ML19093B817
| ML19093B817 | |
| Person / Time | |
|---|---|
| Issue date: | 02/12/2019 |
| From: | Jonathan Barr, Bixler N, Clayton D, Keith Compton Office of Nuclear Regulatory Research, Sandia |
| To: | |
| Shared Package | |
| ML19093B814 | List: |
| References | |
| Download: ML19093B817 (18) | |
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2/12/2019 Overview of Upgrades to MACCS Dispersion Modeling Capabilities 2019 NRC Regulatory Information Conference Atmospheric Transport and Dispersion Modeling for Severe Accident Consequence Analysis K. Compton*, J. Barr*, N. Bixler**, and D. Clayton**
- U.S. Nuclear Regulatory Commission
- Sandia National Laboratories 1
2/12/2019 Outline
- Severe accident consequence analysis with the MELCOR Accident Consequence Code System (MACCS)
- Overview of current MACCS atmospheric transport and dispersion (ATD) model capabilities
- Ongoing dispersion model enhancements
- Potential nearfield dispersion model enhancements 2
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2/12/2019 Overview of Severe Accident Consequence Analysis
- Typically includes modeling the radioactive release to the atmosphere
- Analyses typically estimate the doses and health effects from inhalation, cloudshine, groundshine, skin deposition, and ingestion (e.g., water, milk, meat, crops), as well as costs and other impacts associated with protective actions to reduce exposure 3
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2/12/2019 Considerations for Severe Accident Assessments
- Severe accident probabilistic consequence assessments
- Realistic assessment
- Prospective analysis
- Multiple figures of merit
- Wide temporal and spatial scales
- Computational efficiency needed for modeling multiple possible prospective weather conditions
- Traditional ATD approach for probabilistic consequence analysis is to use a Gaussian plume segment model 4
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2/12/2019 MACCS Modules
- ATMOS
- Source term definition
- Weather sampling algorithms
- Atmospheric transport, dispersion, and deposition
- EARLY (1 to 40 days)
- Doses as modified by emergency phase countermeasures such as sheltering, evacuation, relocation, and potassium iodide ingestion
- Allows modeling of multiple population cohorts
- Acute and latent health effects from early acute exposure
- CHRONC (1 week to >50 years)
- Doses as modified by intermediate and recovery phase protective actions such as relocation, temporary and permanent interdiction, and decontamination
- Latent health effects from chronic exposure to deposited material
- Economic impact from early and late phase protective actions 5
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2/12/2019 ATMOS: Meteorological Data
- MACCS ATMOS Gaussian plume segment model typically reads data from a file containing 1 years worth of observed hourly meteorological data (8,760 observations)
- Wind speed (at 10 meters)
- Wind direction (sector into which wind is blowing)
- Stability class (typically based on lapse rate)
- Accumulated precipitation
- Each plume segment uses up to 1,000 hours0 days <br />0 hours <br />0 weeks <br />0 months <br /> of meteorological data from meteorological file
- Up to 500 plume segments can be defined
- Typical practice is to sample approximately 1,000 different accident initiation times from the 8,760 potential hourly start times 6
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2/12/2019 ATMOS ATD Model Plume Dispersion
- Straightline Gaussian plume segment model
- Userspecified plume dispersion parameterization
- Distancebased power law formulation b d y = a x z = c x
- Distancebased lookup tables: allow formulations that do not fit a simple power law (e.g., Briggs or Eimutis and Konicek formulations)
- Horizontal and vertical scaling factors (YSCALE and ZSCALE)
- ZSCALE typically used to account for surface roughness effects on vertical dispersion
- Longrange dispersion: timebased plume growth model 7
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2/12/2019 ATMOS Gaussian Plume Model Modifications Virtual source model
- Accounts for building wake effects and timevarying meteorological conditions
- User can specify initial plume dimensions to simulate initial dispersion from wake effects Plume Meander
- Userselectable model applies corrections to transverse dispersion coefficients
- Original model (accounts for sampling time)
- Alternative model based on NUREG/CR2260 (accounts for wind speed and stability)
MACCS also includes modifications to account for plume rise, wet deposition, and dry deposition 8
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2/12/2019 ATMOS (Gaussian Plume Segment): Air Concentration
- Illustration showing how plume segments move with wind shifting from northwest to northeast
- Each segment has its own width depending on the amount of dispersion that has occurred as it experiences varying weather conditions
- Each segment has a unique length depending on wind speed
- Wet and dry deposition (not shown) results in plume depletion and buildup of ground concentration 9
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2/12/2019 Accuracy of MACCS
- Probabilistic consequence analysis applications generally require the generation of the statistical distribution of consequence values over annual weather data (i.e., weatheraveraged calculations)
- ATD model fidelity for probabilistic consequence analysis is traditionally considered less significant than for emergency response tools because of the statistical nature of probabilistic consequence analyses
- However, questions about the adequacy of the Gaussian plume model for probabilistic consequence analyses have been raised since at least the 1980s
- A previous study (NUREG/CR6853) showed that MACCS is generally within a factor of two of the National Atmospheric Release Advisory Centers Lagrangian Operational Dispersion Integrator (LODI) code for weatheraveraged calculations 10 10
2/12/2019 Evaluation Attributes for Potential Alternative ATD Codes
