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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)
	v • d • e

Xcel Energy°Monticello Nuclear Generating Plant 2807 W County Rd 75 Monticello, MN 55362 January 29, 2016 L-MT-1 6-00 3 10 CFR 72.7 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Director, Division of Spent Fuel Management Office of Nuclear Material Safety and Safeguards Washington, DC 20555-0001 Monticello Nuclear Generating Plant Docket No. 50-263 Renewed Facility Operating License No. DPR-22 Independent Spent Fuel Storage Installation Docket No. 72-58 Exemption 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 for Nonconforming 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 for Review of Exemption Request for Nonconforming Dry Shielded Canister Dye Penetrant Examinations, dated December 15, 2015 (ADAMS Accession No. ML15350A064)

3) NSPM letter to NRC Document Control Desk, Exemption Request for Nonconforming Dry Shielded Canister Dye Penetrant Examinations, Schedule for Reply to Request for Additional Information, L-MT-16-002, dated January 6, 2016 Pursuant to 10 CFR 72.7, "Specific Exemptions", Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, submitted Reference 1 to request an exemption to the requirements of 10 CFR 72.212(b)(3) and 10 CFR 72.212(b)(1

1) for one NUHOMS Dry Shielded Canister (DSC) designated number 16 due to nonconforming dye penetrant (PT) examinations performed during the loading campaign 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, NSPM requested deferral of the reply to seven (7) RAI questions to February 2, 2016. As I ADO Document Control Desk Page 2 discussed in a January 5, 2016 teleconference, the reply to RAI-5 was possibly going to be deferred later. However, that reply is included herein.Enclosure 1 provides the replies to the eight (8) RAI questions that were provided in Reference 2.Enclosure 2 provides AREVA Calculation 11042-0205 Revision 2, which supports changes made to address RAI-2, RAI-3, and RAI-5.Enclosure 3 provides Technical Report Document 51-9234641-001 "Technical Report of the Demonstration of UT NDE Procedure 54-UT-I114-000

-Phased Array Ultrasonic Examination of Dry Storage Canister Lid Welds". Whereas RAI-4 requested Revision 000 of this document, Revision 001 is provided.

Revision 001 had been issued in January 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 with exemption criteria or the environmental considerations provided in the Reference 1 Exemption Request.Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

Peter A. Gardner Site Vice President Monticello Nuclear Generating Plant Northern States Power Company-Minnesota Enclosures (4)cc: Administrator, Region Ill, USNRC Rob Kuntz, Project Manager, Monticello Nuclear Generating Plant, USNRC Christian Jacobs, Project Manager, Spent Fuel Management, USNRC Resident Inspector, Monticello Nuclear Generating Plant, USNRC L-MT-1 6-003 Enclosure 1 MONTICELLO NUCLEAR GENERATING PLANT EXEMPTION REQUEST FOR NONCONFORMING 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 December 15, 2015.The NRC questions are provided below in italic font and the NSPM response is provided in the normal font.RAI-I: Regarding Exemption Request Enclosure 1, verify the page 38 description of the allowable flaw depth statement, "[Fl]or a 3600 circumferential flaw, an allowable flaw depth of 0. 10" could exist and the weld would still meet ASME weld stress/limit." "Page 1 of 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 Response The cited value of 0.10" on page 38 and the associated limit originates from the analysis provided in the original Exemption Request (Reference 1). The value is supported by footnote 5, which makes an attempt to explain that the statement is still valid when the actual weld size is considered.

Upon further review, it will be clearer to revise the text without the annotations and explanations; making the value on page 38 consistent with the 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 and noted the following correction and clarification:

The Analysis-Based Structural Analysis with Theoretical Flaws is Enclosure 2 (of Reference 3), not Enclosure 3 as erroneously stated in the first sentence.* Several paragraphs in this section are clarified or deleted to better describe the parameters 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 more direct approach to describing the analysis was determined to be more appropriate.

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

The revised analysis should address the modeling anomalies, such as not considering the progressive weld material rupture associated with the linearly increased loading until the complete collapse of the weld. Specifically, two modeling attributes on weld performance should be considered:

(1) the allowable elongation limit of 35% for the EX 308-xx filler metal, and (2) the removal of the ruptured weld from the finite element analysis (FEA) model as load bearing element(s).

With revised collapse loads, also revise the Section 7, "Discussion and Conclusions," descriptions, as appropriate, to recognize that the collapsed loads, and hence, the design margins, are much lower than those being reported could result.In Section 4.4, for the collapse load determination, the applicant stated, "[Tihe prescribed loads are applied to the model, and then are increased linearly until the solution fails to con verge." The staff finds that this load ramping approach relied solely on the numerical performance of the FEA solution algorithm and failed to consider the progressive 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 plate displacement of about 11 inches, which are physically inadmissible, are reported in Figures 26 and 27, respectively.

