ML16035A187

Monticello - Exemption Request for Nonconforming Dry Shielded Canister Dye Penetrant Examinations, Supplemental Information

ML16035A187
Person / Time
Site:	Monticello
Issue date:	01/29/2016
From:	Gardner P A Northern States Power Co, Xcel Energy
To:	Document Control Desk, Division of Spent Fuel Management, Office of Nuclear Reactor Regulation
Shared Package
ML16035A214	List: ML16035A184 ML16035A185 ML16035A186 ML16035A187
References
L-MT-16-003, TAC L25058
Download: ML16035A187 (12)

Text

Xcel Energy°Monticello Nuclear Generating Plant2807 W County Rd 75Monticello, MN 55362January 29, 2016L-MT-1 6-00 310 CFR 72.7U.S. Nuclear Regulatory Commission ATTN: Document Control DeskDirector, Division of Spent Fuel Management Office of Nuclear Material Safety and Safeguards Washington, DC 20555-0001 Monticello Nuclear Generating PlantDocket No. 50-263Renewed Facility Operating License No. DPR-22Independent Spent Fuel Storage Installation Docket No. 72-58Exemption Request for Nonconformingq Dry Shielded Canister Dye Penetrant Examinations, Supplemental Information (TAC No. L25058)

References:

1) NSPM letter to NRC Document Control Desk, Exemption Request forNonconforming Dry Shielded Canister Dye Penetrant Examinations, L-MT-1 5-056, dated September 29, 2015 (ADAMS Accession No.ML1 5275A023)

2) NRC letter to NSPM, First Request for Additional Information forReview of Exemption Request for Nonconforming Dry ShieldedCanister Dye Penetrant Examinations, dated December 15, 2015(ADAMS Accession No. ML15350A064)

3) NSPM letter to NRC Document Control Desk, Exemption Request forNonconforming Dry Shielded Canister Dye Penetrant Examinations, Schedule for Reply to Request for Additional Information, L-MT-16-002, dated January 6, 2016Pursuant to 10 CFR 72.7, "Specific Exemptions",

Northern States Power Company, aMinnesota corporation (NSPM), doing business as Xcel Energy, submitted Reference 1to request an exemption to the requirements of 10 CFR 72.212(b)(3) and 10 CFR72.212(b)(1

1) for one NUHOMS Dry Shielded Canister (DSC) designated number 16due to nonconforming dye penetrant (PT) examinations performed during the loadingcampaign started in September 2013.In Reference 2, the NRC Division of Spent Fuel Management (DSFM) Staff transmitted a request for additional information (RAI) associated with their review of the Exemption

Request, and requested a reply date of January 19, 2016. In Reference 3, NSPMrequested deferral of the reply to seven (7) RAI questions to February 2, 2016. AsIADO Document Control DeskPage 2discussed in a January 5, 2016 teleconference, the reply to RAI-5 was possibly going tobe deferred later. However, that reply is included herein.Enclosure 1 provides the replies to the eight (8) RAI questions that were provided inReference 2.Enclosure 2 provides AREVA Calculation 11042-0205 Revision 2, which supportschanges made to address RAI-2, RAI-3, and RAI-5.Enclosure 3 provides Technical Report Document 51-9234641-001 "Technical Report ofthe Demonstration of UT NDE Procedure 54-UT-I114-000

-Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds". Whereas RAI-4 requested Revision000 of this document, Revision 001 is provided.

Revision 001 had been issued inJanuary 2015 to make clarifications and corrections.

Enclosure 4 provides AREVA Technical Justification Document 54-PQ-1 14-001"Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds".The information offered herein does not affect the conclusions associated withexemption criteria or the environmental considerations provided in the Reference 1Exemption Request.Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

Peter A. GardnerSite Vice President Monticello Nuclear Generating PlantNorthern States Power Company-Minnesota Enclosures (4)cc: Administrator, Region Ill, USNRCRob Kuntz, Project Manager, Monticello Nuclear Generating Plant, USNRCChristian Jacobs, Project Manager, Spent Fuel Management, USNRCResident Inspector, Monticello Nuclear Generating Plant, USNRC L-MT-1 6-003Enclosure 1MONTICELLO NUCLEAR GENERATING PLANTEXEMPTION REQUEST FORNONCONFORMING DRY SHIELDED CANISTER DYE PENETRANT EXAMINATIONS, SUPPLEMENTAL INFORMATION This enclosure provides responses from Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, to a Request for Additional Information (RAI) provided by the Nuclear Regulatory Commission (NRC) on December15, 2015.The NRC questions are provided below in italic font and the NSPM response isprovided in the normal font.RAI-I: Regarding Exemption Request Enclosure 1, verify the page 38 description ofthe allowable flaw depth statement,

"[Fl]or a 3600 circumferential flaw, an allowable flawdepth of 0. 10" could exist and the weld would still meet ASME weld stress/limit."

"Page 1of Enclosure 2, 'Allowable Flaw Size Evaluation in the Inner Top Cover Plate [ITCP]Closure We/ld for DSC #16, "noted that an allowable flaw size of 0. 15 inch is calculated for a 0.25 inch Inner Top Cover Plate weld in DSC #16.This information is needed to complete the review in accordance with 10 CFR 72.236.NSPM ResponseThe cited value of 0.10" on page 38 and the associated limit originates from the analysisprovided in the original Exemption Request (Reference 1). The value is supported byfootnote 5, which makes an attempt to explain that the statement is still valid when theactual weld size is considered.

Upon further review, it will be clearer to revise the textwithout the annotations and explanations; making the value on page 38 consistent withthe value of 0.15 inch that is cited from Page 1 of Enclosure 2 (of Reference 3).Upon review of the RAI, AREVA performed further review of the affected section andnoted the following correction and clarification:

• The Analysis-Based Structural Analysis with Theoretical Flaws is Enclosure 2 (ofReference 3), not Enclosure 3 as erroneously stated in the first sentence.

• Several paragraphs in this section are clarified or deleted to better describe theparameters that were actually analyzed.

The text provided in the ER was developed as a progression from the description provided in the original ER, with supplemental footnotes to describe changes made in the interim.

Upon further review, a moredirect approach to describing the analysis was determined to be more appropriate.

