放射性碘是一种危险的裂变产物,是公众健康的主要问题。特别注意80裂变产物中的碘,因为它的半衰期很短,只有8.02天,高活性,以及潜在的健康危害,例如其在甲状腺中的不可逆积累以及局部引起甲状腺癌的能力。放射性碘可以以气溶胶(碘化铯)的形式释放,元素碘,和核事故后的有机碘化物,可能导致场外和现场污染。过滤式安全壳通风系统(FCVS)是一种安全系统,其主要目标是通过控制通风和去除不同形式的碘来减轻严重事故,以确保人员和环境的安全。在福岛核事故之后,已经对使用干式洗涤器去除碘进行了广泛的研究。本文介绍了干吸附剂除碘的研究现状,特别是福岛10年后,研究差距,以及需要更多关注的挑战。一个好的吸附剂应该是成本有效的;它应该对碘具有高选择性吸附,高热稳定性和化学稳定性,和良好的负载能力;和它的吸附应该保持不受老化和抑制剂如CO的存在的影响,NO2,CH3Cl,H2O,Cl2和辐射。讨论了不同干燥吸附剂的研究,并在上述所有特征的基础上审查了它们作为FCVS潜在过滤器的能力。金属纤维过滤器已广泛用于去除气溶胶,尤其是微米级和纳米级气溶胶。为了设计金属纤维过滤器,纤维的最佳尺寸或尺寸组合,层数,过滤器的负载能力应根据可行性和要求来决定。流动阻力和去除效率之间的平衡也非常重要。沙床过滤器成功地保留了气溶胶,但是它们显示出碘的低捕获率和甲基碘的完全没有捕获率。对于碘和甲基碘的去除,许多吸附剂,如活性炭,沸石,金属有机框架(MOFs),多孔有机骨架(POPs),二氧化硅,气凝胶,钛硅酸盐,等。已被使用。浸渍的活性炭显示出良好的结果,但低的自燃温度和由于老化和NOx等抑制剂导致的吸附下降使它们不太合适。银沸石在甲基碘和碘去除方面非常成功,但它们价格昂贵,并且受到CO的影响。钛硅酸盐,大网状树脂,和硫属凝胶也进行了研究,它们显示出良好的吸附能力,但其热稳定性较低。其他吸附剂,如二氧化硅,MOFs,气凝胶,和POPs也显示出良好的结果,碘吸附和良好的热稳定性,但是在严重事故条件下,对其性能的研究非常有限或没有。这篇综述将有助于研究人员了解不同类型干吸附剂的优缺点。设计高效洗涤器需要优化的重要操作参数,研究的边缘,和可预见的挑战,在去除不同形式的碘。
Radioactive iodine is a hazardous fission product and a major concern for public health. Special attention is paid to iodine out of 80 fission products because of its short half-life of 8.02 days, high activity, and potential health hazards like its irreversible accumulation in thyroid gland and ability to cause thyroid cancer locally. Radioactive iodine can get released in the form of aerosols (cesium iodide), elemental iodine, and organic iodide after a nuclear accident and can cause off-site and on-site contamination. Filtered containment venting system (FCVS) is a safety system whose main objective is mitigation of severe accidents via controlled venting and removal of different forms of iodine to ensure safety of people and environment. After nuclear accidents like Fukushima, extensive research has been done on the removal of iodine by using dry scrubbers. This review paper presents research status of iodine removal by dry adsorbents especially after 10 years of Fukushima to assess the progress, research gap, and challenges that require more attention. A good adsorbent should be cost-effective; it should have high selective adsorption towards iodine, high thermal and chemical stability, and good loading capacity; and its adsorption should remain unaffected by aging and the presence of inhibitors like CO, NO2, CH3Cl, H2O, and Cl2 and radiation. Research on different dry adsorbents was discussed, and their capability as a potential filter for FCVS was reviewed on the basis of all the above-mentioned features. Metal fiber filters have been widely used for removal of aerosols especially micro- and nanoscale aerosols. For designing a metal fiber filter, optimal size or combination of sizes of fibers, number of layers, and loading capacity of filter should be decided according to feasibility and requirement. Balance between flow resistance and removal efficiency is also very important. Sand bed filters were successful in retention of aerosols, but they showed low trapping of iodine and no trapping of methyl iodide at all. For iodine and methyl iodide removal, many adsorbents like activated carbon, zeolites, metal organic frameworks (MOFs), porous organic frameworks (POPs), silica, aerogels, titanosilicates, etc. have been used. Impregnated activated carbon showed good results but low auto-ignition temperature and decline in adsorption due to aging and inhibitors like NOx made them less suitable. Silver zeolites have been very successful in methyl iodide and iodine removal, but they are expensive and affected by presence of CO. Titanosilicates, macroreticular resins, and chalcogels were also studied and they showed good adsorption capacities, but their thermal stability was low. Other adsorbents like silica, MOFs, aerogels, and POPs also showed promising results for iodine adsorption and good thermal stability, but very limited or no research is available on their performance in severe accident conditions. This review will be very helpful for researchers to understand the merits and demerits of different types of dry adsorbents, the important operating parameters that need optimization for designing an efficient scrubber, margin of research, and foreseeable challenges in removal of different forms of iodine.