Kinematics and Thermodynamics of Non-Stoichiometric Oxidation Phase Transitions in Spent Fuel

Stout, R.B.; Kansa, Edward J.; Wijesinghe, A. M.

doi:10.1557/proc-294-25

Cited by 3 publications

(10 citation statements)

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“…H, C and O) in the U0 2 matrix. This transformation occurs with no structural changes, and 2.64 is the highest stoichiometry that can be reached [23][24][25], Dissolution starts and uranium concentration in solution increases (as in test 2-2) until the solubility limit under the experimental conditions has been reached. When uranium concentration is equal to the solubility limit of U0 2 , the formation of the secondary phase (schoepite) controls the solubility.…”

Section: Discussionmentioning

confidence: 99%

Uranium Dioxide Leaching Mechanism in a Synthetic Granitic Groundwater in Oxic Conditions in Function of S/V Ratio at 96 °C

Cachoir¹,

Guittet²,

Gallien³

et al. 1996

Radiochimica Acta

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U0 2 dissolution experiments under oxic conditions have been performed for one, two and five months at 96 °C in function of surface to volume (S/V) ratio. The leachant is representative of a groundwater in equilibrium with a granitic medium. Two different results in function of time and S/V ratio were found. On the one hand, no sign of precipitation of secondary phases has been observed and uranium concentration is around 10 9 mol · Γ'. On the other hand for the five months test, yellow perfectly crystallized phases, identified as schoepite, have been found on the surface of the U0 2 pellets correlated to an uranium concentration equal to 2.77 · 10 4 mol · 1"'.

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Section: Discussionmentioning

confidence: 99%

Uranium Dioxide Leaching Mechanism in a Synthetic Granitic Groundwater in Oxic Conditions in Function of S/V Ratio at 96 °C

Cachoir¹,

Guittet²,

Gallien³

et al. 1996

Radiochimica Acta

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“…The rate of work : that lattice. Also, note that the above energy on spatial domain R + _ is expression does not explicitly represent any oxide expression, which must be zero because the = t._jR fjojdx + _dRcrijnivjdx (3)(4)(5)(6) velocity is arbitrary, hence…”

Section: V(bt)=v(at)+v_}_mentioning

confidence: 99%

“…The next expected spent fuel phase is U308, For homogeneous phase transformations, the full which will require additional oxygen to be nonequilibrium thermodynamic rate response transported into the U409 lattice for the model from equation (3 nine-by-nine matrix (counting the four vector lattice with a O/U of-2.4, its potential intermediate fluxes as vector equations, it would be tensorially a existence will be neglected and equation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) 21 by 21 matrix). This type of model was rewritten to represent the thermodynamic energy developed in reference [3] for the simplified case of rates for a transformation directly from U409 lattice homogeneous phase transformations. The to the U308 lattice.…”

Section: V(bt)=v(at)+v_}_mentioning

confidence: 99%

“…The decomposition functions are defined as P_ = P_I + P_] , P49-P491 + P491, A model describing the deformation response of a contiguous set of lattice cells was developed. [ 3] P38-P3g] + P38], where the single bar symbol The model represented a lattice cell by a set of denotes the continuum response and the single vector attributes. These vector attributes became square bracket denotes the discontinuum response.…”

Section: Introductionmentioning

confidence: 99%

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Kinematics and Thermodynamics Across a Propagating Non-Stoichiometric Oxidation Phase Front in Spent Fuel Grains

Stout¹,

Kansa²,

Wijesinghe³

1994

Applied Mechanics Reviews

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Spent fuel from power reactors contains mixtures, alloy subsets, and compounds of elements; but the aggregate atomic densities in spent fuel are dominated by uranium and oxygen atoms. With the exception of some UO2 fuels with burnable poisons (primarily gadolinia in BWR rods), the other elements with significant atomic densities in spent fuel evolve during reactor operation from neutron reactions and fission plus fission decay events. Due to nuclear decay processes, the intrinsic chemical composition and activity of spent fuel will continue to evolve after it is removed from reactors as its radioactivity decays over time. During the time interval when the radioactivity levels are significant, which is the time interval relevant for design and for performance assessment of a geological repository, it is important to develop an understanding and to develop models that describe potential chemical responses in spent fuel and its potential degradational impacts on repository design and performance. One such potential impact is the oxidation response of spent fuel. The oxidation of spent fuel results in an initial phase change of the UO2 lattice to a U4O9 lattice, and the next phase change is probably to U3O8 although it has not been observed yet at low temperatures (<200°C). The U4O9 lattice is non-stoichiometric with a oxygen to uranium weight ratio (O/U) at ~ 2.4. Preliminary indications are that the UO2 has a O/U of ~ 2.4 at the time just before it transforms into the U4O9 phase.[1,2] Also, in the oxygen weight gain versus time response, a plateau appears as the O/U approaches ~ 2.4. Part of this plateau response is due to geometrical effects of a U4O9 phase change front propagating into UO2 grain volumes. However, the plateau time response may be indicative of a metastable phase change delay kinetics or a diffusional related delay time until the oxygen density can attain a critical value to satisfy the stoichiometry and energy conditions for phase changes. In a previous paper and as a first step, a kinematic and thermodynamic ayalysis was developed to model spatially homogeneous oxidation phase transitions.[3] However, the experimental data clearly show a front of U4O9 lattice structure propagating into grains of the UO2 lattice structure. To describe this spatially inhomogeneous oxidation phase transition, as well as the expected U3O8 phase transition from the U4O9 lattice, lattice models are developed and spatially discontinuous kinematic and energetic expressions are derived. The approach will use concepts from statistical mechanics, discontinuum mechanics, and non-equilibrium thermodynamics. In addition, analytical techniques from shock wave analysis will be used to derive the surface discontinuity energetic expressions across the propagating oxidation phase front.

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“…A test plan addendum was completed and sent to L L P for review and approval. A paper entitled "Kinematics and Thermodynamics of Non-Stoichiometric Oxidation Phase Transitions in Spent Fuel" (Stout, et al, 1993) …”

Section: -184mentioning

confidence: 99%

Site characterization progress report: Yucca Mountain, Nevada, October 1, 1992--March 31, 1993, No. 8

1993

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Kinematics and Thermodynamics of Non-Stoichiometric Oxidation Phase Transitions in Spent Fuel

Cited by 3 publications

References 4 publications

Uranium Dioxide Leaching Mechanism in a Synthetic Granitic Groundwater in Oxic Conditions in Function of S/V Ratio at 96 °C

Uranium Dioxide Leaching Mechanism in a Synthetic Granitic Groundwater in Oxic Conditions in Function of S/V Ratio at 96 °C

Kinematics and Thermodynamics Across a Propagating Non-Stoichiometric Oxidation Phase Front in Spent Fuel Grains

Site characterization progress report: Yucca Mountain, Nevada, October 1, 1992--March 31, 1993, No. 8

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