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Seabrook Station Unit I Fixed IncoreDetector System Analysis Supplementto YAEC-1 855PA

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Licensing Report

May 2014

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Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Paqe i

Nature of Changes

Section(s)Item or Page(s) Description and Justification1 Abstract Discuss new uncertainty analysis

Section 1.1Section 5.3Section 6.2Section 7.0Appendix B


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Page ii

Contents

Paqe

1.0 TECHNICAL EVALULATIO N ................................................................................ 1

1.1 Background ............................................................................................. 1

2.0 NEUTRO N CO NVERSIO N FACTO R .............................................................. 4

2.1 Current Licensing Basis .......................................................................... 4

2.2 Proposed M ethod ................................................................................. 6

3.0 REPLACEM ENT DETECTO RS ........................................................................ 8

3.1 General ................................................................................................... 8

3.2 Current Licensing Basis .......................................................................... 9

3.3 Proposed M odification ........................................................................... 9

4.0 DEPLETIO N CO RRECTIO N FACTO R .......................................................... 11

4.1 Current Licensing Basis ....................................................................... 11

4.2 Proposed M odification ......................................................................... 11

5.0 CO M PARISO N O F FINC RESULTS ............................................................... 12

5.1 General ................................................................................................. 12

5.2 Surveillance Param eter Com parisons ................................................... 12

5.3 Statistical Results ............................................................................... 26

6.0 UNCERTAINTY ANALYSIS ............................................................................ 27

6.1 Current Licensing Basis ....................................................................... 27

6.2 Proposed Uncertainty M odifications .................................................... 306.2.1 Overview .................................................................................... 306.2.2 M ethodology ............................................................................. 316.2.3 Uncertainty Calculation Details .................................................. 366.2.4 Uncertainty Calculation Results ................................................ 386.2.5 Analysis of Significant Trends .................................................. 42

7.0 CO NCLUSIO NS ............................................................................................ 46

8.0 REFERENCES ............................................................................................... 47

APPENDIX A ................................................................................................................. 48

APPENDIX B ................................................................................................................. 71


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Page iii

List of Tables

Table 1 Uncertainty Components and Confidence Multipliers from YAEC-18 5 5 P A .................................................. .......................................... . . 2 9

Table 2 95/95 Uncertainty Limits for FAH and FQ ............................ . . . . . . . . . . . . . . . . . . . . . . . . . . 43

Table B-1 Conservative Trend Slope of FAH UL(95/95) and FQ UL(95/95) for aMaximum of 8 Failed Detector Strings .................................................. 75


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensing Report Page iv

List of Figures

Figure 1 Comparison of Heat Flux Hot Channel Factor FQ for Cycle 1 .................... 14








Figure 9 Comparison of Enthalpy Rise Hot Channel Factor FAH for Cycle 1 ........ 18

Figure 10 Comparison of Enthalpy Rise Hot Channel Factor FAH for Cycle 2 ....... 18



Figure 13 Comparison of Enthalpy Rise Hot Channel Factor FAH for Cycle 5 .......... 20




Figure 17 Comparison of Axial Offset for Cycle 1 ................................................... 22








Figure 25 Flow Diagram of Calculations .................................................................. 35

Figure 26 FAH UL(95/95) Plots for Cycle 14, FAH Near Maximum ........................... 44

Figure 27 FQ UL(95/95) Plots for Cycle 14, FAH Near Maximum ............................. 45

Figure A-1 Measured Signal Divided by Detector Power versus DetectorExposure, O riginal Detectors ............................................................... 55

Figure A-2 Measured Signal Divided by Detector Power versus DetectorExposure, Replacement Detectors ...................................................... 56


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensing Report Page v

Figure A-3 Calculated Gamma Signal Divided by Detector Power versusDetector Exposure, Original Detectors ................................................ 57

Figure A-4 Calculated Gamma Signal Divided by Detector Power versusDetector Exposure, Replacement Detectors ........................................ 58

Figure A-5 Inferred Neutron Signal Divided by Detector Power versus DetectorExposure, O riginal Detectors ............................................................... 59

Figure A-6 Inferred Neutron Signal Divided by Detector Power versus DetectorExposure, Replacement Detectors ...................................................... 60

Figure A-7 Neutron Conversion Factor versus Detector Exposure, OriginalD e te cto rs ........................................................................................... . . 6 1

Figure A-8 Neutron Conversion Factor versus Detector Exposure, ReplacementD e te cto rs ........................................................................................... . . 6 2

Figure A-9 Calculated Gamma Divided by Measured Signal versus DetectorExposure, O riginal Detectors ............................................................... 63

Figure A-10 Calculated Gamma Divided by Measured Signal versus DetectorExposure, Replacement Detectors ...................................................... 64

Figure A-1 1 Depletion Correction Factor .................................................................. 65

Figure A-12 Difference between Predicted and Measured Signals, OriginalDetectors, Proposed M odel ................................................................. 66

Figure A-13 Difference between Predicted and Measured Signals, ReplacementDetectors, Proposed M odel ................................................................. 67

Figure A-14 Ratio of Measured Signals for Original to Replacement Detectors,B atch 1, C ycle 14 .............................................................................. . . 68

Figure A-15 Ratio of Measured Signals for Original to Replacement Detectors,B atch 1, C ycle 15 .............................................................................. . . 69

Figure A-16 Ratio of Measured Signals for Original to Replacement Detectors,B atch 2 , C ycle 15 .............................................................................. . . 70

