Malins, A.; Machida, Masahiko; Vu, T. D.; Aizawa, Kazuya; Ishida, Takekazu*
Nuclear Instruments and Methods in Physics Research A, 953, p.163130_1 - 163130_7, 2020/02
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
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.
Carter, L. M.*; Crawford, T. M.*; Sato, Tatsuhiko; Furuta, Takuya; Choi, C.*; Kim, C. H.*; Brown, J. L.*; Bolch, W. E.*; Zanzonico, P. B.*; Lewis, J. S.*
Journal of Nuclear Medicine, 60(12), p.1802 - 1811, 2019/12
Voxel human phantoms have been used for internal dose assessment. More anatomically accurate representation become possible for skins or layer tissues owing to recent developments of advanced polygonal mesh-type phantoms and thus internal dose assessment using those advanced phantoms are desired. However, the Monte Carlo transport calculation by implementing those phantoms require an advanced knowledge for the Monte Carlo transport codes and it is only limited to experts. We therefore developed a tool, PARaDIM, which enables users to conduct internal dose calculation with PHITS easily by themselves. With this tool, a user can select tetrahedral-mesh phantoms, set radionuclides in organs, and execute radiation transport calculation with PHITS. Several test cases of internal dosimetry calculations were presented and usefulness of this tool was demonstrated.
Omer, M.; Hajima, Ryoichi*
New Journal of Physics (Internet), 21(11), p.113006_1 - 113006_10, 2019/11
Furuta, Takuya; El Basha, D.*; Iyer, S. S. R.*; Correa Alfonso, C. M.*; Bolch, W. E.*
Journal of Radiological Protection, 39(3), p.825 - 837, 2019/09
Despite large variation of human eye, only one computational eye model has been adopted in almost all the radiation transport simulation studies. We thus adopted a new scalable and deformable eye model and studied the radiation exposure by electrons, photons, and neutrons in the standard radiation fields such as AP, PA, RLAT, ROT, by using Monte Carlo radiation transport code PHITS. We computed the radiation exposure for 5 eye models (standard, large, small, myopic, hyperopic) and analyzed influence of absorbed dose in ocular structures on eye size and shape. Dose distribution of electrons is conformal and therefore the absorbed doses in ocular structures depend on the depth location of each ocular structure. We thus found a significant variation of the absorbed doses for each ocular structure for electron exposure due to change of the depth location affected by eye size and shape. On the other hand only small variation was observed for photons and neutrons exposures because of less conformal dose distribution of those particles.
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.
Yeom, Y. S.*; Han, M. C.*; Choi, C.*; Han, H.*; Shin, B.*; Furuta, Takuya; Kim, C. H.*
Health Physics, 116(5), p.664 - 676, 2019/05
Recently, Task Group 103 of the ICRP developed the mesh-type reference computational phantoms (MCRPs), which are planned for use in future ICRP dose coefficient calculation. Performance of major Monte Carlo particle transport codes (Geant4, MCNP6, and PHITS) were tested with MCRP. External and internal exposure of various particles and energies were calculated and the computational times and required memories were compared. Additionally calculation for voxel-mesh phantom was also conducted so that the influence of different mesh-representation in each code was studied. Memory usage of MRCP was as large as 10 GB with Geant4 and MCNP6 while it is much less with PHITS (1.2 GB). In addition, the computational time required for MRCP tends to increase compared to voxel-mesh phantoms with Geant4 and MCNP6 while it is equal or tends to decrease with PHITS.
Hashimoto, Shintaro; Sato, Tatsuhiko
Journal of Nuclear Science and Technology, 56(4), p.345 - 354, 2019/04
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.
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
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.
Han, M. C.*; Yeom, Y. S.*; Lee, H. S.*; Shin, B.*; Kim, C. H.*; Furuta, Takuya
Physics in Medicine and Biology, 63(9), p.09NT02_1 - 09NT02_9, 2018/05
The multi-threading computation performances of the Geant4, MCNP6, and PHITS codes were evaluated using three tetrahedral-mesh phantoms with different complexity. Photon and neutron transport simulations were conducted and the initialization time, calculation time, and memory usage were measured as a function of the number of threads N used in the simulation. The initialization time significantly increases with the complexity of the phantom, but not much with the number of the threads. For the calculation time, Geant4 showed good parallelization efficiency with multi-thread computation (30 times speed-up factor for N = 40) adopting the private tallies while saturation of the speed-up factor were observed in MCNP6 and PHITS (10 and a few times for N = 40) due to the time delay for the sharing tallies. On the other hand, Geant4 requires larger memory specification and the memory usage rapidly increases with the number of threads compared to MCNP6 or PHITS. It is notable that when compared to the other codes, the memory usage of PHITS is much smaller, regardless of both the complexity of the phantom and the number of the threads.
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
Fukushima, Masahiro; Goda, J.*; Bounds, J.*; Cutler, T.*; Grove, T.*; Hutchinson, J.*; James, M.*; McKenzie, G.*; Sanchez, R.*; Oizumi, Akito; et al.
Nuclear Science and Engineering, 189, p.93 - 99, 2018/01
To validate lead (Pb) nuclear cross sections, a series of integral experiments to measure lead void reactivity worths was conducted in a high-enriched uranium (HEU)/Pb system and a low enriched uranium (LEU)/Pb system using the Comet Critical Assembly at NCERC. The critical experiments were designed to provide complementary data sets having different sensitivities to scattering cross sections of lead. The larger amount of the U present in the LEU/Pb core increases the neutron importance above 1 MeV compared with the HEU/Pb core. Since removal of lead from the core shifts the neutron spectrum to the higher energy region, positive lead void reactivity worths were observed in the LEU/Pb core while negative values were observed in the HEU/Pb core. Experimental analyses for the lead void reactivity worths were performed with the Monte Carlo calculation code MCNP6.1 together with nuclear data libraries, JENDL 4.0 and ENDF/B VII.1. The calculation values were found to overestimate the experimental ones for the HEU/Pb core while being consistent for the LEU/Pb core.
Journal of Nuclear Science and Technology, 54(12), p.1310 - 1320, 2017/12
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.
Lerendegui-Marco, J.*; Corts-Giraldo, M. A.*; Guerrero, C.*; Harada, Hideo; Kimura, Atsushi; n_TOF Collaboration*; 114 of others*
EPJ Web of Conferences (Internet), 146, p.03030_1 - 03030_4, 2017/09
Fukushima, Masahiro; Tsujimoto, Kazufumi; Okajima, Shigeaki
Journal of Nuclear Science and Technology, 54(7), p.795 - 805, 2017/07
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.
Ohgama, Kazuya; Aliberti, G.*; Stauff, N. E.*; Oki, Shigeo; Kim, T. K.*
Mechanical Engineering Journal (Internet), 4(3), p.16-00592_1 - 16-00592_9, 2017/06
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
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.
Ohgama, Kazuya; Ikeda, Kazumi*; Ishikawa, Makoto; Kan, Taro*; Maruyama, Shuhei; Yokoyama, Kenji; Sugino, Kazuteru; Nagaya, Yasunobu; Oki, Shigeo
Proceedings of 2017 International Congress on Advances in Nuclear Power Plants (ICAPP 2017) (CD-ROM), 10 Pages, 2017/04
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