Thermodynamics of gas-metal-slag equilibria for applications in in situ and ex situ vitrification melts

Miller, R.L.; Reimann, G.A.

doi:10.2172/10170082

Cited by 5 publications

(12 citation statements)

References 1 publication

(1 reference statement)

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“…Most recently, Annand et al [60] have illustrated the separation of Zr(Fe,Cr) 2 SPPs into metallic Fe 0 clusters and a Zr-Cr oxide in Zircaloy-4 as it oxidises with high-resolution chemical mapping. The oxidation of iron is thermodynamically supported at the oxidation temperature (and at reactor operating temperatures) [61], so the retention of some metallic Fe 0 in the present samples must be a kinetic effect related to the protective nature of the alloy oxides surrounding the clusters and the sizes of some of the iron clusters. The XANES results thus confirm that that iron initially within SPPs does not necessarily oxidise when the mean partial pressure of oxygen at a given depth into the oxide reaches the appropriate level.…”

Section: Xanesmentioning

confidence: 95%

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

Than

Wenman

Bell

et al. 2018

Journal of Nuclear Materials

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Simulations based on density functional theory (DFT) were used to investigate the behaviour of substitutional iron in both tetragonal and monoclinic ZrO 2. Brouwer diagrams of predicted defect concentrations, as a function of oxygen partial pressure, suggest that iron behaves as a p-type dopant in monoclinic ZrO 2 while it binds strongly to oxygen vacancies in tetragonal ZrO 2. Analysis of defect relaxation volumes suggest that these results should hold true in thermally grown oxides on zirconium, which is under compressive stresses. X-ray absorption near edge structure (XANES) measurements, performed to determine the oxidation state of iron in Zircaloy-4 oxide samples, revealed that 3+ is the favourable oxidation state but with between a third and half of the iron, still in the metallic Fe 0 state. The DFT calculations on bulk zirconia agree with the preferred oxidation state of iron if it is a substitutional species but do not predict the presence of metallic iron in the oxide. The implications of these results with respect to the corrosion and hydrogen pickup of zirconium cladding are discussed.

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Section: Xanesmentioning

confidence: 95%

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

Than

Wenman

Bell

et al. 2018

Journal of Nuclear Materials

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“…It is notable that the free energy of formation of PuO 2 , the most likely form of plutonium in the tank waste (Delegard and Jones 2015), from plutonium metal is very similar to that of uranium dioxide, UO 2 , from uranium metal, U (Kleykamp 1985). From the Ellingham diagram presented in Figure 2-4 (based on Darken and Gurry (1953, p. 349) and Kleykamp (1985)), we see that temperatures well above 2000° C (~2300° C, according to the Ellingham diagram, Figure 8, of Miller and Reimann (1993)), and thus well above the nominal 1150°-C glass pool temperature, would be necessary for the negative Gibbs free energy of formation of CO 2 from CO to exceed that of PuO 2 (near that of UO 2 ); i.e., for the following reaction to have a negative Gibbs free energy and thus be thermodynamically feasible:…”

Section: Re1 -Plutonium Metal Formation In Hlw Meltermentioning

confidence: 83%

“…The following two reactions, which compare the production of iron metal from Fe 2 O 3 using carbon and using sugar, respectively, as reductant, show that they differ only in the production of water in the latter reaction: While the heat needed to drive the blast furnace process is provided by the burning of coke as well as the iron oxide reduction reaction itself, the heat in the vitrification process is provided externally and thus can guarantee completion of the Fe(III) oxide-sucrose reaction. Because the iron blast furnace reaction operates at ~900° C, carbon monoxide (CO), which forms above about 600° C from the reaction of elemental carbon with any CO 2 , is the functional reductant (Wiberg 2001;Miller and Reimann 1993). The same would be true for the WTP melters, which operate at 1150° C glass pool temperatures (3.2.1.2 and 4.2.3.6 of Jenkins et al (2013) for the LAW and HLW melters, respectively).…”

Section: Melter Redox Effectsmentioning

confidence: 99%

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Effects Influencing Plutonium-Absorber Interactions and Distributions in Routine and Upset Waste Treatment Plant Operations

