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Source term investigation is a critically important aspect of reactor decommissioning, particularly as the range of nuclides under consideration expands beyond the capabilities of existing analysis methods. In this study, we try to propose a methodology to indirectly determine the radioactivity of long-lived nuclides which are non-γ or low energy in various nuclear waste materials by measuring the radioactivity of 60Co. The critical point of this method is to establish relationship between some easy to measure (ETM) key nuclides, such as certain γ emitters (like 60Co), and the difficult to measure (DTM) nuclides to derive information for the DTM nuclides of interest. To begin, we calculate nuclide bulk densities of 55Fe, 60Co, 63Ni and 152Eu in nuclear waste materials. By constructing inversion matrices and analyzing the intensity matrices of characteristic γ lines emitted by 60Co, we can extract the radioactivity of non-γ radionuclides (55Fe, 63Ni, and 152Eu) present in the nuclear waste materials that are contained within a specific container. Furthermore, our methodology accounts for the influence of voids within the container, thereby ensuring the reliability and validity of the obtained results. This innovative approach offers a promising avenue for efficiently sorting nuclear waste.

Summary: Achieving high selectivity and activity with the oxygen reduction reaction (ORR) is significant for developing efficient energy conversion techniques and chemical production. Here, we report that selective ORRs can be achieved by tuning short-range order in amorphous and crystalline NiO nanosheets (a-NiO NSs and c-NiO NSs, respectively). X-ray absorption spectroscopy analysis reveals that the short-range order of a-NiO NSs and c-NiO NSs mainly adopt the NiO5 pyramidal and NiO6 octahedral structures, respectively. The a-NiO NSs for electrochemical H2O2 production in 0.1 M KOH exhibits both high selectivity over 90% and high activity (1 mA cm−2 at 0.66 V versus RHE), while c-NiO NSs tends to catalyze ORRs through 4-electron pathways to generate H2O. Theoretical calculations indicate that the changed short-range order of a-NiO NSs leads to alteration of Ni d-orbital states, which can regulate the adsorption orientation and strength of ∗OOH intermediates to achieve high selectivity and activity of 2-electron ORRs.

Summary: The size and shape control of amorphous nanomaterials has long been a bottleneck restricting their further development. Here, we present a general approach to synthesize more than twenty kinds of amorphous metal oxide nanosheets. The amorphous state of the nanosheets is determined using aberration-corrected high-resolution transmission electron microscopy and X-ray diffraction. By using extended X-ray absorption fine structure analysis, we demonstrate that amorphous nanosheets have a larger interatomic distance and a looser packing characteristic compared with crystalline counterparts. The as-prepared amorphous FeOx nanosheets are used as sodium-ion batteries anode materials, exhibiting notable performance with a specific capacity of 263.4 mAh g−1 at 100 mA g−1 and long-term cyclic stability. Significantly, a reversible amorphous-crystalline-amorphous structure transformation phenomenon during the cycling test is observed at the atomic scale.