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Journal Articles

Thermally altered subsurface material of asteroid (162173) Ryugu

Kitazato, Kohei*; Milliken, R. E.*; Iwata, Takahiro*; Abe, Masanao*; Otake, Makiko*; Matsuura, Shuji*; Takagi, Yasuhiko*; Nakamura, Tomoki*; Hiroi, Takahiro*; Matsuoka, Moe*; et al.

Nature Astronomy (Internet), 5(3), p.246 - 250, 2021/03

 Times Cited Count:30 Percentile:96.87(Astronomy & Astrophysics)

Here we report observations of Ryugu's subsurface material by the Near-Infrared Spectrometer (NIRS3) on the Hayabusa2 spacecraft. Reflectance spectra of excavated material exhibit a hydroxyl (OH) absorption feature that is slightly stronger and peak-shifted compared with that observed for the surface, indicating that space weathering and/or radiative heating have caused subtle spectral changes in the uppermost surface. However, the strength and shape of the OH feature still suggests that the subsurface material experienced heating above 300 $$^{circ}$$C, similar to the surface. In contrast, thermophysical modeling indicates that radiative heating does not increase the temperature above 200 $$^{circ}$$C at the estimated excavation depth of 1 m, even if the semimajor axis is reduced to 0.344 au. This supports the hypothesis that primary thermal alteration occurred due to radiogenic and/or impact heating on Ryugu's parent body.

JAEA Reports

Systematization and Sophistication of a Comprehensive Performance Assessment Program -Summary Document-

Miki, Takahito*; Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2003-054, 45 Pages, 2003/02

JNC-TJ8400-2003-054.pdf:0.44MB

This study developed analytical programs and procedures based on a method of stochastic radionuclide migration to estimate the feasibility of disposal concepts and to define design specifications, considering the variety of scenarios and disposal concepts divided by depth of repository for TRU nuclides containing waste.

JAEA Reports

Systematization and Sophistication of a Comprehensive Performance Assessment Program

Miki, Takahito*; Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2003-053, 386 Pages, 2003/02

JNC-TJ8400-2003-053.pdf:10.69MB

This study developed analytical programs and procedures based on a method of stochastic radionuclide migration to estimate the feasibility of disposal concepts and to define design specifications, considering the variety of scenarios and disposal concepts divided by depth of repository for TRU nuclides containing waste.

JAEA Reports

Improvement of Biosphere Assessment Methodology for Performance Assessment of Geological Disposal Facility (III)

Miki, Takahito*; Ikeda, Takao*

JNC TJ8400 2003-018, 64 Pages, 2003/02

JNC-TJ8400-2003-018.pdf:1.01MB

This report contains results on study of method of identification of Geosphere-Biosphere Interface (GBI), toxicological impact of non-radioactive contaminants contained in radioactive waste disposal facility and consideration of climate change in long-ter

JAEA Reports

Improvement of Biosphere Assessment Methodology for Performance Assessment of Geological Disposal Facility (III)

Miki, Takahito*; Ikeda, Takao*

JNC TJ8400 2003-017, 342 Pages, 2003/02

JNC-TJ8400-2003-017.pdf:5.64MB

This report contains results on study of method of identification of Geosphere-Biosphere Interface (GBI), toxicological impact of non-radioactive contaminants contained in radioactive waste disposal facility and consideration of climate change in long-ter

JAEA Reports

Feasibility study for mid-depth disposal of wastes solidified by asphalt, plastic and ROBE

Miki, Takahito*

JNC TJ8400 2002-057, 54 Pages, 2002/02

JNC-TJ8400-2002-057.pdf:0.73MB

In this report, feasibility studies for mid-depth disposal of wastes solidified by asphalt, plastic and ROBE which are generated from JNC's Tokai reprocessing plant were carried out. In this study, at first, the characteristics of those wastes were summarized. And FEPs (Features, Events and Processes) regarding safety assessment for mid-depth disposal system were reviewed. Next, stochastic simulations were conducted to clarify the enough conditions in system specification for achieving a target which is well below the dose criteria for groundwater scenarios. Furthermore, important issues which affect disposal barrier systems were extracted using results of stochastic analysis and FEPs considerations. With regard to the environmental impacts of nitrate and boron which are included in the above wastes, literature survey and preliminary numerical analysis regarding flux and concentrations of them around disposal facility were carried out in order to discuss the feasibility. Finally, research programs for the improvement feasibility of mid-depth disposal of those wastes were developed.

