[en] In nuclear power reactors, the thermal energy produced in the fuel is transfered outside the core by a fluid pressure. The envelope containing this fluid, or primary circuit, is a pressure system subject to the regulations on these appliance. The regulations designed for conventional pressure vessels are not well suited for nuclear vessels and 'special measures' concerning them have been worked out within the regulations. These measures are covered by the Order of February 26th 1974 extending the application of boiler and pressure vessel regulations to the nuclear reactor primary system. The main provisions of this text are emphasized: components concerned, manufacture and user responsibilities, choice of materials, quality program, files to be submitted to the authorities. The rules concerning structural analysis of nuclear vessels are examined more in detail. Loading conditions are classified under four different categories. The resistance of vessels must be estimated with special reference to the following damages: excessive distortion; plastic instability; elastoplastic instability; progressive distortion (ratcheting); low cycle fatigue. In view of these requirements the available means of analysis are examined briefly: model tests, limit analysis, plastic finite elements methods, construction code rules, etc. (Auth.)