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JAEA Reports

Utilization of gamma ray irradiation at the WASTEF Facility

Sano, Naruto; Yamashita, Naoki; Watanabe, Masaya; Tsukada, Manabu*; Hoshino, Kazutoyo*; Hirai, Koki; Ikegami, Yuta*; Tashiro, Shinsuke; Yoshida, Ryoichiro; Hatakeyama, Yuichi; et al.

JAEA-Technology 2023-029, 36 Pages, 2024/03

JAEA-Technology-2023-029.pdf:2.47MB

At the Waste Safety Testing Facility (WASTEF), the gamma ray irradiation device "Gamma Cell 220" was relocated from the 4th research building of the Nuclear Science Research Institute in FY2019, and the use of gamma ray irradiation has begun. Initially, Fuel Cycle Safety Research Group, Fuel Cycle Safety Research Division, Nuclear Safety Research Center, Sector of Nuclear Safety Research and Emergency Preparedness, the owner of this device, conducted the tests as the main user, but since 2022, other users, including those outside the organization, have started using it. The gamma ray irradiation device "Gamma Cell 220" is manufactured by Nordion International Inc. in Canada. Since it was purchased in 1989, the built-in 60Co radiation source has been updated once, and safety research related to nuclear fuel cycles, etc. It is still used for this purpose to this day. This report summarizes the equipment overview of the gamma ray irradiation device "Gamma Cell 220", its permits and licenses at WASTEF, usage status, maintenance and inspection, and future prospects.

JAEA Reports

Development of an electrochemical measurement method for carbon steels in radiation source dissolved solution and a corroded specimen analysis method using an imaging plate

Yamashita, Naoki; Aoyama, Takahito; Kato, Chiaki; Sano, Naruto; Tagami, Susumu

JAEA-Technology 2023-028, 22 Pages, 2024/03

JAEA-Technology-2023-028.pdf:1.9MB

At the Fukushima Daiichi Nuclear Power Station (1F), which is currently undergoing decommissioning, there is growing interest in the effects of radiation-emitting radionuclides such as $$^{90}$$Sr and $$^{137}$$Cs on the structural integrity. In particular, the corrosion behavior of carbon steel, which is used in many parts of 1F, is known to change depending on metal cations in solution, but the effects of $$^{90}$$Sr and $$^{137}$$Cs on corrosion are not yet understood. In addition, it is important to investigate the distribution of $$^{90}$$Sr and $$^{137}$$Cs in the rust layer in order to understand the corrosion behavior, but the method has not yet been established. In this study, a glove box was prepared to conduct corrosion tests of carbon steel in NaCl containing $$^{90}$$Sr and $$^{137}$$Cs in the glove box. In addition, in order to clarify the influence of $$^{90}$$Sr and $$^{137}$$Cs, which exist as metal cations in the solution, on the corrosion behavior of carbon steel, we attempted to establish a detection method for radioactive materials in the rust layer using an imaging plate.

JAEA Reports

Optimized phase-field modeling using a modified conservative Allen-Cahn equation for two-phase flows

Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro; Yamashita, Susumu

JAEA-Research 2023-006, 47 Pages, 2023/10

JAEA-Research-2023-006.pdf:3.28MB

This report presents a new surface capturing method based on the phase field model for gas-liquid two-phase flows simulation. In the conventional phase field model, the interface correction strength parameter was determined from the maximum flow velocity in the computational domain, but because the interface correction was applied uniformly to the entire space, it was also applied to locations that did not require correction. In the new method, the phase field parameter or the intensity of the phase field model is extended to have a spatial distribution, allowing us to set the optimal parameters depending on the local flow velocity fields. We also propose a method to derive the optimal phase field parameter based on systematic parameter scans using error analysis of the interface advection test and bubble rising calculations. Through benchmark tests of gas-liquid two-phase flows, the proposed model is verified, and it is shown that the proposed model has higher accuracy than the conventional phase field model.

