Environment and oxidation state of molybdenum in simulated high level nuclear waste glass compositions

Short, Rick; Hand, Russell J.; Hyatt, Neil C.; Möbus, Günter

doi:10.1016/j.jnucmat.2004.11.008

Cited by 72 publications

(60 citation statements)

References 7 publications

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“…12) as well as Pd-Te alloy inclusions. Powellite-structured molybdates of similar composition to (Na,Sr,Nd,La)MoO 4 have previously been reported in borosilicate HLW glasses [22,25,33,61,64,68,69,89], some with its dendritic morphology [15,22,25,33].…”

Section: Sio 2 (α-Cristobalite)mentioning

confidence: 70%

Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

Rose

Woodward

Ojovan

et al. 2011

Journal of Non-Crystalline Solids

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A simulated (inactive) borosilicate high-level waste (HLW) glass was produced on a full-scale vitrification line with composition simulating vitrified oxide fuel (UO 2 ) reprocessing waste. As-cast samples were compositionally homogeneous (Type I microstructure) and/or compositionally inhomogeneous displaying compositional 'banding' and frequently containing 'reprecipitated calcine' (Type II microstructure).Crystal phases identified in as-cast samples were: tetragonal RuO 2 , cubic Pd-Te alloy, cubic (Cr,Fe,Ni,Ru) Sn and U). Cracking in samples was attributed to thermal expansion mismatch between the borosilicate HLW glass matrix and RuO 2 , cristobalite (both α and β), (Na,Sr,Nd,La)MoO 4 and zektzerite on cooling. There was also a contribution from the cristobalite α-β phase transition.

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Section: Sio 2 (α-Cristobalite)mentioning

confidence: 70%

Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

Rose

Woodward

Ojovan

et al. 2011

Journal of Non-Crystalline Solids

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“…The production of alkali molybdates (Na 2 MoO 4 , Cs 2 MoO 4 ), known as yellow phase, are particularly problematic owing to their high water solubility and ability to act as carriers for radioactive cesium and strontium [1,13]. This ability thus creates a contamination risk during final geological deposition by increasing corrosion probabilities [14,15]. While formation of yellow phase can prove detrimental to chemical durability, alkaline earth molybdates (CaMoO 4 ) are comparatively water durable and are stable following synthesis in a borosilicate matrix [12,14,15].…”

Section: Introductionmentioning

confidence: 99%

Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

Patel

Boizot

Facq

et al. 2017

Journal of Non-Crystalline Solids

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A B S T R A C TBorosilicate glasses for nuclear waste applications are limited in waste loading by the precipitation of watersoluble molybdates. In order to increase storage efficiency, new compositions are sought out that trap molybdenum in a water-durable CaMoO 4 crystalline phase. Factors affecting CaMoO 4 combination and glass-inglass phase separation in calcium borosilicate systems as a function of changing [MoO 3 ] and [B 2 O 3 ] are examined in this study in order to understand how competition for charge balancers affects phase separation. It further examines the influence of radiation damage on structural modifications using 0.77 to 1.34 GGy of 2.5 MeV electron radiation that replicates inelastic collisions predicted to occur over long-term storage. The resulting microstructure of separated phases and the defect structure were analyzed using electron microscopy, XRD, Raman and EPR spectroscopy prior to and post irradiation. Synthesized calcium borosilicates are observed to form an unusual heterogeneous microstructure composed of three embedded amorphous phases with a solubility limit~2.5 mol% MoO 3. Increasing [B 2 O 3 ] increased the areas of immiscibility and order of (MoO 4 ) 2 − anions, while increasing [MoO 3 ] increased both the phase separation and crystallization temperature resulting in phases closer to metastable equilibrium, and initiated clustered crystallization for [MoO 3 ] > 2.5 mol%. β-irradiation was found to have favorable properties in amorphous systems by creating structural disorder and defect assisted ion migration that thus prevented crystallization. It also increased reticulation in the borosilicate network through 6-membered boroxyl ring and Si ring cleavage to form smaller rings and isolated units. This occurred alongside an increased reduction of Mo 6 + with dose that can be correlated to molybdenum solubility.In compositions with existing CaMoO 4 crystallites, radiation caused a scattering effect, though the crystal content remained unchanged. Therefore β-irradiation can preferentially prevent crystallization in calcium borosilicates for [MoO 3 ] < 2.5 mol%, but has a smaller impact on systems with existing CaMoO 4 crystallites.

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“…The yellow phase not only accelerates the corrosion of the melter but also reduces the performance of the vitrified product since it can contain problematic radionuclides (e.g. 137 Cs) and can be dissolved if it comes into contact with water [6][7][8]. Therefore, the waste loading capacity for Mo-rich wastes in vitrification has been restricted to avoid the formation of yellow phase.…”

Section: Introductionmentioning

confidence: 99%

“…Mo predominantly occurs as a hexavalent state Mo 6+ in glasses prepared under oxidising and neutral atmospheres, regardless of glass composition [9][10] with each Mo 6+ cation being coordinated with four oxygens to form a MoO4 2-tetrahedron. The average Mo-O distance range is 1.76-1.78 Å, indicating that Mo 6+ has a high field strength range of 1.89-1.94 Å -2 in glass [6,[10][11][12][13] and thus Mo 6+ cations have a strong ordering effect on surrounding oxygens [14]. Consequently, the MoO4 2-tetrahedra can be easily separated from the silicate glass network.…”

Section: Introductionmentioning

confidence: 99%

MoO3 incorporation in magnesium aluminosilicate glasses

Tan

Ojovan

Hyatt

et al. 2015

Journal of Nuclear Materials

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Environment and oxidation state of molybdenum in simulated high level nuclear waste glass compositions

Cited by 72 publications

References 7 publications

Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

Crystallisation of a simulated borosilicate high-level waste glass produced on a full-scale vitrification line

Impacts of composition and beta irradiation on phase separation in multiphase amorphous calcium borosilicates

MoO3 incorporation in magnesium aluminosilicate glasses

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