In this study, a bismuth-based metal−organic framework (Bi-MOF) was investigated in its applicability as an iodine adsorbent at high temperatures for possible applications under severe accidents in a nuclear power plant. Bi-mna was selected among Bi-MOF candidates based on its thermodynamic characteristics, which expected to allow chemisorption of iodine by bismuth. Its iodine adsorption performance was compared with zeolitic imidazolate framework-8 and Cu-BTC and other MOFs which were chosen due to their diversity in iodine adsorption mechanisms. Bi-mna was synthesized at the laboratory scale, and the aforementioned three MOFs were tested for iodine adsorption at various temperatures from 350 to 600 K. The adsorption mechanism of Bi-mna was investigated by conducting various analyses including thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Brunauer−Emmett−Teller. The results showed that Bi-mna has good adsorption performance (700 mg-I/g-adsorbent) while maintaining good thermal stability even at a high temperature (up to 575−600 K). The iodine capture performance of Bi-mna is better, especially at high temperature, in comparison with those of non-MOF adsorbents such as silver-exchanged zeolites and bismuth-embedded SBA-15. Analysis results confirmed that Bi-mna chemically captured iodine by breaking bonds between bismuth and sulfur to form new chemical bonds between iodine and the bismuth in Bi-mna. The results indicate that Bi-mna has the potential to be used in capturing radioiodine at high-temperature environments, such as during nuclear severe accident management. Its use should also be considered as a potential candidate for waste form development.

Codeposition of elements is an important phenomenon in the analysis and understanding of mass transfer in electrorefining of pyroprocessing. This study investigated the codeposition of lanthanides in molten salt. Mass transport experiments were conducted to examine the accuracy of the 1D electrorefining model, ERAD. Three lanthanides (La, Ce, and Gd) were selected because their standard reduction potentials are close to each other which facilitates codeposition. For the electrodeposition experiments, six electrochemical cells were used with varying ratios of lanthanides and the electrode potential ranging from 0.00 V to 0.15 V. This controlled the codeposition environment. The resulting electrodeposits were analyzed by ICP-OES and compared with the simulation results from ERAD. The ERAD input parameters were determined through electrochemical studies. Theoretical codeposition ratios were also analyzed using polarization curves. The study indicated that the current density of each element played a major role in its codeposition, as did thermodynamically determined reduction potentials. The overall results were comprehensively investigated and showed that ERAD can reasonably show the tendency of the codeposition results obtained from the experiments. With minor revision, it is expected that this 1D computer code could be effectively utilized for modeling the mass transport of the electrorefining process of pyroprocessing.

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