Figure B-1 Example Linear Least Square Fits of FAH (UL 95/95) and FQ (UL 95/95) ........ 76


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensina Reoort Paae vi

Nomenclature

(If applicable)

AcronymFAH

FdhFQFIDSNCFGCFDPCST

SGSMCyOTh

lOTh avg

RnCn

CdERMS2D3DOa

Ob

Oc

Od

Ot

Ork

DefinitionEnthalpy rise hot channel factorSame as FAH; nomenclature used in YAEC-1855PAHeat flux hot channel factorFixed Incore Detector SystemNeutron Conversion FactorGamma Correction FactorDepletion Correction FactorTotal calculated detector signalCalculated detector signal due to gammaMeasured signalUnit conversion factor for calculated detector gamma signalThermal neutron fluxAverage thermal neutron fluxNeutron reaction rate for Pt-1 95Same as NCFCoefficient of DPC versus detector exposureDetector exposureRoot Mean SquareTwo-dimensionalThree-dimensionalStandard deviation for signal reproducibilityStandard deviation for analytical methodsStandard deviation for axial power shapeStandard deviation for detector processingStandard deviation for integral detector processingStandard deviation for total system (3D)Standard deviation for integral processing (2D)Confidence interval multiplier


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Paqe vii

ABSTRACT

This document provides modifications to the Fixed Incore Detector System (FIDS)

Analysis methodology described in YAEC-1855PA. The FIDS Analysis methodology

has been in use at Seabrook Station to monitor core power distribution surveillance

parameters since Cycle 5 in 1995. The FIDS uses fixed platinum detectors which are

predominantly gamma sensitive and have a contribution from neutron capture. The

FIDS has operated successfully for over 20 years of operation. In 2007, Seabrook

undertook a phased detector replacement project. The Seabrook specification for

replacement detectors was written to produce a like-for-like replacement of the original

detectors. However, changes in manufacturing techniques required changes to the

FIDS Analysis methodology to incorporate correction factors to normalize the

replacement and the original detector signals to the standard detector performance

required by the analysis methodology. Two replacement detector strings were installed

in Cycle 14 and three detector strings were installed in Cycle 15. During Cycle 16,

Seabrook undertook a program to trend detector performance over the 15 cycles of

operation to determine appropriate modifications to the Fixed Incore Detector Code

(FINC).

Based on the trending analysis, revisions were made to the FIDS Analysis

methodology. The modifications include a more precise method to determine the

detector neutron conversion factor to better predict the neutron portion of the fixed

detector signal based on the predicted neutron reaction rate. Modifications were also

made to track detector exposure and to make a depletion correction to the measured

signal based on the detector exposure. To normalize the replacement and original

detectors, correction factors were quantified and incorporated as a multiplier on the

measured signal of the replacement detectors.

The FINC code was modified to incorporate the revised FIDS Analysis methodology and

the proposed modifications were used to rerun all 15 cycles of flux maps.


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensingq Report Page viii

The measurement of a core power distribution is built upon a series of comparisons

between measured incore signals and predicted incore signals in instrumented locations

of the core, and expansion of the resultant power distribution data to uninstrumented

locations. In YAEC-1855PA the uncertainty for detector processing is calculated by

comparing detector signals measured at various core conditions to predictions of the

detector signals at these same core conditions. While the FIDS uncertainty based on

the difference between measured and predicted detector signals is conservatively

bounding, it is not a good representation of the true measurement uncertainty. The

YAEC-1855PA uncertainty analysis is replaced by a method that propagates the

uncertainties through the FIDS analysis system using a Monte Carlo statistical

simulation and determines a better representation of the true measurement uncertainty

for FQ and FAH over a wide range of conditions. This uncertainty analysis methodology

is similar to that employed by the Reference 5 and 6 core power distribution monitoring

systems previously reviewed and approved by the NRC.

This report describes the detector performance trending analysis of the 15 cycles,

documents the proposed modifications to the FIDS Analysis methodology and provides

a new determination of the resulting measurement uncertainty for the FQ and FAH

Technical Specifications (Tech Specs) surveillance parameters.


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensing Report Paqie 1

1.0 TECHNICAL EVALULATION

1.1 Background

Seabrook Station started Cycle 1 with a combination fixed/movable detector system in

58 locations within the reactor core. The Detector Assemblies at that time

accommodated the movable incore detector path, the qualified core exit thermocouple,

and the five fixed platinum incore detectors. The movable detector system was used

during the first four cycles of operation and was also used to benchmark the fixed

platinum incore detectors. The fixed detector system was licensed by the NRC during

Cycle 3 using the methodology described in YAEC-1855PA (Reference 1). The fixed

platinum incore detectors and the methodology described in YAEC-1855PA have been

used exclusively to monitor the core since Cycle 5.

YAEC-1855PA describes the methodology and uncertainty analysis used to determine

the measured core power distribution using the fixed incore detectors and the

associated uncertainty. The fixed incore detectors are self-powered platinum detectors

which are predominantly gamma sensitive and produce a signal proportional to the local

gamma flux in the reactor core. Although the majority of the signal from the platinum

detectors is derived from the gamma flux, a portion of the signal is due to the neutron

flux from an n,y reaction. There are 58 incore detector assemblies distributed radially

throughout the core. Each assembly contains 5 individual fixed incore detectors

uniformly spaced axially along the height of the core. Thus, a total of 290 detectors are

providing continuous core power distribution information. The detector signals are

scanned once per minute and stored such that they may be retrieved and analyzed to

determine the three dimensional power distribution and associated Tech Spec

surveillance parameters. The computer software package used to analyze the fixed

incore detector signals to determine the power distribution parameters is referred to as

S3FINC and is described in YAEC-1855PA.


.Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensing Report Page 2

S3FINC has two major components. The first is the predictive codes CASMO-3

(Reference 2) for cross section generation and gamma response and SIMULATE-3

(Reference 3) for predicting the core power distribution and individual detector

responses. The second is the Fixed Incore Detector Code (FINC) which uses the

SIMULATE-3 output and measured fixed incore detector signals to determine the

measured core power distribution.

Included in YAEC-1855PA is a discussion on how the detector signals are treated as

inputs to the methodology. Important points to note from YAEC-1855PA are:

* The use of the CASMO-3/SIMULATE-3 for power distribution prediction

* The use of a standard detector approach for power distribution analysis

* The assumption that 25% of the signal is due to neutrons

* The overall uncertainty analysis for use with Tech Specs surveillance of FQ and FAH.

Although not specifically addressed in YAEC-1855PA, detectors need to be replaced

due to long term wear on the high pressure seals and signal connectors. To this extent,

Seabrook has a prototype Replacement Project to replace Detector Assemblies starting

with the OR13 (Cycle 14) refueling outage. Two detectors were replaced during OR13

and three were replaced during OR14 (Cycle 15). Seabrook has also embarked on a

program to analyze data from the first 15 cycles of operation to quantify trends in the

detector performance data and to validate the uncertainty analysis presented in YAEC-

1855PA. This topical report serves as a supplement to YAEC-1 855PA. The changes

proposed are:

* An improved prediction of the neutron component of the detector signal - Neutron

Conversion Factor (NCF),

* Applying correction factors to the measured detector signal of the replacement

detectors to better assure normalization to a standard detector performance -

Gamma Correction Factor (GCF),


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensing Report Page 3

* Accounting and correcting the measured detector signal for detector depletion to

better assure normalization to a standard detector performance - Depletion

Correction (DPC), and

* Replacing the uncertainty analysis with a new analysis that better represents the

true measurement uncertainty for FQ and FAH over a wide range of conditions by

propagating the uncertainties through the FIDS analysis system using a Monte Carlo

statistical simulation method.



2.0 NEUTRON CONVERSION FACTOR

2.1 Current Licensing Basis

The signal from a platinum fixed incore detector is predominantly from gamma

interaction with the platinum. A portion of the detector signal is from neutron interaction

with the platinum, predominantly the Pt-1 95 isotope. It was recognized in both the

topical report YAEC-1855PA and in the associated NRC SER dated 12/23/1993 that the

fraction of the total detector signal due to neutrons is approximate and not well known at

the time. Section 3 of YAEC-1855PA describes the assumptions used to determine an

estimate for the fraction of total detector signal due to neutrons. At that time, public

domain studies and a Seabrook specific sensitivity study based on operational data

were used to determine the estimate of the fraction neutron component to be used as

an input assumption in determining the predicted detector signal. Based on the

literature and the sensitivity study, a value of 25% of the total signal was attributed to

neutrons.

To accommodate the platinum detectors, SIMULATE-3 was modified, to allow the user

to input the fractional neutron component of the predicted detector signal. This fraction

is given in terms of the total detector signal, and it can be distributed by either or both

the fast and thermal neutron flux. The gamma portion of the detector's signal is

determined through the total responses determined in CASMO-3 cases and local

detector neutron flux calculations within SIMULATE-3. This is the standard method of

detector calculations used within SIMULATE-3. The total neutron portion of detector

signal is determined from the input fraction and is then distributed by the SIMULATE-3

calculated relative local thermal neutron flux levels at the detector locations. The

individual detector's gamma and neutron portions are then summed to determine the

detector's total signal.

As described in YAEC-1 855PA, a value of 0.25 was used for the thermal neutron

component of the predicted detector signal. Thus the total gamma signal was

calculated in SIMULATE-3 as:

AREVA Inc. ANP-3243NPRevision I


The above value of ST was used in FINC starting in Cycle 1.



2.2 Proposed Method

To better cover a broader range of reactor core design and operating conditions, a new

formulation for determining the neutron component of the predicted detector signal was

developed. Rather than use the straight 25% of the gamma signal to represent the

neutron portion, it was determined that a more accurate representation of the total

signal could be accomplished by adding a neutron portion to the gamma signal based

on total neutron reaction rate. To do this, a new factor called the Neutron Conversion

Factor (NCF) was introduced. The new formulation using the neutron conversion factor

is shown in Equation 2.

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3.0 REPLACEMENT DETECTORS

3.1 General

The Seabrook specification for replacement detectors was written to produce a like-for-

like replacement of the original detectors. The replacement detectors were built to the

original specification and within the as-built attributes of the original detectors including

detector geometry, dielectric densities and component material impurities. The

replacement detectors were also constrained to the characteristics assumed in the

analysis software licensed for the system. These precautions served to preserve the

like-for-like nature of the replacement detectors to the original detector. Nonetheless,

the manufacturing enhancements developed in more than 20 years of detector service

result in differences in detector performance as observed in gamma testing of the

replacement detectors and archive original detectors.




