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Ichikawa, Yasuaki*; Kimoto, Kazushi*; Matsui, Hiroya
JAEA-Research 2019-005, 32 Pages, 2019/10
JAEA-Research-2019-005.pdf:6.13MB
It is important to evaluate the mechanical stability around the geological repository for high-level radioactive waste, during not only the design, construction and operation phases, but also the post-closure period over several millennia. The rock mass around the tunnels could be deformed in response to time dependent behaviors such as creep and stress relaxation. Therefore, this study has started as a joint research with Okayama University from 2016. This report summarize the results of the joint research performed in fiscal year 2017 and 2018. Based on the research results obtained in fiscal year 2016, automatic measurement system was developed, which can collect very large data on surface elastic wave propagation in a short time, also the applicability of various kinds of parameters derived from measured elastic wave data was examined.
Kimoto, Kazushi*; Ichikawa, Yasuaki*; Matsui, Hiroya
JAEA-Research 2017-009, 18 Pages, 2017/11
JAEA-Research-2017-009.pdf:6.5MB
JAEA has started this study as joint research with Okayama University from 2016. In fiscal year 2016, several kinds of elastic wave velocity were measured using ultra sonic sensors and laser Doppler vibrometer to evaluate the anisotropy of different elastic wave in granite. The velocity measurements were carried out focused on transmitted wave and surface wave. The results showed that strong anisotropy was observed in transmitted P- wave velocity while weak anisotropy was observed in transmitted S-wave and group velocity estimated by surface velocity measurement. In addition, data obtained from surface velocity measurement was partitioned into transmitted and reflected waves and analyzed them in detail. It resulted that elastic wave due to mineral particles consist of granite was dispersed; however, significant dispersion was only observed at specific location.
Ichikawa, Yasuaki*; Kimoto, Kazushi*; Matsui, Hiroya; Kuwabara, Kazumichi; Ozaki, Yusuke
JAEA-Research 2016-018, 23 Pages, 2016/12
JAEA-Research-2016-018.pdf:4.41MB
It is important to evaluate the stability of a repository for high-level radioactive waste not only during the design, construction and operation phases, but also during the post-closure period, for time frames likely exceeding several millennia or longer. The rock mass around the tunnels could be deformed through time in response to time dependent behavior. On the other hand, it was revealed that the chemical reaction of groundwater in a rock had an influence on the long-term behavior. An evaluation of the microcracks to have an influence on this mechanical and chemical coupled phenomena should be worked on chiefly. In fiscal year 2015, using a laser Doppler vibrometer that extends a frequency band up to 20 MHz, and measuring the surface wave transmitted through the granite specimens were estimated group velocity. As a result, group velocity until 100 kHz 
500 kHz, revealed that tends to decrease while vibrating. The group speed estimate from a group delay was shown to be easier than the estimate by wave number - frequency spectrum. This is because in order to improve reliability, the estimated frequency band is by using a spatially averaged waveform. As a result obtained, in the case of the modeling by the viscoelastic theory of the granite and a microcrack nondestructiveness evaluation, it is thought that it is useful information in the future. In order to use the knowledge of this study, there is a need to clarify the correspondence between the microscopic properties of the medium such as a crack and crystal grain and the change of the group velocity.
Ichikawa, Yasuaki*; Kimoto, Kazushi*; Sato, Toshinori; Kuwabara, Kazumichi; Takayama, Yusuke
JAEA-Research 2015-025, 31 Pages, 2016/03
JAEA-Research-2015-025.pdf:13.0MB
It is important to evaluate the stability of a repository for high-level radioactive waste not only during the design, construction and operation phases, but also during the post-closure period, for time frames likely exceeding several millennia or longer. The rock mass around the tunnels could be deformed through time in response to time dependent behavior. On the other hand, it was revealed that the chemical reaction of groundwater in a rock had an influence on the long-term behavior. An evaluation of the microcracks to have an influence on these mechanical and chemical coupled phenomena should be worked on chiefly. In fiscal year 2014, this study performed numerical analysis to examine the supersonic scattering attenuation decrement behavior in the crystalline rock and a measurement sequentially last year. The measurement of the head and surface waves were carried out. As a result, group speed was provided. On the other hand, the spread scattering analysis of the elastic wave by the FDTD (Finite Difference Time-Domain) method made a numerical analysis. However, a laboratory finding is different from expectation of the simulation, and crystal anisotropic influence of a microcrack and rock-forming minerals is thought about as a cause of this estrangement. Therefore it was revealed that it was necessary to examine these two points of influence more in future.
