The Effect of Liquid-Metal Protection Schemes in Inertial Confinement Fusion Reactors

The placement of liquid metals (lithium, lead, and a Pb-Li eutectic Pb₄Li) between the first wall and the source of neutrons has been considered as a mechanism for extending first wall lifetimes in inertial confinement fusion reactors. This scheme is called the Internal Spectral Shifter and Energy Converter (ISSEC). All three liquid metals have been shown to reduce the radiation damage in the Type 316 stainless-steel structural first wall and thus increase the first wall lifetime. On a per-unit thickness basis, a Pb₄Li ISSEC is most effective, followed by lead and lithium in decreasing order. If the first wall is operating at 300°C, it is estimated that ∼50 cm of liquid lithium or liquid lead, or ∼40 cm of liquid Pb₄Li zone will give enough protection to the Type 316 stainless-steel first structural wall so that it may last for 30 yr at a nominal 5 MW/m² wall loading and 70% plant factor. If the wall is operating at 500°C, ∼85 cm of lithium, 50 cm of lead, or 40 cm of Pb₄Li is needed, and at 600°C the required ISSEC thickness goes up to ∼2 m for lithium, ∼70 cm for lead, and 65 cm for Pb₄Li. The lead and Pb₄Li ISSECs increase the total energy multiplication in the reactor, while the lithium ISSEC keeps it about constant. It has been shown that the liquid ISSECs could produce in the first wall a primary knock-on atom spectrum, as well as a gas production to displacement damage ratio, close to that found in fast or thermal fission test reactors, thus allowing more confidence in applying data from current systems to future fusion devices. An overall conclusion of the study is that the Pb-Li eutectic ISSEC has better characteristics than both pure lead and lithium ISSECs, and for best results it should be used at thicknesses ranging from 45 to 65 cm.