One‐Dimensional Cold Cap Model for Melters with Bubblers

Pokorný, Richard; Hilliard, Zachary J.; Dixon, Derek R.; Schweiger, Michael J.; Guillen, Donna Post; Kruger, Albert A.; Hrma, Pavel R.

doi:10.1111/jace.13775

Cited by 45 publications

(70 citation statements)

References 27 publications

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“…Figure displays the CO 2 evolution rate from A19 feed as a function of heating rate, showing the shift of CO 2 evolution to higher temperatures. This is a common feature of thermally activated processes, such as decomposition reactions. Because of this shift, the total amount of CO 2 accumulated in (and later released from) the primary foam increased (see Figure ).…”

Section: Resultsmentioning

confidence: 96%

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Foaming during nuclear waste melter feeds conversion to glass: Application of evolved gas analysis

Hujova

Pokorný

Kloužek

et al. 2018

Int J of Appl Glass Sci

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During the final stages of batch‐to‐glass conversion in a waste‐glass melter, gases evolving in the cold cap produce primary foam, the formation and collapse of which control the glass production rate via its effect on heat transfer to the reacting batch. We performed quantitative evolved gas analysis (EGA) for several HLW melter feeds with temperatures ranging from 100 to 1150°C, the whole temperature span in a cold cap. EGA results were supplemented with visual observation of batch‐to‐glass transition using the feed expansion tests. Upon heating, most of the gases—mainly H2O, CO2, NO, NO2, N2, and O2—evolve at temperatures below 700°C and escape directly to the atmosphere through open porosity. However, as open porosity closes when enough glass‐forming melt appears at ~720°C, the residual gas evolution leads to the formation of primary foam. We found that primary foaming is mostly caused by the decomposition of residual carbonates, though oxygen evolution from iron‐redox reaction can also play a role. We also show that the gas evolution shifts to a higher temperature when the heating rate increases. The implications for the mathematical modeling of foam layer in the cold cap are presented.

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Section: Resultsmentioning

confidence: 96%

“…The gases produced in this layer either directly escape to the atmosphere, or become trapped in the glass‐forming melt, producing a primary foam layer. This foam layer presents a formidable resistance to heat transfer, significantly affecting process throughput …”

Section: Introductionmentioning

confidence: 99%

Foaming during nuclear waste melter feeds conversion to glass: Application of evolved gas analysis

Hujova

Pokorný

Kloužek

et al. 2018

Int J of Appl Glass Sci

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“…During vitrification, nuclear waste is mixed with glass‐forming and modifying additives and charged into an electric melter, where it is converted to molten glass . The conversion takes place within the cold cap, which is reacting melter feed that floats on the melt pool. Feed‐to‐glass conversion reactions produce large amounts of gases that escape from the cold cap to the atmosphere, except a small part that is trapped in the glass‐forming melt and creates foam at the cold cap bottom .…”

Section: Introductionmentioning

confidence: 99%

Effect of sucrose on foaming and melting behavior of a low‐activity waste melter feed

et al. 2019

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Reductants, such as sucrose (C12H22O11), are added to nuclear waste melter feeds containing high fractions of nitrates and nitrites to reduce excessive foaming during feed‐to‐glass conversion, decrease sulfate segregation, and increase technetium retention. The effect of sucrose on foaming and melting reactions during the conversion was examined using the feed volume expansion test, thermogravimetric analysis, evolved gas analysis, x‐ray diffraction, and scanning electron microscopy with energy dispersive x‐ray spectrometry. Different amounts of sucrose were added to vary the carbon to nitrogen (C/N) ratio in the melter feed. As the C/N ratio increased, the extent of foaming decreased, and the N2/NO ratio increased in the evolved gas. Significant foam suppression, rapid gas release at approximately 250°C, and reduction in transition metal oxides were observed at C/N > 1.1.

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“…The graphs of volume expansion vs temperature provide data for further analyses, especially with respect to the bulk density and the heat conductivity of the reacting feeds. Such data are indispensable for mathematical modeling of feed‐to‐glass conversion in the cold cap …”

Section: Introductionmentioning

confidence: 99%

Effects of heating rate, quartz particle size, viscosity, and form of glass additives on high‐level waste melter feed volume expansion

et al. 2016

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Nuclear waste can be vitrified by mixing it with glass‐forming and ‐modifying additives. The resulting feed is charged into an electric glass melter. To comprehend melting behavior of a high‐alumina melter feed, we monitored the volume expansion of pellets in response to heating at different heating rates. The feeds were prepared with different particle sizes of quartz (the major additive component) and with varied silica‐to‐fluxes ratio to investigate the glass melt viscosity effects. Also, we used additional melter feeds with additives premelted into glass frit. The volume of pellets was nearly constant at temperatures <600°C. After a short period of volume shrinkage at ~600°C‐700°C, foam generation produced massive volume expansion. The low heat conductivity of foam hinders the transfer of heat from molten glass to the reacting feed. The extent of foaming increased with faster heating and higher melt viscosity, and decreased with increasing size of quartz particles and fritting of the additives. Volume expansion data are needed for the mathematical modeling of the cold cap.

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One‐Dimensional Cold Cap Model for Melters with Bubblers

Cited by 45 publications

References 27 publications

Foaming during nuclear waste melter feeds conversion to glass: Application of evolved gas analysis

Foaming during nuclear waste melter feeds conversion to glass: Application of evolved gas analysis

Effect of sucrose on foaming and melting behavior of a low‐activity waste melter feed

Effects of heating rate, quartz particle size, viscosity, and form of glass additives on high‐level waste melter feed volume expansion

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