The role of clearance in the management of future fusion reactor radioactive materials

Under the framework of the European Power Plant Conceptual Study (PPCS), studies were carried out on the radioactive material management from future commercial fusion power plants, including among others: clearance and recycling, tritiated waste, waste categorisation, interim storage and final disposal. The present paper is focused on the important role that clearance will have in the management of such material flows. From different studies, performed inside the European Fusion Technology Programme, it is evident that fusion radioactive materials will be characterised by the following specific aspects: • Large volumes; • Mostly solid activated and contaminated material; • Reduced radioactivity in the medium term (< 100 y), no radioactivity in the long term, due to a careful selection of materials; • Low heat generation density and low radiotoxicity; • No transuranic elements beyond trace levels; • No proliferation concerns. These aspects will ensure that fusion materials can be managed so as to leave reduced or even no burden to future generations. The only significant management issue is the relatively large quantities of radioactive materials calculated to be produced. The possibility of drastically reducing this amount is based on the clearance and recycling of material arising from a fusion power plant. While clearance is based on the residual content of radioactivity, recycling involves also a mixture of socio-economic and environmental issues that are being investigated. The present paper will be mostly focused on the important role that might be played by well-defined and harmonised clearance criteria on fusion material management. A categorisation based on the neutron transport and activation calculations carried out on the four different PPCS models has revealed the importance that might be played by the clearance process on the reduction of the amount of material requiring disposal. The four investigated PPCS models span a range from relatively near term, based on limited plasma physics and technology extrapolations, to a rather advanced concept. The technological issues are determined by the different combinations of materials such as armour, structural material, coolant, breeder and neutron multiplier. The activation of the materials in all four Models decays relatively rapidly – very rapidly at first and broadly by a factor ten thousand over a hundred years. For much of this material, after an adequate decay time, the activity falls to levels so low that it could be “cleared” from regulatory control. The estimated share of clearable material ranges up to about 50% of the total mass after 100 years. Exploiting to a full extent the possibility to carry out recycling would reduce to a very limited quantity the amount of material to be disposed of.