JAEA Reports

Feasibilyty study for mid-depth disposal of wastes solidified by asphalt, plastic and ROBE

Miki, Takahito*

JNC TJ8400 2002-056, 416 Pages, 2002/02

JNC-TJ8400-2002-056.pdf:16.57MB

In this report, feasibility studies for mid-depth disposal of wastes solidified by asphalt, plastic and ROBE which are generated from JNC's Tokai reprocessing plant were carried out. In this study, at first, the characteristics of those wastes were summarized. And FEPs (Features, Events and Processes) regarding safety assessment for mid-depth disposal system were reviewed. Next, stochastic simulations were conducted to clarify the enough conditions in system specification for achieving a target which is well below the dose criteria for groundwater scenarios. Furthermore, important issues which affect disposal barrier systems were extracted using results of stochastic analysis and FEPs considerations. With regard to the environmental impacts of nitrate and boron which are included in the above wastes, literature survey and preliminary numerical analysis regarding flux and concentrations of them around disposal facility were carried out in order to discuss the feasibility. Finally, research programs for the improvement feasibility of mid-depth disposal of those wastes were developed.

JAEA Reports

A Comprehensive study on nuclide migration using scenario exploration method (3)

Miki, Takahito*; Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2002-051, 40 Pages, 2002/02

JNC-TJ8400-2002-051.pdf:0.28MB

In this study, for the mid-depth disposal system for TRU wastes, asset of stochastic simulations covering uncertainties corresponding to variety of scenarios, models and parameter values were conducted to; (1)indicate measures to reduce potential exposure based on the knowledge of sensitivity structure (2)introduce new methodology for clarify the requirement of repository system (3)show guidelines of disposal system development by clarifying conditions in system specification for achieving a target which is well below the dose constraint for base scenarios (4)identify scenarios and conditions that could lead to a radiological impact greater than the dose constraint for alternative scenarios In the course of geological disposal for TRU waste, improvement of assessment methodology for the alternative scenarios was carried out.

JAEA Reports

A Comprehensive study on nuclide migration using scenario exploration method (3)

Miki, Takahito*; Oyamada, Kiyoshi*; Ikeda, Takao*

JNC TJ8400 2002-050, 217 Pages, 2002/02

JNC-TJ8400-2002-050.pdf:2.66MB

In this study, for the mid-depth disposal system for TRU wastes, asset of stochastic simulations covering uncertainties corresponding to variety of scenarios, models and parameter values were conducted to; (1)indicate measures to reduce potential exposure based on the knowledge of sensitivity structure (2)introduce new methodology for clarify the requirement of repository system (3)show guidelines of disposal system development by clarifying conditions in system specification for achieving a target which is well below the dose constraint for base scenarios (4)identify scenarios and conditions that could lead to a radiological impact greater than the dose constraint for alternative scenarios In the course of geological disposal for TRU waste, improvement of assessment methodology for the alternative scenarios was carried out.

JAEA Reports

Improvement of biosphere assessment methodology for performance assessment of geological disposal facility (II)

Miki, Takahito*; Yoshida, Hideji*; Ikeda, Takao*

JNC TJ8400 2002-010, 66 Pages, 2002/02

JNC-TJ8400-2002-010.pdf:1.45MB

This report contains results on study of Geosphere-Biosphere Interface (GBI), development of biosphere assessment model for gaseous and volatile radionuclides, review of biosphere assessment and research on safety indicators. Regarding study of Geosphere-Biosphere Interface (GBI), FEP database for the Geosphere-Biosphere Transitions Zone (GBTZ) were compiled. Furthermore, release scenarios were identified from the FEP database, and review of conservativeness and robustness of the conceptual and mathematical models developed previously by JNC were undertaken. Regarding development of biosphere assessment model for gaseous and volatile radionuclides, the conceptual and mathematical models were developed, and it was confirmed that the impact of the exposure pathway regarding gas release to flux-to-dose conversion factor is small. Regarding review of biosphere assessment data, the parameters which were used on JNC second progress report were reviewed and classified using the biosphere data protocol categories. Furthermore, the data for key parameter(important but poorly characterized parameters) were revised. Regarding research on safety indicator, some kinds of safety indicators, especially for the non-radioactive contaminant and for the non-human biota, are reviewed.