As described in YAEC-1855PA, the FINC code depends on the concept of a standard

detector. In the standard detector approach, the raw measured detector signals must

be corrected for individual detector differences. The signal from any individual detector

is a function of the incident flux, the amount of detector material and manufacturing

differences. Thus, each detector's signal must be modified to correspond to a signal

given by a standard detector. The standard detector is one built to exact design

dimensions. Since Cycle 1, each measured detector signal is corrected by a sensitivity

factor. The sensitivity factor is defined as the ratio of the detector surface area to the

surface area of a standard detector. The data required for the calculation of the

sensitivity factors is provided by the detector manufacturer's as-built data of detector

length and weight. The sensitivity factors for the replacement detectors were calculated

in the same manner as the original detectors in Cycle 1 using the as-built length and

weight. This feature in the current licensing basis has not changed. The sensitivity

factor is applied to the measured signal and is used to create a standard detector by

using the manufacturer's measured weight and length for each detector compared to

the weight and length of a standard detector.

3.3 Proposed Modification

The replacement detector specification required that each individual replacement

detector is tested for operation using a gamma source. In addition, to verify

compatibility, original archive detectors are tested in the same gamma source

environment. During the testing, it was noted that the replacement detectors produced

a lower signal than the original detectors in the same gamma field and could not be

corrected by application of the simple sensitivity factor based only on as-built detector

length and weight.



The Gamma Correction Factor (GCF) was introduced in Cycle 14 to make the

replacement detector signal compatible with the signal from the original detectors. The

GCF is input to FINC as a simple multiplier on the measured signal for the replacement

detectors. Different values of the GCF are used for the Batch 1 and Batch 2

replacement detectors based on changes in the manufacturing process. As part of the

trending analysis, the GCF was refined through the trending analysis of Appendix A as

shown in Figure A-14, Figure A-15, and Figure A-16. The trending analysis compared

the difference in signal between the replacement detectors and their symmetric partners

over Cycles 14 and 15 for the Batch 1 replacement detectors and over Cycle 15 for the

Batch 2 replacement detectors. The GCF values reflect in-reactor measurements of

symmetric partners in the Seabrook reactor environment. The value of Batch 1 GCF is

1.0577 and the Batch 2 GCF is 1.0849. The Batch 2 replacement detectors defined the

future manufacturing process. It is the intent to use the Batch 2 GCF for future batches

of replacement detectors. However, since the magnitude of the detector signal can be

affected by the manufacturing process, future batches of detectors may require their

own GCF determined through testing.

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4.0

4.1

DEPLETION CORRECTION FACTOR

Current Licensing Basis

The current licensing basis does not include a depletion correction factor. The modeling

of the effects of elemental platinum depletion is not required as described in YAEC-

1855PA in response to RAI Question 4. [

] Thus, no provisions were provided in

the current licensing basis for a depletion correction.

4.2 Proposed Modification

] This effect is primarily due to

the consumption of the Pt-195 isotope which is the predominant contributor to the

neutron component of the total gamma signal of the detector.

From the trending analysis covering all 15 cycles, a linear Depletion Correction (DPC)

was derived in Appendix A as a function of detector exposure as shown in Figure A-1 1.

Detector exposure is the accumulated fuel exposure of the assembly containing the

detector, averaged over the detector length. With the proposed modification of FINC,

the DPC will be calculated for each detector based on detector exposures using the

derived curve. The DPC will be applied to each individual detector and will vary with

detector exposure. [

From Equation 3, the depletion correction factor utilizes the detector exposure to obtain

a multiplier to be applied to the measured signal for each detector.


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1 855PALicensing Report Page 12

5.0 COMPARISON OF FINC RESULTS

5.1 General

With the completion of the trending analysis in Appendix A, the proposed modifications

to FINC were established. To determine the effect of these modifications on the

surveillance parameters, all 15 cycles of flux maps were rerun with the revised version

of FINC incorporating the proposed modifications. The 15 cycles provides a good test

of the proposed modifications to FINC under an array of operating conditions that

involved changes in fuel management strategy, changes in fuel design, power uprate,

normal core tilt condition and axial offset anomalies. The evaluation of the data is for

flux maps that were run under equilibrium conditions as would be the case for normal

surveillance.

5.2 Surveillance Parameter Comparisons

This section shows the comparison of the original FINC version to the modified FINC

version for the Tech Spec surveillance parameters. Although all 15 cycles of flux maps

were rerun with the modified version of FINC, comparisons are provided here for the

first eight cycles. During these cycles the licensing model used a fixed 25% of the

gamma signal as the neutron portion of the signal and did not include a correction for

detector exposure. The proposed modifications to FINC utilize a neutron conversion

factor and the neutron reaction rate to determine the neutron portion of the signal. The

proposed model also includes a correction for depletion based on the exposure of each

individual detector. The comparisons for the heat flux hot channel factor FQ are

provided in Figure 1 through Figure 8. The value of FQ includes the current

measurement uncertainty of 5.21% and the engineering heat flux uncertainty of 3%.

The comparisons for the enthalpy rise hot channel factor FAH are provided in Figure 9

through Figure 16 and the comparisons for axial offset are provided in Figure 17

through Figure 24. FAH values are shown without any uncertainty because the

uncertainty factor is applied to the limit, as specified in the core operating limits report.



The results provided in Figure 1 through Figure 24 show that performance of the

proposed model compares well to the current licensing basis model. In these figures

the proposed model contains the neutron conversion factor, detector exposure tracking

and the depletion correction. The NCF was introduced in Cycle 9 in 2002 so that a

comparison to the original FINC version, consistent with the current licensing basis

methodology could not be made after Cycle 8.


