Master Powerpoint Briefing

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Geochemistry of Dust in the Proposed Nuclear
Waste Repository at Yucca Mountain, Nevada
2004 Annual Meeting of the Geological Society of
America Zell E. Peterman, Leonid A. Neymark, and
James B. Paces U.S. Geological Survey, Denver
CO November 7, 2004 Denver CO
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Yucca Mountain is a Ridge of Rhyolitic Tuff in
Southern Nevada (Looking South)
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ESF Tunnel (Yellow), Cross Drift (Red), and
Conceptual Emplacement Drifts (Blue)
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Construction of Underground Space Is a Dirty
Business

• Dust is the inevitable product of underground
  mining and construction
• Fine dust is a health hazard for workers in the
  underground and must be controlled thru-
• Ventilation
• Filtration
• Generation reduction by wetting at production
  sites

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Why is Dust Composition Important in a Nuclear
Waste Repository?

• Dust will accumulate on waste canisters and drip
  shields during and after emplacement
• Dust salts may dissolve in water that drips on
  canisters or deliquesce in high humidity
  environments to form brine droplets or films
• These salts or saline waters may accelerate
  corrosion of the canisters

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Sources of Underground Dust

• Mining (TBM, Alpine miner, drill and blast, muck
  haulage)
• comminution of rock including fracture minerals,
  vapor-phase minerals, alteration minerals (clays
  and zeolites)
• Particulates from diesel exhaust
• Salts from evaporated water
• Construction water (tagged with LiBr)
• Pore water migrates to tunnel walls and
  evaporates leaving a salt halo
• Abraded rubber and fiber from conveyor belts

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Sources of Underground Dust (continued)

• Aerosols from lubricating oil, diesel oil,
  grease, hydraulic fluids, etc.
• Ferrous metals from variety of sources
• Concrete particles from emplacement and abrasion
  of inverts
• Salts from human effluents
• Dust from the surface transported into the
  Exploratory Studies Facility (ESF) on materials
  and by the supply air

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Dust Collection

• Dust was vacuumed from the tunnel wall, trapped
  by a cyclone, and deposited in a 250 mL sample
  bottle attached to the cyclone
• Several square meters of surface were vacuumed to
  yield 200 to 400 grams of dust

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Methods

• Chemistry of bulk dust size fractions by standard
  rock analysis methods (XRF, ICPMS, gravimetric,
  titration, combustion)
• Chemistry of leachates by ion chromatography and
  ICPMS
• Mineralogy of soluble salt fraction
• Scanning electron microscope (SEM)
• XRD analyses of evaporated leachates
• Calculation of normative minerals using SALT NORM
  (Bodine and Jones, 1986)

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Particle Size Distribution of ESF Dust (shown in
mesh size)
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Major and Minor Elements in Dust Size Fractions
Relative to Host Rock
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Trace Elements in Dust Size FractionsRelative to
Host Rock
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Major and Trace Element Enrichments in Dust
Relative to Rhyolite

• Major Elements
• FeO (introduced as metallic iron), CO2 (from
  calcite veins) , Organic C and Cl (neoprene
  abraded from conveyor belt etc.), and Cl (from
  water)
• Trace Elements
• Bi, Cd, Co, Cr, Mo, Ni, Sb, V, Zn (metallic
  elements associated with construction and
  materials introduced during construction)

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Soluble Fractions of Surface and Underground Dust

• Underground dust contains a small amount of
  soluble salts
• Dust in main tunnel contains 0.370.18 (1 s)
  weight percent (n66)
• Dust in cross drift contains 0.170.17 (1 s)
  weight percent (n18)
• Surface dust contains a much larger amount of
  soluble salts (Reheis, 2003)
• Atmospheric dust collected at and near Yucca
  Mountain contains 13.38.1 (1 s) weight percent
  (n51)

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Identification of Salt Minerals in Underground
Dust

• SEM examination for S and Cl in dust mounts
• halite, sylvite, gypsum, natroaulnite (also
  pyrite, molybdenite, native sulfur identified)
• No CaCl2 was identified
• XRD analyses of dried leachates
• halite, sylvite, calcite, gypsum, and bassanite
  (2CaSO4H2O)
• salammoniac NH4Cl
• mascagnite (NH4)SO4
• biphosphammite (NH4,K)H2PO4
• weddellite CaC2O42H2O

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Identification of Salt Minerals in Underground
Dust (contd)

• Estimation of soluble minerals from water
  leachates using SALT NORM (Bodine and Jones,
  1986)
• Carbonates (calcite, dolomite, pirsonnite)
• Nitrates (niter, soda niter, ammonia niter)
• Sulfates (glauberite, aphthitalite, thenardite,
  anhydrite, syngenite, mascagnite)
• Chlorides (halite, sylvite, salammoniac)
• Fluorides (fluorite, villiaumite)
• Phosphates (fluorapatite, hydroxyapatite,
  wagnerite)

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Salt Minerals Expected from Atmospheric Dust
Intrusion into Repository (Chemistry from NADP
Red Rocks Site Minerals from SALT NORM)
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Salt Minerals Expected from Atmospheric Dust
Intrusion into Repository
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Nitrate-Chloride Ratios

• Ratio of soluble nitrate-to-chloride is an
  important parameter for corrosion
• Critical weight ratio (NO3/Cl) is approximately
  0.9
• Soluble salts in dust typically have NO3/Cl
  ratios greater than 0.9
• Pore waters typically have NO3/Cl ratios less
  than 0.9

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Nitrate-to-Chloride Weight Ratios in Dust Salts
and Pore water
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Conclusions

• Most of the underground dust is finely comminuted
  rhyolite
• Fine silicate particulates will neutralize acids
  formed in the near-field environment (D.
  Langmuir, 2004)
• Soluble salts are more relevant to corrosion
  issue
• Soluble salts average less than 1 percent of the
  underground dust
• Atmospheric dust contains much larger amounts of
  soluble salts (average13.3 weight percent)
• Nitrate-chloride ratios of both underground and
  atmospheric dust are favorable (greater than 0.9)
• No CaCl2 was identified (none expected)