The residual defect in the pulse height defect of a silicon surface barrier detector is investigated theoretically. An application of the model of charge collection process leads to another candidate for the residual defect than the recombination defect. The residual defect is due to incomplete charge induction by electrons and holes inside a plasma column, which has dielectricity-like property. Quantity of induced charge is shown in a ratio to the number of produced electron-hole pairs as functions of depletion layer thickness, plasma column length and resistivity of the detector. Experimental result of the residual defect of ⁵⁸Ni ion and its analysis method applying this model are presented. The residual defect is successfully explained by this model.

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Finite and 'infinitesimal' thermodynamical cycle calculations have been performed for a 'solid piston' model of a pumped Gaseous Core Fission Reactor with dissociating reactor gas, consisting of Uranium, Carbon and Fluorine ('UCF'). In the finite cycle calculations the influence has been investigated of several parameters on the thermodynamics of the system, especially on the attainable direct (nuclear to electrical) energy conversion efficiency. In order to facilitate the investigation of the influence of dissociation, a model gas, 'Modelium', was developed, which approximates, in a simplified, analytical way, the dissociation behaviour of the 'real' reactor gas. Comparison of the finite cycle calculation results with those of a so-called infinitesimal Otto cycle calculation leads to the conclusion that the conversion efficiency of a finite cycle can be predicted, without actually performing the finite cycle calculation, with reasonable accuracy, from the so-called 'infinitesimal efficiency factor', which is determined only by the thermodynamic properties of the reactor gas used.

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For the evaluation of thermal consequences of a sodium leak accident in the auxiliary buildings of the LMFBRs, the sodium pool combustion codes SOFIRE-MII, ASSCOPS and SPM have been developed. In SOFIRE-MII and ASSCOPS, assumptions are made that the combustion occurs at a pool surface, and the process is controlled solely by the turbulent oxygen transfer from atmospheric gas to the pool surface. Combustion heat is dissipated by turbulent and radiation heat transfers to the gas and surrounding walls. On the contrary, a flame over the pool is modeled in SPM, in which the combustion is controlled by sodium vapor and oxygen supplies by the diffusion from the pool surface and the turbulent mass transfer from the atmospheric gas, respectively.
These codes were validated using experimental results obtained in the large-scale sodium fire test facilities ; SAPFIRE (PNC, Japan) and FAUNA (KfK, Federal Republic of Germany). The comparison revealed that agreements between the codes and the test results are reasonably well.

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Measurements of electrical resistivity were made for oxide films formed by anodic oxidation and steam oxidation (400°C/12 h) on Zr plates with different Fe contents. When the Fe content was higher than about 1, 000 ppm the electrical resistivity of the steam oxide films was almost equivalent to that of the anodic oxide films, while at lower Fe content the former exhibited lower electrical resistivity than the latter by about 13 orders of magnitude. The anodic oxide film was an almost homogeneous single oxide layer. The steam oxide films, on the other hand, were composed of duplex oxide layers. The oxide layer formed in the vicinity of the oxide/metal interface had higher electrical resistivity than the near-surface oxide layer by about 14 orders of magnitude.
The oxide layer in the vicinity of the interface could act as a protective film against corrosion and its electrical resistivity is one important factor controlling the layer protectiveness. The electrical resistivity of the oxide/metal interfacial layer was strongly dependent on the Fe content. One possible reason for Fe to improve the corrosion resistance is that Fe ions would tend to stabilize the tetragonal (or cubic) phase and consequently suppress the formation of open pores and cracks in the interfacial layer.

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Hydrogen solubility in Zr-N and Zr-C alloys with various compositions has been measured at a temperature of 8731, 048 K at a pressure below 100 Pa. All the solubility data closely obeyed Sieverts' law. The presence of carbon and nitrogen in zirconium increased the hydrogen solubility at a fixed pressure and provided the negative effect on the enthalpy of solution. Partial thermodynamic functions of hydrogen in the Zr-N and Zr-C alloys were obtained by a dilute solution model and compared to those obtained previously for Zr-O alloys. Dependence of partial molar quantities of hydrogen on interstitial impurity content in zirconium was discussed in terms of dilatometric effect, configurational effect and other contributions.

