Catalytic oxidation of tritium in air at ambient temperature

Technical Report · Sun Jul 01 04:00:00 EDT 1979

DOI:https://doi.org/10.2172/5844459· OSTI ID:5844459

Sherwood, A E; Monahan, B G; McWilliams, R A; Uribe, F S; Griffith, C M

Tritium/air oxidation kinetic data are derived from ambient-temperature measurements carried out with three precious-metal catalysts. Each catalyst consists of a high-surface-area substrate in pelletized form, onto which precious metal has been dispersed. The metal/substrate combinations investigated are platinum/alumina, palladium/kaolin, and palladium/zeolite. Electron-microprobe scans reveal that the dispersed metal is deposited in each case near the outer surface of the pellet, with metal concentration decreasing exponentially from the pellet surface. Kinetic oxidation measurements are made in a unique apparatus consisting of a large Lucite enclosure with an air atmosphere processed by a recirculating cleanup system. Dual-ionization chambers with an intermediate adsorption bed permit measurement of tritium gas and tritiated water vapor. Rate coefficients are determined from concentration decay following a spike injection of tritium into the enclosure. The catalytic reaction is first-order in tritium concentration in the range 10 to 10/sup 5/ ..mu..Ci/m/sup 3/. Addition of hydrogen carrier gas is unnecessary. Each of the dispersed-metal catalysts is extremely active in promoting tritium oxidation in comparison with self-catalyzed atmospheric conversion; equivalent first-order rate constants are higher by roughly 9 orders of magnitude. The platinum-based catalyst is more effective than the palladium catalysts on a surface-area basis by about a factor of 3. Catalytic activity for all three catalysts declines with time of exposure to air after activation, following a power-law decay with an exponent of -1/2. A model for optimization of the catalyst reactivation cycle is proposed, revealing that the optimum catalyst volume scales with flow rate to the 2/3 power. Ambient-temperature tritium oxidation is cost-effective for small- to intermediate-scale cleanup systems. A heated catalyst is desirable for large-scale systems.

• Research Organization: California Univ., Livermore (USA). Lawrence Livermore Lab.
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 5844459
• Report Number(s): UCRL-52811
• Country of Publication: United States
• Language: English

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70 PLASMA PHYSICS AND FUSION TECHNOLOGY
AIR
ALUMINIUM
AMBIENT TEMPERATURE
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
CATALYSTS
CATALYTIC EFFECTS
CHEMICAL REACTIONS
ELECTRON SCANNING
ELEMENTS
FLUIDS
GASES
HYDROGEN ISOTOPES
INORGANIC ION EXCHANGERS
ION EXCHANGE MATERIALS
ISOTOPES
LIGHT NUCLEI
METALS
MINERALS
NUCLEI
ODD-EVEN NUCLEI
OXIDATION
PALLADIUM
PLATINUM
PLATINUM METALS
RADIOISOTOPES
SUBSTRATES
TRANSITION ELEMENTS
TRITIUM
YEARS LIVING RADIOISOTOPES
ZEOLITES