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Journal Articles

GPU-acceleration of locally mesh allocated two phase flow solver for nuclear reactors

Onodera, Naoyuki; Idomura, Yasuhiro; Ali, Y.*; Yamashita, Susumu; Shimokawabe, Takashi*; Aoki, Takayuki*

Proceedings of Joint International Conference on Supercomputing in Nuclear Applications + Monte Carlo 2020 (SNA + MC 2020), p.210 - 215, 2020/10

This paper presents a GPU-based Poisson solver on a block-based adaptive mesh refinement (block-AMR) framework. The block-AMR method is essential for GPU computation and efficient description of the nuclear reactor. In this paper, we successfully implement a conjugate gradient method with a state-of-the-art multi-grid preconditioner (MG-CG) on the block-AMR framework. GPU kernel performance was measured on the GPU-based supercomputer TSUBAME3.0. The bandwidth of a vector-vector sum, a matrix-vector product, and a dot product in the CG kernel gave good performance at about 60% of the peak performance. In the MG kernel, the smoothers in a three-stage V-cycle MG method are implemented using a mixed precision RB-SOR method, which also gave good performance. For a large-scale Poisson problem with $$453.0 times 10^6$$ cells, the developed MG-CG method reduced the number of iterations to less than 30% and achieved $$times$$ 2.5 speedup compared with the original preconditioned CG method.

Journal Articles

Development and validation of the eutectic reaction model in JUPITER code

Chai, P.; Yamashita, Susumu; Yoshida, Hiroyuki

Annals of Nuclear Energy, 145, p.107606_1 - 107606_13, 2020/09

 Times Cited Count:0 Percentile:100(Nuclear Science & Technology)

The eutectic reaction model in JUPITER code was validated against two series of experimental tests that performed by JAEA. An experiment that aimed to evaluate the eutectic reaction between Zircaloy and Stainless steel, was simulated by JUPITER code to validate its reliability on predicting the binary eutectic reaction phenomenon. A comparison of the simulation and experimental results demonstrates good agreement on the increase rate of the solution depth at various temperature environments. Another series of tests which aimed to predict the eutectic reaction between the control rod blade and channel box in BWR, were simulated by JUPITER code to test its applicability on predicting the eutectic reaction between multiple mixture components. Although the deviation could not be completely eliminated, the reaction performance in the experiment was reasonably reproduced. As a result, it could be concluded that JUPITER code is feasible to predict the eutectic reaction behavior in nuclear severe accident.

Journal Articles

Communication avoiding multigrid preconditioned conjugate gradient method for extreme scale multiphase CFD simulations

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

Supa Kompyuthingu Nyusu, 22(5), p.18 - 29, 2020/09

A communication avoiding multigrid preconditioned conjugate gradient method (CAMGCG) is applied to the pressure Poisson equation in a multiphase CFD code JUPITER, and its computational performance and convergence property are compared against the conventional Krylov methods. The CAMGCG solver has robust convergence properties regardless of the problem size, and shows both communication reduction and convergence improvement, leading to higher performance gain than CA Krylov solvers, which achieve only the former. The CAMGCG solver is applied to extreme scale multiphase CFD simulations with 90 billion DOFs, and its performance is compared against the preconditioned CG solver. In this benchmark, the number of iterations is reduced to $$sim 1/800$$, and $$sim 11.6times$$ speedup is achieved with keeping excellent strong scaling up to 8,000 nodes on the Oakforest-PACS.

Journal Articles

A Numerical simulation method for core internals behavior in severe accident conditions; Chemical reaction analyses in core structures by JUPITER

Yamashita, Susumu; Kino, Chiaki*; Yoshida, Hiroyuki

Proceedings of 2020 International Conference on Nuclear Engineering (ICONE 2020) (Internet), 7 Pages, 2020/08

In order to contribute the improvement of estimation accuracy for severe accident code such as SAMPSON, we have developed the chemical reaction model such as eutectic reaction and oxidation in micro scale, e.g., B$$_{4}$$C-SUS in the control rod blade and UO$$_{2}$$-Zry in fuel rods, and implemented them to the computational fluid dynamics code named JUPITER. And we try to develop the coupled analysis frame work using SAMPSON and JUPITER to decrease uncertainty due to micro scale phenomena which cannot be calculate by severe accident analysis codes. From the preliminary analysis in fuel rod heating analysis by JUPITER using SAMPSON output data, it was revealed that the implemented chemical reaction models work stably and obtain reasonable results.

