Application of Bayesian machine learning for estimation of uncertainty in forecasted plume directions by atmospheric dispersion simulations

Kadowaki, Masanao; Nagai, Haruyasu; Yoshida, Toshiya*; Terada, Hiroaki; Tsuzuki, Katsunori; Sawa, Hiroki*

Journal of Nuclear Science and Technology, 60(10), p.1194 - 1207, 2023/10

https://doi.org/10.1080/00223131.2023.2177763

This study develops an estimation method using machine learning for uncertainty in forecasted plume directions. Bayesian machine learning was used in the machine learning approach. A three-day forecast simulation was conducted every day from 2015-2020, considering a hypothetical release of Cs from a nuclear facility to create training and test datasets for the machine learning. The findings reveal that the rate of good predictability was greater than 50% even in the forecast 36 h later when investigating the effectiveness of the Bayesian model on uncertainty estimation. Additionally, the frequency of miss prediction of higher uncertainty was low (0.9%-7.9%) throughout the forecast period. However, the rate of over-prediction of uncertainty increased with forecast time up to 31.2%, which is acceptable as a conservative estimation. These results show that the Bayesian model used in this study effectively estimates the uncertainty of plume directions predicted through atmospheric dispersion simulations.

Evaluation of uncertainties derived from meteorological forecast inputs in plume directions predicted by atmospheric dispersion simulations

Yoshida, Toshiya; Nagai, Haruyasu; Terada, Hiroaki; Tsuzuki, Katsunori; Sawa, Hiroki*

Journal of Nuclear Science and Technology, 59(1), p.55 - 66, 2022/01

https://doi.org/10.1080/00223131.2021.1951862

Atmospheric transport, dispersion, and deposition models (ATDMs) can support decision-making during nuclear emergencies; however, uncertainties in the ATDM results need to be carefully evaluated. To investigate the uncertainties derived from meteorological forecast inputs, we conducted three-day forecast simulations every day for one year with hypothetical releases of radionuclides (one-hour releases every 6 h) from a nuclear facility. The forecast outputs were compared with the analysis outputs during the same period. The difference between the outputs is treated as the uncertainty in the forecasts and is represented as an angle based on the discrepancy in the plume directions between the analysis and forecast outputs. Using meteorological inputs made by Japan Meteorological Agency, the discrepancy angle (Ang) increased by approximately 10 per day on an annual average basis. Meanwhile, the Ang values were occasionally 4-5 times higher than the annual average during short time periods. Since the Ang time series show seasonal and diurnal changes, the statistical characteristics likely depend on the geographical and meteorological conditions, as well as the types of meteorological inputs. Additionally, a main factor in the uncertainty is the wind-direction difference between the analysis and forecast outputs on scales of more than or less than 100 km.

The -electron state of the heavy fermion superconductor NpPdAl and the isostructural family

Metoki, Naoto; Aczel, A. A.*; Aoki, Dai*; Chi, S.*; Fernandez-Baca, J. A.*; Griveau, J.-C.*; Hagihara, Masato*; Hong, T.*; Haga, Yoshinori; Ikeuchi, Kazuhiko*; et al.

JPS Conference Proceedings (Internet), 30, p.011123_1 - 011123_6, 2020/03

https://doi.org/10.7566/JPSCP.30.011123

Rare earths (4) and actinides (5) provide variety of interesting states realized with competing interactions between the increasing number of electrons. Since crystal field splitting of many-body electron system is smaller than the bandwidth, (1) high resolution experiments are needed, (2) essentially no clear spectrum with well defined peaks is expected in itinerant Ce and U compounds, and (3) Np and Pu is strictly regulated. Therefore, systematic research on magnetic excitations by neutron scattering experiments of localized compounds and rare earth iso-structural reference is useful. We describe the electron states of heavy electron compounds NpPdAl and actinide and rare earth based iso-structural family.

