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Title: Assessment of personal airborne exposures and surface contamination from x-ray vaporization of beryllium targets at the National Ignition Facility

Abstract

Here, this article presents air and surface sampling data collected over the first two years since beryllium was introduced as a target material at the National Ignition Facility. Over this time, 101 experiments with beryllium-containing targets were executed. The data provides an assessment of current conditions in the facility and a baseline for future impacts as new, reduced regulatory limits for beryllium are being proposed by both the Occupational Safety and Health Administration and Department of Energy. This study also investigates how beryllium deposits onto exposed surfaces as a result of x-ray vaporization and the effectiveness of simple decontamination measures in reducing the amount of removable beryllium from a surface. Based on 1,961 surface wipe samples collected from entrant components (equipment directly exposed to target debris) and their surrounding work areas during routine reconfiguration activities, only one result was above the beryllium release limit of 0.2 µg/100 cm 2 and 27 results were above the analytical reporting limit of 0.01 µg/100 cm 2, for a beryllium detection rate of 1.4%. Surface wipe samples collected from the internal walls of the NIF target chamber, however, showed higher levels of beryllium, with beryllium detected on 73% and 87% of the samples duringmore » the first and second target chamber entries (performed annually), respectively, with 23% of the samples above the beryllium release limit during the second target chamber entry. The analysis of a target chamber wall panel exposed during the first 30 beryllium-containing experiments (cumulatively) indicated that 87% of the beryllium contamination remains fixed onto the surface after wet wiping the surface and 92% of the non-fixed contamination was removed by decontaminating the surface using a dry wipe followed by a wet wipe. Personal airborne exposures assessed during access to entrant components and during target chamber entry indicated that airborne beryllium was not present in workers' breathing zones. Finally, all the data thus far have shown that beryllium has been effectively managed to prevent exposures to workers during routine and non-routine work.« less

Authors:
 [1];  [2];  [2]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). ES&H Directorate
  2. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). National Ignition Facility
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1357402
Report Number(s):
LLNL-JRNL-704038
Journal ID: ISSN 1545-9624
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Journal of Occupational and Environmental Hygiene
Additional Journal Information:
Journal Volume: 14; Journal Issue: 6; Journal ID: ISSN 1545-9624
Publisher:
Taylor and Francis
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; 54 ENVIRONMENTAL SCIENCES; Beryllium; decontamination wiping; exposure assessment; National Ignition Facility; x-ray vaporization; surface contamination

Citation Formats

Paik, Samuel Y., Epperson, Patrick M., and Kasper, Kenneth M.. Assessment of personal airborne exposures and surface contamination from x-ray vaporization of beryllium targets at the National Ignition Facility. United States: N. p., 2017. Web. doi:10.1080/15459624.2017.1285495.
Paik, Samuel Y., Epperson, Patrick M., & Kasper, Kenneth M.. Assessment of personal airborne exposures and surface contamination from x-ray vaporization of beryllium targets at the National Ignition Facility. United States. doi:10.1080/15459624.2017.1285495.
Paik, Samuel Y., Epperson, Patrick M., and Kasper, Kenneth M.. Tue . "Assessment of personal airborne exposures and surface contamination from x-ray vaporization of beryllium targets at the National Ignition Facility". United States. doi:10.1080/15459624.2017.1285495. https://www.osti.gov/servlets/purl/1357402.
@article{osti_1357402,
title = {Assessment of personal airborne exposures and surface contamination from x-ray vaporization of beryllium targets at the National Ignition Facility},
author = {Paik, Samuel Y. and Epperson, Patrick M. and Kasper, Kenneth M.},
abstractNote = {Here, this article presents air and surface sampling data collected over the first two years since beryllium was introduced as a target material at the National Ignition Facility. Over this time, 101 experiments with beryllium-containing targets were executed. The data provides an assessment of current conditions in the facility and a baseline for future impacts as new, reduced regulatory limits for beryllium are being proposed by both the Occupational Safety and Health Administration and Department of Energy. This study also investigates how beryllium deposits onto exposed surfaces as a result of x-ray vaporization and the effectiveness of simple decontamination measures in reducing the amount of removable beryllium from a surface. Based on 1,961 surface wipe samples collected from entrant components (equipment directly exposed to target debris) and their surrounding work areas during routine reconfiguration activities, only one result was above the beryllium release limit of 0.2 µg/100 cm2 and 27 results were above the analytical reporting limit of 0.01 µg/100 cm2, for a beryllium detection rate of 1.4%. Surface wipe samples collected from the internal walls of the NIF target chamber, however, showed higher levels of beryllium, with beryllium detected on 73% and 87% of the samples during the first and second target chamber entries (performed annually), respectively, with 23% of the samples above the beryllium release limit during the second target chamber entry. The analysis of a target chamber wall panel exposed during the first 30 beryllium-containing experiments (cumulatively) indicated that 87% of the beryllium contamination remains fixed onto the surface after wet wiping the surface and 92% of the non-fixed contamination was removed by decontaminating the surface using a dry wipe followed by a wet wipe. Personal airborne exposures assessed during access to entrant components and during target chamber entry indicated that airborne beryllium was not present in workers' breathing zones. Finally, all the data thus far have shown that beryllium has been effectively managed to prevent exposures to workers during routine and non-routine work.},
doi = {10.1080/15459624.2017.1285495},
journal = {Journal of Occupational and Environmental Hygiene},
number = 6,
volume = 14,
place = {United States},
year = {Tue Feb 28 00:00:00 EST 2017},
month = {Tue Feb 28 00:00:00 EST 2017}
}

