Development of a High Flux Accelerator-Driven Neutron Irradiation Facility for Nuclear Plant Materials and Applied Neutron Science

中子与物质相互作用的研究巩固了我们对一切事物的理解，从核反应堆中材料的弹性，反应堆内产生的具有医疗应用潜力的放射性核素的产生，一直到理解中子与细胞相互作用的放射生物学，以及癌症形成和治疗的潜力。不像理解质子的相互作用，高通量的质子，甚至离子，是可能的，创造强烈的中子束是极具挑战性的。因此，中子辐照物质的性质是一个仍需进一步研究的领域。对核反应堆的理解尤其如此。目前这一代反应堆有寿命限制，这通常受到材料性能的限制，要么是慢化剂（例如在AGR电站中，这是石墨），反应堆压力容器（例如在压水堆设计中），甚至是用于控制和运行反应堆的电子和机械系统的可靠性。性能退化的测量允许预测其失效寿命，从而提高安全性和保证。然而，这是一种经验方法，更复杂的方法是详细了解损伤机制，以及这些机制如何与宏观材料失效特征（如脆化或辐射辅助腐蚀）联系起来。为了发展这种理解，有必要辐照材料，然后了解它们的性质是如何在微观尺度上发生变化的。然后，这可能被用来激励开发精确的过程模型，这些模型可用于预测材料失效。由于中子辐照设施的有限性，导致使用质子辐照来试图模拟几乎相同的中子。然而，中子在一个非常重要的方面是不同的——它不带电。当质子穿过物质并与原子核发生碰撞时，它的电荷会扰乱电子。因此，损害的类型是非常不同的。为了推动这一领域的发展，需要一个完善的中子辐照计划。这可以在材料测试反应堆中进行，但这些反应堆价格昂贵，访问受限，因此限制了可以进行的研究数量。由于运行中的挑战和费用，新的反应堆测试设施的创建是昂贵和具有挑战性的。一种令人兴奋的替代方法是使用基于加速器的方法，这种方法可以加速质子，并通过核反应将它们转化为中子，从而产生中子通量。要做到这一点，需要一个高电流质子加速器。直到最近，才开发和利用了具有所需性能的可靠加速器。目前的建议是用这种方法在伯明翰大学建立一个基于加速器的中子辐照设施。这将能够产生接近核反应堆内部的中子通量，可用于材料辐照。该设施的灵活性将允许在辐照期间（即在现场）测试材料的降解，以更好地表征材料的变化。其目的是建立一个国家设施，使用户能够制定一个与高通量材料试验反应堆相联系的科学方案。它将利用现有的设施，如伯明翰大学的MC40回旋加速器和国家物理实验室的精确能量中子设施。这种能力的广度将为英国社会提供一套能够支持核部门发展的核设施。

The study of neutron interactions with matter underpins our understanding of everything from the resilience of materials in a nuclear reactor, the production of radionuclides which are produced inside a reactor with potential for medical applications, all the way to understanding the radiobiology of neutron interactions with cells and the potential for both the formation and treatment of cancer. Unlike understanding the interaction of protons, where high fluxes of protons, or even ions, is possible, creating intense beams of neutrons is extremely challenging. As such the properties of matter irradiated by neutrons is an area which still requires advances in research. This is particularly the case for the understanding of nuclear reactors. Present generation reactors have lifetime limits which are often restricted by the materials performance of either the moderator (for example in the AGR power stations this is graphite), reactor pressure vessel (e.g. in PWR designs) or even the reliability of the systems, both electronic and mechanical, that are used in the control and operation of the reactor. Measurements of the degradation of the properties allow a prediction of their lifetime to failure and hence enhances safety and assurance. However, this is rather an empirical approach and a more sophisticated method would be to develop a detailed understanding of the damage mechanisms and how these then link to the macroscopic materials failure characteristics, such as embrittlement or radiation assisted corrosion. To develop this understanding it is necessary to irradiate materials and then understand how their properties are being transformed on the microscopic scale. This may then be used to motivate the development of accurate models of the processes which may be used to predict materials failure. The limited availability of neutron irradiation facilities has resulted in the use of proton irradiation to attempt to simulate the almost identical neutron. However, the neutron is different in a very important way - it is uncharged. As a proton passes through a material, as well as colliding with the atomic nuclei, its charge perturbs the electrons. Thus, the type of damage is very different. To move the field forward a well-developed neutron irradiation programme is required. This can be performed in materials test reactors, but these are expensive, have limited access and thus constrain the volume of research that can be performed. The creation of new reactor test facilities is expensive and challenging due to the challenges and expense in their operation. An exciting alternative is to use an accelerator based approach which accelerates protons and, through a nuclear reaction, converts them to neutrons and thus, a flux of neutrons can be created. To do this requires a high current proton accelerator. It is only recently that credible accelerators with the required properties have been developed and exploited.The present proposal is to use this approach to create an accelerator based neutron irradiation facility at the University of Birmingham. This will be capable of creating neutron fluxes which are close to that inside a nuclear reactor which may be used for materials irradiation. The flexibility of the facility will allow testing of the degradation of materials during the irradiation, i.e. in situ, to better characterise the changes to the material. The intention is to establish a national facility which allows users to develop a scientific programme which links to the higher flux materials test reactors. It will draw in existing facilities such as the MC40 cyclotron at the University of Birmingham, and the precision energy neutron facility at the National Physical Laboratory. This breadth of capability will provide the UK community with a suite of nuclear facilities capable of supporting the development of the nuclear sector.