XQ for Releases From Area Sources

1
X/Q for Releases From Area Sources
2008 RETS-REMP and NUMUG Workshop Jim Key Key
Solutions, Inc. www.keysolutionsinc.com
2
Concerns

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

3
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

4
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

5
(No Transcript)
6
General Gaussian X/Q
Downwind Factor
Vertical Factor
Crosswind Factor
7
General Gaussian X/Q
8
?y Lateral Diffusion Coefficients
9
?zVertical Diffusion Coefficients
10
Atmospheric Stability Categories
11
Ground Level Concentration
Set z 0
12
Crosswind Integrated Concentration
13
Integral Reduces To
14
Crosswind Integrated Concentration
15
Sector Averaged Concentration

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

16
Ground Level Sector Averaged Concentration
17
Ground Level Sector Averaged Concentration
Ground Release
Set H 0
18
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
• S Stability Class
• N Wind Speed Class

19
Ground Level Sector and Time Averaged
Concentration Ground Release
20
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.

21
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).

22
Estimation of Release from Area Source

• Turner (Workbook of Atmospheric Dispersion
  Estimates, 1994)
• Select Virtual Distance - xy - based on ?yo.
• Calculate X/Q using distance of x xy.

23
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

24
Geometry for Point Source
Distance 800 m
25
Simple X/Q for Point Source

• u 0.022 m/s
• x 800 m
• ?zG 7.5 m

26
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 distance20,000 800
  20,800 m.

27
Geometry for Area Source
Point Source
Receptor
Virtual Distance 20,800 m
1600 meters
28
Simple X/Q for Area Source

• u 0.022 m/s
• x 20,800 m
• ?zG 7.5 m

29
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
30
Applying JFD Data to X/Q

• Use Average Wind Speed (Not Max Wind Speed)
• Determine ?yo for Each Stability Class
• Determine Virtual Distance (Xv) for Each
  Stability Class

31
Calculate X/Q Using
32
X/Q for Stability Class A
33
Annual Average X/Q for Receptor

• Point Source X/Q 6.4E-06
• Area Source X/Q 5.7E-07

34
Point Source vs Area SourceX/Q

• Larger Sources Expect Greater Difference
• As Distance to Receptor Increases Difference
  Slowly Decreases

35
Point Source vs Area Source
36
Point Source vs Area SourceX/Q

• For Nearby Receptors Rule of Thumb Appears to be
  X/QArea 1/10 X/Qpoint
• For Distances Out to 10,000 meters
• X/QArea 1/2 X/Qpoint