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

A Preliminary study for boron mixing effect on severe accident scenario in sodium-cooled fast reactor

Yamano, Hidemasa; Morita, Koji*

Proceedings of 13th Korea-Japan Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS13) (Internet), 9 Pages, 2024/11

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.

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 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.

Visualization experiments of radiation heating on the eutectic reaction between BC-SS and its relocation behavior

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

Proceedings of Saudi International Conference On Nuclear Power Engineering (SCOPE2023) (Internet), 8 Pages, 2023/11

In this study, the eutectic behavior and subsequent melt structure of boron migration are observed by a quantitative and high-resolution visualization method using radiative heating. Experiments were conducted using B4C pellet and powder within SS tubes, replicating the actual control rod design in the temperature range of 1150C to 1372C to study long-duration melting and relocation behavior. The visualization technique accurately identified the time of eutectic melting onset and the related temperature, pointing out different values for the pellet and the powder cases.

A Quantitative method of eutectic reaction study between boron carbide and stainless steel

Hong, Z.*; Pellegrini, M.*; Erkan, N.*; Liao, H.*; Yang, H.*; Yamano, Hidemasa; Okamoto, Koji*

Annals of Nuclear Energy, 180, p.109462_1 - 109462_9, 2023/01

https://doi.org/10.1016/j.anucene.2022.109462

A series of experiments were conducted using BC material and SUS304 tubes as a simulant of the real control rods. Reaction rate constant data in the 1450K-1500K range were obtained, and are consistent with the reference values. The reaction layer microstructure observation and the associated chemical composition analysis were also carried onto the experiment samples.

Preliminary analysis of core disruptive accident in sodium-cooled fast reactor using eutectic reaction model of boron-carbide control-rod material

Yamano, Hidemasa; Morita, Koji*

Nihon Kikai Gakkai 2022-Nendo Nenji Taikai Koen Rombunshu (Internet), 5 Pages, 2022/09

It is necessary to simulate a eutectic melting reaction and relocation behavior of boron carbide (B4C) as a control rod material and stainless steel (SS) during a core disruptive accident (CDA) in an advanced large-scale sodium-cooled fast reactor (SFR) designed in Japan. A physical model simulating the eutectic reaction and relocation of the eutectic melt was developed to incorporate into the fast reactor severe accident analysis code SIMMER-IV for the CDA numerical analysis of SFRs. This study applied the SIMMER-IV code with the newly developed model to the CDA analysis of the SFR. This analysis indicated that the SIMMER-IV code using the eutectic reaction model has successfully simulated the eutectic reaction and the upward motion of the eutectic melt in the molten core pool as well as the reactivity transient behavior caused by the molten core material relocation.

Preliminary application of eutectic reaction model on boron carbide and stainless steel to severe accident simulation of sodium-cooled fast reactors

Yamano, Hidemasa; Morita, Koji*

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

For a severe accident (SA) simulation of sodium-cooled fast reactors, a eutectic reaction model between boron carbide (BC) and stainless steel (SS) has been developed to be incorporated into the SA simulation codes: SIMMER-III/IV. To confirm the applicability of SIMMER-IV involving the eutectic reaction model to reactor simulations, this study has preliminarily applied this code with the newly developed physical model to a SA simulation of a large-scale SFR designed in Japan. The simulation results show that the eutectic reaction is caused by the contact between the liquid SS and the broken BC pellets which are released to the coolant channel after the failure of cladding which is melted by the mixture of liquid SS and fuel particles coming from the neighboring fuel assemblies. The liquid eutectic material formed by the reaction stayed in the control assembly and the neighboring fuel assemblies. This preliminary simulation shows that the spreading area of BC-SS eutectic formation is limited within this calculation time.

Effect of BC addition on the solidus and liquidus temperatures, density and surface tension of type 316 austenitic stainless steel in the liquid state

Fukuyama, Hiroyuki*; Higashi, Hideo*; Yamano, Hidemasa

Journal of Nuclear Materials, 554, p.153100_1 - 153100_11, 2021/10

https://doi.org/10.1016/j.jnucmat.2021.153100

The effects of BC addition on the solidus and liquidus temperatures of type 316 austenitic stainless steel (SS), and on the density and surface tension of molten SS, were experimentally studied. The solidus temperature of SS-x mass% BC (from 0 to 10) monotonically decreased from 1666 to 1307 K with BC addition. The liquidus temperature had a minimum at around 2.5 mass% BC, and increased with further BC addition up to 10 mass%. The density and surface tension of molten SS-x mass %BC were successfully measured over a wide temperature range (including an undercooling region) via an electromagnetic-levitation technique. The density of each sample decreased linearly with temperature. The density also monotonically decreased with BC content. Although the addition of BC had no clear effect on the surface tension of SS-x mass %BC, sulfur dissolved in SS316L caused a significant decrease in the surface tension.