NUMUG - Oct Atmospheric Stability Methods & Measurements Robert F. Yewdall PSEG Nuclear LLC NUMUG - Oct 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 Atmospheric Stability History NRC Requirement Uses Of Stability Index NUMUG - Oct 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 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 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 History at PSEG Dispersion analysis originally developed from Brookhaven model Persuaded to estimate dispersion based on NRC requirements NUMUG - Oct Brookhaven Model NUMUG - Oct Early FSAR Analysis All Hours NUMUG - Oct Early FSAR Analysis Stable Only NUMUG - Oct Basis Numerical functions, y (x) and z (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. Miller 1 ..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 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 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 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 What is going on at the release point NUMUG - Oct Possible Differences Between Met Tower and Release Point Land Sea Interfaces Valley Flows Elevation Difference Cliffs and Bluffs NUMUG - Oct NUMUG - Oct Site Area NUMUG - Oct Region NUMUG - Oct NUMUG - Oct Sigma Theta Per ANSI/ANS , 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 Sigma Theta CLASSIFICATION OF ATMOSPHERIC STABILITY PER ANS CATEGORYPASQUILL CLASS SIGMA THETA (ST) EXTREME UNSTABLEAST>=22.5 MODERATE UNSTABLEB 22.5>ST>=17.5 SLIGHTLY UNSTABLEC 17.5>ST>=12.5 NEUTRALD 12.5>ST>=7.5 SLIGHTLY STABLEE7.5>ST>= 3.8 MODERATE STABLEF3.8>ST>=2.1 EXTREMELY STABLEG2.1>ST NUMUG - Oct VERTICAL TEMP DIFF (DT) P-G Class(DEGREE C/100M) ADT