The baffle-to-former bolts are used in Pressurized Water Reactors to attach the baffle plates to the former plates in the reactor vessel lower internals. The resulting structure forms a boundary for the flow of coolant and provides lateral support to the fuel assemblies. Some edge bolts are also present, assembling together the baffle plates. After an operating time of the order of 120 000 hours, some bolts exhibit cracking at the junction of the head and the shaft of the bolt. Examinations of failed bolts have made it possible to identify the cause of cracking as irradiation assisted stress corrosion cracking (IASCC). Up to now, baffle bolt cracking has been detected in units older than 15 years, where the baffle bolts are not cooled (no holes in the former to allow a water flow on the bolt shaft). In Belgium, the concerned units are Tihange 1 and Doel 1-2. The paper summarizes the experience with baffle bolts cracking in Belgian units and the strategy implemented to mitigate this problem, consisting of structural integrity analyses, baffle bolts inspections and replacement, and research programs in the field of IASCC, including examinations of highly irradiated replaced bolts.
|Title of host publication||FONTEVRAUD 8 - Contribution of Materials Investigations & Operating Experience to LWR's Safety, Performance & Reliability|
|Place of Publication||Paris, France|
|State||Published - 15 Sep 2014|
|Event||2014 - FONTEVRAUD 8 : Contribution of Materials Investigations and Operating Experience to Light Water NPPs’ Safety, Performance and Reliability - SFEN - Sociéte Francaise d' Energie Nucléaire, Avignon|
Duration: 15 Sep 2014 → 18 Sep 2014
|Conference||2014 - FONTEVRAUD 8|
|Period||2014-09-15 → 2014-09-18|