Simulation study of the effects of buildings, trees and paved surfaces on ambient dose equivalent rates outdoors at three suburban sites near Fukushima Dai-ichi

Kim, M.; Malins, A.; Yoshimura, Kazuya; Sakuma, Kazuyuki; Kurikami, Hiroshi; Kitamura, Akihiro; Machida, Masahiko; Hasegawa, Yukihiro*; Yanagi, Hideaki*

Journal of Environmental Radioactivity, 210, p.105803_1 - 105803_10, 2019/12

https://doi.org/10.1016/j.jenvrad.2018.09.001

To improve the accuracy of simulations for air dose rates over fallout contaminated areas, the distribution of the radionuclides within the environment should be modelled realistically, e.g. considering differences in radioactivity levels between agricultural land, urban surfaces, and forest compartments. Moreover simulations should model the shielding of rays by buildings, trees and land topography. Here we outline a system for generating three dimensional models of urban and rural areas in Fukushima Prefecture. The Cs and Cs radioactivity distribution can be set flexibly across the different components of the model. The models incorporate realistic representations of local buildings, based on nine common Japanese designs, individual conifer and broadleaf trees, and the topography of the land surface. Models are generated from Digital Elevation Model (DEM) and Digital Surface Model (DSM) datasets, and refined by users assisted with ortho-photographs of target sites. Completed models are exported from the system in a format suitable for the Particle and Heavy Ion Transport code System (PHITS) for the calculation of air dose rates and other radiological quantities. The system is demonstrated by modelling a suburban area 4 km from the Fukushima Daiichi Nuclear Power Plant that has yet to be decontaminated. Air dose rates calculated in PHITS were correlated with measurements taken across the site in a car-borne survey.

Validating polarization effects in -rays elastic scattering by Monte Carlo simulation

Omer, M.; Hajima, Ryoichi*

New Journal of Physics (Internet), 21(11), p.113006_1 - 113006_10, 2019/11

https://doi.org/10.1088/1367-2630/ab4d8a

Solomon; A Monte Carlo solver for criticality safety analysis

Nagaya, Yasunobu; Ueki, Taro; Tonoike, Kotaro

Proceedings of 11th International Conference on Nuclear Criticality Safety (ICNC 2019) (Internet), 9 Pages, 2019/09

A new Monte Carlo solver Solomon has been developed for the application to fuel-debris systems. It is designed not only for usual criticality safety analysis but also for criticality calculations of damaged reactor core including fuel debris. This paper describes the current status of Solomon and demonstrates the applications of the randomized Weierstrass function (RWF) model and the RWF model superimposed voxel geometry.

Estimation method of systematic uncertainties in Monte Carlo particle transport simulation based on analysis of variance

Hashimoto, Shintaro; Sato, Tatsuhiko

Journal of Nuclear Science and Technology, 56(4), p.345 - 354, 2019/04

https://doi.org/10.1080/00223131.2019.1585989

Particle transport simulations based on the Monte Carlo method have been applied to shielding calculations. Estimation of not only statistical uncertainty related to the number of trials but also systematic one induced by unclear physical quantities is required to confirm the reliability of calculated results. In this study, we applied a method based on analysis of variance to shielding calculations. We proposed random- and three-condition methods. The first one determines randomly the value of the unclear quantity, while the second one uses only three values: the default value, upper and lower limits. The systematic uncertainty can be estimated adequately by the random-condition method, though it needs the large computational cost. The three-condition method can provide almost the same estimate as the random-condition method when the effect of the variation is monotonic. We found criterion to confirm convergence of the systematic uncertainty as the number of trials increases.

A Scalable and deformable stylized model of the adult human eye for radiation dose assessment

El Basha, D.*; Furuta, Takuya; Iyer, S. S. R.*; Bolch, W. E.*

Physics in Medicine and Biology, 63(10), p.105017_1 - 105017_13, 2018/05

https://doi.org/10.1088/1361-6560/aab955

With recent changes in the recommended annual limit on eye lens exposures to ionizing radiation by International Commission on Radiological Protection, there is considerable interest in predictive computational dosimetry models of the human eye and its various ocular structures. Several computational eye models to date have been constructed for this purpose but they are typically constructed of nominal size and of a roughly spherical shape associated with the emmetropic eye. We therefore constructed a geometric eye model that is both scalable (allowing for changes in eye size) and deformable (allowing for changes in eye shape), and that is suitable for use in radiation transport studies of ocular exposures and radiation treatments of eye disease. As an example, electron and photon anterior-posterior radiation transport with the constructed eye model was conducted and analyzed resultant energy-dependent dose profiles. Due to anterior-posterior irradiation, the energy dose response was shifted to higher energy for a larger-size eye or an axially deformed eye in prolate shape because the structures were located in deeper depth compared to the normal eye.

