[en] In normal operation, primary coolant circulates in a closed loop to remove heat in the core of a PWR. Radioactive rare gas is contained in primary coolant, and its concentration is the function of the leaking quantity from the break and pinholes of fuel cladding tubes, the removed quantity from purifying system, the leaking quantity from the equipment in a primary cooling system and so on. The radioactive rare gas in bled water is separated and removed when sprayed drops fall and pass through the gaseous phase in a volume control tank. Therefore, the concentration difference of radioactive rare gas exists between the gaseous phase and liquid phase in the volume control tank. In this study, analysis was performed by making an analysis model on the behavior of distributing radioactive rare gas in the coexisting gaseous and liquid phases. As the results, it was confirmed that the continuous purge of the gaseous phase part of a volume control tank was useful, that the various constants used for the analysis were adequate, and that the increase of the volume of the gaseous phase part was also effective to reduce the concentration of radioactive rare gas in primary coolant. (Kako, I.)

[en] Many researches on the flow mode of two-phase flow in horizontal pipes made so far have been related mostly to the pipes with smooth surfaces. In the horizontal two-phase flow at low velocity, bubbles flow along the top walls, and the behavior of the bubbles at this time is considered to be largely affected by the roughness of the walls. Such horizontal two-phase flow at low velocity appears in relation to the separation of bubbles from the surfaces of boiling facing downward, besides the hot leg at the time of small LOCA in PWR plants. In this research, the horizontal two-phase flow of air-water system at atmospheric pressure and normal temperature in a rectangular pipe was used, and mainly the effect of wall roughness on the behavior of bubbles was experimented. The experimental setup is shown. The flow mode was observed, the shape projected on a horizontal plane and the velocity of bubbles were measured with a high speed camera, and the thickness of bubbles was measured when the flow rate of water, that of air and wall roughness were changed. It was found that as the top surface was rougher, bubbles became smaller. Bubbles took the shape so that the sum of potential energy and surface energy became the minimum. The effect of the water velocity and wall roughness on the bubble shape was small. The velocity of bubbles was determined by their size and the water velocity, but the effect of the wall roughness was small. (Kako, I.)

[en] Experiments have been conducted on vortex-induced vibrations of a circular cylinder in high Reynolds number (1x10⁵ < Re < 3x10⁶) water flow. Experimental results of displacements in drag and lift directions by resonant vortex-induced vibrations were compared to evaluate the effects of Reynolds number, the damping ratio and the tapered shape on them. As the results, these effects were confirmed on the criteria of the incipient of resonant vortex-induced vibration and its displacement. (author)

[en] We describe the unsteady flow around two-dimensional circular cylinder bundles supported by the leaf spring in the fluid-elastic vibration. The experiment was carried out in a circuit-type wind tunnel having a 200 mm x 200 mm working section of 2,000 mm length at the Reynolds number Re of 6,300. Two-dimensional circular cylinders with diameter D = 20 mm were aligned at regular spaces S in the square array of three rows. The spacing ratio between two adjoining circular cylinders was constant as S/D = 1.5. The time-mean velocity, turbulent intensities and Reynolds stress were measured by use of a laser Doppler velocimeter. The unsteady flow pattern around an oscillating cylinder was observed by the flow visualization in a water channel. Consequently, it was found that the occurrence of the fluid-elastic vibration is caused by the phenomenon of wake-switch for the circular cylinder bundles of three rows. (author)

[en] Discussions were made on (1) path of radioactive gases which dissolve in primary and secondary systems and leak from equipment, pipings, valves and others during normal operation, then are released from the exhaust systems of containment facilities and buildings, (2) the mechanism of their removal, and (3) sources of their radioactive gases. As the concrete example to realize ''As low as reasonably achievable'', the continuous purge from volume control tanks, the increase of letdown flow rate, the increase of storing time in gas decay tanks and others were proposed, and compared with a standard plant. The sources of generating radioactive wastes, the concentration of fission products in primary and secondary coolants, the quantity of release of rare gas and iodine, and the measures for reducing the quantity of release are described. The quantity of release of rare gas was most in the case of the purge from reactor containment vessels. The proposed measures can reduce the release of rare gas and iodine into the environment. (Kako, I.)

