BADGER* Measurement of Carborundum B-10 Areal Density in Millstone Unit 1 Spent Fuel Racks

R. A. HallDominion, Nuclear Analysis and Fuel

2016 NEI Used Fuel management Conference5/5/2016

*Boron-10 Areal Density Gauge for Evaluating Racks

1

History 6/2011 Millstone Unit 1 BADGER campaign

Carborundum – 50% B4C in Phenolic Resin 5 plates 31 inches tall between rack cells

0.21 inches thick

Contained in welded “pocket” with vent hole

As-built B-10 content ~0.1 – 0.11 g/cm2

Criticality analysis 0.048 g/cm2

Measurements Indicated B-10 content as low as 0.01 g/cm2

No confidence in measured results due to calibration drift, repeatability, noise, etc.

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History Similar to 3/2009 Palisades

Same vintage “Old” BADGER

Indicated B-10 loss as high as 2/3

NRC IN 2009-26

Began redesign of BADGER with NETCO MAVRIC/MCNP modeling

Equipment improvement

Measurement procedure changes

New calibration standards

New measurements August 2013

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BADGER Basics Neutron source head

Springs for geometry consistency

Neutron detector head Shielding

Multiple detectors

Springs for geometry consistency

Calibration stand Analog of rack storage cells

Multiple areal density (AD) standards

Unpoisoned region (no absorber)

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Simplified Calibration Model

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BADGER Basics Sources of bias and uncertainty

Head alignment and spacing

Detector voltage

Electrical noise

Gamma background

Counting statistics

Discriminator setting

Pulse pile-up

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BADGER Process Collect count rate data from calibration stand

Multiple AD standards

Calculate transmission ratio (TR) Absorber region CR / Unpoisoned region CR

Calibration curve Versus AD

Interpolation method

Measure in-rack TR Calculate measured AD

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2013 Calibrations

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MP1 Typical BADGER Calibration Result

CAL 3 DET 3

Unpoisonedregion

Out of rack

Standard 1Standard 2

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2013 Calibration Consistency

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smission Ratio

B‐10 Areal Density (g/ cm2)

MP1 BADGER Calibration DataDetector 2 Transmission Ratio vs B‐10 Areal Density

Scatter in calibration TRsrepresents half the B‐10 AD!

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Lessons Learned Material is very B-10 dense

Calibration curve is relatively flat Measurement is difficult!

Stability and repeatability are crucial Do not assume all measurements are good

Repeat calibrations to verify stability

Reject measurements if unstable/inconsistent

Rack uncertainty ≥ calibration uncertainty Calibrations reveal actual BADGER uncertainty

Do a lot of calibrations!

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Panel MeasurementsPanel Date Time Notes

5‐6‐IN 8/1/2013 11:28 Rejected due to system difficulties

5‐6‐IW 8/1/2013 13:33 Rejected due to system difficulties

5‐6‐INFS 8/5/2013 12:30 Fine scan to confirm 5‐6‐I‐N, not used in analysis

5‐10‐LS2 8/5/2013 15:13 Rejected due to system difficulties

5‐10‐LW 8/6/2013 9:02 Suspect, repeated, rejected

5‐7‐JE 8/6/2013 11:05 Suspect, repeated, rejected

5‐7‐ME 8/6/2013 12:38 Suspect, not repeated, rejected

5‐7‐MW 8/6/2013 14:07 Suspect, repeated, rejected

5‐9‐ME 8/7/2013 8:54 Suspect, repeated, rejected

5‐9‐MW 8/7/2013 10:19 Suspect, not repeated, retained for analysis

5‐9‐MN 8/7/2013 11:48 Suspect, repeated, rejected

5‐9‐MS 8/7/2013 13:17 Suspect, not repeated, retained for analysis

5‐9‐JW 8/8/2013 10:44 Retained for analysis

5‐9‐JE 8/8/2013 12:07 Retained for analysis

5‐9‐JS 8/8/2013 13:34 Retained for analysis

5‐7‐JS 8/12/2013 8:51 Retained for analysis

5‐7‐JEVER 8/12/2013 10:15 Repeat for verification, retained for analysis 

5‐7‐MWVER 8/12/2013 10:51 Repeat for verification, retained for analysis

5‐8‐IEVER 8/12/2013 11:27 Retained for analysis

5‐10‐LWVER 8/12/2013 13:11 Repeat for verification, retained for analysis

5‐9‐MEVER 8/12/2013 13:46 Repeat for verification, retained for analysis

5‐9‐MNVER 8/12/2013 14:27 Repeat for verification, retained for analysis

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“Suspect” Results 8/6/13-8/7/13Repeat measurement does not confirm anomalies

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MP1 BADGER SFP Transmission RatioPanel 5‐10‐LW

Suspect DET 2 Suspect DET 3

Verification DET 2 Verification DET 3

The "cal‐zone" (0.05 g/cm2 AD)

FAIL

PASS

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MP1 BADGER SFP Transmission RatioPanel 5‐9‐MN

Suspect DET 2

Suspect DET 3

Verification DET 2

Verification DET 3

Inter‐panel gap confirmed Unconfirmed 

anomaly

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“Suspect” Results 8/6/13-8/7/13Repeat measurement confirms panel gap at 62”

