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Journal Articles

Measurement of air dose rates over a wide area around the Fukushima Dai-ichi Nuclear Power Plant through a series of car-borne surveys

Ando, Masaki; Nakahara, Yukio; Tsuda, Shuichi; Yoshida, Tadayoshi; Matsuda, Norihiro; Takahashi, Fumiaki; Mikami, Satoshi; Kinouchi, Nobuyuki; Sato, Tetsuro*; Tanigaki, Minoru*; et al.

Journal of Environmental Radioactivity, 139, p.266 - 280, 2015/01

https://doi.org/10.1016/j.jenvrad.2014.05.014
 Times Cited Count：52 Percentile：82.76(Environmental Sciences)

A series of car-borne surveys using the KURAMA and KURAMA-II systems was conducted in a wide area in eastern Japan from June 2011 to December 2012 to evaluate the distribution of air dose rates around the Fukushima Dai-ichi Nuclear Power Plant, and to determine the time-dependent trend of decrease in air dose rates. An automated data processing system was established, which enables analyses of large amounts of data obtained with the use of about 100 units of the measurement system in a short time. The initial data for studying the migration status of radioactive cesium was obtained in the first survey, followed by the other car-borne surveys having wider measurement ranges. Comparing the measured air dose rates obtained in each survey, it was found that the decreasing trend of air dose rates measured through car-borne surveys was larger than that expected from the physical decay of radioactive cesium and that measured using NaI (Tl) survey meters around the road.

JAEA Reports

Construction of a car-borne survey system for measurement of dose rates in air; KURAMA-II, and its application

Tsuda, Shuichi; Yoshida, Tadayoshi; Nakahara, Yukio; Sato, Tetsuro; Seki, Akiyuki; Matsuda, Norihiro; Ando, Masaki; Takemiya, Hiroshi; Tanigaki, Minoru*; Takamiya, Koichi*; et al.

JAEA-Technology 2013-037, 54 Pages, 2013/10

JAEA-Technology-2013-037.pdf:4.94MB

JAEA has been performing dose rate mapping in air using a car-borne survey system KURAMA-II. The KURAMA system is a GPS-aided mobile radiation monitoring system that has been newly developed by Kyoto University Research Reactor Institute in response to the nuclear disaster. The KURAMA system is composed of an energy-compensated scintillation survey meter for measuring dose rate, electric device for controlling both the dose rates and the position data from a GPS module, a computer server for processing and analyzing data from KURAMA, and client PCs for providing for end users. The KURAMA-II has been improved in small-packaging, durability, and automated data transmission. In consequence, dose rate mapping in wide area has become possible in shorter period of time. This report describes the construction of KURAMA-II, its application and a suggestion of how to manage a large number of KURAMA-II.

Journal Articles

Effect of water radiolysis on surface oxide film formed on SUS316L in $$gamma$$-ray irradiated high temperature water

Yamamoto, Masahiro; Kato, Chiaki; Sato, Tomonori; Nakahara, Yukio; Tsukada, Takashi; Watanabe, Atsushi*; Fuse, Motomasa*

Proceedings of Annual Congress of the European Federation of Corrosion (EUROCORR 2013) (CD-ROM), 5 Pages, 2013/09

Major corrosion problems of light water reactor (LWR) which are represented by stress corrosion cracking are affected by dissolved oxygen (DO) concentration in feed water. Many corrosion tests were conducted with the parameter of DO values. Oxygen source of an actual LWR is radiolysis of cooling water and also H$$_{2}$$O$$_{2}$$ is generated. The effect of these species created by water radiolysis to corrosion of structural material was not sufficiently examined. $$gamma$$-ray irradiated experiments were conducted in high temperature water condition using type 316L stainless steels with crevice. The calculation of radiolysis products was not estimated by the effect of radiolysis products. From these results, much complicated reaction seemed to occur at the $$gamma$$-ray irradiated crevice portion.

