The sputtering yield of Mo honeycomb walls was compared with the yield of flat walls in a d.c. Ar glow discharge. Under the experimental condition where the mean energy is approximately 1 keV and the angle of incidence of primary ions strongly distributed around normal, the yield is reduced by a factor of 20 to 30. Before and after the bombardment, the surface topography of the honeycomb targets was observed by a scanning electron microscope.

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The gas-liquid slip ratio and the MHD pressure drop in the two-phase liquid metal flow under a strong magnetic field are treated in relation to the distributions of the gaseous phase and the fluid velocity. From NaK-N2 two-phase experiments, it is found that :
(1) The ratio of the two-phase MHD pressure drop to that of the homogeneous non-slip two-phase flow model is independent of the applied magnetic field strength and the channel geometry (ratio of wall thickness to channel width) and is presented as a function of the ratio of the gas-liquid volumetric flow rate.
(2) The void distribution is affected by the applied magnetic field. The gas bubbles may be pushed away towards the both side walls due to the pinch effect, resulting in the increase of the ratio of the mean void fraction to the one at the channel center with the increasing applied magnetic field.
(3) The gas-liquid slip ratio is not directly dependent on the applied magnetic field strength and the channel geometry and is presented as a function of the ratio of the gas-liquid volumetric flow rate. As a result, the slip ratio decreases with the increasing system pressure and/or the decreasing mixture quality.

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The nuclear characteristics of the thermal blanket and blanket-shield designs are analyzed to provide a basis for optimizing the blanket design of D-D fusion reactors. The thermal blanket is devised to yield high energy deposition in a compact blanket through the use of neutron multiplier and energy converter with 1/v neutron absorption cross section. The blanket-shield design, on the other hand, aims at providing acceptably good shielding characteristics to protect the superconducting magnet by incorporating shielding substances within the blanket itself.
The results of calculation reveal that the thermal blanket design provides only modest energy deposition in the blanket despite its use of beryllium, which is limited in availability. In contrast, the blanket-shield concept is found to offer attractive possibilities in terms of nuclear characteristics, and the results of this analysis point toward the blanket-shield concept as the logical choice for D-D fusion reactor blankets.

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The burnup characteristics of a 300 MWe LMFBR are studied numerically based on three-dimensional calculations.
The analysis covers the effects brought by differences in the assumed positions of the control rods and by changing the number of energy groups adopted for calculating the burnup reactivity loss and the detailed space distribution of major Pu isotopes after prescribed periods of irradiation. Results are also compared between three- and two-dimensional models used for the calculations. The results reveal significant influence of control rod position on the depletion and buildup of Pu isotopes not only in the core region but also in the blanket region.
Burnup calculations based on two energy groups prove to provide a fairly good approximation of the results obtained with three groups ; this is not the case with one-group calculations, so long as the conventional method is adopted for reducing the energy groups. The errors introduced by the approximative methods in estimating the changes brought to the amounts of Pu isotopes resulting from irradiation increases with the atomic weight, in the order 2391311, 240Pu and 241Pu. Hence for accurate estimation of breeding characteristics, it would be necessary to perform three-dimensional burnup calculations with account taken of the individual positions of control rods distributed in discrete channels over the cross sectional plane. The use of an adequate number of energy groups is also essential unless a suitable improved one-group method is adopted.

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An analysis is made of the nuclear safety of a Molten Salt Breeder Reactor (MSBR) using one point kinetics model, with particular attention to the fact that the MSBR, operating on 233U-Th with circulating fuel, has a very small effective delayed neutron fraction, which is conducive to a very high power increase being induced by reactivity addition, particularly when applied sharply.
The analysis proves that the transient phenomena of MSBR initiated by an abnormal reactivity addition do not exceed the bounds of structural safety, in virtue of the very favorable nuclear and thermal characteristics of the MSBR.

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A few-group coarse mesh method has been developed for the calculation of power distribution in 2-dimensional geometry of a fast breeder reactor by extending Askew's one-group coarse mesh method. This method employs modified macroscopic cross sections including group-dependent corrections for coarse meshes of one point per hexagonal assembly and can be easily incorporated into conventional diffusion codes.
Results obtained in few-group 2-dimensional test cases on a prototype fast breeder reactor indicate that this method is as accurate as fine mesh calculations with six mesh points per assembly and the computing time is about 14 of that of fine mesh calculations.

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Experimental studies were carried out on incipient boiling of sodium flowing in an electrically heated seven-pin bundle under forced convection.
In the first series of experiments temperature distributions in the bundle were measured under non-boiling conditions. The measured temperature distributions agreed fairly well with the calculation by the NORMAL code.
In the second series of experiments incipient-boiling (IB) phenomena were investigated, with particular reference to the IB superheat and the voiding patterns. The IB wall superheat decreased with increase in flow velocity. The observed coolant voiding was limited in the central subchannel because of the steep radial temperature gradient in the bundle. In order to describe this voiding process a two-dimensional voiding model was required.

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