As core shroud integrity is essential for continued safe operation of the reactors, Nuclear Power Corporation of India, which owns and operates the twin-unit BWR plant at Tarapur has extended the refuelling shutdown of Unit No. 2 for core shroud inspection. 'AS-IS' visual examination, cleaning of the shroud surface of any loose scales that can mask discontinuities, visual examination of shroud welds (after cleaning) using underwater CCTV system and ultrasonic testing of a few selected welds of the shroud form part of the inspection programme.

Core shroud, which forms a part of Reactor internals is not physically accessible for direct examination. The major challenge to be overcome to accomplish the inspection task is delivering the cleaning head and examinations probes to the desired locations of the shroud after removal of peripheral fuel support plugs. The area of interest is underwater and about 65 feet away from the inspection station. Besides this, the other components and attachments of the reactor internals obstruct movement of the probing arm. In other words, the arm needs to meander to reach the welds to be examined. These intricacies make the programme complex necessitating development of remote operated manipulators to perform examinations. Special manipulators have been indigenously developed for this purpose. However, qualifying the manipulators, developing the cleaning and inspection procedures, training the examiners and assessing the adequacy of inspection tooling to gain confidence in the system capabilities are a few daunting tasks to be accomplished before embarking on the actual inspection. To facilitate the above, a full-scale segmented reactor mock-up incorporating most of the hurdles to be negotiated became necessary.

This paper deals with the design, development, fabrication, installation and commissioning of the mock-up system. It also covers the details regarding qualification of the 'AS-IS' underwater visual examination, surface cleaning manipulators and the examination systems for visual and ultrasonic testing using the mock-up.