[en] The viewpoint about safety engineering in design, the selection of materials and the effect of environment on materials are studied, taking pressure vessels as the example. The pressure vessels are defined in the enforcement ordinance of the labor safety and hygiene low, and prescribed in the high pressure gas control low and others. The stress of cylindrical and spherical vessels due to internal or external pressure and the stress concentration at flanges and nozzle portions are explained. The structural materials for pressure vessels are different according to gas or liquid contained, temperature and pressure. In case of the pressure vessels for nuclear reactors, the change of material properties due to neutron irradiation must be considered especially. Usually low alloy steels such as A 302B or A 533B lined with austenitic stainless steel by build-up welding are used. The effect of neutron irradiation is monitored with surveillance test pieces. The inspection of pressure vessels is carried out during the manufacture and in service. The pressure boundary for reactor coolant must be designed so as to endure the leak test and hydrostatic pressure test carried out during the life term of nuclear power generation plants. The statistics on the damage of pressure vessels in USA and UK are given. (Kako, I.)

[en] In this paper, the authors studied the temperature distribution in a shipping cask for spent nuclear fuels at LOCA (loss-of-coolant accident) after a failure of the cask. The calculation was made on a model of a uni-axial (in radial direction) thermal transfer. The result shows that the decay heat which cannot be cooled down will cause the temperature to go over 1000⁰C at the central part of the cask. A very dangerous accident will occur at such a high temperature; i.e., the vapor of cesium, a radioactive isotope, will flow out from the cask into air, and the water-metal reaction will produce a great deal of heat and hydrogen. Because of this, the nuclear fuels at the central part will collapse and melt down. (author)

[en] In this paper, the authors studied on the temperature distribution in the shipping cask of spent nuclear fuels at LOCA (loss-of-coolant accident) by a failure of the cask. The calculation was made on a model of a radial thermal transfer. The result shows that the decay heat which cannot be cooled down will make the temperature over 1,000⁰C at the central part of the cask. A very dangerous accident will occur at such high temperature, i.e., cesium, a radioactive isotope, will be vaporized to flow out from the cask into air, and the fuel cladding pipes will bring about the water-metal reaction to produce a great deal of heat and hydrogen, by which the nuclear fuels at the central part will collapse and melt down. (author)

[en] It is important to prevent the buckling of thin pipes caused by an external pressure in the heat-exchanger system of a pressurized water reactor. The design code in ASME Sec. III NB considers this point. However, the thickness of pipes is partially thinned down by steam-liquid flow in service, and in design step no consideration is being paid to such a partially thinned down pipe, though much attention should be paid on this point. In this paper, the pressure at failure of a partially thinned pipe under an external pressure was studied. The experimental results show that the failure occurs at unexpectedly small pressure, if the thinned part has some expansion in area, and that the pressure at failure does not follow with the buckling equation given by elastic theory for thin cylinders. (author)