Atmospheric Stability

1
Atmospheric Stability Methods
Measurements

• Robert F. Yewdall
• PSEG Nuclear LLC

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

3
Atmospheric Stability

• History
• NRC Requirement
• Uses Of Stability Index

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

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.

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)

7
History at PSEG

• Dispersion analysis originally developed from
  Brookhaven model
• Persuaded to estimate dispersion based on NRC
  requirements

8
Brookhaven Model
9
Early FSAR Analysis All Hours
10
Early FSAR Analysis Stable Only
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

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

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

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
•  

15
What is going on at the release point
16
Possible Differences Between Met Tower and
Release Point

• Land Sea Interfaces
• Valley Flows
• Elevation Difference Cliffs and Bluffs

17
(No Transcript)
18
Site Area
19
Region
20
(No Transcript)
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.

22
Sigma Theta

• CLASSIFICATION OF ATMOSPHERIC STABILITY PER ANS
  2.5-1984
•  
• CATEGORY PASQUILL CLASS
  SIGMA THETA (ST)
•  
• EXTREME UNSTABLE A STgt22.5
• MODERATE UNSTABLE B
  22.5gtSTgt17.5
• SLIGHTLY UNSTABLE C
  17.5gtSTgt12.5
• NEUTRAL D 12.5gtSTgt7.5
• SLIGHTLY STABLE E 7.5gtSTgt 3.8
• MODERATE STABLE F 3.8gtSTgt2.1
• EXTREMELY STABLE G 2.1gtST

23
VERTICAL TEMP DIFF (DT)

• P-G Class (DEGREE C/100M)
• A DTlt-1.9
• B -1.9ltDTlt-1.7
• C -1.7ltDTlt-1.5
• D -1.5ltDTlt-0.5
• E -0.5ltDTlt1.5
• F 1.5ltDTlt4.0
• G 4.0ltDT
• 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.

24
Example 15 Minute Average
25
Example 15 Minute
26
Stability Comparison Table
27
Stability Comparison - Plot
28
Where Do We Go From Here ?
29
Guidance Current Status

• NRCS 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.

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