A new, finite element solution technique for neutron diffusion equations has been developed. In this method, calculational accuracy is improved by adding imaginary nodal points, subdividing each triangular element into three quadrilateral subelements, and ap-proximating the spatial variation of neutron flux within each element by three linear planes. In the process of solving the algebraic equations, the additional unknown variables are eliminated so that the number of unknowns remains the same as that in the usual finite element method. This technique has been applied to two types of one-group neutron diffusion equations to test its accuracy. It has been shown that the method yields the same degree of accuracy, in eigenvalues and neutron flux distributions, as the usual finite element method when four times as many elements are used. Under the same degree of accuracy, the computing time of the new method is about 1/4 that of the usual method.

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The effect of a magnetic field on laminar natural convection of liquid metal was studied experimentally using NaK as conducting fluid. The magnetic field was imposed horizontally and parallel to a uniformly heated vertical plate, to act perpendicularly across the convective flow. In a low magnetic field, the temperature profile across the layer of flowing fluid acquired an η-shaped profile characterized by a valley close to the wall and a peak further away, which had the effect of raising heat transfer rate above that obtained in the absence of magnetic field. When the magnetic field was intensified, its braking effect on the flow approached the temperature profile to the case of pure heat conduction through solid, to result in dwindling heat transfer rate.

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To evaluate the temperature- and burnup-dependent intraparticle CO/CO₂ pressures for the design of HTGR low-enriched UO2 coated particles, a thermodynamic model has been developed, based on the equilibrium oxygen partition between UO₂, carbon oxide gases and fission product oxides. The model takes into account a change in kernel stoichiometry due to temperature change and fuel burnup, and involves oxygen release correlations established by referring to measured CO content data in the literature.
The analyses of measured CO contents below 1, 400°C for unirradiated particles show that the 0/U ratio of as-coated particle kernel is 2.00012.001. The 0/U ratio in irra-diated particles has been predicted to range from 2.0001 to 1.999 below 2, 000°C, indicating that the oxygen liberated by fission is consumed nearly all in forming fission product oxides and CO/CO₂ gases under normal reactor operating conditions, but at extreme tem-peratures above 2, 000°C the fuel kernel will be reduced to highly hypostoichiometric composition.

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A calculation model was developed to predict shutdown dose rate around the recircula-tion pipes and components in boiling water reactors (BWRs) by simulating the genera-tion, transport, activation and deposition of corrosion products in the primary cooling water. The model is characterized by separating cobalt species in the water into soluble and insoluble materials and then calculating the deposits on the pipe wall for each species using the following considerations :
(1) Soluble cobalt (designated as ionic cobalt) is taken into a spinet structure on the surface after diffusing into the oxide layers.
(2) Insoluble cobalt (designated as crud cobalt) deposits on the oxide layers.
(3) A part of the ionic cobalt released from the crud on the oxide layers is taken into a spinel structure like (1).
The calculated results agree satisfactorily with measurements in two BWR plants. The shutdown dose rate around the recirculation pipes during the entire operating life was calculated to evaluate the effects of the radiation reduction procedures.

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This paper concerns the numerical analysis of rarefied gas flowing through an orifice in a rotating cylinder. The full solutions for the Burnett equations in the steady state are successfully obtained and compared with those for the Navier-Stokes equations. Then, the pressure in the downstream side is chosen as a parameter to give an appropriate Knudsen number and a Much number.
The results show construction of the rarefied gas flow, where the Burnett terms, or the higher order of approximation, reduces the contribution of the viscosity term in the equation of motion and of the conduction term in the equation of energy. The criteria of invalidity for the Navier-Stokes equations and the Burnett equations are discussed, too.

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The improved coarse mesh method, which was originally derived by Askew and applied to fast reactor core calculations by one of the authors, has been applied to boiling water reactor core calculations. Since direct application of the method leads to negative fluxes in the reflector region, a procedure has been developed in which the correction factor for coarse meshes is not utilized in the reflector. The results of the improved coarse mesh calculations were compared with those of fine mesh calculations. The negative fluxes were eliminated and good agreement was obtained for the neutron multiplication factor and power distributions in fuel assemblies near control rods, though the accuracy of power distributions near the reflector was as that of conventional coarse mesh calculations.

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