ML24247A171
| ML24247A171 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/28/2024 |
| From: | Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| CNL-24-041 | |
| Download: ML24247A171 (1) | |
Text
Enclosure 3
Calculation of Atmospheric Dispersion Factors
Exclusion Area Boundary & Low Population Zone
for SQN Units 1 & 2
(6 pages)
CNL-24-041 L94 191003 800
Sequoyah Nuclear Plant Short-Term (Accident) Dispersion Estimates - PAV AN Modeling Meteorological Episode: 2004-2013 Revision 1
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Reviewed By: ~ ~ 'Iv'~ Date: __ O_c_to_b_e_r _2,~2_0_1_9 __
Short-Term Dispersion Estimates Meteorological Episode: 2004-2013 Revision 1
Sequoyah Nuclear Plant Short-Term (Accident) Dispersion Estimates - PAV AN Modeling Meteorological Episode: 2004-2013
This report documents the determination of the short-term atmospheric dispersion coefficients, expressed as /Q, X for the radiological consequence analyses at the Sequoyah Nuclear Plant (SQN) for specified time intervals at the Exclusion Area Boundary (EAB) and the Low Population Zone (LPZ), as required under 10 CFR 100 and 10 CFR 50. The calculations were performed using the PAVAN computer program, NUREG/CR-2858, which was developed and is used by the U.S.
Nuclear Regulatory Commission (NRC) for this type of application. The PAV AN program implements the guidance provided in NRC Regulatory Guide (RG) 1.145, "Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants".
The PAV AN model calculates IQ values based on the theory that material released to the X atmosphere would be normally distributed (Gaussian) about the plume centerline.
PAVAN Input
Using joint frequency distributions (JFDs) of wind direction, wind speed, and atmospheric stability class, the PAV AN program calculates X/Q values as functions of direction, distributed in 22.5-degree compass-point sectors, for six (6) averaging times at the EAB and LPZ.
The input parameters used in the PAV AN model are outlined in Table 1. A ten year period (January 1, 2004 - December 31, 2013) of SQN meteorological tower data were used as input to the PAV AN code. The meteorological tower data met the requirements of RG 1.23 and was validated in accordance with the TV A validation procedures (Environmental Permits and Compliance, Validation of Meteorological Data - Nuclear [EPC-SOP-9.2]). The data recovery over the 2014-2013 period was greater than 90 percent.
Table 1. PAV AN Model Input Parameters
Input Variable Value Reference Containment Building Heil!ht 40.8m Drawing 41N712-1 Containment BuildinJ;!; Min. Cross Sectional Area 1632 m 2 DrawinJ;!; 41N712-1 Wind Sensor Height 9.73 m SQN EDS manual Lower-T Sensor Height 9.25m SQN EDS Manual Intermediate-T sensor Height 45.99m SQN EDS Manual Distance to EAB Release Zone 1 556m FSAR Table 2.3.4-1 Release Zone 2 600m FSAR Table 2.3.4-1 Release Zone 3 509m FSAR Table 2.3.4-1 Distance to LPZ 4828m FSAR Section 2.3.4 Type of Release ground FSAR Section 2.3.4 Building Wake Credit yes FSAR Section 2.3.4
Sequoyah Nuclear Plant 2 Short-Term Dispersion Estimates Meteorological Episode: 2004-2013 Revision 1
Three levels of wind direction and wind speed were available from the SQN tower: A lower, 10-meter (m) level; a middle, 46-m level; and an upper, 91-m level. Based on RG 1.145, a ground release includes all release points that are effectively less than two and one-half times the height of adjacent solid structures. Since the SQN plant release points are less than two and one-half times the containment and turbine building heights, the release mode applied was classified as a ground-level release. For the ground-level release mode in PAV AN, the lower level of wind speed and direction (wind sensor mounted at 9. 73 m) were used as input into the PAV AN model.
PAV AN requires meteorological data that is input in the form of JFDs of wind direction and wind speed by atmospheric stability class. The stability classes were determined based on the classification system given in Table 1 of RG 1.23. The vertical temperatures used to determine stability class were measured at approximately 9.25 m and 45.99 m above ground, and the lapse rates were calculated as degree Celsius (°C) / meter (m). The 2004-2013 wind data were input into PAV AN in terms of JFDs in number of hours, rounded to the nearest integer as required by the program.
According to RG 1.145, calms are classified as hourly average wind speeds below the vane or anemometer starting speed, whichever is higher. The SQN sonic sensor can report minimum non calm wind speeds of 0.1 miles per hour (mph). Since calms were distributed into the first wind speed category in the JFDs, they were not manually distributed in the PAV AN input file. The upper bound wind speed categories used in the PAV AN analysis were defined as follows: :Sl.12 mph (0.50 mis), :Sl.68 mph (0.75 mis), :S2.24 mph (1.00 mis), :S2.80 mph (1.25 mis), :S3.36 mph (1.50 mis), ::::;4.47 mph (2.00 mis), :S6.71 mph (3.00 mis), :S8.95 mph (4.00 mis), :Sl 1.18 mph (5.00 mis), :S13.42 mph (6.00 mis), :Sl 7.90 mph (8.00 mis), and :S22.37 mph (10.00 mis). A conversion factor was used in PAV AN to convert the wind speeds to meters / second.
