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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
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

isfsi i ndependent s pent f uel s torage i nstallation
ISFSI = Independent Spent Fuel Storage Installation

Wet Pool

Dry Pad

RETS REMP Conference 6/24-26/2002

feds regulate to 25 mrem year to real member of public
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

factors affecting compliance
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

plant modifications that increase dose
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

options to demonstrate compliance
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

options to demonstrate compliance cont d
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

options to demonstrate compliance cont d8
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

options to demonstrate compliance cont d10
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

background variation
Background Variation

RETS REMP Conference 6/24-26/2002

distance curves
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

distance curves for on off sources
Distance Curves for “On/Off” Sources

RETS REMP Conference 6/24-26/2002

slide14

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

recipe for m m model and measure
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

contact versus distance model
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

three examples
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

ex 1 bwr n 16 streaming
Ex. #1 - BWR N-16 Streaming

RETS REMP Conference 6/24-26/2002

assignment
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

dose points
Dose Points

RETS REMP Conference 6/24-26/2002

turbine building section
Turbine Building Section

RETS REMP Conference 6/24-26/2002

slide22
Plan

RETS REMP Conference 6/24-26/2002

contact vs distance model
Contact vs Distance Model

RETS REMP Conference 6/24-26/2002

slide24

Calibrated Distance Curve

RETS REMP Conference 6/24-26/2002

slide25

Zoom at Fenceline

RETS REMP Conference 6/24-26/2002

ex 2 nuhoms isfsi 20 bunkers shown
Ex. #2 - NUHOMS ISFSI(20 bunkers shown)

RETS REMP Conference 6/24-26/2002

assignment27
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

facility description
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

slide29

Canister For 24 Assemblies

RETS REMP Conference 6/24-26/2002

slide30

Canister Being Pushed Into Bunker

RETS REMP Conference 6/24-26/2002

slide31

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

model measured
Model / Measured

RETS REMP Conference 6/24-26/2002

ex 3 nac type isfsi
Ex. #3 - NAC Type ISFSI

RETS REMP Conference 6/24-26/2002

assignment34
Assignment
  • Demonstrate compliance
  • Reduce control area

RETS REMP Conference 6/24-26/2002

concrete bunkers
Concrete Bunkers

RETS REMP Conference 6/24-26/2002

contact model
Contact Model

RETS REMP Conference 6/24-26/2002

model predictions
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

measurements in progress
Measurements In Progress

RETS REMP Conference 6/24-26/2002

as a results of using m m modeling and measurement
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

must not exceed 25 mrem per year
“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

contacts
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