L-MT-14-082, Exemption Request for Dry Shielded Canisters 11-16 Dye Penetrant Examinations, Supplemental Information

Exemption Request for Dry Shielded Canisters 11-16 Dye Penetrant Examinations, Supplemental Information

ML14309A194
Person / Time
Site:	Monticello
Issue date:	11/03/2014
From:	Fili K, Wong W Northern States Power Co, Structural Integrity Associates, Xcel Energy
To:	NRC/NMSS/SFST
References
L-MT-14-082, TAC L24939 1301415.301, Rev. 0
Download: ML14309A194 (55)

Text

Monticello Nuclear Generating Plant

@& XcelEnergy" 2807 W County Rd 75 Monticello, MN 55362 November 3, 2014 L-MT-1 4-082 10 CFR 72.7 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Director, Division of Spent Fuel Storage and Transportation 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 Dry Shielded Canisters 11 - 16 Due to Nonconforming Dye Penetrant Examinations, Supplemental Information (TAC No. L24939)

References:

1) NSPM letter to NRC Document Control Desk, L-MT-14-016, Exemption Request for Dry Shielded Canisters 11 - 16 Due to Nonconforming Dye Penetrant Examinations, dated July 16, 2014 (ADAMS Accession No. ML14199A370).

2) NRC letter to Karen D. Fili, Exemption Request for Dry Shielded Canisters 11-16 Due To Nonconforming Dye Penetrant Examinations, Docket No. 72 Supplemental Information Needed, dated September 11, 2014.

Pursuant to 10 CFR 72.7, "Specific Exemptions", the 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 six (6) NUHOMS Dry Shielded Canisters (DSCs) due to nonconforming dye penetrant (PT) examinations performed during the loading campaign started in September 2013.

In Reference 2, Spent Fuel Storage and Transportation (SFST) Staff requested supplemental information to support their review. During a public meeting held on September 24, 2014, SFST Staff and NSPM discussed the approach and schedule to address the SFST request. Subsequently, a reply date of November 3, 2014, was established. provides the replies to the Request for Supplemental Information (RSI) questions as well as the Observation questions.

Document Control Desk Page 2 provides a report that supports the RSI reply provided in Enclosure 1.

Summary of Commitments This letter makes no new commitments and no revisions to existing commitments.

K-aren b-.i Site Vice-President Monticello Nuclear Generating Plant Northern States Power Company-Minnesota Enclosures (2) cc: Administrator, Region Ill, USNRC Terry Beltz, Project Manager, Monticello Nuclear Generating Plant, USNRC Jennifer Davis, Project Manager, Spent Fuel Storage and Transportation, USNRC Resident Inspector, Monticello .Nuclear Generating Plant, USNRC

L-MT-14-082 Page 1 of 13 MONTICELLO NUCLEAR GENERATING PLANT EXEMPTION REQUEST FOR DRY SHIELDED CANISTERS 11-16 DUE TO NONCONFORMING DYE PENETRANT EXAMINATIONS RESPONSE TO NRC REQUEST FOR SUPPLEMENTAL INFORMATION This enclosure provides responses from the Northern States Power Company, a Minnesota corporation (NSPM), doing business as Xcel Energy, to a Request for Supplemental Information (RSI) provided by the Nuclear Regulatory Commission (NRC) on September 11,2014.

The NRC questions are provided below in italic font and the NSPM response is provided in the normal font.

RSI-1: Provide an appropriatetechnicalbasis for the modification of the stress reduction factor. Provide supportingcalculations using an appropriatemodification of the stress reduction factor Also provide supporting calculationsfor the inner top cover plate weld.

The exemption request applies to dry shielded canisters (DSCs) 11-16. These DSCs had non-conforming penetrant testing (PT) during canisterclosure welding operations. The welds with non-conforming PT included:

• Inner top cover plate (ITCP) weld (root and cover PT)

• Siphon port cover plate (SPCP)weld (root and cover PT)

• Vent port cover plate (VPCP) weld (rootand cover PT)

• Test port plug (TPP) weld (root and cover PT)

" Outer top cover plate (OTCP) weld (root,intermediate, and cover PT)

The exemption request concludes, based on a preponderanceof the evidence, that there is a reasonableassuranceof safety for the 20-year service lifetime of DSCs 11

- 16 based on the following:

1. Integrity of the fuel creates a fission product barrier.

2. The quality of the welding process employed provides indication of development of high quality welds.

3. The advantagesof the multi-layer weld technique which includes the low probability for flaw propagation,the subsequent covering of weld layer surface flaws and the indication of development of high quality welds.

4. Visual inspections performed on the welds met quality requirements.

5. The helium leak and DSC backfill testing results verify confinement barrier integrity.

L-MT-14-082 Enclosure 1 Page 2 of 13

6. The lack of a failure mechanism that adversely affects confinement barrier integrity.

7. Stress margins are available in the welds when assuming conservativelylarge flaws.

Section 3.2.5.1 - Inner and Outer Top Cover Plate Weld Justification, includes a justification for a modified stress reduction factor for the ITCP and the OTCP welds.

It is noted that Interim Staff Guidance (ISG)-15 requiresa stress reduction factor of

0. 8 applied to closure welds that are examined by progressive PT ratherthan volumetric examination. It is also noted in the exemption request that the original 61BTH DSC evaluations used a stress reduction factor of 0. 7 for conservatism with respect to the ISG-15 requirement. A modified stress reduction factor of 0. 7 is calculatedfor DSCs 11-16 based on the information provided in the ASME Boiler and Pressure Vessel Code. Specifically, the exemption request states:

The permissible weld reduction factors (ASME Boiler and Pressure Vessel Code, Division 1, Subsection NG, 1998 edition through 2000 Addenda, Table 3352-1) for surface PT and surface visual examination are 0. 4 and 0. 35, respectively. A modified stress reduction factor of 0. 70 (0.80 x 0.35/0.40) is calculated for the non-compliant weld, due to the multiple visual inspections.

