VIBRATIONAL BEHAVIOUR OF TUBES WITH DEGRADED UPPER TUBE SUPPORT PLATES

摘要

In April 1995, during its fourteenth refuelling outage, degradedrnregions were detected at Fessenheim 2 on the upper tube supportrnplate (TSP) of two steam generators (SG). This degradation wasrnlocated in a specific area but for the tubes in this zone, there wasrnno support at this level. Furthermore, small TSP parts couldrnmove in the SG as loose parts during plant operations.rnAfter this observation, TSP degradation was also detected onrnother steam generators. For all of them apart from those atrnGravelines and Fessenheim , TSP damage occurred early in thernlife of the SG and has not evolved.rnTo evaluate corrective and preventive actions needed for thernaffected steam generators in the short and long term, studiesrnwere performed to determine the impact of actual or potentialrndegradation on in-service internals and tube behaviour. Flow raternand distribution determination with and without tube supportrnplate damage were used to evaluate the consequences of thisrndegradation on tube vibrational fatigue .rnFrom these analyses, risk areas were determined to define thernmaintenance policy to be implemented in future years.