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NextGen MURR Working Group established in Missouri
The University of Missouri’s Board of Curators has created the NextGen MURR Working Group to serve as a strategic advisory body for the development of the NextGen MURR (University of Missouri Research Reactor).
Tatsuya Ito, Ryuji Nagaishi, Ryo Kuwano
Nuclear Technology | Volume 210 | Number 8 | August 2024 | Pages 1427-1443
Research Article | doi.org/10.1080/00295450.2023.2299893
Articles are hosted by Taylor and Francis Online.
The retention of hydrogen (H2) bubbles generated by water radiolysis was quantitatively studied in a high-viscous suspension of carbonate slurry consisting of a mixture of suspended solid (SS) of magnesium (Mg) and calcium (Ca) precipitates under strongly alkaline conditions, like the radioactive wastes discharged from the coagulation sedimentation (co-precipitation) process at the multinuclide removal equipment in the Fukushima Daiichi Nuclear Power Station.
The H2 retention properties were evaluated in two types of carbonate slurry with different hydrophilicity: the hydrophilic “current type” and the hydrophobic “return type.” Then, their properties were compared with those in another suspension of clay suspension of bentonite. The hydrophilicity of the surface of the SS particles was evaluated from two different adsorption isotherms of water (H2O) vapor on the surface, as well as those of Mg(OH)2 and CaCO3 particles, simulating the precipitates in the slurry. The H2O molecules were strongly chemically adsorbed on the Mg(OH)2, while they were weakly physically adsorbed on the CaCO3. Since the amount of chemical adsorption on the SS surface of the hydrophilic slurry was almost the same as that on the Mg(OH)2 surface, Mg(OH)2 was found to be dominant on the SS surface.
From the comparison between the amounts of chemical adsorption and H2O in the slurry, it was confirmed that H2O molecules must be shared among the SS particles, and this sharing of H2O molecules formed the structural viscosity in the slurry, different from that in the clay suspension where electrostatic bonding between the fine clay minerals forms the viscosity.
The retention of H2 bubbles in (by) the slurry was evaluated from the difference in the amount of H2 observed with and without stirring the slurry after 60Co γ irradiation. The observed amount increased linearly with increasing absorbed dose by the slurry to obtain H2 generation yield (G-value): Gtotal (with stirring) and Gstat (without stirring). The Gtotal was independent of the sample height, whereas the Gstat decreased with increasing the height. This indicated that the higher the height, the more difficult it was for H2 bubbles to be released. From the direct observation of H2 bubbles after irradiation, the growth of H2 bubbles with increasing the dose was evaluated to obtain the resisting force of H2 bubbles to the slurry. The H2 bubbles were confirmed to be retained in the slurry because the resistance was lower than the shear strength of the slurry (yield value at rest).
The ability of the slurry to retain the H2 bubbles was evaluated from the sample height dependence of the relative G-value, Gstat/Gtotal. The log-log plot of the G-value and height gave a straight line, and the slope of the hydrophilic slurry became larger than that of the hydrophobic one. This difference indicated the effect of structural viscosity, which was observed in the H2 bubble retention in the clay suspension. In addition, the slopes for the hydrophobic slurry and treated water were significantly different, and this indicated the effect of steric hindrance by the SS particles. Therefore, H2 bubbles were retained by not only the structural viscosity but also the steric hindrance in the hydrophilic slurry.
