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Atmospheric Stability – Methods & Measurements

Atmospheric Stability – Methods & Measurements. Robert F. Yewdall PSEG Nuclear LLC. Introduction. Overview Of Atmospheric Stability Classification As It Relates To Commercial Nuclear Power Stations Not Intended To Endorse Any Specific Model Or Atmospheric Dispersion Methodology .

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Atmospheric Stability – Methods & Measurements

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  1. Atmospheric Stability – Methods & Measurements Robert F. Yewdall PSEG Nuclear LLC NUMUG - Oct 2003

  2. Introduction • Overview Of Atmospheric Stability Classification As It Relates To Commercial Nuclear Power Stations • Not Intended To Endorse Any Specific Model Or Atmospheric Dispersion Methodology NUMUG - Oct 2003

  3. Atmospheric Stability • History • NRC Requirement • Uses Of Stability Index NUMUG - Oct 2003

  4. Prescriptive Requirement For NRC Licensees • Regulatory Guide 1.111, Methods for Estimating Atmospheric Transport and Dispersion…. • Regulatory Guide 1.145, Atmospheric Dispersion Models for Potential Accident Consequence Assessment at Nuclear Power Plants. • Standard Review Plan (NUREG 0800) • Standard Format and Content Guide (Reg Guide 1.70) • Draft Regulatory Guide DG-1111, Atmospheric Relative Concentration For Control Room Radiological Habitability Assessment At Nuclear Power Plants NUMUG - Oct 2003

  5. The Paradox – Tower Siting Requirements versus Representation of Dispersion of Effluents at the Point of Release • 1. The need to gather climatological/ meteorological data for site characterization and short term (accident) and long term dispersion estimates. • 2. The need to determine what is happening to the effluent (source term) released from the station. NUMUG - Oct 2003

  6. History - General • Data gathering for station licensing & siting (primarily 10 CFR Part 100). • Early emergency planning • Post TMI • NRC Program and Instrument Requirements Still 1972 vintage (SG 23) NUMUG - Oct 2003

  7. History at PSEG • Dispersion analysis originally developed from Brookhaven model • Persuaded to estimate dispersion based on NRC ‘requirements’ NUMUG - Oct 2003

  8. Brookhaven Model NUMUG - Oct 2003

  9. Early FSAR Analysis All Hours NUMUG - Oct 2003

  10. Early FSAR Analysis Stable Only NUMUG - Oct 2003

  11. Basis Numerical functions, sy(x) and sz(x). employed to describe the lateral and vertical dispersion, were created empirically using Gaussian statistics based on field observations and tracer studies. As described in numerous documents and as identified in an article by C.W. Miller1 “..while these Pasquill-Gifford (PG) curves have been applied to a large variety of different situations, they were actually intended for use under rather limited circumstances: wind speed greater than 2 m/sec, nonbuoyant plumes, flow over open country and downwind distances of only a few km…”. In addition “… values generally applied with the model were originally derived from data gathered on over relatively flat, smooth terrain…” 1 An Examination of Gaussian Plume Dispersion Parameters For Rough Terrain, Atmospheric Environment, (1978) Vol. 12, pp 1359 NUMUG - Oct 2003

  12. Post TMI Requirements • RG 1.97 Instrumentation for Light-Water-Cooled Nuclear Power Plants To Assess Plant and Environs Conditions During and Following an Accident • NUREG 0654 Criteria for Preparation and Evaluation of Radiological Emergency Response Plans and Preparedness in Support of Nuclear Power Plants, Rev Nov 1980 • NUREG 0737, Requirements For Emergency Response Capability, Supp 1, 12/92 • NUREG 0696 Functional Criteria for Emergency Response Facilities, 1981 • License conditions or commitments NUMUG - Oct 2003

  13. Calculation Structure • Atmospheric Stability Is Index Into 7 Category Grouping • Determination Of Stability Is Either By Delta Temperature Or Sigma Theta • Stability Index Currently Defined In A Number Of NRC Regulatory Guides and NUREG • Stability Class Generally Referred To As “ Pasquill – Gifford” or P-G Class NUMUG - Oct 2003

