The ANSI/ANS 2.15 Standard for Modeling Routine Radiological Releases from Nuclear Facilities

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The ANSI/ANS 2.15 Standard for Modeling Routine
Radiological Releases from Nuclear Facilities

• John Ciolek
• AlphaTRAC, Inc.

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Introduction

• setting the stage

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Modeling Standards Plan

• Idea Produce voluntary consensus standards for
  atmospheric modeling
• ANS 2.15 Modeling routine releases of
  radiological material from nuclear facilities
• ANS 2.16 Design basis accident scenario modeling
• ANS 3.8.10 Real-time emergency response modeling
  for accidents
• Working group decided to create the standards
  sequentially
• Build off previous work

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Process for Creating a Standards Documents

• Form working group
• Create Project Initiation Notification (PIN)
• Defines scope and intention
• Create standards document
• Obtain subcommittee technical content approval
• Obtain consensus committee and public review
• Review for compliance with ANSI
• Obtain approval as American National Standard

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The 2.15 Standard

• what is considered

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Subjects Considered in 2.15

• Models
• Model types
• Reference frames
• Time scales
• Release modes
• Sources
• Ground-level and elevated releases
• Mixed-mode releases
• Plume rise
• Aerodynamic effects of buildings

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Subjects Considered in 2.15

• Removal mechanisms
• Radioactive decay, wet and dry deposition
• Geospatial data
• Meteorological data
• Meteorological networks
• Quality assurance
• Note Standard applies only to offsite areas

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Special Subjects

• Recirculation and complex flow
• The modeling process
• Requirements
• Quality assurance

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Recirculation

• and other complexities

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Recirculation Group

• Subgroup formed to investigate influence of
  complex flow which includes
• Recirculation
• Stagnation
• Flow reversal
• Wind shear
• Subgroup charged with determining
• Where complex flow occurs, does it significantly
  contribute to total dose?
• If so, what should be recommended?

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Recirculation Evaluation Process

• Determine current state of knowledge
• Literature search for complex flow atmospheric
  dispersion studies (journals, conference papers,
  books, etc.)
• Interview authors of XOQDOQ
• Review recent communications within NRC
• Analyze influence of complex flow on total dose
• Develop recommendations to working group
• Write white paper to document analysis and
  findings

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Recirculation Group Findings

• Only two studies specifically examine this issue!
• Response to Pilgrim Watch (OKula and Hanna,
  2011)
• Southern Great Plains (LLNL - NUREG/CR-6853,
  2004)
• Problems
• Model grids too coarse
• 4 km grids will only see features gt 8km in extent
• Low resolution of meteorological observations
• Did not look at multiple time scales found to be
  important in literature
• Hours, diurnal, one to three days
• Meteorological averaging times too long
• Used hourly averaged meteorological data

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Problem Using Hourly Observations

• Canyon release from Los Alamos, NM
• One hour plume travel
• Instantaneous puff shown
• Plume returns to release after one hour

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Diurnal Recirculation

• Tetroon Study
• Rocky Flats, CO
• Feb. 9, 1991
• Tetroon returned to release point about 12
  hours after release

Release
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Findings

• Cant base recommendations on Pilgrim Watch or
  Plains studies
• Found several studies that document complex flow
• Hourly, diurnal, and daily signatures
• Impacts can be 2 to 5 times greater
• With pooling and flow reversal, impacts can be
  even greater
• Stability influences recirculation
• Climatology influences recirculation frequency
• Complex flow can occur 15 to 50 of time

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Unanimous Recommendations

• Eliminate recirculation factor
• Explicitly treat complex flow
• If that might have significant effect on results
• We need a conclusive study
• Determine if complex flow significantly affects
  routine release modeling

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DOE Model Comparison Study

• Rapid study (not published)
• Straight-line (EPIcode) vs. variable trajectory
  3-D model (CAPARS system)
• Random sample of start times from one year
• 215 out of 35,040 15-minute data sets
• Four-hour simulations
• Maximum concentration binned at select distances
• No deposition or resuspension

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Complex Domain
Release
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Comparison Results
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Analysis of Modeling

• Results differ based on how material was released
• Results match at some distances (1 - 5 km)
• Differences can be 1 - 2 orders of magnitude
• Suggests that straight-line models
• Are not necessarily the most conservative in
  complex environments
• May greatly over-estimate consequences gt 20 km
  from the release
• Considering complex terrain and flow probably
  will produce significantly different results

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The Modeling Process

• an engineering perspective

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Modeling Process

• Added Modeling Process as first section of 2.15
  document
• Explicitly treats
• Requirements
• Quality assurance
• Complex modeling processes
• Requires variable-trajectory modeling under some
  circumstances

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Requirements

• Must explicitly develop requirements
• Must be achievable
• Must be checked at end of project for completion

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Requirements

• Should include
• Regulatory agencies governing project
• Applicable regulatory limits
• Model selection
• Time scales
• Release modes
• Removal mechanisms
• Input data
• Modeling domain definitions
• Quality assurance

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Quality Assurance

• Must first define QA process to be used
• Can be company-based or national/international-bas
  ed standard
• IEEE, NRC, DOE, etc.
• Must define what components will be applicable to
  project
• Must follow process agreed upon

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Variable-trajectory Models Shall Be Used IF

• You have a requirement to use them
• OR
• Straight-line Gaussian modeling results are gt 10
  of regulatory limits AND
• You have the potential for complex flow within
  your domain AND
• Complex flow occurs gt 15 of the year

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Potential for Complex Flow

• Determined by
• Documented flow features
• Requires qualified meteorologist
• OR
• Known topographical features
• Large bodies of water (gt 500 sq km)
• Smallest area with documented recirculation
• Mountain(s)
• Can ignore mountains lt 150 m tall unless within 2
  km of release
• Valleys more than 50 m deep

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Frequency of Complex Flow

• Can be difficult to determine
• Must quantify how often complex flow features
  happen
• Left to modelers
• Allwine Whiteman (1994) method is acceptable
• Uses one profiler
• Assumes uniform wind field
• Currently investigating practical implementation
  of this process

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Status of the 2.15 Document

• the present state

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ANS 2.15 Document

• Final (Rev. 1) finished
• Sent to ANS-24 February 16, 2011
• ANS-24 review completed
• Comments returned April 15, 2011
• Next steps
• Incorporate comments and return to ANS-24
• Once approved, send to consensus committee
  (Nuclear Facilities Standards Committee)

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The Next Standards Document

• what to expect

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ANS 2.16 Design Basis Accident Modeling

• First working group meeting held April 14, 2011
• Additional DOE design basis modeling expert added
  to working group
• Jeremy Rishel (PNNL) added as co-chair
• Working meeting to be held at June 2011 NUMUG
  meeting
• Still issue of complex modeling role in design
  basis accident modeling

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Questions?

• jciolek_at_alphatrac.com