The keV-neutron capture in ¹³³Cs, ¹⁹⁷Au and ¹⁸¹Ta was studied by measuring the cross section and the emitted gamma-ray spectrum. The neutron was produced with the KUR linear accelerator and a photoneutron target, and the samples were placed at 11.7 m from the neutron source. The gamma-rays following the keV-neutron capture were detected with a pair of C₆D₆ scintillators. The relative capture cross section between 3.2 and 270 keV was normalized to the absolute cross section at 24 keV obtained with an iron-filtered neutron beam. The results of ¹³³Cs and ¹⁹⁷Au are in good agreement with the recently measured and evaluated capture cross sections.
The capture gamma-ray spectrum was obtained by unfolding the observed spectrum with the response functions of the detector. The gamma-ray strength function, which represents the average gamma-ray transition probability, was derived with the spectrum fitting method. The level density distributions used in the calculation of spectrum fitting were investigated and it is found that the constant temperature level density is preferable. The gamma-ray strength functions for ¹⁹⁸Au and ¹³⁴Cs show the 5.5-MeV bump and the deficiency of strength compared with the tail of giant dipole resonance, and that for ¹⁸²Ta does not give the bump but shows the similarity to the tail of giant resonance. The results were compared with other data.

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The effect of (γ, n) reactions of heavy water on beam quality of a biomedical irradiation facility was studied. In an irradiation facility using thermal neutrons from a nuclear reactor, heavy water is widely employed as neutron moderator because of its good nuclear charac-teristics. It is well known that the threshold energy of (γ, n) reactions of heavy water is 2.2 MeV and fast neutrons are generated from the reactions. In 1982, we proposed a tech-nique for the evaluation of (γ, n) reactions using a computer code ANISN-JR. In the present work, with further improved ANISN-JR for the proper estimation of the leakage, the com-parison calculations both with and without (γ, n) reactions were carried out and their results were compared with those of the foil activation experiments at the KUR Heavy Water Facility. In the ignorance of (γ, n) reactions, fast and epithermal neutron fluxes are extremely underestimated for deeper penetration than 80 cm, while the calculated results including (γ, n) reactions give good agreements with experiments.

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A method to obtain an approximate solution to the transport equation, when both sources and collisions show a linearly anisotropic behavior, is outlined and the possible implications for numerical calculations in applied neutronics as well as shielding evaluations are investi-gated.
The form of the differential system of equations taken by the method is quite handy and looks simpler and more manageable than any other today available technique. To go deeper into the efficiency of the method, some typical calculations concerning critical dimen-sions of multiplying systems are then performed and the results are compared with the ones coming from the classical S_N approximations. The outcome of such calculations leads us to think of interesting developments of the method which could be quite useful in alternative to other today widespread approximate procedures, for any geometry, but especially for curved ones.

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The natural frequency f_n and damping constant σ of a bubble in liquid have been deter-mined by observing the resonance of the bubble to forced oscillation. The bubble was re-tained under a rigid plate horizontal disk, and the oscillation was applied by underwater speaker. The applied frequency f was kept constant while letting the bubble increase its volume and vary its radius R. Bubble resonance was detected by observing wrinkles appear-ing on the bubble due to surface waves. Resonance curves relating the amplitude of bubble radius variation to the intensity of applied oscillation is derived theoretically.
Good agreement was seen between the data obtained from experiment and the theoreti-cally derived resonance curves at test to the validity of the method proposed of determining f_n and σ from bubble resonance. The values of σ and of the resonant bubble radius R₀ of large steam bubbles (8.5 mm<R<11.5 mm) in water were determined at f=270, 290 and 358Hz. The results support the assumption that for large bubbles the value of f_n is little influenced by the exchange of mass between liquid and gaseous phases through evaporation and condensation accompanying bubble pressure oscillation. On the other hand, σ is found to be one order of magnitude higher than calculated for steam bubbles without taking into evaporation and condensation the interphase exchange of mass. The effect brought on 5 by the interphase mass exchange can be taken into account by adding a new constant O_ph to the terms constituting the total damping constant.

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The oxygen potentials at 1, 000 and 1, 300°C and the lattice parameters of UO₂ fuels with soluble fission product elements (Zr, Ce, Pr, Nd, Y), simulating high burnup of up to 10%, have been measured by means of thermogravimetry and X-ray diffraction. The oxygen potentials for (U, FP)O_2+x, fuels are higher than pure UO_2+x at a given composition and increase positively with increasing simulated burnup. They can be represented as a function of the mean uranium valence at compositions of 0/M>2.01. The lattice parameters of stoichiometric (U, FP)O_2.00 fuels decrease linearly with simulated burnup, and can be ex-pressed as a (pm) =547.02-0.122B, where B is burnup in %.

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The cladding component chemical transport (CCCT) is one of the important modes of the fuel-cladding chemical interaction (FCCI) of LMFBR. In order to explain this pheno-menon, a model based on the vapor phase chemical transport of cladding components by iodine was proposed by Johnson et al. and Calais et al. In this study, experimental work has been done to check whether such a mechanism can work due to the free iodine generated by the radiolysis of Csl vapor. As a result, it was confirmed that a significant amount of Fe can be transported via vapor phase from the Fe sheet heated at 430°C to the Mo plate heated at 720 or 800°C. Preliminary comparisons between this study and the in-pile irra-diation tests have been made. This result qualitatively supports the appropriateness of the model for the CCCT mechanism based on the vapor phase transport of cladding components by radiation-induced iodine.

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An evaluation model of a turbine meter has been developed to predict two-phase liquid velocity. The model considers the effects of blade configuration and void fraction distribu-tion. In order to verify its applicability, experiments in single-phase and two-phase flows were performed and the model was compared with existing theories. This report describes the model and the experimental results on single-phase and two-phase flows.

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