Concept for a cesium-free negative ion source based on microwave heating of a low work function granular material

Matsubara, Akihiro*; Kokubu, Yoko; Nishio, Kazuhisa*; Kimura, Kenji*; Kashimura, Keiichiro*; Shimada, Koji; Fujita, Natsuko

Nuclear Instruments and Methods in Physics Research B, 568, p.165863_1 - 165863_5, 2025/11

https://doi.org/10.1016/j.nimb.2025.165863

We propose a concept for a cesium-free negative ion source based on microwave heating of granular low work function materials, which allows for both safety and high efficiency. This negative ion source features a structure where the plasma region and the negative ion generation region are adjacent within a microwave cavity. In the negative ion generation region, granular low work function materials heated by microwaves are placed. The sample gas entering the plasma region is excited, then it enters the negative ion generation region. Subsequently, it comes into contact with the surface of the low work function material, changes into negative ions, and finally, is extracted by an electric field. One advantage of this negative ion source is that, by using low work function materials in granular form, the reactive area is more than ten times larger compared to conventional negative ion sources using low work function materials.

Extension of the dynamical Kubo-Toyabe model for precise analysis of ion dynamics in solids by SR

Ito, Takashi; Kadono, Ryosuke*

Kotai Butsuri, 60(4), p.197 - 206, 2025/04

We extended the dynamical Kubo-Toyabe model to resolve inconsistencies in a conventional protocol for SR-based analysis of ion dynamics in solids. Our new model not only provides a means for quantitative analysis based on the immobile-muon assumption, but also offers a method to evaluate the validity of this assumption.

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.

Random media criticality analysis methods in Monte Carlo solver Solomon

Ueki, Taro

Proceedings of 12th International Conference on Nuclear Criticality Safety (ICNC2023) (Internet), 9 Pages, 2023/10

A Monte Carlo Solver Solomon has been under development as an object-oriented code written in the C++14 standards. It consists of regular capabilities of criticality safety analysis and a special capability of random media criticality. In the latter capability, Solomon is equipped with a class for the random media modeled by the incomplete randomized Weierstrass function (IRWF). By this modeling, the uncertainty of random media criticality can be evaluated by executing criticality calculations over many IRWF-replicas. However, it is impossible to know beforehand how many IRWF-replicas should be computed. To deal with this issue, a bounded amplification (BA) technique has been newly equipped in Solomon. Applying BA to IRWF, it is possible to reduce the number of IRWF-replicas by more than 95% in terms of the upper limit estimation of neutron effective multiplication factor. Solomon is also equipped with a voxel-overlay (VO). This functionality is shown to be valuable for evaluating the resonance self-shielding effect.

Improve long periodic ground motion evaluation with the epicenter on the border between Fukushima and Ibaraki prefectures in seismic design of nuclear facilities

Kirita, Fumio; Tominaga, Masahiro; Yamazaki, Toshihiko; Seshimo, Kazuyoshi; Uryu, Mitsuru

JAEA-Research 2022-006, 61 Pages, 2023/02

JAEA-Research-2022-006.pdf:6.24MB

Nuclear Fuel Cycle Engineering Laboratories (NCL) has been observing ground motion for a long time. On the border from northern Ibaraki prefecture to Fukushima prefecture, inland crustal earthquakes occur less frequently until the 2011 off the Pacific coast of Tohoku Earthquake (hereinafter referred to as Tohoku Earthquake). After Tohoku Earthquake, aftershocks have become more frequent in this area, and in the Hamadori region of Fukushima earthquake that a remarkable long periodic component was observed in the NCL seismic observation record. Until now there were no such things that long periodic components were observed at the observation points near the epicenter of April 2011 Fukushima earthquake, but it was thought basin structure in deep basement around the NCL affected the propagation process to NCL by reflection survey result. As basement structure of NCL affected the seismic wave propagation process, the seismic wave repeatedly reflects and refracts. For that reason, long periodic components of seismic waves may be possibly amplified. In this study, in order to refine the long periodic ground motion evaluation, using a three dimensional ground structure model (3D model) that can reflect the shape of the deep basement structure around the NCL. When modeling 3D ground structure which has a width of about 80km and a length of about 110km and ranges from the epicenter area of April 2011 Fukushima earthquake to the northern coastal area of Ibaraki prefecture modeled, improved the optimum ground structure model using multiple observation records and performed simulation analysis.