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  • The emission of x rays and debris ions by the National Ignition Facility direct and indirect targets are compared in this paper. In the indirect drive targets, the fuel capsule is surrounded by a gold case, which filters out all but the hardest x rays from the capsule and collides with the capsule debris, generating large amounts of colder x rays that leave the target through laser entrance holes. The direct drive targets have no such case, so the debris and x rays from the capsule are un-obscured. Computer simulations of both targets demonstrate these differences. 8 refs., 5 figs.,more » 2 tabs.« less
  • We have performed a series of 1-D numerical simulations of the x-ray emission from National Ignition Facility (NIF) targets. Results are presented in terms of total x-ray energy, pulse length, and spectrum. Scaling of x-ray emissions is presented for variations in both target yield and hohlraum wall thickness. Experiments conducted on the Nova facility provide some validation of the computational tools and methods. 6 refs., 6 figs., 2 tabs.
  • Tailored, high-flux, multi-keV x-ray sources are desirable for studying x-ray interactions with matter for various civilian, space and military applications. For this study, we focus on designing an efficient laser-driven non-local thermodynamic equilibrium 3–5 keV x-ray source from photon-energy-matched Ar K-shell and Ag L-shell targets at sub-critical densities (∼n{sub c}/10) to ensure supersonic, volumetric laser heating with minimal losses to kinetic energy, thermal x rays and laser-plasma instabilities. Using HYDRA, a multi-dimensional, arbitrary Lagrangian-Eulerian, radiation-hydrodynamics code, we performed a parameter study by varying initial target density and laser parameters for each material using conditions readily achievable on the National Ignition Facilitymore » (NIF) laser. We employ a model, benchmarked against Kr data collected on the NIF, that uses flux-limited Lee-More thermal conductivity and multi-group implicit Monte-Carlo photonics with non-local thermodynamic equilibrium, detailed super-configuration accounting opacities from CRETIN, an atomic-kinetics code. While the highest power laser configurations produced the largest x-ray yields, we report that the peak simulated laser to 3–5 keV x-ray conversion efficiencies of 17.7% and 36.4% for Ar and Ag, respectively, occurred at lower powers between ∼100–150 TW. For identical initial target densities and laser illumination, the Ag L-shell is observed to have ≳10× higher emissivity per ion per deposited laser energy than the Ar K-shell. Although such low-density Ag targets have not yet been demonstrated, simulations of targets fabricated using atomic layer deposition of Ag on silica aerogels (∼20% by atomic fraction) suggest similar performance to atomically pure metal foams and that either fabrication technique may be worth pursuing for an efficient 3–5 keV x-ray source on NIF.« less
  • Here, indirect drive experiments at the National Ignition Facility are designed to achieve fusion by imploding a fuel capsule with x rays from a laser-driven hohlraum. Previous experiments have been unable to determine whether a deficit in measured ablator implosion velocity relative to simulations is due to inadequate models of the hohlraum or ablator physics. ViewFactor experiments allow for the first time a direct measure of the x-ray drive from the capsule point of view. The experiments show a 15%–25% deficit relative to simulations and thus explain nearly all of the disagreement with the velocity data. In addition, the datamore » from this open geometry provide much greater constraints on a predictive model of laser-driven hohlraum performance than the nominal ignition target.« less