Strategies for the Selection of Substitute Meteorological Data

Ken SejkoraEntergy Nuclear Northeast – Pilgrim

Station

Presented at the 14th Annual RETS-REMP WorkshopSyracuse, NY / 28-30 June 2004

Basis of Problem Pilgrim Station was experiencing problems

with the upper-level wind direction indication on the primary tower

Question: Can Pilgrim substitute data from its backup tower to meet data recovery goals?

Proposed Solution: Compare various multiple measurements of meteorological parameters to determine suitability for substitution

Pilgrim Meteorological Towers Primary Tower

220-ft tall, based at ~80 ft above sea level on vegetated area 270m from ocean

Effective height = 300 ft Wind and temperature at top and 10m

Secondary (Backup) Tower 160-ft tall, based at ~20 ft above sea level in parking

lot 100m from ocean Effective height = 180 ft Wind and temperature at top and 10m

Hourly averages for 2-year period, yielded ~17,500 observations

Tower Placement Guidance Safety Guide 23… minimal guidance

Minimize effects from plant structures ANSI/ANS-2.5-1984

Represent release point Minimize effect from manmade

structures Avoid downwind from plant Distance from structures should be

>10 times the structure height

Tower Placement Guidancecontinued

ANSI/ANS-3.11-2000 More detailed than other guidance Avoid asphalt/concrete surfaces Not endorsed/’required’ by NRC Post-dates most pre-existing nuclear plant

meteorological installations Backup tower fails to meet many

criteria Downwind, nearby buildings, asphalt

Stability Class Frequencies

Stability Class Distribution

0%

10%

20%

30%

40%

A B C D E F G

Stability Class

Fre

qu

en

cy

Primary Backup

Problem with Frequency Data Relative frequencies for two sources do

not reflect the comparability of simultaneous measurements

Identified need for comparing paired measurements through time to determine how well they compare

Summarize comparisons of paired data to determine degree of differences

Agreement Matrix: Stability Class

A B C D E F G

A 1128 426 154 350 64 9 3B 218 171 72 124 14 3 0C 213 152 96 205 28 4 0D 479 429 405 3191 365 29 9E 170 135 105 2041 2996 396 78F 29 10 8 118 557 669 348G 7 8 7 25 85 158 299

Primary Tower

Backup Tower

Agreement Matrix Summary: Summation of Diagonals

Stability Class

Difference

Match 8550 51.5% 8550 51.5%1 3531 21.3% 1812 10.9%2 950 5.7% 413 2.5%3 647 3.9% 377 2.3%4 187 1.1% 67 0.4%5 37 0.2% 9 0.1%6 7 0.0% 3 0.0%

Total 5359 32.3% 2681 16.2%

Primary Tower Conservative

Backup Tower Conservative

Stability Class Differences

Primary vs. Backup Stability

0%10%20%30%40%50%60%

P:T

P:6

P:5

P:4

P:3

P:2

P:1

Ma

tch

B:1

B:2

B:3

B:4

B:5

B:6

B:T

Stability Class Difference

Fre

qu

en

cy

Candidate for Substitution?Delta-T

Primary tower delta-T yields more conservative stability class ~30% of cases

May be good substitute, but consider… Backup tower is in middle of parking lot, and

does not meet ANSI meteorological standards Heating from blacktop, cars, adjacent

buildings, etc. could bias readings, and would be expected to yield more negative delta-T values and lower stability classes

