Waste management aspect of low activation materials

Waste management aspect of candidate low activation materials, namely vanad ium alloy and reduced-activation ferritic steel (RAFS), was examined using two blankets constructed with these materials. One of these two blanket con cepts is a lithium self-cooled vanadium alloy blanket. The other is a heliu m-cooled, Pb83Li17 breeder ferritic steel blanket. The objective of this st udy is to identify the most critical alloying elements and impurities, and to establish the respective allowable concentration limits. This can help t he materials development program to focus the effort on the control of thes e identified elements. Neat-surface burial disposal (10CFR61 Class C waste) and materials recycling are promising scenarios for the waste management o f fusion reactor materials. Hands-on materials recycling is a more demandin g scenario. Extending the cooling time can help to facilitate the materials recycling. Cooling times of 175 and 130 years, respectively, are required for the reduced activation ferritic steel and vanadium alloy (V-4Cr-4Ti) to allow hands-on recycling after 20 MW-y/m(2) service in the power reactor. They are needed to reduce the activities induced in W and Ti, respectively, to less than 10 mu Sv/h gamma dose rate. The best presently available comm ercial and improved intermediate RAFS and V --4Cr-4 Ti may qualify as 10CFR 61 Class C near-surface burial waste. But they are not yet for hands-on rec ycling due to the high levels of impurities such Ag, Al, Ho, Nb, and Tb. Th e predicted ultimate RAFS and V-4Cr-3Ti will have satisfactory levels for h ands-on recycling in Nb ( < 0.05 wppm) and Tb (<0.02 wppm). But further dev elopment in the ultimate high purity alloys is still needed to meet the con centration requirements for Ag ( < 0.03 wppm), Al (70 wppm), and Ho (< 0.03 wppm). (C) 2000 Elsevier Science S.A. All rights reserved.