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Zeolites are expected to be used in buffer materials as an admixture to bentonite to increase their ion exchange ability. The behavior of ion exchange adsorption of Am³⁺ on various zeolites was examined by batch and column methods. The distribution coefficient of Am³⁺, K_d, increased with equilibrium pH from 1.5 to 4.0. L zeolite and mordenite having large pore size yielded relatively large values of K_d over 103 at pH 3.0. The K_d for L zeolite was unaffected by the concentration of coexisting cations, i.e. Na⁺ up to 0.1 M, and K⁺, Ca²⁺ and Mg²⁺ less than 0, 01 M. The Am³⁺ ion was not detected in the effluent passed through the L zeolite column up to 90 bed volumes, even when the feed solution contained a relatively large amount of Na⁺-0.5 M. Americium ion adsorbed on zeolites could be quantitatively eluted with 0.1 M nitric acid.

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Helium stopping powers of Ziegler were fitted by a simple formula of 2-term coeffcients with very good accuracy for a-energy range between 2 and 10 MeV, which covers the a-energies from a decays of most actinides. The values of the coefficients are given for elements whose atomic numbers are 192. The formula was applied to calculate the thick target yield of mixture. The ratios of He-stopping powers of elements relative to oxygen are also tabulated, which are needed to synthesize the thick target yield of mixture from elemental yield values. Using the ratio, the thick target yields of (α, n) reaction on BN and UO₂ were calculated as an example and compared with the measured values.

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Recently, accurate measurements of angular distribution for neutron elastic scattering have been performed. In these experiments, incident neutron energy intervals are narrow, and the large numbers of experimental data points are evenly distributed from forward to backward angles, so that they make it possible to estimate optical model parameters unambiguously. Bayes method which has been developed to estimate nuclear model parameters in nuclear data evaluation⁽¹⁾ is considered to be applicable to estimation of the optical model parameters.
In the present work, new application technique of the Bayes method is developed to estimate the optical model parameters and to investigate energy dependence of the optical model parameters. A demonstration is made for ²⁰⁹Bi, with the angular distribution of elastic scattering and an evaluated total cross section. Because, ²⁰⁹Bi is generally treated as a spherical nucleus and has relatively high level density near the neutron binding energy. Therefore, these characteristics simplify the analysis of low energy scattering data, and this nucleus is suitable to examine an applicability of the Bayes method to the optical model parameter estimation.

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Chemical forms of ¹⁶N in light water reactors (LWRs) have recently been highlighted and studied experimentally and theoretically⁽¹⁾⁽³⁾. Dee to the relatively short-lived nature of ¹⁶N, direct identification of chemical forms in actual LWRs has not been possible. As a substitute for ¹⁶N, ¹³N with a much longer halflife (9.97 min) has been chosen for measurements⁽³⁾. A recent modelling study, however, has pointed out that ¹³N may not behave in an identical way with ¹⁶N in actual reactor primary systems⁽¹⁾.

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The separation of ²³⁵UF₆ particles from gas by an impactor has been studied in the research and development of molecular laser isotope separation of uranium (MLIS). The virtual impactor⁽¹⁾ is an inertial separator containing a 'virtual' surface instead of a solid impaction plate used in the conventional impactor. Therefore, it makes continuous operation possible in the separation of UF₅ particles from gas. In this study, a theoretical investigation for estimation of the separation efficiency of particle in a virtual impactor was carried out in order to design and develop the separation process of particles from gas in MLIS.

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This work consists of conceptual design and experimental studies on an axially heterogeneous core (AHC) for large LMFBRs. Trade-off studies were performed to optimize the AHC, from which it was found out that the AHC has the following advantages compared to the conventional homogeneous core (HOC) ; lower peak linear power, lower peak fast fluence in fuel cladding materials, lower burnup reactivity, lower potential of energetic consequences in hypothetical core disruptive accidents and so on. Aiming at further improvement of the core performance, the AHC core configuration was studied taking control rod operating into account.
Critical experiments of the AHC were performed using the FCA facility at JAERI. The experiments demonstrated satisfactory fundamental nuclear characteristics, such as a flat power distribution. The calculational accuracies for the AHC were found to be nearly the same as those for the HOC.
Through our studies, the AHC with improved safety and economic characteristics was proposed prior to designs in other countries, and the characteristics were demonstrated by experiments. These have provided a technical basis for development of future large LMFBR cores.

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Permeation properties of hydrogen isotopes in first wall candidate materials, both metallic and carbonic, are reviewed with emphases on the elementary processes and mechanisms. Surface impurities such as sulfur and oxygen are closely correlated with the hydrogen permeation rate of various metals, causing a reduction of the molecular recombination coefficient of hydrogen at the surface. The appearance of permeation spike and the substantial change of the permeability are attributed to the changes in impurity composition of the surface. In the case of graphite and other carbon materials, the hydrogen permeation occurs as a molecular flow and the rate strongly depends on pore structure of the bulk material and coated layer.

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