New analysis model of solid body formation in particle method for jet impingement and solidification in severe accidents of SFRs

Imaizumi, Yuya; Kamiyama, Kenji; Matsuba, Kenichi

Annals of Nuclear Energy, 206, p.110658_1 - 110658_10, 2024/10

https://doi.org/10.1016/j.anucene.2024.110658

Generalized extreme value analysis of efficient evaluation of extreme values in random media criticality calculations

Ueki, Taro

Progress in Nuclear Energy, 173, p.105236_1 - 105236_10, 2024/08

https://doi.org/10.1016/j.pnucene.2024.105236

The theme of this paper is how to efficiently analyse extreme realizations of neutron effective multiplication factor (keff) over random media replicas modelled by incomplete randomized Weierstrass function (IRWF). To this end, a new bounded amplification (BA) technique is applied to IRWF. Numerical results indicate that the BA-applied IRWF reduces a required number of random media replicas at least by an order of magnitude. To validate this efficiency gain, generalized extreme value (GEV) analysis is applied to a data set of keff values obtained without applying BA. It turns out that the extreme values of these keff values follow the Weibull distribution. Therefore, the theory of GEV guarantees the existence of the upper limit of these keff values, and the actually computed upper limit is indeed smaller than the top two keff values obtained from an order-of magnitude reduced number of BA-applied IRWF random media replicas. This means that the efficiency gain via BA has been confirmed by GEV analysis.

Ultrasound-assisted removal of contaminants on stainless steel surfaces using nitrogen ultrafine bubble water

Nakahara, Masaumi; Watanabe, So; Kimura, Shuya; Sasaki, Misa*; Inagaki, Hiromitsu*; Moriguchi, Tetsuji*

Progress in Nuclear Energy, 172, p.105195_1 - 105195_8, 2024/07

https://doi.org/10.1016/j.pnucene.2024.105195

A novel removal technique with ultrafine bubbles has been proposed for decommissioning of nuclear facilities. The performance of removal technology with ultrafine bubbles was evaluated in the removal experiments with non-radioactive materials, simulated contaminants precipitated Co oxides. To investigate the influence of difference in the chemical forms, the decontamination experiments were carried out with the fuel pin end plugs contaminated radioactive materials in a hot cell.

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.

Simulation of a jet flow rectified by a grating-type structure using immersed boundary methods

Hirose, Yoshiyasu; Abe, Satoshi; Ishigaki, Masahiro*; Shibamoto, Yasuteru; Hibiki, Takashi*

Progress in Nuclear Energy, 169, p.105085_1 - 105085_13, 2024/04

https://doi.org/10.1016/j.pnucene.2024.105085

Intercalative and non-intercalative photo-recharge using all-solid-state cells for solar energy conversion and storage

Yoshimoto, Masataka*; Tamura, Kazuhisa; Watanabe, Kenta*; Shimizu, Keisuke*; Horisawa, Yuhei*; Kobayashi, Takeshi*; Tsurita, Hanae*; Suzuki, Kota*; Kanno, Ryoji*; Hirayama, Masaaki*

Sustainable Energy & Fuels (Internet), 8(6), p.1236 - 1244, 2024/03

https://doi.org/10.1039/D3SE01636F

Photo-rechargeable systems, which can efficiently convert and store solar energy into chemical energy within single devices, are essential to harness sunlight effectively. Photo-(de)intercalation plays a pivotal role in the functionality of photorechargeable systems. Nevertheless, the photo-(de)intercalation process has not been conclusively confirmed owing to potential interference from side reactions, such as the decomposition of liquid electrolytes and the elution of electrode materials. In this study, we successfully demonstrated photo-responsive Li-deintercalation using an all-solid-state thin-film battery comprised of epitaxially-grown anatase TiO doped with Nb (a-TiO:Nb) as the cathode. Under light irradiation, Li-deintercalation occurred and was subsequently reversibly intercalated into a-TiO:Nb during discharge.

Development of a formulation to predict molten core spreading in an LWR severe accident

Sahboun, N. F.; Matsumoto, Toshinori; Iwasawa, Yuzuru; Wang, Z.; Sugiyama, Tomoyuki

Annals of Nuclear Energy, 195, p.110145_1 - 110145_12, 2024/01

https://doi.org/10.1016/j.anucene.2023.110145

Opposing mixed convection heat transfer for turbulent single-phase flows

Motegi, Kosuke; Shibamoto, Yasuteru; Hibiki, Takashi*; Tsukamoto, Naofumi*; Kaneko, Junichi*

International Journal of Energy Research, 2024, p.6029412_1 - 6029412_22, 2024/01

https://doi.org/10.1155/2024/6029412

Convection, wherein forced and natural convections are prominent, is known as mixed convection. Specifically, when a forced convection flow is downward, this flow is called opposing flow. Several heat transfer correlations have been reported related to single-phase opposing flow; however, these correlations are based on experiments conducted in various channel geometries, working fluids, and thermal flow parameter ranges. Because the definition of nondimensional parameters and their validated range confirmed by experiments differ for each correlation reported in previous studies, establishing a guideline for deciding which correlation should be selected based on its range of applicability and extrapolation performance is important. This study reviewed the existing heat transfer correlations for turbulent opposing-flow mixed convection and the single-phase heat transfer correlations implemented in the thermal-hydraulic system codes. Furthermore, we evaluated the predictive performance of each correlation by comparing them with the experimental data obtained under various experimental conditions. The Jackson and Fewster, Churchill, and Swanson and Catton correlations (Int. J Heat Mass Transf., 1987) can accurately predict all the experimental data. The effect of the difference in the thermal boundary conditions, i.e., uniform heat flux and uniform wall temperature, on the turbulent mixed-convection heat transfer coefficient is not substantial. We confirmed that heat transfer correlations using the hydraulic-equivalent diameter as a characteristic length can be used for predictions regardless of channel-geometry differences. Furthermore, correlations described based on nondimensional dominant parameters can be used for predictions regardless of the differences in working fluids.

Experiment and new analysis model simulating in-place cooling of a degraded core in severe accidents of sodium-cooled fast reactors

Imaizumi, Yuya; Aoyagi, Mitsuhiro; Kamiyama, Kenji; Matsuba, Kenichi; Akaev, A.*; Mikisha, A.*; Baklanov, V.*; Vurim, A.*

Annals of Nuclear Energy, 194, p.110107_1 - 110107_11, 2023/12

https://doi.org/10.1016/j.anucene.2023.110107

Effect of molybdenum release on UO/MOX fuel oxidation under severe light water reactor accident conditions

Liu, J.; Miwa, Shuhei; Karasawa, Hidetoshi; Osaka, Masahiko

Nuclear Materials and Energy (Internet), 37, p.101532_1 - 101532_5, 2023/12

https://doi.org/10.1016/j.nme.2023.101532