(242e) Design and Testing of an Iodine and Tritium Capture System for Used Nuclear Fuel Tritium Pretreatment Processes

Design and Testing of an Iodine and Tritium Capture System for Used Nuclear Fuel Tritium Pretreatment Processes*

R. T. Jubin, B. B. Spencer, and S. H. Bruffey

Oak Ridge National Laboratory, P.O. Box 2008, Oak Ridge, TN 37831, jubinrt@ornl.gov

During the reprocessing of used nuclear fuel, volatile radionuclides will be released into the off-gas of a processing plant, including ³H, ¹⁴C, ⁸⁵Kr, and ¹²⁹I. The management of tritium becomes complex once it enters the aqueous portion of the facility (i.e. the dissolver and downstream processes). One potential way to simplify the management of off-gas streams could be to incorporate an efficient tritium pretreatment (TPT) step in which the UO₂ fuel is oxidized either by air or by NO₂ before dissolution. Oxidation of the UO₂ fuel matrix results in the release of tritium into the off-gas stream. Upfront removal of tritium from the fuel in a pretreatment step, followed by the abatement of tritium, can minimize or eliminate the distribution of tritium throughout the plant, also decreasing or eliminating the need for tritium capture on multiple off-gas streams. The oxidation of the fuel can be accomplished using air, oxygen, or other oxidants such as NO₂. The use of NO₂ in an advanced TPT (ATPT) system allows the oxidation to be performed at lower temperatures and may also result in the quantitative release of iodine from the fuel.

The ATPT off-gas will contain up to 75 vol% NO₂ gas. Silver nitrate–impregnated alumina (AgA) has been identified as the most promising iodine sorbent, and type 3A molecular sieves (3A MS) or silica gel have been identified as the most promising tritium sorbents to treat ATPT off-gas streams [1]. An initial series of tests were conducted in fiscal years 2017–2018 [2] with the intent of demonstrating the recovery of iodine and tritium using these sorbents from a recirculating gas stream that simulated the NO₂ recycle loop envisioned for the ATPT system. These initial tests showed low tritium recoveries and significant variations in the iodine recovery on the AgA. Ultimately, following disassembly of the system, it was concluded that corrosion within the system was at least partially the cause of the poor recovery for both species of interest. One of the conclusions drawn from those initial tests pointed to the reconsideration of the materials of construction.

Based on that recommendation, a new system has been designed and built that uses high nickel alloys wherever possible. The system will be tested in mid-FY 2019 under air and NO₂ TPT conditions. The results of those tests will be reported in this presentation.

1. Spencer, B. B., S. H. Bruffey, J. A. Jordan, and R. T. Jubin, Design of a Tritium and Iodine Removal System for Use with Advanced Tritium Pretreatment, Report nos. ORNL/SPR-2017/116 and NTRD-MRWFD-2017-000311 (Oak Ridge, TN: Oak Ridge National Laboratory, 2017).
2. Jubin, R. T., J. A. Jordan, and, S. H. Bruffey, Testing of an Iodine and Tritium Removal System for Advanced Tritium Pretreatment Off-Gas, Report nos. ORNL/SPR-2018/15 and NTRD-MRWFD-2018-000199 (Oak Ridge, TN: Oak Ridge National Laboratory, 2018).

* This manuscript has been authored by UT-Battelle, LLC, under contract DE-AC05-00OR22725 with the US Department of Energy (DOE). The US government retains and the publisher, by accepting the article for publication, acknowledges that the US 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 US government purposes. DOE 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).