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1 855PALicensinq Report Paqie 14

Figure 1 Comparison of Heat Flux Hot Channel Factor FQ for Cycle 1

2.20 -

2.00 1

1.80 -

0E1.60. -

1.40 -

1.20 -

*Licensing Model OProposed Model1.00 -

0 2000 4000 6000 8000 10000 12000 14D00

Cyde Exposure (MWD/MTU)


1.95

1.90 -

1.85

EE: 1.80 [] 0

1.75 -00

1.75 -01.70

* Licensing Model O Proposed Model1.65

0 2000 4000 6000 8000 10000 12000



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2.00

1.95

00

1.90

E 0E1.85

1.80 -+

1.75 - 0

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1.90

1.85

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1.55

VPOD

100

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2.00 ,

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0 5000 10000 15000 20000 25000



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1.90

1.85

E

1.70

1.65

1 Licensing Model -0 Proposed Model1.60 ,,,

0 5000 10000 15000 20D00

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1.90

1.88

1.86

1.84

•o1.82E

E 1.80

• 1.78

1.76

1.74

1.72

1.70

200000 5000 100O0 15000




Figure 9 Comparison of Enthalpy Rise Hot Channel Factor FAH forCycle I

1.40

1.38

1.36

1.3413

E 1.32

91.30

1.28

1.26

1.24

p

0*

0 0

* Licensing Model 0'Proposed Model

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12000 14000

Figure 10 Comparison of Enthalpy Rise Hot Channel Factor FAH forCycle 2

1.46

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= 1.40

1.38

1.36

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1.34 - I

0 5000 10000 150D0 20000





1.46

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1.42 -

1.41

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0 2000 4000 6000 8000 10000 12000 14000 16000


Figure 12 Comparison of Enthalpy Rise Hot Channel Factor FAH for

Cycle 4

1.46

n n

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1.40

1.38

1.36

*Licensing Model OProposed Model I

1.34 - I

0 5000 10000 15000 20000


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1.49

1.48

1.47

1.46

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1.41

1.40

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1.52 A 17

1E 5

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1.46- i_

1.44 ,

1.42 Licensing Model OProposed Model

0 5000 10000 15000 20000 25000

Clyde Exposure (MWD/MTU)




1.45

1.44

1.43

1.42

E 1.41

E OS1.40

1.39

1.38

1.37

1.360 5000 10000 15000 2000O



1.44

144

1.43

1.431

E1.42~ 00

1.40 -

1.39 -

1.9 #Licensing Mode 1 0Proposed ModelI

0 5000 10000 15000 20000




Figure 17 Comparison of Axial Offset for Cycle 1

0.0

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-8.0

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2000i 100 120 40

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10000 120D0 14000

6.0

5.0

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Seabrook Station Unit I Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Page 24


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Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1 855PALicensinq Report Paqe 26

5.3 Statistical Results

With the proposed modifications, a new uncertainty analysis was performed that better

represents the true measurement uncertainty for FQ and FAH over a wide range of

conditions by propagating the uncertainties through the FIDS analysis system using a

Monte Carlo statistical simulation method. This statistical simulation method replaces

the signal reproducibility and detector processing uncertainty terms in the YAEC-

1855PA uncertainty analysis. [

] The

results of the simulation analysis were statistically combined with the Analytical Methods

and Axial Signal Power Shape uncertainty terms from YAEC-1855PA, which remained

unchanged, and determined a total measurement uncertainty of the FIDS analysis

system of less than 4.0% for FAH and less than 5% for FQ.

The accuracy and functionality of the FIDS analysis system remains comparable to the

original YAEC-1855PA analysis and the Moveable Incore Detector System.



6.0 UNCERTAINTY ANALYSIS


As noted in YAEC-1 855PA, the uncertainty of the fixed incore detector system is

addressed in four individual parts. Each of these parts are quantified and then

statistically combined to achieve a total system uncertainty at a 95/95 confidence level

with a one-sided tolerance limit. The uncertainties associated with FAH and FQ have

traditionally been treated independently. The uncertainty in the three-dimensional

parameter FQ contains all axial and radial components of the system uncertainty.

However, the two-dimensional parameter FAH is an axially integrated quantity that does

not contain the axial uncertainty component. Uncertainties for each of these quantities

are defined independently below.

The total system uncertainty applied to the three-dimensional quantity of FQ defined as:



The second uncertainty factor is applied to the two-dimensional axially integrated

quantity of FAH. The radial or FAH uncertainty requires the combination of three of the

four uncertainty components. The axial power shape uncertainty does not apply to the

integrated radial parameters and the radial detector processing uncertainty contains

only the axially integrated processing component. The system two-dimensional

uncertainty, as applied to FAH, is defined as:

The 95/95 confidence level with a one-sided tolerance limit can be calculated from the

standard deviation for each component and the appropriate confidence level multiplier.

The confidence level multiplier (k) is directly dependent on the size of the data set and

was determined from Reference 4. For reference, the components and confidence

factors from YAEC-1 855PA are provided in Table 1 below.


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1 855PALicensing Report Paae 29

Table I Uncertainty Components and Confidence Multipliers fromYAEC-1855PA



6.2 Proposed Uncertainty Modifications

6.2.1 Overview

A new uncertainty analysis was performed that better represents the true measurement

uncertainty for FQ and FAH over a wide range of conditions by propagating the

uncertainties through the FIDS analysis system using a Monte Carlo statistical

simulation method. This statistical simulation method replaces the signal reproducibility

(aa), and detector processing (Gd and Ge) uncertainty terms in the YAEC-1855PA

uncertainty analysis.

