Environmental Neutron TLD Monitoring for ISFSI

1
Environmental Neutron TLD Monitoring for ISFSI
RETS/REMP Workshop June 2009

• Matthew J. Scannell, NextEra Energy Seabrook

James Giard - AREVA NP Inc. Environmental
Laboratory
Jeffrey Raimondi, AREVA NP Inc. Environmental
Laboratory
2
Introduction
Environmental Neutron TLD Monitoring for ISFSI

• Seabrook Station ISFSI Operational in 3rd
  Quarter, 2008
• ISFSI located amongst occupied buildings (workers
  and members of the public)
• Gamma dose expected to be main component
• Desire minor neutron dose to be quantified
• AREVA-NP Environmental Laboratory TLD Service
• Routine gamma environmental TLD measurements
• Neutron measurement capabilities with 808/814
  badge

3
Presentation Summary
Environmental Neutron TLD Monitoring for ISFSI

• Seabrook Station ISFSI Layout
• ISFSI Facility design
• Surrounding Buildings
• AREVA-NP 808/14 Badge
• Design features
• Determination of Neutron Correction Factor
• Determination of MDDneutron as a function of
  gamma dose
• Expected Neutron Sensitivity
• Seabrook Station ISFSI Monitoring Results
• 3rd Quarter, 2008, during first spent fuel load
  campaign
• 4th Quarter, 2008, after spent fuel loaded
• Summarize 808/814 Badge Capabilities for ISFSI
  Neutron Monitoring

4
Seabrook ISFSI View Looking West
Environmental Neutron TLD Monitoring for ISFSI
5
Seabrook ISFSI View Looking North
Environmental Neutron TLD Monitoring for ISFSI
6
Seabrook ISFSI View Looking South
Environmental Neutron TLD Monitoring for ISFSI
7
Seabrook ISFSI View Looking East
Environmental Neutron TLD Monitoring for ISFSI
8
Seabrook ISFSI NUHOMS Horizontal Storage Modules
with Shield Blocks at Lower Vents
Environmental Neutron TLD Monitoring for ISFSI
9
AREVA-NP 808/814 Badge
Environmental Neutron TLD Monitoring for ISFSI

• 808/814 Badge Lithium Borate Elements
• Three 814 elements (??), natural isotopic
  abundances
• Three 808 elements (?-only), depleted of 6Li and
  10B
• Neutron signal subtract average 808 from average
  814

10
Environmental Neutron TLD Monitoring for ISFSI

• AREVA-NP 808/814 Badge (Continued)
• 808/814 Badge Environmental Holder Configuration
• 808/814 badge cases
• Cases sealed in plastic pouches
• Otterbox water-proof holder

11
Neutron Correction Factor
Environmental Neutron TLD Monitoring for ISFSI

• 808/814 Badge Neutron Correction Factor (NCF)
• Overnight Irradiate 808/814 Badges at HSM lower
  vents
• Neutron dose based on REM-500 tissue equivalent
  proportional counter (TEPC)?
• Gamma dose based on 451B ion chamber
• Total Dose (??) is 162mrem
• Neutron dose is 9.7 mrem (6 of total dose)
• Result NCF 10.5 1.2 mRn/mrem
• ? REMBALL neutron meter (BF3 tube in 9 Cd loaded
  polyethylene sphere) would have given similar
  NCF, within 15

12
Background Measurements
Environmental Neutron TLD Monitoring for ISFSI

• 808/814 Badge Natural Background Measurements
  Prior to ISFSI Operations
• Ninety-seven Field Data Points
• Quarterly measurements at ISFSI Monitoring
  Locations (outside within buildings)
• normally used to establish historical background
• Five Fade Badge Points
• Dosed to known gamma levels (i.e. 200 mrem)
• Placed in field for quarter
• normally used to evaluate TL signal fade

13
Neutron Minimum Detectable Dose Calculation
Environmental Neutron TLD Monitoring for ISFSI

• 808/814 Badge Neutron Sensitivity (MDDneutron)
• MDDneutron 4.65 sn/NCF
  Eq. 1 (Currie)
• sn uncertainty in neutron signal
• NCF 10.5 mRn/mrem
• 808/814 Badge MDDneutron as Function of Gamma
  Dose
• Propagate 814 and 808 element uncertainty curves
  to get sn vs gamma dose curve. Combine with Eq.
  1 to get
• MDDneutron 0.494 (LiBOgamma)0.4331
  Eq. 2
• Where LiBOgamma average 808 element responses.

