Cd Transport in Eutectic LiCl-KCl and Contamination of Zr Metal And Thermal Dehydration of Bulk LiCl-KCl

Researchers at Idaho National Labs have noted unexpectedly high Cd content in empty cladding hulls after processing in the Mark-IV ER. It has been theorized that Cd metal is transporting from the LCC pool through the eutectic LiCl-KCl salt bath to the anode baskets containing the empty hull where it is retained as a Zr-Cd intermetallic. This study sought to replicate the Cd contamination in a dry Ar glovebox using small-scale analogue of the Mark-IV ER salt-Cd metal system.

Anhydrous eutectic LiCl-KCl was an essential regent in this research and experiments were conducted to investigate the feasibility of dehydrating nominally anhydrous salt using a method requiring less equipment and labor than the currently accepted practice using HCl gas. It was found that the new method may prove sufficient with further development.

Studies by K.M. Goff suggested that the Cd species soluble in LiCl-KCl were highly dependent on the presence of carbon and oxygen gas contaminants. Experiments were performed to verify Goff’s findings and distinguish between Cd species using stirred cell ultra-filtration and ICP-MS. These investigations yielded results that were consistent with Goff’s interpretation of the salt chemistry.

The hypothesized retention of Cd by Zr as an intermetallic was investigated by immersing Zr pellets in the glovebox analogue of the Mark-IV ER. The pellets were then cross-sectioned and analyzed using SEM-EDS. Cd was found on the pellet surfaces and in their interiors, but more extensive analysis was not possible. There were concerns that the sample preparation procedure may have resulted in Cd from the pellet surface be smeared onto the interiors of the cross-sections.