JAEA Reports

Improvement of biosphere assessment methodology for performance assessment of geological disposal facility (II)

Miki, Takahito*; Yoshida, Hideji*; Ikeda, Takao*

JNC TJ8400 2002-009, 338 Pages, 2002/02

JNC-TJ8400-2002-009.pdf:8.57MB

This report contains results on study of Geosphere-Biosphere Interface (GBI), development of biosphere assessment model for gaseous and volatile radionuclides, review of biosphere assessment and research on safety indicators. Regarding study of Geosphere-Biosphere Interface (GBI), FEP database for the Geosphere-Biosphere Transitions Zone (GBTZ) were compiled. Furthermore, release scenarios were identified from the FEP database, and review of conservativeness and robustness of the conceptual and mathematical models developed previously by JNC were undertaken. Regarding development of biosphere assessment model for gaseous and volatile radionuclides, the conceptual and mathematical models were developed, and it was confirmed that the impact of the exposure pathway regarding gas release to flux-to-dose conversion factor is small. Regarding review of biosphere assessment data, the parameters which were used on JNC second progress report were reviewed and classified using the biosphere data protocol categories. Furthermore, the data for key parameter(important but poorly characterized parameters) were revised. Regarding research on safety indicator, some kinds of safety indicators, especially for the non-radioactive contaminant and for the non-human biota, are reviewed.

JAEA Reports

JAEA Reports

Improvement of biosphere assessment methodology for performance assessment of geological disposal facility

Yoshida, Hideji*; Miki, Takahito*; *

JNC TJ8400 2001-001, 348 Pages, 2001/02

JNC-TJ8400-2001-001.pdf:10.54MB

This report contains discussions about development of biosphere assessment model for a solid release to a soil Geosphere-Biosphere Interface, refinement of methodology for the selection of parameter values and comparison of parameter values between H12 Report and other Japanese safety assessments. Regarding the development of biosphere assessment model for a solid release to a soil Geosphere-Biosphere Interface, it was confirmed that it can, with some relatively minor modifications, be applied directly to a liquid release to soil. Regarding the refinement of methodology for the selection of parameter values, the data methodology was simplified in which the effort is focused on selecting data for key uncertain parameter. The methodology can be simplified through the use of techniques such as the categorization of available data, the grouping of parameters, the application of stopping rules and the use of the question set and decision tree. Regarding comparison of parameter values between the JNC's second progress report and other Japanese safety assessments, it is recognized that some parameters values which were used in the JNC's second progress report were different from those which were used in other Japanese safety assessment. And it was confirmed that data source and assessment context is very important for the selection of parameter values.

JAEA Reports

Improvement of biosphere model for performance assessment of geological disposal system (III)

Ikeda, Takao*; Yoshida, Hideji*; Miki, Takahito*

JNC TJ8400 2000-046, 264 Pages, 2000/02

JNC-TJ8400-2000-046.pdf:6.73MB

This report contains discussions about methodology for the selection of parameter values, stochastic approach for the biosphere assessment and biosphere modelling for marine discharge case are described. Regarding the methodology for the selection of parameter values, important aspects for the data selection were discussed, and data selection protocol was developed. Regarding the stochastic approach for the biosphere assessment, it is confirmed that Straightforward Monte Carlo Method and Latin Hypercube Sampling Method are the most adequate based on a literature survey. Then stochastic assessment by using biosphere model that was developed in the second progress report was carried out to check the sensitivity of parameter values. Finally, availability of several kind of assessment models for marine discharge case were discussed. It was confirmed that Multiple Compartment Model was the most applicable. Assessment using Multiple Compartment Model was carried out. The results were compared with those derived by numerical model. As a result, the difference between two models were small enough.

JAEA Reports

None

Ikeda, Takao*; Yoshida, Hideji*; Miki, Takahito*

JNC TJ8400 2000-045, 134 Pages, 2000/02

JNC-TJ8400-2000-045.pdf:4.12MB

None

JAEA Reports

Literature survey of redox reactions in the new field

Miki, Takahito*; Sasamoto, Hiroshi; Chiba, Tamotsu*; Inagaki, Manabu*; Yui, Mikazu

JNC TN8400 2000-007, 32 Pages, 2000/01

JNC-TN8400-2000-007.pdf:0.69MB

This report presents a summary of literature survey about geochemical reactions which are important to evaluate the redox conditions in the near field rock mass and buffer. The results of literature survey are summarized as follows; (1)Minerals including ferrous iron and organic materials in the rock mass are important reductants. Initial stage after closure of repository, oxygen will be consumed by pyrite, because the reaction rate between pyrite and oxygen is relatively fast. (2)It is possible to estimate the redox capacity for reductants by rock (mineral)-water iteraction experiment in a laboratory. And it is expected that the ferrous iron-rich rock and higher porosity rock may have bigger redox capacity. (3)It is possible to estimate the oxygen consumption rate by reductants such as minerals including ferrous iron. The rate law and rate constant for the oxidation reaction of ferrous iron in the solution are also determined. As a conclusion, it seems that we can evaluate kinetically the evolution of geochemical conditions in the near field rock mass and buffer by excavation of drifts, based on data derived from these existing literatures.

