Neutronic optimisations of breeder blankets for fusion reactors

• Main Author: Shimwell, Jonathan Gregory
• Other Authors: McMillan, John ; Lilley, Steven
• Published: University of Sheffield 2016
• Subjects: 621.48
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.687253

Fusion is seen by many as the ultimate energy source, capable of providing safe, clean and sustainable energy. Research has been carried out into fusion since the 1920s and substantial progress has been made. While the ultimate goal of providing energy from fusion remains elusive there is a clear understanding of the tasks that must be achieved to make fusion energy a reality. Deuterium and tritium (DT) offer a high probability of fusion when compared to any other combination of isotopes. Consequently DT fusion is the focus of all large scale fusion research programmes. As there is no natural source of tritium, fusion reactors are being designed with tritium breeder blankets to ensure self-sufficiency. The research contained within this thesis contributes to the ongoing development of breeder blankets for fusion reactors in terms of reducing their cost and improving their performance. The thesis follows a general theme of varying material composition to better utilise the local neutron spectra within fusion breeder blankets. The novel contributions of this thesis are as follows: The first contribution of this thesis is a technique that improves the accuracy of simulations involving time varying tritium production [171]. The technique identifies a minimum spacial resolution that should be used when performing burn-up studies in solid-type breeder blankets. Previously the tritium production with respect to time has been overestimated due to lack of spatial segmentation within the breeder blanket. Following on from this a parameter study was carried out to ascertain a more optimal composition for breeder blankets. The results of this study allows blanket designers to minimise the cost of the blanket while increasing the heat generated or maximising the tritium produced. The composition of breeder blankets operating with a DD neutron source was also optimised. This allows breeder blankets to create tritium from DD plasmas more efficiently. The use of DD plasmas to generate tritium is a proposed method of negating the need for an external supply of tritium to start up reactors. The sustainability of fusion is investigated and a method of reducing the use of beryllium within breeder blankets is presented. Blankets utilising this method were also shown to generate more heat, produce more tritium and showed lower peak heating. Varying the isotopic composition of materials was considered as a method to reduce helium production and improve the material properties without additional activity [132]. For the first, time cost benefit analysis of isotopically tailored materials in fusion reactors has been carried out and various methods to offset the enrichment cost have been identified. Multilayer blankets are investigated as a method of increasing the tritium production and are shown to achieve tritium production levels that are unobtainable for blankets with a uniform composition. Higher tritium production from blankets is particularly necessary in reactor designs that involve a reduction in the blanket volume. The composition of structural materials used within breeder blankets was also investigated. New material compositions are considered that offer reduced helium production. Additionally, materials that potentially offer improved material properties (e.g. fracture toughness and yield stress) are shown to be achievable. This is achieved by the addition of enriched Ni or Mo; the enrichment of the natural element allows it to be reintroduced without significant increase in activity. The final chapter summarises the research carried out, makes recommendations with regards to the design of future breeder blankets and presents further research opportunities.