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Published byElyssa Alcott Modified about 1 year ago

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X/Q for Releases From Area Sources 2008 RETS-REMP and NUMUG Workshop Jim Key Key Solutions, Inc. www.keysolutionsinc.com

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Concerns Industry Tritium Issues Have Revealed Many Unanalyzed Dose Pathways –Storm Drains –Ground Water –Service Water –Discharge Basins or Lakes With Little Water Turnover

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Evaporation From Area Sources Has Been Mostly Ignored Tritium Concentrations in Bodies of Water Can Continue to Build Up Release from Such Sources are Estimated to be 10 Ci/yr and Higher

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Application of Gaussian Model to Release from Area Sources Simplify Gaussian Model As Follows –Ground Level Release –Ground Level Receptor Modify From Point Source Geometry to Square Area Geometry

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Standard Gaussian Model

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General Gaussian X/Q Downwind Factor Crosswind Factor Vertical Factor

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General Gaussian X/Q

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y Lateral Diffusion Coefficients

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z Vertical Diffusion Coefficients

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Atmospheric Stability Categories Stability CategoryConditionDescription Lapse Rate AExtremely UnstableSunny Summer Weather-1.9 BModerately StableSunny and Warm-1.9 to –1.7 CSlightly UnstableAverage Day-1.7 to –1.5 DNeutralOvercast Day or Night-1.5 to –0.5 ESlightly StableAverage Night-0.5 to 1.5 FModerately StableClear Night1.5 to 4.0 GHighly StableAdded by NRC> 4.0

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Ground Level Concentration Set z = 0

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Crosswind Integrated Concentration

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Integral Reduces To:

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Crosswind Integrated Concentration

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Sector Averaged Concentration Wind Directions in Each Sector are Distributed Randomly Over Period of Interest Divide Crosswind-Integrated Concentration by Sector Arc Length

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Ground Level Sector Averaged Concentration

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Ground Level Sector Averaged Concentration – Ground Release Set H = 0

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Time-Averaged Concentration Wind Directions in Each Sector are Distributed Randomly Over Period of Interest Calculate X/Q Using Joint Frequency Distribution: f( ,S,N) – Direction –SStability Class –NWind Speed Class

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Ground Level Sector and Time Averaged Concentration – Ground Release

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Estimation of Release from Area Source Assume Point Source at Center of Release –Very Conservative –Does not consider that source is initially distributed over large surface area.

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Estimation of Release from Area Source Turner (Workbook of Atmospheric Dispersion Estimates, 1994) –Treat area source as having initial horizontal standard deviation - yo - related to area width. –Horizontal standard deviation for square source is approximated by L/4.3 (L= Length of a side of the area).

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Estimation of Release from Area Source Turner (Workbook of Atmospheric Dispersion Estimates, 1994) –Select “Virtual Distance” - x y - based on yo. –Calculate X/Q using distance of x + x y.

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Simple Case Calculate X/Q Assuming –Ground Level Release –Emission Source is One Mile Square –Receptor is Due West ½ Mile from Center of Source (i.e. at Boundary) –Assume Worst Case Met Conditions Extremely Stabile (Class G) Calm Conditions (0.04 m/s) Least Dispersion

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Geometry for Point Source 1600 meters Receptor Point Source Distance – 800 m

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Simple X/Q for Point Source u = 0.022 m/s x = 800 m zG = 7.5 m

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Simple X/Q for Area Source Calculate yo based on 1 mile side –1600 meters/4.3 = 372 m From y table/plot look up distance corresponding to yo for stability class of interest. –20000 m Calculate X/Q for virtual distance: 20,000 + 800 = 20,800 m.

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Geometry for Area Source 1600 meters Receptor Point Source Virtual Distance – 20,800 m

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Simple X/Q for Area Source u = 0.022 m/s x = 20,800 m zG = 7.5 m

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Applying JFD Data to X/Q XOQDOQ Provides Summary of JFD Data by Stability Class, Sector and Wind Speed JFD for Receptor in West Sector

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Applying JFD Data to X/Q Use Average Wind Speed (Not Max Wind Speed) Determine yo for Each Stability Class Determine Virtual Distance (X v ) for Each Stability Class

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Calculate X/Q Using:

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X/Q for Stability Class A

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Annual Average X/Q for Receptor Point Source X/Q = 6.4E-06 Area Source X/Q = 5.7E-07

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Point Source vs Area Source X/Q Larger Sources – Expect Greater Difference As Distance to Receptor Increases Difference Slowly Decreases

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Point Source vs Area Source

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Point Source vs Area Source X/Q For Nearby Receptors Rule of Thumb Appears to be X/Q Area ~ 1/10 X/Q point For Distances Out to 10,000 meters X/Q Area ~ 1/2 X/Q point

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