Basic considerations are discussed in the area of LMFBR refueling optimization. The procedure of search for the optimum refueling scheme is based on a systematic enumeration algorithm embodying the heuristic rule "Elimination of Hopeless End States (EHES)". The optimization procedure thus developed reveals the global characteristics of the refueling scheme, on the basis of a macroscopic regression model which describes the burnup-dependent core performance.
Sample numerical results are obtained on problems of optimizing the refueling scheme for the 4-zone zone-loaded and 2-zone scatter-loaded cores of a typical sodium cooled mixed-oxide fueled fast power reactor. Case studies are conducted on the effect of change in the elimination factor adopted in applying the EHES, in the upper or lower boundaries of constraints, in the performance criterion, and in various parameters governing the mode of reactor operation such as the duration of one cycle period. The study has revealed several notable characteristics particular to LMFBR core refueling, such as the common trait of optimized refueling schemes for 2-region cores of repeated identical refueling patterns, and incompatibility between radial power flattening and sustained useful life for the core.

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The influence of a magnetic field on the boiling of stagnant potassium was experimentally studied in the range of field intensity from 0 to 0.7 Tesla under low pressure cover gas. The results indicated that incipient boiling superheat and the location of boiling inception were not influenced by the magnetic field. On the other hand, the magnetic field very appreciably impeded the motion of the liquid column supported above the vapor bubble after boiling was initiated. Another effect of the magnetic field proved to be inhibition of vapor condensation in the void space during the period of descend of the liquid column. As a result the vapor in the void space remained uncondensed, to serve as permanent cushion for the liquid column, which maintained an oscillatory motion, to which corresponding oscillations were registered in the pressure and temperature of the vapor bubble, which changed along the vapor saturation line.

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A method of preparing high purity 143Pr from neutron-irradiated cerium was developed. The cerium oxide used as target material was obtained by decomposing Ce(III) carbonate at 200°220°C, and this was irradiated in a thermal neutron flux of 7.6 X 10¹² n/cm²•sec for 77 hr. The irradiated cerium oxide was dissolved in HNO₃, to separate the ¹⁴³Pr formed therein by cation-exchange, with 0.25 NI citrate as an eluant ; and the final product was prepared in the form of HC1 solution. Approximately 1 mCi of ¹⁴³Pr was obtained after chemical processing of 0.51 g of the cerium oxide. The chemical yield of the 143Pr was over 99%, and its radiochemical purity over 99.99%.
The cerium oxide prepared by the method adopted in this work obviated the draw-back inherent in commercially available Ce(IV) oxide of being difficult to dissolve in HCl or HNO₃.

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Specimens of polycrystalline UO2 were strained in compression at constant strain rate from 0.05 to 10.0/min and at temperatures ranging 900°C2, 000°C. The experimental results revealed characteristic yield point, and the yield stress varied with strain rate and temperature. The present data, obtained at strain rates higher than currently adopted, showed greater sensitivity on strain rate and a higher activation energy for yield flow.
The data are discussed in their relation to the mechanism that controls the yield strength. The yield strength at high strain rate would appear to be controlled primarily by the peierls stress.

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Radiolysis of the CO²-C₃H₈ system by fission fragments (FF) was compared experimentally with those by γ- and (n+γ)-rays. Carbon monoxide formation was observed to reach maximum at 1% propane concentration with all three kinds of radiation. The G(CO) value was found consistently higher with FF than with γ- and (n+γ)-rays, whereas G(C₂H₆) showed the opposite tendency in the difference between FF and the other radiations. The maximum G(CO) value obtained with FF was 6.7, while only 3.6 was attained with the other radiations.
The difference between the radiolysis by FF and by the other radiations was ascribed to reactions taking place within the FF tracks. The rates of in-track reactions and the diffusion out of the tracks were estimated on the basis of Mozumder's track model. This estimation made it clear that, with the rise in the total pressure, CO formation could be expected to be enhanced by FF irradiation, with the reaction CO⁺₂+e^-→CO+O coming to predominate over other reactions constituting the mechanism of CO₂, radiolysis.

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A method is described whereby thermal conductivity and diffusivity can be determined continuously from measurements of the temperature difference between the top and base surfaces of a cylindrical specimen at quasi-steady state performed during heating at constant rate. The technique developed, named the "scanning temperature method", is applicable to small samples of millimeter size. The thermal conductivity and diffusivity of single- and poly-crystal alumina were measured by this method over temperatures ranging from 423 to 873K, with precisions of ±5 and ±10%, respectively. The results agreed fairly well with previously reported values. Errors due to thermal contact resistance, heat leakage and transient effect are discussed.

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