HYDROGEN INGRESS INTO ZIRCONIUM ALLOYS AS A LIFE-LIMITING FACTOR- METHODS OF IN-LINE MONITORING, PREDICTION AND CONTROL

摘要

Zirconium alloys are used as structural components in most nuclear reactors. For example Zr-2.5 wt.%Nb alloy is currently used in the fabrication of pressure tubes in CANDU® (Canada Deuterium Uranium) reactors, and "Zircaloys" are used as fuel cladding in many BWR reactors. In general, zirconium alloys pick up hydrogen (or its isotope deuterium) in reactor primary heat transport system coolant during aqueous corrosion, raising the possibility of hydride formation and delayed hydride cracking at high levels of hydrogen concentration. As a result, the buildup of hydrogen in components due to corrosion could be life limiting. In this paper several mechanisms of in-service hydrogen ingress into zirconium alloys will be discussed to identify the main factors controlling the rate of uptake by the alloy under specific reactor operating conditions. The redistribution of hydrogen due to diffusion will be described along with methods of monitoring and predicting the buildup of hydrogen concentration as a function of operating time. Possible approaches to slow down the rate of ingress will be discussed, which include water chemistry modification and surface conditioning. Innovative non-destructive monitoring techniques developed at "KINECTRICS Inc." will also be addressed.