Importance of shield design in minimizing radioactive-material inventory in tokamaks

An optimization study is carried out for the outboard bulk shielding of the STARFIRE reactor. The optimization criteria used include: (1) reactor accessibility shortly after shutdown; (2) minimization of high-level long-term induced activation; and (3) radiation protection of reactor components. It is shown that with a 1.1 m-thick shield, the biological dose inside the reactor room decreases to approx. 1.5 mrem/h within 24 h after shutdown. It is also shown that more than 90% of the total mass of the radioactive material inventory in STARFIRE has a high potential for recycling within 30 to 50 yr after component replacement or reactor decommissioning