Development of the multi-physics simulation platform JAMPAN

Kamiya, Tomohiro; Kondo, Ryoichi; Fukuda, Takanari; Fukuda, Kodai; Tada, Kenichi; Ono, Ayako; Nagaya, Yasunobu; Yoshida, Hiroyuki

JAEA-Data/Code 2025-021, 28 Pages, 2026/03

JAEA-Data-Code-2025-021.pdf:1.39MB

Japan Atomic Energy Agency has developed a high-fidelity multi-physics platform JAMPAN for connecting single-physics codes such as a neutronics code and a thermal-hydraulics code. It consists of the HDF5 formatted data container and input/output data handler modules to generate the input file and read the output file of the single-physics codes. Users can easily add or exchange the code by implementing input and output data handler modules for this code. JAMPAN is equipped with interfaces compatible with the neutronics code MVP and the thermal-hydraulics codes JUPITER, ACE-3D, and NASCA, enabling neutronics and thermal-hydraulics coupling calculations to provide reference solutions for core analysis codes. Users can select the thermal-hydraulics code depending on the required calculation accuracy. In addition, the fuel rod properties can be calculated using FEMAXI. This report explains the overview of JAMPAN.

Evaluation of interface capturing schemes of VOF method through application to bubble flow with single orifice

Fukuda, Takanari; Yamashita, Susumu; Yoshida, Hiroyuki

Journal of Nuclear Science and Technology, 62(12), p.1264 - 1278, 2025/12

https://doi.org/10.1080/00223131.2025.2581248

This study compared three interface capturing schemes (ICSs) for multi-phase flow simulations based on the VOF method, focusing on bubble volume conservation. The THINC/WLIC scheme showed significant VOF diffusion and underestimated total bubble volume, while the original THINC and PLIC conserved bubble volumes. Moreover, an analysis of THINC/WLIC based on a new visualization approach revealed that VOF fragments were ripped off by shear forces around interface, making it unsuitable for accurate void fraction prediction in boiling water reactors. The original THINC may be a viable alternative to PLIC due to its simplicity.

A Comparative study on the interfacial tension models of the particle method for the liquid-liquid-gas three-phase flow

Fukuda, Takanari

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 10 Pages, 2024/11

Deepening the understanding of the molten core-concrete interaction (MCCI) is of the great importance for the sake of the severe accident managements as well as the fuel debris retrieval. Due to the difficulty to perform the experimental study with the extremely hot corium, the computational fluid dynamics (CFD) is expected to provide physical insights on the thermal-hydraulics taken place in the corium. The particle method are one of the CFDs that have advantages on seamless tracking of the multi-phase multi-component flow, typically involved in the MCCI. However, the adequacy of the modelling methods for the interfacial tension has not yet well investigated, especially for the general multi-phase flow with more than three phases. Hence, in this study, a simple liquid-liquid-gas three phase flow is analyzed with the existing two types of the interfacial tension models: the continuum surface force (CSF) model and the potential model. Through the comparison, it has been implied that the CSF model gives more accurate result with the satisfactory resolution, whereas the stability is strongly dependent on the resolution of the bulk fluid. On the other hand, the potential model outperforms in terms of the stability, presumably because it does not require the numerical estimation of the geometrical information. However the inter-particle potential force seems to induces locally unphysical pressure distribution, which can be especially detrimental on the multiple interface junctions.

Evaluation of the THINC/AWLIC scheme for two-phase flow in pin bundle geometry

Fukuda, Takanari; Uesawa, Shinichiro; Yamashita, Susumu; Yoshida, Hiroyuki

no journal, , 

The volume of fluid (VOF) method is a prominent multiphase flow simulation method. Among different interface capturing schemes (ICSs) in the VOF method, the algorithm of the piecewise linear interface calculation (PLIC) is geometrically rigrous but complex to implement. In contrast, the tangent of hyperbola interface capturing/weighted line interface calculation (THINC/WLIC) offers a simpler algorithm but suffers from numerical diffusion, degrading interface quality. To address this tradeoff, we developed THINC/Advanced WLIC (THINC/AWLIC), which balances implementation cost and interface sharpness. Although these ICSs have undergone numerical benchmarking, their performance in practival engineering conditions has not been sufficiently investigated. To evaluate their applicability to boiling water reactor (BWR) core flows, a liquid-gas two-phase flow in a pin bundle geometry was simulated using PLIC, THINC/WLIC, and THINC/AWLIC, and compared with the void fraction data obtained by an experiment. The notable result is that the void fraction values for simply coded THINC/AWLIC are nearly identical with those of PLIC, which maximizes the geometrical fidelity with the expense of the algorithmic complexity. The results indicate the generally high applicability of THINC/AWLIC in predicting void fraction in pin bundle geometry and its advantages over conventional ICSs. However, regardless of ICSs, the simulation based on the VOF method still fails to reproduce experimental void fraction at low gas flow rates, where bubble coalescence is minimal in experiment.

