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Hata, Kuniki; Takamizawa, Hisashi; Hojo, Tomohiro*; Ebihara, Kenichi; Nishiyama, Yutaka; Nagai, Yasuyoshi*
Journal of Nuclear Materials, 543, p.152564_1 - 152564_10, 2021/01
Times Cited Count：12 Percentile：91.16(Materials Science, Multidisciplinary)Reactor pressure vessel (RPV) steels for pressurized water reactors (PWRs) with bulk P contents ranging from 0.007 to 0.012wt.% were subjected to neutron irradiation at fluences ranging from 0.3 to 1.2
10
n/cm
(E 
1 MeV) in PWRs or a materials testing reactor (MTR). Grain-boundary P segregation was analyzed using Auger electron spectroscopy (AES) on intergranular facets and found to increase with increasing neutron fluence. A rate theory model was also used to simulate the increase in grain-boundary P segregation for RPV steels with a bulk P content up to 0.020wt.%. The increase in grain-boundary P segregation in RPV steel with a bulk P content of 0.015wt.% (the maximum P concentration found in RPV steels used in Japanese nuclear power plants intended for restart) was estimated to be less than 0.1 in monolayer coverage at 1.010 n/cm (E 1 MeV). A comparison of the PWR data with the MTR data showed that neutron flux had no effect upon grain-boundary P segregation. The effects of grain-boundary P segregation upon changes in irradiation hardening and ductile-brittle transition temperature (DBTT) shifts were also discussed. A linear relationship between irradiation hardening and the DBTT shift with a slope of 0.63 obtained for RPV steels with a bulk P content up to 0.026wt.%, which is higher than that of most U.S. A533B steels. It is concluded that the intergranular embrittlement is unlikely to occur for RPV steels irradiated in PWRs.
Aihara, Jun; Hojo, Kiichi; Furuno, Shigemi*; Hojo, Tomohiro; Sawa, Kazuhiro; Yamamoto, Hiroyuki; Motohashi, Yoshinobu*
Materials Transactions, 48(7), p.1896 - 1900, 2007/07
Times Cited Count：0 Percentile：0.01(Materials Science, Multidisciplinary)Silicon carbide(SiC) TEM specimens were annealed, in-situ, at 1273K for 30 minutes after amorphization with 30keV Ne
irradiation to the fluence of 1.9 or 2.310Ne/m at 573K or about 98K. The crystal nucleation and bubble coalescence accompanied by recrystallization were observed in both specimens with the annealing after the irradiations. 2.310Ne/m irradiations in both specimens. The Debye-Sherrer rings of the nucleated crystals well fitted the net pattern of the matrix, even though no ring corresponding to (200) of 
-SiC appeared. Dependence of the crystal nucleation behavior on irradiation temperature was not observed within the present experimental range.
O
-yttria stabilized ZrO composite material irradiated with Ne ions at high temperaturesHojo, Tomohiro*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi
Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.123 - 127, 2006/09
Times Cited Count：2 Percentile：21.09(Instruments & Instrumentation)Spinel and yttria stabilized zirconia (YSZ) are candidates for fuel materials for use in nuclear reactors and the optical and insulating materials for fusion reactors. In the present study, the damage evolution process of polycrystalline spinel-YSZ composite materials has been studied by in situ transmission electron microscope observation during ion irradiation. The irradiation was performed with 30 keV Ne at a flux of 5 10
ions/cm per second at 923 K and 1473 K, respectively. At 923 K, defect clusters and bubbles were formed homogeneously in YSZ grains. On the other hand, at 1473 K, only bubble formation was observed. The bubbles grew remarkably with increasing ion fluence in both grains. Even though the growth of the bubbles was observed in both grains, the average diameter of grown bubbles in spinel grains was larger than those in YSZ ones. The bubbles tended to form along the grain boundary at both temperatures.
Hojo, Tomohiro*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi
Nuclear Instruments and Methods in Physics Research B, 250(1-2), p.101 - 105, 2006/09
Times Cited Count：6 Percentile：43.85(Instruments & Instrumentation)Yttria stabilized zirconia (YSZ) is a candidate material focused as optical and insulating materials in nuclear reactors. Therefore, it is useful to investigate defect formation during irradiation, in order to assess YSZ resistance to radiation damage. In the present study, in situ transmission electron microscopy (TEM) observations were performed on YSZ during 30 keV Ne irradiation in the temperature range of 723-1123 K. For irradiations below 1023 K, defect clusters and bubbles were formed simultaneously. On the other hand, at 1123 K, only bubbles were formed in the initial stage of irradiation. Loops formed later following the bubble formation. It was also observed that, in the early stage of irradiation above 923 K, larger bubbles were formed along the loop planes compared with other areas. TEM observations indicated that dislocation loops formed on three kinds of crystallographic planes: namely, (100), (111) and (112) planes.
