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Embrittlement of Palladium and Palladium-Silver Alloy Cathode Membranes by Tritium

G. Bellanger

Fusion Science and Technology

Volume 27 / Number 1 / January 1995 / Pages 36-45


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Palladium-silver cathodic membranes are used in industrial tritiated water processing to produce very high purity tritium gas and its isotopes. During electrolysis, these adsorb on the cathodic surface, diffuse through the alloy, and finally are desorbed on the side opposite of the cathodic entry surface. This desorption occurs in a gastight compartment separated from the electrolyzer allowing the recuperation of pure isotopes. The diffusion is dependent on cathodic surface, PdAg thickness, temperature, deposits on the surface to favor the adsorption, and applied cathodic potential. Here, the embrittlement of palladium and PdAg alloy cathode membranes and the diffusion and solubility parameters were studied in tritiated water. Voltammetry curves were plotted to ascertain the conditions of cathodic charging with tritium as well as the effect ofradiolytic hydrogen peroxide on palladium or PdAg. From the voltammetric curves, the diffusion coefficient, the surface solubility of tritium, and the thickness of the palladium and PdAg alloy involved were determined. Scanning electron microscope examinations show that the cracking is transgranular in the case of palladium, while it appears to be intergranularfor the PdAg alloy. With palladium, this cracking involves all the surface subjected to charging, whereas for the alloy, only the surface at the electrolyzer gas atmosphere/electrolyte bordering zone would appear to be embrittled. This could be the result of the presence of two tritiated phases in palladium or in palladium-silver. The PdAg alloy is the less sensitive to embrittlement.

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