Page 1 of 7 L-MT-1 6-003Enclosure 1Please consider the markup in the Attachment to this Enclosure to correct and clarifythe text originally provided in Enclosure 2 of Reference 3.RAI-2: Regarding Exemption Request Enclosure 4, revise the limit load analyses forthe determination of the internal pressure and side-drop collapse loads for the top coverplates-to-shell partial penetration welds of the dry shielded canister.

The revisedanalysis should address the modeling anomalies, such as not considering theprogressive weld material rupture associated with the linearly increased loading until thecomplete collapse of the weld. Specifically, two modeling attributes on weldperformance should be considered:

(1) the allowable elongation limit of 35% for the EX308-xx filler metal, and (2) the removal of the ruptured weld from the finite elementanalysis (FEA) model as load bearing element(s).

With revised collapse loads, alsorevise the Section 7, "Discussion and Conclusions,"

descriptions, as appropriate, torecognize that the collapsed loads, and hence, the design margins, are much lower thanthose being reported could result.In Section 4.4, for the collapse load determination, the applicant stated, "[Tiheprescribed loads are applied to the model, and then are increased linearly until thesolution fails to con verge." The staff finds that this load ramping approach relied solelyon the numerical performance of the FEA solution algorithm and failed to consider theprogressive weld material rupture in the analysis model. As a result, large calculated equivalent plastic strains up to 194% in the weld region and corresponding cover platedisplacement of about 11 inches, which are physically inadmissible, are reported inFigures 26 and 27, respectively.

Other justifiable approaches than the limited load analysis discussed above may also beused for demonstrating the weld performance.

This information is needed to complete the review in accordance with 10 CFR 72.23 6.NSPM ResponseAs an alternative to revising the subject limit load analysis (i.e., ARE VA Calculation 11042-0205) to address the modeling anomalies discussed above, a more thoroughexplanation of this analysis and its objectives is provided below.As discussed in Enclosure 2, displacements and strains indicated by a limit loadanalysis have no physical meaning.

Nevertheless, to address questions on thepotential for material rupture due to potentially high plastic strains, supplemental elastic-plastic analysis (EPA) was performed in Appendix A to Enclosure

2. For this EPA, SA-240 Type 304 steel is modeled with a Ramberg-Osgood stress-strain curve usingmaterial properties derived from ASME Code,Section II minimum strength values at theapplicable temperatures.

These material property constants are documented inAppendix Al of Calculation 11042-0205, which is provided in Enclosure 2 to thisPage 2 of 7 L-MT-1 6-003Enclosure 1submittal.

The material behavior is modeled based upon true stresses and true strainsas ANSYS was configured to consider the effects of large deformations with the model.The design loads are applied to determine the maximum strains for the normal andaccident level internal pressure and side drop conditions.

In these loading conditions, the strains peak at about 6%, which is well below the 35% strain limit of the weldmaterial.

RAI-3: Regarding Exemption Request Enclosure 4, revise Table 6, "Summary of LoadCases and Results",

to note that the design internal pressure of 10 psig was combinedwith the gravity load equivalent pressure of 22 psig to result in the listed "Required Design Pressure" of 32 psig for the analysis.

The use of the heading, "Required Design Pressure,

" which can be misleading, shouldproperly be noted for the table.This information is needed to complete the review in accordance with 10 CFR 72.23 6.NSPM ResponseAREVA Calculation 11042-0205 was revised to add a note to Table 6 and revise othertext in the calculation to clarify the origination of the referenced value. This revisedcalculation is provided as Enclosure 2 to this submittal.

RAI-4: Provide the following technical reports referenced in the Non-Destructive Evaluation (NDE) Services Final Report Monticello, DSC-16, Phased Array UT[ultrasonic test] Examination Results of the Inner and Outer Top Cover Lid WeldsDocument Number: I 80-9236027-O00AREVA:

1. Technical Report Document 5 1-9234641-000 "Technical Report of theDemonstration of UT NDE Procedure 54-UT-I114-000

-Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds"2. ARE VA Technical Justification Document 54-P Q-1 14-001 "Phased ArrayUltrasonic Examination of Dry Storage Canister Lid Welds"These reports should contain key information on the NDE examination procedure anddemonstration so that staff can determine that the procedure was adequate to identifyrelevant indications for consideration in the structural evaluation of the closure lid welds.This information is necessary to determine compliance with 10 CFR 72.158, 72.236.Page 3 of 7 L-MT-1 6-0 03Enclosure 1NSPM ResponseThe two requested documents are enclosed to this submittal as Enclosures 3 and 4,respectively.

AREVA Technical Justification Document 54-PQ-1 14-001 describes the limitations ofthe UT examination process.

These limitations have been reviewed to determine theconsistency with the analytical modeling of the weld and UT results.

The reviewdetermined that the analytical model is consistent with this report and these limitations have been factored into the response to RAI #5 below.RAI-5: Provide a justification for using a stress allowable reduction factor of 1.0 for theevaluation of the inner and outer top lid closure welds on DSC-16. /SG-15 sectionX.5.2.3 for Austenitic Stainless and Nickel-Base alloy Steels Cask Design states:* If using UT, the UT acceptance criteria are the same as those of NB-5332 forpre-service examination.

In accordance with Code practice for supplementing volume tric examinations with a surface examination, UT examination must beperformed in conjunction with a root pass and cover pass PT [liquid penetrant test] examination.

• If PT is specified (i.e., no volumetric inspection),

a stress reduction factor of 0. 8must be applied to the weld design.The examination performed on DSC-16 includes a volumetric phased array ultrasonic test (PA UT) of the entire inner top lid closure weld/and a compliant PT of the final weldpass. The root pass PT was determined to be noncompliant.

For the inner top lidclosure weld, the NDE performed includes a volumetric PAUT examination of most ofthe weld except for the section of the weld around the siphon and vent port block. Boththe root pass and final weld pass PT were determined to be noncomp/iant.

It is alsonoted that for the inaccessible portion of the inner top lid closure plate weld around thesiphon and vent port block the test was performed manually.

Finally it is noted that UTmethods including PAUT cannot be used to reliably identity indications in the root passor near the toe of a weld/because these areas have geometric reflectors that can maskrelevant indications.

