The Active 'Ingredient' in CANLUB

Abstract

There is evidence that formation of Cs(ZrxIyC) compounds is the chemical step involved in preventing stress-corrosion cracking (SCC) of fuel sheathing. One of the recent key findings is that SCC of unirradiated Zircaloy sheathing is observed only when CANLUB was "over-baked". This result appears to be consistent with results obtained by various analytical techniques that show that if one of the key components in CANLUB was decomposed then SCC would occur. Since there is a possible link between fuel oxidation and graphite coating, the synthesis of Zr6I12C compounds using a different type of coating (without graphite) was also investigated. These results will assist in improving CANLUB specifications which will result in improvements in manufacturers' process controls, so that CANLUB continues to be effective. An increased understanding of CANLUB chemistry is also needed to improve the coating for advanced CANDU fuels that will be irradiated to extended burnups.