Section 3.2.5.1 also includes a summary of the calculations using the modified stress reduction factors for normal and accident conditions:

When the modified stress reduction factor and other conservatisms are included as describedabove are applied for normal conditions, the stress ratio of calculated stress to allowable stress is 0.52 and 0.79 for the ITCP and OTCP welds, respectively. For accident conditions, the stress ratio is 0.84 and 0. 71 for the ITCP and OTCP welds, respectively. Therefore, adequate design margins exist for the ITCP and OTCP welds when evaluated againstconservative stress allowable values.

Two key points in the analysis provided in the exemption request include point #4, the use of visual inspections that met quality standards,andpoint #7, the stress margins in the welds assuming conservatively large flaws.

The modified stress reduction factor calculated in Section 3.2.5. 1 indicates that stress reduction factors from ASME Boiler and Pressure Vessel Code, Division 1, Subsection NG, 1998 Edition through 2000 Addenda Table NG-3352-1 were used.

There are several issues with the proposed approach in the exemption request.

1. Table NG-3352-1 does not include a weld type and category that is representativeof the ITCP and OTCP welds used in the 61BTH canister.

2. Table NG-3352-1 does not contain stress reduction factors for multiple visual examinations.

L-MT-14-082 Page 3 of 13

3. Table NG-3352-1 and subsection NG-3350 do not identify permissible combinations of stress reduction factors based on combinations of conforming (or non-conforming) examinations.

Although not specifically identified, it appearsthat the exemption request is based on the Type VI Category D or Category E welds which are not pressure boundary welds. Table NG-3352-1 indicates that the stress reduction factor for a Type VI Category D or Category E weld is 0.35. Stress reduction factors based on multiple visual examinationsare not identified for any of the types and categoriesof welds included in Table NG-3352-1. In the exemption request, the calculatedstress reduction factor for multiple visual inspections for the ITCP and OTCP is 0. 7. By this calculation,the exemption request uses allowable stresses for welds with multiple visual examinations that are a factor of 2x (0.7/0.35) greaterthan the same welds with a single surface visual examination. The technicalbasis for this modified stress reduction factor is not provided.

The 2x increase in allowable stress with the modified stress reduction factor in the exemption request is also inconsistent with the stress reduction factors for multiple versus single examination methods that are included in Table NG-3352-1. For example, the stress reduction factors for surface PT, root and final PT, and progressive PT for a Type VI Category D or CategoryE welds are 0.4, 0.45, and

0. 55 respectively. In other words, based on the stress reduction factors in Table NG-3352-1, the allowable stresses in Type VI Category D or CategoryE welds with progressive PT are a factor of 1.3 75x (0.55/0.4) greatercompared to allowable stresses in welds where only a surface PT was performed. For welds with a root and final PT, the allowable stresses are a factor of 1. 125x greater (0.45/0.4) compared to the allowable stresses in weld where only a surface PT was performed.

It is noted that the final PT reexaminationof the OTCP weld on DSC #16 identified an indication that was not identified in the visual examination. This observation calls into question the technical basis of relying on the visual examination to determine the integrityof the OTCP and ITCP welds.

Finally, Section 3.2.5.1 of the exemption request refers to calculations conducted for both the ITCP and OTCP welds. Controlling load combinations stress results are provided in Enclosure 2, Tables I and 2 for the OTCP closure weld. No controlling load combination stress results were provided for the ITCP closure weld.

In summary, the exemption request contains calculations using modified stress reduction factors that are not supportedby the referenced table NG-3352-1 of the ASME Boiler and pressure vessel code. No technical basis is provided to support the modification of the stress reduction factor used in the supporting calculations.

Supporting calculations for the inner top cover plate weld were not provided.

This information is requiredby the staff to determine compliance with 10 CFR 72.236 (c-f, j, I).

L-MT-14-082 Page 4 of 13 REPLY:

The DSC confinement boundary is designed to the requirements of the ASME Boiler

& Pressure Vessel Code Section III, Subsection NB with Code alternatives as identified in Section 1.1.12.4 of the Technical Specifications for the Standardized NUHOMS system (NRC Certificate of Compliance 1004). As indicated in the approved Code alternatives, the field closure welds do not satisfy all of the requirements of Subsection NB. Therefore, the evaluation of the condition provided in the exemption request is not intended to be compliant with Code requirements, but rather a valid technical argument for accepting the stated condition with a reasonable assurance of safety.

Subsection NB presumes that all welds are subject to volumetric inspection, such that no weld quality factors are defined within Subsection NB. In developing the basis for the exemption request, a key aspect was to develop an appropriate penalty to the allowable stress values for the nonconforming PT examination; e.g., a reasonable and rational basis for analysis. This additional reduction factor is applied to the baseline requirement for the stress allowable value for compliant PT (i.e., ISG-15 establishes a stress allowable reduction factor of 0.80 for compliant PT condition).

NRC requested that NSPM provide technical justification for the modified stress allowable reduction factor of 0.70 selected to evaluate the closure welds with the nonconforming PT examinations. In the exemption request, AREVA TN utilized the ASME Boiler & Pressure Vessel Code guidance provided in Table NG-3352-1 to apply an appropriate stress allowable reduction factor to the field closure welds involving nonconforming PT.