This information is necessary to determine compliance with 10 CFR 72.2 12(b)(3),

72.236.NSPM ResponseThe mockup used in the PAUT process development (i.e., mockup of the Inner TopCover Plate and Outer Top Cover Plate weld configuration) contained weldmanufacturing flaws intentionally distributed in locations that would be expected with theweld process used for the DSC lid closure welds. Approximately 30% of those flawswere placed at the weld root and 27% were placed near the weld toe to demonstrate Page 4 of 7 L-MT-1 6-0 03Enclosure Ithat they could be reliably detected in the presence of typical geometric responses fromthose regions.

The flaws include incomplete root penetration, lack of fusion, andtungsten inclusions.

Section 8.0 of AREVA document 54-PQ-1 14-001 (Enclosure 4 tothis submittal) provides results of the ultrasonic data gathered for these flaws anddemonstrates that the PAUT process can effectively detect these flaws. Furthermore, the qualification performed on the blind mockup provides objective evidence thatdetection of flaws in these regions of the weld is not a problem.

The blind mockup usedfor qualification contained a similar percentage/number and distribution of flaws as thedevelopment mockup. Although the flaw information for the blind mockup cannot bedisclosed in order to preserve the security of the mockup for future qualifications, EPRIand NRC personnel present at the demonstration have reviewed that information.

Inaddition, uncertainties in the PAUT examination are accounted for by using a 0.8reduction factor on the limit load. This factor, which is in agreement with ISG-1 5[Reference 2], conservatively accounts for any additional limitations in the efficacy of thePAUT examinations and also accounts for the inaccessible area around the vent andsiphon block as well as the geometric reflectors at the root and near the toe of the weld.RAI-6: Clarify that the shortened helium leak calibration "stabilization period" for heliumleak testing of certain DSC ITCP welds did not result in an inaccurate helium leak testmeasurement.

Appendix E of Enclosure 1 Exemption Request indicates that the DSC helium leak testcalibration intervals of 27 seconds to 47 seconds were below the approved procedure's 60 second stabilization period. Clarify that individuals qualified in writing helium leaktesting procedures, such as an American Society of Nondestructive Testing (ASNT)Level Ill, determined that the change in procedure did not affect the helium leak testresult.This information is needed to determine compliance with 10 CFR 72.122, 72.126,72.236.NSPM ResponseAs documented in the Xcel Energy Corrective Action Program (CAP), the shortened helium leak calibration "stabilization period" for helium leak testing of certain DSC InnerTop Cover Plate (ITCP) welds did not result in an inaccurate helium leak testmeasurement.

Technical justification for this determination was provided in the CAP byan individual qualified in writing helium leak testing procedures.

This justification wasbased on the low magnitude of the recorded helium readings and the experience of thequalified ASNT NDT Level Ill examiner.

In fact, this individual making this determination was the author of the subject procedure employed in the loading campaign.

Page 5 of 7 L-MT-1 6-003Enclosure 1RAI.7: Clarify that the subcontractor's helium leak test procedure for helium leak testingof the siphon and vent port covers and the shell to ITCP weld did not result in aninaccurate helium leak test measurement.

Appendix E of Enclosure 1 Exemption Request indicates that a subcontractor's heliumleak test procedure was used for helium leak testing rather than the approvedprocedure.

Clarify that individuals qualified in writing helium leak testing procedures, such as an ASNT Level Ill, approved the subcontractor's helium leak test procedure.

This information is needed to determine compliance with 10 CFR 72.122, 72.126,72.236.NSPM Response:

To clarify the actual condition reported in the Xcel Energy CAP and correct amisconception in the RAI: no unapproved subcontractor procedure was used for heliumleak testing of the siphon and vent port covers and the shell to ITCP weld. Although thetext in the Exemption Request may have implied that a subcontractor's procedure wasused rather than the approved procedure, this was not the case. in fact, the procedure that Xcel Energy approved for use, and the procedure that was actually used to performthe subject helium leak testing was a procedure developed by Trivis sub-supplier (RRLNDT Consulting).

This procedure is designated TN61ITN61BTH-HMSLD, Revision 1.Thus, the condition described in the CAP did not result in an inaccurate leak testmeasurement.

The source of the RAI's misconception is the following statement in the Exemption Request (Appendix E, page 69 of 74), which was less than clear in describing the"procedures" under question:

A subcontractor used their own procedure for helium leak testing of the siphonand vent port covers and the shell to ITCP weld. The completed procedure doesnot reference use of the subcontractor procedure.

This is a documentation issueand does not affect any DSC design or TS requirements.

This statement could be more accurately stated as:The vendor procedure (TN61/TN61 BTH-HMSLD, Revision

1) that thesubcontractor used for helium leak testing of the siphon and vent port covers andthe shell to ITCP weld had been developed by that same vendor and approvedby Xcel Energy for use. However, the high-level Xcel Energy procedure (designated 9506) that controls the overall cask loading operation (including thehelium leak test) does not reference that vendor procedure.

This is adocumentation issue and does not affect any DSC design or TS requirements.

As a documentation issue associated with the high-level procedure (9506) and not thehelium leak test procedure, there was no review of the condition by an ASNT Level Ill.Page 6 of 7 L-MT-1 6-003Enclosure 1Note further that the subject vendor procedure (TN61/TN61 BTH-HMSLD, Revision 1)was prepared by an individual qualified in writing helium leak testing procedures.

Thiswas the same ASNT NOT Level Ill examiner discussed in the reply to RAI-6.RAI-8: Clarify whether or not additional controls will be provided for the transfer of DSC16 to and into the horizontal storage module (HSM). If additional controls will beprovided, please specify what those controls will be.The applicant states in several places in Enclosure 1 that, "NSPM will provide additional controls to the transfer of DSC 16 to the HSM. These controls are added to increasethe safety of the move," and similar statements (pages 1, 22, 25, and 43). However,Section 3.1.3, on page 23 of Enclosure 1 reads, "no additional controls on the transferof DSC 16 to the HSM are needed."

The statements are inconsistent.

This information is needed to determine compliance with 10 CFR 72. 7.NSPM ResponseWithout the value of PAUT volumetric examinations on the subject DSC, the originalExemption Request (Reference

1) included additional controls on DSC loading in aneffort to improve margins of safety. However, during internal Xcel Energy review of thecurrent Exemption

Request, the actual risk-reduction value of the originally-conceived additional controls was challenged based on collateral adverse effects on siteoperations and other practical implications.