Journal Articles

Effects of $$gamma$$-ray irradiation and crevice-like shape on the corrosion of type 316L stainless steel in high-temperature water

Nakahara, Yukio; Kato, Chiaki; Yamamoto, Masahiro; Watanabe, Atsushi*; Fuse, Motomasa*

Proceedings of Symposium on Water Chemistry and Corrosion in Nuclear Power Plants in Asia 2009 (CD-ROM), p.226 - 231, 2009/10

The irradiation effect to high-temperature water in nuclear power plant has been regarded as one of important issues for preventing corrosion and stress corrosion cracking of plant materials. However, the effects of surface reaction and configurations of material on irradiated high-temperature water chemistry have been studied little because of the difficulty of measuring the environment. In this work, we have done a series of corrosion tests of Type 316L stainless steel in high-temperature water in order to estimate the effects of $$gamma$$-ray irradiation and crevice-like shape on the water chemistry. Test specimens immersed in high-temperature water of 288 $$^{circ}$$C were $$gamma$$-ray irradiated for 500 hours. The absorbed dose rate of $$gamma$$-ray irradiation was estimated to be 30 kGy h$$^{-1}$$. The dimensions of the disk-like specimens were 16 mm in diameter by 0.5 mm in thickness. The surfaces of the specimens were mechanically finished with #800 emery paper. Sets of two specimens attached closely in order to simulate a crevice-like environment were also immersed. The surfaces of the specimens were analyzed using SEM, TEM, and laser Raman spectrometer. The results of surface analyses indicated that $$gamma$$-ray irradiation enhanced the precipitation of iron oxide on the surface and the thickness of inner oxide layer became thicker by $$gamma$$-ray irradiation. $$gamma$$-ray irradiation also changed the morphology of oxide on the surface faced to the crevice-like environment.

Journal Articles

Effects of $$gamma$$-ray irradiation on the high temperature oxidation of austenitic stainless steel in supercritical water

Nakahara, Yukio; Yamamoto, Masahiro; Karasawa, Hidetoshi*; Kiuchi, Kiyoshi; Katsumura, Yosuke*

Proceedings of 16th Pacific Basin Nuclear Conference (PBNC-16) (CD-ROM), 6 Pages, 2008/10

Three types of commercial-grade austenitic stainless steel, Type 304L, Type 316L, and Type 310S, were immersed in deaerated supercritical water (SCW) of 25 MPa, 550 $$^{circ}$$C with $$gamma$$-ray irradiation for 1000 hours in total. Absorbed dose rates in SCW are estimated at 5-15 kGy h$$^{-1}$$. High temperature oxidation experiments resulted in the formation of two-layer oxide film in which the outer layer is porous iron oxide and the inner layer is dense iron-chromium-nickel oxide. Rate constants of parabolic rate law in net weight gains of Type 304L SS and Type 310S SS are decreased as the $$gamma$$-ray exposure rate is increased. The net weight gain of $$gamma$$-ray irradiated Type 316L SS is sharply fluctuating and decreasing, because the flaking of the outer layer occurred. Hematite is formed in the outer layer on all irradiated samples of examined alloys. The concentration of chromium on the surface is increased by $$gamma$$-ray irradiation. A chromium-rich part in the inner layer accompanying a nickel-rich part in the metal is formed along to the oxide/metal interface of $$gamma$$-ray irradiated Type 304L SS, non-irradiated and $$gamma$$-ray irradiated Type 316L SS.

Journal Articles

Deuterium pumping experiment with superpermeable Nb membrane in JFT-2M tokamak

Nakamura, Yukio*; Sengoku, Seio; Nakahara, Yukio*; Suzuki, Naoyuki*; Suzuki, Hajime*; Oyabu, Nobuyoshi*; Busnyuk, A.*; Notkin, M.*; Livshits, A.*

Journal of Nuclear Materials, 278(2-3), p.312 - 319, 2000/04

https://doi.org/10.1016/S0022-3115(99)00243-3
 Times Cited Count：15 Percentile：68.65(Materials Science, Multidisciplinary)

no abstracts in English

Oral presentation

Effect of $$gamma$$ ray irradiation on the corrosion of stainless steel in supercritical water

Nakahara, Yukio; Karasawa, Hidetoshi*; Yamamoto, Masahiro; Kiuchi, Kiyoshi; Katsumura, Yosuke*

no journal, , 

A supercritical water-cooled nuclear reactor (SCWR) has been under review as one of advanced reactors. Corrosion tests of several types of stainless steel in supercritical water (25MPa, 400$$sim$$500$$^{circ}$$C) were executed under $$gamma$$ ray irradiation in order to clarify the effect of $$gamma$$ ray on the corrosion. The results of the tests shows that the corrosion of stainless steel was progressed by the growth and degradation of surface oxide film, the dependence of the parabolic rate law constant on temperature can be fit with Arrhenius' equation, $$gamma$$ ray irradiation changed the property of surface oxide film.

