Choi, B.; Nishida, Akemi; Takito, Kiyotaka; Tsutsumi, Hideaki*; Takada, Tsuyoshi
Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 8 Pages, 2023/05
no abstracts in English
Choi, B.; Nishida, Akemi; Li, Y.; Takada, Tsuyoshi
Earthquake Engineering and Resilience (Internet), 1(4), p.427 - 439, 2022/12
no abstracts in English
Kataoka, Takahiro*; Ishida, Tsuyoshi*; Naoe, Shota*; Kanzaki, Norie; Sakoda, Akihiro; Tanaka, Hiroshi; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*
Journal of Radiation Research (Internet), 63(5), p.719 - 729, 2022/09
Sakoda, Akihiro; Ishida, Tsuyoshi*; Kanzaki, Norie; Tanaka, Hiroshi; Kataoka, Takahiro*; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*
International Journal of Environmental Research and Public Health, 19(13), p.7761_1 - 7761_12, 2022/07
In specific situations such as bathing in a radon spa, where the radon activity concentration in thermal water is far higher than that in air, it has been revealed that radon uptake via skin can occur and should be considered for more precise dose evaluation. The primary aim of the present study was to numerically demonstrate the distribution as well as the degree of diffusion of radon in the skin, with a focus on its surface layers (i.e., stratum corneum). We made a biokinetic model that included diffusion theory at the stratum corneum, and measured radon solubility in the stratum corneum to get a crucial parameter. The implementation of the model suggested that the diffusion coefficient in the stratum corneum was as low as general radon-proof sheets. The depth profile of radon in the skin was found to be that after a 20-minute immersion in water, the radon activity concentration at the top surface skin layer was approximately 1000 times higher than that at the viable skin layer. The information on the position of radon as a radiation source would contribute to special dose evaluation where specific target cell layers are assumed for the skin.
Aoyagi, Kazuhei; Ishii, Eiichi; Chen, Y.*; Ishida, Tsuyoshi*
Rock Mechanics and Rock Engineering, 55(4), p.1855 - 1869, 2022/04
Safety assessments related to the long-term migration of radionuclides in high-level radioactive waste disposal repositories need to consider the evolution of permeability associated with excavation-damaged-zone (EDZ) fractures. We observed EDZ fractures preserved by resin injection around a gallery in the Horonobe Underground Research Laboratory in Japan with the aim of assessing the sensitivity of aperture to shear displacement (i.e., dilation angle) in EDZ fractures. To date, shear displacement along EDZ fractures has not been quantified despite its importance for estimating the evolution of fracture aperture around excavations after the repository is backfilled. Enlarged photographs of EDZ fractures fixed by resin were examined to obtain reliable and accurate measurements of the shear displacement and aperture of EDZ fractures without additional disturbance. Measured shear displacement and fracture aperture are poorly correlated, meaning that fracture aperture is insensitive to shear displacement after fracture formation. This insensitivity is closely reproduced by a previously reported empirical relationship and is attributed to the relatively high levels of normal stress acting on fracture surfaces at 350 m depth, which suppress shear-induced dilatation. Considering this insensitivity between fracture aperture and shear displacement, shear-induced dilation of EDZ fractures is estimated to be negligible even if the fractures are shear-displaced after the repository is backfilled, so long as the normal stress acting on fracture surfaces does not reduce substantially. The applied resin injection and fracture observations constitute a useful tool for helping to assess the likelihood of shear-induced dilation after the repository is backfilled.
Choi, B.; Nishida, Akemi; Muramatsu, Ken*; Itoi, Tatsuya*; Takada, Tsuyoshi*
Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 5 Pages, 2020/08
After the 2011 Fukushima accident, the seismic regulation for Nuclear Power Plants (NPP) have been strengthened to take countermeasures against accidents beyond design basis conditions. Therefore, the importance of seismic probabilistic risk assessment has drawn much attention. Uncertainty quantification is a very important issue in the fragility assessment for NPP buildings. In this study, the authors focus on the epistemic uncertainty that can be reduced, and aims to clarify the effects due to different modeling methods of NPP buildings on seismic response results. As the first step of this study, the authors compared the effects on seismic response using two kinds of modeling methods. In order to evaluate the effect, seismic response analysis was performed on two types of building models; the three dimensional finite element model and the conventional lumped mass with sway-rocking model. As the input ground motion, the authors adopted 200 types of simulated seismic ground motions generated by fault rupture models with stochastic seismic source characteristics. For the uncertainty quantification, the authors conducted statistical analyses of the effects on seismic response results of two kinds of modeling methods on building response for each input ground motions, and quantitatively evaluated the uncertainty of response considering different modeling methods. In particular, the difference in modeling methods clearly appeared near the openings of the floors and walls. The authors also report on the knowledge about these three-dimensional effects in seismic response analysis.