Journal Articles

Numerical simulation method using a Cartesian grid for oxidation of core materials under steam-starved conditions

Yamashita, Susumu; Sato, Takumi; Nagae, Yuji; Kurata, Masaki; Yoshida, Hiroyuki

Journal of Nuclear Science and Technology, 60(9), p.1029 - 1045, 2023/09

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

Development of a numerical simulation method for air cooling of fuel debris by JUPITER

Yamashita, Susumu; Uesawa, Shinichiro; Ono, Ayako; Yoshida, Hiroyuki

Mechanical Engineering Journal (Internet), 10(4), p.22-00485_1 - 22-00485_25, 2023/08

A detailed evaluation for air cooling of fuel debris in actual reactors will be essential in fuel debris retrieval under dry conditions. To understand the heat transfer in and around fuel debris, which is assumed as a porous medium in the primary containment vessel (PCV) mechanistically, we newly applied the porous medium model to the multiphase and multicomponent computational fluid dynamics code named JUPITER (JAEA Utility Program for Interdisciplinary Thermal-hydraulics Engineering and Research). We applied the Darcy-Brinkman model as for the porous medium model. This model has high compatibility with JUPITER because it can treat both a pure fluid and a porous medium phase simultaneously in the same manner as the one-fluid model in multiphase flow simulation. We addressed the case of natural convection with a high-velocity flow standing out nonlinear effects by implementing the Forchheimer model, including the term of the square of the velocity as a nonlinear effect to the momentum transport equation of JUPITER. We performed some simple verification and validation simulations, such as the natural convection simulation in a square cavity and the natural convective heat transfer experiment with the porous medium, to confirm the validity of the implemented model. We confirmed that the result of JUPITER agreed well with these simulations and experiments. In addition, as an application of the updated JUPITER, we performed the preliminary simulation of air cooling of fuel debris in the condition of the Fukushima Daiichi Nuclear Power Station unit 2 including the actual core materials. As a result, JUPITER calculated the temperature and velocity field stably in and around the fuel debris inside the PCV. Therefore, JUPITER has the potential to estimate the detailed and accurate thermal-hydraulics behaviors of fuel debris.

Journal Articles

Development of numerical simulation method of natural convection around heated porous medium by using JUPITER

Uesawa, Shinichiro; Yamashita, Susumu; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Proceedings of 30th International Conference on Nuclear Engineering (ICONE30) (Internet), 9 Pages, 2023/05

For contaminated water management in decommissioning Fukushima Daiichi Nuclear Power Stations, reduction in water injection, intermittent injection water and air cooling are considered. However, since there are uncertainties of fuel debris in the PCV, it is necessary to examine and evaluate optimal cooling methods according to the distribution state of the fuel debris and the progress of the fuel debris retrieval work in advance. We have developed a method for estimating the thermal behavior in the air cooling, including the influence of the position, heat generation and the porosity of fuel debris. Since a large-scale thermal-hydraulics analysis of natural convection is necessary for the method, JUPITER developed independently by JAEA is used. It is however difficult to perform the large-scale thermal-hydraulics analysis with JUPITER by modeling the internal structure of the debris which may consist of a porous medium. Therefore, it is possible to analyze the heat transfer of the porous medium by adding porous models to JUPITER. In this study, we report the validation of JUPITER applied the porous model and discuss which heat transfer models are most effective in porous models such as series, parallel and geometric mean models. To obtain validation data of JUPITER for the natural convective heat transfer analysis around the porous medium, we performed the heat transfer and the flow visualization experiments of the natural convection in the experimental system including the porous medium. In the comparison between the experiment and the numerical analysis with each model, the numerical result with the geometric mean model was the closest of the models to the experimental results. However, the numerical results of the temperature and the velocity were overestimated for those experimental results. In particular, the temperature near the interface between the porous medium and air was more overestimated.