Accordingly, the DSC 16 Exemption Request was issued with the intent that "no additional controls on the transfer of DSC16 to the HSM are needed."

Statements to the contrary (pages 1, 22, 25, and 43), are alegacy of the original/withdrawn exemption request (Reference

1) and should have beendeleted.

Please consider them null and void.

References:

1. NSPM letter to NRC Document Control Desk, L-MT-1 4-01 6, Exemption Request forDry Shielded Canisters 11 -16 Due to Nonconforming Dye Penetrant Examinations, dated July 16, 2014 (ADAMS Accession No. ML14199A370).

2. NRC Spent Fuel Project Office Interim Staff Guidance (ISG)-15 Materials Evaluation, January 10, 2001.3. NSPM letter to NRC Document Control Desk, Exemption Request forNonconforming Dry Shielded Canister Dye Penetrant Examinations, L MT-I15-056, dated September 29, 2015 (ADAMS Accession No. ML15275A023)

Attachment:

Markup of Exemption Request for RAI-1 Reply (2 pages)Page 7 of 7 L-MT-1 6-003Enclosure 1 Attachment, Markup of Exemption Request for RAI-1 ReplyL-MT- 15-056EndosurfThe OTCP weldwas subsequently restored to 0.50inch; therefore, further analyvsis ofthe outer top coverplate was notperformed.

The)rnglnl designLbasis analysisremains applicble.

eland (2)o a finit~e, elemn~t limit o Iadpatalysi assuming l Tdstributons examination.

1. An ss-Based Stutua Analsis Flaws:The calculation provided in Endosure,3 provides an anatysis of thestructural adequacy of a DSC assuming a theoretical weld flaw existingin both ITCP and OTCP welds. The potential flaw Is assumed toreside in a full circumference around the ITCP and OTCP welds (i.e.,throughout the entire weld). 0.-15"For the ITCP weld, the wecld depthl is assumed to be fild ihacritical flaw evaluated for the 3600 c~rcumference, Tlcalculation determined an 'acceptable' allowable flaw size, that i, a flaw size thatwill ensure that ASME weld stress lImnits are sti For a_360dreumferentla flaw, an allowable flaw depth of 040- could exist andteweld would still meet ASME weld stress limits;5.All the component

-stresses remain below the stress allowable limits. The flaw isNevaluated as eithr occurring on the surface or subsurface of the weld.FoLr the.. O"TCP weld, the weld dept ht wasL redluced

/to 0.8 A~to fi law eaiateld~

for1 r-the~G Ae-Ir" umftr ne Tihe thral lod t_ t rsecondai iloadl would tend toWreuc ith thelll i Iulcl intiffnesIo thr com-oet.Cnservati'elnala weldar stresserdci atrws aplede toaoedfrthe 0.4CP a ld. O k h TCP weld c the QTredcuction faetermiof panl pepnebaeo PTa sie, tihatk is,the0 Since wol tl etA welds aternn s lim itshA the compeuireents 5Note that Uthe flaw size calculated herein was based on IPage 1 of 2 L-MT-1 6-003Enclosure 1 Attachment, Markup of Exemption Request for RAI-1 ReplyL-Mr-1 15-056Enclosure 1the weld reduction factor is reduced beyond 0.80 based on a set oftheoretical flaw distributions that might conceivably have goneundetected during DSC dlosure weld examinations.

Thus, an analysis-based stress aloable reduction factor of 0.70 was calculated (seeEndosre 3) to support the value of 0.70 used in the analysis ofrecord.OThe asndsTC of flawcszed useding thue root ua<m onay of the qaeindiS) mthon, forn on DSC8( 1C weldhasd y Ultasni ITCest, (PAUleTerelore, thes calrcuelat adn eronsrtos that sullden.agni Whlued n the weodsfind ate reductonfabexpctariond othe coseatisfatore ipcrudedanc dfeacrie DSoC forte apesic forvc noml crnde of the DCPotrenrtioa o calcatd stress toDS 1 aoanbie saterzes i0.2aned 0.9n oreut fthe rTC ndsp eldns, repeormely Fonera accyert conditione OTheones DStC i6 0a 4 n dh 0.71aton for the actuand OC prolds,rdopcuetiel ntherefo reor (seute dsecion m.rg2ns eitFor the fIawsethfed asupions tofsla sizseusedons the calcmul niation bondanyos hindicxiations found" ont DS 16gt by Phasedera Ultrasoni Test3) PAT)eThreorpsie, eethiscalclatwendemonstrapotes tasuficient ma rgint Isicludedinthe welds andaraceriasional dexpnectatio of satifatory.0 perfhormance ofaeachdD45"for the desig sicmervice, lifeimeohe apStPotentialPweld flaws inds DI6cn beocharacnteried baswtedo althedresltws ofn theeinspeciosu=

pefoawmed onles thie ftha laert ofo the OCconDsCe16andthel obevtossue o6"faw Therac , tua wling pronclessht documenhte ayeis n the A rPor (see sectio 1w3.2) For the flawestal identifiediin those re-inspectonitos, thwaimum sindicatint wariscomposite efact of al wel flaws repoted.

fors Dcnlso 16plresut oe ahcnervtivelcnsdle f law chaacteizatio efre.sasnlefa fdepth ocuringaroun 4 9 of h ed icmeene7h4 apistPage 2 of 2 QF0212, Revision 5 (FP-SC-RSI-04)Pae1o1 Page 1 of 1XcelEnergy@

SHIPPING DOCUMENTNORTHERN STATES POWER -MND/B/A Xcel EnergyMonticello Nuclear Plant, 2807 W Hwy. 75, Monticello, MN 55362Date: 1/9/01Shipping DocumentTracking Number:Ship To:USNRC11555 Rockville PikeRockville, MD 20852-2738 Attention Of: Doc ControlCarrier:

UPS -Standard Overnight RMA No:Pro / Tracking No: PO0/ Contract No:Packaging:NubroPakgs1 WehtDangerous Goods/ UN/NA No: Insurance Est. ValueReason for Shipment:

Overnight Shipment to USNRCMelody lmholte -Please ensure tracking number is communicated to me -melody.imholte@xenuclear cornItem No. Qty. Unit Description Catalog ID/Q1 1 Env Submittal to NRC L-MT-16-003 By signin ~ipp du are-declan~ng, to the best of your knowledge, that the matenal bei g shipped is incompliac ihXe nr rate Policies.