- Essential features
- Treats Lagrangian particles
- Code executable files can be distributed to users (either by Sandia National Laboratories or directly from the developer)
- Source code available in case modifications are required for integration
- Code has adequate quality assurance (QA)
- Treats threedimensional (3D) wind field (gridded data)
- Desirable features
- Can model both puffs and particles
- Supports a variety of gridded weather data formats
- Facilitates graphical postprocessing 11 11
2/12/2019 Features of Potential Alternative ATD Codes HYSPLIT FLEXPART LODI CALPUFF RASCAL SCIPUFF Dispersion Lagrangian/ Lagrangian Lagrangian/ Gaussian Gaussian Gaussian Gaussian Gaussian Developer/ NOAA & Aus. Norwegian Inst. LLNL/ TRC/ PNNL/ Titan/
Primary Bureau of Met./ for Air Research/ DOE EPA NRC DTRA, NASA, Europe U.S. Army Customers Universities, Weather Any gridded data WRF, MM5 WRF, ADAPT CALMET, Surface data Surface or Data MM5, etc. gridded data Surface User input at any User input at any User input at User input at User input at Unknown Roughness resolution, or resolution any any any 1 degree resolution resolution resolution Availability/ NOAA/Yes Norwegian Inst. Only via TRC/No NRC/Yes Titan/No Source Code for Air Research/ Web/No Europe/Yes QA/Verifica Yes, open Open literature Yes, open Yes Yes Yes tion and literature literature Validation Platforms Unix/Linux, Unix/Linux, PC Unix/Linux PC PC PC PC, Mac Graphics Yes User plots output Yes Yes Yes Yes Computer Can be high/ Can be high/ Can be high/ Can be high Moderate Can be high Time needs multiple needs multiple needs processors processors multiple processors 12 12
2/12/2019 Selected Alternative ATD Code: HYSPLIT
- Selected for integration into MACCS as a modern alternative to the Gaussian plume segment model
- Developed and maintained by the National Oceanic and Atmospheric Administration (NOAA) Air Resources Laboratory
- Can compute trajectories as well as complex transport, dispersion, chemical transformation, and deposition
- Accepts a wide variety of publicly available gridded meteorological data, including both North American and global datasets
- Models dispersion using either puffs or particles:
- [P]uffs expand until they exceed the size of the meteorological grid cell (either horizontally or vertically) and then split into several new puffs, each with its share of the pollutant mass. *
- [A] fixed number of particles are advected about the model domain by the mean wind field and spread by a turbulent component. *
2/12/2019 Potential MACCS Enhancements for NonLightWater Reactors (NonLWRs)
- Evaluating potential code development needs for designspecific issues
- Radionuclide screening
- Radionuclide chemical form
- Aerosol size
- Aerosol shape factor
- Radionuclides with complex transport characteristics (e.g., tritium)
- Evaluating potential code development needs for siterelated issues
- Nearfield atmospheric transport
- Decontamination modeling 14 14
2/12/2019 NearField Atmospheric Transport
- MACCS currently has a simple virtual source model for building wake effects; its user guide (NUREG/CR6613) cautions against use closer than 500 meters
- Licensees for nonLWRs (and small modular reactors) desire a smaller emergency planning zone and site boundary than for large LWRs; therefore, better modeling of nearfield phenomena may be beneficial Wind tunnel simulation of streamlines near a cubic building Schulman, L.L., D.G. Strimaitis, and J.S. Scire (2000). Development and Evaluation of the PRIME Plume Rise and Building Downwash Model, Journal of the Air & Waste Management Association, 50:3, 378-390 15 15
2/12/2019 NearField Atmospheric Transport Example QUICURB simulation of wind
- Various options for addressing vectors nearfield ATD
- Modifications to Gaussian plume segment ATD model
- Lagrangian particle tracking ATD using simplified 3D wind field models
- Lagrangian particle tracking ATD using CFD modeling of 3D wind field
- Considerations for evaluating options Example QUICPLUME simulation of urban
- Extent of practical acceptance in the user transport and dispersion community
- Simplicity of use
- Computational efficiency
- Cost and time efficiency
- Accuracy
- Feasibility for probabilistic application QUIC Factsheet, Los Alamos National Laboratory 16 16
2/12/2019 Summary
- The current version of MACCS is an efficient and highly flexible probabilistic consequence analysis tool with many userconfigurable options
- Code enhancements are nearing completion to introduce results computed by HYSPLIT into MACCS
- Examining the applicability of current and potential approaches for modeling nearfield dispersion phenomena where building wakes may be important 17 17
2/12/2019 ACRONYMS AND REFERENCES Acronyms
- ATD: Atmospheric Transport and Dispersion
- FLEXPART: FLEXible PARTicle Dispersion Model
- HYSPLIT: Hybrid Single Particle Lagrangian Integrated Trajectory Model
- LODI: Lagrangian Operational Dispersion Integrator
- MACCS: MELCOR Accident Consequence Code System
- NOAA: National Oceanic and Atmospheric Administration
- QUIC: Quick Urban & Industrial Complex Dispersion Modeling System References
- Chanin, D., and M.L. Young (1998). Code Manual for MACCS2: Volume 1, Users Guide (NUREG/CR6613), Sandia National Laboratories, Albuquerque, NM, May 1998
- Molenkamp, C.R., N.E. Bixler, C.W. Morrow, J.V. Ramsdell, Jr., and J.A. Mitchell (2004). Comparison of Average Transport and Dispersion Among a Gaussian, a TwoDimensional, and a ThreeDimensional Model (NUREG/CR6853), Lawrence Livermore National Laboratory, Livermore, CA, October 2004
- Schulman, L.L., D.G. Strimaitis, and J.S. Scire (2000). Development and Evaluation of the PRIME Plume Rise and Building Downwash Model, Journal of the Air & Waste Management Association, 50:3, 378-390
- Snell, W.G., and R.W. Jubach (1981). Technical Basis for Regulatory Guide 1.145, Atmospheric Dispersion Models for Potential Accident Consequence Assessments at Nuclear Power Plants (NUREG/CR2260),