Vitrification of F-area americium/curium: feasibility study and preliminary process recommendation

Abstract

Work was performed to identify a process to vitrify the contents of F- canyon Tank 17.1. Tank 17.1 contains the majority of americium (Am) and curium (Cm) contained in the DOE Complex. Oak Ridge National Laboratory (ORNL) has made a formal request for this material as fuel for production of Cf252 and other transplutonium actinides. The Am and Cm (and associated lanthanide fission products) are currently in nitric acid solution. Transportation of the intensely radioactive Am/Cm in liquid form is not considered possible. As a result, the material will either be solidified and shipped to ORNL or discarded to the Tank Farm. Nuclear Materials Processing Technology (NMPT), therefore, requested Defense Waste Processing Technology (DWPT) to determine if the Tank 17.1 material could be vitrified, and if it was vitrified could the americium and curium be successfully recovered. Research was performed to determine if the Tank 17.1 contents could indeed be mixed with glass formers and vitrified. Additional studies identified critical process parameters such as heat loading, melter requirements, off-gas evolution, etc. Discussions with NMPT personnel were initiated to determine existing facilities where this work could be accomplished safely. A process has been identified which will convert the Am/Cm material into approximately 300kg of glass. This will be done by initially removing the large quantities of transition metals and aluminum. Oxalic acid will be added to Tank 17.1 and the actinides and lanthanides will be precipitated as oxalates. The remaining aqueous fraction will be removed and the lanthanides and actinides will then be redissolved. The solution will be evaporated and steam stripped down to approximately 100g/I solids and 1N nitric acid prior to being transferred into a receipt/feed tank in the Multi- Purpose Processing Facility (MPPF - formerly Section 18 of F-Canyon). The Am/Cm solution will then be fed directly into a bushing melter. Glass beads will be added simultaneously alongside the solution and the mixture will be vitrified and cast into stainless steel canisters. The filled glass canisters will be allowed to cool and deconned prior to packaging for transport to ORNL. The melter will be capable of a minimum 1-2kg/hr glass output, so total processing time will be on the order of a few hundred hours. The glass is a borosilicate composition designed to be selectively attacked by nitric acid. Complete recovery of Am and Cm surrogates (La, and Nd) from the glass has been demonstrated by a nitric acid extraction technique. While the glass can be attacked by concentrated acid, it is approximately 1000 times more durable than the required specification for high- level waste glass. The Am/Cm glass produced will simultaneously act as both a product Am/Cm glass is not processed by ORNL. This document details the results of our initial effort. Supporting documents concerning heat generation, off-gas modeling, melter design, and a process engineering flowsheet developed by NMPT are included.