Investigation of the safe removal of fuel debris: multi-physics simulation

现代计算代码在评估核电设施的行为并确保它们在进入非预期运行情景时对公众、设施工作人员和环境造成的危害降至最低方面非常有用。这项提议将开发这样的方法，并将建立一个准确、健壮、高效和经过验证的模拟工具，并能够确定我们可以对模型施加的置信度。它将用于预测反应堆退役的可能后果，并在严重核事故后进行清理。它还寻求帮助建立先进的计算方法，以调查严重事故期间反应堆行为的各个方面。这项拟议的技术将有助于提供超出目前可能的精度，并将允许探索无法通过实验重现的物理学。这里提出的工作旨在通过为对照基准案例核实和确认计算工具奠定基础，然后将其用于模拟更复杂/现实的情景，从而实现这一点。该项目将结合英国和日本学术界和工业界的专业知识。该项目将研究严重核事故中碎片退役的两个方面，以及事故期间堆芯材料演变的预测。堆芯材料的演变对于退役非常重要，因为它有助于确定反应堆内部结构的最终状态。由于福岛一个受损反应堆的状况，干式退役可能是必要的，因为堆芯不会被水淹没，这种新的燃料去除方法将在这里进行研究。干式除尘的一个问题是，它引入了与释放到大气中的放射性粉尘相关的问题。当堆芯打开，部分碎片被切割和移除时，就会产生粉尘排放。这些颗粒物将在空气中分散和移动，因此将对现场人员和直接环境构成危险。为了减轻尘埃传播的严重性，将在堆芯周围部署细雾喷雾，以捕获和清除空气中的尘埃颗粒。这种方法的适宜性(以及是否保持对环境的足够屏蔽)将在这里确定，将开发先进的建模方法来模拟反应堆内的粉尘扩散和颗粒与水滴的相互作用。使用精细喷雾还可以克服第二个问题，即通过从碎片中提供足够的热量去除来进行干燥去除，否则，如果堆芯被淹，就会得到充分的管理。此外，我们亦会在这项建议内建立一个模型架构，以研究这方面的安全问题。这项工作的结果将有助科学家和工程师了解退役活动的过程和意外情况。它们将有助于改进未来的设计，并帮助运营商对此类事件做出反应。此外，它们将有助于提高安全性，限制损害，并向政策制定者通报设计完整性。重要的是，这项工作的成果将向公众展示我们对安全的承诺，以增强他们对核技术的信心。

Modern computational codes can be very useful in assessing the behaviour of nuclear power facilities and ensuring that they present minimal hazard to; the public, facility workers and the environment when they enter unintended operating scenarios. This proposal will develop such methods, and will establish a simulation tool that is; accurate, robust, efficient and validated, and able to determine the levels of confidence that we can place on the models. It will be used for predicting possible consequences of reactor decommissioning and clean up following a severe nuclear accident. It also seeks to help establish advanced computational methods to investigate aspects of reactor behaviour during severe accidents. The technology proposed will help provide accuracy that is beyond what is currently possible, and will allow the physics to be explored that cannot be reproduced through experiment. The work proposed here seeks to achieve this by developing a basis for the verification and validation of computational tools against benchmark cases that will then be used to simulate more complex/realistic scenarios. The project will combine the expertise from the UK and Japan, both within academia and industry.This project will investigate two aspects of decommissioning of its debris from severe nuclear accidents as well as the prediction of the evolution of core's materials during an accident. The evolution of the core material is important for decommissioning as it helps determine the final state of the internal structures within the reactor. Due to the condition of one of the Fukushima's stricken reactors, dry decommissioning, where the core is not flooded with water, may be necessary, and this novel method of fuel removal will be investigated here. An issue with dry removal is that it introduces the problem associated with radioactive dust being released into the atmosphere. Dust emissions will occur when the core is opened and parts of its debris are cut and removed. These particles will disperse and move within the air and so will present dangers to both site personnel and the immediate environment. To mitigate the severity of dust propagation fine mist sprays will be deployed within the core's surroundings to capture and remove dust particles from the air. The suitability of such an approach (and whether sufficient shielding to the environment is maintained) will be determined here where advanced modelling methods will be developed to simulate dust dispersion within the reactor and the particles' interaction with the water droplets. Using fine sprays may also overcome a second issue regarding dry removal by providing sufficient heat removal from the debris, which would have been otherwise been sufficiently managed had the core been flooded. A modelling framework will also be developed within this proposal to investigate this safety aspect.The outcomes of this work will help scientists and engineers understand the processes during decommissioning activities as well as accident scenarios. They will help improve future designs and aid operators' responses to such events. In addition, they will help to enhance safety, limit damage and inform policy makers on design integrity. Importantly, the outcomes of this work will demonstrate to the public our commitment to safety in order to strengthen their confidence in nuclear technology.