Upon further discussion with the Staff at the public meeting held on September 24, 2014, it was apparent that the NRC Staff did not concur with the approach proposed in Reference 1. In response, an alternative analytical approach has been developed to derive a value of modified stress allowable reduction factor. This approach is described in Enclosure 2 of this submittal. It uses a finite element model (FEM) of the field closure welds for the ITCP and OTCP together with the associated top closure geometry of the 61 BTH DSC. The intent of this engineering study was to develop a quantitative basis for the modified stress allowable reduction factor to address the lack of a compliant PT examination for the Monticello Nuclear Generating Plant (MNGP) DSCs associated with the subject exemption request.

Finite element models were developed based on the geometry of the 61 BTH DSC with a sufficiently detailed mesh size in the area of the field closure welds to support the modeling of a variety of weld flaws. Both unflawed and flawed models were developed. In the "flawed models", defects were modeled in the welds in the radial, circumferential and laminar orientations by deactivating elements from the model, essentially creating structural discontinuities in the welds, with a variety of depths and distributions. The flawed models were intended to envelop the type and

L-MT-14-082 Page 5 of 13 distribution of flaws that could have remained undetected using a visual test (VT) only examination method, considering the weld process utilized for the field closure welds.

The models were subjected to loading due to internal pressure and side drop load cases. The resultant weld stresses in the unflawed model were then compared to the stresses in the flawed models to quantify the relationship between welds with no flaws to welds with flaws. This comparative analysis supports the definition of a modified stress allowable reduction factor based on the ratio of the comparative stresses for the load cases analyzed, which is considered appropriate for the MNGP exemption request, where only VT examination is being credited for field weld non-destructive examination (NDE).

The results of the engineering study support the use of a-modified stress allowable reduction factor of 0.70. For the OTCP, the finite element model of circumferential flaw case Circ #2 involving through-wall flaws with a flaw length of approximately 2" in every 5" of weld represents a flaw population which is extremely conservative for the purpose of evaluating the MNGP canisters subject to the exemption request. As indicated in the SIA calculation, this type of flaw size and distribution is extremely unlikely to exist given the type of weld process utilized, the quality program involved in the welding process, the qualification of the weld operator, the favorable weld conditions, the rather forgiving weld process utilized, and the application of a compliant VT examination. For this flaw distribution (Circ #2), the comparative stress ratio for the pressure load case is 0.703 and for the side drop load case is 0.720. The flaw distribution associated with Circ #1 involving through-wall flaws with a flaw length of approximately 3.5" in every 5" of weld represents a flaw population which is not realistic for the MNGP canisters subject to the exemption request, and therefore is provided for comparison purposes only. The finite element results for the ITCP are bounded by the OTCP. Therefore, based on the results of the finite element analysis, the use of a modified stress allowable reduction factor of 0.70 is justified.

As submitted in Reference 1, the modified stress allowable reduction factor of 0.70 utilized in AREVA TN calculation 11042-0204 has been applied to the structural analysis of record documented in Section T.3 of the Standardized NUHOMS Updated Final Safety Analysis Report (UFSAR) for the 61 BTH DSC, to evaluate the impact of possible flaw distributions on the MNGP DSCs that are the subject of the exemption request. This calculation demonstrates acceptable results.

To better characterize the design margins available for the ITCP and OTCP welds under primary loading, AREVA TN evaluated 1 the controlling load combinations for the design of the ITCP and OTCP welds by removing conservatism in the analysis 1 These evaluations consist of engineering computations (hand calculations) using existing design criteria except as modified for the "actual" conditions described herein. These were prepared and peer-checked, but not subjected to full design control measures of a 10 CFR 72 Appendix B Quality Assurance Program.

L-MT-14-082 Page 6 of 13 and utilizing the actual mechanical properties of the material. This evaluation was performed to determine the minimum value of the modified stress allowable reduction factor that could be tolerated under more realistic conditions. As indicated in AREVA calculation NUH61BTH-0200 (provided in response to RSI-2), the controlling load case for the ITCP weld during transfer conditions includes internal pressure and corner drop loads (reference Load Case TR-9 from Table 54 of calculation NUH61 BTH-0200). During storage conditions, the controlling load case for the ITCP weld includes deadweight, internal pressure and seismic loads (reference Load Case HSM-8 from Table 54 of calculation NUH61 BTH-0200).

Similarly, the controlling load case for the OTCP weld during transfer conditions includes internal pressure and corner drop loads (reference Load Case TR-9 from Table 52 of calculation NUH61BTH-0200). During storage conditions, the controlling load case for the OTCP weld includes deadweight, internal pressure and seismic loads (reference Load Case HSM-8 from Table 52 of calculation NUH61 BTH-0200).

For the storage condition subject to seismic loads, the MNGP site specific seismic requirements are significantly less than the design basis seismic input for the NUHOMSO system which specifies a Zero Period Acceleration (ZPA) of 0.30g horizontal and 0.20g vertical for the HSM-H with the 61 BTH DSC. The MNGP site specific design basis earthquake has a horizontal ZPA of 0.12 with a vertical ZPA of 0.08, which is only 40% of the NUHOMS design basis.

The actual material test values for the base material and weld filler material associated with the ITCP and OTCP components were obtained to provide a more realistic evaluation of the mechanical strength of the welds. Thus, the most limiting yield strength is 45 ksi which represents an approximate 50% increase over the nominal yield strength of 30 ksi for Type 304 stainless steel. The most limiting tensile strength is 82 ksi which represents an approximate 10% increase over the nominal tensile strength of 75 ksi for Type 304 stainless steel.

