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Aoyagi, Kazuhei; Ozaki, Yusuke; Tamura, Tomonori; Ishii, Eiichi
Proceedings of 4th International Conference on Coupled Processes in Fractured Geological Media; Observation, Modeling, and Application (CouFrac2024) (Internet), 10 Pages, 2024/11
In high-level radioactive waste disposal, it is crucial to estimate the transmissivity of gallery excavation-induced fractures, i.e., excavation damaged zone (EDZ) fractures, because EDZ fractures can be a radionuclide migration pathway after the backfilling of the facility is completed. From previous research, the transmissivity of the fracture can be estimated through the empirical equation using the parameter ductility index (DI), which corresponds to the effective mean stress normalized to the tensile strength of the rock. In this research, we performed a hydromechanical coupling analysis of a gallery excavation at the Horonobe Underground Research Laboratory to estimate the transmissivity of the EDZ fracture before the excavation. At first, we simulated the gallery excavation at 350 m and showed that the measured transmissivity was within the range of the estimated transmissivity using the DI. After that, we also predicted the excavation of a gallery at 500 m by setting the hydromechanical parameters acquired from the laboratory tests before the excavation. The estimated transmissivity at 500 m was one order of magnitude less than that at 350 m. This result might be related to the closure of the fracture under high-stress conditions and low rock strength.
Aoyagi, Kazuhei; Ishii, Eiichi
Rock Mechanics and Rock Engineering, 52(2), p.385 - 401, 2019/02
Times Cited Count:22 Percentile:68.14(Engineering, Geological)Excavation of deep underground openings induces permeable fractures around the opening due to stress redistribution. Such a zone is called excavation damaged zone (EDZ). In a high-level radioactive waste disposal project, the EDZ might provide pathways for the migration of radionuclides around the facility. Thus, this study focused on the development of a method for estimating the highest potential hydraulic conductivity in the EDZ around a gallery in the Horonobe Underground Research Laboratory, Japan. Borehole televiewer surveys, rock core observations, and hydraulic tests were undertaken to investigate the extent and magnitude of hydraulic conductivity in the EDZ around the gallery. The observed extent of the EDZ shows good agreement with the EDZ estimated from hydro-mechanical coupling analysis. The measured hydraulic conductivities of the EDZ are within the range of those based on the Mean Stress Index (MSI), which is defined as the ratio of the effective mean stress derived from numerical analyses to the tensile strength of intact rock. Given that the rock mass is relatively homogeneous and artificial damage (e.g., blasting-induced damage) can be neglected, as in the Horonobe Underground Research Laboratory, the MSI model is likely to be applicable in estimating the highest potential hydraulic conductivity in the EDZ.
Aoyagi, Kazuhei; Ishii, Eiichi
Dai-14-Kai Iwa No Rikigaku Kokunai Shimpojiumu Koen Rombunshu (Internet), 6 Pages, 2017/01
The objective of this research is to investigate the hydro-mechanical properties of excavation damaged zones (EDZs) along the galleries excavated in 250 m and 350 m depths. We conducted hydraulic tests, BTV observations and core analyses. As a result, in the 250 m gallery, the extent of the EDZ was 1.0 m into the gallery wall. The hydraulic conductivity was increased by 2 to 3 orders of magnitudes compared with that of intact rock. On the other hand, in the 350 m gallery, the extent of the EDZ was 0.4 m into the gallery wall; the hydraulic conductivity was increased by 5 orders of magnitudes compared with that of intact rock. We investaged the difference of the characteristics of the EDZs on the basis of competence factor and ductility index. As a result, it was estimated that an extent of an EDZ decreases with decrease of competence factor; a hydraulic conductivity in an EDZ increases with decrease of ductility index.
Tsuru, Tomohito; Chrzan, D. C.*
Scientific Reports (Internet), 5, p.8793_1 - 8793_8, 2015/03
Times Cited Count:73 Percentile:86.93(Multidisciplinary Sciences)Much of the world's future economy hedges on the ability to improve the efficiency of mechanical machines without sacrificing their performance. This requires the development of lighter and stronger structural alloys. Magnesium alloys are very promising for structural applications, but they suffer from a fatal flaw. The mobility of the dislocations is determined by the bonding within the alloy, and this bonding is best modeled using approaches rooted firmly in quantum mechanics. Here, we compute the electronic structure of a screw dislocation gliding on a prismatic plane within Mg as it passes over its Peierls barrier. We show that the ductility of Mg is increased because some substitutional additions strongly bind to and stabilize a compact core structure for screw dislocations that are formally able to glide on both the basal and prismatic planes.
Udagawa, Yutaka; Nagase, Fumihisa; Fuketa, Toyoshi
JAERI-Research 2005-020, 40 Pages, 2005/09
In order to investigate effects of quenching temperature and cooling rate before quench on cladding ductility reduction under LOCA conditions, samples cut from non-irradiated 1717-type Zircaloy-4 cladding tubes for PWRs were oxidized in steam at 1373 and 1473 K, cooled at 2 to 7 K/s, and quenched at 1073 to 1373 K. The quenched samples were subjected to ring compression test, microstructure observation, and Vickers hardness test. Quenching temperature decrease obviously increased area fraction of
phase in the radial cross section of the cladding, and reduced cladding ductility. Slow-cooling rate decrease increased unit size and hardness of precipitated
phase, while
phase area fraction and cladding ductility were not significantly changed.
phase is harder than the surrounding region in the metallic layer and has higher oxygen content, indicating its low ductility. Consequently, increase in the area fraction in the cladding is a main cause of the reduction in cladding ductility with decrease in the quenching temperature.