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

This information is needed to complete the review in accordance with 10 CFR 72.23 6.NSPM Response As 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 thorough explanation of this analysis and its objectives is provided below.As discussed in Enclosure 2, displacements and strains indicated by a limit load analysis have no physical meaning. Nevertheless, to address questions on the potential 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 using material properties derived from ASME Code,Section II minimum strength values at the applicable temperatures.

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

The material behavior is modeled based upon true stresses and true strains as 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 and accident 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 weld material.RAI-3: Regarding Exemption Request Enclosure 4, revise Table 6, "Summary of Load Cases and Results", to note that the design internal pressure of 10 psig was combined with 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, should properly be noted for the table.This information is needed to complete the review in accordance with 10 CFR 72.23 6.NSPM Response AREVA Calculation 11042-0205 was revised to add a note to Table 6 and revise other text in the calculation to clarify the origination of the referenced value. This revised calculation 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 Welds Document Number: I 80-9236027-O00AREVA:

1. Technical Report Document 5 1-9234641-000 "Technical Report of the Demonstration 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 Array Ultrasonic Examination of Dry Storage Canister Lid Welds" These reports should contain key information on the NDE examination procedure and demonstration so that staff can determine that the procedure was adequate to identify relevant 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 03 Enclosure 1 NSPM Response The 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 of the UT examination process. These limitations have been reviewed to determine the consistency with the analytical modeling of the weld and UT results. The review determined 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 the evaluation of the inner and outer top lid closure welds on DSC-16. /SG-15 section X.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 for pre-service examination.

In accordance with Code practice for supplementing volume tric examinations with a surface examination, UT examination must be performed 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. 8 must 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 weld pass. The root pass PT was determined to be noncompliant.

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

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

Finally it is noted that UT methods including PAUT cannot be used to reliably identity indications in the root pass or near the toe of a weld/because these areas have geometric reflectors that can mask relevant indications.

This information is necessary to determine compliance with 10 CFR 72.2 12(b)(3), 72.236.NSPM Response The mockup used in the PAUT process development (i.e., mockup of the Inner Top Cover Plate and Outer Top Cover Plate weld configuration) contained weld manufacturing flaws intentionally distributed in locations that would be expected with the weld process used for the DSC lid closure welds. Approximately 30% of those flaws were placed at the weld root and 27% were placed near the weld toe to demonstrate Page 4 of 7 L-MT-1 6-0 03 Enclosure I that they could be reliably detected in the presence of typical geometric responses from those regions. The flaws include incomplete root penetration, lack of fusion, and tungsten inclusions.

Section 8.0 of AREVA document 54-PQ-1 14-001 (Enclosure 4 to this submittal) provides results of the ultrasonic data gathered for these flaws and demonstrates that the PAUT process can effectively detect these flaws. Furthermore, the qualification performed on the blind mockup provides objective evidence that detection of flaws in these regions of the weld is not a problem. The blind mockup used for qualification contained a similar percentage/number and distribution of flaws as the development mockup. Although the flaw information for the blind mockup cannot be disclosed in order to preserve the security of the mockup for future qualifications, EPRI and NRC personnel present at the demonstration have reviewed that information.

In addition, uncertainties in the PAUT examination are accounted for by using a 0.8 reduction 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 the PAUT examinations and also accounts for the inaccessible area around the vent and siphon 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 helium leak testing of certain DSC ITCP welds did not result in an inaccurate helium leak test measurement.

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

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

This justification was based on the low magnitude of the recorded helium readings and the experience of the qualified 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 6-003 Enclosure 1 RAI.7: Clarify that the subcontractor's helium leak test procedure for helium leak testing of the siphon and vent port covers and the shell to ITCP weld did not result in an inaccurate helium leak test measurement.

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

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 a misconception in the RAI: no unapproved subcontractor procedure was used for helium leak testing of the siphon and vent port covers and the shell to ITCP weld. Although the text in the Exemption Request may have implied that a subcontractor's procedure was used 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 perform the subject helium leak testing was a procedure developed by Trivis sub-supplier (RRL NDT Consulting).

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

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 siphon and vent port covers and the shell to ITCP weld. The completed procedure does not reference use of the subcontractor procedure.

