Investigating eutectic behavior and material relocation in BC-stainless steel composites using the improved MPS method

Ahmed, Z.*; Wu, S.*; Sharma, A.*; Kumar, R.*; Yamano, Hidemasa; Pellegrini, M.*; Yokoyama, Ryo*; Okamoto, Koji*

International Journal of Heat and Mass Transfer, 250, p.127343_1 - 127343_17, 2025/11

https://doi.org/10.1016/j.ijheatmasstransfer.2025.127343

Development of ARKADIA for the innovation of advanced nuclear reactor design process (Development of the design optimization support tool, ARKADIA-Design)

Tanaka, Masaaki; Doda, Norihiro; Hamase, Erina; Kuwagaki, Kazuki; Mori, Takero; Okajima, Satoshi; Kikuchi, Norihiro; Yoshimura, Kazuo; Matsushita, Kentaro; Hashidate, Ryuta; et al.

Nihon Kikai Gakkai Rombunshu (Internet), 91(943), p.24-00229_1 - 24-00229_12, 2025/03

https://doi.org/10.1299/transjsme.24-00229

To assist conceptual studies of various reactor systems conducted by private sectors in nuclear power innovation, an innovative design system named ARKADIA (Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle) has been developed. In this paper, focusing on the ARKADIA-Design, achievements in the development of optimization processes in the fields of the core design, the plant structure design, and the maintenance schedule planning, as major function of ARKADIA-Design, and numerical analysis methods including coupled analysis to be used for the detailed analysis to confirm the plant performance after optimization are introduced at this point in time.

Investigation of reactivity coefficient characteristics in actinide burning core concept for the future phaseout of a fast reactor fuel cycle

Mori, Tetsuya; Oki, Shigeo

Nuclear Technology, 20 Pages, 2025/00

https://doi.org/10.1080/00295450.2025.2472530

This study investigates the characteristics of the Doppler coefficient and sodium void reactivity of a burning fast reactor core concept, which was constructed in a previous study. This concept allows for multiple recyclings of plutonium and minor actinides (transuraniums (TRU)). TRU degradation due to multiple recycling deteriorates the reactivity coefficients through indirect effects, such as by hardening the neutron spectrum and steepening the energy gradient of neutron importance. Using silicon carbide (SiC) structural material improves the reactivity coefficient by causing an opposite indirect effect of TRU degradation. This improvement results not only from neutron spectrum softening due to the neutron moderation effect from C but also from the neutron leakage effect resulting from the low structural material density. The disadvantage of increased calculation uncertainty by using SiC structural material can be practically ignored. Furthermore, the burning core has Doppler coefficient enhancement characteristics by the moderated neutron reflection effect from outside the core. This characteristic has the potential to provide a new measure for reactivity coefficient deterioration due to TRU degradation. The reactivity coefficient characteristics clarified in this study can provide valuable knowledge for future detailed designs and design improvements of a TRU burning core.

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.

Validation study on SFR core bowing codes using Joyo ex-core experiment data; Single duct bowing benchmark

Ohgama, Kazuya; Doda, Norihiro; Uwaba, Tomoyuki; Futagami, Satoshi; Tanaka, Masaaki; Yamano, Hidemasa; Ota, Hirokazu*; Ogata, Takanari*; Wozniak, N.*; Shemon, E.*; et al.

Proceedings of International Conference on Nuclear Fuel Cycle (GLOBAL2024) (Internet), 4 Pages, 2024/10

To enhance the accuracy of the safety evaluations in sodium-cooled fast reactors, it is necessary to develop a method to realistically evaluate the reactivity caused by core deformation. In this regard, Japan and the United States jointly conducted a benchmark analysis of thermal bowing experiments of a single duct of Joyo-type fuel assembly. The aim was to confirm the validity of the core bowing analysis codes. Comparisons of analysis and test results revealed that the core bowing analysis codes used by both countries were able to reasonably predict the axial distribution of horizontal duct displacement of a single duct due to thermal bowing and the contact load on the duct pad.