Journal Articles

Double diffusive dissolution model of UO$$_{2}$$ pellet in molten Zr cladding

Ito, Ayumi*; Yamashita, Susumu; Tasaki, Yudai; Kakiuchi, Kazuo; Kobayashi, Yoshinao*

Journal of Nuclear Science and Technology, 60(4), p.450 - 459, 2023/04

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

JAEA Reports

Development of a test method for electrochemical measurements of stainless steel in nitric acid solution containing neptunium-237 under gamma-ray irradiation

Yamashita, Naoki; Irisawa, Eriko; Kato, Chiaki; Sano, Naruto; Tagami, Susumu

JAEA-Technology 2022-035, 29 Pages, 2023/03

JAEA-Technology-2022-035.pdf:2.54MB

In the treatment process of the current commercial reprocessing plant (Rokkasho Reprocessing Plant), the high-level liquid waste concentrator is the equipment that treats the most corrosive solution. In the high-level liquid waste concentrator, the extracted liquid waste after separation of uranium and plutonium is heated, concentrated, and reduced in volume. Therefore, the amount of gamma- rays emitted from fission products and the concentration of corrosive metal ion species such as neptunium-237 ($$^{237}$$Np) are the highest in the reprocessing process, and the amount of corrosion in the high-level liquid waste concentrate canner is expected to be large. In this study, in order to clarify the effect of gamma-rays on the corrosion reaction of stainless steel in nitric acid solutions containing $$^{237}$$Np from the electrochemical viewpoint, the corrosion test apparatus for heat transfer surfaces in an airtight concrete cell at the Waste Safety TEsting Facility (WASTEF) of Nuclear Science Research Institute was modified to enable electrochemical measurements under gamma-ray irradiation. The effect of gamma-rays on the corrosion reaction taking place on the stainless steel surface was discussed from the electrochemical test results obtained. As a result, changes in the immersion potentials of stainless steel and the polarization curves due to chemical species caused by radiolysis of gamma-ray irradiation were confirmed.

JAEA Reports

R&D and maintenance management of the WASTEF Facility (FY2021)

Sano, Naruto; Yamashita, Naoki; Hoshino, Kazutoyo*; Tsukada, Manabu*; Sawauchi, Fumiya*; Otake, Yoshinori; Ichise, Kenichi; Tagami, Susumu

JAEA-Technology 2022-034, 47 Pages, 2023/03

JAEA-Technology-2022-034.pdf:2.81MB

The Waste Safety Testing Facility (WASTEF) was established in 1982 as an experimental facility for long-term storage of solidified high-level radioactive waste generated in the reprocessing of spent light water reactor fuel and the subsequent safety assessment of geological disposal. It is a historic facility that started operation in 1982. This facility consists of 5 concrete cells, 1 lead cell, 6 glove boxes, and 7 hoods, and is a large-scale facility that can use nuclear fuel materials including uranium and plutonium and radioactive isotopes including TRU. In this facility, research and development requested by the research department is carried out in the Hot Material Examination Section. In addition, patrol inspections, self-inspections, etc. are also carried out as maintenance management based on safety regulations. This report summarizes the overview of WASTEF facilities, the results of operation, maintenance and management work in FY2021, and the future outlook.

Journal Articles

Benchmark simulation code for the thermal-hydraulics design tool of the accelerator-driven system; Validation and benchmark simulation of flow behavior around the beam window

Yamashita, Susumu; Kondo, Nao; Sugawara, Takanori; Monji, Hideaki*; Yoshida, Hiroyuki

Journal of Nuclear Science and Technology, 22 Pages, 2023/00

To confirm the validity of the thermal-hydraulics design tool based on the Ansys Fluent, we used a detailed computational fluid dynamics code named JAEA Utility Program for Interdisciplinary Thermal-hydraulics Engineering and Research (JUPITER) for the thermal-hydraulics around the beam window (BW) of the Accelerator-Driven System (ADS). The Fluent uses the Reynolds-Averaged Navier-Stokes (RANS) model and can quickly calculate the turbulent flow around the BW as a BW design tool. At first, we compared the results of JUPITER with the experimental results using a mock-up BW system in water to confirm the validity of JUPITER. As a result, we confirmed that numerical results are in good agreement with the experimental results. Thus, we showed that JUPITER could be used as a benchmark code. We also performed a benchmark simulation for the Fluent calculation using validated JUPITER to show the applicability of JUPITER as an alternative of experiments. As a result, the mean values around the BW agreed with each other, e.g., the mean velocity profile for stream and horizontal directions. Therefore, we confirmed that JUPITER showed a good performance in validating the thermal-hydraulics design tool as a fluid dynamics solver. Moreover, Fluent has enough accuracy as a thermal-hydraulics design tool for the ADS.

