Towards a better understanding of clogged steam generators: a sensitivity analysis of dynamic themohydraulic model output

Communication available online at http://hans.wackernagel.free.fr/article_ICONE_final_140311.pdfInternational audienceTube support plate clogging of steam generators affects their operating and requires frequent maintenance operations. A diagnosis method based on dynamic behaviour analysis is under development at EDF to provide means of optimisation of maintenance strategies. Previous work showed that the dynamic response to a power transient of the wide range level measurement contains informations about the clogging state of steam generators. The diagnosis method consists of comparisons of the measured dynamic response with simulations on a mono-dimensional dynamic steam generator model for various input clogging configurations. In order to assess the potential of this method, a sensitivity analysis has been conducted through a quasi-Monte Carlo scheme to compute sensitivity indices for each half tube support plate's clogging ratio. Sensitivity indices are usually defined for scalar model outputs. Principal component analysis has been used to determine a small subset of variables that condense the information about the shape of the response curves. Finally, estimation variability was assessed by construction of bootstrap confidence intervals. The results showed that half of the preselected input variables have negligible influence and allowed to rank the most important ones. Interactions of input variables have been estimated to exert only a small influence on the output. The effects of clogging on the steam generator dynamics has been characterised qualitatively and quantitatively

Sensitivity analysis and dimension reduction of a steam generator model for clogging diagnosis

International audienceNuclear steam generators are subject to clogging of their internal parts which causes safety issues. Diagnosis methodologies are needed to optimize maintenance operations. Clogging alters the dynamic behaviour of steam generators and particularly the response of the wide range level (WRL - a pressure measurement) to power transients. A numerical model of this phenomenon has previously been developed. Its input variables describe the spatial distribution of clogging and its output is a discretization of the WRL dynamic response. The objective of the present study is to characterize the information about the clogging state of a steam generator that can be inferred from the observation of its WRL response. A methodology based on several statistical techniques is implemented to answer that question. Principal component analysis reveals that clogging alters the WRL response mainly in two distinct ways. Accordingly, the output can be summarized into a vector of dimension 2. A sensitivity analysis is carried out to rank the input variables by magnitude of influence. It has shown that they can be divided into two groups corresponding to the two sides of the steam generator. Finally, sliced inverse regression is used to reduce the input dimension from 16 to 2. A sampling issue that arises when the input dimension is high is addressed. The simplification of the original problem yields a diagnosis methodology based on response surface techniques