Consistent with the assumptions outlined in the SQN Offsite Dose Calculation Manual (ODCM) and Final Safety Analysis Report (FSAR), the onsite meteorological data is representative of the actual transport and diffusion characteristics of the site vicinity. No terrain adjustment factors were applied. The PAV AN model also requires containment building dimensions and distances to the EAB and LPZ. The containment building dimensions were provided in the SQN 41N712-1 engineering drawings. The distances to the EAB and LPZ were provided in the SQN FSAR.
Quality Assurance (QA) of PAV AN
PAV AN is not in the TV A-NPG software QA program, but it is widely utilized in the industry and is acceptable for use by the NRC. In lieu of the QA requirements, a test case from NUREG/CR-2858 Appendix B (Test Case #1) was modeled with the TVA-installed version of the PAVAN code to show that the model was performing as intended. As summarized in Table 2, the TV A test case results compared exactly to those in NUREG/CR-2858 Appendix B.
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Short-Term Dispersion Estimates Meteorological Episode: 2004-2013 Revision 1
PAV AN Results
RG 1.145 requires that the XIQ values at the EAB and LPZ be calculated based on both a directionally dependent methodology (maximum sector) and a directionally independent methodology (overall site limit) and that the most conservative (highest) values be chosen.
Therefore, consistent with RG 1.145, the PAV AN model calculates the maximum sector IQ by X taking the IQ X value exceeded 0.5% of the time based on a cumulative probability distribution of XIQ values for each sector. Also in accordance with RG 1.145, the model calculates an overall site IQ Xvalue by selecting the IQ X value that is exceeded 5 percent of the total time based on an overall cumulative probability distribution for all directions combined. The higher of the two values was then chosen to be the bounding IQ X value for each of the time periods analyzed. Tables 3-5 present the bounding IQ X values for SQN utilizing meteorological data from 2004-2013 at the EAB and LPZ, respectively.
Table 3. Exclusion Area Boundary (EAB) IQ Values (seclm 3X )
0.5th and 5% /Q X Values (sec/ml)
Direction EAB Time Period Direction-Dependent IQ Independent X XIQ 0.5% Maximum Sector 5% Site Limit EAB-1 (556m) 0-2 Hours 8.82E-04 SSW 6.60E-04 EAB-2 (600m) 0-2 Hours 7.76E-04 SSW 5.81E-04 EAB-3 (509m) 0-2 Hours l.02E-03 SSW 7.65E-04
Table 4. Low Population Zone (LPZ) IQ Values (seclm 3X )
0.5thand5% /Q XValues (sec/ml)
Direction LPZ Time Period Direction-Dependent IQ Independent X XIQ 0.5% Maximum Sector 5% Site Limit LPZ (4828m) 0-2 hours 8.78E-05 SSW 6.26E-05 LPZ (4828m) 0-8 Hours 4.45E-05 SSW 3.36E-05 LPZ (4828m) 8-24 Hours 3.l 7E-05 SSW 2.46E-05 LPZ (4828m) 1-4 Days 1.52E-05 SSW 1.25E-05 LPZ (4828m) 4-30 Days 5.26E-06 SSW 4.73E-06
Table 5. Bounding IQ Values (seclm 3X ) at the EAB and LPZ
Bounding /Q X Values (sec/ml)
Based on 2004-2013 Meteorology Location 0-2 Hours 0-8Hours 8-24 Hours 1-4 Days 4-30Days EAB(509m) 1.02E-03 -- -- -- --
LPZ (4828m) 8.78E-05 4.45E-05 3.l 7E-05 l.52E-05 5.26E-06
Sequoyah Nuclear Plant 5 Short-Term Dispersion Estimates Meteorological Episode: 2004-2013 Revision 1
References
NUREG/CR-2858, PNL-4413, "PAVAN: An Atmospheric Dispersion Program for Evaluating Design Basis Accidental Releases of Radioactive Materials from Nuclear Power Stations", Richland, WA, November 1982.
Tennessee Valley Authority, Environmental Permits and Compliance, Air Program Support Document, Reference Document EPC-SOP-9.2, "Environmental Permits and Compliance, Validation of Meteorological Data-Nuclear." August 2013.
Tennessee Valley Authority, Sequoyah Nuclear Plant, Off site Dose Calculation Manual (ODCM), Revision
- 58. December 2012.
Tennessee Valley Authority, Sequoyah Nuclear Plant, Units 1-2 Engineering Drawings, 41N712-1.
December 2012.
Tennessee Valley Authority, Sequoyah Nuclear Plant, Environmental Data Station Manual (EDS), Module 11-C, Meteorological Monitoring. March 2007.
Tennessee Valley Authority, Sequoyah Nuclear Plant, Final Safety Analysis Report (FSAR), Amendment 24.
U.S. Nuclear Regulatory Commission. Regulatory Guide 1.145, Revision 1, "Atmospheric Dispersion Models for Potential Accident Consequence Assessment at Nuclear Power Plants," Washington, D.C.,
November 1982 (Revised February 1983 to correct page 1.145-7).
U.S. Nuclear Regulatory Commission. Regulatory Guide 1.23, Revision 1, "Meteorological Monitoring Programs for Nuclear Power Plants", Washington, D.C., March 2007.
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