Creep of zirconium alloy pressure tubes is a prime concern in PHWRs. In addition to diameter creep, bending creep occurs in horizontal pressure tube due to bending moments induced by weight of the fuel, coolant and tube. With time, the pressure tube will sag and may eventually contact the calandria tube. In the areas of high bending moments, the radius of curvature may become small enough to prevent the fuel bundles from sliding freely during fuelling operation. This would be undesirable. Hence it is important to measure periodically the defection of pressure tube to ensure that bending creep is not excessive and to obtain the data for future design. A technique using Linear Variable Differential Transformers (LVDTs) was initially developed to measure local curvature at a number of points inside the dry pressure tube. The deflection was computed from double integration of curvature data. The technique was implemented in the form of manually operated tool which has been used for pre- service measurement in Indian PHWRs. Recently, a technique using servo-inclinometer has been developed to measure the slope at many points along the length of heavy water filled active pressure tubes. The sag is computed from single integration of slope readings. The technique is being implemented in BARC Channel Inspection System (BARCIS) for in-service inspection of coolant channels of Indian PHWRs. The paper describes both the techniques and presents results of measurements.
Publication Source: Trends in NDE Science & Technology; Proceedings of the 14th World Conference on Non-Destructive Testing, New Delhi, 8-13 December 1996.Vol. 2, pages 381 - 384 Publisher:Ashgate Publishing Company
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