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Recent experiences with ultrasonic inspection of baffle former bolts

: Debnar, A.; Alaerts, L.; Spies, M.; Minogue, P.; Epineau, C.

Bieth, M. ; European Commission:
8th International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components 2010. Proceedings : 29 September - 1 October 2010, Berlin, Germany
Luxembourg: European Union, 2010 (JRC Scientific and Technical Reports)
ISBN: 978-92-79-20321-3
International Conference on NDE in Relation to Structural Integrity for Nuclear and Pressurised Components <8, 2010, Berlin>
Fraunhofer ITWM ()
nuclear inspection; ultrasonic; modeling; crack; bolt; robot

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 ana lysis approach. Based on blind test qualification testing performed on sample bolts a high degree of confidence could be achieved. This paper will describe the qualification process in more detail. 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. 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 thes e different approaches.