Analysis of Krypton-85 Legacy Waste Forms: Part I

In 2010, the Idaho National Laboratory was in the process of removing legacy materials from one of their hot cells. As part of this clean-out effort, five metal capsules and some loose zeolite material were identified as test specimens produced in the late 1970s as part of research and development (R&D) conducted under the Airborne Waste Management Program. This specific R&D effort examined the encapsulation of ⁸⁵Kr within a collapsed zeolite structure for use as a potential waste form for long-term storage. These reclaimed capsules and loose material presented a unique opportunity to study a potential ⁸⁵Kr waste form after three half-lives have elapsed. Of the five capsules, the walls of two had been cut or breached during previous experiments. The aim of this study was to produce mounted samples from the two breached samples that could be handled with minimal shielding, assess the physical condition and chemical composition of the capsule walls for each breached sample, and determine if any loss of capsule wall integrity was directly attributable to rubidium, the decay product of ⁸⁵Kr. The sectioning and mounting of the breached capsules was successfully completed. The capsule wall of these ⁸⁵Kr legacy waste form capsules was examined by optical microscopy and by scanning electron microscopy and energy-dispersive spectroscopy. Substantial corrosion was observed throughout each capsule wall. The bulk of the capsule wall was identified as carbon steel, while the weld material used in capsule manufacture and/or sealing was identified as stainless steel. A notable observation was that the material used for Kr encapsulation was found adhered to the walls of each capsule and had a chemical composition consistent with zeolite minerals. The results of studies on the retention of Kr by the encapsulation material will be discussed in a subsequent paper. Three legacy capsules remain in storage at Oak Ridge National Laboratory and may not have been breached. These represent an exciting opportunity for continued ⁸⁵Kr waste form studies and will provide more indication as to whether the corrosion observed in Capsules 2 and 5 is attributable to the breach of the capsule, to Rb-induced corrosion, or to another cause.