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

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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.