshi; Takamine, Jun; Hajima, Ryoichi; Hayakawa, Takehito; et al.

Kaku Busshitsu Kanri Gakkai (INMM) Nihon Shibu Dai-34-Kai Nenji Taikai Rombunshu (Internet), 10 Pages, 2013/10

The forming of MF in severe accidents of nuclear reactors such as Units 1 - 3 of Fukushima-Daiichi NPP (Nuclear Power Plant) inevitably change the category of the nuclear reactor from "item facility" to "bulk-handling facility". At removal of the MF it is necessary to break chunks of MF into relatively small blocks by using some tools, resulting in debris that consists of cut or small rock-like debris and particle (or grain)-like debris in bulk form. This paper presents a categorization of debris of MF and two possible non-destructive assay (NDA) technologies for precise measurement which could be applied to the NM accountancy of MF debris. One of them is Neutron Resonance Densitometry (NRD) for particle-like (or grain-like) debris, and another is NRF (Nuclear Resonance Fluorescence) NDA using LCS (Laser Compton Scattered) -rays (mono-energetic -rays) for cut or small rock-like debris. The paper also describes about the recent development of these two technologies.

Feasibility studies and development of NDA technologies for nuclear materials in the melted fuels formed in severe accidents

Seya, Michio; Harada, Hideo; Kitatani, Fumito; Koizumi, Mitsuo; Tsuchiya, Harufumi; Iimura, Hideki; Kureta, Masatoshi; Takamine, Jun; Hajima, Ryoichi; Hayakawa, Takehito; et al.

Kaku Busshitsu Kanri Gakkai (INMM) Nihon Shibu Dai-33-Kai Nenji Taikai Rombunshu (Internet), 10 Pages, 2012/10

This paper presents feasibility (selection) study of NDA techniques, NRD (Neutron Resonance Densitometry) and LCSG-NRF (LCS -rays interrogation Nuclear Resonance Fluorescence), to measure nuclear material (NM) in debris of melted fuel with high precision. The melted fuel under consideration here is the one formed by the severe loss of coolant accidents of such as Units 1 - 3 of Fukushima-Daiichi NPP. NRD based on NRTA (Neutron Resonance Transmission Analysis) and NRCA (Neutron Resonance Capture Analysis) utilizing the TOF (Time of Flight) method is intended for measurement of NM (all isotopes of U/Pu) in particle-like debris. LCSG-NRF using intense LCS (Laser Compton Scattered) -rays (mono-energetic -rays) is to measure NM (all isotopes of U/Pu) in small rock-like debris and cut-shape debris (cylindrical, slab-shpape). In this paper we also summarize advantages of two techniques compared with other NDA techniques.

Performance-based improvement of the leakage rate test program for the reactor containment of HTTR; Adoption of revised test program containing "Type A, Type B and Type C tests"

Kondo, Masaaki; Kimishima, Satoru*; Emori, Koichi; Sekita, Kenji; Furusawa, Takayuki; Hayakawa, Masato; Kozawa, Takayuki; Aono, Tetsuya; Kuroha, Misao; Ouchi, Hiroshi

JAEA-Technology 2008-062, 46 Pages, 2008/10

JAEA-Technology-2008-062.pdf:11.62MB

The reactor containment of HTTR is tested to confirm leak-tight integrity of itself. "Type A test" has been conducted in accordance with the standard testing method in JEAC4203 since the preoperational verification of the containment was made. Type A tests are identified as basic one for measuring containment leakage rate, it costs much, however. Therefore, the test program for HTTR was revised to adopt an efficient and economical alternatives including "Type B and Type C tests". In JEAC4203-2004, following requirements are specified for adopting alternatives: upward trend of leakage rate by Type A test due to aging should not be recognized; criterion of combined leakage rate with Type B and Type C tests should be established; the criteria for Type A test and combined leakage rate test should be satisfied; correlation between the leakage rates by Type A test and combined leakage rate test should be recognized. Considering the performances of the tests, the policies of corresponding to the requirements were developed, which were accepted by the regulatory agency. This report presents an outline of the tests, identifies issues on the conventional test and summarizes the policies of corresponding to the requirements and of implementing the tests based on the revised program.

CGR behavior of low carbon stainless steel of hardened heat affected zone in PLR piping weld joints

Ando, Masami*; Nakata, Kiyotomo*; Ito, Mikiro*; Tanaka, Norihiko*; Koshiishi, Masato*; Obata, Ryoji*; Miwa, Yukio; Kaji, Yoshiyuki; Hayakawa, Masao*

Proceedings of 13th International Conference on Environmental Degradation of Materials in Nuclear Power Systems (CD-ROM), 16 Pages, 2007/00

Long term SCC growth tests for nuclear grade stainless steel (SUS316(NG)) were conducted in a simulated BWR environment using specimens taken from mock-up PLR piping weld joints to obtain the crack growth rate (CGR) of the hardened heat affected zone due to weld shrinkage around weld, in order to develop the CGR curve which will be used for flaw evaluation. The piping joints were made of forged and extracted materials with several welding techniques. The obtained CGRs were higher than that of solution heat treated material. The CGRs for hardened SUS316(NG) have a correlation with hardness regardless of materials and welding techniques. The CGRs increased with hardness in the range from 210 to 250 Hv. The CGR acceleration mechanism in hardened HAZ of low carbon stainless steel was estimated based on the strain distribution and the AFM image around a SCC crack tip. It was suggested that the interaction of the plastic strain gradient at a crack tip and local strain along GBs.

Report of investigation on malfunction of reserved shutdown system in HTTR

Hamamoto, Shimpei; Iigaki, Kazuhiko; Shimizu, Atsushi; Sawahata, Hiroaki; Kondo, Makoto; Oyama, Sunao; Kawano, Shuichi; Kobayashi, Shoichi; Kawamoto, Taiki; Suzuki, Hisashi; et al.

JAEA-Technology 2006-030, 58 Pages, 2006/03

JAEA-Technology-2006-030.pdf:10.69MB

During normal operation of High Temperature engineering Test Reactor (HTTR) in Japan Atomic Energy Agency (JAEA), the reactivity is controlled by the Control Rods (CRs) system which consists of 32 CRs (16 pairs) and 16 Control Rod Drive Mechanisms (CRDMs). The CR system is located in stand-pipes accompanied by the Reserved Shutdown System (RSS). In the unlikely event that the CRs fail to be inserted, the RSS is provided to insert BC/C pellets into the core. The RSS shall be designed so that the reactor should be held subcriticality from any operation condition by dropping in the pellets. The RSS consists of BC/C pellets, hoppers which contain the pellets, electric plug, driving mechanisms, guide tubes and so on. In accidents when the CRs cannot be inserted, an electric plug is pulled out by a motor and the absorber pellets fall into the core by gravity. A trouble, malfunction of one RSS out of sixteen, occurred during a series of the pre-start up checks of HTTR on February 21, 2005. We investigated the cause of the RSS trouble and took countermeasures to prevent the issue. As the result of investigation, the cause of the trouble was attributed to the following reason: In the motor inside, The Oil of grease of the multiplying gear flowed down from a gap of the oil seal which has been deformed and was mixed with abrasion powder of brake disk. Therefore the adhesive mixture prevented a motor from rotating.