The FIDS analysis system is statistical in nature. Consequently, the determination of

the measured peaking factor is affected by detector measurement variability, the

number and layout of available detectors, signal replacement techniques, expansion of

the measured power to uninstrumented core locations, and any differences between

predicted and true power distribution. Accordingly, a range of conditions need to be

considered in determination of the system uncertainty. For this reason the FIDS

analysis system uncertainty has been determined using the Monte Carlo statistical

simulation method in which [

] The FIDS analysis system determines the measured power

distribution FAH and FQ surveillance parameters from these simulated detector signals

using the power distribution processing methodology described in Section 4.0 of YAEC-

1855PA, including the proposed modifications described in Sections 2.2, 3.3, and 4.2 of

this document. In the simulation, a range of detector failures is considered in

combination with a range of perturbations between the predicted and true power

distribution.

This uncertainty analysis methodology is similar to that employed by the Reference 5

and 6 core power distribution monitoring systems previously reviewed and approved by

the NRC.



6.2.2 Methodology

The FIDS analysis system contains two major software components: FINC and

SIMULATE-3. In normal core monitoring, SIMULATE-3 provides the predicted detector

signals and a predicted power distribution. FINC uses the measured and predicted

detector signals to adjust the predicted power distribution to produce the measured

power distribution. This algorithm is described in YAEC-1855PA, Section 4.4.

For the uncertainty calculation, [

I





] The uncertainty factors for

Analytical Methods and Axial Signal Power Shape (ob and Oc in Equations 7 and 8 of

YAEC-1855PA) are retained because those effects cannot be analyzed by this

uncertainty methodology.

FQ UL(95/95) and FAH UL(95/95) are also computed with an equivalent non-parametric

method that does not assume the distributions are normal. [

[

I




Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensingq Report Page 35

Figure 25 Flow Diagram of Calculations



6.2.3 Uncertainty Calculation Details

6.2.3.1 Physics Analytical Methods Uncertainty

The CASMO-3 and SIMULATE-3 code package used to generate all analytical

predictions for power distribution related parameters has not changed since the initial

licensing analysis in YAEC-1855PA. Since the physics analysis methods have not

changed, the analytical methods uncertainty, 0 b, has not changed

6.2.3.2 Axial Power Shape Uncertainty

As noted in YAEC-1855PA, the axial profiles calculated by SIMULATE-3 are the basis

for determining the measured axial power shapes from the fixed detector data within the

core. Measured axial power distributions are determined from the fixed incore detector

signals and from the detailed axial power shapes generated by the SIMULATE-3

analytical model. Since the SIMULATE-3 methodology has not changed, the axial

power shape uncertainty, ao, has not changed.

6.2.3.3 Simulation Uncertainty Analysis

6.2.3.3.1 Operating State Points

Three operating state points were chosen for the uncertainty analysis:

* Cycle 14, cycle exposure where FNH is near the maximum, excluding the beginning

of cycle non-equilibrium cases.

* Cycle 14, cycle exposure where FQ is near the maximum, excluding the beginning of

cycle non-equilibrium cases.

* Cycle 13, cycle exposure where axial offset is near minimum (largest negative value)

and the Axial Offset mismatch is also near maximum.



6.2.3.3.2 Perturbations in Measured Power Distributions

6.2.3.3.3 Detector Signal Variance

Detector signal variance consists of reproducibility of detector responses, uncertainty in

plant parameter measurements, variability in reactor conditions, uncertainty in detector

sensitivity corrections (including sensitivity, gamma, and depletion corrections), and

uncertainty in the detector predictive model. [

I



6.2.4 Uncertainty Calculation Results

Three reactor operating state points were analyzed. [

I


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6.2.5 Analysis of Significant Trends


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensing Report Paqe 43

Table 2 95/95 Uncertainty Limits for FAH and FQ



Figure 26 FAH UL(95/95) Plots for Cycle 14, FAH Near Maximum



Figure 27 FQ UL(95/95) Plots for Cycle 14, FAH Near Maximum



7.0 CONCLUSIONS

The information provided here to supplement YAEC-1 855PA shows the modifications

made to the FINC code to improve the accuracy and accommodate replacement

detectors consistent with the concept of the standard detector as noted in YAEC-

1855PA. The modifications to FINC utilize the information determined from an

extensive trending program to analyze the first 15 cycles of operation of Seabrook. The

rerun of 15 cycles of flux maps showed detector performance data Which provides

confidence in the proposed method of analysis.

The current licensing basis uncertainty analysis methodology is replaced with a new

methodology that determines the true measurement uncertainty for FQ and FAH. These

uncertainties are specific to the analytical physics methods, CASMO-3 and SIMULATE-

3 and the incore data processing code, FINC, and the general design of the platinum

fixed detectors for Seabrook Station. Conservatively bounding measurement

uncertainty values of 4.0% for FAH and 5.0% for FQ for the FIDS analysis methodology

are proposed. These are slightly higher than the values supported by the uncertainty

analysis and are consistent with the Moveable Incore Detector System (MIDS).


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1 855PALicensinq Report Paqe 47

8.0 REFERENCES

1. Joseph P. Gorski, "Seabrook Station Unit 1 Fixed Incore Detector System

Analysis," YAEC-1855PA, October 1992.

2. M. Edenius and Bengt-Herman Forssen, "CASMO-3: A Fuel Assembly

Burnup Program, User's Manual," STUDSVIK/NFA-89/3, January 1991.

