CALCULATING THE SHRAPNEL GENERATION AND SUBSEQUENT DAMAGE TO FIRST WALL AND OPTICS COMPONENTS FOR THE NATIONAL-IGNITION-FACILITY

The purpose of this work is to computationally assess the threat from shrapnel generation on the National Ignition Facility (NIF) first wall , final optics, and ultimately other target chamber components. Shrapn el is defined as material that is in a solid, liquid, or clustered-vap or phase with sufficient velocity to become a threat to exposed surfac es as a consequence of its impact. Typical NIF experiments will be of two types, low neutron yield shots in which the capsule is not cryogen ically cooled, and high yield shots for which cryogenic cooling of the capsule is required. For non-cryogenic shots, shrapnel would be produ ced by spalling, melting, and vaporizing of ''shine shields'' by absor ption and shock wave loading following 1-omega and 2-omega laser radia tion. For cryogenic shots, shrapnel would be generated through shock w ave splitting, spalling, and droplet formation of the cryogenic tubes following neutron energy deposition. Motion of the shrapnel is determi ned not only by particle velocities resulting from the neutron deposit ion, but also by both x-ray and ionic debris loading arising from expl osion of the hohlraum. Material responses of different target area com ponents are computed from one-dimensional and two-dimensional stress w ave propagation codes. Well developed rate-dependent spall computation al models are used for stainless steel spall and splitting. Severe cel l distortion is accounted for in shine-shield and hohlraum-loading com putations. Resulting distributions of shrapnel particles are traced to the first wall and optics and damage is estimated for candidate mater ials. First wall and optical material damage from shrapnel includes cr ater formation and associated extended cracking.