Detailed activation properties of silicon carbide calculated with EASY-99

Silicon carbide (SiC) has long been considered as a possible candidate for advanced fusion plants because of its good activation properties. However, there have been concerns about the production of long-lived 26Al that could give difficulties in the disposal of material following decommissioning. SiC has been considered in detail in the work done under the latest phase of the European SEAFP programme, and this paper reports results from that study. The activation calculations have been performed using the most recent version of the European Activation System (EASY-99). EASY-99 comprises the inventory code FISPACT-99 and the EAF-99 nuclear data libraries. The activation calculations described above are performed for particular plant designs and for particular components. A new methodology that is independent of the particular neutron spectrum involves the use of ‘importance’ diagrams. These indicate regions in the decay time/neutron energy plane where radionuclides contribute more that 50% of a radiological quantity such as activity or γ dose rate. Such diagrams have been produced for SiC containing realistic levels of impurities and show clearly which radionuclides are dominant at various neutron energies and decay times. With pathway information for each radionuclide, it is possible to determine whether the radionuclide has been produced from the base material or from impurities. Such a full study of SiC is able to indicate under what conditions in a fusion plant this material would be suitable from an activation standpoint, and indicates the acceptable impurity levels. Pure silicon carbide has excellent radiological properties at short times, but at medium-to-long times, it is inferior to other low-activation materials. The good short-term properties remain when impurities are added, so long as careful control of the amounts is exercised. 26Al is the major problem for the long-term behaviour. Irradiated SiC could not be cleared, and would probably require disposal.