A method of numerical viscoelastic stress analysis is described suitable for concrete structures operating at elevated temperatures. The paper describes how approximate numerical methods of elastic analysis of the finite element type can be extended to incorporate the viscoelastic behavior of structural concrete of the quasi-static type.
A new eight parameter viscoelastic model is proposed to represent concrete behavior in the loaded and unloaded stage. The deformational expressions for the proposed viscoelastic analogue are also developed.
Finally, as a result of courve-fitting procedures, the evaluation of the creep law coefficients are obtained for creep laws appropriate to a test regime.
The proposed method is of general application providing that the properties of concrete are assessed reasonably well.
The analytical predictions are compared with experimental results obtained on concrete model specimens loaded for 3% months, at a temperature of 80°C.

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A unified diffusion coefficient which is applicable not only to fuel drawers but also to sodium followers or control-rod drawers has been derived by extending the Benoist method to analyze the sodium-void worths in fast critical assemblies including singularities such as sodium followers and control-rod drawers. The unified diffusion coefficient has been obtained by calculating average neutron leakage rates in perpendicular and parallel directions in a super-cell consisting of different drawers such as fuel drawers and sodium followers by using transport theory. Then the interference effect of the neutron streaming between different drawers on diffusion coefficients is taken into account. Diffusion coefficients of fuel drawers, sodium followers and control-rod drawers contained in the ZPPR-3 modified phase 3 core have been calculated on the basis of the present method, Benoist's method, Seki & Sasaki's method and the conventional method, and the results have been compared. The applicability of the unified diffusion coefficient to sodium-void worth calculations has been checked in one- and two-dimensional test geometries, and it has been found that the use of the unified diffusion coefficient leads to reasonable results without adopting the transport corrections in the models including sodium followers. Further the sodium-void worths in the ZPPR-3 modified phase 3 core have been analyzed using the unified diffusion coefficient.

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A new power-flattening method has been proposed for boiling water reactors (BWRs) which have an axially skewed power distribution caused by the void fraction distribution. In present BWRs, the skewed power distribution is avoided by using shallow control rods and/or axially distributed gadolinia fuel bundles. These means are effective for the axial power shape control, but perturb the self-power-flattening effect due to fuel burnup. The power-flattening method proposed here extensively utilizes this effect in the equilibrium cycle core. Based on this method, a new BWR core design and operating strategy, the WNS core concept, has been realized for reactor operation with no shallow control rod insertion and no fuel bundle shuffling. Studies of the WNS core has shown that the proposed power-flattening method has the potential to improve capacity factors, increase operating thermal margins and simplify reactor operations in comparison with current BWR cores.

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The partition equilibrium of iodine in the aqueous mixtures of sodium hydroxide and boric acid was investigated and was compared with the case of the aqueous solution without boric acid. It was found that the reactions of iodine species with boric acid and its derivatives were negligible and the only effect of the addition of boric acid on the partition of iodine species in the solution came out through the shift of hydrogen ion concentration. The hydrogen ion concentration can be evaluated by taking into consideration the dissociation of boric acid and the formation of polymeric borate ion besides a series of reactions of iodine species in the solutions. The observed equilibrium concentrations of various iodine species agreed well with those calculated from the concentration of the total iodine and the calculated hydrogen ion concentration.

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Equilibrium oxygen and carbon potentials of impure He containing small amounts of Impurities such as CO, CO₂, CH₄, H₂, H₂O and O₂ at 1, 073 and 1, 273 K were studied. The calculation of equilibrium composition of impurities was carried out assuming the gas-gas and gas-metal reactions. The diagrams, expressed with atomic oxygen fraction O/S and atomic carbon fraction C/S were represented and showed a wide range of equilibrium oxygen and carbon potentials of impure He. A parameter, (O-C)S showing the difference between atomic oxygen and carbon fraction, was found to give a measure of both oxygen and carbon potentials of gas mixtures. The results of the calculation showed that the oxygen and carbon potentials of the impure He with (O-C)S value of around zero was easily affected by the small variation of the gas composition. The corrosion behaviors of Inconel 617 in various impure He gases at 1, 273 K could be explained by (O-C)/S values.

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The permeation time-lag method have been used to determine the permeabilities, diffusion coefficients and solubilities of hydrogen and deuterium in type 304 stainless steel of three kinds of surface treated specimens ; with oxide film, reduced by H₂ gas and Pd coated. For the specimen with a thin oxide film the permeability increased abruptly at the temperature higher than 1, 050 K owing to reduction of the oxide film by H₂ gas introduced. The permeability and diffusion coefficient for hydrogen-reduced specimens agreed with those for Pd-coated specimens showing the data of bulk diffusion limited. The isotope effects for permeability Φ_H/Φ_D, diffusion coefficient D_H/D_D and solubility were about 1.4, 1.2 and 1.1, respectively. From these values θ(=hν/k) =1, 530±50K and θ' (=hν'/k) =2, 740±20K were obtained by the quantum effect of a harmonic approximation.

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Accuracies of various interpolation methods used for the "table look-up" method of resonance shielding factors are studied. The cubic spline interpolation is shown to produce the most excellent and stable accuracies with short computing time.
The effects of the differences in the effective cross sections given by the various interpolation methods on nuclear characteristics of fast reactors are calculated by using the JAERI-Fast Set Version II. The maximum deviations of the effects are summarized as follows : 0.2% for the effective multiplication factor, 1.5% for the control rod reactivity worth, 6% for Doppler effect, 2.5% for the reaction rate distribution in the blanket region and negligible small for the sodium void effect, respectively, in typical fast reactor.

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A polyethylene solidification process of the low- and intermediate-level radioactive wastes generated from nuclear power facilities has already been developed. However, the density of polyethylene solidified filtersludge and spent ion-exchange resin is less than the value of 1.2, which is considered to be necessary for a waste solid to be dumped into sea. This lack of the density may cause these polyethylene solidified wastes to float on the sea surface and carry the radioactivity to the human environment, when the sealed waste containers happen to be damaged for some reasons.
In this study, a trial is made to prepare polyethylene products having the higher density, and the products was adjusted to have the density of higher values than 1.2 by mixing about 3233W/O of cupper slag. These polyethylene products showed the monoaxial compressive strength of above 150 kg/cm² and the good stability in deionized water for immersion period of 500 days. The volume reduction factor of these heavier polyethylene products to which cupper slag was added also becomes smaller, but it shows still twice as large as that of the cement- and asphalt-solidified wastes.

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