'OptiClean' - Optimised laser cleaning for safe nuclear decontamination and decommissioning

2011年3月11日午餐后不久，由9.0级东北大地震引发的15米高的海啸吞没了福岛第一核电站（FDNPP），使该电站及其重要的周边基础设施和提供紧急反应堆堆芯冷却的多个安全层陷入瘫痪。由于缺乏持续的堆芯冷却供应，在接下来的几天里，为了应对反应堆内的临界温度和压力，注入海水作为最后的手段来提供紧急堆芯冷却。然而，这种绝望的努力是不够的，每个反应堆压力容器（RPV）中的温度上升到超过2,000摄氏度;导致核燃料组件中的铀熔化（部分或全部）并垂直向下腐蚀通过RPV，进入主安全壳（PCV）的底部-以及覆盖广泛PCV的内部体积。在英国，塞拉菲尔德包括第一个商业发电站（考尔德霍尔，有四个镁诺克斯反应堆）和生产钚的温斯凯尔堆1和2，为英国最初的核武器计划提供燃料。匆忙组装导致对报废、废物管理和运营后退役的规划很少，这意味着这些设施仍然存在高度危险。然而，塞拉菲尔德的危险消除挑战在英国并不独特，大量的Magnox电站也在长期“维护和保养”之前开始“加速退役”。NDA产业中许多最紧迫和最复杂的退役挑战涉及放射性污染表面的去污，已经考虑了许多方法来解决这个问题，激光清洁成为有前途的候选者。激光烧蚀（或“激光清洗”）是国际核工业快速净化表面固定放射性材料的新兴退役工具，最近被确定为在英国NDA Estate使用的“有前途的技术”。它对核退役特别有吸引力，因为它不仅是非接触式的，而且产生的二次固体和水废物的体积比替代的物理和化学方法小得多。然而，仍然存在一些根本性的挑战，阻碍了该技术的广泛实施：-该技术的烧蚀性质可能会产生局部大气污染。由于烧蚀的放射性材料的空气传播微粒性质，废物收集和处置是复杂的。另外的“之前”和“之后”的表征调查是必要的，以规划去污活动和评估激光清洁的质量。这个及时的、跨学科的、有影响力的提案通过开发新颖的颗粒物控制和收集策略，结合创新的光学表征，来规划和评估清洁活动，从而解决了这些和其他挑战。通过这种方式，它将减少激光清洁的负担、风险和管理费用，从而使其在国际上得到更广泛的应用。这将特别适用于FDNPP，但也适用于英国的塞拉菲尔德和其他遗留核场地。我们将利用实验室评估的知识，制作一个原型光纤耦合的“OptiClean”系统，用于集成到我们为NNUF计划开发的LBR-SuperDroid上。该平台由一个大型履带式机器人平台SuperDroid HD 2组成，顶部安装了一个KUKA LBR IIWA 14机器人机械手。它的跟踪特性允许远程门道规模的访问与额外的爬楼梯能力，而LBR是一个七自由度的机器人机械手与力反馈传感人类安全的互动。

Shortly after lunch on the 11th March 2011, a 15 m high tsunami triggered by the magnitude 9.0 Great Tohoku earthquake engulfed the Fukushima Daiichi Nuclear Power Plant (FDNPP) - crippling the site, its essential surrounding infrastructure and the multiple safety layers the provided emergency reactor core cooling. Resulting from this absence of sustained core cooling provision, over the following days and in response to critical temperatures and pressures within the reactors, seawater was injected as a final resort to provide emergency core cooling. However, this desperate effort was insufficient, and temperatures rose in each of the reactor pressure vessels (RPVs) to in-excess of 2,000C; causing the uranium contained within the nuclear fuel assemblies to melt (partially or fully) and corrode vertically downwards through the RPV, into base of the primary containment vessel (PCV) - as well as coating the internal volume of the extensive PCV. In the UK, the Sellafield site includes the first commercial power-generating station (Calder Hall, with four Magnox reactors) and the plutonium-producing Windscale Piles 1 and 2, that fuelled the UK's original nuclear weapons programme. The haste to assemble led to little planning for end-of-life retirement, waste management and post-operational decommissioning, meaning that such facilities still present high hazards. The hazard removal challenges at Sellafield are, however, not unique in the UK, with the large number of Magnox stations also embarking on "accelerated decommissioning" ahead of long-term "care and maintenance". Many of the most pressing and complex decommissioning challenges across the NDA estate concern the decontamination of radiologically contaminated surfaces, with numerous methods having been considered to address this, and laser cleaning emerging as the promising candidate. Laser ablation (or "laser cleaning") is an emerging decommissioning tool for the international nuclear industry to rapidly decontaminate surface-fixed radioactive materials, having recently been identified as a "promising technique" for use across the UK NDA Estate. It is particularly attractive for nuclear decommissioning as it is not only non-contact, but also produces much smaller volumes of secondary solid and aqueous wastes than alternative physical and chemical methods. However, some fundamental challenges remain which prevent widespread implementation of the technique:- The ablative nature of the technique can generate localised atmospheric contamination.- Waste collection and disposal are complicated due to the airborne particulate nature of the ablated, radioactive material.- Additional 'before' and 'after' characterisation surveys are necessary to plan the decontamination activities and assess the quality of laser cleaning.This timely, cross-disciplinary, and impactful proposal addresses these and other challenges by developing novel particulate containment and collection strategies, integrated with innovative optical characterisation, for planning and assessing cleaning activities. In this way, it will reduce the burden, risks and overheads of laser cleaning, leading to its broader international utilisation. This would be particularly applicable at FDNPP, but also at Sellafield and other legacy nuclear sites in the UK. We will use knowledge from the laboratory assessments to make a prototype fibre coupled, 'OptiClean' system for integration onto our LBR-SuperDroid, as developed for the NNUF programme. The platform consists of a SuperDroid HD2, a large tracked robotic platform, with a KUKA LBR IIWA 14 robotic manipulator mounted on the top. Its tracked nature allows for remote doorway-scale accesses with additional stair-climbing capabilities whilst the LBR is a seven degrees of-freedom robotic manipulator with force feedback sensing for human-safe interaction.