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Vives I Batlle J.,Belgian Nuclear Research Center | Beaugelin-Seiller K.,Institute for Radiological Protection and Nuclear Safety | Beresford N.A.,UK Center for Ecology and Hydrology | Copplestone D.,University of Stirling | And 13 more authors.
Radiation and Environmental Biophysics | Year: 2011

An exercise to compare 10 approaches for the calculation of unweighted whole-body absorbed dose rates was conducted for 74 radionuclides and five of the ICRP's Reference Animals and Plants, or RAPs (duck, frog, flatfish egg, rat and elongated earthworm), selected for this exercise to cover a range of body sizes, dimensions and exposure scenarios. Results were analysed using a non-parametric method requiring no specific hypotheses about the statistical distribution of data. The obtained unweighted absorbed dose rates for internal exposure compare well between the different approaches, with 70% of the results falling within a range of variation of ±20%. The variation is greater for external exposure, although 90% of the estimates are within an order of magnitude of one another. There are some discernible patterns where specific models over- or under-predicted. These are explained based on the methodological differences including number of daughter products included in the calculation of dose rate for a parent nuclide; source-target geometry; databases for discrete energy and yield of radionuclides; rounding errors in integration algorithms; and intrinsic differences in calculation methods. For certain radionuclides, these factors combine to generate systematic variations between approaches. Overall, the technique chosen to interpret the data enabled methodological differences in dosimetry calculations to be quantified and compared, allowing the identification of common issues between different approaches and providing greater assurance on the fundamental dose conversion coefficient approaches used in available models for assessing radiological effects to biota. © 2010 Springer-Verlag.

Kido H.,Ibaraki University | Kido H.,Visible Information Center Inc. | Fujiwara H.,Japan National Institute for Agro - Environmental Sciences | Jamsran U.,Mongolian State University of Agriculture | Endo A.,Ibaraki University
Journal of Environmental Radioactivity | Year: 2012

To evaluate the quantities of 137Cs from past nuclear tests being transported to and deposited in Japan by naturally-occurring phenomena, the authors developed long-range transport models for 137Cs considering Asian dust. The simulation using these models backed the observed recent increase of 137Cs deposition along the coast of the Sea of Japan in early spring. For the sake of public safety, it is vital to ascertain whether an increase of radioactive deposition is caused by natural phenomena or a nuclear accident. The observations in recent years have suggested that dust and soil containing 137Cs is transported from the regions around Inner Mongolia to Japan by the wind. In this paper, using observation data from the early spring of 2002 and 2006, the authors have found good agreement between the simulations and the measurements. The simulations reproduced the entrainment of 137Cs and subsequent transport to Japan caused by strong winds associated with low pressure areas around the Inner Mongolian grasslands. The most likely cause of high-level 137Cs deposition over northern Japan during March 2002 was 137Cs associated with particles transported at low-altitude (1 km) and subjected to precipitation on the 22nd to 24th. © 2011 Elsevier Ltd.

Hato S.,Ibaraki University | Hato S.,Visible Information Center Inc. | Kinase S.,Ibaraki University | Kinase S.,Japan Atomic Energy Agency
Transactions of the Atomic Energy Society of Japan | Year: 2016

It is important to accurately estimate the intake quantity for reliable internal exposure assessments. The intake quantity has been estimated by using the least-squares method. However, to use the least-squares method, the number of radioactivity measurements must be more than the number of intakes. To remedy this restriction, this study suggests an estimation method using singular value decomposition that is available regardless of the relation between the numbers of measurements and intakes. Moreover, this study introduces a procedure to calculate the intake quantity from the measurements with uncertainty. © 2016 Atomic Energy Society of Japan, All Rights Reserved.

Ebashi T.,Japan Atomic Energy Agency | Kawamura M.,Japan Atomic Energy Agency | Kawamura M.,Mitsubishi Group | Inagaki M.,Japan Atomic Energy Agency | And 8 more authors.
Materials Research Society Symposium Proceedings | Year: 2014

We have developed a "Relative Rates Method" to make bounding calculations regarding radionuclide migration due to uplift/erosion ("exhumation") of a HLW repository. Results show that this method can apply to a wide range of different uplift rates and erosion rates. In addition, for the long time period, it was shown that the relative difference of uplift rate / erosion rate and potential hydraulic change arising from extreme uplift/erosion could affect radionuclide release and migration, thus uplift/erosion concerns should be fed back to site selection. Our method provides a credible and defensible basis for analysis and interpretation of possible uplift/erosion impacts for future volunteer sites. © 2014 Materials Research Society.

Yotsuji K.,Japan Atomic Energy Agency | Tachi Y.,Japan Atomic Energy Agency | Nishimaki Y.,Visible Information Center Inc.
Materials Research Society Symposium Proceedings | Year: 2014

The integrated sorption and diffusion (ISD) model has been developed to quantify radionuclide transport in compacted bentonite. The current ISD model, based on averaged pore aperture and the Gouy-Chapman electric double layer (EDL) theory can quantitatively account for diffusion of monovalent cations and anions under a wide range of conditions (e.g., salinity, bentonite density). To improve the applicability of the current ISD model for multivalent ions and complex species, the excluded volume effect and the dielectric saturation effect were incorporated into the current model, and the modified Poisson-Boltzmann equations were numerically solved. These modified models had little effect on the calculation of effective diffusivity of Sr2+/Cs+/I-. On the other hand, the model, modified considering the effective electric charge of hydrated ions, calculated using the Gibbs free energy of hydration, agreed well with the diffusion data including those of Sr2+. © 2014 Materials Research Society.

Yoshikawa H.,Japan Atomic Energy Agency | Ito T.,Visible Information Center Inc. | Ise K.,Japan Atomic Energy Agency | Sasaki Y.,Japan Atomic Energy Agency
Materials Research Society Symposium Proceedings | Year: 2014

To evaluate a change of chemical species of groundwater composition by the metabolism of microbes, which will be introduced to deep underground from the surface and be in a deep underground, is important for the discussion of the microbial effects on the performance assessment of the high-level radioactive waste repository. The purpose of this study is to develop of a microbial kinetics database to evaluate their activities in the deep underground environment. Some microbial metabolism data were collected and constructed their kinetics database for aerobic, denitrifying, manganese reducing, iron reducing, sulfate reducing, methanogenic and acetogenic bacteria to evaluate above groundwater chemistry. About 1260 data were selected by literature survey for some journals and books published from 1960s and summarized in this microbial kinetics database. Some sensitivity analyses were performed for some parameter of metabolism of microbes. © 2014 Materials Research Society.

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