Mean velocity and velocity fluctuation in a test channel that consisted of five subchannels with and without ferrule-type spacer were measured using air as a working fluid, to clear turbulence intensity enhancement due to spacer. Measurements were performed at Reynolds number of 0.5-1.2×10⁵, which simulated vapor flow velocity of annular-dispersed flow in BWR condition. It was confirmed that magnitudes of velocity fluctuations in radial direction were proportional to Reynolds number and square root of friction factor downstream from a spacer. New spacer effect model to describe turbulence intensity enhancement due to the spacers was developed. In the model, dependence of the velocity fluctuation on ferrule thickness was correlated by blockage ratio. It was found that the present spacer model is applicable to prediction of turbulence intensity enhancement due to spacer.

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The MOX (mixed oxide) fuels, 29.97 wt% (analytical value is 28.08 wt%) plutonium in 8.3 or 12.1 wt% enriched uranium were irradiated up to 120 GWd/t in the MARK-II core of JOYO. The irradiated MOX fuels were dissolved in 8M nitric acid solution. Anion exchange chromatographic procedures were developed for the isolation of neptunium contained in these MOX solutions. Neptunium-237 was separated from the other actinides by using the developed chromatographic technique and the content of ²³⁷Np was determined by α spectrometry.
It was found that the content of ²³⁷Np slightly increased with increasing burnup. The content did not exceed 0.08 wt% in the 30 wt% MOX fuels irradiated up to about 120 GWd/t. Model calculation by ORIGEN-2 reproduces well the observed content of ²³⁷Np.

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The internal pressures in the large and normal grain UO₂ pellet rods irradiated at a linear heat rate of <29kW/m up to 21GWd/t U were studied to clarify the effect of in-pile densification and fission gas release. The large grain (grain size: 23μm) pellets were manufactured from the active powder produced by the new ADU (ammonium diuranate) process. The pore structure of the large grain pellets mainly consisted of coarse pores that were formed by adding a poreformer. The pore structure of the normal grain (8μm) pellets made from the current powder consisted of fine pores. In-pile and out-of-pile densification of the large grain pellets were smaller than those of the normal pellets and occurred owing to the disappearance of fine pores as fabricated. The increase in free volume of the large grain fuel rod did not occur significantly owing to its smaller densification during the initial irradiation period. The fuel stack length change during irradiation was predicted with the in-pile densification and swelling model. The increase in grain size decreased fission gas release by diffusion. As a result, it was found that the internal pressure of the large grain fuel rod was reduced after 10GWd/t U.

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Selective ionophoric mobility of plutonium with ease of concentration upgradation from aqueous nitrate solutions was investigated. A thin flat-sheet supported liquid membrane (SLM) impregnated with tri-iso-amyl phosphate (TAP) was used. Accurel polypropylene hydrophobic microporous membrane 'Enka' was tested as the solid polymeric support. The source phase generally contained extremely dilute (ca. 10^-6mol/dm^-3) to moderately concentrated plutonium(IV) nitrate solutions (ca. 10^-3mol/dm^-3) in about 4mol/dm^-3 HNO₃. Membrane permeability and selectivity dependency on variables like nitric acid concentration in the source phase, carrier concentration, receiving phase composition, etc. were systematically evaluated. More than 90% pertraction of plutonium could be easily accomplished in single run employing a feed solution consisting of about 1mg/dm^-3 Pu and 4mol/dm^-3 HNO₃, carrier concentration of 0.8mol/dm^-3 TAP/dodecane; the receiving phase was 0.5mol/dm^-3 sodium carbonate or 0.5mol/dm^-3 ascorbic acid. The selective diffusivity of plutonium(IV) was observed from various effluents originating from fuel reprocessing operations. Reusability of membrane supports was also found to be satisfactory.

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Flow fields of nitrogen (N₂) and argon (Ar) gases in a low pressure impactor are visualized by using a Laser Induced Fluorescence (LIF) technique of iodine molecules under typical MLIS (Molecular Laser Isotope Separation) operating conditions for uranium hexafluoride (UF₆). The flow fields with different pressure ratios (downstream pressure/upstream pressure) and nozzle-to-plate distance are examined. It is shown that various shock waves exist in the low pressure impactor. The axisymmetric Euler equation is solved by using the Harten-Yee TVD method. The calculated shapes and locations of shock agree well with experimental data obtained by LIF. The calculated solutions compared with those previously calculated, however, a remarkable difference is observed between these two calculated results.
With the aid of calculated flow fields, the collection efficiency is determined by tracking the particle trajectories. The diameter of 50% collection is found to be dependent on the pressure ratios and nozzle-to-plate distance. It is shown that the dependency of diameter of 50% collection on these parameters is different between this study and previously calculated one.

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The structure of uranyl nitrato complex with CMPO[n-Octyl(phenyl)-N, N-diisobutylcarbamoylmethylpho-sphine oxide] in solid state and in non-aqueous solvents without containing free CMPO has been studied by using IR spectrophotometer, ¹³C- and ³¹P-NMR. The carbonyl(_νCO) and phosphoryl(_νPO) stretching bands of coordinated CMPO were observed at lower wavenumber than the corresponding bands of free CMPO in both the states. The ¹³C and ³¹P peaks assigned to the carbonyl carbon and phosphoryl phosphine of coordinated CMPO was detected in the lower field than that of free CMPO. From these results, it was concluded that the uranyl nitrato complex with CMPO in both the states has the structure with two nitrate and one CMPO coordinated as bidentate in the equatorial plane of uranyl ion, i.e., UO₂(NO₃)₂•CMPO. Furthermore, the electrochemical studies of UO₂(NO₃)₂•CMPO complex in CH₃CN have been carried out using cyclic and normal pulse voltammetric methods. It was found that the UO₂(NO₃)₂•CMPO complex is reduced to U(V) complex at around -1.22V vs. Fc/Fc+ (ferrocene/ferrocenium) and that the resulting reductant is oxidized to U(VI) at around +0.04V vs. Fc/Fc+.

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A computerized support system for the emergency technical advisory body (ETAB) in Japan (COSTA) is being developed by the Japan Atomic Energy Research Institute to provide useful information for the ETAB during a reactor accident emergency. A major function of COSTA is to identify plant status and predict accident progression in real time based on emergency data reported by the utility of the affected plant. This function could not be achieved if severe accident analysis codes are used directly because the use of these codes would take extensive computing time.
This paper describes a real-time prediction technique for accident progression in a PWR containment during a severe accident when water on the containment floor flows into the reactor cavity (wet cavity). The technique developed combines a knowledge-based expert system with a multivariate analysis method, which makes it possible to predict accident progression in real time and to quickly cope with changing emergency situations. The results predicted with this technique was compared with the results by two severe accident analysis codes, THALES and STCP, and the technique reproduced well the results by the codes.

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A dynamic food chain model DYNACON was developed to simulate the radionuclide transfer on agricultural ecosystems. DYNACON estimates the radioactivity in each compartment of food chains for three radionuclides, nine plant species and five animal products as a function of the deposition date. A number of the parameter values used in this study are representative of Korean agricultural conditions. The model was expressed by coupled differential equations and the radioactivity in each compartment was solved as a function of time following an acute deposition. Although DYNACON is structurally based on existing models, it was designed in order to simulate more realistic radionuclide behavior in Korean agricultural conditions and to save computation time. It was found that the radioactivity in foodstuffs depends strongly on the date of deposition. A comparative study between DYNACON and an equilibrium model showed good agreement for depositions that occur during the growing season of plants. DYNACON is going to be implemented in a Korean real-time dose assessment system FADAS.

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