10 Years of operating experience of the valves in the safety systems on Caorso plant

The Operating Experience (O.E.) of the valves in the safety related systems on Caorso plant has been analysed. The valves have been grouped according to system, type and manufacturer. All the data on the failures have been respectively drawn out by the O.E. data bank and, in some cases, they have been integrated by informations collected directly on the plant. The events and the relevant causes have been analysed, particularly taking into account the repetitive events. Most of the failures were discovered during the surveillance tests, giving a positive indication of the effectiveness of the periodic test program. It was also that concluded hardware problems caused more failures than human errors both during operation and maintenance. Abnormal distributions of failures on the valves and on their components have been found out. Weak components both mechanical and electrical and pertinent corrective measures have been identified, aimed to eliminate the recurring failure modes