Évolution des connaissances à l'occasion des études de thermohydraulique nucléaire

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In the introduction, it is explained why the two-phase flows are so important in nuclear engineering specially for the water moderated reactors (BWR and PWR). The geometry of the core (bundles), the power and flow distribution are so complex that detailed thermohydraulics computer codes are needed for having a good prediction of the behavior of the core in normal and accidental conditions. For very low probability accidents, the system is beyond the normal technological limits and the thermohydraulics phenomena are controling the evolution and must be predicted as realistically as possible. The method for safety analysis is illustrated by the figure 1 : it must be noted that the basic research is far upstream of the reactor application, but cannot be neglected if a credible extrapolation from the tests to the reactor is needed. In part 2, the present state of the knowledge in two-phase flows is summarized and the needs for a better understanding are listed for - flows in pipes - transient flows - thermal phenomena - theoretical aspects. In part 3, the author shows how it is possible to use the methods and knowledge obtained in nuclear field for non-nuclear applications. In part 4, the evolution of the needs for research in nuclear field is indicated : much more emphasis must be given to the incidental behavior of the reactors and to the small accidents. A better knowledge is also needed on the behavior of the different components in such conditions. The most important topics for developping useful basic research concern similarity, instrumentation, transient flows, multidimensionnal flows, thermal phenomena specially direct condensation.