During the refueling outage at the Leibstadt Nuclear Power Plant in August 2002 and 2003 some severely worn hydraulic snubber pins were found at a main steam line support inside the turbine building. Possible causes of the failure were considered to be increased loads due to the implementation of a snubber reduction program in the 1996 to 1998 time period, or flow-induced vibration from the extended power uprate implemented in four steps from 1998 to 2002. During the 2003 outage, a vibration measurement program as well as a root cause analysis were started to check the integrity of the whole system and to reduce or eliminate the degradation mechanism. The dynamic measurement data obtained during the 2003 power ascension showed that the vibration acceptance criteria were met. However, the main steam line support with the worn snubber pins experienced a horizontal relative movement between the pins and the clamps. This started at a power level corresponding to an intermediate power uprate step. Four different pragmatic local design solutions were considered to prevent the severe wear.

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