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.

Decommissioning of uranium handling facility for development of nuclear fuel manufacturing equipment

Kageyama, Tomio; Denuma, Akio; Koizumi, Jin*; Odakura, Manabu*; Haginoya, Masahiro*; Isaka, Shinichi*; Kadowaki, Hiroyuki*; Kobayashi, Shingo*; Morimoto, Taisei*; Kato, Yoshiaki*; et al.

JAEA-Technology 2022-033, 130 Pages, 2023/03

JAEA-Technology-2022-033.pdf:9.87MB

Uranium handling facility for development of nuclear fuel manufacturing equipment (Mockup room) was constructed in 1972. The Mockup room has a weak seismic resistance and is deteriorating with age. Also, the original purpose with this facility have been achieved and there are no new development plans using this facility. Therefore, interior equipment installed in this facility had been dismantled and removed since March 2019. After that, the Mockup room was inspected for contamination, and then controlled area in the Mockup room was cancelled on March 29th 2022. A total of 6,549 workers (not including security witnesses) were required for this work. The amount of non-radioactive waste generated by this work was 31,300 kg. The amount of radioactive waste generated by this work was 3,734 kg of combustible waste (103 drums), 4,393 kg of flame resistance waste (61 drums), 37,790 kg of non-combustible waste (124 drums, 19 containers). This report describes about the dismantling and removing the interior equipment in the Mockup room, the amount of waste generated by this work, and procedure for cancellation the controlled area in the facility.

Simulation of the self-propagating hydrogen-air premixed flame in a closed-vessel by an open-source CFD code

Thwe Thwe, A.; Terada, Atsuhiko; Hino, Ryutaro; Nagaishi, Ryuji; Kadowaki, Satoshi

Journal of Nuclear Science and Technology, 59(5), p.573 - 579, 2022/05

https://doi.org/10.1080/00223131.2021.1990153

The simulations of the combustion of self-propagating hydrogen-air premixed flame are performed by an open-source CFD code. The flame propagation behavior, flame radius, temperature and pressure are analyzed by varying the initial laminar flame speed and grid size. When the initial laminar speed increases, the thermal expansion effects become strong which leads the increase of flame radius along with the increase of flame surface area, flame temperature and pressure. A new laminar flame speed model derived previously from the results of experiment is also introduced to the code and the obtained flame radii are compared with those from the experiments. The formation of cellular flame fronts is captured by simulation and the cell separation on the flame surface vividly appears when the gird resolution becomes sufficiently higher. The propagation behavior of cellular flame front and the flame radius obtained from the simulations have the reasonable agreement with the previous experiments.

Toward development of a framework for prediction system of local-scale atmospheric dispersion based on a coupling of LES-database and on-site meteorological observation

Nakayama, Hiromasa; Yoshida, Toshiya; Terada, Hiroaki; Kadowaki, Masanao

Atmosphere (Internet), 12(7), p.899_1 - 899_16, 2021/07

https://doi.org/10.3390/atmos12070899

In this study, first, we conducted meteorological observations by a Doppler LiDAR and simple plume release experiments by a mist spraying system at the site of Japan Atomic Energy Agency. Then, we developed a framework for prediction system of local-scale atmospheric dispersion based on a coupling of large-eddy simulation (LES) database and on-site meteorological observation. The LES-database was also created by pre-calculating high-resolution turbulent flows in the target site at mean wind directions of class interval. We provided the meteorological observed data with the LES database in consideration of building conditions and calculated three-dimensional distribution of the plume by a Lagrangian dispersion model. Compared to the instantaneous shot of the plume taken by a digital camera, it was shown that the mist plume transport direction was accurately simulated. It was concluded that our proposed framework for prediction system based on a coupling of LES-database and on-site meteorological observation is effective.

Effects of pressure and heat loss on the unstable motion of cellular-flame fronts caused by intrinsic instability in hydrogen-air lean premixed flames

Kadowaki, Satoshi; Thwe Thwe, A.; Furuyama, Taisei*; Kawata, Kazumasa*; Katsumi, Toshiyuki; Kobayashi, Hideaki*

Journal of Thermal Science and Technology (Internet), 16(2), p.20-00491_1 - 20-00491_12, 2021/00

https://doi.org/10.1299/jtst.2021jtst0021

Effects of pressure and heat loss on the unstable motion of cellular-flame fronts in hydrogen-air lean premixed flames were numerically investigated. The reaction mechanism for hydrogen-oxygen combustion was modeled with seventeen reversible reactions of eight reactive species and a diluent. Two-dimensional unsteady reactive flow was treated, and the compressibility, viscosity, heat conduction, molecular diffusion and heat loss were taken into account. As the pressure became higher, the maximum growth rate increased and the unstable range widened. These were due mainly to the decrease of flame thickness. The burning velocity of a cellular flame normalized by that of a planar flame increased as the pressure became higher and the heat loss became larger. This indicated that the pressure and heat loss affected strongly the unstable motion of cellular-flame fronts. In addition, the fractal dimension became larger, which denoted that the flame shape became more complicated.

