Nuclear Assessment of Shielding Configuration Options for Final Optics of HAPL Laser Fusion Power Plant

The High Average Power Laser (HAPL) power plant has targets that are directly driven by forty KrF laser beams. Three-dimensional neutronics calculations were performed directly in the exact CAD model of the HAPL final optics system to assess the impact of the biological shielding configuration on the nuclear environment at the GIMM and dielectric focusing and turning mirrors. In the initial configuration, the biological shield fully encloses the GIMM sand associated dielectric mirrors. We assessed another configuration where the shield is moved farther from the target to fully enclose the dielectric mirrors leaving the GIMM in the open space between the chamber and the biological shield. A variation of this configuration utilizes 40 neutron traps attached to the inner surface of the biological shield behind the GIMMs. It is concluded that the shielding configuration with all optics including the GIMM being fully enclosed in the biological shield is the preferred option since it results in the lowest nuclear environment at the dielectric mirrors, provides better GIMM support, reduces the volume to be maintained under vacuum, and requires the least amount of concrete shield.