Neutron inelastic scattering study of the -electron states in NdPdAl

Metoki, Naoto; Yamauchi, Hiroki; Suzuki, Hiroyuki*; Kitazawa, Hideaki*; Kamazawa, Kazuya*; Ikeuchi, Kazuhiko*; Kajimoto, Ryoichi; Nakamura, Mitsutaka; Inamura, Yasuhiro

Journal of the Physical Society of Japan, 87(8), p.084708_1 - 084708_7, 2018/08

https://doi.org/10.7566/JPSJ.87.084708

Inelastic neutron scattering experiments were carried out in order to study the -electron states of NdPdAlThe CEF levels at 0K, 35.4K, 88.3K, 101.5K, and 198.8K were clarified from the excitation spectra. The ground state contains the orbital with as a main component due to a large negative BK, which is the origin of the strong uniaxial anisotropy. The estimated magnetic moment, the calculated susceptibility, magnetization curve, and specific heat are in good agreement with the experimental data. The existence of a common charge distribution with CePdAl and PrPdAl. Indicates that a localized character is important even in actinide-based iso-structural compounds as actually observed in UPdAl and also NpPdAl, in which the valence crossover plays important role for the heavy fermion superconductivity.

Neutron powder diffraction study on the magnetic structure of NdPdAl

Metoki, Naoto; Yamauchi, Hiroki; Kitazawa, Hideaki*; Suzuki, Hiroyuki*; Hagihara, Masato*; Frontzek, M. D.*; Matsuda, Masaaki*; Fernandez-Baca, J. A.*

Journal of the Physical Society of Japan, 86(3), p.034710_1 - 034710_5, 2017/03

https://doi.org/10.7566/JPSJ.86.034710

Magnetic structure of NdPdAl has been studied by means of neutron powder diffraction. We observed remarkable magnetic reflections with the modulation vector = (1/2 0 0) below the ordering temperature = 1.2 K. We found a collinear magnetic structure of Nd moment of 2.9(1) at 0.3 K parallel to the -axis, where the ferromagnetically ordered planes stack with four Nd layer period of ++-- sequence along the direction with the distance between adjuscent Nd layers to be . This is very similar to CePdAl with = (0.23 0.23 0) and the Ce moment parallel to the -axis. These structures with in-plane modulation is a consequence of the two dimensional nature of fermi surface topology in this family, coming from unique crystal structure with very long tetragonal unit cell and large distance 7 between the rare earth layers separated by Al and two Pd layers.

Neutron diffraction of ice and water in hydrogels

Sekine, Yurina; Kobayashi, Riki*; Chi, S.*; Fernandez-Baca, J. A.*; Suzuya, Kentaro; Fujisaki, Fumika*; Ikeda, Kazutaka*; Otomo, Toshiya*; Fukazawa, Tomoko*; Yamauchi, Hiroki; et al.

JPS Conference Proceedings (Internet), 8, p.033009_1 - 033009_6, 2015/09

https://doi.org/10.7566/JPSCP.8.033009

Neutron diffraction profiles of low-DO-content poly-N,N,-dimethylacrylamide (PDMAA) hydrogels were measured from 100 to 300 K to investigate the structure and properties of water in hydrogels. A broad diffraction observed at temperatures lower than 220 K indicates the existence of amorphous ice in the hydrogels at low temperatures. During the heating process, diffraction peaks from ice crystals appear in the profiles. These peaks indicate that cubic ice and hexagonal ice exist at T 220 K. We refined the structure parameters of these ices in the hydrogel, which indicate the existence of low-density ice in the hydrogel.