Three-dimensional cellular premixed flames generated by hydrodynamic and diffusive-thermal instabilities (Effects of unburned-gas temperature and heat loss)

Kadowaki, Satoshi; Nogami, Masato*; Thwe Thwe, A.; Katsumi, Toshiyuki*; Yamazaki, Wataru*; Kobayashi, Hideaki*

Nihon Kikai Gakkai Rombunshu (Internet), 85(879), p.19-00274_1 - 19-00274_13, 2019/11

https://doi.org/10.1299/transjsme.19-00274

We dealt with three-dimensional cellular premixed flames generated by hydrodynamic and diffusive-thermal instabilities to elucidate the effects of unburned-gas temperature and heat loss by adopting the three-dimensional compressible Navier-Stokes equation. As the unburned-gas temperature became lower and the heat loss became larger, the growth rate decreased and the unstable range narrowed. With a decrease of unburned-gas temperature, the normalized growth rate increased and the normalized unstable range widened, which was because the temperature ratio of burned and unburned gases became larger. The obtained hexagonal cellular fronts were qualitatively consistent with the experimental results. As the heat loss became larger, the burning velocity of a cellular flame normalized by that of a planar flame increased. This was because diffusive-thermal effects became stronger owing to the increase of apparent Zeldovich number caused by the decrease of flame temperature.

Development of hydrogen behavior simulation code system; Outline of code system and validation using existing data

Terada, Atsuhiko; Matsumoto, Masaaki*; Sugiyama, Hitoshi*; Kamiji, Yu; Kadowaki, Satoshi*; Hino, Ryutaro

Proceedings of 23rd International Conference on Nuclear Engineering (ICONE-23) (DVD-ROM), 6 Pages, 2015/05

In the Fukushima Daiichi Nuclear Power Station (NPS) accident, hydrogen was generated by oxidation reaction of the cladding and water etc, then leaked into the NPS building, and finally led to occurrence of hydrogen explosion in the building. This resulted in serious damage to the environment. To improve the safety performance of the NPS, especially on the hydrogen safety under severe accident conditions, a simulation code system has been developed to analyze hydrogen behaviors including diffusion, combustion, explosion and structural integrity evaluation. This developing system consists of CFD and FEM tools in order to support various hydrogen user groups of students, researchers and engineers. Preliminary calculated results obtained with above mentioned tools, damage of piping induced by hydrogen combustion, agreed well with existing test data.

Development status of hydrogen behavior simulation for NPP containment; Hydrogen combustion simulation

Terada, Atsuhiko; Kamiji, Yu; Hino, Ryutaro; Sugiyama, Hitoshi*; Matsumoto, Masaaki*; Kadowaki, Satoshi*

no journal, , 

no abstracts in English

Simulation of the behavior of spherically expanding H-air premixed flame

Thwe Thwe, A.; Hino, Ryutaro; Terada, Atsuhiko; Kadowaki, Satoshi

no journal, , 

We performed the two- and three-dimensional simulations to investigate the behavior of spherically expanding H-air premixed flame by using XiFoam. The equivalence ratio was set to unity. The ignition started from the center of domain, and the flame expanded spherically and became wrinkle. The obtained flame radius has the agreement with the experimental result.

LES analysis on impact of the forest canopy arrangement on dry deposition

Nakayama, Hiromasa; Kadowaki, Masanao; Yoshida, Toshiya

no journal, , 

Dry deposition is a phenomenon that gaseous and particulate substances deposit onto ground surfaces by atmospheric turbulence and/or gravity settling. Because forest areas have larger surface areas than those over grass or bare soil, air pollutants are efficiently deposited onto them. Especially, in the upstream edge of forest canopy, total amount of dry deposition becomes highly large by the effects of active advective and turbulence transport and large dry deposition velocity. In general, meso-scale meteorological simulation (MMS) models predict deposited amount at each computational grid based on several tens kinds of land use categories. However, real forest areas consist of various scale of forest patches. Such inhomogeneous forest canopy arrangements are not considered in sub-grid scale in MMS models. There are various methods of investigating dry deposition under the influence of forest area arrangements in detail, e.g., observations and computational fluid dynamics (CFD). It is well known that observations are a rational tool to provide reliable data. However, those are time-consuming, costly, and have a limitation of capturing detailed spatial distributions. On the other hand, the CFD technique has been recognized as a helpful tool with the rapid development of computational technology. In this study, we conducted LESs of turbulent flows, dispersion and dry deposition for different arrangements of two-dimensional forest canopy under a condition of the same area, and investigated the influence of forest canopy arrangements on dry deposition. It is found that the total amount of dry deposition shows a tendency to become larger as the forest canopy is arranged more sparsely and the total area of the canopy edge becomes larger. Our simulation results imply that it is expected to improve computational accuracy by considering the forest canopy arrangements in sub-grid scale when predicting dry deposition by MMS models.