The photonuclear reaction ²D(γ, n) was utilized to measure the intensity of the weak 2, 505 keV γ-ray in the decay of ⁶⁰Co. A point-like source was used to cause the reaction in heavy water, and the neutrons generated were detected with a BF₃ counter. The observed intensity per decay was I(2, 505) = (2.0±0.4) × 10^-8, which was smaller than previous estimates by about one order of magnitude. From the present result the reduced transition probability B_ex(E4) and the partial half-life T_1/2(E4) of the crossover E4-transition between the 2, 505 keV, 4⁺ and the ground levels in ⁶⁰Ni was estimated as B_ex(E4) = (7.0 ± 1.4) × 10^-100e²•cm⁸ and T_1/2 (E4) 15 ± 3 μsec, respectively.

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Prandtl's mixing length theory is applied in a theoretical study of the frictional pressure drop of gas-solids suspension flows, with consideration given to the different modes of flow around a particle depending of the conditions of flow. The flow channel was divided into three regions-(a) the "F-region" of non-interacting flow, (b) the "E-region" of interacting flow around the particles, and (c) the "P-region" occupied by the particles. The particular phenomenon known as 'drag reduction' is also analyzed on the basis of the same theory. The principles used being based on the perturbation theory, the analysis does not agree with the experimental results in the range of high solids/gas mass loading ratio. For small loading ratios, as well as for suspensions not liable to agglomeration, the agreement obtained between theory and experiment was quite good.

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Among various fluctuating quantities in a BWR plant the present authors dealt with core channel flow fluctuations. Using the instrumented fuel assemblies (IFA) installed in the Japan Power Demonstration Reactor IC core, fluctuations of the inlet and outlet channel flow rates were observed at power operation condition. Correlation analyses of the fluctuating signals revealed the followings : (a) the flow fluctuations in any WA channel showed almost uncorrelated cross-correlation with other IFA channel flow, (b) cross-correlation between the neutron density fluctuations and each IFA channel flow fluctuations also showed little correlation, and (c) the forced circulation pump flow showed unexpectedly weak correlation with the core channel flow.
To attempt to explain the above facts, some hypotheses are introduced : (1) Each channel will be actuated by an independent weak noise source. (2) The fluctuating flow of a channel will interfere with each other, then the interferences will spread to the whole core and balance in a stationary state forming a certain statistical pattern. A dynamic equation of the channel flow fluctuations is introduced based on the above hypotheses, and the covariance functions of inter-channel flow fluctuations are calculated. The hypotheses are discussed by comparing with the results of identification by the use of an autoregressive model.

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Unirradiated zirconium specimens and specimens irradiated to a fluence of 4.1 x 10¹⁹ n/cm² were subjected to tensile deformation at room temperature. During the straining, the specimens were removed at intervals from the testing machine for microphotographic inspection, to determine the progress of slip line density Ns, the twin volume fraction Vt and the twin density Nt, as function of strain. The effect of neutron irradiation on these values were studied in detail. The resulting data indicated that the neutron irradiation inhibited the growth of twins in the early stage of deformation, up to a plastic strain ε_p of about 11%, beyond which level the irradiation tended instead to inhibit nucleation. Between growth of twins and nucleation, it was the latter phenomenon that was found more effective in promoting slip deformation. The break in the slope of plots relating the reciprocal work hardening dε/dσ to the true plastic stress σ_p gave the twin stress σ_T which proved to represent a good approximation of the stress of twin nucleation.

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A mathematical model for chromatographic isotope separation systems is derived starting from a simple theoretical equation for concentration profiles in an ideal displacement chromatogram. The theoretical equation is combined with appropriate material balances to develop a set of equations which relate the size, production rate and start-up time of chromatographic separation equipment to the degree of isotope enrichment. These equations are easy to use, and require a minimum of empirical data.
The model incorporates a series of simplifying assumptions which are valid for displacement chromatographies where the isotopic separation coefficient is small and the degree of enrichment accomplished in a single column is not very high. Thus the model is applicable to most isotope separation systems of practical interest (including uranium enrichment), although it may be inadequate for certain special cases.

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All-Interconnected Cascades is proposed as an example of production system to be designed to produce a number of side products of enriched uranium. To analyze the transient characteristics of the side product assays in the proposed cascades system, the code TWIN-SS is developed. If the rotor power supply loss for UF₆ centrifuges occurs for a short time in the finishing and/or the base cascades, an allowable power loss time permitting the side product assays to be maintained within the product assay specifications is revealed. Furthermore, even if a long time power supply loss occurs in one base cascade, it is shown that the side product assays can be controlled without the shut-down of the operation of All-Interconnected Cascades by operating an interstage reflux in the finishing cascade.

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The electron-irradiation studies on Hastelloy-X in the temperature range of 400600°C to a dose of about 40 dpa have revealed that Hastelloy-X is much more resistant to void swelling compared to Type 316 stainless steel. The low void swelling in Hastelloy-X is attributable to small void size which arises from long incubation period for void nucleation and low climbing rate of dislocations. The magnitude of the incubation period depends on the stability of void embryo ; the void in Hastelloy-X is not considered to be stabilized with solute atom segregation as seen in Type 316 stainless steel, and then, the high dislocation density is essential for the void nucleation. The stabilization of void embryo also affects the void number density, especially at high temperature where vacancy supersaturation rate is low. And the small void number density in Hastelloy-X results in very small void swelling at a high temperature (600°C).

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The relationship between the fraction leached and the ratio of surface area and volume (S/V) of a specimen has been studied in order to evaluate the safety of a cement composite for disposal. The leaching fraction of radionuclides was measured for the different S/V ratios. In a case of either ¹³⁷Cs, ⁹⁰Sr or ⁶⁰Co, the amount leached is directly proportional to the S/V ratio. It is in harmony with the empirical formula proposed here, which can be derived from the diffusion equation with a semi-infinite plane source model.
The amounts of ¹³⁷Cs, ⁹⁰Sr and ⁶⁰Co leached from a cement composite of 2001 drum size are estimated on the basis of the above relation, referring to the data obtained with a cylindrical shape specimen (4. 5 cm in dia. and 4. 4 cm high)

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The self-shielding factors for elastic removal cross sections of light and medium weight nuclides were calculated for the parameter, σ₀ within the conventional concept of the group constant sets. The numerical study were performed for obtaining a simple and accurate method. The present results were compared with the exact values and the conventional ones, and shown to be remarkably improved. It became apparent that the anisotropy of the elastic scattering did not affect to the self-shielding factors though it did to the infinite dilution cross sections. With use of the present revised set, the neutron flux were calculated in an iron medium and in a prototype FBR and compared with those by the fine spectrum calculations and the conventional set. The present set showed the considerable improvement in the vicinity of the large resonance regions of sodium, iron and oxygen.

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