No abstract available

[en] Graphite is porous material so that gaseous diffusion through pores and atomic diffusion on pores are intrinsically important in evaluating the hydrogen retention and permeation rate of graphite. Linear pressure dependence of permeability was found in the down to ∼10^-2 Pa region suggesting the viscous flow limiting kinetics. Extremely large temperature dependence of permeability was observed, but could not be adequately explained by the existing models. Extensive studies are needed to understand this aspect of hydrogen behavior in graphite

[en] The oxidation behavior of the heat-resistant Fe-base alloy Incoloy 800 has been investigated in the vicinity of 1000⁰C under oxygen pressures ranging from 1 x 10^-4 to 2 x 10^-1 atm. The rate of oxidation has been determined by the weight gain using a Cahn RG Electrobalance. Metallographic, electron microprobe and X-ray diffraction studies of the oxidized specimens have been carried out. The rate of oxidation is parabolic but tends to slightly decrease with the progress of oxidation. Cold rolling of the specimen accelerates the rate of oxidation. The dependence of the oxidation rate upon oxygen pressure is slightly smaller than that theoretically expected for the scale of pure Cr₂O₃. The oxidized specimen has a layer structure of the outer porous scale, the inner dense scale, the complicated scale-substrate interface region and the internally-oxidized substrate in sequence from the outer side. The outer scale is principally composed of oxides of Cr and Mn, but it also contains smaller quantities of oxides of Ti, Fe, Ni etc. Oxygen partial pressure of the reaction affects the composition of the outer scale. The inner scale is principally composed of Cr₂O₃. Most of the oxides of Al and Si are present in the scale-substrate interface region and the internally-oxidized substrate region. The existence ratio of the spinel phase against the rhombohedral phase in the outer part of scale considerably increases with the progress of oxidation. (auth.)

[en] It was attempted to take up the behavior of nuclear fuel in cores and summarize it by the expert committee on the irradiation behavior of nuclear fuel from fiscal 1978 to fiscal 1980 from the following viewpoints. The behavior of nuclear fuel in cores has been treated separately according to each reactor type, accordingly this point is reconsidered. The clearly understood points and the uncertain points are discriminated. It is made more easily understandable for people in other fields of atomic energy. This report is that of the group on the chemical interaction, and the first report of this committee. The chemical interaction as the behavior of fuel in cores is in the unseparable relation to the mechanical interaction, but this relation is not included in this report. The chemical interaction of fuel and cladding tubes under irradiation shows different phenomena in LWRs and FBRs, and is called SCC and FCC, respectively. But this point of causing the difference must be understood to grasp the behavior of fuel. The mutual comparison of oxide fuels for FBRs and LWRs, the stress corrosion cracking of zircaloy tubes, and fuel-cladding chemical interaction in FBRs are reported. (Kako, I.)

[en] This issue is the collection of the paper presented at the title meeting. The 15 of the presented papers are indexed individually. (J.P.N.)

[en] Monocarbides of thorium, ThC and (Th,U)C, are interesting as alternative fertile material to be used in nuclear breeder systems. They have high metal density, high thermal conductivity and wide homogeneous composition range. Specimens were prepared by carbothermic reduction. Vapor pressures of non-stoichiometric ThCsub(1±y) and (Thsub(1-y),U_y))Csub(1-x) were measured by means of Knudsen effusion mass spectrometry. The activities of thorium and carbon of ThCsub(1±y) were derived from the measured vapor pressures of thorium. The change of these activities with C/M ratio was found to be smaller than that of UCsub(1±x), claiming a better irradiation performance of ThC compared to UC. Based on the vapor pressure measurement of (Thsub(1-y_,U_y)Csub(1-x), Gibbs energy of formation of (Thsub(1-y),U_y)C was derived as a function of uranium fraction y. Estimation of the chemical state of various fission products in irradiated thorium-uranium mixed monocarbide fuel pins was performed by utilizing SOLGASMIX computer code. In carbide fuel pins more amounts of fission product containing secondary phases are to be formed than in oxide fuel pins. Fuel-cladding chemical interaction will be much more alleviated in thorium carbide fuel pins compared with oxide fuel pins. (author). 18 refs., 13 figs

[en] Some of the important physical and chemical aspects of hydrogen transport in fusion reactor materials are investigated. A typical steady state model for hydrogen transport in metals assumes bulk diffusion and surface recombination of hydrogen as two major rate-determining processes. The model can be applied to evaluate hydrogen recombination rate coefficient, k_R, from the experimental values of permeation rate, and, when k_R is known, allows to estimate hydrogen isotope permeation rate and inventory under fusion relevant conditions. Similar model can be presented for graphite, but it has to be such that it is able to explain the formation of hydrocarbons due to interaction with hydrogen. Furthermore, thermochemical approach was employed to examine the extent to which the experimental results on hydrocarbon formation from graphite due to chemical sputtering or thermal desorption can be explained from a point of view of thermochemistry. (author). 56 refs

[en] In case of liquid sodium leaks from the cooling tubes in fast breeder reactors, reaction of sodium oxide with iron, the main constituent of the structural materials, occurs. So, to obtain the thermodynamic data of Na-Fe complex oxides is important to understand the precise corrosion mechanism and to develop effective means to prevent or mitigate the corrosion. In this study, heat treatment of pellets of Na₂O-FeO complex oxides was performed under either of such conditions as an Ar gas flow method, a pyrex tube/vacuum seal method and a stainless steel holder/Ar gas sealing method. By utilizing the stainless steel/Ar gas sealing method, Na₄FeO₃ was obtained with high purity. (author)

[en] In the establishment of fuel cycle of tritium, it is important to make research on how the sweep gas composition affects the surface properties of breeder materials and the release of tritium from the surface of them. In this study, the change of contact potential difference (CPD) between Li₄SiO₄ and Pt was measured in various gas compositions with a high temperature Kelvin probe. The work function change of Li₄SiO₄ was obtained from the measured CPD and the work function change of Pt which was estimated from blank tests. From the results, the effect of oxygen deficient layer near the surface of Li₄SiO₄ was observed, and the effect of OH^- at the surface of Li₄SiO₄ was considered. (author)

[en] A study has been carried out to clarify conditions for inducing the T-to-B transformation of Nb₂O₅ in the scale on niobium and also to clarify the effect of the B-Nb₂O₅ crystals on the oxidation kinetics of niobium by use of X-ray diffraction and metallographic techniques. A preoxidation at around 800⁰C was found to induce the T-to-B Nb₂O₅ transformation in the scale on an electropolished Nb specimen with a subsequent oxidation at 850⁰C. The T-Nb₂O₅ crystals in the scale on a mechanically-polished Nb specimen as well as those in the oxide at specimen edges transformed to M-Nb₂O₅ instead of B-Nb₂O₅ even though the same two-step oxidation procedure were performed. The difference between the to-B-transformable T-Nb₂O₅ and the to-M-transformable T-Nb₂O₅ could be explained by the amount of the strain and disorder in the crystal lattices. The B-Nb₂O₅ crystals in the scale on Nb were not formed so much as to considerably affect the scaling rate of Nb. (auth.)