For a zero-power reactor, a new approach is proposed for extending the frequency response obtained by pile modulation experiment to account for dependency in space and energy, and the result is compared with the power spectral density of reactor noise.
While in a point reactor model, the square modulus of the reactor transfer function and the power spectral density are proportional to each other, this relation is no longer applicable to the generalized case.
Some quantitative discussions are made in this regard for the particular case of a bare homoge-neous reactor with mono-energetic neutrons.

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We estimated the isotope effect on surface diffusion flow assuming that this flow originates in the hopping of adsorbed molecules, and obtained the conclusion that surface diffusion flow in monolayer adsorption has an isotope effect comparable to Kundsen flow. Based on this conclusion, and applying the new model for surface diffusion mechanism proposed previously, we analyzed isotope separation by gaseous diffusion in which Kundsen flow is accompanied by surface diffusion flow.
In addition to the theoretical treatment, we made experiments on isotope separation under con-ditions of surface diffusion flow rate comparable to or a few times greater than that of Knudsen flow, and verified that the isotope effect on surface diffusion flow obeys the proposed theory. It was observed that the separation efficiency with the coverage (θ) around unity is much poorer than with low surface concentrations.

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Equations were derived for the reflection and transmission functions of γ-rays through slabs of finite thickness, making use of the invariant imbedding principle. Numerical solutions were obtained for the reflection function (albedo) of semi-infinite medium. The results agreed well with the solutions by Monte Carlo method. Comparisons were also made with experimental results. Fair agreement was obtained except for the angular distribution of the reflected photons from light elements.

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The distribution ratio of uranium between tri-n-butyl phosphate and water decreased with the addition of water-insoluble carboxylic acids such as benzoic, lauric, oleic and stearic acids at various concentrations of nitric acid. It is suggested that the decrease of uranium distribution ratio may be due to hydrogen bond formation between tri-n-butyl phosphate and carboxylic acid. It was indicated from infrared spectrometry that a strong hydrogen bond is formed between tri-n-butyl phosphate and carboxylic acid. In other cases, water-soluble carboxylic acids such as acetic, adipic and oxalic acids had no effect at all on the distribution ratio of uranium at various concentrations of nitric acid.

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he behavior of cladding tubes, both stainless steel and zircaloy under the post-accidental conditions of coolant loss has been discussed, based on the results of three experiments performed this time. The effect of oxidation in post-accidental steam atmosphere up to temperatures where the cladding tube should burst with the pressure of entrapped fission product gas was found to be negligible. The bursting behavior of tubes containing pre-determined amounts of inert gas cor-responding to the amounts of released fission product gas that should be present in various states of fuel usage was also examined. No effect of corrosion in zircaloy-2 that should affect its strength could be found up to a weight gain corresponding to several years of use under normal operating conditions, either in the burst strength or creep burst behavior.

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