[en] Experimental results of studying the thermohydraulic instability of the modes of water natural convection under conditions of the BWR reactor startup are presented. Effect of water under heating at the channel input and the effect of pressure in the system are studied. The diagrams of the safe modes of the coolant flow during the BWR reactor startup are constructed by means of the obtained data

[en] A fissile package must be subjected to a fire test of 800 deg. C for 30 minutes. For a package that contains enriched uranium hexafluoride (UF₆), the temperature of the contents has to be kept below 121 deg. C in order to avoid rupture of a 30B cylinder. A previous study on heat transfer mechanisms in an enriched UF₆ package type 'DOT-21PF-1' found that decomposed gas with a temperature of around 100 deg. C generated from heated phenolic foam thermal insulation was a major heat source heating the cylinder in the initial period of the fire test, in addition to the heat conducted from the outer surface through the thermal insulator into the interior of the package. Mitsubishi Materials Corporation has developed a new packaging for enriched UF₆ 'MST-30' that also uses phenolic foam as the thermal insulator, and has performed a fire test of 800 deg. C for 30 min, which also indicated the temperature history of the package interior affected by heating from the decomposed gas. In this study, a laboratory test was carried out to identify the kind of gas generated from the heated phenolic foam. The test found that the decomposed gas was water vapour. Since water vapour has a large latent heat, it has a large heat transfer coefficient when it condenses on a cool surface. By taking the water vapour heating mechanism into account, an analytical model was developed for MST-30 to simulate the measured cylinder temperature history. Analytical models to evaluate the cylinder temperature under the 800 deg. C/30 min fire test considering conservativeness are also presented. (author)

[en] Practical thresholds for water leak-tightness of small leaks were determined by experimentation. Measurements for small leak samples were taken of air leakage rates and water leakage rates for identical leak samples in order to identify parameters that influence water leak-tightness threshold. Four types of leaks were evaluated: a fine wire inserted in an O-ring seal, a glass capillary tube, a stainless steel orifice, and a scratched valve stem on a 1 inch UF₆ cylinder valve. Experimental results demonstrated that the key parameter for water leak-tightness is the opening size of the leak hole. The maximum allowable hole size to achieve water leak-tightness ranged from 10 to 20 μm in diameter in this study. Experimental results with 1 inch UF₆ cylinder valve samples demonstrated that the acceptance criteria for preshipment leakage test, 1x10^-3 ref-cm³.s^-1, as prescribed in ANSI N14.5 is an appropriate value from the point of view of water leak-tightness for enriched UF₆ packages. The mechanism of water leak-tightness is plugging by tiny particles existing in water. The water used in experiments in this study contained far fewer particles than in water assumed to be encountered under accident conditions of transport. Therefore, the water leak-tightness threshold determined in this study is a conservative value in a practical evaluation. (author)

[en] Revised IAEA Regulations for the Safe Transport of Radioactive Materials (ST-1) set forth incremental requirements for the transport of uranium hexafluoride (UF₆. Of extreme importance is the new requirement (para. 677 (b)) that mandates the leak-tightness of the cylinder valve under accident conditions of transport. This new requirement is added from the point of view of the criticality safety of UF₆. A new package, known as 'MST-30', of Type A Fissile material for enriched UF₆, has been developed by Mitsubishi Materials Corporation to satisfy both new regulatory requirements and the present transport system. MST-30 reinforces the value protection function and utilises the high-density polyurethane foam as a shock absorbing media, instead of natural wood components. This paper (i) reviews the historical background that motivated the development, (ii) presents the design concept and features of the MST-30 package, and (iii) reports on the compliance test results that demonstrated the MST-30's superior ability to withstand accident conditions of transport. (author)

[en] For studies on the characteristics of bubble flow in a rectangular channel (20 x 100 mm) a new electrode-mesh tomograph have been applied. The measuring principle is based on local conductivity measurement and a signal concerning. The applied sensor scans the local void fraction distribution in 2 parallel planes, separated 1.5 mm in flow direction, with a resolution of 3.0 x 2.2 mm and a overall sampling rate of 1200 Hz (all 256 points). Algorithm for the calculation of the local instantaneous void fraction distribution and the true gas velocity are presented. Based on these values the approximate shape of bubbles have been reconstructed and the gas volume flow through the sensor evaluated. The superficial gas velocity as well as the local distribution of the gas volume flux can be calculated. An extensive sensitivity study illustrating the applicability and accuracy is presented, based on experimental observations as well as theoretical considerations. The evaluated results are compared with high-speed video observations of the flow field as well as data comparing the reconstructed volume flow with measurements by a laminar flow meter. Good agreement can be stated. (author)

[en] A theoretical model has been developed to study the local heat transfer coefficient of a condensing vapour in the presence of a noncondensable gas, where the gas/vapour mixture is flowing downward inside a vertical tube. The two-phase heat transfer is analysed using an annular flow pattern with a liquid film at the tube wall and a turbulent gas/vapour core. The gas/vapour core is modeled using the analogy between heat and mass transfer. The model incorporates Nusselt equation with McAdams modifier and Blangetti model for calculating the film heat transfer coefficient, Moody and Wallis correlations to account for film waviness effect on gas/vapour boundary layer. The suction effect due to condensation, developing flow and property variation of the gas phase is also considered. A comparative study of heat transfer coefficient and vapour mass flow rate has been made with various models to account for condensate film resistance and condensate film roughness. Results show that for very high Reynolds number, the condensation heat transfer coefficient is higher than the film heat transfer coefficient

No abstract available

[en] The first wall and blanket cooling systems using liquid metals such as Li, Li-Pb alloys and K are superior to those using normal fluids such as He or water because of liquid metals' higher heat transfer characteristics, lower operational pressure at high temperature, and simpler system of tritium self-breeding. However, under a magnetic field as high as about 10T in a magnetic confined fusion reactor, the liquid metal single-phase flow cooling system receives very high MHD pressure drop and the enhancement of heat transfer, the authors have proposed advanced cooling systems which employ the following liquid metal two-phase flows: a He-Li two-phase annular-mist flow and low-pressure Li or K boiling flows, because it has been expected that overall electrical conductivity can be reduced in the two-phase mixture and the laminarization may be suppressed by two-phase agitating motions. The He-Li two-phase flow system has an additional merit of preheating the cooling circuit by hot helium flow before lithium charge, and the liquid metal boiling flow system has the merits of its simplicity and high thermal efficiency by constructing topping cycle. The advantages of these liquid metal two-phase flow cooling systems are discussed as well as their disadvantages

[en] The purpose of this paper is to discuss the recent circumstances in Indonesia concerning nuclear energy program and try to anticipate the challenges and the future trend on the application of nuclear power for electricity generation. It is indispensable for Indonesia with regard to development of industries and improvement of the quality of life to establish sufficient and stable electric power supply. A national energy policy has been adopted, in its way to secure the continuity of energy supply at affordable price; to enhance the people's quality of life, and to reserve an adequate supply of oil and gas as important sources to fund national development program. It is expected that nuclear energy will reduce the dependence on a single type of fuel, economize energy utilization, as well as to support environmental program by applying clean-energy technology. (author)

[en] In this study, the electrical conductance method was applied to measure the liquid film thickness between the individual bubbles and the wall in a narrow channel. This method consists of two different conductance measurements. One measures the conductance between electrodes on an inner wall, and the film thickness is estimated. Other measures the conductance between two sensors which are installed on the opposing walls of the channel. This conductance is related to void fraction in the gap. Therefore, two-dimensional distributions of the liquid film thickness and void fraction can be measured simultaneously. (author)