Ichikawa, Yasuaki*; Kimoto, Kazushi*; Sato, Toshinori; Sanada, Hiroyuki; Kuwabara, Kazumichi
JAEA-Research 2014-027, 25 Pages, 2015/02
JAEA-Research-2014-027.pdf:16.92MB
The rock and the rock mass are known to show time-dependent behavior such as creep and the stress-relaxation. It is to evaluate long-term rock mechanics stability that the important theme understanding the property. From the research study until now, it is rock mechanics and chemical coupled phenomenon to have an influence on the long-term behavior. It is a theme to develop technique to model this coupled phenomenon, and to analyze. About an evaluation of the microcrack to have an influence on this coupled phenomenon, it is the theme that we should work on in a long-term rock mass behavior study chiefly. This study developed numerical analysis to check the ultrasonic scattering decrement behavior by the microcrack of the crystalline rock and the measurement technique. The FDTD method which modelled a crack was used for numerical analysis by split node. It depends on the simulation technique that it developed that useful knowledge was provided by elastic wave modeling. On the other hand, the ultrasonic measurement in a rock sample was measured by the water immersion method. As a result, we understood that we could acquire useful information to evaluate the scattering decrement of an elastic wave in a rock sample.
Takayama, Yusuke*; Ikuta, Yuki*; Iizuka, Atsushi*; Kawai, Katsuyuki*; Taki, Tomihiro; Sakao, Ryota; Ichikawa, Yasuaki*
Unsaturated Soils; Research & Applications, p.659 - 665, 2014/06
In this paper, a multiple unsaturated soil barrier consisting of gravel, sand and bentonite-mixed soil layers is considered as a hardly permeable covering to prevent rainwater from infiltrating into waste deposits. Not only the quite low permeability of bentonite-mixed soil layer but also a function of capillary barrier between granular layers having different water-retention capabilities is expected to prevent water infiltration. A series of numerical simulation is carried out to evaluate performance of the multiple soil barrier using saturated/unsaturated soil/water coupled FE computation technique. The multiple unsaturated soil barrier system considered here is 10m long and 1.5 m thick consisting of sandy soil surface, sand filter, gravel layer, sand filter and bentonite-mixed clayey layer. And the soil barrier system is assumed to be placed as a covering with a 5% inclination on the waste deposit. The performance of the multiple soil barrier system is shown as a management chart to maintain impermeable ability associated with possible rainfall intensity. Particularly, in this paper, actual rainfall record in Okayama area is employed to determine the rainfall intensity which is imposed as a boundary condition in the computation. According to the simulation results, it is found that the capillary barrier is a key issue in evaluating the long term performance of the barrier system. And, it is confirmed that the barrier system considered in this paper can work well against the maximum intensity of the rainfall in the past record.
Ichikawa, Yasuaki*; Kimoto, Kazushi*; Sato, Toshinori; Tanno, Takeo; Hikima, Ryoichi; Sanada, Hiroyuki
JAEA-Research 2013-045, 69 Pages, 2014/03
JAEA-Research-2013-045.pdf:9.51MB
Rock mass is a complex material including several classes of discontinuities and inhomogeneous/anisotropic minerals. If observing rock samples, we know that crystalline rock is a complex of minerals, grain boundaries and microcracks. In this study, the series of experiments were managed by a flow-through type changing temperature, pH and applied stress. Attenuation of ultrasonic waves in rock is investigated experimentally using an intact but coarse-grained granite core sample. For ultrasonic measurements, piezoelectric transducers are used in a through-transmission mode. With the estimated response function, phase and amplitude spectra of the transmitted ultrasonic waves are investigated quantitatively to evaluate the attenuation and change in travel time.
nucleus 
NoAsai, Masato; Tsukada, Kazuaki; Sakama, Minoru*; Haba, Hiromitsu*; Ichikawa, Takatoshi*; Ishii, Yasuo; Toyoshima, Atsushi; Ishii, Tetsuro; Nishinaka, Ichiro; Nagame, Yuichiro; et al.