Please print and sign your name legibly.SWIP Making Shipment:

Date:Receivedl By: Date:For wikIcali use ondyUse of this form as a procedural aid does not require retention as a quality record.

Xcel Energy°Monticello Nuclear Generating Plant2807 W County Rd 75Monticello, MN 55362January 29, 2016L-MT-1 6-00 310 CFR 72.7U.S. Nuclear Regulatory Commission ATTN: Document Control DeskDirector, Division of Spent Fuel Management Office of Nuclear Material Safety and Safeguards Washington, DC 20555-0001 Monticello Nuclear Generating PlantDocket No. 50-263Renewed Facility Operating License No. DPR-22Independent Spent Fuel Storage Installation Docket No. 72-58Exemption Request for Nonconformingq Dry Shielded Canister Dye Penetrant Examinations, Supplemental Information (TAC No. L25058)

References:

1) NSPM letter to NRC Document Control Desk, Exemption Request forNonconforming Dry Shielded Canister Dye Penetrant Examinations, L-MT-1 5-056, dated September 29, 2015 (ADAMS Accession No.ML1 5275A023)

2) NRC letter to NSPM, First Request for Additional Information forReview of Exemption Request for Nonconforming Dry ShieldedCanister Dye Penetrant Examinations, dated December 15, 2015(ADAMS Accession No. ML15350A064)

3) NSPM letter to NRC Document Control Desk, Exemption Request forNonconforming Dry Shielded Canister Dye Penetrant Examinations, Schedule for Reply to Request for Additional Information, L-MT-16-002, dated January 6, 2016Pursuant to 10 CFR 72.7, "Specific Exemptions",

Northern States Power Company, aMinnesota corporation (NSPM), doing business as Xcel Energy, submitted Reference 1to request an exemption to the requirements of 10 CFR 72.212(b)(3) and 10 CFR72.212(b)(1

1) for one NUHOMS Dry Shielded Canister (DSC) designated number 16due to nonconforming dye penetrant (PT) examinations performed during the loadingcampaign started in September 2013.In Reference 2, the NRC Division of Spent Fuel Management (DSFM) Staff transmitted a request for additional information (RAI) associated with their review of the Exemption

Request, and requested a reply date of January 19, 2016. In Reference 3, NSPMrequested deferral of the reply to seven (7) RAI questions to February 2, 2016. AsIADO Document Control DeskPage 2discussed in a January 5, 2016 teleconference, the reply to RAI-5 was possibly going tobe deferred later. However, that reply is included herein.Enclosure 1 provides the replies to the eight (8) RAI questions that were provided inReference 2.Enclosure 2 provides AREVA Calculation 11042-0205 Revision 2, which supportschanges made to address RAI-2, RAI-3, and RAI-5.Enclosure 3 provides Technical Report Document 51-9234641-001 "Technical Report ofthe Demonstration of UT NDE Procedure 54-UT-I114-000

-Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds". Whereas RAI-4 requested Revision000 of this document, Revision 001 is provided.

Revision 001 had been issued inJanuary 2015 to make clarifications and corrections.

Enclosure 4 provides AREVA Technical Justification Document 54-PQ-1 14-001"Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds".The information offered herein does not affect the conclusions associated withexemption criteria or the environmental considerations provided in the Reference 1Exemption Request.Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

Peter A. GardnerSite Vice President Monticello Nuclear Generating PlantNorthern States Power Company-Minnesota Enclosures (4)cc: Administrator, Region Ill, USNRCRob Kuntz, Project Manager, Monticello Nuclear Generating Plant, USNRCChristian Jacobs, Project Manager, Spent Fuel Management, USNRCResident Inspector, Monticello Nuclear Generating Plant, USNRC L-MT-1 6-003Enclosure 1MONTICELLO NUCLEAR GENERATING PLANTEXEMPTION REQUEST FORNONCONFORMING DRY SHIELDED CANISTER DYE PENETRANT EXAMINATIONS, SUPPLEMENTAL INFORMATION This enclosure provides responses from Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, to a Request for Additional Information (RAI) provided by the Nuclear Regulatory Commission (NRC) on December15, 2015.The NRC questions are provided below in italic font and the NSPM response isprovided in the normal font.RAI-I: Regarding Exemption Request Enclosure 1, verify the page 38 description ofthe allowable flaw depth statement,

"[Fl]or a 3600 circumferential flaw, an allowable flawdepth of 0. 10" could exist and the weld would still meet ASME weld stress/limit."

"Page 1of Enclosure 2, 'Allowable Flaw Size Evaluation in the Inner Top Cover Plate [ITCP]Closure We/ld for DSC #16, "noted that an allowable flaw size of 0. 15 inch is calculated for a 0.25 inch Inner Top Cover Plate weld in DSC #16.This information is needed to complete the review in accordance with 10 CFR 72.236.NSPM ResponseThe cited value of 0.10" on page 38 and the associated limit originates from the analysisprovided in the original Exemption Request (Reference 1). The value is supported byfootnote 5, which makes an attempt to explain that the statement is still valid when theactual weld size is considered.

Upon further review, it will be clearer to revise the textwithout the annotations and explanations; making the value on page 38 consistent withthe value of 0.15 inch that is cited from Page 1 of Enclosure 2 (of Reference 3).Upon review of the RAI, AREVA performed further review of the affected section andnoted the following correction and clarification:

• The Analysis-Based Structural Analysis with Theoretical Flaws is Enclosure 2 (ofReference 3), not Enclosure 3 as erroneously stated in the first sentence.

• Several paragraphs in this section are clarified or deleted to better describe theparameters that were actually analyzed.

The text provided in the ER was developed as a progression from the description provided in the original ER, with supplemental footnotes to describe changes made in the interim.

Upon further review, a moredirect approach to describing the analysis was determined to be more appropriate.

Page 1 of 7 L-MT-1 6-003Enclosure 1Please consider the markup in the Attachment to this Enclosure to correct and clarifythe text originally provided in Enclosure 2 of Reference 3.RAI-2: Regarding Exemption Request Enclosure 4, revise the limit load analyses forthe determination of the internal pressure and side-drop collapse loads for the top coverplates-to-shell partial penetration welds of the dry shielded canister.

