GREEN CDT Solidification Routes for Encapsulation of Radioiodine

在英国，迄今为止已经产生了超过150，000立方米的放射性废物。大多数放射性废物需要固化成稳定的废物形式，最常见的是转化为陶瓷废物形式，玻璃化形成稳定的玻璃，或将其封装在水泥中以防止释放到生物圈中。然而，许多废物流与上述调节过程不相容。放射性碘是特别成问题的，因为它以各种化学形式的碘存在于溶解器废气和含水废物流中，包括那些容易挥发的碘。最近的工作表明，通过在水泥中包封来固定放射性碘和固体吸附剂具有显著的潜力。放射性废物的固化比其他放射性碘固化工艺（如低温玻璃烧结和热等静压）更容易，更便宜，更快，并且避免了碘挥发或与碘负载吸附剂不相容的问题。然而，水泥中的固定行为与其他废物形式（例如陶瓷、玻璃）中的固定行为有很大不同，这是由于水和固态化学之间的巨大差异，以及每种情况下的加工路线。关于哪些参数对可靠应用至关重要的信息很少。这个博士探讨了放射性碘负载的固体吸附剂的封装固化路线，检查水泥澄清剂中的放射性核素-矿物相互作用，以通过热处理产生的更常见的废物为基准。它采用原位表征方法（包括表面特定技术，光谱和微观结构表征）来研究放射性核素-矿物相互作用的机制和动力学，以及对废物性能的影响。通过这个，我们将发现控制放射性碘固定的基本过程，并设计，生产和测试具有增强性能的新型废物制剂。

In the UK, over 150,000m3 of radioactive waste has been produced to date. Most of this radioactive waste needs conditioning by solidification into a stable wasteform, most commonly by conversion to a ceramic wasteform, vitrification to form a stable glass, or encapsulating it in cement to prevent release to the biosphere. Many waste streams, however, are not compatible with the above conditioning processes. Radioiodine is particularly problematic, as it is present in dissolver off-gas and aqueous waste streams in various chemical forms of iodine, including those that easily volatilise. Recent work has shown significant potential for immobilisation of radioiodine and solid adsorbents by encapsulation in cement. Cementation of radioactive waste is easier, cheaper, and faster than other radioiodine solidification processes such as low-temperature glass sintering and hot isostatic pressing, and avoids issues regarding volatilisation of iodine, or incompatibility with iodine-loaded adsorbents. However, immobilisation behaviour in cements differs significantly from that in other wasteforms (e.g. ceramics, glasses), due to extensive differences between aqueous and solid-state chemistry, and processing routes in each case. There is little information on what parameters are critical to reliable application. This PhD explores solidification routes for encapsulation of radioiodine-loaded solid adsorbents, examining radionuclide-mineral interactions in cement encapsulants, benchmarked against more common wasteforms produced via thermal treatment. It adopts an in-situ characterisation approach (including surface-specific techniques, spectroscopic and microstructural characterisation) to investigate mechanisms and kinetics of radionuclide-mineral interactions, and effects on wasteform performance. Through this we will discover the fundamental processes controlling immobilisation of radioiodine, and design, produce and test novel wasteform formulations with enhanced performance.