Journal Articles

Gas-liquid two-phase flow analysis using multi-phase field method

Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro; Yamashita, Susumu

Dai-36-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (Internet), 5 Pages, 2022/12

The conventional Allen-Cahn type multi-phase field method was modified to conserve not only the sum of the masses of all phases but also the mass of each phase. The interface advection calculations within a two-dimensional rotational velocity field were performed as a verification problem, and the conservation was successfully achieved. The proposed method was used to calculate the horizontally aligned pair of bubbles rising, and it was found that the bouncing phenomenon between bubbles can be calculated at 1/50 resolution of the high-resolution calculation by Zhang et al. using the volume of fluid method.

Journal Articles

A Numerical simulation method to evaluate heat transfer of fuel debris in air cooling by JUPITER, 1; Project overview and the applicability to the actual reactor system

Yamashita, Susumu; Uesawa, Shinichiro; Ono, Ayako; Yoshida, Hiroyuki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 8 Pages, 2022/10

no abstracts in English

Journal Articles

A Numerical simulation method to evaluate heat transfer of fuel debris in air cooling by JUPITER, 2; Validation of porous model for natural convective heat transfer

Uesawa, Shinichiro; Yamashita, Susumu; Shibata, Mitsuhiko; Yoshida, Hiroyuki

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 8 Pages, 2022/10

Journal Articles

Vibration of cantilever by jet impinging in axial direction

Tobita, Daiki*; Monji, Hideaki*; Yamashita, Susumu; Horiguchi, Naoki; Yoshida, Hiroyuki; Sugawara, Takanori

Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 5 Pages, 2022/10

Journal Articles

Development of the simplified boiling model applied to the large-scale detailed simulation

Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-13) (Internet), 12 Pages, 2022/09

Japan Atomic Energy Agency is developing the computational fluid dynamics code, JUPITER, based on the volume of fluid (VOF) method to analyze detailed thermal-hydraulics in a reactor. The detailed numerical simulation of boiling from a heating surface needs a substantial computational cost to resolve the microscale thermal-hydraulic phenomena such as the bubble generation from a cavity and evaporation of a micro-layer. This study developed the simplified boiling model from the heating surface to reduce the computational cost, which will apply to the detailed simulation code based on the surface tracking method such as JUPITER. We applied the simplified boiling model to JUPITER, and compared the simulation results with the experimental data of the vertical heating surface in the forced convection. We confirmed the degree of their reproducibility, and the issues to be modified were extracted.

Journal Articles

Development of the simplified boiling model applied for the large scale simulation by the detailed two-phase flow analysis based on the surface tracking

Ono, Ayako; Yamashita, Susumu; Sakashita, Hiroto*; Suzuki, Takayuki*; Yoshida, Hiroyuki

Dai-26-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 4 Pages, 2022/07

JAEA is implementing a simulation of a two-phase flow in the reactor core by TPFIT and JUPITER which are developed by JAEA based on the surface tracking method. However, it is impossible to simulate a boiling on the heating surface in the large-scale domain by this type of simulation method since the simulation of boiling based on the surface tracking method needs the fine mesh which sufficiently resolves the initiation of boiling. Therefore, JAEA started to develop the simplified boiling model applied for the two-phase flow in the fuel assemblies. In this study, the simulation results of the convection boiling on a vertical heating surface and the comparison between the simulation results and experimental results are shown.

