Construction of the world's most powerful laser, the National Ignition Facility (NIF), will soon begin at the Lawrence Livermore National Laboratory. During peak operations, the NIF will conduct as many as 600 experiments per year and attain fusion yields as high as 1200 MJ/year producing 4.3 x10²⁰ 14 MeV neutrons. To ensure the safe operation of the NIF with high neutron yields, several radiological design limits were set forth in the NIF Preliminary Safety Analysis Report (PSAR). These include limiting the annual prompt dose in occupied areas of the facility to 30 mrem/year, limiting the annual prompt dose to 50 mrem/year outside the facility, limiting the annual dose at the nearest site boundary to 0.1 mrem/year, and limiting the annual occupational dose to 10 personÐrem/year.

To prevent unnecessary exposure of personnel and the public to radiation, the NIF Target Bay and Switchyards will make use of thick concrete shields, but these shields will contain many penetrations for beamlines, utilities, and personnel access. Detailed, three-dimensional Monte Carlo modeling of the NIF geometry has been completed to ensure that the PSAR radiological design limits will be met. This modeling has considered many different design features and modifications that have been made as the Title I and Title II designs have progressed. The effects of penetration size and location as well as wall and roof thicknesses within the NIF Target Bay and Switchyards have been investigated. The effects of using an approximate model for the 48 beam penetrations within the target chamber have also been determined and incorporated into our analyses.

Annual prompt doses have been calculated for many different locations inside and outside the facility, and the annual dose at the nearest site boundary has been scaled from previous results. These doses all meet the radiological design limits for annual prompt doses. Of the 10 personÐrem/year limit for occupational doses, only 0.5 personÐrem/year will be due to prompt doses received by workers within the NIF.

* Work performed under the auspices of the U. S. Department of Energy by Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.