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

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

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

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

Standard Gaussian Model

General Gaussian X/Q Downwind Factor Crosswind Factor Vertical Factor

General Gaussian X/Q

 y Lateral Diffusion Coefficients

 z Vertical Diffusion Coefficients

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

Ground Level Concentration Set z = 0

Crosswind Integrated Concentration

Integral Reduces To:

Crosswind Integrated Concentration

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

Ground Level Sector Averaged Concentration

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

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

Ground Level Sector and Time Averaged Concentration – Ground Release

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.

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).

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.

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

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

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

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, = 20,800 m.

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

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

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

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

Calculate X/Q Using:

X/Q for Stability Class A

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

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

Point Source vs Area Source

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