Analysis of propagating temperature perturbations in the primary circuit of PWRs

Abstract

Temperature perturbations circulating with the primary coolant are investigated using noise data measured at nominal power of a VVER-440 reactor. An average, one-loop model is introduced to improve the through-core correlation between the inlet and outlet temperature measurements. The sources, frequency dependence and life cycle of the perturbations are determined using a kind of spectrum decomposition method. The investigation is based on the analyses of auto and cross power spectral density functions between the temperature noise measured in the hot and cold legs of the primary circuit as well as at the core outlet. Transfer properties of the loop investigated in previous papers of the authors were also used. The RMS (Root Mean Square) ratio and APSDs (Auto Power Spectral Densities) were found not to change during a fuel cycle in operation at nominal power. The feedback through the circulation of the primary coolant was found to be about 8%, it should therefore be considered in the evaluation of real measurement data. The main sources of the noise arising in the primary circuit are the steam generator, the reactor core and the upper plenum.