3. K.S. Smith, K.R. Rempe and D.M. VerPlanck, "SIMULATE-3: Advanced

Three-Dimensional Two-Group Reactor Analysis Code, Methodology,"

STUDSVIK/NFA-89-04, November 1989.

4. D.B. Owen, Factors for One-Sided Tolerance Limits and for Variables

Sampling Plans, SCR607, US Dept. of Commerce, March 1963.

5. R. Kochendarfer, "Statistical Universal Power Reconstruction with Fixed

Margin Technical Specifications," ANP-1 0301 P-A. AREVA, Inc.,

September 2013.

6. R. Kochendarfer, C. T. Rombaugh and A.Y. Cheng, Fixed Margin

Technical Specifications," BAW-10158P-A. Babcock and Wilcox, August

1986.

7. Carl A. Bennett and Normal L. Franklin, "Statistical Analysis in Chemistry

and the Chemical Industry", John Wiley & Sons, New York, 1954.

8. Gerald J. Hahn and Samuel Shapiro, "Statistical Models in Engineering",

John Wiley & Sons Inc., New York, 1967.

9. Mary Gibbons Natrella, "Experimental Statistics", National Bureau of

Standards", 1963.



APPENDIX A

The trending analysis processed the measured signal data for 15 cycles of Seabrook

operation. The trending analysis used the calculation sequence of cross section

generation by CASMO-3, power prediction generation by SIMULATE-3 and measured

data processed by FINC. The CASMO-3 and SIMULATE-3 codes are the same

versions used in YAEC-1855PA and have not changed. The trending analysis

contained the use of the Neutron Conversion Factor (NCF) that was introduced in

Cycle 9.

CASMO-3 provides the cross section input and gamma response to SIMULATE-3. The

power distribution predictions, predicted gamma signal, and neutron reaction rate are

produced by SIMULATE-3. For the trending analysis, the data extracted from

SIMULATE-3 was the three dimensional power distributions, the detector gamma signal

and the nodal neutron reaction rate for platinum. FINC processed the measured signals

correcting for the surface area to obtain results for a standard detector.

Post processing software and Excel spreadsheets were used to analyze the data. The

following pieces of data were used in the trending analysis:

" The measured signal, SM, from FINC corrected for surface area to correct to a

standard detector.

* The predicted gamma signal, SG, for the five detector levels came from SIMULATE-3

without modification.

" The detector neutron reaction rate came from the 3D predicted nodal neutron

reaction rate for platinum from SIMULATE-3 and collapsed by the post processing

software over the detector length and axial location to obtain Rn.



" Detector power was generated by the post processing software from the 3D nodal

assembly power fraction from SIMULATE-3. The nodal assembly power fraction

was collapsed over the detector length and axial location to generate a detector

power in megawatts.

* Detector exposure was generated by the post processing software from the 3D

nodal assembly exposure from SIMULATE-3. The nodal assembly exposure was

collapsed over the detector length and axial location to generate a detector exposure

in GWD/MTU. The detector exposure was accumulated to be current for each flux

map.

* A power independent measured detector signal was generated by the post

processing software by dividing the measured signal, SM, by the detector power.



The trending analysis is based on 15 cycles of Seabrook operation as summarized

below:

* Seabrook contains 58 detector strings with 5 detectors per string.

* The 15 cycles comprise 813 reactor flux maps.

" Failed detectors or detector strings were removed, i.e., no signal produced.

" The analysis considered only original detectors for the determination of the NCF and

DPC. Replacement detectors were incorporated into the figures to show

consistency.

* This resulted in 221,226 unique data points.

" A total of 145 anomalous flux maps were removed. Non-equilibrium flux maps and

flux maps with an axial offset anomaly were removed in order to obtain a good

estimate of the NCF and DPC parameters. A total of 145 flux maps were removed.

* The result was that 180,393 unique data points were used in the trending analysis.

The results of the trending analysis are provided in Figure A-1 through Figure A-16.

The trending analysis for the original detectors is over all 15 cycles while the trending

for the replacement detectors is over Cycle 14 and 15 for the Batch 1 replacement

detectors and Cycle 15 for the Batch 2. replacement detectors. Where applicable, the

figures show a linear fit through the data as a solid black line.

Figure A-1 shows the measured signal (SM) divided by the detector power versus

detector exposure for the original detectors. Figure A-2 shows the measured signal

divided by the detector power versus detector exposure for the replacement detectors.

The overall trend shows a decrease in signal as a function of detector exposure for both

the original and replacement detectors. The trend shows changes due to changes in

neutron and gamma spectrum during cycle burnup; changes from cycle to cycle due to

core design and operating conditions; and changes due detector depletion.



Figure A-3 shows the calculated gamma signal (Cy*SG from Equation 2 in Section 2.2)

divided by the detector power versus detector exposure for the original detectors.

Figure A-4 shows the calculated gamma signal divided by the detector power versus

detector exposure for the for the replacement detectors. The overall trend shows a

decrease in the calculated gamma signal as a function of detector exposure for both the

original and replacement detectors. The trend shows that the predictive model captures

the effect of changes during the cycle, changes in core design and fuel management

strategy and changes in operation conditions. The predictive model does not account

for detector depletion.