14
MDD Equation Comparison
Environmental Neutron TLD Monitoring for ISFSI

• Compare MDDneutron Eq. 1 points and Eq. 2
  Line for Field data

15
MDD Equation Comparison (Continued)
Environmental Neutron TLD Monitoring for ISFSI

• Compare MDDneutron Eq. 1 points and Eq. 2
  Line on Field Fade data

16
MDD Sensitivity
Environmental Neutron TLD Monitoring for ISFSI

• Expected Annual Neutron Sensitivity for Workers
  and Members of Public

Quarterly Expected 365-Day 2000-hour 400-hour 12-hour
Gamma Quarterly Public at Workers Public at Public at
Signal MDDneutron Site Boundary On Site Fitness Center SN Center
(mR) (mrem) (mrem) (mrem) (mrem) (mrem)

40 2.44 9.8 2.2 0.45 0.013


17
Analysis of ISFSI 808/814 Badge Neutron Results
Environmental Neutron TLD Monitoring for ISFSI

• MDDneutron as Function of Gamma Dose
• MDDneutron 0.494 (LiBOgamma)0.4331
  Eq. 2
• Based on 4.65 sn/NCF
• Critical Level LCneutron as Function of Gamma
  Dose
• LCneutron 0.248 (LiBOgamma)0.4331
  Eq. 3
• Based on 2.33 sn/NCF

18
Seabrook ISFSI Gross Gamma and Neutron Results
(mrem)
Environmental Neutron TLD Monitoring for ISFSI

• Third Quarter, 2008 Outside Locations and
  Buildings

19
Seabrook ISFSI Gross Gamma and Neutron Results
(mrem)
Environmental Neutron TLD Monitoring for ISFSI

• Fourth Quarter, 2008 Outside Locations and
  Buildings

20
Seabrook ISFSI Gross Gamma and Neutron Results
(mrem)
Environmental Neutron TLD Monitoring for ISFSI

• Third Quarter, 2008 ISFSI PA Fence, Spent Fuel
  Loading Campaign

21
Seabrook ISFSI Gross Gamma and Neutron Results
(mrem)
Environmental Neutron TLD Monitoring for ISFSI

• Fourth Quarter, 2008 ISFSI PA Fence, Shield
  Blocks at HSM Vents

22
Seabrook ISFSI Monitoring Results
Environmental Neutron TLD Monitoring for ISFSI

• Comparison of Neutron Contribution to Dose at
  ISFSI PA Fence
• NCF determined at HSM vent is conservative once
  HSM vents are shielded.
• Sky-shine neutrons are lower energy spectrum than
  at HSM vents
• Sky-shine neutron-to-gamma ratio different than
  at HSM vents.

Measurement Location Neutron Percentage of Total Dose
Survey Instruments at HSM vent (From NCF Determination) 6
Average of ISFSI Fence Locations Tl-75, 77, 78 and 79 Third Quarter 2008, During Spent Fuel Loading 5
Average of ISFSI Fence Locations Tl-75, 77, 78 and 79 Fourth Quarter 2008, Shield Blocks at HSM Vents 22
23
Presentation Conclusions
Environmental Neutron TLD Monitoring for ISFSI

• AREVA-NP 808/14 Badge for ISFSI Neutron
  Monitoring
• Simple methods to determine NCF at suitable
  location with available survey meters
• Good neutron sensitivity for monitoring worker
  and public doses
• Curve established for MDDneutron as a function of
  gamma dose is applicable to each badge
  measurement.
• NCF will, if anything, yield conservative neutron
  doses when the neutron spectrum shifts to lower
  energy
• When sky-shine predominates
• as distance from ISFSI increases

24
Presentation Conclusions (Continued)
Environmental Neutron TLD Monitoring for ISFSI

• Seabrook Station ISFSI Monitoring Results
• 3rd Quarter, 2008, Spent Fuel Loading Campaign
• No dose increases in surrounding buildings, or
  outside ISFSI
• ISFSI fence locations near HSMs had gamma
  neutron dose increase. (ISFSI fence was boundry
  of restricted area)
• Neutron is 5 of total dose (neutron 6 at
  HSM vents)
• 4th Quarter, 2008, HSM lower vents shielded by
  Jersey barriers
• No dose increases in surrounding buildings, or
  outside ISFSI.
• ISFSI fence locations near HSMs had gamma
  neutron dose increase. Much less than 3rd
  quarter (due to shield blocks)
• Neutron is 22 of total dose (neutron 5 for
  3rd Quarter)
• Neutrons from sky-shine may be conservatively
  reported due to neutron energy spectrum being
  lower than at HSM vents.

25
Questions ?
Environmental Neutron TLD Monitoring for ISFSI