Estimation and characterisation of the neutron-induced radioactivity in fusion reactor materials is the basis for their classification in view of radiotoxicity. In the present study has been performed evaluations of Clearance Index (CI), Contact Dose (CD) and Decay Heat Rate (HR) for a European DEMO concept based on HCLL blanket technology, including their time behaviour and significance of particular nuclides. The main objective was to determine the activation of the various materials and components in order to quantify the amount and characteristics of wastes from the DEMO machine. Calculations of induced activity in the system, indicated sometimes the dominant contribution of very rare reactions or nuclides with hundreds years of decay. Activation and decay heat levels of the components were calculated with the use of FISPACT-2007 and EAF-2007 library, on the basis of neutron fluxes throughout the structures of the tokamak calculated with the use of MCNP and the DEMO model from CCFE. The final material balance was assessed as well.

An international collaborative study is examining the back-end of the fusion materials cycle and the different options for the management of irradiated material. In the EU, following from earlier work, the irradiated material inventory in two PPCS near-term models has been analysed with increasing detail and taking into account the newest findings in the field, for the first time for PPCS-B. The suitability of this material to follow the recycling and disposal routes has been estimated and compared in a comprehensive manner. A novel scheme is presented for the evaluation of the technical difficulty of operations on active material. Results highlight the conservatism of previous studies: all material is technically suitable for recycling shortly after shutdown (<5 years), and a few decades of storage suffice for the vast majority to be apt for undemanding techniques or equipment; some of it, however, requires active cooling during its interim storage. Disposal in several EU low-level repositories is also considered; rejection of metal streams is found to be 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 over-stringent and arbitrary for fusion: the development of relevant standards in the EU appears necessary.

A small steady state spherical tokamak (ST) offers an attractive system for producing simultaneously the neutron. particle and heat fluxes necessary to effectively test and optimise blanket modules, first wall structures and other components under the required fusion power plant conditions. This component test facility (CTF) would complement and extend the qualification of materials by IFMIF and could operate in association with DEMO thus reducing the risk of delays, and extending the options, during this crucial stage of the development of commercial fusion power.The ST-CTF offers many advantages including low tritium consumption, ease of maintenance and a compact assembly and would operate in a strongly driven mode in which Q similar to 1. The current drive would be provided by a mix of bootstrap current and neutral beam injection systems. The blanket modules under test are removed and replaced using a casking system and the entire centre column assembly can be relatively easily removed via a hydraulic lift system beneath the tokamak assembly. The single turn toroidal field coil has a water-cooled copper centre rod with multiple return limbs, which requires a low voltage, high current power supply. The poloidal field coils are also water-cooled but use a glass fibre reinforced cyanate ester resin insulation that offers higher radiation resistance and higher operating temperatures than the conventional epoxy resin systems. When operated in L-mode most of the exhaust power is directed to the outer legs of the double null divertor configuration where high power densities and high material erosion rates are developed. A novel divertor target based on the use of a cascading flow of pebbles is one option being developed for this application. Crown Copyright (C) 2008 Published by Elsevier B.V. All rights reserved.

The demanding neutronic environment in a future fusion power plant will require a thorough understanding of the mechanisms at work in producing displacement damage, their magnitudes, and their effects on the materials and their properties. It is a pre-requisite to have a precise understanding of the Primary Knock-on Atom (PKA) energy spectra caused by 14.1MeV fusion neutrons in order to have a good foundation for a quantitative determination of the damage driving phenomena produced as a result of neutron encounters. At the higher neutron energies involved in fusion compared to fission, inelastic collisions become very much more significant. This adds to the complexity of estimates of the deposited energy. A Monte-Carlo transport code (MCNP5) has been adapted to provide neutron induced PKA energy spectra for both elastic and inelastic neutron collisions. The introduction of PKA calculations of this type to an MCNP code is new. The Norgett–Robinson–Torrens [M. Norgett, M. Robinson, I. Torrens, A proposed method of calculating displacement dose rates, Nucl. Eng. Design 33 (1975) 50–54] modification to the Kinchin–Pease [G. Kinchin, R. Pease, The displacements of atoms in solids by radiation, Rep. Prog. Phys. 23 (1955) 1–51] model of atomic displacements allows a convenient normalisation measure, the displacements per atom (dpa), allowing for both elastic and inelastic neutron collisions. Application of this work to models of the Power Plant Conceptual Study (PPCS) [G. Marbach, I. Cook, D. Maisonnier, The EU power plant conceptual study, Fusion Eng. Design 63–64 (2002) 1–9] very efficiently generates the PKA spectra and dpa damage as a function of location, providing data that can be used in the design of both power plants and materials testing facilities.