Quantitative monitoring and diagnosis of French PWRs' internal structures vibrations by excore neutron noise and accelerometers analysis

Abstract

Systematic efforts to understand internal structures vibratory phenomena and develope monitoring techniques, have been carried out in order to set up a systematic surveillance of french PWRs. Recent developments concerning: . the knowledge of vibratory phenomena . the quatitative interpretation of excore neutron noise from the results of 2D transport calculations . the development of monitoring methods and the corresponding experience on operating reactors. - Knowledge of vibratory phenomena . the results of recent experiments on the SAFRAN loop are summarized. . the results of vibratory calculations of a model describing the lower and upper internal structures and the fuel in normal conditions, are presented the results of direct vibration measurements, performed on the BUGEY 5 and TRICASTIN 1 reactors, with a special instrumentation, during cold and hot tests, are described. - Quantitative interpretation of excore neutron noise measurements. 2D transport calcultations are presented. The corresponding results (scale factors) allow to relate any displacement of each structure (fuel, core barrel, thermal shield) to the corresponding effect on excore detectors. Comparison of the predicted displacements, using neutron noise and calculated scale factors, with direct vibration measurements is discussed. Importance of relative displacement of each structure is emphasized. - Development of monitoring techniques and corresponding experience on operating reactors. Evolution with time of excore neutron noise and accelerometers signals are presented for the french 900 MWe operating PWRs. Conclusions are drawn concerning monitoring techniques and alarm levels.