Temperature Frequencies

Temperature Class Distribution

0%5%

10%15%20%25%

-10

-0

0-1

0

10

-20

20

-30

30

-40

40

-50

50

-60

60

-70

70

-80

80

-90

90

-10

0

Temperature Class

Fre

qu

en

cy

Primary Backup

Temperature Differences

Primary vs. Backup Temperature

0%10%20%30%40%50%60%

T:S

>P -8 -6 -4 -2 0 2 4 6 8

T:P

>S

Temp.Difference: Primary - Backup

Fre

qu

ency

Candidate for Substitution?Temperature

>75% readings from both towers are within ±2 degrees of each other

Acceptable substitute, but consider… Backup tower is in middle of parking lot,

and does not meet ANSI meteorological standards

Heating from blacktop, cars, adjacent buildings, etc. could bias readings

Wind Speed Frequencies

Wind Speed Distribution

0%10%20%30%40%50%60%

Calm-0.95

0.95-3.5 3.5-7.5 7.5-12.5 12.5-18.5

18.5-24 >24

Wind Speed Class - mph

Fre

qu

en

cy

Primary Upper Backup Upper Primary Lower Backup Lower

Wind Speed Differences: Primary vs. Backup, Upper Level

Primary vs. Backup Upper Wind Speed

0%10%20%30%40%50%60%

P:T

P:6

P:5

P:4

P:2

P:2

P:1

Ma

tch

B:1

B:2

B:3

B:4

B:5

B:6

B:T

Upper Speed Class Difference

Fre

qu

en

cy

Wind Speed Differences: Primary vs. Backup, Lower Level

Primary vs. Backup Lower Wind Speed

0%10%20%30%40%50%60%

P:T

P:6

P:5

P:4

P:2

P:2

P:1

Mat

ch B:1

B:2

B:3

B:4

B:5

B:6

B:T

Lower Speed Class Difference

Fre

qu

enc

y

Wind Speed Differences: Primary, Upper vs. Lower Level

Primary Upper vs. Lower Wind Speed

0%

20%

40%

60%

80%

100%

U:T

U:6

U:5

U:4

U:2

U:2

U:1

Ma

tch

L:1

L:2

L:3

L:4

L:5

L:6

L:T

Speed Class Difference

Fre

qu

en

cy

Wind Speed Differences: Backup, Upper vs. Lower Level

Backup Upper vs. Lower Wind Speed

0%

20%

40%

60%

80%

100%

U:T

U:6

U:5

U:4

U:2

U:2

U:1

Ma

tch

L:1

L:2

L:3

L:4

L:5

L:6

L:T

Speed Class Difference

Fre

qu

en

cy

Candidate for Substitution?Wind Speed

Upper readings > lower readings… expected

Differences in wind speeds as a function of height would make substitution difficult Possible correction factors by extrapolation

The fact that the lower level of primary tower shows lowest wind speeds may indicate influence of nearby trees Implications to wind direction at this location

Wind Direction Frequencies

Wind Direction Distribution

0%

5%

10%

15%

20%

N

NE E

SE S

SW W

NW

Wind Direction

Fre

qu

en

cy

Primary Upper Primary Lower Backup Upper Backup Lower

Wind Direction Differences: Primary vs. Backup, Upper Level

Primary vs. Backup Upper Wind Direction

0%10%20%30%40%50%60%

CC

W:T

CC

W:5

CC

W:4

CC

W:3

CC

W:2

CC

W:1

Ma

tch

CW

:1

CW

:2

CW

:3

CW

:4

CW

:5

CW

:T

Upper Direction Difference

Fre

qu

en

cy

Wind Direction Differences: Primary vs. Backup, Lower Level

Primary vs. Backup Lower Wind Direction

0%10%20%30%40%50%60%

CC

W:T

CC

W:5

CC

W:4

CC

W:3

CC

W:2

CC

W:1

Mat

ch

CW

:1

CW

:2

CW

:3

CW

:4

CW

:5

CW

:T

Lower Direction Difference

Fre

qu

ency

Wind Direction Differences: Primary, Upper vs. Lower Level

Primary Upper vs. Lower Wind Direction

0%10%20%30%40%50%60%

CC

W:T

CC

W:5

CC

W:4

CC

W:3

CC

W:2

CC

W:1

Mat

ch

CW

:1

CW

:2

CW

:3

CW

:4

CW

:5

CW

:T

Direction Difference

Fre

qu

ency

Wind Direction Differences: Backup, Upper vs. Lower Level

Backup Upper vs. Lower Wind Direction

0%10%20%30%40%50%60%

CC

W:T

CC

W:5

CC

W:4

CC

W:3

CC

W:2

CC

W:1

Ma

tch

CW

:1

CW

:2

CW

:3

CW

:4

CW

:5

CW

:T

Direction Difference

Fre

qu

en

cy

Candidate for Substitution?Wind Direction

Primary tower seems to indicate slight counterclockwise bias compared to backup at both levels Alignment? Topography effect?

Candidate for Substitution?Wind Direction

Primary tower upper level shows clockwise bias compared to lower level Alignment? Potential effects of nearby trees? Lower level of primary tower exhibits

greatest fluctuations… evidence of influence of trees?

When coupled with low wind speeds at this level, may point to influence from trees

Candidate for Substitution?Wind Direction

Backup tower upper and lower levels show good agreement

Acceptable substitute, but consider… Backup tower is in middle of parking lot,

and does not meet ANSI meteorological standards

The good agreement may indicate minimal influence from nearby structures, but difficult to quantify

Summary Delta-T, temperature, and wind direction

show potential for substitution, but need to consider placement of backup tower (non-ANSI)

Wind speed is poor candidate for substitution

Lower wind speed and direction readings at primary tower may indicate influence of nearby trees and topography

Summary - continued Of all readings from backup tower,

upper wind direction would likely be least affected by adjacent structures, and would be most suitable for substitution Need to resolve potential bias? Upper wind speed may also be candidate,

but would need to be adjusted for height difference

Summary - continued Although backup tower location does not

meet ANSI standards in regard to ground cover, adjacent buildings, etc., its readings appear reasonable and acceptable for backup use if primary is lost Local data is better than alternate data from

a remote site Most remote sites (airport, NWS) are not

equipped to provide met data for emergency operations