The public perception of fusion power is that it will provide a clean source of abundant nuclear energy. This is not wholly accurate. Currently planned fusion reactors will use the deuterium-tritium (DT) reaction for power generation. This reaction produces 14 MeV neutrons which, as they cannot be magnetically confined, impinge upon the reactor structure. This will cause nuclear activation within reactor components which, at reactor end of life, will need to be disposed of as radioactive waste. Of particular interest is the waste prospects of structural steels, given the large scale of Tokamak fusion reactors.
The current proposals for the DEMO fusion reactor are that all waste can be disposed of as low level waste 50 to 100 years after reactor shut down. However, recent work (Gilbert .et.al 2019) has shown that DEMO’s near plasma steel structures will fail to be classified as low level waste 100 years after reactor end of life under the UK’s and France’s low level waste criteria. It was shown that long lived radionuclides were being produced in the steels studied: the European low activation steel Eurofer and stainless steel type 316. These results are the motivation for a new study, covering a greater number of steels and waste repositories to assess the waste landscape for fusion steels. This work will present an overview of 5 (UK plus 4) currently available low level waste repositories, the differences between their low level waste criteria and discuss the origins of the criteria. This will demonstrate that the factors required to define a sample as ‘low level waste’ are as much geographical as they are physical. Then the results of detailed inventory simulations, performed with the inventory code FISPACT-II and the latest TENDL nuclear data library, will be presented. These subjected the 12 steels (Eurofer and 4 additional low activation steels as well as 7 standard steels) studied, all of which could see use in future fusion power plants, to neutron irradiation scenarios characteristic of two regions of the DEMO reactor: the plasma facing Blanket region and the near plasma Vacuum Vessel. These results will reveal that the waste classification behaviour of all of the steels studied is remarkably similar, regardless of whether the steels were developed for reduced activation or not. The results will show that fusion steel waste can only be classed as ‘low level’ by a purposeful choice of material and destined repository. Possible waste reduction strategies and the prospects for the disposal of waste from DEMO and DEMO-like fusion power plants will be discussed.