Development of hydrogen gas getters for TRU waste
- John P.
- Eugene J.
- Eric
- Mark
- Marc J.
Alpha radiolysis of hydrogenous waste and packaging materials generates hydrogen gas in radioactive storage containers. For this reason, the flammable gas (hydrogen) concentration in waste shipment containers (Transuranic Package Transporter-II or TP-II containers) is limited to the lower explosion limit of hydrogen in air (5 vol%). The use of hydrogen getters is being investigated to prevent the build up of hydrogen during storage and transport of the TP-II containers (up to 60 days). Preferred hydrogen getters are solid materials that scavenge hydrogen from the gas phase and chemically and irreversibly bind it in the solid state. One proven getter, 1,4-bis(phenylethynyl)benzene or DEB, belongs to a class of compounds called alkynes, which are characterized by the presence of carbon-carbon triple bonds. These carbon atoms will, in the presence of suitable catalysts such as palladium, irreversibly react with hydrogen to form the corresponding saturated alkane compounds. Because DEB contains two triple bonds, one mole of DEB reacts with 4 moles of hydrogen. The standard formulation for the 'DEB getter' is a mixture of 75% DEB and 25% carbon catalyst (5% palladium on carbon). Certain chemicals such as volatile organic compounds (VOCs) are known to 'poison' and reduce the activity of the catalyst. Therefore, in addition to the standard formulation, a semi-permeable barrier that encapsulates and protects the getter and its catalyst from poisons was also developed. The uncoated and polymer coated getter formulations were subjected to tests that determined the performance of the getters with regard to capacity, operating temperature range (with hydrogen in nitrogen and in air), hydrogen concentration, poisons, aging, pressure, reversibility, and radiation effects. This testing program was designed to address the following performance requirements: (1) Minimum rate for hydrogen removal of 1.2E-5 moles hydrogen per second for 60 days; (2) Sufficient getter material within the TP-II to ensure that no more than 50% of getter material is consumed during the 60 days; and (3) Adequate hydrogen removal rate from the getter reaction in the absence of the recombination reaction of hydrogen to produce water. This conservative approach provides a measure of safety for waste shipments by ensuring that sufficient getter material is present and by not taking credit for the recombination reaction. The rationale for measuring and reporting the hydrogen removal rate at 50% getter capacity is thus derived. All of the coated getters as well as the uncoated DEB performed well above the performance requirements. Coating the DEB with polymers did not significantly enhance getter performance in the presence of poisons relative to uncoated DEB. The next phase of the project is to evaluate a scaled-up getter package for performance under waste shipping conditions anticipated in the TP-II.
- Research Organization:
- Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 977477
- Report Number(s):
- LA-UR-04-0980; LA-UR-04-980; TRN: US1002928
- Resource Relation:
- Conference: Submitted to Waste Management'04 Conference, February 29-March 4, 2004, Tucson, AZ
- Country of Publication:
- United States
- Language:
- English
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