Impact of Target-Material Activation on Personnel Exposure and Radioactive Contamination in the National Ignition Facility

Detailed activation analyses are performed for the different materials under consideration for use in the target capsules and hohlraums during the ignition campaign of the National Ignition Facility (NIF). Results of the target-material activation are additionally used to estimate the levels of contamination within the NIF Target Chamber (TC) and the workplace controls that are necessary for safe operation. The analysis examined the impact of using Be-Cu and Ge-doped hydrocarbon capsules on the external dose received by workers during maintenance activities. Five days following a 20-MJ shot, dose rates inside the TC due to the two proposed capsule materials are small (~ 0.01 ¿Sv/h). Gold and depleted uranium (DU) are considered as potential hohlraum materials. Following a shot, gold will be deposited on the TC first wall. On the other hand, while noble-gas precursors from the DU are expected to stay in the TC, most of the noble gases are pumped out of the chamber and end up on the cryopumps. The dose rates inside the TC due to activated gold or DU, at five days following a 20-MJ shot, are about 10 ¿Sv/h. Dose rates in the vicinity of the cryopumps (containing noble ¿fission¿ gases) drop off to about 10 ¿Sv/h during the first 12 h following the shot. Contamination from activation of NIF targets will result in levels in the NIF TC above U.S. Department of Energy surface contamination limits. Objects removed from the TC will need to be managed as radioactive material. However, the results suggest that airborne contamination from resuspension of surface contamination will not be significant and is at levels that can be readily managed by negative ventilation when accessing the TC attachments.