The revisedanalysis should address the modeling anomalies, such as not considering theprogressive weld material rupture associated with the linearly increased loading until thecomplete collapse of the weld. Specifically, two modeling attributes on weldperformance should be considered:

(1) the allowable elongation limit of 35% for the EX308-xx filler metal, and (2) the removal of the ruptured weld from the finite elementanalysis (FEA) model as load bearing element(s).

With revised collapse loads, alsorevise the Section 7, "Discussion and Conclusions,"

descriptions, as appropriate, torecognize that the collapsed loads, and hence, the design margins, are much lower thanthose being reported could result.In Section 4.4, for the collapse load determination, the applicant stated, "[Tiheprescribed loads are applied to the model, and then are increased linearly until thesolution fails to con verge." The staff finds that this load ramping approach relied solelyon the numerical performance of the FEA solution algorithm and failed to consider theprogressive weld material rupture in the analysis model. As a result, large calculated equivalent plastic strains up to 194% in the weld region and corresponding cover platedisplacement of about 11 inches, which are physically inadmissible, are reported inFigures 26 and 27, respectively.

Other justifiable approaches than the limited load analysis discussed above may also beused for demonstrating the weld performance.

This information is needed to complete the review in accordance with 10 CFR 72.23 6.NSPM ResponseAs an alternative to revising the subject limit load analysis (i.e., ARE VA Calculation 11042-0205) to address the modeling anomalies discussed above, a more thoroughexplanation of this analysis and its objectives is provided below.As discussed in Enclosure 2, displacements and strains indicated by a limit loadanalysis have no physical meaning.

Nevertheless, to address questions on thepotential for material rupture due to potentially high plastic strains, supplemental elastic-plastic analysis (EPA) was performed in Appendix A to Enclosure

2. For this EPA, SA-240 Type 304 steel is modeled with a Ramberg-Osgood stress-strain curve usingmaterial properties derived from ASME Code,Section II minimum strength values at theapplicable temperatures.

These material property constants are documented inAppendix Al of Calculation 11042-0205, which is provided in Enclosure 2 to thisPage 2 of 7 L-MT-1 6-003Enclosure 1submittal.

The material behavior is modeled based upon true stresses and true strainsas ANSYS was configured to consider the effects of large deformations with the model.The design loads are applied to determine the maximum strains for the normal andaccident level internal pressure and side drop conditions.

In these loading conditions, the strains peak at about 6%, which is well below the 35% strain limit of the weldmaterial.

RAI-3: Regarding Exemption Request Enclosure 4, revise Table 6, "Summary of LoadCases and Results",

to note that the design internal pressure of 10 psig was combinedwith the gravity load equivalent pressure of 22 psig to result in the listed "Required Design Pressure" of 32 psig for the analysis.

The use of the heading, "Required Design Pressure,

" which can be misleading, shouldproperly be noted for the table.This information is needed to complete the review in accordance with 10 CFR 72.23 6.NSPM ResponseAREVA Calculation 11042-0205 was revised to add a note to Table 6 and revise othertext in the calculation to clarify the origination of the referenced value. This revisedcalculation is provided as Enclosure 2 to this submittal.

RAI-4: Provide the following technical reports referenced in the Non-Destructive Evaluation (NDE) Services Final Report Monticello, DSC-16, Phased Array UT[ultrasonic test] Examination Results of the Inner and Outer Top Cover Lid WeldsDocument Number: I 80-9236027-O00AREVA:

1. Technical Report Document 5 1-9234641-000 "Technical Report of theDemonstration of UT NDE Procedure 54-UT-I114-000

-Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds"2. ARE VA Technical Justification Document 54-P Q-1 14-001 "Phased ArrayUltrasonic Examination of Dry Storage Canister Lid Welds"These reports should contain key information on the NDE examination procedure anddemonstration so that staff can determine that the procedure was adequate to identifyrelevant indications for consideration in the structural evaluation of the closure lid welds.This information is necessary to determine compliance with 10 CFR 72.158, 72.236.Page 3 of 7 L-MT-1 6-0 03Enclosure 1NSPM ResponseThe two requested documents are enclosed to this submittal as Enclosures 3 and 4,respectively.

AREVA Technical Justification Document 54-PQ-1 14-001 describes the limitations ofthe UT examination process.

These limitations have been reviewed to determine theconsistency with the analytical modeling of the weld and UT results.

The reviewdetermined that the analytical model is consistent with this report and these limitations have been factored into the response to RAI #5 below.RAI-5: Provide a justification for using a stress allowable reduction factor of 1.0 for theevaluation of the inner and outer top lid closure welds on DSC-16. /SG-15 sectionX.5.2.3 for Austenitic Stainless and Nickel-Base alloy Steels Cask Design states:* If using UT, the UT acceptance criteria are the same as those of NB-5332 forpre-service examination.

In accordance with Code practice for supplementing volume tric examinations with a surface examination, UT examination must beperformed in conjunction with a root pass and cover pass PT [liquid penetrant test] examination.

• If PT is specified (i.e., no volumetric inspection),

a stress reduction factor of 0. 8must be applied to the weld design.The examination performed on DSC-16 includes a volumetric phased array ultrasonic test (PA UT) of the entire inner top lid closure weld/and a compliant PT of the final weldpass. The root pass PT was determined to be noncompliant.

For the inner top lidclosure weld, the NDE performed includes a volumetric PAUT examination of most ofthe weld except for the section of the weld around the siphon and vent port block. Boththe root pass and final weld pass PT were determined to be noncomp/iant.

It is alsonoted that for the inaccessible portion of the inner top lid closure plate weld around thesiphon and vent port block the test was performed manually.

Finally it is noted that UTmethods including PAUT cannot be used to reliably identity indications in the root passor near the toe of a weld/because these areas have geometric reflectors that can maskrelevant indications.

This information is necessary to determine compliance with 10 CFR 72.2 12(b)(3),

72.236.NSPM ResponseThe mockup used in the PAUT process development (i.e., mockup of the Inner TopCover Plate and Outer Top Cover Plate weld configuration) contained weldmanufacturing flaws intentionally distributed in locations that would be expected with theweld process used for the DSC lid closure welds. Approximately 30% of those flawswere placed at the weld root and 27% were placed near the weld toe to demonstrate Page 4 of 7 L-MT-1 6-0 03Enclosure Ithat they could be reliably detected in the presence of typical geometric responses fromthose regions.

