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.

Conversion of melter feed to glass occurs in the cold cap that floats on the melt pool in a nuclear waste glass melter. The conversion rate (the melting rate or the glass production rate) is controlled by the heat flux delivered to the cold cap from the molten glass. In an attempt to analyze the intricate relationship between the rate of heating, the feed foaming response, and the rate of melting, we measured the change in feed volume at different heating rates by using several melter feeds known to exhibit a wide range of melting rates under identical melter operating conditions. As expected, the maximum foam porosity increased as the heating rate increased.However, contrary to expectation, the temperature at which the foam reached maximum volume either decreased or increased with the heating rate, depending on the feed composition. A change in maximum foam temperature from the feed volume expansion test indicates a similar change of the cold-cap bottom temperature, which influences the heat flow to the cold cap, and thus the rate of melting. K E Y W O R D Sfeed-to-glass conversion, foaming, heat flux, melting rate 402 | LEE Et aL.

Allostery through DNA is increasingly recognized as an important modulator of DNA functions. Here, we show that the coalescence of protein-induced DNA bubbles can mediate allosteric interactions that drive protein aggregation. We propose that such allostery may regulate DNA's flexibility and the assembly of the transcription machinery. Mitochondrial transcription factor A (TFAM), a dual-function protein involved in mitochondrial DNA (mtDNA) packaging and transcription initiation, is an ideal candidate to test such a hypothesis owing to its ability to locally unwind the double helix. Numerical simulations demonstrate that the coalescence of TFAM-induced bubbles can explain experimentally observed TFAM oligomerization. The resulting melted DNA segment, approximately 10 base pairs long, around the joints of the oligomers act as flexible hinges, which explains the efficiency of TFAM in compacting DNA. Since mitochondrial polymerase (mitoRNAP) is involved in melting the transcription bubble, TFAM may use the same allosteric interaction to both recruit mitoRNAP and initiate transcription.

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