ML12328A125

Licensee Slides from 11/20/12 Pre-Submittal Meeting to Discuss LAR for Spent Fuel Criticality (TAC ME8896 and ME8897)

ML12328A125
Person / Time
Site:	Comanche Peak
Issue date:	11/20/2012
From:	Luminant Generation Co
To:	Plant Licensing Branch IV
Singal B K
References
TAC ME8896, TAC ME8897
Download: ML12328A125 (30)

Text

Lumin Spent Fuel Pool Criticality L i cen se Amendm ent Request Pre-Submitt al Meeting November 20, 2012 SFP Meeting Agend a I* I'" . 'jl

• Introductions Purpose CPNPP Spent Fuel Pool Criticality Background and Status Proposed Technical Specification Changes Meeting Summary and Conclusion 1

Introductions I'" 1 ,= Luminant Power Company Ben Mays Tim Hope Jimmy Seawright Matt Weeks Cody Lemons Vice President, Engineering Manager, Nuclear Licensing Consulting Engineer -Regulatory Affairs Manager, Core Performance Engineering Core Performance Engineer Westinghouse Electric Company Kris Cummings Andrew Blanco Fuel Licensing Manager Senior Engineer I Purpose To provide the NRC an overview of the upcoming Spent Fuel Pool License Amendment Request, which will supplement Technical Specifications to address fuel discharged from post-uprate conditions.

This License Amendment Request will satisfy the commitment to prepare and submit a LAR, as specified in Confirmatory Action Letter 4-12-004.

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I CPNPP Proposed Approach Note that this License Amendment Request will be the first of 2 LAR's CPNPP has committed to submitting related to Spent Fuel Pool Criticality. The First LAR (discussed in this presentation):

will supplement TS 3.7.17 with limitations which will bound storage of fuel depleted at post-uprate conditions, will implement additional controls which ensure significant additional margin is maintained, and The Second LAR will "modernize" the CPNPP Analysis, and will include a full-scope reanalysis of the storage .... Goals Goals regarding this submittal:

II": 1) Continue the safe storage of the discharged fuel inventory at CPNPP Demonstrate continued compliance with regulatory requirements including 10CFR50.68 Restore limited ability for CPNPP to utilize the Region II storage racks for discharge fuel Enable limited ability to store fuel from 2RF13 (and future cycles) in a thermally dispersed configuration.

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CPNPP Proposed Approach The discussion will be divided into two focus areas: Addressing the impacts of increased power level on .. the current Analysis of Record, and associated changes to the fuel burnup limits ofTS 3.7.17. Incorporating additional reactivity marginIncreased Soluble Boron Limit of TS 3.7.16 Administrative Controls for Low Margin Assemblies added to TS4.3 Addressing Impact of Power Uprate The License Amendment Request wi" revise Figure 3.7.17-2, Burnup vs Initial Enrichment limits for "3 out of 4" storage.

• The existing limit wi" be identified as "Power History

• A second limit wi" be added, identified as "Power History> 3458 MWth and :s 3612 MWth" Requirements for determining the applicable curve wi" be clarified in the TS Bases, to specify that inclusion in any cycle with a Rated Thermal Power of up to 3612 MWth requires use of the higher limit

• Because CPNPP does not utilize fuel with initial enrichment values below 2% in Uprate Conditions, the post-uprate curve is conservatively "flat" below this value. 4

Addressing Impact of Power Uprate ..... ...c. ACCEPTABLE I" Draft revision to Figure 3.7.17-2 . I UNACCEPTABLE IT-,."'" t----+--t--I j -++ I Initial U-235 [nrlchment Iw/ol I' Addressing Impact of Power Uprate Figures 3.7.17-1 ("4 out of 4" limits) and 3.7.17-3 ("2 out of 4" will also be

• The existing burnup limits will be identified as "Power History 3458 MWth" No new curves applicable to Uprate fuel will be added to these Figures

• The TS Bases will be revised to clarify that:

• fuel irradiated at Uprate conditions cannot be stored in Region II in a "2 of 4" or "4 of 4" configuration, and IF the limitations are not satisfied for "3 of 4" storage , THEN the assembly will be limited to either: * "1 of 4" storage, or storage in Region I

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Addressing Impact of Power Uprate To support the revision to Figure 3.7.17-2, CPNPP will utilize the results of an analysis performed in 2010. The resulting administrative controls derived from this analysis were provided to the NRC during the May 2012 baseline inspection.