Journal Articles

Locally mesh-refined lattice Boltzmann method for fuel debris air cooling analysis on GPU supercomputer

Onodera, Naoyuki; Idomura, Yasuhiro; Uesawa, Shinichiro; Yamashita, Susumu; Yoshida, Hiroyuki

Mechanical Engineering Journal (Internet), 7(3), p.19-00531_1 - 19-00531_10, 2020/06

A dry method is one of practical methods for decommissioning the TEPCO's Fukushima Daiichi Nuclear Power Station. Japan Atomic Energy Agency (JAEA) has been evaluating the air cooling performance of the fuel debris by using the JUPITER code based on an incompressible fluid model and the CityLBM code based on the lattice Boltzmann method (LBM). However, these codes were based on a uniform Cartesian grid system, and required large computational time and cost to capture complicated debris structures. We develop an adaptive mesh refinement (AMR) version of the CityLBM code on GPU based supercomputers and apply it to thermal-hydrodynamics problems. The proposed method is validated against free convective heat transfer experiments at JAEA. It is also shown that the AMR based CityLBM code on 4 NVIDIA TESLA V100GPUs gives 6.7x speedup of the time to solution compared with the JUPITER code on 36 Intel Xeon E5-2680v3 CPUs.

Journal Articles

Numerical simulation of two-phase flow in 4$$times$$4 simulated bundle

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

Mechanical Engineering Journal (Internet), 7(3), p.19-00583_1 - 19-00583_12, 2020/06

JAEA is implementing the 3D detailed nuclear-thermal-coupled analysis code to analyze the transition state of the core and to reduce the likelihood of the design. In the development plan, the computational fluid dynamics code based on the VOF method, JUPITER, is applied for TH part of the 3D detailed nuclear-thermal-coupled analysis code.

Journal Articles

Development of numerical simulation method to evaluate detailed thermal-hydraulics around beam window in ADS

Yamashita, Susumu; Sugawara, Takanori; Yoshida, Hiroyuki

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 7 Pages, 2019/12

In order to simulate detailed flow behavior of LBE around the beam window, a numerical simulation code that can evaluate the complicated flow behavior is required. To simulate complicated and large-scale flow behavior, we apply JUPITER which originally developed in JAEA for melt relocation behavior in SAs and that can treat complicated flow behavior and has a capacity of massively parallel computing. In this paper, by using JUPITER, numerical simulations were performed for unsteady thermal-hydraulics simulation around the beam window to know tendency of LBE flow field. In addition, problems to be solved and important parameters to simulate thermal-hydraulic behavior around the beam window will be discussed.

Journal Articles

Study on the two-phase flow in simulated LWR fuel bundle by CFD code

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

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.666 - 677, 2019/08

An evaluation methodology of critical heat fluxes (CHFs) based on a mechanism for fuel assemblies in light water reactors (LWRs) is needed in order to design and evaluate the safety for the fuel assemblies in LWRs. In our study, the numerical simulation with surface-tracking will be applied for the two-phase flow in fuel assemblies in order to obtain the detail data relating to the size and velocity of bubbles in the subchannel, which is needed to predict the CHF based on the mechanism. In this study, the numerical simulation of two-phase flow in 4$$times$$4 bundle was implemented by using JUPITER in order to establish the evaluation method of the size and velocity of bubbles by the numerical simulation, which is the multi-physics simulation code and enable to track the gas-liquid surface. The simulation results are validated by the curve of flow regime for air-water under the adiabatic condition. The bubble and velocity of bubbles obtained by simulation results are analyzed.

Journal Articles

Fuel debris' air cooling analysis using a lattice Boltzmann method

Onodera, Naoyuki; Idomura, Yasuhiro; Kawamura, Takuma; Uesawa, Shinichiro; Yamashita, Susumu; Yoshida, Hiroyuki

Proceedings of 27th International Conference on Nuclear Engineering (ICONE-27) (Internet), 6 Pages, 2019/05

A dry method is one of practical methods for decommissioning the TEPCO's Fukushima Daiichi Nuclear Power Station. Japan Atomic Energy Agency (JAEA) has been evaluating the air cooling performance by using the JUPITER code. However, the JUPITER code requires a large computational cost to capture debris' structures. To accelerate such CFD analyses, we use the CityLBM code, which is based on the lattice Boltzmann method (LBM) and is highly optimized for GPUs. The CityLBM code is validated against free convective heat transfer experiments at JAEA, and the similar accuracy as the JUPITER code is confirmed regarding the prediction capability of heat transfer and the resulting temperature distributions. It is also shown that the elapse time of a CityLBM simulation on GPUs is reduced to 1/6 compared with that of the corresponding JUPITER simulation on CPUs with the same number of GPUs and CPUs. The results show that the LBM is promising for accelerating thermal convective simulations.