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MP1 BADGER SFP Transmission RatioPanel 5‐9‐ME

Suspect DET 2

Suspect DET 3

Verification DET 2

Verification DET 3

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“Suspect” Results 8/6/13-8/7/13Repeat measurement does not confirm anomalies

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MP1 BADGER SFP Transmission RatioPanel 5‐7‐MW

Suspect DET 2

Suspect DET 3

Verification DET 2

Verification DET 3

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“Suspect” Results 8/6/13-8/7/13Repeat measurement does not confirm anomalies

Lessons Learned System can generate phantom anomalies

When in doubt, REPEAT

System can generate biased TR Getting it wrong is easy, harder to get it right

Multiple repeat measurements are your friend

Don’t trust, question the data and verify

Stability and repeatability are crucial Do not assume all measurements are good

Repeat measurements to confirm

Repeat measurements are more valuable than additional panel measurements

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Effect of BADGER UncertaintyBADGER uncertainty creates a population distribution

Calibration measurements display uncertainty Un-degraded material, known B-10

For 0.05 g/cm2 B-10 calibration standard

TR Det2 = 0.121 ± 5.4%

TR Det3 = 0.122 ± 5.1%

Plot TR data as a CDF Calibration TR = 0.121 ± 5.3%

0.05 g/cm2 B-10

Rack panel TR= 0.089 ± 9.1% > 0.05 g/cm2 B-10

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Effect of BADGER Uncertainty Low and high TR values may be BADGER artifact, not degradation

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Fraction of Observations  (%)

Transmission Ratio Cumulative DistributionMP1 BADGER Calibrations and Rack Measurements 

Rack Meas Cal 0.05 AD

Cal 0.03 AD Normal CDF

Above mean TR ≠ degraded calibration standard

Below mean TR ≠ enriched calibration standard

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Lessons Learned System uncertainty

Visible in repeat calibrations

Quantifiable with repeat calibrations

Creates a distribution of results

Will be reflected in measured panel results Low TR points not likely super-enriched in B-10

High TR points may not represent low B-10

Statistical artifact or real B-10 change? Re-measure high and low TR panels / sections

High B-10 if low TR persists

Low B-10 if high TR persists

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MP1 Measured B-10 AD EstimateBest estimate avg. AD=0.087 (0.10 – 0.11 as-built)

y = 41.48x ‐ 1.0687R² = 0.9997

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Square Root of B‐10 Areal Density

Calibration Curve Extrapolation Average Rack AD Estimation

Average of Calibrations

Average MP1 Rack 1/TR

Linear (Average of Calibrations)

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MP1 ResultsCalibrations vs Panel Measurements

Panel average TR max/min range similar to cals 1.24 for panels (10)

1.18 for “good” calibrations (9)

Expect higher variation in panels (> AD than cals)

Panel TR SD (~9%) > 0.05 AD Cal. SD (~5%) Possible non-uniform B-10 loss

Possible variation in original manufacture AD

Expect higher variation in panels (> AD than Cals)

One panel gap found

No gross degradation found

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MP1 ResultsPoint-wise and panel average AD estimates

Best estimate AD for panel population 760 measured points

0.087 g/cm2 B-10 (0.048 criticality basis)

Panel average best estimate AD (10 panels) 0.086 g/cm2 B-10 average panel

0.071 g/cm2 B-10 minimum panel

0.104 g/cm2 B-10 maximum panel

Variation somewhat higher than calibrations (7.9% SD vs 5.3% SD)

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MP1 ResultsThe bottom line

~13-21% loss of B-10 (average) in 35 years

Consistent with coupon experience Kewaunee coupon trend ~14% loss in 30 years

“Old” BADGER AD results not reliable at MP1 No gross degradation found

Measured TR population distribution similar to calibration populations but with more B-10

Re-measure of panel 5-6-I-W 2013 vs 2011

2011 “degradation” NOT confirmed (next slide)

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MP1 BADGER Panel 5‐6‐I‐W2011 vs 2013

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2011_Det_1

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Revisiting Palisades Palisades measured gross degradation, BUT

MP1 and Palisades have the same material

“Old” BADGER gave invalid results at MP1

Palisades used old BADGER

Coupons indicate gradual B-10 loss

Is the original conclusion right?

“It is important to note that the significant degradation of the Carborundum plate at Palisades occurred without any indication from TOC [total organic carbon] or the coupons at another plant, indicating the failure of these techniques in this instance”.    [NRC Technical Letter, June 2013]

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Revisiting Palisades

“The only two BADGER campaigns known to have been conducted have shown significant panel degradation at both pools….. these results of significant phenolic resin absorber degradation at both plants tested by BADGER, which represent the only information available to directly assess absorber performance, are noteworthy and concerning”.   [NRC Technical Letter, June 2013]

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Questions?

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BADGER* Measurement of Carborundum B-10 Areal Density in Millstone Unit 1 Spent Fuel Racks

R. A. HallDominion, Nuclear Analysis and Fuel

2016 NEI Used Fuel management Conference5/5/2016

*Boron-10 Areal Density Gauge for Evaluating Racks

28