Simulation of the Post-Shot Radiation Environment in the National Ignition Facility

Journal Article · Fri Jun 29 00:00:00 EDT 2018 · Fusion Science and Technology

DOI:https://doi.org/10.1080/15361055.2018.1471961· OSTI ID:1557056

Khater, Hesham ^[1]; Brereton, Sandra ^[1]; Dauffy, Lucile ^[1]; Hall, Jim ^[1]; Hansen, Luisa ^[1]; Kim, Soon ^[1]; Pohl, Bertram ^[1]; Sitaraman, Shiva ^[1]; Verbeke, Jerome ^[1]; Young, Mitchell ^[1]

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1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

The National Ignition Facility at Lawrence Livermore National Laboratory is the world’s biggest and most energetic laser system for inertial confinement fusion. The NIF is designed to perform shots with varying fusion yield (up to 20 MJ or 7.1 × 10¹⁸ neutrons per shot). A great number of diagnostic instruments are present inside the target chamber (TC) and target bay (TB) during shots. The gamma dose rates due to neutron activation are estimated at various decay times following the high-yield (20-MJ) shots. Several components, like the snout assemblies of the diagnostic instrument manipulators and target positioners are inserted inside the TC, close to the target during the shot. These components represent major sources of gamma decay after retraction outside the TC. Five days after a 20-MJ shot, dose rates near the highly activated (retracted) parts are on the order of 1 mSv/h and dose rates within the TB outside the TC but at distance from the retracted components drop to about 50 to 70 μSv/h. The dose is dominated by decay of ²⁴Na (T_1/2 = 14.95 h) and waiting for two additional days drops the dose rates significantly. Seven days following a 20-MJ shot, dose rates in the immediate vicinity of the retracted components drop to <0.2 mSv/h and the general ambient dose rates within the TB (away from retracted components) near the TC drop to <10 μSv/h. Dose rates at much larger distances from the TC (near TB wall) are an order of magnitude lower. Detailed radiation transport simulations are performed to create detailed dose rate maps for all floors inside the TB. The maps are used to measure worker stay-out times following shots before entry is permitted into the TB.

• Research Organization: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• Grant/Contract Number: AC52-07NA27344
• OSTI ID: 1557056
• Report Number(s): LLNL-JRNL-746277; 930635
• Journal Information: Fusion Science and Technology, Vol. 74, Issue 4; ISSN 1536-1055
• Publisher: American Nuclear Society
• Country of Publication: United States
• Language: English

Related Subjects

61 RADIATION PROTECTION AND DOSIMETRY
National Ignition Facility
post-shot dose
neutronics
Monte Carlo