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Recent experiences with ultrasonic inspection of baffle former bolts

Erfahrungen bei der Ultraschallprüfung von Kernumfassungschrauben
: Debnar, A.; Alaerts, L.; Spies, M.; Minogue, P.; Epineau, C.

Deutsche Gesellschaft für Zerstörungsfreie Prüfung e.V. -DGZfP-, Berlin:
8th International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components 2010. CD-ROM : Berlin, Germany, from 29th of September to 1st of October 2010
Berlin, 2011 (DGZfP Proceedings BB 125)
Paper Th.2.C.5
International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components <8, 2010, Berlin>
Fraunhofer ITWM ()
ultrasound; nuclear inspection; robot; modeling; validation

Baffle Former Bolts are vital joint elements of the reactor core internal structure. Since 1989, successive UT inspections in various European plants have revealed a trend of progressive indications. Different bolt and locking designs have been used during the initial design and building phase of the plants. Lock-bar style bolts are one type of bolts which are used in numerous plants in Europe and the US. Lock-bar style bolts pose a challenge due to limited ultrasonic probe access availability. Furthermore, the inspection approach has to capture indications in the bolt threaded region as well as in the bolt head to shank interface. During recently performed qualifications in Europe the ultrasonic inspection of lock-bar style bolts has been improved by using advanced probe design and an an alysis approach. Based on blind test qualification testing performed on sample bolts a high degree of confidence could be achieved. Inner hexagon (hex) bolts with a locking washer represent another design used in several plants in Europe and the US. This bolt design poses another challenge based on varying cone dimensions and limited access through the inner hex. Ultrasonic beam field simulations have been performed to support and verify laboratory and qualification testing. This paper describes the qualification process in more detail. Furthermore, field experiences will be presented. These inspections were performed employing a variety of delivery platforms including robotic manipulators and submarines. This will provide a basis for the comparison of the respective benefits of these d ifferent approaches.