Development of a mock-up for NDE of BWR core shroud welds

One of the significant failures reported by Boiling Water Reactor (BWR) fraternity in the nineties has been the reactor core shroud weld cracking, which continues to be a matter of concern for BWR owners world over. Nuclear Power Corporation of India Limited, which owns and operates the twin-unit BWR plant at Tarapur, has carried out NDE of its unit 2 reactor core shroud in January 1996. This inspection included as-is visual inspection, cleaning, post-cleaning visual inspection and ultrasonic examination of the core shroud upper welds. The major challenges to be overcome in accomplishing the inspection task have been delivering the cleaning head and examination probes to the desired locations of the shroud. Remotely operated manipulators have been indigenously developed for this purpose. Qualifying the manipulators, developing the procedures, training examiners and assessing adequacy of inspection tooling to gain confidence in system capabilities were a few daunting tasks to be accomplished before embarking on the actual inspection. To facilitate these, a full scale mock-up incorporating most of the hurdles to be negotiated was developed and installed at reactor site. This paper gives a brief description of these development efforts. (author)