Kobashi, Yusuke*; Kataoka, Takahiro*; Kanzaki, Norie; Ishida, Tsuyoshi*; Sakoda, Akihiro; Tanaka, Hiroshi; Ishimori, Yuu; Mitsunobu, Fumihiro*; Yamaoka, Kiyonori*
Radiation and Environmental Biophysics, 59(3), p.473 - 482, 2020/08
Radon therapy has been traditionally performed globally for oxidative stress-related diseases. Many researchers have studied the beneficial effects of radon exposure in living organisms. However, the effects of thoron, a radioisotope of radon, have not been fully examined. In this study, we aimed to compare the biological effects of radon and thoron inhalation on mouse organs with a focus on oxidative stress. Male BALB/c mice were randomly divided into 15 groups: sham inhalation, radon inhalation at a dose of 500 Bq/m or 2000 Bq/m, and thoron inhalation at a dose of 500 Bq/m or 2000 Bq/m were carried out. Immediately after inhalation, mouse tissues were excised for biochemical assays. The results showed a significant increase in superoxide dismutase and total glutathione, and a significant decrease in lipid peroxide following thoron inhalation under several conditions. Additionally, similar effects were observed for different doses and inhalation times between radon and thoron. Our results suggest that thoron inhalation also exerts antioxidative effects against oxidative stress in organs. However, the inhalation conditions should be carefully analyzed because of the differences in physical characteristics between radon and thoron.
Aoyagi, Kazuhei; Chen, Y.*; Ishii, Eiichi; Sakurai, Akitaka; Miyara, Nobukatsu; Ishida, Tsuyoshi*
JAEA-Research 2019-011, 50 Pages, 2020/03
In this research, we performed the resin injection experiment at the 350 m Gallery of Horonobe Underground Research Laboratory in order to identify the distribution of fractures induced around the gallery owing to excavation. We also observed the rock cores obtained around the resin injection borehole under ultraviolet light. As a result, the extent of the development of EDZ fracture was 0.9 m from the gallery wall. In the depth within 0.4 m from the gallery wall, the density of the EDZ fracture is higher than the depth more than 0.4 m from the gallery wall. As a result of the analysis on the fracture aperture by image processing, the fractures with a large aperture (1.02 mm in maximum) were observed within 0.3 m from the gallery wall, while the maximum aperture was 0.19 mm in the depth more than 0.3 m from the gallery wall.
Choi, B.; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*
Nihon Jishin Kogakkai Rombunshu (Internet), 20(2), p.2_1 - 2_16, 2020/02
no abstracts in English
Aoyagi, Kazuhei; Chen, Y.*; Ishii, Eiichi; Sakurai, Akitaka; Ishida, Tsuyoshi*
Proceedings of 5th ISRM Young Scholars' Symposium on Rock Mechanics and International Symposium on Rock Engineering for Innovative Future (YSRM 2019 and REIF 2019) (USB Flash Drive), 6 Pages, 2019/12
In the excavation of a repository for high-level radioactive waste (HLW) disposal, it is important to understand the hydro-mechanical characteristics of the Excavation Damaged Zone (EDZ) induced around the gallery because EDZ can lead to the migration pathway of radionuclides. Thus, we performed the resin injection experiment at the 350 m gallery of Horonobe Underground Research Laboratory in Japan to investigate the characteristics of fractures induced around the gallery wall in excavation. In the experiment, we developed a low viscosity resin mixed with a fluorescent substance and injected to the borehole drilled about 1 m in length. After the experiment, we overcored around the injection borehole. The observation on the cut surface of the overcore under ultraviolet light revealed that the fractures were distributed within 0.8 m from the gallery wall. Fractures are interconnected each other in particular within 0.25 m from the niche wall. Furthermore, fractures with large aperture (about 1.0 mm) were developed in that region. These observed results will be fundamental information for understanding of the fracturing process in the EDZ.
Choi, B.; Nishida, Akemi; Shiomi, Tadahiko; Muramatsu, Ken*; Takada, Tsuyoshi*
Transactions of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 8 Pages, 2019/08
In this study, to clarify the influence of the uncertainty of the input seismic ground-motion response of a nuclear power plant (NPP) building, we examined seismic-response analysis results using two different methods of modeling buildings and then compared the results to evaluate effects related to differences between the models. The two methods we used are the three-dimensional (3D) finite-element (FE) model (mainly composed of shell elements) and the conventional sway-rocking (SR) model. Also, using features of the 3D FE model, we analyzed the spatial features of the response results. In this paper, we describe the differences in seismic response obtained by the 3D FE model and the SR model based on simulated input ground motions, and we discuss the influence of the characteristics of the input ground motion on the maximum-response acceleration of the modeled NPP building.
