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

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.

The main impact of the proposed facilities will be to i) the nuclear industry associated with nuclear the safe operation of nuclear reactors, ii) the nuclear regulator charged with the oversight of the safe operation of the UK nuclear fleet, iii) those charged with maintaining the nuclear waste facilities and the decommissioning of sites, iv) the development of geological waste facilities, v) the creation of next generation of nuclear plants such as Gen IV and fusion, vi) those developing next generation SMR and AMR designs.

The impact will be via the ability to characterise the degradation of materials under irradiation, and hence develop, an enhanced understanding of the lifetime of nuclear plant materials, mitigation strategies and radiation resistant or tolerant materials. Loss of operation of nuclear power plant reactors costs an estimated £1M/day and for a fleet of nuclear reactors the commercial impact is billions of pounds per year. The safe operation of nuclear reactors is of prime interest to the UK public and the ONR. The level of confidence is directly related to the ability to understand the performance and safety of nuclear power plant. The characterisation of nuclear materials is the most critical issue. Future developments in the field of nuclear energy, fission and fusion, rely on having a skilled workforce with a deep understanding of nuclear power technology and the underpinning science. The skills base the facility will create will be of high importance to the development of the sector.

The High Flux Accelerator-Driven Neutron Irradiation Facility for Nuclear Plant Materials and Applied Neutron Science will deliver the above impact by establishing a facility which will i) deliver a fundamental nuclear materials research programme, ii) develop collaborative research between the academic community and the nuclear industry and iii) allow commercial irradiation measurements to be performed by the nuclear industry.

The facility will develop a national training programme that will establish a series of training opportunities related to working with nuclear accelerators, materials irradiation, radioprotection and nuclear safety, nuclear instrumentation and techniques, nuclear data and measurement and dosimetry and metrology. The aim is to boost the UK skills base with high end expertise with direct benefit to the nuclear industry and related sectors such as medical physics and cancer therapy.