Hydride Formation Process for the Powder Metallurgical Recycle of Zircaloy from Used Nuclear Fuel
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abstract
A Zircaloy recycle process is being investigated based on the underlying principle that Zr reacts with H2 to form ZrH2, which is the same reaction that produces performance limiting ZrH2 formations in reactor cladding. However, in the proposed application, hydride formation is an enabling phenomenon that will embrittle and crumble Zircaloy as a precursor for milling and dehydration to form Zircaloy metal powder. Hydride formation experiments were performed to quantify the primary process variables of time and temperature. These experiments were performed by hydriding nuclear grade Zircaloy-4 tubes under flowing gas (Ar-5 pct H2) for various times and temperatures. The results were used to create a correlation for the formation of zirconium hydride as a function of time and temperature. Further, it was observed that it was much more effective to hydride the Zircaloy-4 tubes at temperatures below the -- eutectoid temperature of 818 K (545 C), presumably related to the high hydrogen solubility of -Zr. Samples treated below this temperature readily crumbled during the hydride formation reaction and were subsequently easily ground to powder, making this the ideal temperature range for the proposed recycle method. Hydrogen pickup was faster above 818 K (545 C), but the samples were generally tougher. 2010 The Minerals, Metals & Materials Society and ASM International.
