Circular polarization measurement of -rays emitted from S(n,)S reaction with polarized neutrons

Endo, Shunsuke; Fujioka, Hiroyuki*; Ide, Ikuo*; Iinuma, Masataka*; Iwamoto, Nobuyuki; Iwamoto, Osamu; Kameda, Kento*; Kawamura, Shiori*; Kimura, Atsushi; Kitaguchi, Masaaki*; et al.

EPJ Web of Conferences, 329, p.05003_1 - 05003_3, 2025/06

https://doi.org/10.1051/epjconf/202532905003

no abstracts in English

Photonuclear reaction cross-section evaluation of Ta and Bi considering experimental double differential cross-section data

Nguyen, T. T. H.*; Iwamoto, Nobuyuki; Sanami, Toshiya*

EPJ Web of Conferences, 322, p.10004_1 - 10004_3, 2025/03

https://doi.org/10.1051/epjconf/202532210004

Bubble flow analysis using multi-phase field method

Sugihara, Kenta; Onodera, Naoyuki; Sitompul, Y.; Idomura, Yasuhiro; Yamashita, Susumu

EPJ Web of Conferences, 302, p.03002_1 - 03002_10, 2024/10

https://doi.org/10.1051/epjconf/202430203002

In simulations of gas-liquid two-phase flows using conventional interface capture methods, we observed that when bubbles come close to each other, they tend to merge numerically, despite experimental evidence indicating that they would repel each other. Given the significant impact of sequential numerical coalescence on flow patterns, it is necessary to regulate the merging behavior of close bubbles. To address this issue, we introduced the Multi- Phase Field (MPF) method, which mitigates bubble coalescence by applying an independent fluid fraction function to each bubble. In this study, we employed the MPF based on the N-phase model to minimize numerical errors associated with surface interactions at triple junction points. Additionally, we implemented the Ordered Active Parameter Tracking (OAPT) method to efficiently store several hundreds of fluid fraction functions. To validate the MPF method, we conducted analysis of turbulent bubbly pipe flows and compared the results against experimental data from Colin et al. The validation results showed reasonable agreements with respect to the bubble distribution and the flow velocity profiles.

Implementation of track length estimator for flux distribution tallies using proper orthogonal decomposition in one-dimensional geometry

Kondo, Ryoichi; Endo, Tomohiro*; Yamamoto, Akio*

EPJ Web of Conferences, 302, p.04002_1 - 04002_10, 2024/10

https://doi.org/10.1051/epjconf/202430204002

In the recent study, we have developed an efficient flux distribution tallying method in the Monte Carlo calculation toward the high-fidelity, large scale multi-physics simulation. In this method, the proper orthogonal decomposition is applied to the flux distribution tallies. While the tallying method was implemented with the collision estimator in the previous study, the track length estimator is implemented in the present study to obtain the tally with lower statistical error. The implementation of the flux distribution tally with the track length estimator is compared with that of the collision estimator and the normal track length estimator in a one-dimensional problem. The numerical results reveal that the distribution tally using the POD with the track length estimator can obtain a more precise solution compared with that with the collision estimator. Therefore, in terms of the statistical error, the relationship between the distribution tally with track length and collision estimator is similar to that between the conventional track length and collision estimators.

GPU-enabled ensemble data assimilation for mesh-refined lattice Boltzmann method

Hasegawa, Yuta; Idomura, Yasuhiro; Onodera, Naoyuki

EPJ Web of Conferences, 302, p.03005_1 - 03005_9, 2024/10

https://doi.org/10.1051/epjconf/202430203005

We implemented the ensemble data assimilation (DA) method, the local ensemble transform Kalman filter (LETKF), into the mesh-refined lattice Boltzmann method (LBM) for turbulent flows. Both the LETKF and the mesh-refined LBM were fully implemented on GPUs, so that they are efficiently computed on modern GPU-based supercomputers. We examined the DA accuracy against the flow around a cylinder. The result showed that our method enabled accurate DA with spatially- and temporarily-sparse observation data; the error of the assimilated velocity field with the observation interval of and the observation resolution (1.56% of the total computational grids) was smaller than the amplitude of the observation noise, where is the period of the Krmn vortex and is diameter of the square cylinder.