Yamano, Hidemasa; Nishida, Akemi; Choi, B.; Takada, Tsuyoshi*
Transactions of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 10 Pages, 2019/08
The objective of this study is to assess cliff edge effects, which are greatly important for nuclear power plants. Through assessments of failure probabilities (fragility), this study examined seismic margins of simulated two kinds of thin- and thick-walled reactor vessels by using response waveforms of the reactor building with/without a seismic isolation system obtained by seismic response analyses. The fragility analyses showed that the seismic isolation technology largely reduced the structural response effects nearly twice as much as that of the non-isolated plant. In focusing on uncertainty of response factor of components, the seismic isolation plant has a significant margin compared to the non-isolated plant even if factors from 0.5 to 2.0 are taken into account. This study concluded that the seismic isolation technology is effective to avoid cliff-edge effects.
Nishida, Akemi; Choi, B.; Yamano, Hidemasa; Itoi, Tatsuya*; Takada, Tsuyoshi*
Transactions of 25th International Conference on Structural Mechanics in Reactor Technology (SMiRT-25) (USB Flash Drive), 9 Pages, 2019/08
In this research, the seismic safety of a nuclear power plant (NPP) is treated as a system in which the various cliff edge effects are identified and quantified based on the concepts of risk and defense in depth. An aim of this research is to develop a methodology for avoiding these cliff edge effects. In order to examine how the cliff edge state specified and evaluated in the seismic response analysis of the building system, we investigated the seismic isolation mechanism related to physical cliff edges and the modeling effects of the building system related to knowledge oriented cliff edges. In particular, with regard to knowledge-oriented cliff edges, we quantitatively evaluated the uncertainty within the same floor which is evaluated by a three-dimensional building model and tried to reflect it on the fragility evaluation. This paper presents and discusses these results.
Ishida, Tsuyoshi*; Fujito, Wataru*; Yamashita, Hiroto*; Naoi, Makoto*; Fujii, Hirokazu*; Suzuki, Kenichiro*; Matsui, Hiroya
Rock Mechanics and Rock Engineering, 52(2), p.543 - 553, 2019/02
We pressurized and injected water in a hole drilled downward from a floor of the 500 m level gallery in MIU, central Japan. Acoustic emissions (AEs) monitored with 16 sensors in four boreholes located 1 m away from the HF hole exhibited two-dimensional distributions, which likely delineate a crack induced by the fracturing. Expansions of the regions in which AEs occurred were observed only immediately after the first and second BDs. Many AE events in other periods were distributed within the regions where AE events had already occurred. The initial motion polarities of P-waves indicate that tensile-dominant AE events occurred when the regions expanded and they were distributed primarily on the frontiers of the regions where AE events had already occurred. The experimental results suggest that increasing the injection flow rate is effective for generating new cracks in the refracturing, with the new crack expansions being induced by tensile fracturing.
Nishida, Akemi; Choi, B.; Yamano, Hidemasa; Takada, Tsuyoshi*
Proceedings of 2018 ASME Pressure Vessels and Piping Conference (PVP 2018), 11 Pages, 2018/07
This study identified and quantified possible cliff edge effects through a seismic safety evaluation of a nuclear power plant, based on the concepts of risk and defense in depth. Cliff edges of the both physical and knowledge-based type were considered in this study. We investigated a seismic isolation effect, etc., for physical cliff edges, and the modeling of the target structure, boundary conditions, etc., for knowledge-based cliff edges. Response analysis was performed using a sway-rocking (SR) model and a three-dimensional model of the target building. The seismic isolation effect of the base-isolated building was confirmed by comparison to the results of earthquake-resistant building. In the case of a collision with the retaining wall of the base-isolated building, the level of damage was found to depend on the modeling of the collision condition assumed. On the other hand, the study confirmed the differences between the results from the SR model and the three-dimensional model.