Study on eutectic melting behavior of control rod materials in severe accidents of sodium-cooled fast reactors, 4; Analyzing Eutectic Melting and Relocation Dynamics in BC-stainless steel using the Moving Particle Semi-Implicit (MPS) Method

Ahmed, Z.*; Wu, S.*; Pellegrini, M.*; Okamoto, Koji*; Sharma, A.*; Yamano, Hidemasa

Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NTHOS-14) (Internet), 14 Pages, 2024/08

The analysis show that once eutectic reaction occurs, the boron diffuses into the stainless steel (SS) wall. Melting initiates at the BC and SS interface, with melt flow following SS cladding penetration. Also, we observed that as temperature rises, a proportional increase in the boron concentration within the melt. The updated MPS method indicated a computational capability of the eutectic reaction model used to effectively analyze control rod eutectic reactions, simulating severe accidents, and its subsequent relocation to understand the effect of BC ingress into the core.

Study on eutectic melting behavior of control rod materials in severe accidents of sodium-cooled fast reactors, 2; Modeling of multi-phase eutectic reaction behavior

Morita, Koji*; Yamano, Hidemasa

Proceedings of 14th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation, and Safety (NTHOS-14) (Internet), 12 Pages, 2024/08

This paper describes the generalized model developed for these eutectic reactions between boron carbide (BC) and stainless steel (SS) as well as for the reactions that occur between eutectic reaction products in the solid and liquid states and SS or BC. We also describe the thermophysical property model based on thermophysical property data.

Development of ARKADIA for the innovation of advanced nuclear reactor design process (Development status of the design optimization support tool, ARKADIA-Design)

Tanaka, Masaaki; Doda, Norihiro; Hamase, Erina; Kuwagaki, Kazuki; Mori, Takero; Okajima, Satoshi; Kikuchi, Norihiro; Yoshimura, Kazuo; Matsushita, Kentaro; Hashidate, Ryuta; et al.

Dai-28-Kai Doryoku, Enerugi Gijutsu Shimpojiumu Koen Rombunshu (Internet), 5 Pages, 2024/06

To assist conceptual studies of various reactor systems conducted by private sectors in nuclear power innovation, development of an innovative design system named ARKADIA (Advanced Reactor Knowledge- and AI-aided Design Integration Approach through the whole plant lifecycle) is undergoing. In this paper, focusing on the ARKADIA-Design, achievements in the development of optimization processes in the fields of the core design, the plant structure design, and the maintenance schedule planning, as major function of ARKADIA-Design, and numerical analysis methods to be used for the detailed analysis to confirm the plant performance after optimization are introduced at this point in time.

Study on the difference between BC powder and BC pellet regarding the eutectic reaction with stainless steel

Hong, Z.*; Ahmed, Z.*; Pellegrini, M.*; Yamano, Hidemasa; Erkan, N.*; Sharma, A. K.*; Okamoto, Koji*

Progress in Nuclear Energy, 171, p.105160_1 - 105160_13, 2024/06

https://doi.org/10.1016/j.pnucene.2024.105160

In this study, it is found that the eutectic reaction between BC powder and stainless steel (SS) is considerably more rapid than that between the BC pellet and SS. The derived reaction rate constant values for powder and pellet cases are consistently based on the reference values. Also, a composition analysis using SEM/EDS was conducted for the detailed microstructures of the powder and pellet samples. In the powder case, only one thick layer is found as the reaction layer consisting of (Fe, Cr)B precipitate, including BC powder. In the pellet case, two layers are found in the reaction layer.

Comparison on safety features among HTGR's Reactor Cavity Cooling Systems (RCCSs)

Takamatsu, Kuniyoshi; Funatani, Shumpei*

Nuclear Engineering and Technology, 56(3), p.832 - 845, 2024/03

https://doi.org/10.1016/j.net.2023.09.036

The objectives of this study are as follows: to understand the characteristics, degree of passive safety features for heat removal were compared for RCCSs based on atmospheric radiation and based on atmospheric natural circulation under the same conditions. Therefore, the authors concluded that the proposed RCCS based on atmospheric radiation has the advantage that the temperature of the RPV can be stably maintained against disturbances in the outside air (ambient air). Moreover, methodology to utilize all the heat emitted from the RPV surface for increasing the degree of waste-heat utilization was discussed.