DUPLEX CLADDINGS PERFORMANCE AT HIGH BURN-UP

摘要

There is a desire for the nuclear industry to extend the discharge burn-up of the fuel, combined with power uprates, and extended operating cycles, whereby the fuel cycle costs can be reduced. However, this implies new, and more severe operating regimes that change the conditions for corrosion, hydriding and irradiation induced growth of Zr-based materials. For PWR operation, various types of Duplex cladding have been developed to meet the new requirements, and the resulting performance has generally been successful. Two types of Westinghouse Duplex claddings, irradiated at KWG, Germany, to a rod average burn-up close to 70 MWd/kgU have been Post-Irradiation Examined at the Institute for Transuranium Elements, Karlsruhe. The two Duplex rods reveal low irradiation induced rod growth of 0.45%, excellent corrosion resistance with a maximum oxide thickness of only 35 urn and a low concentration of hydrides with no radial hydrides detected. There is only a slight accumulation of hydrides in the bonding zone between the inner and outer components. None of the studied cladding parameters reveal any tendency towards an accelerated mode at high burn-up We conclude that both types of Duplex cladding have demonstrated an excellent performance with a significant margin, and are thus capable of irradiation to even higher burnup levels.