Spent-fuel special-studies progress report: probable mechanisms for oxidation and dissolution of single-crystal UO/sub 2/ surfaces
Due to the complexity of the structural, microstructural and compositional characteristics of spent fuel, basic leaching and dissolution mechanisms were studied with UO/sub 2/ matrix material, specifically with single-crystal UO/sub 2/, to isolate individual contributory factors. The effects of oxidation and oxidation-dissolution were investigated in different oxidation conditions, such as in air, oxygenated solutions and deionized water containing H/sub 2/O/sub 2/. In addition, the effects of temperature on dissolution of UO/sub 2/ were studied in autoclaves at 75 and 150/sup 0/C. Also, oxidation and dissolution measurements were investigated via electrochemical methods to determine if those techniques could be applied to the characterization of leaching and dissolution of spent fuel in a hot cell. Finally, the effects of radiation were explored since the radiolysis of water may create a localized oxidizing condition at or near the spent fuel-solution interface, even in neutral or reducing conditions as commonly found in deep geological environments. The oxidation and oxidation-dissolution mechanisms for UO/sub 2/ are proposed as follows: The UO/sub 2/ surface is first oxidized in solution to form a UO/sub 2+x/ surface layer several angstroms thick. This oxidized surface has a high dissolution rate since the UO/sub 2+x/ reacts with the dissolved O/sub 2/, or H/sub 2/O/sub 2/, to form uranyl complex ions in a U(VI) state. As the uranyl ions exceed the solubility limits in solution, they become hydrolyzed to form solid deposits and suspended particles of UO/sub 3/ hydrates. The thickness and porosity of the deposited UO/sub 3/ hydrate surface-film is dependent on temperature, pH and deposition time. A long-term dissolution rate is then determined by the nature of the surface film, such as porosity, solubility and mechanical properties.
- Research Organization:
- Battelle Pacific Northwest Labs., Richland, WA (United States)
- DOE Contract Number:
- AC06-76RL01830
- OSTI ID:
- 6854511
- Report Number(s):
- PNL-3566; TRN: 81-006598
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE WASTES FROM NUCLEAR FACILITIES
SPENT FUEL STORAGE
RESEARCH PROGRAMS
URANIUM DIOXIDE
DISSOLUTION
LATTICE PARAMETERS
LEACHING
OXIDATION
ACID CARBONATES
AIR
BRINES
EXPERIMENTAL DATA
HIGH TEMPERATURE
HYDROGEN PEROXIDE
MEDIUM TEMPERATURE
PH VALUE
SODIUM COMPOUNDS
SURFACES
TEMPERATURE EFFECTS
WASTE-ROCK INTERACTIONS
WATER
X-RAY DIFFRACTION
ACTINIDE COMPOUNDS
ALKALI METAL COMPOUNDS
CHALCOGENIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
DATA
DIFFRACTION
FLUIDS
GASES
HYDROGEN COMPOUNDS
INFORMATION
NUMERICAL DATA
OXIDES
OXYGEN COMPOUNDS
PEROXIDES
SCATTERING
SEPARATION PROCESSES
STORAGE
URANIUM COMPOUNDS
URANIUM OXIDES
050900* - Nuclear Fuels- Transport
Handling
& Storage
052002 - Nuclear Fuels- Waste Disposal & Storage