Journal Articles

Validation and verification for the melting and eutectic models in JUPITER code

Chai, P.; Yamashita, Susumu; Nagae, Yuji; Kurata, Masaki

Proceedings of 9th Conference on Severe Accident Research (ERMSAR 2019) (Internet), 14 Pages, 2019/03

In order to obtain a precise understanding of molten material behavior inside RPV and to improve the accuracy of the SA code, a new computational fluid dynamics (CFD) code with multi-phase, multi-physics models, which is called JUPITER, was developed. It optimized the algorithms of the multi-phase calculation. Besides, the chemical reactions are also modeled carefully in the code so that the melting process could be treated precisely. A series of verification and validation studies are conducted, which show good agreement with analytical solutions and previous experiments. The capabilities of the multi-physics models in JUPITER code provide us another useful tool to investigate the molten material behaviors in the relevant severe accident scenario.

Journal Articles

Coupled analysis of fuel debris distribution and recriticality by both multiphase/multicomponent flow and continuous energy neutron transport Monte Carlo simulations

Yamashita, Susumu; Tada, Kenichi; Yoshida, Hiroyuki; Suyama, Kenya

Nippon Genshiryoku Gakkai Wabun Rombunshi, 17(3/4), p.99 - 105, 2018/12

In order to reveal melt relocation behaviors of core internals phenomenologically and to reduce the uncertainties of the melt relocation analysis in existing SA analysis codes, in JAEA, the numerical simulation code for melt relocation and accumulation behaviors based on computational fluid dynamics named JUPITER has been developed. In this paper, to consider the estimation method for fuel debris composition and its re-criticality, we performed the melt accumulating and spreading simulation to the pedestal region by JUPITER and also performed re-criticality analysis by Monte Carlo Codes for Neutron Transport Calculations based on Continuous Energy and Multi-group Methods (MVP) using detailed fuel debris composition data obtained by JUPITER. From the coupled analysis on fuel debris distribution by JUPITER and MVP, we had prospects for a detailed possibility of re-criticality of fuel debris with detailed fuel debris distribution.

Journal Articles

Free convective heat transfer experiment to validate air-cooling performance analysis of fuel debris

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

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 6 Pages, 2018/11

Journal Articles

Numerical simulation of thermal hydraulics around a beam window in accelerator-driven system

Yamashita, Susumu; Yoshida, Hiroyuki

Proceedings of 11th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS-11) (Internet), 5 Pages, 2018/11

To investigate detailed flow behaviors around the beam window of accelerator driven system (ADS), large scale simulation for unsteady thermal hydraulics around the beam window was performed using JUPITER. The input data, such as the beam window and nozzle, is designed as accurate as possible using the computer aided design software. As a result, the flow pattern around the beam window is quite different from previous results in which the steady flow is assumed. The flow pattern of the Lead-Bismuth Eutectic around the beam window and the exit of the nozzle were very complicated. According to complicated flow around those structures, the temperature distribution on the beam window is also complicated. Thus, it is confirmed that the complicated flow around structures will affect to the temperature distribution in the structures and the effect of flow field on the temperature must be evaluated.

Journal Articles

Communication avoiding multigrid preconditioned conjugate gradient method for extreme scale multiphase CFD simulations

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

Proceedings of 9th Workshop on Latest Advances in Scalable Algorithms for Large-Scale Systems (ScalA 2018) (Internet), p.17 - 24, 2018/11

 Times Cited Count:0 Percentile:100

A communication avoiding (CA) multigrid preconditioned conjugate gradient method (CAMGCG) is applied to the pressure Poisson equation in a multiphase CFD code JUPITER, and its computational performance and convergence property are compared against CA Krylov methods. In the JUPITER code, the CAMGCG solver has robust convergence properties regardless of the problem size, and shows both communication reduction and convergence improvement, leading to higher performance gain than CA Krylov solvers, which achieve only the former. The CAMGCG solver is applied to extreme scale multiphase CFD simulations with $$sim 90$$ billion DOFs, and it is shown that compared with a preconditioned CG solver, the number of iterations is reduced to $$sim 1/800$$, and $$sim 11.6times$$ speedup is achieved with keeping excellent strong scaling up to 8,000 nodes on the Oakforest-PACS.