[en] An experimental and analytical study on the mass flux and reaction force of water single-phase and steam-water two-phase jets discharged from a thin nozzle was carried out. The mass flux of water jet is well predicted using the Bernoulli's equation with the contraction coefficient, but the recovery of contraction at the nozzle exit should be considered to evaluate the reaction force. The L/D of the nozzle affects the mass flux and reaction force of the two-phase jet, i.e., the mass flux decreases and the reaction force increases with the L/D. The behavior of high-temperature water jet is similar to that of the water jet if the L/D is smaller or nozzle inlet pressure is higher. The behaviors of the mass flux and the reaction force show hysteresis depending on the decrease or increase of nozzle inlet pressure. The mass flux and reaction force can be well predicted by the critical flow analysis based on a separated flow model with the non-equilibrium parameter. (author)

[en] The verification test of flow induced vibration (FIV) in U-bend tube bundles of steam generator (SG) have been carried out using model steam generator, equipped with the large scale U-bend tube bundles, in a freon two-phase flow loop. The objectives of this program are to confirm the margin of FIV of SG U-bend and to advance the evaluation techniques of Thermal-hydraulic flow and FIV for SG U-bend. This report (Part 1) shows the experimental facilities which is included the modeling of a steam generator and the results of thermal-hydraulic test which is included the results of analysis. Another results are shown in Part 2 and Part 3 report. The conclusion of this paper is that void fraction and velocity profile of U-bend tube bundle are obtained in detail and analysis code (FIT-III) is verified very well by using these data. Therefore, it is considered that the results of FIT-III are valid for evaluation of flow induced vibration in actual SG. (author)

[en] Significant improvements in surface wettability and boiling heat transfer on oxide film coated-materials by radiation induced surface activation (RISA) phenomenon were confirmed in our previous study. To delineate the RISA effect in actual boiling systems or in a high-temperature and high-pressure environment, this study aimed at obtaining the contact angle, an indicator of macroscopic surface wettability, of water droplets on various materials such as stainless steel, aluminum and zircaloy plates before and after γ-ray irradiation at ambient temperatures up to 300degC. Before γ-ray irradiation or under the conditions without the RISA effect, measured contact angles decreased when the temperature was below 250degC, clustered around a straight line at temperatures below 120degC, and clustered around another line in the range from 120 to 250degC. At temperatures above 250degC, contact angles remained constant independent of temperature, and contrary to the existing theoretical model, no highly hydrophilic condition or null contact angle condition was achieved. The effects of ambient pressure, gas atmosphere, and material type on the contact angle condition were insignificant. On the other hand, after γ-ray irradiation or conditions with the RISA effect, super-hydrophilicity or null contact angle was achieved after 830 kGy γ-ray irradiation where the temperature was less than 200degC. At temperatures exceeding 200degC, super-hydrophilicity by the RISA effect was not achieved even after 2700 kGy γ-ray irradiation, although a slight improvement in surface wettability was confirmed. (author)

[en] Nuclear energy is fascinating on various points: enormous amount of energy, securing fuels, possibility of solving the global warming, etc. However, it's known that using nuclear energy involves dangerous and safety of nuclear power plant (NPP) is required. Study about NPP safety has been conducted by many researchers. In addition, concern for NPP safety has increased in resent years because of happening of some NPP accidents and newly establishment of NPP. In this paper, detection method of core abnormal phenomena is considered. They are: construction of this method, sensitivity analysis of transient phenomena, and examination for the validity of this method. Transient phenomena dealt with this study are: (A) small break and leak, (B) change in feedwater flow rate, (C) loss of feedwater heating. As a result, this method shows some validity to (B) and (C) but doesn't show to (A). (author)

[en] A conceptual design study of the Japan Sodium-cooled Fast Reactor (JSFR) is in progress in “the Fast Reactor Cycle Technology Development (FaCT) project”. In this project, a two-loop primary system is adopted in order to economize the plant construction cost. The reduction of the number of loops for the primary cooling system increases the primary coolant flow rate per loop. The mean sodium velocity in the pipes increases to over 9 m/s and Reynolds number in the hot-leg pipes is about 4x10⁷. In the JSFR the pipe thickness is designed to be considerably thinner than that of a light water reactor, because the fast reactor is operated at low pressure and high temperature. One of the issues for the piping design is to understand the behavior of flow-induced vibration that is derived from the hydraulic characteristics under high Reynolds number conditions. We made a flow-induced vibration test facility that simulates the hot-leg piping with a 1/3-scale model. Flow-induced vibration experiments were performed using this facility to evaluate and confirm the integrity of piping against the flow-induced vibration. In these tests, we investigate flow patterns and fluctuating pressures on the pipe wall. This paper describes a summary of the 1/3-scale experimental results under the rectified-flow, swirl-flow and deflected-flow conditions at the inlet of the hot-leg piping. (author)