Selection method for observation points using Bayesian LASSO at estimating radiation source distribution from air dose rates

Yamada, Susumu; Machida, Masahiko; Tanimura, Naoki*

EPJ Web of Conferences, 302, p.16004_1 - 16004_10, 2024/10

https://doi.org/10.1051/epjconf/202430216004

When we decommission a reactor building, it is desirable to identify the radiation source distribution for safety. It has been reported that the source distribution can be estimated from the measured air dose rates at appropriate observation points by minimizing an evaluation function using the Least Absolute Shrinkage and Selection Operator (LASSO). However, it is difficult to decide on suitable points in advance. Therefore, we estimate the posterior distribution from the prior distribution of the source amounts, which are calculated by the standard LASSO, using the Bayesian LASSO, and evaluate the predictive distribution of the evaluated air dose rates at the candidate observation points from the posterior distribution. We select the additional observation point based on the variances of the predictive distributions. We confirmed that the method can estimate the source distribution with fewer additional observation points than when adding ones randomly in most cases.

Intriguing aspects of light baryon resonances

Khemchandani, K. P.*; Martnez Torres, A.*; Kim, S.-H.*; Nam, S.-I.*; Hosaka, Atsushi; Nagahiro, Hideko*

EPJ Web of Conferences, 301, p.03001_1 - 03001_10, 2024/08

https://doi.org/10.1051/epjconf/202430103001

no abstracts in English

Evaluation of thermal neutron scattering law of nuclear-grade isotropic graphite

Nakayama, Shinsuke; Iwamoto, Osamu; Kimura, Atsushi

EPJ Web of Conferences, 294, p.07001_1 - 07001_6, 2024/04

https://doi.org/10.1051/epjconf/202429407001

Graphite is a candidate of moderator in innovative nuclear reactors such as molten salt reactors. Scattering of thermal neutrons by the moderator material has a significant impact on the reactor core design. To contribute to the development of innovative nuclear reactors, an evaluation method of thermal neutron scattering law for reactor grade graphite was studied. The inelastic scattering component due to lattice vibration was evaluated based on the phonon density of states computed with first-principles lattice dynamics simulations. The simulations were performed for ideal crystalline graphite. The coherent elastic scattering component due to crystal structure was evaluated based on neutron transmission and scattering experiments recently performed in the J-PARC/MLF facility. In comparison with the neutron transmission experiments, it was found that the quantification of small-angle neutron scattering due to structures larger than crystal, such as pores in graphite, is important. Based on the above methods, thermal neutron scattering law data for reactor-grade graphite at room temperature were evaluated.

Present status of an R-matrix analysis code AMUR for cross-section evaluation in resolved resonance region

Kunieda, Satoshi

EPJ Web of Conferences, 284, p.03014_1 - 03014_4, 2023/05

https://doi.org/10.1051/epjconf/202328403014

For thorough understanding resonant theories and cause of discrepancies among different cross-section measurements, development of an R-matrix analysis code AMUR is being progressed. The code is organized by "theoretical" and "experimental" classes based on the object-oriented framework. In the theoretical class, with sharing the same compound nucleus, the independent distant poles can optionally be assumed for the simultaneous analysis of different projectile + nucleus pairs to see the relation between the channel radius and the theoretical background. In the experimental class, to simulate experimental conditions, calculated cross-sections can be corrected by the Doppler broadening, resolution functions, re-normalization, adding contaminant elements. I demonstrate some example analyses of measured cross-sections with AMUR both for the light and heavier nuclei to show effects of those new options. Also, preliminary results will be shown from analyses for experimental data of J-PARC/ANNRI.

New results in the modeling of fission and radiative neutron capture with FIFRELIN

Litaize, O.*; Piau, V.*; Chalil, A.*; Ogawa, Tatsuhiko; Chebboubi, A.*; Gk, A.*; Gunsing, F.*; Kessedjian, G.*; Lhuillier, D.*; Mancusi, D.*; et al.

EPJ Web of Conferences, 284, p.04014_1 - 04014_4, 2023/05

https://doi.org/10.1051/epjconf/202328404014

The Monte-Carlo code FIFRELIN was originally developed for the simulation of first chance fission of fissile nuclei. In this study, its interfaces to radiation transport code PHITS, extension for neutron capture reactions, and a function to calculate neutrinos from fission fragments were developed. In order to extend FIFRELIN for neutron capture reactions, accurate gamma-ray yield was obtained by tuning the level density considering the nuclide species and excitation energy. Accurate neutrino yield was obtained by adopting up-to-date database on the thermal neutron capture state. JAEA developed an interface of FIFRELIN to PHITS to perform new FIFRELIN benchmark using FIFRELIN-DCHAIN joint calculation.