Irradiated material management in near-term fusion power plants
The back-end of the materials cycle plays a key role in maximising the environmental benefits of fusion power generation. Under the auspices of the International Energy Agency (IEA) a worldwide collaborative study has examined the different options for the management of fusion irradiated material focusing on the EU and US standpoints; this document reports the contribution of UKAEA to this project. Following from earlier European work in the field, the irradiated material inventory in two near-term fusion power plants in the European Power Plant Conceptual Study (PPCS) has been computed and analysed with increasing detail and applying the newest findings in the field of fusion waste management, for the first time for PPCS-B. The suitability of this material to follow the two main management routes envisaged, recycling and disposal, has been estimated and compared in a comprehensive manner, the latter for the first time in this kind of study in the EU. A novel scheme has been developed providing a coarse but insightful tool to evaluate the technical difficulties of treatments and operations on active material. Results of these analyses highlight the over-conservatism of previous studies; all the material in these plants is suitable for recycling shortly (<1y) after plant shutdown. Furthermore, a few decades of storage suffice for the vast majority to be suitable for undemanding techniques or equipment; however some of this material requires active (but not wet) cooling during its interim storage. Disposal in EU low level repositories has been considered; in decreasing order of amount of material accepted, the cases analysed were Germany (Konrad), UK and France (CSA). In the latter case, rejection of metal streams arises largely due to stringent limits on Nb-94 and C-14 activation products. It is pointed out, however, that all disposal criteria were developed for fission waste and are rather over-stringent and arbitrary for fusion: the need to develop relevant standards for fusion in the EU, in a similar way to the US, appears pertinent. In all cases, release from regulatory control (clearance) for either disposal or reuse depends chiefly on the decay of the Ni-63 activation product. Focus has been given to the assessment of long-lived activity: estimation of the amount and radiotoxicity of secondary wastes generated during recycling operations in PPCS-AB and PPCS-B materials has been made. Both PPCS models produce similar C-14 levels to fission, however mobility is much lower in fusion. PPCS-B performs better in terms of production rate per electrical unit, however an impurity-free PPCS-AB is also a C-14 free plant, whereas PPCS-B is not. Alleviation to these issues is achieved by material choices and strict impurity control prior to service in the plant.