Physical Review C, 87(1), p.014332_1 - 014332_6, 2013/01
Times Cited Count：6 Percentile：43.66(Physics, Nuclear)The spin-parity and neutron configuration of the ground state of No have been identified through 
-decay spectroscopy. The No is the nucleus with the largest neutron number whose spin-parities and single-particle configurations have ever been identified. The neutron 9/2
[615] configuration was assigned to the ground state of No as well as to the 231.4 keV level in 
Fm. This allowed us to establish energy spacings and order of the neutron single-particle orbitals in such heaviest nuclear region. The appearance of the 9/2[615] ground state at 
=157 implies that the order of the neutron orbitals between the =152 and 162 deformed shell gaps should change considerably with increasing neutron number.
Ichikawa, Yasuaki*; Tanno, Takeo; Hikima, Ryoichi; Sanada, Hiroyuki; Matsui, Hiroya; Sato, Toshinori
JAEA-Research 2012-003, 34 Pages, 2012/04
JAEA-Research-2012-003.pdf:3.33MB
A rock mass is a complex entity, including several classes of discontinuities and numerous heterogeneous and anisotropic minerals. From investigations of rock samples, we know that crystalline rock is a complex mix of minerals, grain boundaries and microcracks. Deformation and failure mechanisms may be more completely understood if we are able to correctly characterize the microscale composition and grain boundary properties. Amongst the rock-forming minerals, especially quartz and biotite in granite, numerous microcracks are developed. It is important to study coupled mechanical and chemical factors in crystalline rock for long-term behavior study. This report presents the results of the following FY2010 activities. (1) Explanation of nonlinear fracture mechanics, (2) Pressure dissolution experiments of using specimens of single quartz, (3) Theory study on the rate of quartz dissolution, (4) Homogenization theory for fractured rock
Ichikawa, Yasuaki*; Choi, J. H.*; Tanno, Takeo; Hirano, Toru*; Matsui, Hiroya
JAEA-Research 2011-007, 91 Pages, 2011/06
JAEA-Research-2011-007.pdf:8.75MB
We first surveyed the classical theories of fracture mechanics, and discussed the subcritical crack growth (SCG), which is observed under less load than the fracture toughness Kc. This SCG is a result of coupled mechanical and chemical effect. The SCG for granite was treated on this basis. We performed pressure dissolution experiments using specimens of single crystal quartz, since the dissolution reaction is engaged with a deformation and failure process of polycrystalline rock. The series of experiments were managed by a flow-through type changing temperature, pH and applied stress. Si concentrations we here measured. We first surveyed the theories of pressure solution. Then we proposed a theory of saluting velocity of quart which accounts for the effects of temperature, chemical (pH), solid pressure and pore pressure.
Fm
populated via the decay of NoAsai, Masato; Tsukada, Kazuaki; Haba, Hiromitsu*; Ishii, Yasuo; Ichikawa, Takatoshi*; Toyoshima, Atsushi; Ishii, Tetsuro; Nagame, Yuichiro; Nishinaka, Ichiro; Kojima, Yasuaki*; et al.
Physical Review C, 83(1), p.014315_1 - 014315_12, 2011/01
Times Cited Count：24 Percentile：79.14(Physics, Nuclear)Excited states in Fm populated via the decay of No are studied in detail through -
coincidence and fine structure measurements. Spin-parities and neutron configurations of the excited states in Fm as well as the ground state of No are definitely identified on the basis of deduced internal conversion coefficients, lifetimes of transitions, rotational-band energies built on one-quasiparticle states, and hindrance factors of transitions. It is found that the excitation energy of the 1/2[620] state in =151 isotones increases with the atomic number, especially at 
100, while that of the 1/2[631] state decreases at =100. Energy systematics of the one-quasiparticle states in the =151 isotones are discussed in terms of the evolution of nuclear deformation involving the hexadecapole and hexacontatetrapole deformations.
Ichikawa, Yasuaki*; Choi, J. H.*; Hirano, Toru; Matsui, Hiroya
JAEA-Research 2009-027, 48 Pages, 2009/10
JAEA-Research-2009-027.pdf:3.75MB
On the radioactive waste disposal, the long-term mechanical stability of tunnel was required. Therefore, we have been developing the method evaluating the stability. This report describes the works in the FY2008. Chapter 1 is the overview. In Chapter 2 we performed pressure dissolution experiments using specimens of single crystal quartz, since the dissolution reaction is engaged with a deformation and failure process of polycrystalline rock. After applying stress the surface of contacted area of quartz was observed by microscope and found traces of dissolution and reprecipitation. We managed two types of experiment; a closed solution experiment and a flow-through experiment. We discussed the Si dissolution rate based on the experimental results measured by ICP-AES. Fundamental mechanism of time-dependent creep and stress relaxation for crystalline rocks was discussed in Chapter 3 based on a concept of mechano-chemical coupling phenomena (as treated in Chapter 2) at micro-crack tips.
