Stephanie H. Bruffey

Analysis of Krypton-85 Legacy Waste Forms: Part I

Abstract 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.

Performance Criteria for Capture and/or Immobilization Technologies - Milestone Report

The capture and subsequent immobilization of the four regulated volatile radionuclides (3H, 14C, 85Kr, and 129I) from the off-gas streams of a used nuclear fuel (UNF) reprocessing facility has been a topic of substantial research interest for the US Department of Energy and its international colleagues. Removal of some or all of these radionuclides (e.g., based upon fuel burnup, fuel type, cooling time) from the plant effluent streams prior to discharge to the environment is required to meet regulations set forth by the US Environmental Protection Agency. Upon removal, the radionuclide, as well as associated sorbents that cannot be cost-effectively regenerated, is destined for conversion to a waste form. Research in separation and capture methodologies has included a wide range of technologies, including liquid caustic scrubbing systems, solid adsorbents, and cryogenic distillation. The studies of waste forms have been correspondingly diverse. In considering the technologies available for future development and implementation of both sorbents and waste forms, it is necessary to identify benchmark measures of performance to evaluate objectively each sorbent system or waste form.

Initial Effects of NOx on Idodine and Methyl Iodine Loading of AgZ and Aerogels

This initial evaluation provides insight into the effect of NO on the adsorption of both I2 and CH3I onto reduced silver-exchanged mordenite (Ag0Z). It was determined that adsorption of CH3I onto Ag0Z occurs at approximately 50% of the rate of I2 adsorption onto Ag0Z, although total iodine capacities are comparable. Addition of 1% NO to the simulated off-gas stream results in very similar loading behaviors and iodine capacities for both iodine species. This is most likely an effect of CH3I oxidation to I2 by NO prior to contact with the sorbent bed. Completion of tests including NO2 in the simulated off-gas stream was delayed due to vendor NO2 production schedules. A statistically designed test matrix is partially completed, and upon conclusion of the suggested experiments, the effects of temperature, NO, NO2, and water vapor on the sorption of CH3I and I2 onto Ag0Z will be able to be statistically resolved. This work represents progress towards that aim.

Milestone Report - M3FT-15OR03120215 - Recommend HIP Conditions for AgZ

The purpose of this study was to continue research to determine if HIPing could directly convert I-Ag0Z into a suitable waste form. Fiscal year (FY) 2015 work completed studies of Phase IIA, IIB, and IIC samples. Product consistency testing (PCT) of Phase IIA samples resulted in iodine release below detection limit for six of twelve samples. This is promising and indicates that a durable waste form may be produced through HIPing even if transformation of the zeolite to a distinct mineral phase does not occur. From PCT results of Phase IIA samples, it was determined that future pressing should be conducted at a temperature of 900°C. Phase IIC testing continued production of samples to examine the effects of multiple source materials, compositional variations, and an expanded temperature range. The density of each sample was determined and x-ray diffraction (XRD) patterns were obtained. In all cases, there was nothing in the XRD analyses to indicate the creation of any AgI-containing silicon phase; the samples were found to be largely amorphous.

Milestone Report - M4FT-14OR0312022 - Co-absorption studies - Design system complete/test plan complete

The objective of this test plan is to describe research that will determine the effectiveness of silver mordenite and molecular sieve beds to remove iodine and water (tritium) from off-gas streams arising from used nuclear fuel recycling processes, and to demonstrate that the iodine and water can be recovered separately from one another.