Oral presentation

Influence of $$gamma$$ ray irradiation on surface film structures of stainless steels created in super critical water environment

Yamamoto, Masahiro; Nakahara, Yukio; Karasawa, Hidetoshi*; Katsumura, Yosuke*

no journal, , 

Super critical water cooling reactor (SCWR), which has higher energy efficiency than existent reactor, has been planned and examined. To realize the SCWR system, it is important to ensure the reliabilities of the materials used in the super critical condition. Some types of stainless steels were immersed in super critical water with $$gamma$$-ray irradiated condition. After the test, the surface films of stainless steels were analyzed. It was found that hematite (Fe$$_{2}$$O$$_{3}$$) was formed on the surface of oxide film with $$gamma$$-ray irradiation. Contrastingly, complex oxide including Cr and Ni was formed on the surface without $$gamma$$-ray irradiation.

Oral presentation

Effects of $$gamma$$-ray irradiation on the high temperature oxidation of stainless steel in supercritical water

Nakahara, Yukio; Yamamoto, Masahiro; Kato, Chiaki; Kiuchi, Kiyoshi; Karasawa, Hidetoshi*; Katsumura, Yosuke*

no journal, , 

Corrosion experiments of stainless steel (SS) in supercritical water (SCW) have done with a flowing SCW loop including a $$gamma$$-ray irradiated autoclave. Three types of commercial-grade austenitic SS, Type 304L, Type 316L, and Type 310S, were examined. The condition of SCW was adjusted to the core environment of a SCW reactor system. Test samples of the SS were immersed in deaerated pure SCW (25 MPa, 550 $$^{circ}$$C). Feed water was circulated at a flow rate of 4 L h$$^{-1}$$. Absorbed dose rates near the surface of the test samples in SCW were estimated at 5-15 kGy h$$^{-1}$$. The time dependence of net weight gains followed parabolic rate law except $$gamma$$-ray irradiated Type 316L SS. The net weight gains of $$gamma$$-ray irradiated Type 304L SS and Type 310S SS were larger than those of the non-irradiated. Rate constants of parabolic rate law in net weight gains of Type 304L SS and Type 310S SS were decreased as the $$gamma$$-ray exposure rate was increased. The net weight gain of $$gamma$$-ray irradiated Type 316L SS was fluctuating and decreasing widely, because the exfoliation of the surface oxide occurred. On the surface of all the samples, the formation of two-layer oxide film in which the outer layer was porous iron oxide and the inner layer was dense iron-chromium-nickel oxide occurred. Iron oxide in the outer layer was magnetite (Fe$$_{3}$$O$$_{4}$$) with non-irradiated samples. Hematite ($$alpha$$-Fe$$_{2}$$O$$_{3}$$) was additionally formed in the outer layer with $$gamma$$-ray irradiated samples. A chromium-rich part in the inner layer was formed along to the oxide/metal interface of $$gamma$$-ray irradiated Type 304L SS.

Oral presentation

Research on improvements of the assessment technique of stress corrosion cracking

Tsukada, Takashi; Yamamoto, Masahiro; Miwa, Yukio; Kato, Chiaki; Nakano, Junichi; Nakahara, Yukio; Sato, Tomonori; Uchida, Shunsuke

no journal, , 

In order to develop a technical basis necessary to improve the assessment technique of SCC, in this research, the influence of water radiolysis and irradiation dose rate on SCC behavior were studied which was indispensable to understand SCC behavior in actual power plants. In addition, the present status of SCC assessment techniques were summarized and analyzed systematically, and the present issue to improve the techniques was extracted.

