Comparison of the AEOLUS3 Atmospheric Dispersion Computer Code with NRC Codes PAVAN and XOQDOQ 13th...

Comparison of the AEOLUS3 Atmospheric Dispersion Computer Code with NRC Codes PAVAN and XOQDOQ

13th NUMUG Conference, October 2009, San Francisco, CA

Theodore A. MessierPrincipal Scientist

Comparison of the AEOLUS3 Atmospheric Dispersion Code with NRC Codes PAVAN and XOQDOQ. – October 2009 - p.3

AEOLUS3

The AEOLUS3 computer code is licensed for use by AREVA NP from ENTECH Engineering (www.entechengineering.com)

AEOLUS3 implements the guidance in U.S. Nuclear Regulatory Commission (NRC) Regulatory Guides 1.145 and 1.111

AEOLUS3 results can be found in submittals to the NRC from operating nuclear plants

AEOLUS3 was used by AREVA for four COLA’s

PAVAN and XOQDOQ

PAVAN implements the guidance in U.S. Nuclear Regulatory Commission (NRC) Regulatory Guide 1.145

XOQDOQ implements the guidance in U.S. Nuclear Regulatory Commission (NRC) Regulatory Guide 1.111

Comparison Methodology

The computer codes were run using the same input information (plant-specific input as well as site-specific meteorological data)

Five meteorological data sets were used

AEOLUS3 was set to use NRC sigma methodology

A ground level accidental release was modeled using AEOLUS3 and PAVAN

A ground level, an elevated, and a mixed mode normal effluent release were modeled using AEOLUS3 and XOQDOQ

Accident Atmospheric Dispersion Results – Site 1

1.000E-04

1.000E-03

1 10 100 1000

Time (hours)

AEOLUS3

Figure 1: Accident X/Q Comparison, EAB Maximum of Sector Values, Site 1

Figure 2: Accident X/Q Comparison, LPZ Maximum of Sector Values, Site 1

1.000E-05

1.000E-04

1.000E-03

1 10 100 1000

Time (hours)

AEOLUS3

1.000E-05

1.000E-04

1.000E-03

1.000E-02

1 10 100 1000

Time (hours)

AEOLUS3

1.000E-06

1.000E-05

1.000E-04

1.000E-03

1 10 100 1000

Time (hours)

AEOLUS3

1.000E-05

1.000E-04

1.000E-03

1.000E-02

1 10 100 1000

Time (hours)

AEOLUS3

1.000E-06

1.000E-05

1.000E-04

1.000E-03

1 10 100 1000

Time (hours)

AEOLUS3

1.000E-05

1.000E-04

1.000E-03

1 10 100 1000

Time (hours)

AEOLUS3

1.000E-06

1.000E-05

1.000E-04

1.000E-03

1 10 100 1000

Time (hours)

AEOLUS3

Accident Atmospheric Dispersion Results

Results are within a factor of 1.4 on average (AEOLUS3/PAVAN)

Within a factor of 2.8 at most

AEOLUS3 results are more conservative in almost all cases

Normal Effluent Atmospheric Dispersion Results

Ground Level Release – Site 1

Figure 9: Normal Effluent X/Q Comparison, Ground Level Release, Maximum Sector Values, Site 1

1.000E-08

1.000E-07

1.000E-06

1.000E-05

1.000E-04

1.000E-03

100 1000 10000 100000

Downwind Distance (meters)

AEOLUS3

XOQDOQ

1.000E-08

1.000E-07

1.000E-06

1.000E-05

100 1000 10000 100000

AEOLUS3

XOQDOQ

1.000E-08

1.000E-07

1.000E-06

1.000E-05

1.000E-04

100 1000 10000 100000

AEOLUS3

XOQDOQ

1.000E-08

1.000E-07

1.000E-06

1.000E-05

1.000E-04

100 1000 10000 100000

AEOLUS3

XOQDOQ

Normal Effluent Ground Level Release Atmospheric Dispersion Results

Results are within a factor of 0.9 on average (AEOLUS3/XOQDOQ)