Applying these more realistic conditions for primary loading, the calculated stress may be reduced and the allowable stress increased accordingly. For the transfer load case TR-9, this would result in no change to the calculated stress, but an increase in allowable stress to approximately 51 ksi which would support a modified stress allowable reduction factor as low as 0.45 for the most limiting condition for both the ITCP and OTCP welds. For the storage load case HSM-8, this would result in a calculated stress of approximately 9 ksi, with an allowable stress of approximately 24.5 ksi, which would support a modified stress allowable reduction factor as low as 0.40 for the most limiting condition involving the ITCP weld.

In summary, the modified stress allowable reduction factor of 0.70 utilized in the evaluation is justified based on the results of the FEM analysis performed by SIA.

However, using more realistic conditions, a modified stress allowable reduction factor of 0.45 could be tolerated for primary loading, while continuing to ensure the

L-MT-14-082 Page 7 of 13 design basis functions of the DSC closure are maintained and the confinement boundary function of the ITCP weld is preserved.

RSI-1 provided an observation that the VT examination performed on the OTCP weld for DSC Unit #16 did not identify an indication that was subsequently identified in the final PT reexamination. This is not unexpected as VT examination provides a less rigorous interrogation of the weld surface than PT examination, which forms the basis for imposing the greater penalty associated with the modified stress allowable reduction factor. Enclosure 2 of this submittal provides further discussion about the expected weld quality and the flaw sizes that could reasonably be identified for the DSCs of this exemption request.

RSI-1 questioned why the load combinations provided in the calculation submitted with the exemption request were limited to the OTCP closure weld. The controlling load combinations provided for the OTCP closure weld are included in the exemption request for the purpose of demonstrating that the reduced thickness of the OTCP weld is acceptable. The ITCP closure welds are not subject to a reduced thickness condition, and therefore, those controlling load combinations were not provided in the supporting calculation 11042-0204, Rev. 2. However, the controlling load combinations for the ITCP weld are included in the design basis structural calculation NUH61 BTH-0200, Rev. 0 provided in response to RSI-2.

RSI-2: Submit Reference 5.2, TN Calculation NUH61BTH-0200, Rev. 0, "NUHOMS-61BTH Type I Dry Shielded CanisterShell Assembly StructuralAnalysis," and, for Load Cases TR-9, -10, and -11, provide schematics and summary descriptionsof the finite element analysis (FEA) models with propernotations to depict model attributes,including geometry, element types, loading, and boundary conditions to facilitate staff review. Also, include the input and output files for the FEA, per ISG-21, in the submittal.

This information is requiredby the staff to determine compliance with 10 CFR 72.236.

REPLY: Reference 5.2 and the input / output files for the FEA associated with Load Cases TR-1 0 and TR-1 1 have been stored on electronic medium and hand-delivered to Spent Fuel Storage and Transportation (SFST) Staff at a public meeting held on September 24, 2014. Stresses on the weld, allowable stresses and stress ratios for the OTCP and ITCP can be found in Tables 52-54 (pp. 113-115) of the NUH61 BTH-0200 RO evaluation. A summary description and schematics of the finite element model including weld details can be found in Section 8 (pp. 44-52) in the calculation. The weld stress analysis can be found in Section 9.2 (p. 55) of the evaluation. These electronic files contain information that is proprietary to AREVA-TN. Accordingly, NSPM and AREVA-TN request that this information not be released to any third parties and that it be destroyed or returned after use.

L-MT-1 4-082 Page 8 of 13 No FEA was performed for Load Case TR-9. This case was evaluated by hand calculation. Therefore, no further information is provided for this load case.

RSI-3: Provide a technical basis for the "line welds," pin-connection, assumption for the Y2" partialpenetrationlid-to-shell weld for the OTCP, given that, in previous FEAs for the canistershell assemblies, including those listed in Tables K.3. 7-13 and T.3. 7-16 of the NUHOMS Updated Final Safety Analysis Report (UFSAR) , the subject weld was not explicitly called out for stress margin evaluations. Specifically, using load combination TR-10 as an example, justify that the calculated primary stress of 11.4 ksi for the weld in Table I of the calculation in the exemption request, is a conservative representationof the primary membrane and the primary membrane-plus-bending stress intensities of 32.34 ksi and 55.21 ksi, respectively.

It is unclearhow the lid-to-shell weld FEA discretizationand the section cut for post-processing of nodal values to obtain the membrane and membrane-plus-bending stress intensities as reportedin Table K.3.7-13 referenced above, are simulated with line weld stresses involving both shear and normal components. Similarly, it is unclearhow the stress acceptance criteriaare applied conservatively for the line welds as modeled. The basis andjustification are needed for staff to perform its safety review.

This information is requiredby the staff to determine compliance with 10 CFR 72.236.

REPLY: The technical basis for modeling the "line weld" and pin-connection for the OTCP to shell weld is described in section 8 of design calculation NUH61 BTH-0200 provided in response to RSI-2.

The 61BTH Type 1 DSC is shown on drawing NUH61BTH-1000-SAR in UFSAR Section T.1.5. Drawing NUH61BTH-1000-SAR also documents the additional features/options implemented in the 61 BTH Type 1 DSC. The 61 BTH Type 1 DSC design is the same as the 61 BT DSC documented in Appendix K with a few additional features/options.

The ANSYS analytical models for drop analyses of the 61 BTH DSC shell assembly are summarized in UFSAR Section T.3.7.4.2.3 and results are summarized in Table T.3.7-2 for the NUHOMS 61 BTH Type 1 DSC shell. Table T.3.7-16 provides the results for ITCP and OTCP stress analysis, but does not include the associated field closure welds. The primary membrane and the primary membrane-plus-bending stresses of 32.34 ksi and 55.21 ksi, respectively, for TR-1 0 reported in Table 43 of NUH61BTH-0200, Rev. 0 and Table T.3.7-16 of the UFSAR are the controlling load combination stress results for the ITCP, not the OTCP closure welds, and therefore are not applicable for comparison. The maximum stresses in the welds are summarized in Table T.3.7-2, where maximum primary stresses are 0.36 ksi and 11.40 ksi for vertical and horizontal drop accidents, respectively. No new

L-MT-14-082 Page 9 of 13 evaluations have been made for this exemption request except for the scaling up of the stresses in a 0.48" closure weld on the OTCP from a design value of 0.50".

