An Initial Assessment of Potential Production Technologies for Epsilon-Metal Waste Forms

Abstract

SUMMARYThis report examines and ranks seven materials processing techniques that may be used to consolidate the undissolved solids, reduced soluble technetium, and soluble noble metals from nuclear fuel reprocessing into a low-surface area waste form. Commercial vendors of processing equipment were contacted and literature researched to gather information for this report. Typical equipment and their operation, corresponding to each of the seven techniques, are described in the report based upon the discussions and information provided by the vendors. Although the report does not purport to describe all the capabilities and issues of various consolidation techniques, it is anticipated that this report will serve as a guide by highlighting the key advantages and disadvantages of these techniques.The processing techniques described in this report were broadly classified into those that employed melting and solidification, and those in which the consolidation takes place in the solid-state. Four additional techniques were examined that were deemed impractical, but were included for completeness. The techniques were ranked based on criteria such as flexibility in accepting wide-variety of feed-stock (chemistry, form, and quantity), ease of maintenance, hot cell space requirements, generation of additional waste streams, cost, and any special considerations. Based on the assumption of ~2.5 L of waste to be consolidated per day, sintering based techniques, namely, microwave sintering, spark plasma sintering and hot isostatic pressing, were ranked as the top-3 choices, respectively. Melting and solidification based techniques were ranked lower on account of generation of volatile phases and difficulties associated with reactivity and containment of the molten metal.

Molten salt reactors and electrochemical reprocessing: synthesis and chemical durability of potential waste forms for metal and salt waste streams

“…An elemental dot map of the 17.5 wt-% ZrO 2 waste form surface is shown in Figure 5. These techniques ranked highly in a review of processing technologies for an ε-metal waste form, as they minimised difficulties such as volatility and reactivity found in melting and solidification-based methods like furnace, induction, and arc melting [95].

Figure 5. Epsilon (ε) metal waste forms.

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Technetium Immobilization Forms Literature Survey

“…Much of the recent work on the ε-metal alloy has focused on identification and characterization of methods for producing the alloy. Among the methods considered are arc melting, induction melting (inert gas or vacuum), hot uniaxial pressing, HIP, spark plasma sintering (SPS), microwave sintering, and furnace melting (Strachan et al 2010;Rohatgi and Strachan 2011). Cui et al (2001) used a cold-crucible levitation melting apparatus to conduct melting at 1800°C in an argon atmosphere.…”