Aihara, Jun; Hojo, Kiichi; Furuno, Shigemi*; Shimura, Kenichiro; Hojo, Tomohiro*; Sawa, Kazuhiro; Yamamoto, Hiroyuki; Motohashi, Yoshinobu*
Nuclear Instruments and Methods in Physics Research B, 242(1-2), p.441 - 444, 2006/01
Times Cited Count：1 Percentile：12.86(Instruments & Instrumentation)no abstracts in English
Aihara, Jun; Hojo, Tomohiro*; Furuno, Shigemi*; Ishihara, Masahiro; Sawa, Kazuhiro; Yamamoto, Hiroyuki; Hojo, Kiichi
Nuclear Instruments and Methods in Physics Research B, 241(1-4), p.559 - 562, 2005/12
Times Cited Count：5 Percentile：41.08(Instruments & Instrumentation)Silicon carbide (SiC) specimens prepared for the TEM (transmission electron microscope) observation were amorphized with 30keV Ne or 4.5keV He ion irradiation at room temperature and successively annealed at 1273K in the TEM. Ne and He were selected as irradiation ion species to change the concentration of implanted rare gas atoms. The energy and flux of these ion species were selected in order to get similar dpa depth profiles and dpa rates based on TRIM calculation. In this condition, peak ion implantation of He was estimated to be about 5 times as large as that of Ne for the same peak dpa. Crystal nucleation occurred with annealing in the specimen irradiated with He up to 6.3dpa(peak), however, no crystal nucleation was observed in the specimen irradiated with Ne up to 15dpa(peak); Namely, crystal nucleation occurred with less dpa in the case of He irradiation than in the case of Ne irradiation. It was found that the concentration of implanted inert gas atom influences the crystal nucleation behavior.
Aihara, Jun; Sawa, Kazuhiro; Furuya, Yoshio*; Hojo, Tomohiro*; Furuno, Shigemi*; Yamamoto, Hiroyuki; Hojo, Kiichi; Ishihara, Masahiro
Journal of the American Ceramic Society, 88(8), p.2319 - 2321, 2005/08
Times Cited Count：0 Percentile：0.02(Materials Science, Ceramics)no abstracts in English
Kikuchi, Makoto*; Motohashi, Yoshinobu*; Ito, Tsutomu*; Sakuma, Takaaki*; Shibata, Taiju; Baba, Shinichi; Ishihara, Masahiro; Sawa, Kazuhiro; Hojo, Tomohiro*; Tsuji, Nobumasa*
Nihon Kikai Gakkai Kanto Shibu Ibaraki Koenkai (2004) Koen Rombunshu (No.040-3), p.57 - 58, 2004/09
no abstracts in English
Hojo, Tomohiro; Aihara, Jun; Hojo, Kiichi; Furuno, Shigemi*; Yamamoto, Hiroyuki; Nitani, Noriko; Yamashita, Toshiyuki; Minato, Kazuo; Sakuma, Takaaki*
Journal of Nuclear Materials, 319, p.81 - 86, 2003/06
Times Cited Count：18 Percentile：74.43(Materials Science, Multidisciplinary)no abstracts in English
single crystals with helium and Xenon ions at RT and 923KHojo, Kiichi; Hojo, Tomohiro; Sasajima, Naohiko*; Shirasu, Noriko; Yamashita, Toshiyuki; Minato, Kazuo; Furuno, Shigemi*
AIP Conference Proceedings 680, p.647 - 652, 2003/00
no abstracts in English
irradiationHojo, Tomohiro*; Yasuhara, Akira*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi
no journal, ,
Yttria stabilized zirconia (YSZ) is a candidate material as optical and insulating materials in nuclear reactors. The investigation of defect formation under the ion irradiation is therefore required to assess YSZ resistance for radiation damage. Ion irradiation and nanostructural observations were simultaneously performed by transmission electron microscope (TEM) equipped with ion accelerator and X-ray spectrometer (EDS). YSZ was irradiated with 30 keV Ne ions with a flux of 310
ions/cm at 923 K. It is clearly observed that the dislocation loops are formed along (110) crystal plane. The measurements across the loops by EDS show that the composition of oxygen on loops decreases and zirconium increases compared with the matrix. It is also shown that the intensity of Ne increases at the loop. From the previous studies, it was observed that bubbles were formed preferentially on loop planes. It is implied that the irradiated Ne tends to exist in the loops as bubbles.
irradiationHojo, Tomohiro*; Yasuhara, Akira*; Yamamoto, Hiroyuki; Aihara, Jun; Furuno, Shigemi*; Sawa, Kazuhiro; Sakuma, Takashi*; Hojo, Kiichi
no journal, ,
Yttria stabilized zirconia (YSZ) is a candidate material as optical and insulating materials in nuclear reactors. The investigation of defect formation under the ion irradiation is therefore required. In the present study, YSZ was irradiated with 30 keV Ne ions with a flux of 310 ions/cm at 923 K. Compositional changes were analyzed by energy dispersive X-ray spectrometer (EDS) equipped with transmission electron microscope. From the observation of micrographs, it was shown that dislocation loops were formed on three kinds of crystallographic planes, namely, on (110), (111) and (112) planes. The dislocation loops inhabiting on (110) crystal plane were analyzed by EDS along the loops. The average composition between the vicinity of loops and the matrix is compared. On the basis of the obtained results, it is observed composition of oxygen on loops decreases and zirconium increases compared with the matrix.
