GREEN CDT Solidification Routes for Encapsulation of Radioiodine

在英国，到目前为止已经产生了超过15万立方米的放射性废物。大多数放射性废物需要通过固化成稳定的废物形式进行调节，最常见的方法是将其转化为陶瓷废物形式，玻璃化以形成稳定的玻璃，或将其包裹在水泥中以防止释放到生物圈。然而，许多废流与上述调节过程不兼容。放射性碘尤其有问题，因为它以各种化学形式的碘存在于溶解废气和含水废水中，包括那些容易挥发的碘。最近的研究表明，通过将放射性碘和固体吸附剂包裹在水泥中来固定放射性碘和固体吸附剂的潜力巨大。放射性废物的胶结比其他放射性碘固化过程更容易、更便宜、更快，例如低温玻璃烧结和热等静压，并避免了碘的挥发或与负载碘的吸附剂不兼容的问题。然而，水泥中的固定行为与其他废物形式(如陶瓷、玻璃)中的固定行为有很大不同，这是由于水和固体化学以及每种情况下的处理路线之间的巨大差异。有关哪些参数对可靠应用至关重要的信息很少。该博士论文探索了装载放射性碘的固体吸附剂的固化途径，检测了水泥密封剂中的放射性核素-矿物相互作用，并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、光谱和微结构表征)来研究放射性核素-矿物相互作用的机理和动力学，以及对废物性能的影响。通过这一过程，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旧配方。

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.