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

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 geometricalmore » 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.« less
Authors:
; ;
Publication Date:
OSTI Identifier:
10188019
Report Number(s):
UCRL-JC--112821; CONF-9306116--2
ON: DE93041108; TRN: 93:023950
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Conference
Resource Relation:
Conference: 1. joint meeting of the Society of Engineering Science, Inc., and the American Society of Mechanical Engineering and the American Society of Civil Engineers,Charlottesville, VA (United States),6-9 Jun 1993; Other Information: PBD: Sep 1993
Research Org:
Lawrence Livermore National Lab., CA (United States)
Sponsoring Org:
USDOE, Washington, DC (United States)
Country of Publication:
United States
Language:
English
Subject:
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS; 36 MATERIALS SCIENCE; SPENT FUELS; CHEMICAL COMPOSITION; URANIUM OXIDES; PHASE TRANSFORMATIONS; URANIUM DIOXIDE; OXIDATION; DEFORMATION; THERMODYNAMICS; EQUATIONS; MATHEMATICAL MODELS; TIME DEPENDENCE; CRYSTAL LATTICES 050700; 360202; FUELS PRODUCTION AND PROPERTIES; STRUCTURE AND PHASE STUDIES