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 f uture source of fusion energy. The compactness of the LAR machine impo ses 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 ope rates 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 e xtended period of time. The analysis indicated that the lifetime of th e CP is limited by the Class C low level waste disposal requirements. Identification of potential radioactive waste problems for the Cu cond uctor has resulted in either limiting the lifetime of the unshielded C P to 0.12 FPY (corresponding to a fluence of 0.3 MWy/m(2)) of shieldin g 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 radwast e and replacement cost, increase the system availability, and alleviat e most of the CP radiation damage problems. We have assessed the effec ts of neutron fluence on conductor resistivity, swelling, and atomic d isplacement. 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 allo ys experience hardening and loss of ductility under neutron irradiatio n.