Delegard

Sinkov

Fiskum

2015

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Permanganate Effects -The solubilities of (hydr)oxide compounds of aluminum, cadmium, chromium, iron, and uranium (but not manganese and nickel), and of plutonium itself, increase with alkaline concentration and thus help preserve the plutonium/absorber ratio in solution. However, the ratio may be altered in permanganate oxidative dissolution of discrete plutonium phases such as PuO 2 ,PuO 2 •xH 2 O, or other low-solubility tetravalent plutonium because of oxidation to more soluble pentavalent or hexavalent plutonium. The ratio also may be altered because of oxidative leaching of Cr(III) phases while compounds of other absorber elements (e.g., aluminum, iron, nickel) are largely redox-indifferent. Plutonium dissolution from genuine washed sludge with permanganate is significantly enhanced by an increase in NaOH concentration, increasing by an average factor of 70 when permanganate oxidative leaching is undertaken at 3 M NaOH as compared with 0.1 or 0.25 M NaOH. The increase is likely due to plutonium being more readily oxidized to the more soluble hexavalent state. Dissolved plutonium species in alkaline solution, irrespective of oxidation state, are anionic so they are not expected to sorb onto the cation-sorbing resin used for 137 Cs removal. Indeed, such sorption is observed to be negligible. Excess permanganate does not appear to have an appreciable effect on the distribution of plutonium to solution based on oxidative leaching of REDOX Process sludge simulants and genuine Cr(III)-bearing Hanford tank sludges. In lab testing, intentional over-dosage of permanganate did not lead to enhanced plutonium leaching at lower alkalinity (0.09 to 0.25 M NaOH), while at higher alkalinity (3 M NaOH), the plutonium concentration increase to ~0.00036 g Pu/L was relatively low and could be mitigated by adding Cr(III) nitrate to the permanganate/manganate-bearing slurry to eliminate excess oxidant, form MnO 2 , and remove ~95% of the solubilized plutonium by coprecipitation. Separate testing showed that plutonium dissolution in the presence of excess permanganate at 2 to 4 M NaOH also can be mitigated by addition of hydrogen peroxide, removing ~75% of the solubilized plutonium. In treatment with Sr/Mn(VII) for 90 Sr and transuranic element removal from Envelope C supernates, both coprecipitated plutonium that remains undissolved and the residual soluble plutonium, should be protected with 100 to 1000 times higher neutron absorber concentrations based on AN-102 supernate studies. Although experimental data on 239 Pu decontamination from AN-107 supernates are lacking, it is likely that plutonium decontamination by Sr/Mn(VII) treatment was similar to that of AN-102 supernates based on solution composition and total alpha analyses. Decontamination of tank SY-101 from dissolved plutonium by permanganate treatment also is found. Overall, treatment of Envelope C wastes by Sr/Mn(VII) should improve criticality safety by carrying plutonium into the solid phase in the presence of co-precipitated iron and especially manganese.Cerium an...

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“…Orthorhombic α-, tetragonal βand body-centered cubic (BCC) γ-phases are stable up to 667°C, between 667° and 771°C, and above 771°C, respectively [14][15][16][17]. The α-U has undesirable characteristics as a nuclear fuel such as low hardness, rapid oxidation, low corrosion resistance and anisotropic irradiation behavior [18][19][20][21]. A single crystal of α shortens in a-axis and extends in b-axis, and there is no significant change in c-axis during irradiation under 500˚C [16,22], leading to dimensional instability [23,24].…”

Section: Introductionmentioning

confidence: 99%

Phase decomposition of γ-U (bcc) in U-10 wt% Mo fuel alloy during hot isostatic pressing of monolithic fuel plate

Park

Eriksson

Newell

et al. 2016

Journal of Nuclear Materials

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Eutectoid decomposition of γ-phase (cI2) into α-phase (oC4) and γ'-phase (tI6) during the hot isostatic pressing (HIP) of the U-10 wt.% Mo (U10Mo) alloy was investigated using monolithic fuel plate samples consisting of U10Mo fuel alloy, Zr diffusion barrier and AA6061 cladding. The decomposition of the γ-phase was observed because the HIP process is carried out near the eutectoid temperature, 555°C. Initially, a cellular structure, consisting of γ'-phase surrounded by α-phase, developed from the destabilization of the γ-phase. The cellular structure further developed into an alternating lamellar structure of α-and γ'-phases. Using scanning electron microscopy and transmission electron microscopy, qualitative and quantitative microstructural analyses were carried out to identify the phase constituents, and elucidate the microstructural development based on time-temperature-transformation diagram of the U10Mo alloy. The destabilization of γ-phase into α-and γ'-phases would be minimized when HIP process was carried out with rapid ramping/cooling rate and dwell temperature higher than 560°C.

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Thermodynamics of gas-metal-slag equilibria for applications in in situ and ex situ vitrification melts

Cited by 5 publications

References 1 publication

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

Modelling and experimental analysis of the effect of solute iron in thermally grown Zircaloy-4 oxides

Effects Influencing Plutonium-Absorber Interactions and Distributions in Routine and Upset Waste Treatment Plant Operations

Phase decomposition of γ-U (bcc) in U-10 wt% Mo fuel alloy during hot isostatic pressing of monolithic fuel plate

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