Systems Requirement Document for the MSRE U-233 Conversion System

The fissile material reclamation activities for the MSRE remediation project include the removal and recovery of uranium from the off-gas system, from the stored fuel salt, and finally, from the uranium-laden charcoal in the Auxiliary Charcoal Bed (ACB). Each of these operations produces an uranium/fluoride compound that is not suitable for long-term storage. The uranium-fluoride compounds can be stored for a limited period of time in pressure vessels. The interim-storage vessels are designed to handle the internal pressure buildup from gases formed by radiolysis of the uranium-fluoride compounds. The conversion process will take the pressurized vessels from interim storage and process the materials in a hot cell located at Building 4501. The gas in the vessels will be vented through chemical traps and then the traps will be processed to convert the various uranium-fluoride compounds to a stable uranium oxide form. This will be done one trap at a time. The chemical form of uranium being extracted from the off-gas system and from fuel salt fluorination process is uranium hexafluoride UF6. During the operations at MSRE, the UF6 is chemisorbed onto sodium fluoride (NaF) traps where it forms the complex, 2NaF·UF6. The conversion process that will be installed in the Building 4501 Hot Cell D will recover the UF6 from the NaF traps by decomposition of the binary complex at elevated temperatures (>300 C). After the uranium is extracted from the NaF traps, it is collected in the conversion process reaction vessel. The reaction vessel is then hydrolized and heated through several step operations up to 900 C in order to convert the material to a stable uranium oxide. The ACB at MSRE contains uranium-laden charcoal with unstable CxF compounds. After extraction at MSRE, this material will be delivered to Building 4501 Hot Cell D for processing to a stable oxide. The charcoal conversion process is still under development, with mockup and full scale testing of the proposed flow sheet funded in FY 99 and FY 00. The uranium-laden charcoal has been pre-treated with ammonia to prevent the deflagration of the CxF if localized heating (>approximately150 C) occurs during the charcoal removal process. Prior to removal, the treatment will be performed a second time to denature the 1 to 5% reformation of CxF that has occurred due to radiolysis of NH4F. The uranium-laden charcoal will be physically extracted and stored in several pressure vessels at MSRE until the conversion process is designed and installed in Hot Cell A in Building 4501