A semiconductor γ-ray detector using high resistivity P-type silicon crystals has been developed for nuclear power plants. Since the operating temperature requirement is high (≤60°C) in these plants, the electrical thermal noise of the detector element due to the reverse current has to be decreased. The reverse current of the silicon diffused p-n junction fabricated by a planar process was evaluated and satisfactory results were obtained.
The detector elements were applied to a γ-ray area monitor and also to a personal dosimeter with an IC card, as a means for reducing manpower requirements in radiation control work. Performance tests were carried out in a nuclear power plant and the practicality of these applications was confirmed.

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Direct numerical simulation using the three-dimensional and time-dependent finite difference scheme which have been reported in the previous paper is performed for turbulent natural convection in a horizontal concentric annulus. Numerical results are obtained for the Rayleigh number based on the gap width from 1.0×10⁶ to 1.72×10⁷. To verify the validity of the present scheme, numerical results dealt with statistically are compared with other experimental data and numerical solutions and the effect of grid size on spatial resolution capability is investigated. It is shown that time-averaged quantities deduced from appropriate spatial resolution are in good agreement with experimental results, whereas turbulence quantities are excessively estimated when spatial resolution is insufficient.

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Effects of Fe and Ni contents on nodular corrosion susceptibility and hydrogen pick-up of Zircaloy were investigated. Total number of 31 Zr alloys having different chemical compositions; five Zr-Sn-Fe-Cr alloys, eight Zr-Sn-Fe-Ni alloys and eighteen Zr-Sn-Fe-Ni-Cr alloys, were melted and processed to thin plates for the corrosion tests in the environments of a high temperature (510°C) steam and a high temperature (288°C) water.
In addition, four 450kg ingots of Zr-Sn-Fe-Ni-Cr alloys were industrially melted and BWR fuel cladding tubes were manufactured through a current material processing sequence to study their producibility, tensile properties and corrosion resistance.
Nodular corrosion susceptibility decreased with increasing Fe and Ni contents of Zircaloys. It was seen that the improved Zircaloys having Fe and Ni contents in the range of 0.30[Ni]+0.15[Fe]≥0.045 (w/0) showed no susceptibility to nodular corrosion.
An increase of Fe content resulted in a decrease of hydrogen pick-up fraction in both steam and water environments. An increase of Fe and Ni content of Zircaloys in the range of Fe≤0.25w/0 and Ni≤0.1w/0 did not cause the changes in tensile properties and fabricabilities of fuel cladding tube. The fuel cladding tube of improved Zircaloy, containing more amount of Fe and Ni than the upper limit of Zircaloy-2 specification showed no susceptibility to nodular corrosion even in the 530°C steam test.

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