Techniques to measure deflection of pressure tubes in Indian pressurized heavy water reactors (PHWRs)

Creep of zirconium alloy pressure tubes is prime concern in PHWRs. The diameter and bending creep occurs in horizontal pressure tubes. The pressure tube sags and may contact the calandria tube. Radius of curvature may become small to prevent fuel bundles from sliding. A technique using LVDTs (Linear Voltage Differential Transformers) was developed to measure local curvature and deflection inside the pressure tubes. The technique was implemented in pre-service measurement. A technique using servo-inclinometer has been developed to measure slope and sag along the length of heavy water filled tubes. The technique is being implemented for in-service inspection of pressure tubes. (author)