The conditions necessary and sufficient for the radiation monitoring are investigated, when a considerable amount of radioactive argon is continuously released from reactors. According to the present regulation the maximum permissible concentration in air of ⁴¹A is 5×10^-7μc/ml occupationally, and it is expected to be reduced before long. In any case, it is commonly regarded as necessary to detect the concentration of ⁴¹A upto about 10^-8μc/ml in the case of the monitoring for the public living in the neigborhood of a reactor site. And such a detector necessarily costs much and is troublesome for the practical use, even if it is technically feasible. In this paper, it is shown on the analysis of the effect of ⁴¹A that there is the possibility to practice the monitoring for the public, only with the devices detectable for the local concentration about 10^-65×10^-7μc/ml and γ detectors of the standard type. It is also mentioned that the contribution of ⁴¹A to the genetic dose of the population might be detectable.

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We studied on the mock-up flow test of the natural uranium, heavy water cooled and moderated research reactor named JRR-3, 10 MW in thermal power. This mock-up test equipment is constructed with the main loop of heavy water flow, containing a mock-up core tank, a circulating pump, a flow control system and a water level regulating system.
This report presents data on the following tests:
(1) the flow resistance of the model fuel element
(2) the vibration of the model fuel element by flow
(3) the leakage through the contact part between the model fuel element and its seat
(4) the flow distribution of the fuel elements from the lower plenum of the core tank
(5) the flow characteristics of the total system on the effect of the flow control mechanism
(6) the flow of the model fuel element when the clearance between the fuel element and its seat was changed

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This paper describes the photographic behavior and electric characteristics of deuterium plasma in heavy current linear pulse discharges which were obtained in our experimental research. The behavior is clarified by means of high speed and ordinary cameras, and the electric characteristics are obtained by measuring the discharge current and terminal voltage between the electrodes of discharge tube.
According to the photographic research by a high speed camera, the plasma core is continuously kept at tube axis for a while after the first pinch occurred, and its shape does not change so much with discharge current. Moreover, the diameter of the above plasma core, which is taken by a high speed camera, is almost equal to the plasma shape of the photograph taken by an ordinary camera. We have found that the plasma column is maintained with a considerable stability, even though the distributed return circuit on the circumference of the tube is taken off by about 1/4 or less. In case of deuterium plasma, length of time from the start of discharge to the first pinch coincides fairly well with the calculated value obtained from Leontovich's equation.

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Starting from the fcmiliar integro-differential equation describing the slowing-down and diffusion of neutrons, the critical radius of a two-region thermal neutron reactor with spherical symmetry has been calculated by the Wiener-Hopf method. The only assumption is that the diffusion coefficient is proportional to the slowing-down length, which may be less restrictive than generally made. Using the Fermi slowing-down model, the critical radius of the internal region is calculated from an asymptotic solution in each region in which the external region is finitely extended. In that expression the extrapolation distance for the internal region can be also found. The integrals appearing in those expressions is numerically evaluated with little labor. Finally, two numerical examples are given and the results are compared with those obtained by the elementary diffusion approximation.

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The accurate determination of minute amounts of boron contained in materials and fuels for reactors is one of the very important problems because of the large cross section of boron for thermal neutrons.
The method studied by the present authors is based on the coloration of boron with curcumin.
The procedure is as follows.
Methanol and sulphuric acid are added into a distilling flask and 25ml of methanol is distilled to expel boron contained in the reagents. A sample containing 0.052μg of boron is weighed into the distilling flask, and dissolved in sulphuric acid.
Immediately 2025ml methanol is distilled and the distillate is caught in calcium hydroxide suspension.
After evaporating the suspension to dryness on a water bath, hydrochloric acid and oxalic acid-curcumin are added and the dish is placed in a thermostat held at temperature of 58±0.5°C.
The boron complex is extracted from the residue with ethanol and the color is measured at the wave length of 540mμ.
This method makes it possible to determine 0.050.1ppm of boron within the error of 5%, and is applied to determine the amount of boron in metal beryllium and beryllium hydroxide.

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Experimental studies were carried out on the melting and fabrication of low purity reactor grade zirconium, high purity reactor grade zirconium, Zircaloy-2 and commercial zirconium. The results were as follows;
(1) Sound ingots were obtained.
(2) It was recognized that hot workability (forging and rolling) were good.
(3) Effects of cold rolling, annealing temperature, time, atmosphere and cooling rate on the mechanical properties of the respective materials were discussed and optimum rolling and annealing procedure was established.
(4) Recrystallization diagrams were shown and the grain growth characteristics were compared with that of other materials.
(5) It was found that VHN measured at the surface is higher than VHN in the section and the difference was found to increase with cold rolling.

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The Atomic Energy Research Institute, the predecessor of the Japan Atomic Energy Research Institute, was established on Nov. 30, 1955, and the Tokai village in Ibaragi Pref. was selected as the site of the Institute on Apr. 6, 1956. The Japan Atomic Energy Research Institute was established on June 15, 1956, and the construction of JRR-1 and other facilities started on Aug. 10, 1956.
Today, three years after the start of construction in the quiet Tokai village, many facilities of the Institute have been completed and the total building area covers more than 30, 000m², where a staff of 700 is already working. During the construction, the principal aim was to make facilities adequate for nuclear research.
Particularly careful measures were provided for radiation protection to research workers and the general public. The problems of radiation shielding air tight construction and ventilation for radio-active fission products etc. have been studied and the results were applied in designing the facilities.
In the present paper, various aspects of the site, plan of construction and the outlines of the principal building facilities such as JRR-1, synthesis laboratory, JRR-2, 10kc ⁶⁰Co and Linac radiation facilities, Hot Lab. and JRR-3 are described.

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