Nucleonic Design for a Compact Tokamak Fusion Reactor Blanket and Shield

One of the characteristics of a compact tokamak fusion reactor such as NUWMAK is high power density (∼10 MW/m3) and thus high neutron wall loading (∼5 MW/m2). The most crucial design requirements for a tokamak fusion reactor blanket and shield are (a) adequate tritium breeding ratio (>1.10), (b) high blanket energy multiplication (≥1.2), (c) adequate magnet protection, and (d) low radioactivity. The magnet protection criterion for a compact reactor is particularly essential in the inner region of the torus close to the toroidal axis because of limited space availability for shielding. A very effective shielding material such as tungsten must be used for this purpose. The design requirements have been satisfied by the selection of blanket and shielding materials as well as their zone thicknesses and heights. The nucleonic design features of the NUWMAK are as follows. A tritium breeding ratio of 1.54 is obtained. Li62Pb38 eutectic is used as the breeding and thermal energy storage material. The total nuclear heating in the blanket and shield is ∼17.2 MeV per deuterium-tritium neutron. The performance of the superconducting magnet will be satisfactory for more than 2 yr of continuous operation through the use of a 35-cm-thick tungsten shield that extends 2.5 m above the midplane on the inboard part of the torus. The radioactivity is lowered by using a titanium alloy as the structural material and large amounts of lithium lead as the blanket material. One day after shutdown, the dose rate outside the outer shield drops below 2.6 mrem/h, and it is favorable to hands-on shift maintenance.