Laser-driven multi-modal probe beams for nuclear waste inspection

该提案旨在开发一种革命性的新工具，用于使用激光驱动的x射线和中子束脉冲对核废料包装进行隔离检查。这将是布里斯托尔大学界面分析中心（IAC）、Sellafield有限公司、贝尔法斯特女王大学（QUB）和STFC中央激光设施（CLF）之间的合作项目。通过在很短的时间内发射极高能量的激光，产生一个强烈的x射线辐射点并投射到探测器板上。与医用x射线类似，任何放置在明亮的x射线源和照相胶片或数字图像板之间的物体都可以被详细捕获。然而，由于使用了非常高的能量，对含有铀废料的包裹进行成像是可能的，铀废料是地球上密度最大的材料之一。自1952年以来，塞拉菲尔德一直负责英国所有核废料的安全储存和再处理。几十年的研究和发展已经产生了更易于管理的核废料形式。然而，一些问题仍然存在，特别是自20世纪60年代以来储存的老化的“遗留”核废料。在考虑在地质处置设施中长期储存之前，需要确定废物的组成和降解状态以及密封容器。由于放射性和在储存过程中形成的危险腐蚀产物，对废弃容器进行破坏性调查被认为是太危险而不能进行的。因此，提出了一种非破坏性的、隔离的容器评估方法。为了对核废料包装内部进行目视检查，高能x射线被用来产生样品的图像。产生x射线的典型方法既不能达到所需的分辨率，也不能提供穿透大而致密的废物容器所需的能量。因此，有人建议利用CLF的千兆瓦瓦火神激光器来产生这种分析所需的必要高能x射线。此外，火神激光设备能够产生与高能x射线平行的中子束。用中子束探测废物容器，容器内的任何可裂变物质都会发生少量裂变，并释放出次级中子。根据反应的裂变物质，发射的中子将产生一个独特的特征，可以用来识别样品中存在的特定同位素。对这些数据的分析有可能进行同位素量化，从而确定高放射性铀-235与同位素不同且放射性低得多的铀-238的确切数量。虽然该提案的最初目标是通过单发方法对样品进行表征，但最终目标是开发一种能够通过构建小尺寸高能偶极子激光器以及能够快速获取数据的相应传感器来每秒发射10次的系统。在这样一个系统的预期中，这个项目的一个组成部分旨在改进现有的探测器技术，重点是快速图像捕获和中子探测。该项目的最后一部分是制作一个商业案例，以追求快速燃烧分析系统的最终发展，以形成核废料包装扫描设施的基础。与CT扫描非常相似，通过在多次图像采集期间旋转废物容器，可以构建内容物的3D轮廓。这项技术将使我们能够深入探测废物容器的内部并详细评估其内容物，而无需进行任何破坏性调查或干扰潜在的有毒，焦性和放射性内容物。我们认为，这项技术将具有向其他产生核废料的国家出口的极好的全球潜力。

This proposal aims to develop a revolutionary new tool for the stand-off inspection of nuclear waste packages using laser-driven x-rays and neutron beam pulses. This will be a collaborative project between the University of Bristol's Interface Analysis Centre (IAC), Sellafield Limited, Queen's University Belfast (QUB) and the STFC Central Laser Facility (CLF). By firing an extremely high-energy laser for a very short duration, an intense spot of x-ray radiation is generated and projected towards detector plates. In a similar manner to medical x-rays, any object placed between the bright source of x-rays and either photographic film or digital image plates, is captured in detail. However, because a very high energy is used, imaging of packages containing uranium waste, one of the densest materials on Earth, is possible.Since 1952, Sellafield has been responsible for safe storage and reprocessing of all the UK's nuclear waste. Decades of research and development have resulted in more manageable forms of nuclear waste. However, a number of problems remain, particularly with the ageing 'legacy' nuclear waste that has been stockpiled since the 1960s. Before long term storage in a geological disposal facility is considered, the composition and degradation state of the waste material and containment vessels needs to be established. Due to the radioactivity and dangerous corrosion products formed during storage, a destructive investigation of the waste containers is considered far too hazardous to be performed. Therefore, a non-destructive, stand-off evaluation of the containers is proposed.For a visual inspection of the internals of a nuclear waste package, high-energy x-rays are used to create an image of the sample. Typical means of producing x-rays do not achieve either the resolution required or the energy to penetrate through the large, dense waste containers. Therefore, it has been proposed that the petawatt Vulcan laser at the CLF is utilised to generate the necessary high-energy x-rays required for this analysis.In addition, the Vulcan laser facility is capable of producing a beam of neutrons in parallel with the high-energy x-rays. By probing the waste containers with a neutron beam any fissile material contained inside will undergo a small amount of fission and emit secondary neutrons. Depending on the fissile material that reacts, the emitted neutrons will generate a unique signature which can be used to identify the particular isotope present in the sample. Analysis of this data holds the potential for isotopic quantification, thus identifying the exact quantity of highly radioactive uranium-235 compared to the isotopically different, and far less radioactive, uranium-238.Whilst the initial aims of this proposal are for characterisation of samples via a single-shot approach, the end goal is the development of a system capable of firing up to ten times a second by construction of a small footprint, high-energy DiPOLE laser with the corresponding sensors capable of rapid data acquisition. In anticipation of such a system, one component of this project aims at improving existing detector technology with a focus on rapid image capture and neutron detection.The final section of the project is the production of a business case to pursue the eventual development of a fast firing analysis system to form the basis of a nuclear waste package scanning facility. Much like CT scanning, by rotating the waste container during multiple image acquisition a 3D profile of the contents can be constructed. This technique would allow us to probe deep inside the waste containers and assess their contents in detail without any destructive investigation or disturbance to the potentially toxic, pyrophoric, and radioactive contents. We consider that this technology would have excellent global export potential to other nations producing nuclear waste.