Development of advanced neutronics/thermal-hydraulics coupling simulation system, 12; BWR whole core coupling calculations using MVP/NASCA

Tada, Kenichi; Kondo, Ryoichi; Kamiya, Tomohiro; Fukuda, Takanari; Ono, Ayako; Nagaya, Yasunobu; Yoshida, Hiroyuki

no journal, , 

JAEA has developed the multi-physics platform JAMPAN. In the previous presentation, we implemented the flow rate calibration function to JAMPAN for the MVP/NASCA coupling calculation of the BWR multi-fuel assembly geometry. Using this function, we performed the whole core coupling calculation using MVP/NASCA. For the whole BWR calculations, we prepared two types of input files. One is the hypothetical whole core geometry consisting of a 99 fuel assembly obtained from the OECD/NEA Phase-3C benchmark. The other is the initial loading core of Peach Bottom unit 2 obtained from the OECD/NEA Peach Bottom turbine trip benchmark. We will show the results of both whole-core BWR coupling calculations in the present presentation.

Investigation of the applicability of detailed two-phase flow simulation for void fraction distribution in a 33 rod bundle geometry

Fukuda, Takanari; Uesawa, Shinichiro; Yamashita, Susumu; Yoshida, Hiroyuki

no journal, , 

In the anticipation of more extensive application of JAEA's detailed multi-phase flow simulation code JUPITER for reactor core flow, the code was applied in bubbly and churn flows in a 33 pin bundle modeling a BWR fuel assembly. Three interface capturing methods were tested: PLIC (high accuracy), THINC/WLIC (low computational cost), and THINC/AWLIC (a balanced approach). For churn flow, all methods reproduced experimental void fractions well provided sufficient resolutions. However, THINC/WLIC showed numerical diffusion at coarse resolution, making void frection prediction unreliable. For bubbly flow, on the other hand, none of the methods accurately reproduced void fractions due to numerical bubble coalescence.

Development of fluid-rigid strongly coupled particle method for the estimation of the relocation behavior of damaged in-core structures

Fukuda, Takanari; Yoshida, Hiroyuki

no journal, , 

The presenters have developed a new fluid-rigid coupled particle method for the estimation of the relocation of in-core structures mechanically interacting with fluid phases existing in a reactor. Amid a severe accident, there might exist relatively large in-core structure, the scale of which is comparable to that of the maximum spatial scale of the fluid (e.g. scale of containment vessel). Such a calculation configuration can result in numerical instability with the conventional fluid-rigid weakly coupled methods. Hence, we have derived fluid-rigid strongly coupled time-development equations on the basis of Hamilton's least action principle and developed a new particle method for solving those equations numerically.

Development of advanced neutronics/thermal-hydraulics coupling simulation system, 13; BWR fuel assembly calculation with MVP/ACE-3D

Fukuda, Takanari; Yoshida, Hiroyuki; Kamiya, Tomohiro; Suzuki, Takayuki*; Tada, Kenichi; Nagaya, Yasunobu

no journal, , 

JAEA has been engaged in the development of JAMPAN, a platform for multi-physics simulations, to enable the numerical simualtons for enhancing the quality and safety of the light water reactor design. In this study, ACE-3D, which is based on a three-dimensional two-fluid model capable of general-purpose multidimensional thermal-hydraulic calculations, was selected as the thermal-hydraulic calculation code. Furthermore, a JAMPAN module was developed to facilitate a coupled MVP/ACE-3D neutronics/thermal-hydraulics simulation. In the presentation, the results of the simulation for an 88 BWR fuel assembly with JAMPAN will be presented.

Comparative evaluation of the interface capturing schemes in bundle bubbly flow

Fukuda, Takanari; Uesawa, Shinichiro; Yamashita, Susumu; Suzuki, Takayuki*

no journal, , 

Advancements in high-performance computing are enabling the application of computational fluid dynamics (CFD) to engineering-scale multi-phase flow problems. The volume of fluid (VOF) method, which tracks interface movement via scalar VOF value transport, is widely used in CFD. Among interface capturing schemes (ICSs), the piecewise linear interface calculation (PLIC) is the most geometrically accurate but computationally complex. In contrast, the tangent of hyperbola interface capturing/weighted line interface calculation (THINC/WLIC) offers a simpler algorithm but suffers from numerical diffusion, degrading interface quality. To address this tradeoff, we developed THINC/Advanced WLIC (THINC/AWLIC), which balances implementation cost and interface sharpness. Although these ICSs have undergone numerical benchmarking, their performance in complex engineering scenarios remains underexplored. To evaluate their applicability to boiling water reactor (BWR) core flows, a liquid-gas two-phase flow in a 33 bundle system experiment was simulated using PLIC, THINC/WLIC, and THINC/AWLIC. The results showed that PLIC and THINC/AWLIC maintained sharp interfaces and provided realistic results but required nearly three times the computational time of THINC/WLIC. While THINC/WLIC was computationally efficient, it exhibited qualitative discrepancies, including unphysical bubble coalescence and volume dissipation. This led to reduced void fractions near the pin-gap region due to fewer bubble coalescences, attributed to bubble size reduction from volume dissipation. A comparison between numerical simulations and experimental void fraction data will be presented to facilitate further discussion.