Critical evaluation of the thermal properties of Th02 and Th1−yUy02 and a survey of the literature data on Th1−yPuy02

Thoria Ehancement of Nuclear Reactor Safety

“…The calculated ratio of the thermal conductivity of ThO 2 versus UO 2 (phonon contribution) at 1800 K as used in (Bakker et al, 1997;Lewis et al, 2002) is 1.02 and compares well with the estimated values in Table 2 for various functionals (LDA (Ceperley and Alder, 1980), WC (Wu and Cohen, 2006), LDA+U (Cococcioni and Gironcoli, 2005) (urania), B3LYP (Becke, 1993) (thoria) and experimental data).…”

“…The experimental value of the melting temperature of urania (3120±30 K (Adamson et al, 1985)) is lower than that evaluated as the most accurate (Bakker et al, 1997) value at exact stoichiometry (3651±17 K (Ronchi and Hiernaut, 1996)) and other evaluated melting temperatures between 3323 and 3663 K (Bakker et al, 1997). However as Table 1 shows the estimated melting temperature of thoria is lower than urania and it is underestimated by more than 300 K while for urania agreement is good for most functionals (except of PBE).…”

“…The phonon contribution to the thermal conductivity is expressed by the same equation as for urania (Equation 4a) except that there is no dependence on stoichiometry deviation (x) for parameters A and B and the following values were proposed by Bakker et al (1997): A = 0.0042 mKW −1 and B = 0.000225 mW −1 . Belle and Berman (1984) it was pointed out that there are many uncertainties with evaluation of a radiative contribution to a thermal conductivity as it may depend on the relative mean free path and dimensions of the radiative objects' surface roughness that are not included in the original black body radiation model.…”

“…The red dot dash curve represents the total conductivity of thoria, which is calculated as a sum of phonon contribution (Bakker et al, 1997), indicated by red triangles and polaron and radiative contribution as described above. It can readily be verified that the thermal conductivity of thoria is much higher at low temperatures than for urania and at high temperatures the phonon contribution decreases significantly, being only a few percent higher as evaluated in Table 2 for minimal conductivity ratios of thoria versus urania.…”

Advanced Proliferation Resistant, Lower Cost, Uranium-Thorium Dioxide Fuels for Light Water Reactors (Progress report for work through June 2002, 12th quarterly report)

“…Only a few measurements of thermal conductivity have been made for ThO 2 -PuO 2 fuel (Bakker et al 1997). The integrated, with respect to temperature, thermal conductivity of a mixture of 97.28wt% ThO 2 and 2.72 wt% PuO 2 was measured by irradiation of fuel elements with central thermal couples (Jeffs 1968).…”