Physical Properties of Highly Active Liquor Containing Molybdate Solids

Dunnett, Barbara F.; Ward, Tracy R.; Roberts, Rachel D.; Cheesewright, Jonathan

doi:10.1016/j.proche.2016.10.004

Cited by 3 publications

(8 citation statements)

References 4 publications

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“…The Scanning Electron Micrograph (SEM) images in Figure 1 show the CPM, TiO 2 and two morphologies of ZM (cuboidal and wheatsheaf) referred to as ZM-a and ZM-b, respectfully. The images for CPM and ZM-a are in agreement with those published by Paul et al and Dunnett et al [ 23 , 33 ]. CPM is known to generally exhibit a roughly spheroidal shape, consisting of agglomerated nanoclusters, whereas ZM is most commonly known to be discrete cuboidal in shape.…”

Section: Resultssupporting

confidence: 91%

“…Several studies have looked into both CPM and ZM, specifically relating to the issues they cause within the HASTs, the challenge they pose to the Waste Vitrification Plant (WVP) and the in situ conversion of CPM to ZM [ 1 , 2 , 21 , 22 , 23 , 31 , 32 , 33 ]. Given the complexity of CPM and ZM dispersion behaviour, there is a critical need to study their synthesis and physical behaviour under a wide range of conditions.…”

Section: Introductionmentioning

confidence: 99%

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Synthesis and Physical Property Characterisation of Spheroidal and Cuboidal Nuclear Waste Simulant Dispersions

2018

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This study investigated dispersions analogous to highly active nuclear waste, formed from the reprocessing of Spent Nuclear Fuel (SNF). Non-radioactive simulants of spheroidal caesium phosphomolybdate (CPM) and cuboidal zirconium molybdate (ZM-a) were successfully synthesised; confirmed via Scanning Electron Microscopy (SEM), powder X-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectroscopy. In addition, a supplied ZM (ZM-b) with a rod-like/wheatsheaf morphology was also analysed along with titanium dioxide (TiO2). The simulants underwent thermal gravimetric analysis (TGA) and size analysis, where CPM was found to have a D50 value of 300 nm and a chemical formula of Cs3PMo12O40·13H2O, ZM-a a D50 value of 10 μm and a chemical formula of ZrMo2O7(OH)2·3H2O and ZM-b to have a D50 value of 14 μm and a chemical formula of ZrMo2O7(OH)2·4H2O. The synthesis of CPM was tracked via Ultraviolet-visible (UV-Vis) spectroscopy at both 25 °C and 50 °C, where the reaction was found to be first order with the rate constant highly temperature dependent. The morphology change from spheroidal CPM to cuboidal ZM-a was tracked via SEM, reporting to take 10 days. For the onward processing and immobilisation of these waste dispersions, centrifugal analysis was utilised to understand their settling behaviours, in both aqueous and 2 M nitric acid environments (mimicking current storage conditions). Spheroidal CPM was present in both conditions as agglomerated clusters, with relatively high settling rates. Conversely, the ZM were found to be stable in water, where their settling rate exponents were related to the morphology. In acid, the high effective electrolyte resulted in agglomeration and faster sedimentation.

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Section: Resultssupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Synthesis and Physical Property Characterisation of Spheroidal and Cuboidal Nuclear Waste Simulant Dispersions

2018

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“…This study focused on characterising the behaviour of crystalline caesium phosphomolybdate (herein labelled 'CPM' for concision) and zirconium molybdate (herein labelled 'ZM'), which are known to be two of the most significant solids formed during processing of highly active raffinate, which precipitate when acid waste solutions containing certain levels of molybdenum are concentrated, following the removal of uranium and plutonium species [44][45][46][47]. Non-active, but chemically similar, CPM and ZM waste simulants, were manufactured according to a procedure outlined previously [44].…”

Section: Methodsmentioning

confidence: 99%

“…This paper seeks to de-convolute these effects through investigations on particles both academically interesting and industrially important. In particular, we utilize spheroidal, cubic and rectangular cuboidal colloids of caesium phosphomolybdate and zirconium molybdate, which have been previously synthesised [44], as non-active simulants of precipitates produced during the treatment of raffinate from nuclear fuel reprocessing [45][46][47]. While similar in their bulk chemistry, the distinct shape effects on their sedimentation behaviour were studied in batch settling trials at various concentrations,…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

