Wooyong Um

Significant environmental impacts of terrestrial uranium mining, coupled with rapidly exhausting land-based uranium reserves, pose major concerns for the long-term sustainability of global nuclear energy production. Uranium extraction from seawater (UES) offers an environmentally friendly and virtually limitless alternative to conventional mining. Herein, we report hierarchically porous alginate-based aerogel microreactors (M8AO@A-PAA) fabricated by encapsulating an amidoxime-functionalized zirconium-based metal–organic framework, MOF-808-AO, via a facile ionotropic gelation strategy. The resulting M8AO@A-PAA demonstrated outstanding mechanical and structural stability after prolonged seawater exposure exceeding four weeks. The M8AO@A-PAA microreactors exhibited excellent uranium uptake performance, achieving a maximum adsorption capacity of 528.2 mg g⁻¹, high selectivity (Kd>4.0×10⁴ mL g⁻¹), and superior regenerability (>80% elution efficiency) maintained after five cycles. Notably, M8AO@A-PAA showed promising uranium capture performance in natural seawater (0.202 mg g-1day-1). Furthermore, XPS analysis revealed uranyl–amidoxime coordination as the dominant uranium binding mechanism, with a synergistic contribution of carboxyl groups. These findings were well corroborated by density functional theory (DFT) calculations, confirming the thermodynamic favorability of the uranyl-amidoxime-carboxyl coordination complex (Eads = -90.88 kcal mol⁻¹).

Decommissioning of nuclear facilities results in concrete waste contaminated with radioactive cesium (Cs-137), posing serious ingestion risks. However, studies on the in vivo bioavailability of cesium in solid matrices remain scarce. This research aimed to assess cesium’s bioavailability from Cs-contaminated concrete using male Sprague Dawley rats that received single oral doses of 100 or 1000 mg of Cs per kg. Blood and urine samples were collected over a 24-hour period, and the relative bioavailability was determined through area-under-the-curve analysis. Estimates for bioavailability varied significantly between biomarkers and dosages. At 100 mg kg−1, the blood-based bioavailability was 90.9%, whereas the urine-based estimate was 54.8%. However, this trend reversed at the higher dose of 1000 mg kg−1, with urine demonstrating 99.5% bioavailability and blood showing 52.0%, respectively. Urine measurements were more consistent with in vitro bioaccessibility, indicating they might better reflect overall absorption. Exposure to cesium affected trace element balance, leading to positive correlations with zinc but negative correlations with iron. This in turn resulted in conditions such as erythrocytosis (red blood cell counts are above 8.10 × 1012/L), leukocytosis (white blood cell counts exceeding 20 × 109/L), elevated potassium levels (above 7.0 mmol/L), increased creatinine concentrations (up to 118.9 μmol/L), and lower albumin levels, which show temporary renal and hepatic stress. These results suggest that the current risk assessment, assuming complete cesium absorption, may overestimate ingestion hazards from contaminated concrete, supporting the use of the urine-based monitoring as a more reliable and practical tool for occupational radiation protection during nuclear decommissioning.

The separation and enrichment of tritium from radioactive wastewater remain critical challenges in the nuclear power and fusion industries. While hydrogen isotope separation from H₂/D₂ gas mixtures has been demonstrated using electrochemical pumping systems with Nafion|graphene composite membranes, their application in liquid water remains limited, despite tritium and deuterium predominantly existing as water molecules. This limitation primarily arises from the swelling behavior of Nafion, which absorbs water and induces defects in the graphene layer. In this study, we propose a modified Nafion|graphene composite membrane structure, where graphene is transferred onto polytetrafluoroethylene-reinforced Nafion, to enable efficient hydrogen isotope (¹H, ²H, and ³H) separation in liquid water. The monolayer graphene exhibited six-fold higher conductivity for H⁺ over D⁺ under electrically driven conditions, while diffusion-driven transport showed lower isotope selectivity due to the contribution of the vehicular mechanism. Notably, graphene imposed a 1.7-fold higher diffusion energy barrier for tritium than for deuterium, indicating that the separation is governed by zero-point energy differences in O-H(D, T)···O bonding. These results highlight the role of transport mechanism and graphene integrity in isotope separation performance and suggest a practical pathway toward implementing graphene-based membranes in polymer electrolyte membrane water electrolysis systems for tritium concentration and removal.