Table NB-3217-1 classifies membrane stress at a junction of shell and flat head as local membrane stress and bending stress at the junction as secondary stress. The above classifications can be made provided that the bending moment at the edge is not required to maintain bending stress in the middle of the flathead (i.e., OTCP) to acceptable limits. Due to these classifications, two models are analyzed for Level A conditions. The first model has the OTCP to shell weld explicitly modeled and the second model pins the OTCP to shell at the weld location. The primary stresses are calculated from the second, "pinned" model while the secondary stresses are calculated from the first model where the weld is explicitly modeled. For Level D conditions, where secondary stresses do not need to be compared against an ASME allowable stress limit, only the second model is used for the analysis and primary stresses are evaluated.

For the OTCP weld, the primary stresses are determined assuming the OTCP to DSC shell weld as a pin connection with no moment transfer across the weld. Nodal forces are extracted at the root of the weld model and are used to determine the weld stresses. For the secondary stress evaluation, the OTCP weld is modeled using 3-D solid elements. The stresses resulting from this configuration are categorized as primary + secondary stresses. The primary + secondary stresses are determined by linearizing the stresses along three different paths within the weld model. The resulting maximum membrane and bending stress intensity values (the difference between the principal stresses) are then used for the evaluation.

In summary, the modeling assumptions utilized for the original analysis of the OTCP closure weld are appropriate for the geometry of the weld joint, and provide acceptable results.

RSI-4: For the structuralintegrity evaluation of the line welds, identify ASME Code, Section III, Subsection NB, requirement exceptions with justificationsand compensatory measures, including the NB-3210 provisions of the design by analysis evaluation methods and stress acceptance criteriafor the subject partialpenetration lid-to-shell weld.

The calculation No. 11042-0204 introduces a design by analysis weld evaluation analysis/evaluationmethod, which appearsto be substantively different from those in Subsection NB. As such, similarto those in Table 4.9-1 of the NUHOMS UFSAR, a code exceptions summary is needed for the staff to considerthe exceptions in performing safety review of the exemption request.

This information is required by the staff to determine compliance with 10 CFR 72.236.

L-MT-14-082 Page 10 of 13 REPLY:

The intent of calculation 11042-0204 provided in support of the exemption request is to perform an evaluation for a potentially flawed weld condition. It is not intended to perform the design of the weld joint, which is addressed in calculation NUH61 BTH-0200 provided in response to RSI-2.

The Code Alternatives for the field closure welds of the NUHOMS 61 BTH system are provided in Table T.3.1-2 of the Standardized NUHOMS UFSAR, as shown below.

Reference ASME Code Code Requirement Alternatihes,Justification & Compensatory Measures SectionfArticle The shell to the outer top cover weld, the shell to the inner top cover/weld, the siphonlvent cover welds and the vent and siphon block welds to the shell are all partial penetration welds.

As an alternative to the NDE requirements of NB-5230 for Category C welds, all of these closure welds will be Category Cweld joints in multi-layer welds and receive a root and final PT vessels and similar weld joints examination, except for the shell to the outer top cover NB-4243 and in other components shall be full weld. The shell to the outer top cover weld will be a NB-5230 penetration joints. These welds multi-layer weld and receive multi-level PT examination shall be examined by UT or RT in accordance with the guidance provided in ISG-15 for and either PT or MT. NDE. The multi-level PT Examination provides reasonable assurance that flaws of interest will be identified. The PT examination is done by qualified personnel, in accordance with Section V and the acceptance standards of Section 11, Subsection NB-5000.

All of these welds will be designed to meet the guidance I provided in ISG-15 for stress reduction factor.

For the subject exemption request, the stress allowable reduction factor of 0.80 defined in ISG-15 is modified to define a greater penalty on stress allowable values in order to address the lack of a compliant PT examination for the affected DSCs.

The justification for use of the modified stress allowable reduction factor is provided in the response to RSI-1.

The evaluation methodology utilized to address the potential for flaws to exist in the field closure welds is based on flaw evaluation methodology from Appendix C of Section XI of the ASME B&PV Code, which provides an appropriate analytical process for determining allowable flaw size. It is acknowledged that the use of such flaw evaluation methodology is not recognized by ASME Subsection NB-3210 for design by analysis, since NB-3210 provides design rules under Section III which do not account for flaws in welds. Therefore, the evaluation methodology utilized in the subject exemption request to address the field closure welds with noncompliant PT is founded on the design basis for the NUHOMS 61 BTH system, with the application of appropriate analytically based technical considerations.

L-MT-1 4-082 Page 11 of 13 Observations OBS-1: Provide the measuredheat loads at time of fuel loading for DSCs 11-16.

Provide a table showing the measured decay heat values at time of fuel loading for DSCs 11-16. This is to provide information regardinghow much the actual heat loading is below the design heat limit for each DSC. The information will help assure that fuel cladding and cask component temperaturesremain below the limits for each DSC (DSCs 11-16).

This information is required by the staff to determine compliance with 10 CFR 72.236(0.