  14. Calculation Structure - Cont • Index Form Discrete Values (can create large steps in dose projections) • NRC Regs Require Delta Temperature Index To Be Used For Determination Of Long Term & Accident Dispersion Calculations • For Emergency Preparedness Purposes - Could Use Sigma Theta As Substitute For Delta Temperature Or For Sigma Y NUMUG - Oct 2003

  15. What is going on at the release point NUMUG - Oct 2003

  16. Possible Differences Between Met Tower and Release Point • Land – Sea Interfaces • Valley Flows • Elevation Difference – Cliffs and Bluffs NUMUG - Oct 2003

  17. NUMUG - Oct 2003

  18. Site Area NUMUG - Oct 2003

  19. Region NUMUG - Oct 2003

  20. NUMUG - Oct 2003

  21. Sigma Theta • Per ANSI/ANS- 2.5-1984, the standard deviation of horizontal wind direction fluctuations shall be determined by statistical analysis of samples from no less than 180 instantaneous values of lateral wind direction during the sample period (i.e. if the sampling period is 15 minutes, values sampled at every five-second interval or less are acceptable); likewise, if the sampling period is one hour, 20 second sampling intervals or less are acceptable. Maximum sampling time is one hour. NUMUG - Oct 2003

  22. Sigma Theta • CLASSIFICATION OF ATMOSPHERIC STABILITY PER ANS 2.5-1984 • CATEGORY PASQUILL CLASS SIGMA THETA (ST) • EXTREME UNSTABLE A ST>=22.5 • MODERATE UNSTABLE B 22.5>ST>=17.5 • SLIGHTLY UNSTABLE C 17.5>ST>=12.5 • NEUTRAL D 12.5>ST>=7.5 • SLIGHTLY STABLE E 7.5>ST>= 3.8 • MODERATE STABLE F 3.8>ST>=2.1 • EXTREMELY STABLE G 2.1>ST NUMUG - Oct 2003

  23. VERTICAL TEMP DIFF (DT) • P-G Class (DEGREE C/100M) • A DT<=-1.9 • B -1.9<DT<=-1.7 • C -1.7<DT<=-1.5 • D -1.5<DT<=-0.5 • E -0.5<DT<=1.5 • F 1.5<DT<=4.0 • G 4.0<DT Regulatory Guide 1.23 Table 2 defines the seven stability classifications that are based on ranges from sigma theta. Sigma Theta is a measure of standard deviation. NUMUG - Oct 2003

  24. Example – 15 Minute Average NUMUG - Oct 2003

  25. Example – 15 Minute NUMUG - Oct 2003

  26. Stability Comparison Table NUMUG - Oct 2003

  27. Stability Comparison - Plot NUMUG - Oct 2003

  28. Where Do We Go From Here ? NUMUG - Oct 2003

  29. Guidance – Current Status • NRC’S CURRENT POSITION ON METEOROLOGY (05/02) • SAFETY GUIDE 23 (AKA, R.G. 1.23) IS STILL IN EFFECT. • PROPOSED REV. 1, AND 2nd PROPOSED REV. 1 TO R.G. 1.23 WERE NEVER ADOPTED. • AT PRESENT, THERE IS NO EFFORT, ONGOING OR PLANNED WITHIN NRC, FOR AN UPDATE OR REVISION. • NRC IS WAITING FOR AN INDUSTRY TRADE GROUP (e.g. NUMUG) TO TAKE THE INITIATIVE TO GET ANSI/ANS-3.11 RECOGNIZED. NUMUG - Oct 2003

  30. Issues • NRC Support/ Recognition of Met Standard ANSI/ANS 3.11 • Prescriptive nature of dispersion modeling ( i.e., delta Ts) • Location of meteorological monitoring relative to release location • No change in temporal, spatial changes in condition for 50 miles • Met validation and quality programs requirement inconsistent with effluent release validation requirements • Station support following removal from Tech Specs NUMUG - Oct 2003

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