Oral presentation

Changes of the surface of SUS316L immersed in high-temperature water caused by $$gamma$$-ray irradiation

Nakahara, Yukio; Yamamoto, Masahiro; Ishijima, Yasuhiro; Kato, Chiaki

no journal, , 

500-hour experiments have been done in order to study the effects of $$gamma$$-ray irradiation (the absorption rate $$sim$$ 30 kGy/h) on the corrosion of 316L stainless steel immersed in high-temperature (288 $$^{circ}$$C) water. Difference between $$gamma$$-ray irradiated and non-irradiated specimen surfaces were discussed with the results of surface analyses after the experiments. TEM cross sections of the surfaces of specimens solely immersed in the water show that $$gamma$$-ray irradiation made surface oxide film thicker and the formation of oxide grains on the surface more apparent. The change of corrosive environment caused by the irradiation enhanced the precipitation of oxide on the surface. Surface analysis of crevice-simulating specimens was also done by laser Raman spectroscopy. No definite peak was seen in the spectrum of non-irradiated condition. The peaks of compound oxide of Fe, Ni, and Cr were seen in the spectrum of $$gamma$$-ray irradiated condition. These results should indicate that the change of corrosive environment inside the crevice caused by the irradiation promoted the corrosion.

Oral presentation

$$gamma$$-ray irradiation effects on the corrosion of type 316L stainless steel in a gap filled with high-tempertaure water

Nakahara, Yukio; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi; Watanabe, Atsushi*; Fuse, Motomasa*

no journal, , 

no abstracts in English

Oral presentation

Effect of $$gamma$$-ray irradiation on corrosion of crevice portion of stainless steel in high temperature water

Yamamoto, Masahiro; Nakahara, Yukio; Kato, Chiaki; Tsukada, Takashi; Wada, Yoichi*; Fuse, Motomasa*

no journal, , 

Oxidants, such as hydrogen peroxide, are created by radiolysis of water in the light water reactor. It is easily estimated that the reactions are accelerated rather on the metal surface than the bulk water. Furthermore, a crevice portion concentrates more oxidants because of retardation of diffusion of them. Stainless steel samples having crevices were examined to clarify the effects of $$gamma$$ ray irradiation on corrosion at crevice portion. Difference of corrosion features were determined by some surface analytical techniques. And the effect of diffusion process of oxidants in the crevice was evaluated by calculation using FEM method.

Oral presentation

Crevice corrosion behavior of type 316L stainless steel in $$gamma$$-ray irradiated high-temperature water

Nakahara, Yukio; Kato, Chiaki; Yamamoto, Masahiro; Tsukada, Takashi; Watanabe, Atsushi*; Fuse, Motomasa*

no journal, , 

Irradiation effects on the corrosion of stainless steel (SS) in high-temperature water have been studied. The corrosion in diffusion-restricted environment was examined with simulated crevice-shape samples. Test specimens were made of Type 316L SS. The specimens have been immersed in deaerated high purity water of 288 $$^{circ}$$C with $$gamma$$-ray irradiation for 500 hours. The source of the $$gamma$$ rays was $$^{60}$$Co. The maximum absorbed dose rate in the water was estimated to be about 30 kGy h$$^{-1}$$. Characteristics of the surface oxide formed on the tested secimens have been analyzed using SEM, laser Raman Spectrometer (LRS), and TEM/EDX. On the surface of the irradiated specimens immersed as the crevice-shape samples, precipitated particles were observed but the surface was not fully covered with the particles. Besides the particles, bigger particles were observed on the surface. The LRS spectra indicated that the smaller particles were Fe-Ni spinels and the bigger particles were $$alpha$$-Fe$$_{2}$$O$$_{3}$$. In-depth profiles of the surface taken using TEM/EDX showed that the smaller particles were Fe-Ni spinels and the bigger particles were $$alpha$$-Fe$$_{2}$$O$$_{3}$$. The bigger particles of $$alpha$$-Fe$$_{2}$$O$$_{3}$$ were only observed in $$gamma$$-ray irradiated crevice portion. It indicated that oxidants created by the irradiation changed the potential to nobler direction in the crevice-like environment.

