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Estimates of ISFSI Site Boundary Doses

Estimates of ISFSI Site Boundary Doses. Andrew Hodgdon, Jo Ann Pelczar Radiological Engineering Group and Mel Gmyrek Environmental Laboratory FRAMATOME ANP DE&S 400 Donald Lynch Boulevard Marlborough, MA 01752 Telephone: (978) 568-2522 e-mail: Melvin.Gmyrek@Framatome-ANP.com.

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Estimates of ISFSI Site Boundary Doses

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  1. Estimates of ISFSI Site Boundary Doses Andrew Hodgdon, Jo Ann Pelczar Radiological Engineering Group and Mel Gmyrek Environmental Laboratory FRAMATOME ANP DE&S 400 Donald Lynch Boulevard Marlborough, MA 01752 Telephone: (978) 568-2522 e-mail: Melvin.Gmyrek@Framatome-ANP.com RETS REMP Conference 6/24-26/2002

  2. ISFSI = Independent Spent Fuel Storage Installation Wet Pool Dry Pad RETS REMP Conference 6/24-26/2002

  3. Feds Regulate to 25 mrem/yearto Real Member of Public • There are: • Plants without ISFSIs • Plants with ISFSIs • Decommissioned Plants with ISFSIs • Regulations: • (plant) 40CFR190 “provide reasonable assurance that annual dose does not exceed 25 millirems” • (ISFSI) 10CFR72.104 “annual dose to real individual beyond controlled area must not exceed 25 mrem” RETS REMP Conference 6/24-26/2002

  4. Factors Affecting Compliance 1. State limit is lower than Fed’s (2 plants) 2. Small Site (< 3000 feet to boundary) 3. Public access to the site (roads, camp) 4. Nearby dwellings (homes and condominiums) 5. Nearby schools 6. Nearby commercial properties RETS REMP Conference 6/24-26/2002

  5. Plant Modifications That Increase Dose • Add ISFSI • 20 mrem/h contact (typical) • Dose is higher at vents • Hydrogen Water Chemistry • BWR only • 100 mR/hr turbine area • Store Old Steam Generators • 1 mR/h contact • Sell-off property • Up-rate power • Store waste (old turbine blades) RETS REMP Conference 6/24-26/2002

  6. Options to Demonstrate Compliance • 1. Take credit for Occupancy • 2. Predict with Models • 3. Make Measurements • 4. Model and Measure (M&M) • 5. Buy Property • 6. Build Shield or Berm • 7. Limit ISFSI Loads • less fuel • lower burnup • longer decay time RETS REMP Conference 6/24-26/2002

  7. Options to Demonstrate Compliance(cont’d) • 1. Take Credit for Occupancy • Start with conservative calculation(s) • Residents (100%) • School, roads, visitors center, hikers, clam diggers, etc. (<100%) • Administrative requirements to update basis yearly RETS REMP Conference 6/24-26/2002

  8. Options to Demonstrate Compliance(cont’d) • 2. Predict With Models (Without Measurements) • Highly uncertain and/or very expensive • MicroSkyshine • Simple • Greater than 100% errors • MCNP - very detailed, more accurate but expensive RETS REMP Conference 6/24-26/2002

  9. RETS REMP Conference 6/24-26/2002

  10. Options to Demonstrate Compliance(cont’d) • 3. Make Measurements (Without Models) • Background variation (noise) swamps dose rate (signal) • Detection Limit is 70 mrem/year* • Distance curve is required • (* The detection limit for “on/off” sources, like BWR N-16, is 10 mrem/year) RETS REMP Conference 6/24-26/2002

  11. Background Variation RETS REMP Conference 6/24-26/2002

  12. Distance Curves • Highly problem dependent • Add significant error • Are very hard to measure • Can be measured for rare “on/off” sources • Turning the source on and off allows the background to be measured at the same location and at nearly the same time. Unfortunately, an ISFSI is always on. • Here are the four Distance Curves we know about RETS REMP Conference 6/24-26/2002

  13. Distance Curves for “On/Off” Sources RETS REMP Conference 6/24-26/2002

  14. Options to Demonstrate Compliance(cont’d) • 4. Model and Measure (M&M) • Pro • More accurate • Model (MCNP) provides distance curve • Surveys validate the results • Model suitable for further engineering • Con • Need experts in modeling and measurements RETS REMP Conference 6/24-26/2002

  15. Recipe forM & M (Model and Measure) • 1. Set up model (MCNP) • contact model • distance model • 2. Take contact surveys to calibrate model • 3. Take near surveys to validate distance curve • 4. Run model at boundary to get answer RETS REMP Conference 6/24-26/2002

