Mechanisms of Retention and Transport of Fission Products in Virgin and Irradiated Nuclear Graphite

英国在先进气冷反应堆的运行方面有着长期的经验，这些反应堆依赖于许多吨核级石墨，石墨具有双重作用，首先是减速（中等）中子以增强核裂变，其次是在反应堆堆芯中的相当极端的环境中提供结构，包括高温和强辐射。例如高温气体反应堆和熔盐反应堆也依赖于石墨，并且需要对其在辐照下，特别是在高温条件下的性质有很好的科学了解。因此，在这些新的反应堆概念可以通过设计过程并获得运行许可之前，需要进行基础研究以揭示石墨行为的潜在机制。这些新反应堆设计的一个大问题是石墨中活化的裂变产物的保留，以及随后在退役期间它们的潜在释放。这包括用于卵石床模块化反应堆设计的燃料卵石中的复杂石墨基质材料。这是一种联合实验-计算方法，用于测量裂变产物（FP）-碘（I），铯（Cs），氪（Kr），锶（Sr），钌（Ru）和银（Ag）以及铕（Eu）在四种石墨等级- HOPG，NBG-18，PCEA和IG-110中的扩散率，并使用涉及电子结构，原子，在曼彻斯特和拉夫堡的英国研究小组将与设在中央佛罗里达大学、北卡罗来纳州州立大学和橡树岭国家实验室的美国研究小组一起研究这个问题。曼彻斯特将对AGR和Magnox反应堆计划的遗留石墨进行实验测量，拉夫堡将使用理论方法来阐明FP在服务开始时的石墨现实模型中的电子结构和能量景观，以及暴露于中子和伽马辐射数十年后的石墨。

The UK has long experience in the operation of Advanced Gas-cooled Reactors, which rely many tonnes of nuclear-grade graphite which has a dual role, firstly to slow down (moderate) neutrons to enhance nuclear fission and secondly to provide structure in the rather extreme environment in the reactor core, comprising high temperatures and intense radiation.Designs of reactor for the next generation of nuclear reactors being developed in the USA, such as high temperature gas reactors and molten salt reactors also rely on graphite, and will require a good scientific understanding of its properties under irradiation, particularly under higher temperature conditions. Therefore, fundamental studies are required to reveal the mechanisms underlying graphite behavior, before these new reactor concepts can be taken through the design process and be licensed for operation.A big issue for these new reactor designs is the retention of activated fission products within graphite, and their subsequent potential release during decommissioning. This includes the complex graphitic matrix material used in fuel pebbles for Pebble Bed Modular Reactor designs. This is a joint experimental-computational approach to measure the diffusivities of fission products (FPs) - Iodine (I), Cesium (Cs), Krypton (Kr), Strontium (Sr), Ruthenium (Ru) and Silver (Ag), and Europium (Eu) in four graphite grades - HOPG, NBG-18, PCEA and IG-110, and uncover the mechanisms of transport using multiscale simulations involving electronic structure, atomistic, and phase field methodsThe UK teams at Manchester and at Loughborough will be working with the USA groups based in University of Central Florida, North Carolina State University and Oak Ridge National Laboratory on this problem. Manchester will be contributing experimental measurements on legacy graphite from the AGR and Magnox reactor programmes and Loughborough will be using theoretical methods to elucidate electronic structure and energy landscapes of the FPs within realistic models of the graphite at the beginning of service, and graphite after decades of exposure to neutron and gamma radiation.