Choi, B.; Nishida, Akemi; Li, Y.; Muramatsu, Ken*; Takada, Tsuyoshi*
Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 9 Pages, 2018/07
After the 2011 Fukushima accident, nuclear power plants are required to take countermeasures against accidents beyond design basis conditions. In seismic probabilistic risk assessment (SPRA), uncertainty can be classified as either aleatory uncertainty, which cannot be reduced, or epistemic uncertainty, which can be reduced with additional knowledge and/or information. To improve the reliability of SPRA, efforts should be made to identify and reduce the epistemic uncertainty caused by the lack of knowledge. In this study, we focused on the difference in seismic response by modeling methods, which is related epistemic uncertainty. We conducted a seismic response analysis with two kinds of modeling methods; a three-dimensional finite-element model and a conventional sway-rocking stick model, by using simulated various input ground motions, which is related to aleatory uncertainty. And then we quantified the seismic floor response results of the various input ground motions of each modeling methods. For the uncertainty quantification related to different modeling methods, we further perform a statistical analysis of the floor response results of the nuclear reactor building. Finally, we discussed how to utilize the results from these calculations for the quantification of uncertainty in fragility analysis for SPRA.
Kanzaki, Norie; Kataoka, Takahiro*; Kobashi, Yusuke*; Yunoki, Yuto*; Ishida, Tsuyoshi*; Sakoda, Akihiro; Ishimori, Yuu; Yamaoka, Kiyonori*
Radioisotopes, 67(2), p.43 - 57, 2018/02
We previously reported that low-dose radiation induces the anti-oxidative function in many organ systems of mice. This results in the suppression of several kinds of oxidative stress-induced damage. This study was conducted with the objective of revealing the health effects of low-dose radiation obtained from our previous reports and searching for a new treatment based on low-dose radiation, such as radon therapy. We extracted the characteristics of the effects of low dose radiation suppressing diseases and enhancing the anti-oxidative function using fuzzy answer by self-organizing map (SOM) based on mutual knowledge. The relationship between the suppressive effect and increased antioxidative function was shown in our result, and the concentration dependence of the effect against pain was shown on the output map. Although the effect against other organs depending on concentration was unpredictable, our results indicate that low-dose radiation may also be suitable for treatment of liver disease and brain disease.
Aoyagi, Kazuhei; Chen, Y.*; Sakurai, Akitaka; Ishii, Eiichi; Ishida, Tsuyoshi*
JAEA-Research 2017-014, 49 Pages, 2018/01
In this research, we performed the resin injection experiment at the 350 m gallery of the Horonobe Underground Research Laboratory in order to identify the three dimensional distribution of fractures induced around the gallery owing to excavation. To this end, the low viscosity resin mixed with a fluorescent substance was developed and applied to the in situ resin injection experiment. As a result, the resin was successfully penetrated into the fractures around the gallery without disturbing their situation and then fixed within them. After the experiment, the rock cores around the injection borehole were drilled for the observation. The observation under ultraviolet light revealed that the extent of the development of fractures was about 0.9 m into the borehole wall. In addition, the aperture of the fractures distributed within 0.3 m from the gallery wall was ranged 1 to 2 mm, and that distributed from 0.3 to 0.9 m was less than 1 mm. On the other hand, in the borehole televiewer (BTV) survey, only one fracture within 0.2 m from the wall could be detected owing to the resolution of the survey system. Thus, it is expected that the BTV survey underestimate the extent of the development of fractures.
Choi, B.; Nishida, Akemi; Itoi, Tatsuya*; Takada, Tsuyoshi*
Geosciences (Internet), 8(1), p.1_1 - 1_22, 2018/01
After the Tohoku earthquake in 2011, we observed that aftershocks tended to occur in a wide region after such a large earthquake. These aftershocks resulted in secondary damage or delayed rescue and recovery activities. However, it is difficult to evaluate the hazards of an aftershock before the main shock due to various uncertainties. For possible great earthquakes, we must make decisions based on such uncertainties, and it is important to quantify the various uncertainties. We previously proposed a probabilistic aftershock occurrence model that is expected to be useful to develop plans for recovery activities after future large earthquakes. In this paper, engineering applications of the proposed approach for probabilistic aftershock hazard analysis are shown for demonstration purposes. One application is to use aftershock hazard maps to plan recovery activities. Another application is to derive load combination equations of the load and resistance factor design (LRFD) considering the simultaneous occurrence of tsunamis and aftershocks for the tsunami-resistant design of tsunami evacuation buildings and nuclear facilities.
Choi, B.; Nishida, Akemi; Muramatsu, Ken*; Takada, Tsuyoshi*
Proceedings of 12th International Conference on Structural Safety & Reliability (ICOSSAR 2017) (USB Flash Drive), p.2206 - 2213, 2017/08
In order to clarify the influence of the difference of modeling method on the variation of the result of seismic response analysis of nuclear facility, seismic response analysis using various simulated input ground motions was carried out and the sensitivity analyses of the variations in seismic response was conducted. In particular, we focused on the maximum acceleration response of reactor building shear walls, the effect of modeling method on response result and the factors of response variation were described and discussed.