Initial nuclear assessment for a low aspect ratio power plant

Recent interest in the low aspect ratio (LAR) concept has led the U.S. ARIES team to examine the credibility of this advanced concept as a future source of fusion energy. The compactness of the LAR machine imposes severe constraints on the Cu center post (CP) which thus plays an important role in the design. In view of the fact that the machine operates for 40 y with a relatively high neutron wall loading of 4 MW/m(2), the CP will be operating in a severe radiation environment for an extended period of time. The analysis indicated that the lifetime of the CP is limited by the Class C low level waste disposal requirements. Identification of potential radioactive waste problems for the Cu conductor has resulted in either limiting the lifetime of the unshielded CP to 0.12 FPY (corresponding to a fluence of 0.3 MWy/m(2)) of shielding the CP with 20-30 cm of shield. Since it is not feasible to replace hundreds of tonnes of Cu every 2 months, the CP should be shielded to prolong the lifetime to 4 years or more, reduce the cumulative radwaste and replacement cost, increase the system availability, and alleviate most of the CP radiation damage problems. We have assessed the effects of neutron fluence on conductor resistivity, swelling, and atomic displacement. Even though the radiation-induced swelling and changes to Cu resistivity due to transmutations are small at 0.3 MWy/m(2), there is serious concern about the degradation of properties as all Cu alloys experience hardening and loss of ductility under neutron irradiation.