The ANSI/ANS 2.15 Standard for Modeling Routine Radiological Releases from Nuclear Facilities John Ciolek AlphaTRAC, Inc.

Introduction …setting the stage NUMUG: June 27-29, 20112

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 : Real-time emergency response modeling for accidents Working group decided to create the standards sequentially –Build off previous work NUMUG: June 27-29, 20113

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 NUMUG: June 27-29, 20114

The 2.15 Standard …what is considered NUMUG: June 27-29, 20115

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 NUMUG: June 27-29, 20116

…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 NUMUG: June 27-29, 20117

Special Subjects Recirculation and complex flow The modeling process Requirements Quality assurance NUMUG: June 27-29, 20118

Recirculation …and other complexities NUMUG: June 27-29, 20119

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? NUMUG: June 27-29,

Recirculation Evaluation Process Determine current state of knowledge –Literature search for complex flow atmospheric dispersion studies (j ournals, 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 NUMUG: June 27-29,

Recirculation Group Findings Only two studies specifically examine this issue! –Response to Pilgrim Watch (O’Kula and Hanna, 2011) –Southern Great Plains (LLNL - NUREG/CR-6853, 2004) Problems: –Model grids too coarse 4 km grids will only see features > 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 NUMUG: June 27-29,

Problem Using Hourly Observations Canyon release from Los Alamos, NM One hour plume travel Instantaneous puff shown Plume returns to release after one hour NUMUG: June 27-29,

Diurnal Recirculation Tetroon Study Rocky Flats, CO Feb. 9, 1991 Tetroon returned to release point about ~ 12 hours after release Release NUMUG: June 27-29,

Findings Can’t 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 NUMUG: June 27-29,

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 NUMUG: June 27-29,

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, minute data sets Four-hour simulations Maximum concentration binned at select distances No deposition or resuspension NUMUG: June 27-29,

Complex Domain Release NUMUG: June 27-29,

Comparison Results EPIcode CAPARS 95th Percentile 50th Percentile Interquartile EPIcode CAPARS 95th Percentile 50th Percentile Interquartile NUMUG: June 27-29,

Analysis of Modeling Results differ based on how material was released Results match at some distances (1 - 5 km) Differences can be orders of magnitude Suggests that straight-line models: –Are not necessarily the most conservative in complex environments –May greatly over-estimate consequences > 20 km from the release Considering complex terrain and flow probably will produce significantly different results NUMUG: June 27-29,

The Modeling Process …an engineering perspective NUMUG: June 27-29,

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 NUMUG: June 27-29,

Requirements… Must explicitly develop requirements Must be achievable Must be checked at end of project for completion NUMUG: June 27-29,

…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 NUMUG: June 27-29,

Quality Assurance Must first define QA process to be used –Can be company-based or national/international-based standard IEEE, NRC, DOE, etc. Must define what components will be applicable to project Must follow process agreed upon NUMUG: June 27-29,

Variable-trajectory Models Shall Be Used IF… You have a requirement to use them OR Straight-line Gaussian modeling results are > 10% of regulatory limits AND You have the potential for complex flow within your domain AND Complex flow occurs > 15% of the year NUMUG: June 27-29,

Potential for Complex Flow Determined by: Documented flow features –Requires qualified meteorologist OR Known topographical features: –Large bodies of water (> 500 sq km) Smallest area with documented recirculation –Mountain(s) Can ignore mountains < 150 m tall unless within 2 km of release –Valleys more than 50 m deep NUMUG: June 27-29,

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 NUMUG: June 27-29,

Status of the 2.15 Document …the present state NUMUG: June 27-29,

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) NUMUG: June 27-29,

The Next Standards Document …what to expect NUMUG: June 27-29,

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 NUMUG: June 27-29,

Questions? NUMUG: June 27-29,