Simulations of heat and oxygen diffusion in UO2 nuclear fuel rods

Ramírez, José Ramón; Stan, Marius; Cristea, Paul Dan

doi:10.1016/j.jnucmat.2006.08.018

Cited by 69 publications

(74 citation statements)

References 40 publications

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“…which can be adopted for UO 2+x since Q is shown to have a weak dependence on the plutonium content [25,32]. Moreover, one can assume a similar thermal diffusion ratio k T for the two ceramics, and since the chemical oxygen diffusivities in (U, Pu)O 2+x and UO 2+x are similar (especially at higher temperatures) as seen in Fig.…”

Section: Interstitial Oxygen Diffusion In the Fuel Matrixmentioning

confidence: 99%

“…(13) and (15) because the thermal conductivity, k, is also a function of the stoichiometry deviation, x, as described below. A time-dependent model for heat conduction is considered so that the current treatment can be eventually extended for transient conditions, to determine if fuel centerline melting can occur in defective fuel during a power pulse [32]. For instance, the ratio of the thermal diffusivity-to-mass diffusivity can be interpreted as the time required for the stoichiometry deviation field to reach steady-state compared to the time for the temperature field to reach its equilibrium state.…”

Section: Heat Conduction In the Solidmentioning

confidence: 99%

“…For instance, the ratio of the thermal diffusivity-to-mass diffusivity can be interpreted as the time required for the stoichiometry deviation field to reach steady-state compared to the time for the temperature field to reach its equilibrium state. Since this ratio varies greatly, this disparity in the characteristic times of heat and oxygen diffusion can play an important role in the transient behaviour of fuel under sudden changes in operating conditions [32]. The specific heat capacity C p (in J mol À1 K À1 ), as a function of temperature T (K) and x, follows from the thermodynamic treatment: C p ðx; T Þ ¼ 52:174 þ 45:806x þ ð87:951 Â 10 À3 À 7:3461 Â 10 À2 xÞT þ ð1 À xÞfÀ84:241 Â 10 À6 T 2 þ 31:542…”

Section: Heat Conduction In the Solidmentioning

confidence: 99%

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A conceptual model for the fuel oxidation of defective fuel

Higgs

Lewis

Thompson

et al. 2007

Journal of Nuclear Materials

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Section: Interstitial Oxygen Diffusion In the Fuel Matrixmentioning

confidence: 99%

Section: Heat Conduction In the Solidmentioning

confidence: 99%

Section: Heat Conduction In the Solidmentioning

confidence: 99%

See 1 more Smart Citation

A conceptual model for the fuel oxidation of defective fuel

Higgs

Lewis

Thompson

et al. 2007

Journal of Nuclear Materials

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“…Besides, recent studies show that burnup plays a major role in uranium dioxide (UO 2 ) transport properties and significantly changes thermal conductivity [2]. Nuclear fuel rods operate under strong temperature gradients ($4 Â 10 5 K/m), which causes changes in stoichiometry due to oxygen redistribution [3]. In turn, increase of stoichiometry lowers thermal conductivity, which increases temperature gradients even further.…”

Section: Introductionmentioning

confidence: 99%

High-precision molecular dynamics simulation of UO2–PuO2: Anion self-diffusion in UO2

Potashnikov

Boyarchenkov

Nekrasov

et al. 2013

Journal of Nuclear Materials

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h i g h l i g h t s" We perform MD simulation of oxygen diffusion in UO2 (up to 50 000 ions and 1 ls time)." We reached 1400 K and 10 À12 cm 2 /sec, which allowed direct comparison to experiments." S-shaped T-dependence of activation energy and k-peak of its derivative were obtained. " Continual superionic phase transition (rather than first or second order) was proved. t r a c tOur series of articles is devoted to high-precision molecular dynamics simulation of mixed actinide-oxide (MOX) fuel in the approximation of rigid ions and pair interactions (RIPI) using high-performance graphics processors (GPU). In this article we study self-diffusion mechanisms of oxygen anions in uranium dioxide (UO 2 ) with the 10 recent and widely used sets of interatomic pair potentials (SPP) under periodic (PBC) and isolated (IBC) boundary conditions. Wide range of measured diffusion coefficients (from 10 À3 cm 2 /s at melting point down to 10 À12 cm 2 /s at 1400 K) made possible a direct comparison (without extrapolation) of the simulation results with the experimental data, which have been known only at low temperatures (T < 1500 K). A highly detailed (with the temperature step of 1 K) calculation of the diffusion coefficient allowed us to plot temperature dependences of the diffusion activation energy and its derivative, both of which show a wide ($1000 K) superionic transition region confirming the broad k-peaks of heat capacity obtained by us earlier. It is shown that regardless of SPP the anion self-diffusion in model crystals without surface or artificially embedded defects goes on via exchange mechanism, rather than interstitial or vacancy mechanisms suggested by the previous works. The activation energy of exchange diffusion turned out to coincide with the anti-Frenkel defect formation energy calculated by the lattice statics.

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“…Detailed simulations have been conducted for defective fuel elements under normal operating conditions [6][7][8], however, these simulations do not cover the possibility of a molten phase. Thus a treatment is need for these conditions.…”

Section: Introductionmentioning

confidence: 99%