  16. Contact versus Distance Model • Contact Model • Details inside the building or bunker • Complex • 10 to 20 hours to run • Results in contact dose rates • Distance Model • Starts where contact model leaves off • Simple • Runs in 10 minutes • Results in site boundary dose rates RETS REMP Conference 6/24-26/2002

  17. Three Examples • Ex. #1 BWR N-16 Streaming (presented at ANS RPSD 98) • Ex. #2 NUHOMS ISFSI (presented at ANS RPSD 02) • Ex. #3 NAC ISFSI (in process) RETS REMP Conference 6/24-26/2002

  18. Ex. #1 - BWR N-16 Streaming RETS REMP Conference 6/24-26/2002

  19. Assignment • Shorten outage by a half day by removing some N-16 shielding while at power. • Risk - violate boundary limit. • Solution - use M&M to: • Guide shield removal • Validate boundary dose at end of year RETS REMP Conference 6/24-26/2002

  20. Dose Points RETS REMP Conference 6/24-26/2002

  21. Turbine Building Section RETS REMP Conference 6/24-26/2002

  22. Plan RETS REMP Conference 6/24-26/2002

  23. Contact vs Distance Model RETS REMP Conference 6/24-26/2002

  24. Calibrated Distance Curve RETS REMP Conference 6/24-26/2002

  25. Zoom at Fenceline RETS REMP Conference 6/24-26/2002

  26. Ex. #2 - NUHOMS ISFSI(20 bunkers shown) RETS REMP Conference 6/24-26/2002

  27. Assignment • Build contact dose rate model to: • Permit further engineering (more fuel in bunker) • Permit site boundary calculations RETS REMP Conference 6/24-26/2002

  28. Facility Description • 900 PWR Assemblies in 36 bunkers • 10 metric tons fuel per bunker • 16 kW heat • 4E16 photons/second/bunker (measured value) • 4E9 neutrons/second/bunker (measured value) • Major Nuclides - Cs-137, Co-60, and Cm-244 RETS REMP Conference 6/24-26/2002

  29. Canister For 24 Assemblies RETS REMP Conference 6/24-26/2002

  30. Canister Being Pushed Into Bunker RETS REMP Conference 6/24-26/2002

  31. Results • 1. Built MCNP Model • 2. Used Contact Surveys to Calibrate Model • neutrons <1 mrem/h (not reported here) • photons 20 to 100 mR/h • 3. Distance Model Not Yet Completed RETS REMP Conference 6/24-26/2002

  32. Model / Measured RETS REMP Conference 6/24-26/2002

  33. Ex. #3 - NAC Type ISFSI RETS REMP Conference 6/24-26/2002

  34. Assignment • Demonstrate compliance • Reduce control area RETS REMP Conference 6/24-26/2002

  35. Concrete Bunkers RETS REMP Conference 6/24-26/2002

  36. Contact Model RETS REMP Conference 6/24-26/2002

  37. Model Predictions • Contact Model • Runs take 8 hours • 20 mrem/h contact • Neutrons at vents and top • Distance Model • Runs take 10 minutes • 25 mrem/year at about 740 feet • Neutron dose less than 4% • Model provides spectrums RETS REMP Conference 6/24-26/2002

  38. RETS REMP Conference 6/24-26/2002

  39. Measuring Background(Reuter-Stokes HPIC - ISFSI Empty) RETS REMP Conference 6/24-26/2002

  40. Measurements In Progress RETS REMP Conference 6/24-26/2002

  41. As a Results of Using M & M(Modeling and Measurement) • Ex. #1 – Saved a half day during the refuel outage • Ex. #2 - Built a validated model • will be used to analyze higher loading • will be used for site boundary doses • Ex. #3 - Work in progress to reduce Control Area RETS REMP Conference 6/24-26/2002

  42. “Must Not Exceed 25 mrem per year” • Measurement alone can’t demonstrate compliance • Models alone can’t demonstrate compliance • What works is modeling and measurement combined RETS REMP Conference 6/24-26/2002

  43. CONTACTS Andrew Hodgdon (Radiological Engineering Group) (978) 568-2750 Andrew.Hodgdon@Framatome-ANP.com Framatome ANP DE&S 400 Donald Lynch Boulevard Marlborough, MA 01752 Mel Gmyrek (Environmental Laboratory) (978) 568-2522 Melvin.Gmyrek@Framatome-ANP.com Framatome ANP DE&S Environmental Laboratory 29 Research Drive Westborough, MA 01581-3913 RETS REMP Conference 6/24-26/2002

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