(327a) Tritium Management Approaches and Their Impacts on Tritium Distribution within a Unf Reprocessing Plant

During the reprocessing of used nuclear fuel (UNF), volatile radionuclides are released from the fuel matrix and will be discharged from the facility stack if no recovery processes are in place to limit their release. The volatile radionuclides of concern are ³H, ¹⁴C, ⁸⁵Kr, and ¹²⁹I.

While iodine is typically the focus of most off-gas capture studies due to the high decontamination factor (DF) requirements and multiple release pathways, prior studies have indicated that the control of tritium could also be a significant issue for future reprocessing plants, especially if relatively short-cooled fuels are being processed [1,2]. A previous study by Jubin and Spencer [3] examined the accumulation and distribution of tritium in an aqueous-based reprocessing plant as well as the impacts of various approaches to remove the tritium from the aqueous and off-gas streams. The evaluated off-gas streams included the dissolver off-gas (DOG), the vessel off-gas (VOG), and the melter off-gas (MOG). The extent to which the various streams must be treated to achieve the overall specified facility tritium DFs was examined. The previous study assumed that the head-end of the UNF reprocessing plant was a typical chop/leach operation in which no effort is made to remove the tritium from the fuel prior to dissolution.

The current study expands upon that work with the addition of a tritium pretreatment operation in which most, if not all, of the tritium is volatilized from the fuel prior to the dissolution step. Thus the amount of tritium that reaches the aqueous portion of the plant is minimized. This study examines the impact of incomplete volatilization of tritium from the fuel, the impact of tritium pretreatment on tritium concentrations within the plant, and the estimated volumes of tritiated waste that would be generated. Comparisons are made with the waste generated in two limiting cases: complete volatilization of the tritium in the fuel and no volatilization of the tritium. In all cases, comparable levels of tritium controls are utilized to limit the emissions to provide the same overall plant-wide tritium DF.

1. R. JUBIN, N. SOELBERG, D. STRACHAN, and G. ILAS, Assessments and Options for Removal and Immobilization of Volatile Radionuclides from the Processing of Used Nuclear Fuel, FCR&D-SWF-2011-000305, UT‑Battelle, LLC, Oak Ridge National Laboratory (2011).

2. R. JUBIN, N. SOELBERG, D. STRACHAN, and G. ILAS, Fuel Age Impacts on Gaseous Fission Product Capture During Separations, FCRD-SWF-2012-000089, PNNL-22550, UT‑Battelle, LLC, Oak Ridge National Laboratory (2012).

3. R. T. JUBIN and B. B. SPENCER, “Tritium Distribution and Capture Requirements for UNF Reprocessing,” Transactions of the American Nuclear Society, Vol. 114, New Orleans, La. (June 12–16, 2016).

   This manuscript has been authored by UT-Battelle, LLC, under Contract No. DE-AC0500OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a nonexclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for the United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).