Electrode properties of LiMnO (2/) for a lithium-battery cathode in several charge-discharge potential ranges

Nakao, Yasuhiro*; Ozawa, Kiyoshi*; Fujii, Hiroki*; Mochiku, Takashi*; Iwai, Hideo*; Tsuchiya, Yoshinori*; Igawa, Naoki

Transactions of the Materials Research Society of Japan, 38(2), p.229 - 233, 2013/12

https://doi.org/10.14723/tmrsj.38.229

LiMnO powder with a monoclinic cell related to the space group of 2/ was synthesized by a simplified coprecipitation method. Its electrode properties as a lithium-battery cathode were investigated in the charge-discharge potential ranges of 2.0 - 4.6, 2.0 - 4.8, and 2.0 - 5.0 V. In all the potential ranges, the electrochemical capacities gradually increased during cycling, and the increased capacities significantly depended on the potential ranges. Compared to the discharge capacities for the potential ranges of 2.0 - 4.6 and 2.0 - 5.0 V, the former merely increased from 12.5 to 22.5 mAhg between the 1st and 99th cycles, whereas the latter increased from 20.0 to 110.2 mAhg during the same cycling. The structural variation in LiMnO is induced by the cycling, the rhombohedral phase is detected during cycling in the potential range of 2.0 - 5.0 V.

Structure and properties of ferroelectric ice

Fukazawa, Hiroshi; Arakawa, Masashi*; Kagi, Hiroyuki; Yamauchi, Hiroki; Chakoumakos, B. C.*; Fernandez-Baca, J. A.*

Physics and Chemistry of Ice 2010, p.421 - 428, 2011/03

Whether or not ice in the universe exists as ferroelectric is a question that has attracted interest in astrophysics and physical chemistry, because long-range electrostatic forces, caused by the ferroelectricity, might be an important factor for materials evolution and hydrogen bonding. From neutron diffraction and scattering measurements, we have studied ice with impurities, such as potassium, sodium and lithium, that acted as a catalyst. Time-resolved diffraction experiments show that ferroelectric ice XI with hydrogen-ordered arrangement nucleates and grows with time for about 5 days. We found that the doped ice that has once been converted to ice XI is a stronger ferroelectric ice than that has never been converted. We also show the existence of the ferroelectric ice under high-pressure and its formation from compressed amorphous ice.

CO motion in carbon dioxide deuterohydrate determined by applying maximum entropy method to neutron powder diffraction data

Igawa, Naoki; Taguchi, Tomitsugu; Hoshikawa, Akinori*; Fukazawa, Hiroshi; Yamauchi, Hiroki; Utsumi, Wataru; Ishii, Yoshinobu*

Journal of Physics and Chemistry of Solids, 71(6), p.899 - 905, 2010/06

https://doi.org/10.1016/j.jpcs.2010.03.039

Crystal structures of carbon dioxide deuterohydrate were studied by neutron powder diffraction at temperatures from 10 to 200 K. Maps of scattering length density distribution were obtained using a maximum entropy method, which clarified the motion of CO molecules in the hydrate. In small cages, the carbon atom of the CO molecule is at the center of the cage, and the oxygen atoms of CO revolve freely around the carbon atom. In large cages, the carbon atom also is at the center of the cage, but the oxygen atoms tend to revolve around the carbon atom along the plane parallel to the hexagonal facets of the cage.

Development of asymmetric reflection-type germanium monochromator for neutron beam enhancement

Yamauchi, Hiroki; Ishii, Yoshinobu*; Igawa, Naoki; Fukazawa, Hiroshi; Utsumi, Wataru

JAEA-Research 2008-077, 28 Pages, 2008/10

JAEA-Research-2008-077.pdf:24.52MB

The neutron powder diffractometer, HRPD, can provide high-resolution data that meet the many users' needs until now. On the other hand, the demand of high-efficiency is growing in the recent years. In order to improve the source intensity and measurement efficiency, the authors tried to develop asymmetric reflection-type Ge monochromators. The mosaic crystals (20 in the horizontal direction) were cut at an angle of 40 relative to the Ge,3,3,1 reflecting planes. The diffraction results of standard Si samples reveal that peak intensities by the asymmetric type are improved 1.2 times larger than those by the existing symmetric type, but integrated intensities are almost comparable each other. For mosaic crystals, asymmetric reflections in compression geometry intensify the current density, but reflectivity is always less than that in symmetric reflections, and thus the suppression of the reflectivity just cancels out the enhancement of the current density.