The flaws include incomplete root penetration, lack of fusion, andtungsten inclusions.

Section 8.0 of AREVA document 54-PQ-1 14-001 (Enclosure 4 tothis submittal) provides results of the ultrasonic data gathered for these flaws anddemonstrates that the PAUT process can effectively detect these flaws. Furthermore, the qualification performed on the blind mockup provides objective evidence thatdetection of flaws in these regions of the weld is not a problem.

The blind mockup usedfor qualification contained a similar percentage/number and distribution of flaws as thedevelopment mockup. Although the flaw information for the blind mockup cannot bedisclosed in order to preserve the security of the mockup for future qualifications, EPRIand NRC personnel present at the demonstration have reviewed that information.

Inaddition, uncertainties in the PAUT examination are accounted for by using a 0.8reduction factor on the limit load. This factor, which is in agreement with ISG-1 5[Reference 2], conservatively accounts for any additional limitations in the efficacy of thePAUT examinations and also accounts for the inaccessible area around the vent andsiphon block as well as the geometric reflectors at the root and near the toe of the weld.RAI-6: Clarify that the shortened helium leak calibration "stabilization period" for heliumleak testing of certain DSC ITCP welds did not result in an inaccurate helium leak testmeasurement.

Appendix E of Enclosure 1 Exemption Request indicates that the DSC helium leak testcalibration intervals of 27 seconds to 47 seconds were below the approved procedure's 60 second stabilization period. Clarify that individuals qualified in writing helium leaktesting procedures, such as an American Society of Nondestructive Testing (ASNT)Level Ill, determined that the change in procedure did not affect the helium leak testresult.This information is needed to determine compliance with 10 CFR 72.122, 72.126,72.236.NSPM ResponseAs documented in the Xcel Energy Corrective Action Program (CAP), the shortened helium leak calibration "stabilization period" for helium leak testing of certain DSC InnerTop Cover Plate (ITCP) welds did not result in an inaccurate helium leak testmeasurement.

Technical justification for this determination was provided in the CAP byan individual qualified in writing helium leak testing procedures.

This justification wasbased on the low magnitude of the recorded helium readings and the experience of thequalified ASNT NDT Level Ill examiner.

In fact, this individual making this determination was the author of the subject procedure employed in the loading campaign.

Page 5 of 7 L-MT-1 6-003Enclosure 1RAI.7: Clarify that the subcontractor's helium leak test procedure for helium leak testingof the siphon and vent port covers and the shell to ITCP weld did not result in aninaccurate helium leak test measurement.

Appendix E of Enclosure 1 Exemption Request indicates that a subcontractor's heliumleak test procedure was used for helium leak testing rather than the approvedprocedure.

Clarify that individuals qualified in writing helium leak testing procedures, such as an ASNT Level Ill, approved the subcontractor's helium leak test procedure.

This information is needed to determine compliance with 10 CFR 72.122, 72.126,72.236.NSPM Response:

To clarify the actual condition reported in the Xcel Energy CAP and correct amisconception in the RAI: no unapproved subcontractor procedure was used for heliumleak testing of the siphon and vent port covers and the shell to ITCP weld. Although thetext in the Exemption Request may have implied that a subcontractor's procedure wasused rather than the approved procedure, this was not the case. in fact, the procedure that Xcel Energy approved for use, and the procedure that was actually used to performthe subject helium leak testing was a procedure developed by Trivis sub-supplier (RRLNDT Consulting).

This procedure is designated TN61ITN61BTH-HMSLD, Revision 1.Thus, the condition described in the CAP did not result in an inaccurate leak testmeasurement.

The source of the RAI's misconception is the following statement in the Exemption Request (Appendix E, page 69 of 74), which was less than clear in describing the"procedures" under question:

A subcontractor used their own procedure for helium leak testing of the siphonand vent port covers and the shell to ITCP weld. The completed procedure doesnot reference use of the subcontractor procedure.

This is a documentation issueand does not affect any DSC design or TS requirements.

This statement could be more accurately stated as:The vendor procedure (TN61/TN61 BTH-HMSLD, Revision

1) that thesubcontractor used for helium leak testing of the siphon and vent port covers andthe shell to ITCP weld had been developed by that same vendor and approvedby Xcel Energy for use. However, the high-level Xcel Energy procedure (designated 9506) that controls the overall cask loading operation (including thehelium leak test) does not reference that vendor procedure.

This is adocumentation issue and does not affect any DSC design or TS requirements.

As a documentation issue associated with the high-level procedure (9506) and not thehelium leak test procedure, there was no review of the condition by an ASNT Level Ill.Page 6 of 7 L-MT-1 6-003Enclosure 1Note further that the subject vendor procedure (TN61/TN61 BTH-HMSLD, Revision 1)was prepared by an individual qualified in writing helium leak testing procedures.

Thiswas the same ASNT NOT Level Ill examiner discussed in the reply to RAI-6.RAI-8: Clarify whether or not additional controls will be provided for the transfer of DSC16 to and into the horizontal storage module (HSM). If additional controls will beprovided, please specify what those controls will be.The applicant states in several places in Enclosure 1 that, "NSPM will provide additional controls to the transfer of DSC 16 to the HSM. These controls are added to increasethe safety of the move," and similar statements (pages 1, 22, 25, and 43). However,Section 3.1.3, on page 23 of Enclosure 1 reads, "no additional controls on the transferof DSC 16 to the HSM are needed."

The statements are inconsistent.

This information is needed to determine compliance with 10 CFR 72. 7.NSPM ResponseWithout the value of PAUT volumetric examinations on the subject DSC, the originalExemption Request (Reference

1) included additional controls on DSC loading in aneffort to improve margins of safety. However, during internal Xcel Energy review of thecurrent Exemption

Request, the actual risk-reduction value of the originally-conceived additional controls was challenged based on collateral adverse effects on siteoperations and other practical implications.

Accordingly, the DSC 16 Exemption Request was issued with the intent that "no additional controls on the transfer of DSC16 to the HSM are needed."

Statements to the contrary (pages 1, 22, 25, and 43), are alegacy of the original/withdrawn exemption request (Reference

1) and should have beendeleted.

