Kinematics and thermodynamics across a propagating non-stoichiometric oxidation phase front in spent fuel grains

Conference · Wed Sep 01 04:00:00 EDT 1993

OSTI ID:10188019

Stout, R B; Kansa, E J; Wijesinghe, A M

Spent fuel contains mixtures, alloy and compound, but are dominated by U and O except for some UO{sub 2} fuels with burnable poisons (gadolinia in BWR rods), the other elements evolve during reactor operation from neutron reaction and fission + fission decay events. Due to decay, chemical composition and activity of spent fuel will continue to evolve after removal from reactors. During the time interval with significant radioactivity levels relevant for a geological repository, it is important to develop models for potential chemical responses in spent fuel and potential degradation of repository. One such potential impact is the oxidation of spent fuel, which results in initial phase change of UO{sub 2} lattice to U{sub 4}O{sub 9} and the next phase change is probably to U{sub 3}O{sub 8} although it has not been observed yet below 200C. The U{sub 4}O{sub 9} lattice is nonstoichiometric with a O/U weight ratio at 2.4. Preliminary indications are that the UO{sub 2} has a O/U of 2. 4 at the time just before it transforms into the U{sub 4}O{sub 9} phase. In the oxygen weight gain versus time response, a plateau appears as the O/U approaches 2.4. Part of this plateau is due to geometrical effects of a U{sub 4}O{sub 9} phase change front propagating into UO{sub 2} grain volumes; however, this may indicate a metastable phase change delay kinetics or a diffusional related delay time until the oxygen density can satisfy stoichiometry and energy conditions for phase changes. Experimental data show a front of U{sub 4}O{sub 9} lattice structure propagating into grains of the UO{sub 2} lattice. To describe this spatially inhomogenous oxidation phase transition, as well as the expected U{sub 3}O{sub 8} phase transition from the U{sub 4}O{sub 9} lattice, lattice models are developed and spatially discontinuous kinematic and energetic expressions are derived. 9 refs.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 10188019
• Report Number(s): UCRL-JC--112821; CONF-9306116--2; ON: DE93041108
• Country of Publication: United States
• Language: English

Related Subjects

050700
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
36 MATERIALS SCIENCE
360202
CHEMICAL COMPOSITION
CRYSTAL LATTICES
DEFORMATION
EQUATIONS
FUELS PRODUCTION AND PROPERTIES
MATHEMATICAL MODELS
OXIDATION
PHASE TRANSFORMATIONS
SPENT FUELS
STRUCTURE AND PHASE STUDIES
THERMODYNAMICS
TIME DEPENDENCE
URANIUM DIOXIDE
URANIUM OXIDES