Ichikawa, Yasuaki*; Seno, Yasuhiro*; Hirano, Toru; Nakama, Shigeo; Matsui, Hiroya
JAEA-Research 2008-090, 52 Pages, 2008/11
JAEA-Research-2008-090.pdf:13.05MB
This report describes the results of the works in the fiscal year 2007. In Chapter 1, we described the overview and background of this study. In Chapter 2 a reaction theory of pressure dissolution of quartz was proposed and by using a homogenization analysis the dissolution of quartz in bentonite was simulated by a modified diffusion model. In Chapter 3 CLSM was used to acquire clearly focused three-dimensional images of granite specimens of Mizunami underground lab for stress relaxation tests, and observed the change of micro-scale structure including the mineral configuration under applying compression stress. The local strain distributions suggest that a shearing mode is dominant in the granite samples. In Chapter 4 a strong discontinuity concept is introduced in the micro-scale problem of the multi-scale homogenization analysis, and Toki granite sample problems were solved.
Ichikawa, Yasuaki*; Seno, Yasuhiro; Nakama, Shigeo; Sato, Toshinori
JAEA-Research 2008-005, 60 Pages, 2008/03
JAEA-Research-2008-005.pdf:28.54MB
In this research we aim to clarify a long term behavior of crystalline rocks, and performed the following subjects: (1) Uniaxial and stress relaxation tests under observation of a confocal laser scanning microscope (CLSM) by using granite specimens of Mizunami underground lab. (2) Pressure dissolution experiment using specimens of quartz single crystal and glass beads. (3) Theory establishment of pressure dissolution of quartz and a homogenization analysis for quartz dissolution. In Chapter 2 CLSM was used to acquire clearly focused three-dimensional images of granite specimens of Mizunami underground lab for uniaxial and stress relaxation tests, and observed the change of microscale structure including the mineral configuration under applying compression stress. The local strain distributions were calculated by using quadrilateral meshes of finite elements arranged on the surface of each specimen. In Chapter 3 we performed pressure dissolution experiments using specimens of quartz single crystal and glass beads, since the dissolution reaction is engaged with a deformation and failure process of polycrystalline rock. After applying stress the surface of contacted area of quartz was observed by CLSM and found traces of dissolution and reprecipitation. In Chapter 4 a reaction theory of pressure dissolution of quartz was proposed and by using a homogenization analysis the dissolution of quartz in bentonite was simulated.
measurements of 
Pm, 
Sm, 
Eu, 
Gd and 
Tb using a total absorption BGO detectorHayashi, Hiroaki*; Akita, Yukinori*; Suematsu, Osamu*; Shibata, Michihiro*; Asai, Masato; Sato, Tetsuya; Ichikawa, Shinichi; Nishinaka, Ichiro; Nagame, Yuichiro; Osa, Akihiko; et al.
European Physical Journal A, 34(4), p.363 - 370, 2007/12
Times Cited Count：16 Percentile：71.35(Physics, Nuclear) values of Eu and Gd were measured for the first time using a total absorption BGO detector, and the data of Pm, Sm, and Tb obtained previously were reanalyzed. These nuclei were produced by the proton-induced fission of 
U at the JAEA-Tokai tandem accelerator facility, and separated from the reaction products using an on-line isotope separator. The deduced mass excesses and two-neutron separation energies were compared with those of atomic mass evaluations and theoretical predictions.
Fujii, Naoki; Ichikawa, Yasuaki*
Oyo Rikigaku Rombunshu, 9, p.323 - 332, 2006/08
Diffusion in bentonite clay is investigated by the homogenization analysis, which related the microscale structural and chemical characteristics to the macroscale behavior. However, the diffusion coefficient of the cation by calculation is smaller than the effective diffusion coefficient by experiment. This difference is caused by the surface diffusion. In order to resolve the surface diffusion by numerical analysis, we formulated the phenomenon owing to the cation thickening model on the clay surface by the homogenization technique. The numerical result showed that the total diffusion increase with the increase in a distribution ratio of cation. The increase in the diffusion flux under the increase in a local concentration gradient causes surface diffusion.
decay of Cm and the new isotope 
CmAsai, Masato; Tsukada, Kazuaki; Ichikawa, Shinichi; Sakama, Minoru*; Haba, Hiromitsu*; Nishinaka, Ichiro; Nagame, Yuichiro; Goto, Shinichi*; Kojima, Yasuaki*; Oura, Yasuji*; et al.