REPLY: Decay heat values at the time of fuel loading are not measured, but are calculated. Total decay heat loads were calculated based on the calculated decay heat rates of individual fuel assemblies that existed several months prior to the actual DSC loading. These total decay heat loads (in kilowatts - kW) are summarized in the table below:

DSC Total Calculated Decay Heat (kW) 11 10.96 12 10.88 13 10.79 14 10.77 15 10.75 16 10.72 The design decay heat load for the Type 1 DSC 61 BTH is 19.4 kW (Reference TS 1.2.1, Table 1-1t, Figure 1-19).

Based on the heat transfer capabilities of the Type 1 DSC 61 BTH design, the Technical Specifications (i.e., TS 1.2.18) do not impose any time restrictions for the Transfer Cask when loaded with this type of DSC.

OBS-2: Provide the maximum DSC surface temperaturesmeasured at the closure welds at the time of PT examination (DSCs 11-16).

Provide a table listing the maximum DSC surface temperaturesmeasured at the innertop cover plate weld, the siphon port cover plate weld, and the vent port cover plate weld, at the time of PT examination for all DSCs 11-16.

The information will provide a basis to assure that the satisfactoryPT exams have been completed on the closure welds of each DSC (DSCs 11-16).

L-MT-1 4-082 Page 12 of 13 This information is required by the staff to determine compliance with 10 CFR 72.236(0.

REPLY: The following table provides the highest DSC surface temperatures (in degrees Fahrenheit - 'F) that were recorded in work orders for the listed closure welds at the time of PT examination.

DSC Weld Location Surface Temp (fF) 11 Inner Top Cover Plate 110 11 Siphon Port Cover Plate 149 11 Vent Port Cover Plate 148 12 Inner Top Cover Plate 158 12 Siphon Port Cover Plate 160 12 Vent Port Cover Plate 162 13 Inner Top Cover Plate 179 13 Siphon Port Cover Plate 176 13 Vent Port Cover Plate 189 14 Inner Top Cover Plate 145 14 Siphon Port Cover Plate 190 14 Vent Port Cover Plate 190 15 Inner Top Cover Plate 151 15 Siphon Port Cover Plate 128 15 Vent Port Cover Plate 130*

16 Inner Top Cover Plate 138 16 Siphon Port Cover Plate 136 16 Vent Port Cover Plate 148

• This value is the highest credible recorded value. One other erroneously high value was recorded for the Vent Port Root PT, and has been discounted. This error is recorded and resolution is tracked in NSPM's corrective action program (CAP 1453122).

OBS-3: Clarify the intent of, or modify, as appropriate,the statement in Section 2.0, Conservatism/Assumptionson page 4 of the exemption request, "[h]owever, conservatively the secondarystresses are scaled, increased,for the reduction in the OTCP weld size."

The "line welds" assumption for the lid-to-shell configurationresults in weld reactions in shear and tensile force components, which are necessitatedfor force equilibrium for the inner and outer top cover plates resisting the canisterinternalpressure and canister drop inertia forces. As such, stresses associatedwith the line welds ought to be categorized as primary for invoking appropriatestress acceptance criteria.

L-MT-14-082 Page 13 of 13 This information is requiredby the staff to determine compliance with 10 CFR 72.236.

REPLY: Addressed in the reply to RSI-3.

OBS-4: Clarify the intent of, or modify, as appropriate,the statement in Section 7.1 on page 7, OTCP weld for reduced Weld Size Evaluation, "[t]he three components of the secondarystress are membrane (Pm), bending (Pb) and thermal stress (Q)."

Only thermal stress can be consideredsecondary. See technicalbasis comment in the previous observation (OBS-3).

This information is requiredby the staff to determine compliance with 10 CFR 72.236.

REPLY: Addressed in the reply to RSI-3.

OBS-5: For Table I explain the basis for determining the Service Level D, allowable stresses of 32.4 ksi, 29.4 ksi, and 31.1 ksi for load cases TR-9, TR-10, and TR-11, respectively.

Identical at-temperaturestress allowables should be used for the same weld analyzed.

This information is requiredby the staff to determine compliance with 10 CFR 72.236.

REPLY: The stress allowable values reported in Table 1 for load cases TR-9, TR-10 and TR-1 1 differ from one another because they are taken at different temperatures; each case using the temperature associated with the particular load cases analyzed.

This accounts for the difference in stress allowable values between the load cases.

Refer to Section 7.5 of AREVA calculation NUH61BTH-0200.

References:

1. NSPM letter to NRC Document Control Desk, L-MT-14-016, Exemption Request for Dry Shielded Canisters 11 - 16 Due to Nonconforming Dye Penetrant Examinations, dated July 16, 2014 (ADAMS Accession No. ML14199A370).

2., NRC letter to Karen D. Fili, Exemption Request for Dry Shielded Canisters 11-16 Due To Nonconforming Dye Penetrant Examinations, Docket No. 72 Supplemental Information Needed, dated September 11,2014.

L-MT-14-082 ENCLOSURE 2 STRUCTURAL INTEGRITY ASSOCIATES, INC.