Figure A-5 shows the inferred neutron signal [ ] divided by the detector

power versus detector exposure for the original detectors. The overall trend shows a

decrease in the inferred neutron signal as a function of detector exposure. Figure A-6

shows the inferred neutron signal divided by the detector power versus detector

exposure for the replacement detectors. Due to the short exposure time and the small

number of replacement detectors, the overall trend shows no discernible decrease in

the inferred neutron signal as a function of detector exposure.

To isolate the effect of detector depletion, the Neutron Conversion Factor (NCF)

calculated from Equation 6 is used. Figure A-7 shows the NCF versus detector

exposure for the original detectors. The overall trend shows very slight decrease in the

NCF as a function of detector exposure. From this data a linear relationship for the

NCF was determined as NCF = A + B*E where E is the detector exposure in GWD/MTU

and A and B are the constants of the linear equation. For comparison, Figure A-8

shows the NCF versus detector exposure for the for the replacement detectors. Again,

due to the short exposure and the small number of replacement detectors, the overall

trend shows no discernible decrease or increase in the NCF as a function of detector

exposure. It should be noted that the NCF for all detectors is derived from the original

detectors only. Figure A-8 is intended to show the similarity in NCF between original

and replacement detectors.


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Paqe 52

Figure A-9 shows the calculated gamma signal divided by the measured signal as a

function of detector exposure for the original detectors. From this figure it is clear that

the gamma portion of the signal has been approximately 75% of the total signal. The

refinement made in Cycle 9 to use the NCF rather than a straight 25% of the gamma

portion of the signal more accurately represents the change in the neutron portion of the

signal with changing core conditions. Figure A-10 shows the calculated gamma signal

divided by the measured signal as a function of detector exposure for the replacement

detectors. The trend of the replacement detectors appears to be consistent with that of

the original detectors.

From the 15 cycles of trend data, there are observed trends in the measured signal, the

calculated gamma signal, and the inferred neutron signal. [

I

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Figure A-12 shows the difference between the predicted and measured signals for the

original detectors using the proposed model. This figure shows there is no trend in the

data with exposure and provides a basis for the proposed model.



Replacement detector strings were installed in Cycle 14 (Batch 1) and Cycle 15

(Batch 2). The replacement detectors were constructed to be similar to the original

detectors, but are slightly less sensitive than the original detectors due primarily to

changes in the manufacturing process. The change in sensitivity was noted and the

FINC code was modified to introduce a batch dependent Gamma Correction Factor. As

part of the trending analysis, the change in the Batch 1 and Batch 2 sensitivity was

refined by comparing the measured signal from the replacement detectors to their

symmetric partners of original detectors. The detector signals were corrected for

depletion effects using the DPC from above. The comparisons are shown graphically in

Figure A-14 and Figure A-15 for the Batch 1 detectors and in Figure A-16 for the Batch

2 detectors.

Figure A-1 3 shows the difference between the predicted and measured signals for the

replacement detectors using the proposed model with the Gamma Correction Factor.

This figure shows there is no trend in the data with exposure but a small bias. Since the

bias is small, this provides a basis for the proposed model with the replacement

detectors.

Using the approach of comparing to symmetric partners, the Gamma Correction Factor

(GCF) is computed as:

Equation 11 GCF = Signal from Original Detector * DPC

Signal from Replacement Detector * DPC

Gamma Correction Factor for the replacement detectors is provided by detector batch

and the GCF for Batch 1 is 1.0577 and the GCF for Batch 2 is 1.0849. These values

with be input to FINC as constants to be applied to the Batch 1 and Batch 2 measured

signals as simple multipliers.



Figure A-1 Measured Signal Divided by Detector Power versus Detector Exposure, Original Detectors



Figure A-2 Measured Signal Divided by Detector Power versus Detector Exposure, Replacement Detectors -



Figure A-3 Calculated Gamma Signal Divided by Detector Power versus Detector Exposure, Original Detectors



- Figure A-4 Calculated Gamma Signal Divided by Detector Power versus Detector Exposure, Replacement Detectqor



Figure A-5 Inferred Neutron Signal Divided by Detector Power versus Detector Exposure, Original Detectors



-Figure A-6 Inferred Neutron Signal Divided by Detector Power versus Detector Exposure, Replacement Detectors



Figure A-7 Neutron Conversion Factor versus Detector Exposure, Original Detectors



Figure A-8 Neutron Conversion Factor versus Detector Exposure, Replacement Detectors



Figure A-9 Calculated Gamma Divided by Measured Signal versus Detector Exposure, Original Detectors



Figure A-10 Calculated Gamma Divided by Measured Signal versus Detector Exposure, Replacement Detectors



Figure A-11 Depletion Correction Factor



Figure A-12 Difference between Predicted and Measured Signals, Original Detectors, Proposed Model



Figure A-1 3 Difference between Predicted and Measured Signals, Replacement Detectors, Proposed Model



Figure A-14 Ratio of Measured Signals for Original to Replacement Detectors, Batch 1, Cycle 14



Figure A-15 Ratio of Measured Signals for Original to Replacement Detectors, Batch 1, Cycle 15 -



- Figure A-16 Ratio of Measured Signals for Original to Replacement Detectors, Batch 2, Cycle 15



APPENDIX B




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Table B-1 Conservative Trend Slope of FAH UL(95/95) and FQUL(95/95) for a Maximum of 8 Failed Detector Strings


Seabrook Station Unit 1 Fixed Incore Detector System Analysis Supplement to YAEC-1855PALicensinq Report Paqe 76

Figure B-1 Example Linear Least Square Fits of FAH (UL 95/95) and FQ(UL 95/95)

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