Characterization of germanium detectors for the measurement of the angular distribution of prompt -rays at the ANNRI in the MLF of the J-PARC

Takada, Shusuke*; Okudaira, Takuya*; Goto, Fumiya*; Hirota, Katsuya*; Kimura, Atsushi; Kitaguchi, Masaaki*; Koga, Jun*; Nakao, Taro*; Sakai, Kenji; Shimizu, Hirohiko*; et al.

Journal of Instrumentation (Internet), 13(2), p.P02018_1 - P02018_21, 2018/02

https://doi.org/10.1088/1748-0221/13/02/P02018

A Power spectrum approach to tally convergence in Monte Carlo criticality calculation

Ueki, Taro

Journal of Nuclear Science and Technology, 54(12), p.1310 - 1320, 2017/12

AA2017-0413.pdf:1.05MB

https://doi.org/10.1080/00223131.2017.1365022

In Monte Carlo criticality calculation, confidence interval estimation is based on the central limit theorem (CLT) for a series of tallies. A fundamental assertion resulting from CLT is the convergence in distribution (CID) of the interpolated standardized time series (ISTS) of tallies. In this work, the spectral analysis of ISTS has been conducted in order to assess the convergence of tallies in terms of CID. Numerical results indicate that the power spectrum of ISTS is equal to the theoretically predicted power spectrum of Brownian motion for effective neutron multiplication factor; on the other hand, the power spectrum of ISTS for local power fluctuates wildly while maintaining the spectral form of fractional Brownian motion. The latter result is the evidence of a case where a series of tallies is away from CID, while the spectral form supports normality assumption on the sample mean.

Analyses with latest major nuclear data libraries of the fission rate ratios for several TRU nuclides in the FCA-IX experiments

Fukushima, Masahiro; Tsujimoto, Kazufumi; Okajima, Shigeaki

Journal of Nuclear Science and Technology, 54(7), p.795 - 805, 2017/07

https://doi.org/10.1080/00223131.2017.1299644

A series of integral experiments was conducted in FCA assemblies with systematically changed neutron spectra covering from the intermediate to fast ones. The experiments provide systematic data of central fission rates for TRU nuclides containing minor actinides, Np, Pu, Pu, Pu, Am, Am, and Cm. Latest major nuclear data libraries, JENDL-4.0, ENDF/B-VII.1, and JEFF-3.2, were tested using benchmark models regarding the fission rate ratios relative to Pu. For all the libraries, the benchmark tests by a Monte Carlo calculation code show obvious overestimations particularly for the fission rate ratios of Cm to Pu. Additionally, a large discrepancy about by 20% between the libraries is revealed for the fission rate ratio of Pu to Pu measured in the intermediate neutron spectrum. The cause of discrepancy is furthermore clarified by sensitivity analyses.

Implementation of tetrahedral-mesh geometry in Monte Carlo radiation transport code PHITS

Furuta, Takuya; Sato, Tatsuhiko; Han, M. C.*; Yeom, Y. S.*; Kim, C. H.*; Brown, J. L.*; Bolch, W. E.*

Physics in Medicine and Biology, 62(12), p.4798 - 4810, 2017/06

https://doi.org/10.1088/1361-6560/aa6b45

A new function to treat tetrahedral-mesh geometry, a type of polygon-mesh geometry, was implemented in the Particle and Heavy Ion Transport code Systems (PHITS). Tetrahedral-mesh is suitable to describe complex geometry including curving shapes. In addition, construction of three-dimensional geometry using CAD software becomes possible with file format conversion. We have introduced a function to create decomposition maps of tetrahedral-mesh objects at the initial process so that the computational time for transport process can be reduced. Owing to this function, transport calculation in tetrahedral-mesh geometry can be as fast as that for the geometry in voxel-mesh with the same number of meshes. Due to adaptability of tetrahedrons in size and shape, dosimetrically equivalent objects can be represented by tetrahedrons with much fewer number of meshes compared with the voxels. For dosimetric calculation using computational human phantom, significant acceleration of the computational speed, about 4 times, was confirmed by adopting the tetrahedral mesh instead of the voxel.

Comparative study on burnup characteristics of a 1500 MWe metal fuel sodium-cooled fast reactor

Ohgama, Kazuya; Aliberti, G.*; Stauff, N. E.*; Oki, Shigeo; Kim, T. K.*

Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 8 Pages, 2017/04