Environmental Neutron TLD Monitoring for ISFSI

Matthew J. Scannell, NextEra Energy Seabrook

James Giard - AREVA NP Inc. Environmental Laboratory

Jeffrey Raimondi, AREVA NP Inc. Environmental Laboratory

RETS/REMP Workshop June 2009

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• 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

Environmental Neutron TLD Monitoring for ISFSI

Introduction

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• 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

Environmental Neutron TLD Monitoring for ISFSI

Presentation Summary

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Environmental Neutron TLD Monitoring for ISFSI

Seabrook ISFSI View Looking West

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Environmental Neutron TLD Monitoring for ISFSI

Seabrook ISFSI View Looking North

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Environmental Neutron TLD Monitoring for ISFSI

Seabrook ISFSI View Looking South

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Environmental Neutron TLD Monitoring for ISFSI

Seabrook ISFSI View Looking East

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Environmental Neutron TLD Monitoring for ISFSI

Seabrook ISFSI NUHOMS® Horizontal Storage Modules with Shield Blocks at Lower Vents

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• 808/814 Badge Lithium Borate Elements – Three 814 elements (η+γ), natural isotopic abundances

– Three 808 elements (γ-only), depleted of 6Li and 10B

– Neutron signal subtract average 808 from average 814

Environmental Neutron TLD Monitoring for ISFSI

AREVA-NP 808/814 Badge

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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

Environmental Neutron TLD Monitoring for ISFSI

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• 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)ξ

– Gamma dose based on 451B ion chamber

– Total Dose (η+γ) is 162mrem

– Neutron dose is 9.7 mrem (6% of total dose)

– Result: NCF = 10.5 + 1.2 mR*n/mrem

ξ REMBALL neutron meter (BF3 tube in 9” Cd loaded polyethylene sphere) would have given similar NCF, within 15%

Environmental Neutron TLD Monitoring for ISFSI

Neutron Correction Factor

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• 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

Environmental Neutron TLD Monitoring for ISFSI

Background Measurements

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• 808/814 Badge Neutron Sensitivity (MDDneutron)

– MDDneutron = 4.65 * σn/NCF [Eq. 1] (Currie)

σn = uncertainty in neutron signal

NCF 10.5 mR*n/mrem

• 808/814 Badge MDDneutron as Function of Gamma Dose– Propagate 814 and 808 element uncertainty curves to get σn vs

gamma dose curve. Combine with [Eq. 1] to get:

– MDDneutron = 0.494 * (LiBOgamma)0.4331 [Eq. 2]

Where LiBOgamma = average 808 element responses.

Environmental Neutron TLD Monitoring for ISFSI

Neutron Minimum Detectable Dose Calculation

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MDD Equation Comparison

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

Environmental Neutron TLD Monitoring for ISFSI

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20 30 40 50 60 70

808 LiBO Gamma Signal (mR*)

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MDD Equation Comparison (Continued)

Compare MDDneutron [Eq. 1] points and [Eq. 2] Line on Field & Fade data

Environmental Neutron TLD Monitoring for ISFSI

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0 100 200 300 400 500 600

808 LiBO Gamma Signal (mR*)

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MDD Sensitivity

Expected Annual Neutron Sensitivity for Workers and Members of Public

Environmental Neutron TLD Monitoring for ISFSI

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 S&N Center

(mR*) (mrem) (mrem) (mrem) (mrem) (mrem)

40 2.44 9.8 2.2 0.45 0.013

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• MDDneutron as Function of Gamma Dose

– MDDneutron = 0.494 * (LiBOgamma)0.4331 [Eq. 2]

Based on 4.65 σn/NCF

• Critical Level LCneutron as Function of Gamma Dose

– LCneutron = 0.248 * (LiBOgamma)0.4331 [Eq. 3]

Based on 2.33 σn/NCF

Environmental Neutron TLD Monitoring for ISFSI

Analysis of ISFSI 808/814 Badge Neutron Results

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Seabrook ISFSI Gross Gamma and Neutron Results (mrem)Third Quarter, 2008 Outside Locations and Buildings

Environmental Neutron TLD Monitoring for ISFSI

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TL-67

SB

-35

SB

-38

SB

-37

SB

-31

SB

-30

TL-44

SB

-36

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-33

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-34

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-15

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-16

SB

-39

SB

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TL-68

TL-69

TL-12

TL-13

TL-11

TL-10

TL-36

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Seabrook ISFSI Gross Gamma and Neutron Results (mrem)

Fourth Quarter, 2008 Outside Locations and Buildings

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Environmental Neutron TLD Monitoring for ISFSI

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Seabrook ISFSI Gross Gamma and Neutron Results (mrem)

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

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Environmental Neutron TLD Monitoring for ISFSI

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Seabrook ISFSI Gross Gamma and Neutron Results (mrem)

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

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Environmental Neutron TLD Monitoring for ISFSI

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Seabrook ISFSI Monitoring Results

• 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.

Environmental Neutron TLD Monitoring for ISFSI

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%

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• 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

Environmental Neutron TLD Monitoring for ISFSI

Presentation Conclusions

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• 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 HSM’s 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 HSM’s 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.

Environmental Neutron TLD Monitoring for ISFSI

Presentation Conclusions (Continued)

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Environmental Neutron TLD Monitoring for ISFSI

Questions ?