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Nagara, Shuichi
Journal of MMIJ, 123(4,5), p.200 - 205, 2007/05
The dose rate has been measured using radiophotoluminescence glass dosimeter (RPLD) in and around the Yotsugi Mill Tailings Pond in Ningyo-toge Mine for a proper understanding of the dose rate distribution. The result shows a relatively higher dose rate at mid- to up-stream of the tailings pond than the rest of it, which is 0.20 to 0.27
Gy/h at a height of 1m. The results also show a tendency that dose rates are low at a height of 1m and are high on the ground in the final quarter (January to March).
Ota, Masakazu*; Iida, Takao*; Yamazawa, Hiromi*; Nagara, Shuichi; Ishimori, Yuu; Sato, Kazuhiko; Tokizawa, Takayuki
Journal of Nuclear Science and Technology, 44(5), p.791 - 800, 2007/05
Times Cited Count：16 Percentile：70.27(Nuclear Science & Technology)A study on the effectiveness of clay-mixed soil as a barrier against radon exhalation from soil surface was carried out at a closed uranium mine in Japan. Continuous observations of radon flux at a clay-covered soil surface and a bare soil surface, radon concentration in soil air and soil moisture content were carried out for 80 days. The mean of radon flux of the clay-covered plot was one fifth of that of the bare plot. This result indicates that clay-mixed soil worked effectively for reduction of radon exhalation from the soil surface. A numerical analysis with a one-dimensional radon transport model for unsaturated soil was carried out to evaluate the effectiveness of the barrier under dry weather conditions. Calculation results suggested that the barrier works effectively even under the dry condition.
Koga, Osamu; Nagara, Shuichi; Sato, Kazuhiko; Tokizawa, Takayuki
JNC TN6410 2005-001, 38 Pages, 2005/03
JNC-TN6410-2005-001.pdf:1.33MB
Mesh models are formed to carry out simulations of the groundwater flow and the solute transport at around former Yotsugi Open-Pit Mine and Yotsugi Mill Tailings Dam. Also, hydraulic field survey and literature survey are carried out to set boundary conditions and property values for the simulations.Mesh models are formed for Yotsugi Open-Pit Mine, Yotsugi Mill Tailings Dam and the wide area so that boundary conditions could be given to the model for Yotsugi Mill tailings Dam. These three models are confirmed to perform properly for analyses.Hydraulic field survey is carried out in the wide area to estimate the groundwater distribution and to understand the top hydraulic head boundary of the model. As result, groundwater level at the ridge used as a boundary of the model is set to be twenty meters depth.Values of effective diffusion coefficient, specific storage and absolute density are set to be used for the simulation of the solute transport by the literature survey.
Koga, Osamu; Nagara, Shuichi; Matsumura, Toshihiro; Takeuchi, Akira*; Takeda, Shinji; Yamamoto, Masahiro*; Sato, Kazuhiko
JNC TN6440 2004-003, 66 Pages, 2004/03
JNC-TN6440-2004-003.pdf:1.95MB
To analyze high precision in groundwater flow and radionuclide transport around Yotsugi open-pit mining place site and around Yotsugi mill tailing yard, besides the topic in past analysis is extracted, following it did examination of the corresponding method and arrangement of physical properties value.
Nagara, Shuichi; Yamamoto, Masahiro*; Koga, Osamu; Takeuchi, Akira; Matsumura, Toshihiro; Takeda, Shinji; Sato, Kazuhiko
JNC TN6420 2004-001, 75 Pages, 2004/03
JNC-TN6420-2004-001.pdf:2.93MB
The radon concentration in groundwater summarized around the Yotsugi open-pit site has been measured from 2002 to 2003 and examined radon observation system built in 2001. Moreover, the maintenance actual result of the radon observation system was summarized.
Nagara, Shuichi; Matsumura, Toshihiro; Sato, Kazuhiko; Tokizawa, Takayuki
JNC TN6400 2004-005, 34 Pages, 2002/03
JNC-TN6400-2004-005.pdf:1.46MB
A one-dimensional numerical solute-transport analysis utilizing a simulation code named NESTOR, involving a literature survey on analytical parameters has been carried out for the purpose of an understanding radionuclide transport in groundwater in and around the former Yotsugi open pit site at the Ningyo-Toge Environmental Engineering Center, JNC. Prior to the analysis, data set was prepared referring to available documents on site characteristics and one on disposal of radwaste. A simplified model in which the site was divided into seven blocks according to its geographical-hydrological feature and has boreholes downward regarded as assessment points was applied on the analysis. As a result, The highest concentrations of radionuclide is 8.57
10
Bq/m of Po-210 at assessment points. The highest concentration of U-238 is in the order of magnitude of 10 Bq/m. This figure is lower by 1 order than a standard value for mine- and waste-water on the safety rule of Ningyo-Toge mine and the same orders as surface-water on the agreement with Okayama prefecture. If the analysis result in this time and the present concentration in groundwater are measured, the former data became lower about 7 orders by U-238 concentrations and became lower about 6 orders by Ra-226 concentrations. It is thought that this cause is that U and Ra which exist around the former Yotsugi open pit sit before taking reclamation cannot be taking into consideration in analysis.
; Tokizawa, Takayuki; *; Nagara, Shuichi*
JNC TY6400 2000-014, 39 Pages, 2000/05
JNC-TY6400-2000-014.pdf:1.35MB
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Yu, Runlan*; Sato, Kazuhiko; Nagara, Shuichi*; Yamana, Satoshi
Donen Giho, (105), p.73 - 78, 1998/03
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