Nagase, Fumihisa; Fuketa, Toyoshi
Journal of Nuclear Science and Technology, 41(12), p.1211 - 1217, 2004/12
Times Cited Count:20 Percentile:76.04(Nuclear Science & Technology)Hydride precipitation along the radial-axial plane increases in high burn-up BWR fuel claddings. The radial hydrides may have an important role during fuel behavior in a RIA and may reduce ductility of the cladding under PCMI conditions. In order to promote a better understanding of the influence of the radial hydrides on cladding failure behavior under the PCMI conditions, tube burst tests were conducted for unirradiated BWR claddings charged with 200 to 650 ppm of hydrogen. About 20 to 30% of hydrides were re-oriented and precipitated along the radial-axial plane. The claddings exhibited large burst openings with an axial crack at room temperature and 373 K. However, the influence of the radial hydrides on both burst pressure and residual hoop strain was very small. It is accordingly expected that ductility of high burn-up BWR cladding is significantly reduced not only by precipitation of radial hydrides as far as hydrogen concentration and radial hydride fraction range in the present study.
Nagase, Fumihisa; Uetsuka, Hiroshi
JAERI-Research 2002-023, 23 Pages, 2002/11
To obtain basic data to evaluate fuel rod integrity during abnormal transient and accident of LWRs, high burnup PWR fuel claddings were heated for 0 to 600s at temperatures of 673 through 1173K, and the mechanical property changes were examined by using ring tensile test at room temperature. As a result of the test, it was shown that strength and ductility of the cladding are changed depending on heating temperature and time. The mechanical property changes by temperature transients are considered to be correspondent mainly to recovery of irradiation defect, recovery and recrystallization of the Zircaloy, phase transformations, and associated change of the hydride distribution and morphology. Comparison with unirradiated claddings suggested that irradiation effects are not completely annealed out by the short-term annealing at high temepratures. Radial change of hydrogen concentration was measured for the high burnup PWR fuel cladding and very high hydrogen concentration of about 2400wtppm was detected at the cladding periphery.
Ioka, Ikuo; Miwa, Yukio; Tsuji, Hirokazu; Yonekawa, Minoru; Takada, Fumiki; Hoshiya, Taiji
JSME International Journal, Series A, 45(1), p.51 - 56, 2002/01
The low cycle creep-fatigue test with tensile strain hold of the austenitic stainless steel irradiated to 2dpa was carried out at 823K in vacuum. The applicability of creep-fatigue life prediction methods to the irradiated specimen was examined. The fatigue life on the irradiated specimen without tensile strain hold time was reduced by a factor of 2-5 in comparison with the unirradiated specimen. The fraction of intergranular fracture increased with increasing strain hold time. The decline in fatigue life of the irradiated specimen with tensile strain hold was almost equal to that of the unirradiated specimen. For the irradiated specimen, the time fraction damage rule trends to yield unsafe estimated lives and the ductility exhaustion damage rule trends to yield generous results. However, all of data were predicted within a factor of three on life by the linear damage rule.
Kurata, Yuji; Nakajima, Hajime
Journal of Nuclear Materials, 228, p.176 - 183, 1996/00
Times Cited Count:12 Percentile:70.17(Materials Science, Multidisciplinary)no abstracts in English
Kurata, Yuji; ; ; Shindo, Masami; Nakajima, Hajime;
Journal of Nuclear Science and Technology, 32(11), p.1108 - 1117, 1995/11
Times Cited Count:3 Percentile:36.48(Nuclear Science & Technology)no abstracts in English
Kurata, Yuji; ; ; Shindo, Masami; Nakajima, Hajime;
JAERI-Research 95-037, 42 Pages, 1995/06
no abstracts in English
Kurata, Yuji; Nakajima, Hajime
Journal of Nuclear Science and Technology, 32(6), p.539 - 546, 1995/06
Times Cited Count:7 Percentile:58.78(Nuclear Science & Technology)no abstracts in English
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JAERI-M 83-086, 103 Pages, 1983/06
no abstracts in English
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Journal of Nuclear Science and Technology, 18(10), p.802 - 810, 1981/00
Times Cited Count:16 Percentile:84.98(Nuclear Science & Technology)no abstracts in English
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Journal of Nuclear Science and Technology, 15(2), p.152 - 155, 1978/02
Times Cited Count:1no abstracts in English
Ogawa, Yutaka; Kondo, Tatsuo; ;
Proc.of 2nd Japan-US HTGR Safety Technology Seminar,Material Properties and Design Method Session, 9 Pages, 1978/00
no abstracts in English
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JAERI-M 6601, 26 Pages, 1976/06
no abstracts in English
JAERI-M 6538, 27 Pages, 1976/05
no abstracts in English
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JAERI-M 6182, 20 Pages, 1975/07
no abstracts in English
Ozawa, K.;
Physica Status Solidi, 30, p.K69 - K71, 1968/00
no abstracts in English