JAEA Reports

Preliminary analysis for evolution of redox conditions in the near field

Chiba, Tamotsu*; Sasamoto, Hiroshi; Miki, Takahito*; Inagaki, Manabu*; Yui, Mikazu

JNC TN8400 99-027, 144 Pages, 1999/06

JNC-TN8400-99-027.pdf:19.19MB

It is planned that high level radioactive waste is going to be disposed under deep geological environment. It is believed that the chemical condition of deep groundwater is generally anoxic and reducing. However, during construction and operation phase of repository, oxygen will diffuse some distance into the surrounding rock mass, and diffused oxygen may remain in the surrounding rock mass even after repository closure. In such a case, the transitional redox condition around the drift is not preferable in view point of safety assessment for HLW disposal. Hence, it is very important to evaluate evolution of redox conditions in the near field. This report describes results of preliminary analysis for evolution of redox conditions in the near field rock mass and buffer after repository closure based on the model developed by Chiba et al. (1999). The results of preliminary analysis are summalized as follows : (1)The decrease of oxygen in the near field rock mass and buffer are affected by pH of groundwater and surface area of iron-bearing minerals. (2)The decrease of oxygen in the near field rock mass takes place at time scales lower than 500 years in considering the hypothetical reference groundwater pH range for H12 report. It is implicated that the redox conditions in the near field rock mass will recover to reducing conditions. (3)The decrease of oxygen in the buffer takes place at time scales lower several tens years under neutral to weakly alkaline pH values of porewater in the buffer, even if it is assumed that residual oxygen in the near field rock mass after repository closure will diffuse into the buffer. On the other hand, under weakly acid pH values of porewater in the buffer, it may be presumed that oxygen remain in the buffer at time scale more than 500 years.

JAEA Reports

Model development to evaluate evolution of redox conditions in the near field

Sasamoto, Hiroshi; Yui, Mikazu; Chiba, Tamotsu*; Miki, Takahito*; Inagaki, Manabu*

JNC TN8400 99-019, 30 Pages, 1999/02

JNC-TN8400-99-019.pdf:2.24MB

Deep underground is thought to be a potential place for high level radioactive waste repository. It is believed that the chemical condition of deep groundwater is generally anoxic and reducing. However, during construction and operation phase of repository, oxygen will diffuse some distance into the surrounding rock mass, and diffused oxygen may remain in the surrounding rock mass even after repository closure. In such a case, the transitional redox condition around the drift is not preferable in view point of safety assessment for HLM disposal. Hence, it is very important to evaluate evolution of redox conditions in the near field. This report describes the status of model development to evaluate evolution of redox conditions in the near field. We use the commercial solver to equate the mathematical equations which mean evolution of redox condition in the near field. The target area modeled in this report are near field rock mass and engineered barrier (buffer). In case of near field rock mass, we consider the following two geological media : (1) porous media for sedimentary rock, (2)fractured media for crystalline rock. In case of the engineered barrier, we the regard buffer as porous media. We simulate the behavior of dissolved oxygen and Fe$$^{2+}$$ in groundwater during evolution of redox condition in the near field rock mass and the buffer. In case of the porous media, we consider diffusion of chemical species as dominant transport mechanism. On the other hand, in case of the fractured media, we consider diffusion of chemical species in rock matrix and advection of that (only dissolved oxygen considered in this model) in fracture as transport mechanism. We also use the rate raw of iron oxidation reaction and dissolution of Fe-bearing minerals in this model besides.

Oral presentation

Provisional dose calculation to examine the radiation protection in geological disposal of high-level radioactive waste

Nakai, Kunihiro*; Kai, Michiaki*; Okoshi, Minoru; Kato, Tomoko; Yamaguchi, Tetsuji; Sasaki, Takayuki*; Hattori, Takatoshi*; Miyazaki, Shinichiro*; Yoshizawa, Yuji*; Higuchi, Natsuko*; et al.

no journal, , 

no abstracts in English

Oral presentation

The Evaluation of the radon dose of radioactivity in high-level radioactive waste geological disposal facility

Yoshizawa, Yuji*; Kai, Michiaki*; Okoshi, Minoru; Kato, Tomoko; Yamaguchi, Tetsuji; Sasaki, Takayuki*; Hattori, Takatoshi*; Miyazaki, Shinichiro*; Higuchi, Natsuko*; Tokonami, Shinji*; et al.

no journal, , 

no abstracts in English

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