Displacement of hydrogen position in di-hydride of V-Ti-Cr solid solution alloys

Sakaki, Koji*; Kim, H.*; Majzoub, E. H.*; Machida, Akihiko*; Watanuki, Tetsu*; Ikeda, Kazutaka*; Otomo, Toshiya*; Mizuno, Masataka*; Matsumura, Daiju; Nakamura, Yumiko*

Acta Materialia, 234, p.118055_1 - 118055_10, 2022/08

https://doi.org/10.1016/j.actamat.2022.118055

Fully chelating NO-pentadentate planar ligands designed for the strongest and selective capture of uranium from seawater

Mizumachi, Takumi*; Sato, Minami*; Kaneko, Masashi; Takeyama, Tomoyuki*; Tsushima, Satoru*; Takao, Koichiro*

Inorganic Chemistry, 61(16), p.6175 - 6181, 2022/04

https://doi.org/10.1021/acs.inorgchem.2c00306

Based on unique 5-fold equatorial coordination of UO, water-compatible pentadentate planar ligands, Hsaldian and its derivatives, were designed as strong and selective capture of UO in seawater. In the simulated seawater condition (0.5 M NaCl + 2.3 mM HCO/CO, pH 8), saldian shows the strongest complexation with UO to form UO(saldian) (log = 28.05 0.07), which is more than 10 order of magnitude greater than amidoxime-based or -inspired ligand systems most commonly employed for U capture from seawater. Good selectivity for UO from other metal ions coexisting in seawater was also demonstrated.

Weierstrass function methodology for uncertainty analysis of random media criticality with spectrum range control

Ueki, Taro

Progress in Nuclear Energy, 144, p.104099_1 - 104099_7, 2022/02

AA2021-0677.pdf:0.99MB

https://doi.org/10.1016/j.pnucene.2021.104099

Randomized Weierstrass function (RWF) has been under development for evaluating the uncertainty of random media criticality due to the material mixture under disorder. In this work, the modelling capability of RWF is refined so that the spectrum range can be controlled by specifying its lower and upper ends of the frequency domain variable. As a result, it becomes possible to make fair criticality comparison among replicas of random media under inverse power law power spectra. Technically, the infinite sum of trigonometric terms in RWF is extended to cover the arbitrarily low frequency domain and then truncated to finite terms for the sole purpose of spectrum range control. This means that the refinement is free of the convergence issue towards a fractal characteristic of Weierstrass function and thus termed Incomplete Randomized Weierstrass function (IRWF). As a demonstration, a three-dimensional version of IRWF is applied to the mixture of three fuels with different burnups in a water-moderated environment. Monte Carlo criticality calculations are carried out to evaluate the uncertainty of neutron effective multiplication factor due to the indeterminacy of the fuel mixture formation.

Prediction of stability constants for novel chelates design in minor actinides partitioning over lanthanides using density functional theory calculation

Kaneko, Masashi; Sasaki, Yuji; Wada, Eriko*; Nakase, Masahiko*; Takeshita, Kenji*

Chemistry Letters, 50(10), p.1765 - 1769, 2021/10

https://doi.org/10.1246/cl.210402

Density functional theory calculation is applied to predict the stability constants for Eu and Am complexes in aqueous solution for molecular modelling of novel separation agents for minor actinides over lanthanides. Logarithm of experimental stability constants correlates with calculated complex formation enthalpies with high reproducibility (R 0.98). Prediction of stability constants of novel chelates is demonstrated and indicates a potential availability of the derivatives of diethylenetriaminepentaacetic acid type chelate in acidic condition and enhancement of Am selectivity over Eu.

Density functional study on Am(III)/Eu(III) selectivity using crown ether type ligands

Fukasawa, Yuto*; Kaneko, Masashi; Nakashima, Satoru*

Journal of Radioanalytical and Nuclear Chemistry, 329(1), p.77 - 84, 2021/07

https://doi.org/10.1007/s10967-021-07685-0

Density functional theory calculations were applied to understand the selectivity between Am and Eu ions with the crown ethers type ligands. 18C6 is predicted to form the most stable complex with Eu and show the higher stability for Am over Eu, being consistent with previously reported Am/Eu selectivity. We modeled N- and S-donor complexes by using framework of 18C6 complex and analyzed the complexation Gibbs energies, indicating that 18C6 with N-donor atoms is suitable for both complexation and higher Am stability over Eu due to the stronger covalent interaction.