Advances and Challenges in the Design and Development of Adsorption Materials for Capturing the Volatile Polonium Species

Radiotoxic polonium-210 (210Po), a pure α emitter with the energy of 5.3 MeV and a half-life of 138.4 days, is primarily produced via the activation of atoms of metallic bismuth by high-energy and high-dose neutron or proton bombardment in lead-bismuth fast reactor and accelerator-driven systems during normal operation. Within the normal operation temperature of 473 to 680 K, part of the hazardous 210Po-containing species will evaporate and accumulate in the cover gas above the lead-bismuth eutectic coolant. Although the relative concentration of the 210Po-containing species in the cover gas is on the order of a ppm level, the radiological hazard and chemical toxicity still cannot be ignored. To ensure the safe handling of lead-based reactors, suitable cover gas filter/purification systems should be fixed. Unfortunately, one of the key issues in the development of suitable filters is the lack of accurate knowledge about the chemical interaction between the candidate filter materials and the 210Po-containing species. Meanwhile, owing to the radioactivity and high toxicity of 210Po, the reported experimental data and practical information available for the design and synthesis of efficient adsorbents targeting volatile 210Po remain extremely scarce, not to mention dedicated review articles on this topic. A periodic summary plays a significant role in the design and development of efficient adsorbents for practical application in lead-based reactors. In this review, we systematically summarize the advances in the design and preparation of adsorbents for volatile 210Po species in the cover gas at operating temperatures that have been reported in databases such as Willy, Royal Society of Chemistry, Elsevier, Springer, and American Chemical Society in the period between the 1960s and the 2020s. In this review, strategies involved in the screening and investigation on the candidate materials toward the capture of volatile 210Po species in the cover gas are categorized into three main areas: theoretical computational methods, thermochromatography techniques, and experimental investigations. Based on the consensus and key findings summarized from the reported literature, we further conclude that metallic materials, especially precious metals, are particularly suitable for the adsorption of the volatile 210Po species, and that the adsorption strength is significantly influenced by the material type and surface properties. Moreover, we provide a detailed analysis of the interaction mechanisms between Po-containing species and the surfaces of various candidate materials, while also highlighting key challenges and proposing specific future research directions, such as introducing defect sites to enhance the adsorption strength and the adsorption selectivity of Po on material surfaces, as well as incorporating nanostructures to prolong the interaction time, thereby improving the overall adsorption efficiency. This work aims to offer valuable insights into the rational design of materials targeting volatile 210Po capture and to inspire further developments in the relevant field.