Problem
CANDU nuclear reactors contain fuel-filled pressure tubes mounted within calandria tubes, which are normally separated by a gas-filled annular gap (the “PT/CT gap”).
Contact between the two tubes must be avoided to prevent deterioration of the zirconium-based pressure tube material.
Due to the unique geometry of the reactor, periodic measurement of the annular gap width is made from inside the water-filled pressure tube. Current inspection technology uses Eddy Current methods, which do not provide sufficient measurement accuracy.
Scope of Work
The project objective was to develop an improved inspection technology based on Ultrasonic Testing (UT) in the nuclear industry.
The unique inspection technology system configuration, with the UT transducer immersed in a water-filled pressure tube and the annular space filled with gas, presented significant technical challenges.
Solution
Kinectrics developed an innovative nuclear inspection technique based on excitation of resonant standing waves in the gas-filled gap and measurement of the reflected response.
The nuclear inspection technique uses a low frequency, wide bandwidth probe transmitter in a pitch-catch pair of transducers excited by a sine burst with a large number of cycles.
The excitation of the PT/CT gap resonance reveals a frequency, which is uniquely related to the absolute value of gap width.
This advanced inspection technique for the nuclear industry is currently in laboratory testing with the potential to be incorporated into on-reactor NDE tooling in the near future.
Benefits
Accurate measurement of the PT/CT gap width of CANDU reactors can extend tube and plant life by removing conservatism from tube contact predictions. It can also be used to confirm or rule out possible tube contact, helping utility owners better manage their high-value assets.
