Neutron Activation Measurements for Materials used in Fusion Reactors.

Today’s high demand for power (electricity) is dominantly supplied from power stations burning fossil fuels. At the risk of depletion of the Earth’s supply of fossil fuel, developments in alternative sources of power include nuclear power and renewable energy (e.g. wind turbines). Current nuclear power plants rely on fission reactors which generates significant amount of energy but at the cost of unwanted radioactive by-products. Fusion power is seen as an alternative source of electricity in the future, producing less waste than their fission counterpart. Understanding how materials behave under the influence of a high flux of neutrons will be valuable towards the future design of the fusion reactor. Analysis from neutron activated foils resulted in cross-section measurements that were a few order of magnitudes larger than published values (Jendl 4.0). To suppress background contributions to the detector, an anticoincidence system was developed at the University of York. The system utilise both passive and active shielding, for the latter, a plastic scintillator (BC404, Saint-Gobain Crystals) was used to veto contribution from (high energy) cosmic rays that can be registered in the primary detector (Ge(Li), Ortec). Experiments using a 22Na calibration source saw a reduction of counts of 45% and 36% in the 511keV and 1274keV photopeaks respectively. A current material of interest is a PAK alloy predominantly made up of iron, where small foil samples where irradiated at the ASP facility (AWE Aldermaston, UK) to observe for reoccurring reactions and the induced activity of the foil itself. Data from three experiments (EXPT92, EXPT93, and EXPT102) were provided by Steven Lilley (Culham Centre for Fusion Energy). From the identified γ-ray peaks from the EXPT92 dataset (sample), the induced activity of a 1g test sample irradiated for 5 minutes, had an equivalent dose-rate (in air) of 13.4nSv.hr-1 at 1m