This is a documentation issue and 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 the subcontractor used for helium leak testing of the siphon and vent port covers and the shell to ITCP weld had been developed by that same vendor and approved by Xcel Energy for use. However, the high-level Xcel Energy procedure (designated 9506) that controls the overall cask loading operation (including the helium leak test) does not reference that vendor procedure.

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

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

This was 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 DSC 16 to and into the horizontal storage module (HSM). If additional controls will be provided, 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 increase the 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 transfer of DSC 16 to the HSM are needed." The statements are inconsistent.

This information is needed to determine compliance with 10 CFR 72. 7.NSPM Response Without the value of PAUT volumetric examinations on the subject DSC, the original Exemption Request (Reference

1) included additional controls on DSC loading in an effort to improve margins of safety. However, during internal Xcel Energy review of the current Exemption Request, the actual risk-reduction value of the originally-conceived additional controls was challenged based on collateral adverse effects on site operations and other practical implications.

Accordingly, the DSC 16 Exemption Request was issued with the intent that "no additional controls on the transfer of DSC 16 to the HSM are needed." Statements to the contrary (pages 1, 22, 25, and 43), are a legacy of the original/withdrawn exemption request (Reference

1) and should have been deleted. Please consider them null and void.

References:

1. NSPM letter to NRC Document Control Desk, L-MT-1 4-01 6, Exemption Request for Dry 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 for Nonconforming 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 6-003 Enclosure 1 Attachment, Markup of Exemption Request for RAI-1 Reply L-MT- 15-056 Endosurf The OTCP weld was subsequently restored to 0.50 inch; therefore, further analyvsis of the outer top cover plate was not performed.

The)rnglnl design Lbasis analysis remains applicble.

el and (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 the structural adequacy of a DSC assuming a theoretical weld flaw existing in both ITCP and OTCP welds. The potential flaw Is assumed to reside 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 iha critical flaw evaluated for the 3600 c~rcumference, Tlcalculation determined an 'acceptable' allowable flaw size, that i, a flaw size that will ensure that ASME weld stress lImnits are sti For a_360 dreumferentla flaw, an allowable flaw depth of 040- could exist and teweld would still meet ASME weld stress limits;5.All the component-stresses remain below the stress allowable limits. The flaw is Nevaluated 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 r secondai iloadl would tend toWreuc ith thelll i Iulcl intiffnesIo thr com-oet.Cnservati'elnala weldar stresserdci atrws aplede toaoed frthe 0.4CP a ld. O k h TCP weld c the QT redcuction faetermiof panl pepnebaeo PTa sie, tihatk is, the0 Since wol tl etA welds aternn s lim itshA the compeuireents 5 Note that Uthe flaw size calculated herein was based on I Page 1 of 2 L-MT-1 6-003 Enclosure 1 Attachment, Markup of Exemption Request for RAI-1 Reply L-Mr-1 15-056 Enclosure 1 the weld reduction factor is reduced beyond 0.80 based on a set of theoretical flaw distributions that might conceivably have gone undetected during DSC dlosure weld examinations.

Thus, an analysis-based stress aloable reduction factor of 0.70 was calculated (see Endosre 3) to support the value of 0.70 used in the analysis of record.OThe asndsTC of flawcszed useding thue root ua<m onay of the qae indiS) mthon, forn on DSC8( 1C weldhasd y Ultasni ITCest, (PAUle Terelore, 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 DC Potrenrtioa o calcatd stress toDS 1 aoanbie saterzes i0.2aned 0.9n o reut fthe rTC ndsp eldns, repeormely Fonera accyert conditione OThe ones DStC i6 0a 4 n dh 0.71aton for the actuand OC prolds, rdopcuetiel ntherefo reor (seute dsecion m.rg2ns eitFor the fIaws ethfed asupions tofsla sizseusedons the calcmul niation bondanyos h indicxiations found" ont DS 16gt by Phasedera Ultrasoni Test3) PAT)e Threorpsie, eethiscalclatwendemonstrapotes tasuficient ma rgint Is icludedinthe welds andaraceriasional dexpnectatio of satifatory.0 perfhormance ofaeachdD45"for the desig sicmervice, lifeimeohe apSt PotentialPweld flaws inds DI6cn beocharacnteried baswtedo althed resltws ofn theeinspeciosu=

pefoawmed onles thie ftha laert ofo the OC conDsCe16andthel 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 waris composite efact of al wel flaws repoted. fors Dcnlso 16plresut oe ah cnervtivelcnsdle f law chaacteizatio efre.sasnlefa f depth ocuringaroun 4 9 of h ed icmeene7h4 apist Page 2 of 2 QF0212, Revision 5 (FP-SC-RSI-04)Pae1o1 Page 1 of 1 XcelEnergy@

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