To determine the TS 3.7.17-2 limit for "3 out of 4" storage for a power level up to 3612 MWth,

• CPNPP utilized the methodology of the Analysis of Record which was approved by the NRC in 2001 (Reference ML012560143),

• The 2010 analysis utilized the specific codes and versions utilized in the Analysis of Record. I Addressing Impact of Power Uprate Changes to the inputs utilized in the original analysis are:

• Power level input changed from 3565 MWth to 3612 MWth=*1

• Thermal Flow input changed to represent uprated conditions I No other inputs were changed. Note that use of T-inlet value from original analysis is conservative

, for post uprate (actual moderator temperature lowered for the uprate, so using pre-uprate temperature is conservative)

Parameter Reactivity Impact Reactivity Impact of Power Change Changes to Reactivity Credits/Penalties 0.00478 Addition of Administrative Margin 0.00500 Total Reactivity Change Compensated by Revised TS 3.7.17-2 for the Uprate 0.01010 II 6

Addressing Impact of Power Uprate The CPNPP Analysis of Record is a site specific analysis based on a modified version of the Westinghouse Methodology described in , WCAP-14416-NP.

Prior to 2001, a non-conservatism in the WCAP-14416-NP methodology was identified.

This issue was addressed in the CPNPP Analysis of Record prior to receiving NRC approval.

-The NRC stated in a letter to Westinghouse that the methodology contained in WCAP-14416, other than the axial burnup bias, was still acceptable for use in new analyses (Reference ML012080337)

-The axial burnup bias is specifically addressed in the approved CPNPP Analysis of Record. -The 2010 Analysis was performed consistent with the Analysis of Record regarding the axial burnup bias Increasing Reactivity Margin During the May 2012 Baseline Inspection ofthe SFP configuration, the NRC indicated concerns with certain aspects the current Analysis of

• The Analysis of Record does not include Depletion Uncertainty in the unborated case (as was appropriate for the timeframe)

• The Analysis of Record does not consider the impact of burnable poisons on spent fuel reactivity.

To assure compliance with 10 CFR 50.68 and Design Basis Technical Specification 4.3.1, CPNPP has quantified uncredited reactivity margin in the SFP.

• The quantification of reactivity margin in the SFP offsets the concerns indicated by the NRC Low margin assemblies have been identified and collocation of low margin assemblies is managed through administrative controls which provide additional margin 7

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Increasing Reactivity Margin The 2001 Analysis of Record includes many aspects assumptions which are conservative utilizing conservative assumptions for axial burnup shape used to correct the axial burnup bias; ignoring the effect of annular axial blankets; ignoring decay time credit; Ignoring the presence of discharged Control Rods (RCCA) and spent burnable absorbers (i.e., WABA) in the spent fuel Increasing Reactivity Margin Two Technical Specification changes are proposed which will increase the subcritical margin in the Spent Fuel Pool: Increase Boron Requirement:

Increase the SFP Boron Concentration Limit of TS 3.7.16 from 2000 ppm to 2400 ppm Administrative Controls for Low Margin Assemblies:

Controls which manage collocation of low-margin assemblies in close proximity will be described in the FSAR A change to the Technical Specification Fuel Storage Design Features (TS 4.3.1.1) will reference the appropriate FSAR section 8

Increase Boron Requirement The increase in Soluble Boron limit from 2000 ppm to 2400 ppm provides significant margin in the portions of the analysis which credit soluble boron. The SFP boron is typically maintained above this value during normal operation.

Note that the Analysis of Record credits a maximum of 1900 ppm for accident scenarios. This change increases the margin above this value from 100 ppm to 500 ppm. more than 4000 pcm additional margin Administrative Controls for Low Margin Assemblies Administrative controls provide additional margin to the limits of 10CFR50.68 , which also requires Keff to be less than 1.0 with no soluble boron.

• The proposed method uses conservative estimates for various negative reactivity affects to determine the estimated reactivity margin for each fuel assembly. Administrative controls on fuel storage utilize the estimated reactivity margin to ensure multiple low margin fuel assemblies are not stored in close proximity.

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• • Administrative Controls for Low Margin Assemblies Examples of low margin fuel assemblies would include fuel with the following attributes:

• A burnup value close to the minimum value required by TS 3.7.17 for storage in its current configuration

• Contains less than 5 years of decay time

• Does not contain a discharged RCCA (which has a large negative reactivity affect due to neutron absorption)

• Does not contain a discharged discreet burnable poison (which have a smaller negative reactivity affect due to the water displacement)

Administrative Controls for Low Margin Assemblies An overview of the process used to determine acceptability of a storage configuration is described below. Step 1: Determine an estimate of "Reactivity Margin" for each fuel assembly which will be stored in Region II. Various credits are taken, which are shown in the following 2 slides. Each applicable credit is 'summed' for each fuel assembly to determine the total Estimated Uncredited Reactivity Margin. An assembly with no decay time, no excess burnup, and no insert, would have very near 0 pcm of excess reactivity margin. This assembly would most closely represent the nominal fuel assembly assumed in the Analysis of Record, and in the current TS 3.7.17 limits. 10

Administrative Controls for Low Margin Assemblies 150 pcm for each assembly with a Nominal Fuel Density of < 95.5% (Analysis of Record assumes 96.5%). 1000 pcm for any assembly containing a discharged RCCA.