Journal Articles

Development of numerical simulation method to evaluate molten material behaviors in nuclear reactors

Yamashita, Susumu; Yoshida, Hiroyuki

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 12 Pages, 2018/10

In order to simulate the relocation phenomena phenomenologically around the reactor core and inside pedestal without assumptions, inputted information, empirical knowledge and given scenarios, a numerical simulation code based on computational fluid dynamics, JUPITER, that can phenomenologically evaluate the melting phenomena has been developed in JAEA. We confirm the applicability of JUPITER to the corium spreading process inside the pedestal by simulating corium spreading behaviors and its distributions under several parameters such as the corium inflow condition. And we investigated detailed fuel debris distribution inside the pedestal and the cavity named sump pit located on the lower part of PCVs, that is distribution for each component of core materials such as stainless steel (SUS), bron carbide (B$$_{4}$$C), zircaloy (Zry) and uranium dioxide (UO$$_{2}$$). As a result, since JUPITER uses interface capturing scheme which can treat complicated behavior of interfaces such as a large deformation and a complicated separation among interfaces, the corium was spread with complicated mixing behavior and the distribution of fuel debris tend to accumulate complicatedly inside sump pits. Since existing SA analysis codes difficult to treat such complicated phenomena and the complicated fuel distribution, those result might be contributed to an understanding of circumstances inside PCV and, ultimately, also contributed to reactor decommissioning process.

Journal Articles

Validation of free-convective heat transfer analysis with JUPITER to evaluate air-cooling performance of fuel debris in dry method

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

Mechanical Engineering Journal (Internet), 5(4), p.18-00115_1 - 18-00115_13, 2018/08

Journal Articles

Development of numerical simulation method to evaluate molten material behaviors in nuclear reactors; Estimation of fuel debris distribution in the pedestal

Yamashita, Susumu; Yoshida, Hiroyuki

Proceedings of 26th International Conference on Nuclear Engineering (ICONE-26) (Internet), 6 Pages, 2018/07

Journal Articles

Large-scale simulations on molten material behavior in severe accidents of nuclear reactors

Yamashita, Susumu; Ina, Takuya*; Idomura, Yasuhiro; Yoshida, Hiroyuki

Dai-31-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (DVD-ROM), 7 Pages, 2017/12

no abstracts in English

Journal Articles

A Numerical simulation method for molten material behavior in nuclear reactors

Yamashita, Susumu; Ina, Takuya; Idomura, Yasuhiro; Yoshida, Hiroyuki

Nuclear Engineering and Design, 322, p.301 - 312, 2017/10

 Times Cited Count:13 Percentile:7.51(Nuclear Science & Technology)

In recent years, significant attention has been paid to the precise determination of relocation of molten materials in reactor pressure vessels of boiling water reactors (BWRs) during severe accidents. To address this problem, we have developed a computational fluid dynamics code JUPITER, based on thermal-hydraulic equations and multi-phase simulation models. Although the Poisson solver has previously been a performance bottleneck in the JUPITER code, this is resolved by a new hybrid parallel Poisson solver, whose strong scaling is extended up to $$sim$$200k cores on the K-computer. As a result of the improved computational capability, the problem size and physical models are dramatically expanded. A series of verification and validation studies are enabled, which are in agreement with previous numerical simulations and experiments. These physical and computational capabilities of JUPITER enable us to investigate molten material behaviors in reactor relevant situations.

Journal Articles

Development of numerical simulation method to evaluate heat transfer performance of air around fuel debris, 1; Effect of the debris shape

Yamashita, Susumu; Uesawa, Shinichiro; Yoshida, Hiroyuki

Proceedings of 25th International Conference on Nuclear Engineering (ICONE-25) (CD-ROM), 8 Pages, 2017/07

101 (Records 1-20 displayed on this page)