Conference Proceedings Paper
FRACTURE PROTECTION OF CANDU ZR-2.5NB PRESSURE TUBES WITH HIGH HYDROGEN EQUIVALENT CONCENTRATION
11th International Conference on CANDU® Maintenance and Nuclear Components - 2017 Oct. 01-04
P. Doddihal (Kinectrics Inc.)
D. Scarth (Kinectrics Inc.)
P. Mosbrucker (Kinectrics Inc.)
J. Lam (Ontario Power Generation)
M. Craven (Ontario Power Generation)
The core of a CANDU (CANada Deuterium Uranium) pressurized heavy water reactor includes horizontal Zr-2.5Nb alloy pressure tubes that contain the fuel. Pressure-temperature limits are used in CANDU reactors for normal operation heat-up and cool-down conditions to maintain margins against fracture. The pressure-temperature limits are determined by postulating a 20 mm long axial through-wall crack in the pressure tube and using a fracture toughness-based calculation procedure. Due to a corrosion reaction with the heavy water coolant, pressure tubes absorb high levels of deuterium in service, resulting in high levels of hydrogen equivalent concentration. Experiments have shown that high hydrogen equivalent concentration reduces the fracture toughness of pressure tube material at low temperatures below the normal operating temperature during reactor heat-up and cool-down. New fracture toughness curves that are applicable to material with high hydrogen equivalent concentration have been developed to address this issue. These curves are being used to develop new pressure-temperature limits for fracture protection of CANDU pressure tubes. The methodology for deriving the pressure-temperature limits for a CANDU Zr-2.5Nb pressure tube using the new fracture toughness curves is described in this presentation. Preliminary results of pressure-temperature limits for a CANDU reactor are also provided.
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