• Note that this value is a conservatively low estimate of the actual reactivity impact. 200 pcm for any assembly containing a discharged BPRAIWABA. This is a conservatively low estimate for the water displacement affects of these inserts. Note that they contain absorber pins in varying amounts up to 24 pins (the estimate for 200 pcm is representative of the presence of 8 pins in one assembly in a 3 of 4 configuration).

Administrative Controls for Low Margin Assemblies 1000 pcm is credited for every 5000 MWD/MTU of excess burnup beyond the required value for storage in the current configuration.

Decay Time credit is applied, up to a maximum of 1351 pcm, based on the table below. No interpolation is performed, and the lower value in a range is utilized for conservatism.

Decay Time Reactivity (pcm) < 5 years 0 5 -10 years 534 10-15 years 900 15-20 years 1,161 >20 1,351 11

Administrative Controls for Low Margin Assemblies Step 2: For each storage location, review the reactivity margin of the eight adjacent locations (in a 3x3 array).

• The value of keff in the SFP is dependent on more than the single fuel assembly being reviewed; it is also dependent upon the surrounding fuel storage cells. By calculating an average value of the surrounding reactivity margins, an improved understanding of the reactivity margin of that area is achieved This "average" value is only intended to identify areas of the SFP where multiple low margin assemblies could be stored in close proximity

• Average values are not calculated for assemblies which meet the burnup requirements for a denser configuration based on the TS 3.7.17 limit Administrative Controls for Low Margin Assemblies Step 3: Compare minimum value of Averaged Reactivity Margin with a baseline standard A baseline value of Averaged Reactivity Margin of 1363 pcm was established in the May 2012 inspection.

CPNPP committed to the NRC (ref TXX-12-000148) to maintain this level of margin, and therefore this baseline value will continue to be utilized.

IF the proposed fuel movement would result in a configuration which has a minimum averaged reactivity margin value below the established baseline, THEN:

• the fuel movement sequence will NOT be performed, and

• changes to the sequence will made to satisfy the baseline value before moving fuel. 12

Administrative Controls for Low Margin Assemblies Example configurations which would be RESTRICTED due to the Administrative Controls:

Example #1: 5 assemblies with no excess decay t i me or burnup (beyond the TS 3.7.17 requirements), but each of which has an RCCA stored within the fuel assembly. Each assembly has a nominal density 95.5%, which provides an additional 150 pcm credit. RCCA o decaf Oe_xee:uSU RCCA RCCA RCCA o deQy 0 decaf 0 do_ G exc:aM. 8U 0 .XCftl BU 0 exC8Ui BU RCCA OdeQy o excnaBlJ The " averaged reactivity margin" value for the center location would only be 1150 pem, less than the baseline value of 1363 pcm. Administrative Controls for Low Margin Assemblies Example configurations which would be RESTRICTED due to the Administrative Controls:

Example #2: 5 assemblies with no excess decay time , but each with burnup values 5000 MWD/MTU beyond the beyond the TS 3.7.17 requirements.

The center assembly contains an RCCA. The " estimated reactivity margin" value for the center location is 2150 pcm (1000 for BU + 1000 for RCCA + 150 for dens i ty), but the surrounding assemblies would only have 1150 pcm. The " averaged reactivity margin" in the center location would therefore be 1350 pem , slightly less than the established baseline. 13

Administrative Controls for Low Margin Assemblie s This example provides a SATISFACTORY result. Example #3: 5 assemblies with no excess burnup , but each has 15 years of decay time. Two of the assemblies contains a d i scharged WABA. 110_ 15,..docoJ o...,...eu The "estimated reactivity margin" value for the center and left locations is 1511 pcm (1161 for decay + 200 for insert + 150 for density), but the surrounding assemblies would only have 1311 pcm. The "averaged reactivity margin" in the center location would therefore be 1391 pem, slightly above than the established baseline .

• However , if one WABAwas removed , the value would fall to 1351 pcm , below the baseline. Administrative Controls for Low Margin Assemblies The above examples demonstrate the high level of conservatism provided by this approach.

• The NRC reviewed the configuration in Region 1\ in May which established the baseline margin value for our

• CPNPP has utilized this method of margin management since June 2012. No safety concerns regarding the current SFP configuration were identified in the Confirmatory Action Letter.

• CPNPP has evaluated the margin impacts of storing the discharged fuel from 2RF13 into Region II, and determined that the established baseline would be maintained.

However, this fuel is currently stored in Region I per commitments.

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I Summary and The License amendment Request Supplement TS 3.7.17 by adding a burnup vs. enrichment curve for "3 of 4" storage at uprated conditions, using methods utilized in the CPNPP Analysis of Record. Revise TS 3.7.16 to increase the required SFP soluble boron to 2400 ppm Provide Administrative Controls in the FSAR (referenced from TS 4.3.1) which manage storage of low margin fuel assemblies.

These controls provide confidence that the 10CFR 50.68 limits remain satisfied.

Questions I Open Discussion 15