Journal Articles

Optimization of phase field variables in gas-liquid two-phase flow problems

Sugihara, Kenta; Onodera, Naoyuki; Idomura, Yasuhiro; Yamashita, Susumu

Keisan Kogaku Koenkai Rombunshu (CD-ROM), 27, 5 Pages, 2022/06

The phase-field method has been successfully applied to various multi-phase flow problems as an interface tracking method for gas-liquid interfaces. However, the accuracy of the phase-field method depends on hyper-parameters, which are empirically adjusted for each problem. The phase-field method sustains sharp interfaces by the balance between the numerical viscosity of the advection term and the interface modification by the diffusion and anti-diffusion terms. Based on this fact, we propose a method for deriving the optimal hyper-parameters in a non-empirical manner by performing a basic error analysis of the interface advection.

Journal Articles

Numerical simulation of two-phase flow in fuel assemblies with a spacer grid using a mechanistically based method

Ono, Ayako; Yamashita, Susumu; Suzuki, Takayuki*; Yoshida, Hiroyuki

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 16 Pages, 2022/03

JAEA is developing the methodology to predict the critical heat flux based on a mechanism in order to reduce the cost for full mock-up test. The evaluation method based on a mechanism is expected to be able to predict in the wide range of parameter under the unexpected conditions including the severe accident. In this study, the JUPITER code developed by JAEA is examined to apply for the two-phase flow simulation of LWR fuel assembly with the spacer grid. The benchmark data of single-phase flow in the bundle with the spacers by KAERI were used to validate the simulation result by JUPITER. Moreover, the single-phase flow simulation was conducted by another simulation method, STAR-CCM+, as a supplemental analysis to consider the effect of the different simulation methods. Finally, the two-phase flow simulation for the bundle with the spacer was conducted by JUPITER. The effect of the spacer with a vane on the bubble behavior is discussed.

Journal Articles

Iterative methods with mixed-precision preconditioning for ill-conditioned linear systems in multiphase CFD simulations

Ina, Takuya*; Idomura, Yasuhiro; Imamura, Toshiyuki*; Yamashita, Susumu; Onodera, Naoyuki

Proceedings of 12th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems ScalA21) (Internet), 8 Pages, 2021/11

 Times Cited Count:0 Percentile:51.94

A new mixed-precision preconditioner based on the iterative refinement (IR) method is developed for preconditioned conjugate gradient (P-CG) and multigrid preconditioned conjugate gradient (MGCG) solvers in a multi-phase thermal-hydraulic CFD code JUPITER. In the IR preconditioner, all data is stored in FP16 to reduce memory access, while all computation is performed in FP32. The hybrid FP16/32 implementation keeps the similar convergence property as FP32, while the computational performance is close to FP16. The developed solvers are optimized on Fugaku (A64FX), and applied to ill-conditioned matrices in JUPITER. The P-CG and MGCG solvers with the new IR preconditioner show excellent strong scaling up to 8,000 nodes, and at 8,000 nodes, they are respectively accelerated up to 4.86$$times$$ and 2.39$$times$$ from the conventional ones on Oakforest-PACS (KNL).

Journal Articles

Summary results of subsidy program for the "Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy and Thermal Behavior Estimation of Fuel Debris))"

Koyama, Shinichi; Nakagiri, Toshio; Osaka, Masahiko; Yoshida, Hiroyuki; Kurata, Masaki; Ikeuchi, Hirotomo; Maeda, Koji; Sasaki, Shinji; Onishi, Takashi; Takano, Masahide; et al.

Hairo, Osensui Taisaku jigyo jimukyoku Homu Peji (Internet), 144 Pages, 2021/08

JAEA performed the subsidy program for the "Project of Decommissioning and Contaminated Water Management (Development of Analysis and Estimation Technology for Characterization of Fuel Debris (Development of Technologies for Enhanced Analysis Accuracy and Thermal Behavior Estimation of Fuel Debris))" in 2020JFY. This presentation summarized briefly the results of the project, which will be available shortly on the website of Management Office for the Project of Decommissioning and Contaminated Water Management.

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