In multi-dimensional thermal hydraulic analysis, when flow is oblique to computational grid lines, false or numerical diffusion is generated by the upwind difference scheme which is almost essential at high-Peclet-number flow. This diffusion causes a large computational error, especially in the pure upwind difference scheme; therefore, some measures have been devised to improve the finite difference method. Also in the finite element method, the Streamline Upwind/Petrov-Galerkin method, and equivalent to this, the Balancing Dissipation method have been used to remedy the above problem. In this paper, however, it is shown that these finite element methods often provide numerical solutions with over- and undershoot or with spatial oscillation, which are caused by indirect 'upwinding'. As a replacement of these methods, a straightforward 'upwinding' in the finite element method is introduced in this study. The present method provides numerical solutions without causing the above problem, and is applicable to a wide range of the Peclet number.

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Combined forced and free convective heat transfer characteristics were experimentally investigated for water flowing under about 1 atm in a narrow vertical rectangular (750 mm long, 50 mm wide and 18 mm in gap) channel heated from both sides. Experiments were carried out for both downward and upward forced convective flows for Reynolds number Re of 4 x 10¹5 × 10⁵ and Grashof number Gr of 5 × 10⁴4 × 10¹¹, where the distance x from the inlet of the channel is adopted as the characteristic length in Re and Gr. As the results, the following were revealed :
(1) Heat transfer coefficients for the combined convective flow region can be expressed in simple forms with a dimensionless parameter Gr/(Re^21/8Pr^1/2) which is constituted by Gr, Re and Prandtl number Pr.
(2) From the above-mentioned simple expressions it can be identified that the combined convective heat transfer is significant for the condition of 2.5 × 10^-4 < Gr/ (Re^21/8 pr^2/1) < 1.8 × 10^-3.
(3) In the present experiment, little significant differences were observed in heat transfer characteristics between the combined convective flow region with upward forced convective flow and that with downward forced convective flow.

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Analysis of large break LOCA (loss-of-coolant accident) of a commercial PWR (pressurized water reactor) is made with the THYDE-P2 code under the LOFT (Loss-of-Fluid Test) L2-3 condition. Subcooled reflooding is calculated to occur, whereas in LOFT L2-3 saturated reflooding seems to have been observed. Except for this fact, despite the thermal and geometrical differences, the calculated results show that the LOFT system well simulates PWR-LOCA under the LOFT L2-3 condition. The existing safety criteria are satisfied by the commercial PWR's with a big margin in case of LOCA under the LOFT L2-3 condition.

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Some characters on micro structure and chemical composition of hydrous titanium oxide (HTO) and its granules crosslinked with polyacrylic acid hydrazide (PAH) were measured. And by using agitated tank system, seawater uranium adsorption properties of HTO and its granules were evaluated. Based on these results, the mechanism of adsorption and the effect of granulation were discussed. Pore diffusion appeared to occur in macro pore and adsorption seemed to occur mainly on inner surface of the macro pore. The pore diffusion coefficient and adsorption capacity of the granulated HTO were found to be little affected by crosslinking or by granule diameter. With increase of granule diameter the liquid-film mass transfer coefficient of the crosslinked granule increased. It was shown that PAH is a binder with good seawater permeability.

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Deposition profiles of corrosion products on fuel surfaces and products chemical compositions were determined at Shimane Nuclear Power Plant, a low-crud BWR. The deposited amounts were expressed as functions of crud concentration in the reactor water, fuel burnup and flow velocity in a fuel channel. The results could be predicted satisfactorily by the crud deposition model based on microlayer evaporation and drying out phenomena. The amount depositing at high flow velocity gave saturated values which were inversely proportional to the flow velocity (∝1/v), while those at low velocity did not reach saturated values, but rather were proportional to 1/v³. The depositing corrosion products could be divided into two layers, inner and outer, with more Co ions being taken into the former layer.

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Axisymmetric concentration profiles of an isotope separating thermal diffusion column with continuous feed and draw-offs were calculated by solving the convection-diffusion equation using Newton iterative method, where the flow variables are specified from the input data. Computations were performed for ³⁶Ar and ⁴⁰Ar gas mixture within the cylindrical column having inner hot radius of 0.15 mm and an outer cold radius of 7.5 mm, between which the temperature differs by 515 K. The rate of feed F, supplied into the middle-height point of the column, was varied from 2.72 x 10^-4 g/s (10 cm³/min at 25°C) to 5.45 x 10³ g/s (200 cm³/min), while the cut θ, or the ratio of the upper drawing-off to feeding rates, from 0.1 to 0.9. The pattern of concentration profile depends largely on the value of the total transport (that is, θ F in the upper section and -(1-θ) F in the lower section), and the two different patterns are linked at the feed point. The effect of changes in hot wire temperature (723973 K, temperature differences: ΔT= 435685 K) and in cold wall radius (r_c= 7.5 and 5 mm) were also analyzed to find the value of F/(ΔT•r⁴_c) less than 0.02/(s•K•cm) is necessary for effective separation.

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Leaching behavior of simultaneously synthesized composite waste form of monazite- and zirconium phosphate-type was investigated by making use of simulated high level waste (HLW).
The obtained results showed that the leach rates of the composite forms are very low compared to that of the borosilicate glass waste form, indicating that the composite is regarded as being significant to immobilize HLW grossly like vitrification.

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Stagnant liquid lithium contained in a vertically 1.3 m long and 46 mm I.D. 316-SS cylindrical vessel up to a 0.3 m level was heated by a concentrically inserted heater pin of 12.5 mm O.D. and 54 mm active length. The parallel magnetic field to the vessel was imposed by a superconducting magnet. The experiment covered the ranges of the lithium temperature: 320510°C, the heat flux: 1040 W/cm², the transverse B: 01.2 T (Ha = 02, 730) and the parallel B = 03T (Ha = 06, 860).
The temperature fluctuation is enhanced by imposing a weak magnetic field of B = 0.10.3 T for both parallel and transverse fields and almost completely suppressed with increasing to B = 1 T in the case of the transverse field but its low frequency component still remains large, becoming oscillatory, up to B = 3 T in the case of parallel field. The heat transfer shows a similar trend to the temperature fluctuation. It increases singularly by a weak B especially in the perpendicular sector to the transverse magnetic field and decreases with increasing B. In the case of parallel magnetic field, the heat transfer increases in a weak field of B = 0.10.5 T, the same as in the transverse magnetic field, but it does not decrease so much in a strong field of </>B = 13 T, presenting a rather higher value than in B = 0 T.

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In order to calculate criticality parameters of nuclear fuel solution systems, number densities of nuclides relating to the medium such as water or organic solvent are needed and generally calculated from density equations.
Densities of uranyl nitrate-nitric acid and uranyl nitrate-gadolinium nitrate-nitric acid solutions were precisely measured, and two empirical density equations for the solutions were derived as functions of concentrations of solutes, temperature and their products from regression analysis of a number of experimental data.
The density equation for the solution of UO₂(NO₃)₂-HNO₃ was compared with published equations and discussed from the viewpoint of the atomic number density of hydrogen.
Density equations for the solution of UO₂(NO₃)₂-Gd(NO₃)₃-HNO₃ have not been reported so far and the effect of gadolinium on the hydrogen atomic number density in the uranium solution has been neglected. The present equation gives accurate number density in the relevant medium.

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