Physical Review C, 73(6), p.067301_1 - 067301_4, 2006/06
Times Cited Count：21 Percentile：76.1(Physics, Nuclear)no abstracts in English
-decay half-lives of new neutron-rich rare-earth isotopes 
Pm, 
Sm, and GdIchikawa, Shinichi; Asai, Masato; Tsukada, Kazuaki; Haba, Hiromitsu*; Nagame, Yuichiro; Shibata, Michihiro*; Sakama, Minoru*; Kojima, Yasuaki*
Physical Review C, 71(6), p.067302_1 - 067302_4, 2005/06
Times Cited Count：18 Percentile：74.03(Physics, Nuclear)The new neutron-rich raer-earth isotopes Pm, Sm, and Gd produced in the proton-induced fission of 238U were identified using the JAERI on-line isotope separator (JAERI-ISOL) coupled to a gas-jet transport sysetm. The half-lives of Pm, Sm, and Gd were determined to be 1.5
0.2s, 2.40.5s, and 4.81.0s, respectively. The partial decay scheme of Gd wes constructed for - coincidence data. The improved half-life values of 25.62.2s wes obtained for the previously identified isotope Tb. The half-lives measured in the present study are in good agreement with the theoretical predictions calculated by the second generation of the gross theory with the atomic masses evaluated by the Audei and Wapstra.
Ichikawa, Yasuaki*
JNC TJ7400 2005-003, 60 Pages, 2005/02
JNC-TJ7400-2005-003.pdf:16.18MB
Rock mass is a complex material including several classes of discontinuities and inhomogeneous/anisotropic minerals. If observing rock samples, we know that crystalline rock is a complex of minerals, grain boundaries and microcracks. Deformation and failure mechanism may be understood if we characterize correctly the microscale composition and grain boundary properties. However rock minerals, especially quartz and biotite of granite, involves a lot of microcracks. A microcrack propagation is initiated by these existing crack tips, and runs into feldspar domain beyond the grain boundary. This suggests difficulty of its theoretical treatment. On the other hand sandstone which is a sedimentary rock mainly consists quartz and feldspar crystals, and bonding materials fills the interbrain space, so the mechanical behaviors may be similar to the crystalline rock. In order to clarify a long-term behavior of the crystalline rock we here treated the following two subjects:(1)Observation of microcrack initiation and propagation by Confocal Laser Scanning Microscope(CLSM)under stress relaxation tests(before loading and at each loading stage),(2)Stress-dissolution analysis of rocks with silicate minerals and characterization of the time-dependent deformation/failure behaviors. First, CLSM was used to acquire clearly focused three-dimensional images of granite specimens, and observed the change of microscale structure including the mineral configuration under applying compression stress. Then though microcracks have ever thought to be initiated and propagated on intergranular boundaries, we understand through the CLSM observation that new microcracks are generated from the ends of pre-existing cracks which are distributed in quartz and biotite. Second, in order to simulate the experimental results which indicate that initiation and propagation of microcracks control the stress-relaxation phenomenon, we introduce a coupled analysis method of stress-dissolution phenomena.
Am and its EC-decay daughter 
PuAsai, Masato; Sakama, Minoru*; Tsukada, Kazuaki; Ichikawa, Shinichi; Haba, Hiromitsu*; Nishinaka, Ichiro; Nagame, Yuichiro; Goto, Shinichi*; Kojima, Yasuaki*; Oura, Yasuji*; et al.
European Physical Journal A, 23(3), p.395 - 400, 2005/02
Times Cited Count：16 Percentile：71.27(Physics, Nuclear)The EC decay of Am has been studied through -ray spectroscopy. Two EC-decaying states have been found in Am with half-lives of 3.6 min and 2.9 min. In Pu, we have found the 
octupole band and two-quasiparticle states one of which is a 
isomer with a 1.2 
s half-life. The EC transitions from Am to the two-quasiparticle states in Pu show small 
values of 4.8--5.3, which allowed us to assign proton-neutron configurations of Am and the two-quasiparticle states.