Please consider them null and void.

References:

1. NSPM letter to NRC Document Control Desk, L-MT-1 4-01 6, Exemption Request forDry Shielded Canisters 11 -16 Due to Nonconforming Dye Penetrant Examinations, dated July 16, 2014 (ADAMS Accession No. ML14199A370).

2. NRC Spent Fuel Project Office Interim Staff Guidance (ISG)-15 Materials Evaluation, January 10, 2001.3. NSPM letter to NRC Document Control Desk, Exemption Request forNonconforming Dry Shielded Canister Dye Penetrant Examinations, L MT-I15-056, dated September 29, 2015 (ADAMS Accession No. ML15275A023)

Attachment:

Markup of Exemption Request for RAI-1 Reply (2 pages)Page 7 of 7 L-MT-1 6-003Enclosure 1 Attachment, Markup of Exemption Request for RAI-1 ReplyL-MT- 15-056EndosurfThe OTCP weldwas subsequently restored to 0.50inch; therefore, further analyvsis ofthe outer top coverplate was notperformed.

The)rnglnl designLbasis analysisremains applicble.

eland (2)o a finit~e, elemn~t limit o Iadpatalysi assuming l Tdstributons examination.

1. An ss-Based Stutua Analsis Flaws:The calculation provided in Endosure,3 provides an anatysis of thestructural adequacy of a DSC assuming a theoretical weld flaw existingin both ITCP and OTCP welds. The potential flaw Is assumed toreside in a full circumference around the ITCP and OTCP welds (i.e.,throughout the entire weld). 0.-15"For the ITCP weld, the wecld depthl is assumed to be fild ihacritical flaw evaluated for the 3600 c~rcumference, Tlcalculation determined an 'acceptable' allowable flaw size, that i, a flaw size thatwill ensure that ASME weld stress lImnits are sti For a_360dreumferentla flaw, an allowable flaw depth of 040- could exist andteweld would still meet ASME weld stress limits;5.All the component

-stresses remain below the stress allowable limits. The flaw isNevaluated as eithr occurring on the surface or subsurface of the weld.FoLr the.. O"TCP weld, the weld dept ht wasL redluced

/to 0.8 A~to fi law eaiateld~

for1 r-the~G Ae-Ir" umftr ne Tihe thral lod t_ t rsecondai iloadl would tend toWreuc ith thelll i Iulcl intiffnesIo thr com-oet.Cnservati'elnala weldar stresserdci atrws aplede toaoedfrthe 0.4CP a ld. O k h TCP weld c the QTredcuction faetermiof panl pepnebaeo PTa sie, tihatk is,the0 Since wol tl etA welds aternn s lim itshA the compeuireents 5Note that Uthe flaw size calculated herein was based on IPage 1 of 2 L-MT-1 6-003Enclosure 1 Attachment, Markup of Exemption Request for RAI-1 ReplyL-Mr-1 15-056Enclosure 1the weld reduction factor is reduced beyond 0.80 based on a set oftheoretical flaw distributions that might conceivably have goneundetected during DSC dlosure weld examinations.

Thus, an analysis-based stress aloable reduction factor of 0.70 was calculated (seeEndosre 3) to support the value of 0.70 used in the analysis ofrecord.OThe asndsTC of flawcszed useding thue root ua<m onay of the qaeindiS) mthon, forn on DSC8( 1C weldhasd y Ultasni ITCest, (PAUleTerelore, thes calrcuelat adn eronsrtos that sullden.agni Whlued n the weodsfind ate reductonfabexpctariond othe coseatisfatore ipcrudedanc dfeacrie DSoC forte apesic forvc noml crnde of the DCPotrenrtioa o calcatd stress toDS 1 aoanbie saterzes i0.2aned 0.9n oreut fthe rTC ndsp eldns, repeormely Fonera accyert conditione OTheones DStC i6 0a 4 n dh 0.71aton for the actuand OC prolds,rdopcuetiel ntherefo reor (seute dsecion m.rg2ns eitFor the fIawsethfed asupions tofsla sizseusedons the calcmul niation bondanyos hindicxiations found" ont DS 16gt by Phasedera Ultrasoni Test3) PAT)eThreorpsie, eethiscalclatwendemonstrapotes tasuficient ma rgint Isicludedinthe welds andaraceriasional dexpnectatio of satifatory.0 perfhormance ofaeachdD45"for the desig sicmervice, lifeimeohe apStPotentialPweld flaws inds DI6cn beocharacnteried baswtedo althedresltws ofn theeinspeciosu=

pefoawmed onles thie ftha laert ofo the OCconDsCe16andthel obevtossue o6"faw Therac , tua wling pronclessht documenhte ayeis n the A rPor (see sectio 1w3.2) For the flawestal identifiediin those re-inspectonitos, thwaimum sindicatint wariscomposite efact of al wel flaws repoted.

fors Dcnlso 16plresut oe ahcnervtivelcnsdle f law chaacteizatio efre.sasnlefa fdepth ocuringaroun 4 9 of h ed icmeene7h4 apistPage 2 of 2 QF0212, Revision 5 (FP-SC-RSI-04)Pae1o1 Page 1 of 1XcelEnergy@

SHIPPING DOCUMENTNORTHERN STATES POWER -MND/B/A Xcel EnergyMonticello Nuclear Plant, 2807 W Hwy. 75, Monticello, MN 55362Date: 1/9/01Shipping DocumentTracking Number:Ship To:USNRC11555 Rockville PikeRockville, MD 20852-2738 Attention Of: Doc ControlCarrier:

UPS -Standard Overnight RMA No:Pro / Tracking No: PO0/ Contract No:Packaging:NubroPakgs1 WehtDangerous Goods/ UN/NA No: Insurance Est. ValueReason for Shipment:

Overnight Shipment to USNRCMelody lmholte -Please ensure tracking number is communicated to me -melody.imholte@xenuclear cornItem No. Qty. Unit Description Catalog ID/Q1 1 Env Submittal to NRC L-MT-16-003 By signin ~ipp du are-declan~ng, to the best of your knowledge, that the matenal bei g shipped is incompliac ihXe nr rate Policies.

Please print and sign your name legibly.SWIP Making Shipment:

Date:Receivedl By: Date:For wikIcali use ondyUse of this form as a procedural aid does not require retention as a quality record.