Oral presentation

Research for the improvement of SCC evaluation method including the effect of radiation on water, 2; Oxide film structures and environmental parameters on type 316L stainless steel under $$gamma$$-ray irradiation in high temperature water

Kato, Chiaki; Nakahara, Yukio; Yamamoto, Masahiro; Tsukada, Takashi

no journal, , 

It is well known that the decomposition of water by irradiation results in the formation of oxidants, such as hydrogen peroxide and radical species. Inside crevices, the effect of diffusion restriction and surface reactions may become more significant, so that the environments are expected to be different from those in the outsides. Therefore the structural effects using crevice-like specimen have been discussed and corrosion acceleration effects were introduced. In this work, the effects of $$gamma$$-ray irradiation and structure on the corrosion of Type 316L SS in high-temperature water of 288 $$^{circ}$$C were examined. We also consider structures of the oxide film on the stainless steel using transmission electron microscope and Raman spectroscope in order to show the differences made by the irradiation and structure. In addition, the environment inside irradiated crevices was estimated from results of the modeling of the oxide film and stable oxide states based on the E-pH diagram.

Oral presentation

Research for the improvement of SCC evaluation method including the effect of radiation on water, 3; Influence of materials and dissolved oxygen related to oxide film structures on stainless steel under $$gamma$$-ray irradiation in high temperature water

Yamamoto, Masahiro; Nakahara, Yukio; Kato, Chiaki; Tsukada, Takashi; Suzuki, Kazuhiro; Hatakeyama, Yuichi; Watanabe, Atsushi*; Fuse, Motomasa*

no journal, , 

It is well known that the decomposition of water by irradiation results in the formation of oxidants, such as hydrogen peroxide (H$$_{2}$$O$$_{2}$$) and radical species. The oxidant such as H$$_{2}$$O$$_{2}$$ promote nobler electrochemical corrosion potential (ECP) of stainless steels (SSs) and change oxide instructors as corrosion products on stainless steels surface. In this work, the effects of $$gamma$$-ray irradiation and structure on the corrosion of Type 316L SS and 304L SS in high-temperature water of 288C were examined. We also consider structures of the oxide film on the stainless steel using transmission electron microscope (TEM) and Raman spectroscope in order to show the differences made by the irradiation and structure. In addition, the effect of diffusion restriction and surface reactions may become more significant Inside crevices, so that the environments are expected to be different from those in the outsides.

Oral presentation

Research for the improvement of SCC evaluation method including the effect of radiation on water, 1; Objectives and outline of the research

Tsukada, Takashi; Yamamoto, Masahiro; Kato, Chiaki; Nakano, Junichi; Nakahara, Yukio; Sato, Tomonori; Ugachi, Hirokazu; Kondo, Keietsu

no journal, , 

no abstracts in English

Oral presentation

Development and application of a car-borne survey system, KURAMA, Kyoto University RAdiation MApping system, 4; A Joint regional radiation survey with a KURAMA-II monitoring system by local governments and JAEA

Nakahara, Yukio; Sato, Tetsuro; Matsuda, Norihiro; Saito, Kimiaki

no journal, , 

In order to illustrate the whole effects of the accident at Fukushima Dai-ichi Nuclear Power Station in detail, a joint regional radiation survey with a KURAMA-II monitoring system has been done by local governments and JAEA in 9 prefectures (from Miyagi through Yamanashi) and the metropolis of Tokyo. The summary of the survey and the problems related to the survey is reported in the presentation.

Oral presentation

Development and application of car-borne survey system, KURAMA, Kyoto University RAdiation MApping system, 6; Awaiting solution for application of KURAMA-II

Tsuda, Shuichi; Yoshida, Tadayoshi; Nakahara, Yukio; Saito, Kimiaki

no journal, , 

no abstracts in English

Oral presentation

Study on distribution and migration of radioactive substances around the Fukushima Daiichi Nuclear Power Plant, 3; Measurement of air dose rate by a series of vehicle-borne survey

Ando, Masaki; Nakahara, Yukio; Sato, Tetsuro; Matsuda, Norihiro; Saito, Kimiaki

no journal, , 

no abstracts in English

21 (Records 1-20 displayed on this page)