An Appraisal of the Effect of Graphite Interlayers on the Tolerance of Water Reactor Fuel Rods to Power Ramp Defects

As a result of a post-irradiation metallographic study of power-ramped Canadian natural uranium, heavy-water-moderated and -cooled power (CANDU) reactor fuel rods, it was recently concluded that the observed beneficial effects of graphite CANLUB coating on CANDU fuel’s tolerance to power-ramp defects stem primarily from the interaction of the coating with fission products, rather than by lubrication of the fuel-cladding interface. These arguments are based on a consideration of fuel cracking patterns and the assumption that stress corrosion crack growth within the cladding is the controlling event in the failure process. While these arguments are examined in detail, the present reappraisal leads to the same view of the primary origin of the beneficial effects of graphite coatings on CANDU fuel rod performance.