Elevated Release, No Terrain or RCF – Site 5

Figure 13: Normal Effluent X/Q Comparison, Elevated Release, Maximum Sector, Site 5

1.000E-08

1.000E-07

100 1000 10000

AEOLUS3

XOQDOQ

Elevated Release, RCF Included – Site 5

Figure 14: Normal Effluent X/Q Comparison, Elevated Release with RCF, Maximum Sector, Site 5

1.000E-08

1.000E-07

1.000E-06

100 1000 10000

AEOLUS3

XOQDOQ

Elevated Release, Terrain Included – Site 5

Figure 15: Normal Effluent X/Q Comparison, Elevated Release with Terrain, Maximum Sector, Site 5

1.000E-08

1.000E-07

1.000E-06

100 1000 10000

AEOLUS3

XOQDOQ

* Note: Maximum values are not in same sector

1.000E-09

1.000E-08

1.000E-07

1.000E-06

1.000E-05

100 1000 10000 100000

Downwind Distance (miles)

AEOLUS3

XOQDOQ

1.000E-09

1.000E-08

1.000E-07

100 1000 10000 100000

AEOLUS3

XOQDOQ

1.000E-09

1.000E-08

1.000E-07

100 1000 10000 100000

AEOLUS3

XOQDOQ

Normal Effluent Elevated Release Atmospheric Dispersion Results

Effect of Terrain and Recirculation Correction on Normal Effluent Elevated

Release Atmospheric Dispersion

Figure 19: Effect of Terrain and Recirculation Correction on Model Comparison of Elevated Releases

0 1 2 3 4 5 6

Terrain

Neither

1.0 = perfect match

Average0.960.971.00

Normal Effluent Atmospheric Dispersion Results Mixed Mode Release, No Terrain

or RCF – Site 1

Figure 20: Normal Effluent X/Q Comparison, Mixed Mode Release, Maximum Values, Site 1

1.000E-09

1.000E-08

1.000E-07

1.000E-06

1.000E-05

100 1000 10000 100000

AEOLUS3

XOQDOQ

Normal Effluent Atmospheric Dispersion Results Mixed Mode Release, Terrain

Included – Site 1

Figure 21: Normal Effluent X/Q Comparison, Mixed Mode Release with Terrain, Maximum Values, Site 1

1.000E-08

1.000E-07

1.000E-06

1.000E-05

1.000E-04

100 1000 10000 100000

AEOLUS3

XOQDOQ

Included – Site 1

Figure 22: Normal Effluent X/Q Comparison, Mixed Mode Release with “Matching” Terrain, Maximum Values, Site 1

1.000E-08

1.000E-07

1.000E-06

1.000E-05

1.000E-04

100 1000 10000 100000

AEOLUS3

XOQDOQ

Included – Site 1

Figure 23: Normal Effluent X/Q Comparison, Mixed Mode Release with “Bounding” Terrain, Maximum Values, Site 1

1.000E-08

1.000E-07

1.000E-06

1.000E-05

1.000E-04

100 1000 10000 100000

AEOLUS3

XOQDOQ

or RCF – Site 4

Figure 24: Normal Effluent X/Q Comparison, Mixed Mode Release with No Terrain or RCF, Maximum Values, Site 4

1.000E-09

1.000E-08

1.000E-07

1.000E-06

1.000E-05

100 1000 10000 100000

AEOLUS3

XOQDOQ

or RCF – Site 3

1.000E-09

1.000E-08

1.000E-07

1.000E-06

1.000E-05

100 1000 10000 100000

AEOLUS3

XOQDOQ

or RCF – Site 2

1.000E-09

1.000E-08

1.000E-07

1.000E-06

1.000E-05

100 1000 10000 100000

AEOLUS3

XOQDOQ

Normal Effluent Mixed Mode Release Atmospheric Dispersion Results

AEOLUS3 produced more conservative results within the first 7,000 to first 15,000 meters (4.3 to 9.3 miles) downwind