CALCULATION PACKAGE 1301415.301 TITLE:

DEVELOPMENT OF AN ANALYSIS BASED STRESS ALLOWABLE REDUCTION FACTOR (SARF)

DRY SHIELDED CANISTER (DSC) TOP CLOSURE WELDMENTS REVISION 0, OCTOBER 2014 39 pages follow

V pStructural Integrity Associates, Inc File No.: 1301415.301 Project No.: 1301415 CALCULATION PACKAGE Quality Program Type: Z Nuclear R] Commercial PROJECT NAME:

Monticello ISFSI - DSC 11 through 16 Exemption Request CONTRACT NO.:

1005, Release 48, Amendment 6 CLIENT: PLANT:

Xcel Energy Monticello Nuclear Generating Station CALCULATION TITLE:

Development of an Analysis Based Stress Allowable Reduction Factor (SARF) - Dry Shielded Canister (DSC) Top Closure Weldments Document Affected Project Manager Preparer(s) &

Revision Pages Revision Description Approval Checker(s)

Signature & Date Signatures & Date 0 1 - 30 Initial Issue Preparer:

A-i - A-2 B-1 -B-7 Wilson Wong Richard Bax 10/23/14 10/23/14 Checkers:

James W. Axline 10/23/14 J. Wu 10/23/14 C. Fourcade 10/23/14 Page 1 of 30 F0306-01 R2

CAWukv nb"Amf kne Table of Contents 1.0 O B JEC TIV E ............................................................................................................ 4 2.0 TECHNICAL APPROACH .................................................................................... 5 2.1 Finite Element Model and Flaw Simulation ................................................. 5 3.0 ASSUMPTIONS / DESIGN INPUTS ...................................................................... 6 4.0 CALCU LA TION S ..................................................................................................... 7 4.1 Pressure Loading ........................................................................................... 7 4.2 Side Drop Loading ....................................................................................... 8 5.0 RESULTS OF ANALYSIS ...................................................................................... 8

6.0 CONCLUSION

S AND DISCUSSION ................................................................. 10 7.0 REFEREN CES ....................................................................................................... 12 APPENDIX A ANSYS INPUT FILES .......................................................................... A-1 APPENDIX B SI REPORT 1301415.405, REVISION 0, "EXPECTATIONS FOR FIELD CLOSURE WELDS ON THE AREVA-TN NUHOMS 61BTH TYPE 1 & 2 TRANSPORTABLE CANISTER FOR BWR DRY FUEL STORAGE,"......................................................................... B-1 File No.: 1301415.301 Page 2 of 30 Revision: 0 F0306-01R2

SbuUIWV hyANOWK List of Tables Table 1: OTCP Stress Reduction Factor Results - Pressure Loading ............................. 13 Table 2: OTCP Stress Reduction Factor Results - Side Drop Loading ............................ 14 Table 3: ITCP Stress Reduction Factor Results - Pressure Loading ................................ 15 Table 4: ITCP Stress Reduction Factor Results - Side Drop Loading .............................. 16 Table 5: OTCP and ITCP Deflection Load Cases - Pressure Load Case .......................... 17 List of Figures Figure 1. Finite Element Model and OTCP and ITCP Details .......................................... 18 Figure 2. OTCP Postulated Flaw Configuration - Radial #1 ........................................... 19 Figure 3. OTCP Postulated Flaw Configuration - Radial #2 ........................................... 20 Figure 4. OTCP Postulated Flaw Configuration - Laminar ............................................. 21 Figure 5. OTCP Postulated Flaw Configuration - Circumferential #1 ............................. 22 Figure 6. OTCP Postulated Flaw Configuration - Circumferential #2 ............................. 23 Figure 7. OTCP Postulated Flaw Configuration - Circumferential #3 ......................... 24 Figure 8. OTCP Postulated Flaw Configuration - Circumferential #4 ............................ 25 Figure 9. ITCP Postulated Flaw Configuration - Circumferential ................................... 26 Figure 10. OTCP Pressure Load Case - Displaced Shape (Exaggerated) ......................... 27 Figure 11. ITCP Pressure Load Case - Displaced Shape (Exaggerated) .......................... 28 Figure 12. Side D rop Model .......................................................................................... 29 Figure 13. OTCP and ITCP Stress Path Definitions ......................................................... 30 File No.: 1301415.301 Page 3 of 30 Revision: 0 F0306-01 R2

VSnuI hPffy AMOO Wc-1.0 OBJECTIVE The objective of this calculation is to develop a quantitative basis for a stress allowable reduction factor (SARF) to address weld quality in the inner top cover plate (ITCP) and outer top cover plate (OTCP) weldments of the NUHOMS dry shielded canister (DSC) system. This workscope is in support of the USNRC CofC Exemption submittal for DSC's 11 through 16, currently at the Monticello Nuclear Generating Plant (MNGP).

Weld quality is described as a global effect, for which a factor is used to reduce the stress allowables to account for potentially less than sound weldments. The SARF has historically been tied to the level of non-destructive examination (NDE) performed on the weldment. That is to say, the greater the degree of NDE performed (such as volumetric) the greater the SARF (less reduction in stress allowable).

The ASME Code [5, NG-3352] contains values for SARF for a range of NDE. Specifically, a VT only scope of NDE would state an SARF of 0.35 for a partial penetration weldment. However, it should be clearly noted that the ASME Code table for SARF's has no limitations/definitions/requirements on the weld size, the weld/base metal materials, the welding configuration, the welding position, and most importantly, the welding process. In addition, as this table is from NG, the level and comprehensiveness of the design analysis is less than that for an NB-type component, such as the DSC. The 0.35 SARF is a conservative factor that addresses all types of welding. In the case of the DSC weldments, these are specific joint geometries, with high quality materials, favorable welding positions, and again, most importantly, a high purity welding processes (GTAW), and therefore, strict adherence to the 0.35 SARF number for a VT only NDE examination weldment is not warranted.

The intent of this calculation, for this exemption request only, is to evaluate a series of postulated weld flaws and determine, for each configuration, the effect on the unflawed stress results. The effect of the stress results will be comparative, performed by comparing the analysis results of the flawed configuration to those from the same geometry, but in an unflawed configuration.

The determination of the impact on stress results will be performed by finite element analysis (FEA) in which selected elements of the ITCP and OTCP weldments will be "removed" to represent "flawed/suspect" weld quality.

Various distributions of flaw size (length and depth) and frequency (spacing), will be examined.

