Waste management aspect of low activation materials

AbstractWaste management aspect of candidate low activation materials, namely vanadium alloy and reduced-activation ferritic steel (RAFS), was examined using two blankets constructed with these materials. One of these two blanket concepts is a lithium self-cooled vanadium alloy blanket. The other is a helium-cooled, Pb83Li17 breeder ferritic steel blanket. The objective of this study is to identify the most critical alloying elements and impurities, and to establish the respective allowable concentration limits. This can help the materials development program to focus the effort on the control of these identified elements. Near-surface burial disposal (10CFR61 Class C waste) and materials recycling are promising scenarios for the waste management of fusion reactor materials. Hands-on materials recycling is a more demanding 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/m2 service in the power reactor. They are needed to reduce the activities induced in W and Ti, respectively, to less than 10 μSv/h gamma dose rate. The best presently available commercial and improved intermediate RAFS and V–4Cr–4Ti may qualify as 10CFR61 Class C near-surface burial waste. But they are not yet for hands-on recycling due to the high levels of impurities such Ag, Al, Ho, Nb, and Tb. The predicted ultimate RAFS and V–4Cr–4Ti will have satisfactory levels for hands-on recycling in Nb (<0.05 wppm) and Tb (<0.02 wppm). But further development in the ultimate high purity alloys is still needed to meet the concentration requirements for Ag (<0.03 wppm), Al (70 wppm), and Ho (<0.03 wppm).