XOQDOQ produced more conservative results further downwind

Effect of Terrain on Normal Effluent Mixed Mode Release Atmospheric

Dispersion

Figure 27: Effect of Terrain on Model Comparison of Mixed Mode Releases

0 1 2 3 4 5 6

Downwind Prediction Point

Matching

Not Matching

Two Sets

1.0 = perfect match

Average1.061.251.85

Differences between the Codes

AEOLUS3 calculates average wind speed values for each wind speed group input by the user and stability class combination using every pertinent wind speed in the meteorological database

PAVAN and XOQDOQ compute average wind speed values based just on the wind speed group values input to the codes

PAVAN and XOQDOQ deviate from Regulatory Guide 1.145 in the computation of atmospheric dispersion coefficient values for atmospheric stability class G

AEOLUS3 reads the terrain height and RCF values for each receptor (sector and downwind distance) while XOQDOQ reads a grid of terrain height values (not necessarily at the receptor location, depends on user input; linearly interpolates if necessary)

Differences between the Codes - 2

Dispersion and deposition at coastal sites (sea breeze effects) and in deep river valleys.

Use of multi-year hourly meteorological data (20 year maximum).

Vertical plume reflection correction in all cases.

Gamma atmospheric dispersion factors (physically speaking, the gamma χ/Q for a given finite plume can be used to define the equivalent concentration in a semi-infinite cloud at ground level which will yield the same gamma radiation exposure as the finite plume itself).

A parabolic interpolation option that exactly matches the horizontal and vertical dispersion coefficient curves presented in Figures 1 and 2 in NRC Regulatory Guide 1.145.

Dry and wet deposition capability.

AEOLUS3 includes features not available in either PAVAN or XOQDOQ:

Disagreements between Source Code and Documentation

In PAVAN subroutine CHIQ, the maximum wind speed value for each wind speed group is used to determine the short-term atmospheric dispersion factors for each location for both ground level and elevated releases. Section 4.4 of NUREG/CR-2858 (Reference 6) states that, for ground level releases, the average wind speed value for each wind speed group is used to determine the short-term atmospheric dispersion factors. This leads to non-conservative results, since in Gaussian plume theory, χ/Q is inversely proportional to wind speed.

In XOQDOQ subroutine RISE, the value for the variable S (restoring acceleration per unit vertical displacement for adiabatic motion in the atmosphere) is given as 8.75E-04 for stability class E. Section 4.20 of NUREG/CR-2919 (Reference 7) states that the value for the variable S is 8.7E-04 for stability class E. (Minimal impact)

Possible Reasons for Differences in Results

AEOLUS3 analyses the hourly wind speed observations in the entire meteorological database to determine the average wind speed corresponding to each stability class and wind-speed-group combination input by the user. PAVAN and XOQDOQ compute average wind speed values based just on the wind speed group values input to the codes.

PAVAN uses the maximum, rather than the average, wind speed value for each wind speed group to determine the short-term atmospheric dispersion factors for ground level releases. Since atmospheric dispersion factors are inversely proportional to wind speed according to Gaussian plume theory, the higher wind speeds would make for lower atmospheric dispersion factors.

PAVAN and XOQDOQ limit the size of the horizontal dispersion coefficient (σy) to 1000 meters (AEOLUS3 does the same if the code is run using the NRC dispersion coefficient option but does not limit the size of σy if the code is run using the ENTECH dispersion coefficient option).

Summary

AEOLUS3 accident χ/Q results are within a factor of 1.4 on average (AEOLUS3/PAVAN) with AEOLUS3 results being more conservative than PAVAN in almost all cases

AEOLUS3 normal effluent ground level release results are within a factor of 0.9 on average (AEOLUS3/XOQDOQ)

AEOLUS3 normal effluent elevated release results are within a factor of 0.8 on average (AEOLUS3/XOQDOQ)

AEOLUS3 normal effluent mixed mode release results are within a factor of 2.4 on average with AEOLUS3 producing more conservative results within the first 7,000 to first 15,000 meters (4.3 to 9.3 miles) downwind (depending on the meteorological data set) and XOQDOQ producing more conservative results further downwind

Comparison of the AEOLUS3 Atmospheric Dispersion Computer Code with NRC Codes PAVAN and XOQDOQ 13th...

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