Multi-component gas transport in the fuel-to-clad gap of candu fuel rods during severe accidents

Szpunar, Barbara; Lewis, Brent J.; Arimescu, V.I.; Dickson, R.; Dickson, L.W.

doi:10.1016/s0022-3115(01)00422-6

Cited by 5 publications

(7 citation statements)

References 24 publications

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“…1. We assume here the time of origin of simulation to be the time after the zircalloy cladding has fully oxidised since, as calculated before (Szpunar et al, 2001), there is no significant urania fuel oxidation earlier due to a low value of oxygen potential in the presence of hydrogen originating from the oxidation of zirconium in steam.…”

Section: The Temperature Profile In the Defective Fuel Rodsmentioning

confidence: 99%

“…Recently fuel oxidation models in steam atmosphere were evaluated (Szpunar, 2012b) and while a more accurate equation for a steam dissociation was provided it was also demonstrated that there was not much effect on the calculated stoichiometry deviation; therefore we use here the simplified model used previously (Lewis et al, 2002;Szpunar et al, 2001). The estimate of equilibrium stoichiometry deviation (Blackburn, 1973) used here is conservative at high temperatures and the difference in the calculated equilibrium stoichiometry deviation at low temperatures from more conservative models is not significant (Szpunar and Szpunar, 2012).…”

Section: The Temperature Profile In the Defective Fuel Rodsmentioning

confidence: 99%

“…Another study (Szpunar et al, 2001) shows that urania fuel does not start to oxidize until the protective Zircaloy cladding is fully oxidized. However during the oxidation of Zircalloy cladding hydrogen is produced (Zr+2HO 2 →ZrO 2 +2H 2 ) and it may explode as happened during the Fukushima accident.…”

Section: Introductionmentioning

confidence: 99%

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Thoria Ehancement of Nuclear Reactor Safety

Szpunar

2013

Physics International

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The recent nuclear accident in Fukushima demonstrates that a nuclear mishap should be viewed using interdisciplinary tools. For example, the urania fuel melts not only because of enhanced neutron flux but also because its thermal conductivity degrades when it oxidizes. Here we present the application of first principles calculations to evaluate the structural, mechanical and thermal properties of traditional urania fuel and new, inherently safer thoria fuel. Knowledge of the lattice constants for higher oxidation state oxides of uranium is important in nuclear safety analysis, since the formation of U 3 O 8 in a defective fuel element can cause cracking or split the fuel sheath after disposal, due to a net 32-36% volume increase. This contrasts with thoria fuel where such oxidation does not occur during accident. The comparison between these two fuels is provided with respect to reactor safety. In an exemplary simulation we show that replacement of urania fuel by thoria prevents central melting in the fuel rod.

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Section: The Temperature Profile In the Defective Fuel Rodsmentioning

confidence: 99%

Section: The Temperature Profile In the Defective Fuel Rodsmentioning

confidence: 99%

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Thoria Ehancement of Nuclear Reactor Safety

Szpunar

2013

Physics International

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“…Originally, numerical iterative method was used to solve Equation (8) for b. However, it has been found later that, for low concentrations of hydrogen and high temperatures, there is no convergence, and an analytical solution of the cubic equation resulting from Equation (8) needs to be implemented to solve this problem [17].…”

Section: Steam Dissociationmentioning

confidence: 99%

Assessment of the models of urania fuel oxidation in steam-rich atmosphere

Szpunar

2012

Journal of Nuclear Science and Technology

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The urania fuel oxidation model for a steam-rich atmosphere developed by Cox et al. using the extensive experimental database has been subsequently used widely but with some inconsistencies in implementations. They are listed and evaluated in this work to help improve the existing models as well as for future model development. The comparison of the equilibrium stoichiometry deviation, calculated using various models, is also given. Small differences between the equilibrium constants used for steam dissociation are found. In one application, the original model for steam dissociation was rewritten in terms of component partial pressures for simplification. It is shown that the modified model differs from the original model by a multiplicative factor (1 7 p O 2 /P tot ). A more complex equation that preserves total pressure is derived. However, the effect on the calculated fuel oxidation is much smaller than the effect of the uncertainty of the equilibrium stoichiometry deviation. The discrepancies in stoichiometry deviations and the estimate of the surface area of a pellet may lead to a double underprediction of fuel oxidation rate.

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“…Any hydrogen production will significantly reduce the oxygen potential in the gap. Thus, in addition to a physical barrier, the sheath also acts as a chemical barrier while oxidation of the sheath is occurring [157][158][159].…”

Section: Gap Transportmentioning

confidence: 99%