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Sophisticated R&D Results in New M5™ Advanced Cladding

It's true that good things come with time and tenacity. More than a decade ago, Framatome began an exhaustive search for what would become the ultimate in high-performance cladding and structural material for fuel assemblies. The resulting material, the newly approved Alloy M5™, is now being used in Fragema and Framatome Cogema Fuels fuel assembly designs.

Framatome and its partners, Cezus and Zircotube, developed this high-performance zirconium alloy with superior corrosion resistance that allows higher burnup, with improved operating margins.

Such a feat could not have occurred without the painstaking efforts of dedicated teams of personnel. The teams' extensive development program set a new standard for high performance cladding—and offers both significant fuel cycle cost savings and enhanced operating margins for utilities.

What distinguishes M5 from other Zirconium/Niobium alloys is its ternary composition (Zr-1% Nb-0) and the control of thermal–mechanical processing parameters.

"The resulting alloy microstructure is highly stable and provides the best in-reactor cladding and structural component performance of any zirconium alloy available," said Garry Garner, FCF Advisory Engineer.

"The development research began by analyzing and testing twenty potential advanced alloys," said Garner. "Eventually, six alloys were chosen for manufacturing studies and continued testing."

The research included selection of final metallurgical properties, eliminating two more alloys from further consideration. The four remaining alloys were exposed in more than a dozen research and commercial reactors with widely varying conditions (high lithium, high power density, high temperature, and sub-cooled boiling) that ranged from normal to severe. After years of rigorous analyses, the first twenty alloys were narrowed to two, ultimately leading to the selection of M5 for the compilation of an extensive operational database.

From the most extensive development process of its kind in the nuclear industry, Alloy M5 has emerged as Framatome's choice for high-burnup, high-service application. "Today, this alloy is fully developed, licensed and in full production," said Garner.