In-service inspection of zircaloy pressure tube of CIRUS reactor

The pressurized water loop (PWL) of Cirus uses a 10 meter long zircaloy tube of 57.9 mm ID and 5.4 mm wall thickness. The loop has been used for irradiation testing of various experimental fuel pins since 1972. As part of the refurbishment programme, the condition of Zircaloy-2 pressure tube of the pressurized water loop was investigated by Eddy current and ultrasonic testing. The eddy current probe was balanced over a portion of the tube and the differential signals were recorded for the entire length of the tube. For ultrasonic flaw scanning, gadgets were fabricated and scanning was carried out to evaluate the condition of irradiated pressure tube. For ultrasonic testing an annular probe holder matching to the internal diameter of the zircaloy tube was used for immersion scanning. The probe holder fitted with 10 MHz line focused ultrasonic probes inclined at 28 deg in axial and circumferential directions. A normal spot focused probe was also used to measure wall thickness and detection of laminar flaws. Axial and circumferential grooves of 3% wall thickness depth on ID and OD were used as standard calibration defects. The eddy current and ultrasonic tests did not detect any defect of unacceptable size in the zircaloy pressure tube. (author)