Impact of Coating Defects on Performance of Coated Zirconium Cladding

Abstract

The Advanced Fuels Campaign has made progress in developing an ability to fabricate high quality 'generic' chromium coatings applied to commercial nuclear cladding alloys free of the proprietary considerations inherent to the industry materials. The availability of such source material is critical for execution of fundamental studies as well as open collaboration between the national laboratories, within Office of Nuclear Energy programs, and the Nuclear Regulatory Commission. This milestone report provides insights on the impact of processing parameters on the microstructure of 7 micron Cr-coated Zircaloy-4. Coatings were applied using High Power Impulse Magnetron Sputtering (HiPIMS). Scanning electron microscopy was utilized to investigate the overcoating of cladding and cross-sections of the interface. Characterization confirmed that a high quality, continuous coating was achieved. Burst testing was then performed to evaluate the performance of high-quality coatings to coatings that contain known flaws and uncoated materials. Results demonstrated that coatings containing flaws allowing for direct exposure of the base cladding to atmosphere exhibit burst behavior matching that of the uncoated material. However, continuous coatings resulted in measurable improvement. This work will be expanded in FY22 to include a broader set of mechanical property studies and test irradiations.

Mechanical properties of Zircaloy cladding tubes and contributions to M.E.T.A. mechanical property database

“…The US Department of Energy's Advanced Fuels Campaign (AFC) is pursuing accident-tolerant fuel materials to increase the "coping time" in the event of a loss-of-coolant accident scenario [19,20]. One of the main materials pursued by industry and the AFC is chromium-coated zirconium alloys because of their increased oxidation resistance.…”

“…This setup was used to obtain the coating materials' mechanical property information and to compare the sensitivities of the machining method used to manufacture the specimens. The Zircaloy-4 material was found to have divots on the outside surface that hindered coating adherence [20], so the Zircaloy-4 was hand-polished prior to coating. As a result, select tests were also performed with hand-polished uncoated tubes as well.…”

“…As a result, select tests were also performed with hand-polished uncoated tubes as well. More information on the Zircaloy-4 material can be found in Garrison et al [21], and the coating methodologies can be found in Graening et al [20]. Tests were performed at room temperature and at 300°C on an Instron 5966 electromechanical test system or on an MTS electromechanical system, based on system availability.…”