Experimental measurement of pre-melting and melting of thorium dioxide

Ronchi, C.; Hiernaut, J.-P.

doi:10.1016/0925-8388(96)02329-8

Cited by 73 publications

(61 citation statements)

References 16 publications

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“…However, the general trend of the entire actinide dioxide series, reported in Figure 8, 3,5,7,[28][29][30][31] changes considerably when new values for NpO 2 and PuO 2 are taken into account instead of old ones. Figure 8 also shows that the difference between old and new melting temperatures of actinide dioxides increases with the atomic number of the actinide.…”

Section: Discussionmentioning

confidence: 99%

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Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements

Böhler

Welland

Bruycker

et al. 2012

Journal of Applied Physics

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This work revisits the melting behaviour of neptunium dioxide, an actinide compound which can be produced in the nuclear fuel during operation, and which has an important impact on the nuclear fuel and waste radioactivity especially on the very long term. The present experimental approach employs remote laser heating under controlled atmosphere and fast pyrometry. This technique circumvents problems encountered by more traditional heating techniques, in particular, the reaction between sample and containment at temperatures beyond 2500 K. In addition, only a small amount of sample material is required, which is an advantage with respect to the radioactivity and limited availability of neptunium. The NpO 2 melting/freezing temperature has been measured to be 3070 K 6 62 K, much higher than previous values (around 2830 K) obtained by more traditional thermal analysis methods. The large amount of experimental data collected allowed a consistent statistical analysis. It seems likely, although not fully evident from the present results, that the high oxygen potential at temperatures around melting leads to a slightly hypo-stoichiometric congruent melting composition, as already observed in other actinide (ThO 2 , PuO 2 ) and lanthanide oxides (e.g., CeO 2 ). Finally, a recently developed phase-field model was used for the simulation of the observed thermograms, allowing a deeper insight in material properties that are difficult to directly measure. For example, a polaron contribution to the high-temperature thermal conductivity, well accepted for the commonly studied actinide oxide UO 2 , is shown here to likely be present in NpO 2 .

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Section: Discussionmentioning

confidence: 99%

“…Comparison between old (induction furnace heating in a tungsten crucible) 3,[29][30][31] and new (quasi-containerless laser heating) 5,7,28 data points for the melting/solidification temperatures of dioxides of the actinide series. Data for the dioxides of protactinium and trans-plutonium actinides are missing or considered as unreliable.…”

Section: Figmentioning

confidence: 99%

Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements

Böhler

Welland

Bruycker

et al. 2012

Journal of Applied Physics

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“…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).…”

Section: Melting Temperaturementioning

confidence: 93%

“…It is widely discussed that thoria is not only four times more abundant but also that nuclear reactors based on thorium would be safe, with the risk of reactor core melt-down eliminated due not only to higher thermal conductivity but also a much higher fuel melting temperature: 3651±17 K (Ronchi and Hiernaut, 1996) versus 3120±30 K (Adamson et al, 1985) for urania. However it is seldom discussed that thoria does not oxidize to the higher oxidation states like urania.…”

Section: Introductionmentioning

confidence: 99%

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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“…The MD calculated changes in enthalpy (H(T)-H(300 K)) and density of Th0.9375U0.0625O2, Th0.875U0.125O2, Th0.8125U0.1875O2, Th0.75U0.25O2 and Th0.6875U0.3125O2 for both solid and liquid phases were fitted to equations (7)- (8) as well as (9)- (10) [7] argued that the curvature corrections made by other researchers on the ThO2 or UO2 rich sides of the temperature composition curve need not be the same, because the loss of 'O' from UO2 in the UO2-rich side might be different from that of the ThO2 rich side and hence recommended a value of 3643 ± 30 K. Ronchi et al [9] recently measured the melting temperature of ThO2 experimentally (under both stoichiometric and hypostoichiometric conditions) by heating a spherical sample with four symmetrically spaced pulsed Nd YAG lasers and observing the cooling/heating curve with time. For stoichiometric ThO2, the measured melting point was 3651 ± 17 K [9] and their data is consistent with the data generated by…”

Section: Enthalpy and Density Variation Of Th Rich (Thu)o2 And (Thpmentioning

confidence: 99%

Melting behavior of (Th,U)O2 and (Th,Pu)O2 mixed oxides

Ghosh

Kuganathan

Galvin

et al. 2016

Journal of Nuclear Materials

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The melting behaviors of pure ThO2, UO2 and PuO2 as well as (Th,U)O2 and (Th,Pu)O2 mixed oxides (MOX) have been studied using molecular dynamics (MD) simulations. The MD calculated melting temperatures (MT) of ThO2, UO2 and PuO2 using two-phase simulations, lie between 3650-3675 K, 3050-3075 K and 2800-2825 K, respectively, which match well with experiments. Variation of enthalpy increments and density with temperature, for solid and liquid phases of ThO2, PuO2 as well as the ThO2 rich part of (Th,U)O2 and (Th,Pu)O2 MOX are also reported. The MD calculated MT of (Th,U)O2 and (Th,Pu)O2 MOX show good agreement with the ideal solidus line in the high thoria section of the phase diagram, and evidence for a minima is identified around 5 atom% of ThO2 in the phase diagram of (Th,Pu)O2 MOX.

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Experimental measurement of pre-melting and melting of thorium dioxide

Cited by 73 publications

References 16 publications

Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements

Revisiting the melting temperature of NpO2 and the challenges associated with high temperature actinide compound measurements

Thoria Ehancement of Nuclear Reactor Safety

Melting behavior of (Th,U)O2 and (Th,Pu)O2 mixed oxides

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