Shosuke Imoto

Hydrogen transport in stainless steels

Abstract The precise measurements of hydrogen permeability (φ) and diffusivity (D) were performed for some stainless steels and high temperature materials utilizing an extremely purified hydrogen under pressure of 0.001–0.1 MPa at temperatures between 500 and 1200 K. Most of the determined values of φ and D give good Arrhenius relationship against inverse temperature. The effect of alloying elements, particulary, of Cr is discussed by comparing the obtained values of φ and D.

Chemical state of fission products in irradiated UO2

The chemical state of fission products in irradiated UO2 fuel has been estimated for FBR as well as LWR on the basis of equilibrium calculation with the SOLGASMIX-PV code. The system considered for the calculation is composed of a gas phase, a CaF2 type oxide phase, three grey phases, a noble metal alloy, a mixed telluride phase and several other phases each consisting of single compound. The distribution of elements into these phases and the amount of chemical species in each phase at different temperatures are obtained as a function of oxygen potential for LWR and FBR. Changes of the chemical potential of the fuel-fission products system during burnup are also evaluated with particular attention to the difference between LWR and FBR. Some informations obtained by the calculation are compared with the results of post irradiation examination of UO2 fuels.

Permeation and reemission of deuterium, implanted in first wall materials

Abstract The permeation rate and the reemission rate of deuterium during the implantation of 20 keV deuteron have been measured for samples of nickel and molybdenum with use of a quadrupole mass-spectrometer. The results have shown that the behavior of implanted hydrogen is largely affected by the radiation damage introduced by the bombardment in the temperature range of 300–500°C for nickel and above 600°C for molybdenum. Some of results, for example, a decrease of the permeation rate with prolonged implantation, can be explained by a diffusion model including the trapping of hydrogen in the damaged region.

Cluster Model for Electronic Structure and Bonding Mechanism of Interstitial Hydrogen in Iron Series Transition Metals

Electronic structure calculations have been carried out for small clusters of iron series transition metals containing an interstitial hydrogen atom by the discrete variational Xα method. The hydrogen-metal bonding level is formed below the bottom of the d band. The electron transfer from metal to hydrogen occurs, though the additional electron by hydrogenation occupies the 3 d hole to raise the Fermi level. The covalent bonding between H 1 s and metal 3 d is rather strong in all cases. Change in metal-metal bond by interstitial hydrogen is also significant in the bonding mechanism.

Spectroscopic studies on the uranyl complexes with 1,2-disubstituted benzenes

Abstract Uranyl complexes with a series of 1,2-disubstituted benzenes, such as phthalic acid (H 2 ph), salicylic acid (Hsal), pyrocatechol (H 2 pc), anthranilic acid (Hant), o -aminophenol (amph), and o -phenyleneediamine (phen), have been prepared and studied by i.r., electronic and NMR spectroscopy. Characteristic i.r. stretching frequencing (4000-200 cm −1 ) are reported for each complex. One or two new strong bands are observed in the region of 340–500 nm in all the complexes except uranyl phthalate, which are considered to be due to the charge transfer transition from the pπ orbital of the donor atoms to 5 f - and/or 6 d -orbitals of uranium. Characteristic proton magnetic resonance spectra of the complexes are also reported and discussed in relation to the magnetic anisotropy of the uranyl ion and to the drainage of electron density from the donor atom to the metal.

Direct evidence of uranium(V) intermediates by electron spin resonance in photo- and electrolytic reduction processes of uranyl complexes in organic solutions

Abstract ESR and optical spectra of pentavalent uranium have been observed in both processes of photo- and electrolytic reduction of UO2(dimethylsulphoxide)5(ClO4)2, UO2(NO3)2 · 5dimethylsulphoxide and UO2(NO3)2 · 2triethylphosphate in each corresponding organic ligand solution. The optical spectra measured in both reductions of these complexes indicate the formation of uranium(V) (λmax; 770, 970 and 1400 nm). Uranyl perchlorate shows a nearly symmetric ESR signal with g1 = 2.5 and the linewidth of 150 mT (type 1) in both photo- and electrolytic reduction processes. Nitrates show the type 1 signal in electrolytic reduction but an asymmetric signal with g1 = 1.97 (type 2) in photoreduction. These results reflect the difference in the first coordination spheres of perchlorate and nitrate complexes.

Electron spin resonance spectra and magnetic susceptibilities of mixed oxides, MUO3 (M; Li, Na, K, and Rb), of pentavalent uranium

Abstract In all magnetic susceptibility versus temperature curves for MUO 3 (M; Li, Na, K and Rb) a sharp spike appeared at 16–32 K. Magnetic susceptibilities are one order smaller than those of normal U(V) complexes. ESR spectra are very broad and have g -values of 2–4.

Energy Band Structure of Uranium Compounds with NaCI Type Structure

Non-relativistic and relativistic band structures of NaCl type uranium compounds were calculated with tight-binding approximation based on the rigid band concept. The calculations revealed that the narrow 5f band played important role, and from the desity of states curve the Fermi levels of these compounds were found to lie on or near the 5f band. Moreover, spin-orbit and crystalline field effects were seen to split the 5f band further into five sub-bands. The Fermi levels proved to be related to the lowest sub-band, in which two states were included, and the width of this sub-band was estimated to be 0.05eV. The validity of the foregoing band structure based on calculation is discussed in reference to specific heat at low temperatures and also to magnetic properties.

Hartree-Fock-Slater Model Cluster Calculations. II. Hydrogen Chemisorption on Transition Metal Surfaces

Self-consistent Hartree-Fock-Slater model cluster calculations are carried out in order to investigate the electronic structure of hydrogen chemisorption on transition metal surfaces. Orbital energies and results of Mullikens population analysis are presented for HNi5, HNi9, HPd9 and HW9 clusters. The level structures of the clusters are also given by density-of-states (DOS) curves and compared with the experimental UPS and EELS spectra. Hydrogen chemisorption gives rise to bonding levels near the bottom of the valence band and antibonding ones on the top. The energy difference between them in HNi9 is in good agreement with that obtained by EELS. It is concluded that not only localized d electrons but also sp electrons play important roles in hydrogen-metal bondings. Details of hydrogen-metal bond formation, electronic charge transfer and their differences with adsorbate metals are also discussed.

Photoelectron spectra of uranium(IV), (V) and (VI) complexes

Abstract Satellites were observed on 4f photoelectron spectra of uranium (IV) complexes, while none was seen for diamagnetic uranyl complexes. Photoelectron lines of oxygen 1s coordinated to the uranium ion were broad for NaUO 3 and uranyl complexes.