“…All species exhibit very low pH isoelectric points (IEPs), with the IEP for CPM in particular being only around pH ~1.5 (just outside of the maximum measureable range) while the IEPs for ZM and ZMCA are around pH 3 and 4, respectively. The slight differences between ZM and ZMCA are interesting, owing to the fact that they are chemically identical in the bulk [44,47]. The only modification comes from the surface adsorption of citric acid, which leads a complex formation on particular surfaces, retarding the growth of those planes, resulting in the rod like confirmation [44].…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

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Influence of shape and surface charge on the sedimentation of spheroidal, cubic and rectangular cuboid particles

et al. 2017

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This study investigated the complex settling behaviour of colloidal particles with varied surface charge and shape factors, of specific relevance to nuclear waste processing. Caesium phosphomolybdate (CPM), zirconium molybdate (ZM) and zirconium citromolybdate (ZMCA) were firstly synthesised, producing spheroidal, cubic and rectangular cuboidal morphologies respectively, and compared to agglomerated titania. While zeta-potential measurements indicated all simulant particles attained low isoelectric points, surface group leaching rendered suspensions very acidic, with CPM around its IEP, and ZM/ZMCA stable and positively charged. In sedimentation tests at various concentrations in water and 2 M HNO3, CPM and titania were found to settle with extremely high hindered settling exponents, consistent with aggregated structures. Exponents for ZM and ZMCA in water were both also well above values for spherical particles; however, this was assumed to be due to heightened drag effects from relative shape factors, rather than aggregation. ZMCA in particular showed a very high exponent of ~11.4, due to the propensity for the rod-like particles to settle in a flat conformation. For ZM in acid, double layer compression from the high electrolyte aggregated the dispersions, correlating to a significant increase in the settling exponent. An extended Stokes relationship was additionally used to understand theoretical limits of shape and aggregation on particle size prediction from hindered settling curves. Importantly, calculated sizes were consistent for the stable ZM and ZMCA in water, despite their non-sphericity and enhanced drag. The relationship failed however with agglomerated suspensions, highlighting its application as a general stability test for sedimenting dispersions.

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Development of a Multi-technique Characterization Portfolio for Stainless Steels Exposed to Magnox Reprocessing Liquors

Barton,

Denman,

Grebennikova

et al. 2023

ACS Omega

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AISI Type 304 stainless steel coupons have been exposed to a simulant aqueous environment representative of the Magnox Reprocessing Plant (MRP) at Sellafield, UK. The experiments were performed for extended time periods (up to 420 days) at elevated temperatures to develop a comprehensive understanding of the extent, nature, and depth of contamination for pipework and vessels in Magnox spent nuclear fuel reprocessing environments. This will inform upcoming decommissioning work which represents a major post-operational challenge. Previous relevant literature has focused on developing fundamental understanding of contamination mechanisms of stainless steels in simplistic, single-element systems, which lack elements of industrial relevance. Contamination behavior is expected to be drastically different in these more complex environments. A characterization portfolio has been developed to enable detailed assessment of corrosion and contamination behavior in acidic reprocessing environments. Solution, surface, and depth analysis determined that uptake was dominated by the elements present in highest concentrations within the environment, namely, Mg, Nd, and Cs. Most contaminants were incorporated into a relatively thin surface oxide layer (<100 nm) in metal oxide form, although there were some exceptions (Cs and Sr). Grain boundary etching was present despite very low corrosion rates (3 μm year −1 ). As a result of this lack of corrosion, diffusion of contaminants beyond the immediate surface (10− 20 nm) did not occur, evidenced through depth profiling. As a result of these findings, surface-based decontamination techniques minimizing excess secondary waste generation can be further developed in order to reduce the environmental and economic burden associated with decommissioning activities.

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Physical Properties of Highly Active Liquor Containing Molybdate Solids

Cited by 3 publications

References 4 publications

Synthesis and Physical Property Characterisation of Spheroidal and Cuboidal Nuclear Waste Simulant Dispersions

Synthesis and Physical Property Characterisation of Spheroidal and Cuboidal Nuclear Waste Simulant Dispersions

Influence of shape and surface charge on the sedimentation of spheroidal, cubic and rectangular cuboid particles

Development of a Multi-technique Characterization Portfolio for Stainless Steels Exposed to Magnox Reprocessing Liquors

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