The intent of this calculation is to analytically determine the type of flaw distribution that would justify a specific SARF. A separate work scope has been performed to evaluate, for the specific DSC weldments (DSC's 11 through 16), what are the expected type and density of flaw distributions. It is the overall intent for this project workscope that it can be shown that the type of flaw distribution, which would support an acceptable SARF, will be of significantly greater magnitude than those populations that would be expected for the type of welding used for the DSC weldments.

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VanvWhEy A OW We 2.0 TECHNICAL APPROACH The determination of the impact of weld quality on stress results (SARF) will be performed by the finite element methods. Both the flawed and unflawed geometry of the top end of the DSC will be modeled.

To represent the presence of postulated flaws, selected elements within the model will be removed and analyses performed using representative load cases. By comparing the results from the unflawed and flawed FE models for these loads cases, a ratio, or stress allowable reduction factor can be determined.

A range of flaws will be analyzed to develop a range of SARF values corresponding to the range of flaw populations.

Typical types of flaws will be considered, and a range of distributions of flaw size (length and depth) and frequency (spacing), will be examined.

Three types of flaws will be addressed.

• Radial: a postulated flaw oriented in a plane radial to the DSC longitudinal axis and spanning the weldment from cover plate to shell.

• Circumferential: a planar flaw oriented in a plane parallel to the DSC axis and oriented circumferentially around the DSC.

• Laminar: a planar flaw in a plane perpendicular to the longitudinal axis of the DSC and spanning the weldment from cover plate to shell.

In the determination of what flaw types to analyze in the OTCP and the ITCP, the size/volume of the weldment was considered. The OTCP weldment is both large in size and volume absolutely, and also relative, to the weldment volume of the ITCP. Therefore, all three types of flaws are evaluated for the OTCP. The ITCP weldment, due to its reduced weldment size, is evaluated using a single flaw of significant cross-section, which represents elements of all three types. Figures showing these flaw types, location, and orientation are shown in Figures 2 through 9.

2.1 Finite Element Model and Flaw Simulation A single finite element model (FEM) is developed using the ANSYS finite element analysis software [2].

The model represents a 1800 sector of the upper end of the DSC. The model includes the outer top cover plate and weldment, the inner top cover plate and weldment, and a portion of the DSC shell.

The FEM utilizes the ANSYS 3-D structural element (SOLID45). The unflawed model contains all portions of the two weldments.

The modeling of the postulated flaw is done by "killing" the selected elements that represent the flaw size and location, using the EKILL command in ANSYS. This command deactivates the element such that it contributes near zero stiffness to the overall stiffness matrix. The result is a redistribution of loading and stresses around "killed" elements.

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The ANSYS model of the top end geometry is shown in Figure 1 which illustrates the full model and then localized sections through the OTCP and ITCP.

3.0 ASSUMPTIONS / DESIGN INPUTS The top end geometry of the DSC is defined in Reference 3. The OTCP, ITCP, and DSC shell dimensions, as well as the materials, are provided in Reference 3. A number of assumptions were made during development of the finite element model, which are listed as follows:

• The model consists of a half-symmetric portion of the inner top cover plate (ITCP), outer top cover plate (OTCP), and the top 20 inches of the outer DSC cylinder. The 20 inches equates to greater than 4.04Rt, thus avoiding any end affects at the free end constraint. The model is constructed of approximately 840,000 SOLID45 elements to ensure adequate mesh refinement for the ITCP and OTCP welds in the circumferential direction.

• The OTCP is modeled with the top surface set 1/8 of an inch below the end of the DSC. The J-groove weld preparation is as shown in Reference 3. The weldment is shown flush with the surface of the OTCP and not set below, as is allowed by the Reference 3 field assembly drawing.

The modeled set back weldment is considered acceptable as this is a comparative analysis and the same geometries are used in both the flawed and unflawed condition.

• The ITCP is modeled as a flat plate and the closure weldment is modeled flush with the top surface of the ITCP.

• The DSC shell, the OTCP, the ITCP, and the OTCP and ITCP weldments are modeled as SA-240, Type 304 stainless steel. Material properties are taken from Reference 4. Standard room temperature material properties for Type 304 stainless steel are used: Young's Modulus = 28.30E6, Density = 0.283 lbs/in3 , and Poisson's Ratio of 0.3.

• The analysis is performed at 70'F. This temperature is selected as this is a comparative analysis and both the unflawed and flawed runs utilize the same temperature.

• The bottom edge of the outer cylinder is fixed in the axial and circumferential directions, and symmetry boundary constraints are placed on the symmetry plane. For the side drop runs, the outer cylinder is released in the circumferential direction and is supported at the point of "impact" via radial displacement couples to a support block with reduced stiffness properties.

• The analyses are all treated as elastic.

" The localized effects of the vent and siphon block and the ITCP weldment are not modeled. This is acceptable as the weldment connection to the V/S block (1/4" groove) is similar to the majority portions of the ITCP weldment, and the intent is to determine the effects of global weld quality, not localized stress concentrations. The effect of stress discontinuity at the V/S block will be addressed by the design analysis which models this explicitly, and then uses the SARF to further modify the stress allowables.

• The siphon/vent port cover plates are not modeled as the nominal stresses (primarily due to pressure) are sufficiently low to accommodate extremely low SARF's. Assuming a 3/16" closure groove weld [3] on a nominal 2 inch diameter cover plate results in a weld shear stress of File No.: 1301415.301 Page 6 of 30 Revision: 0 F0306-0 1R2

10"vc MWOMyOWKWO less than 500 psi. Thus even a worst case SARF of 0.10, would be acceptable given the nominal weld filler metal shear stress allowable of 0.6 Sm [5, NB-3227.2] = 0.6 * -16 ksi = -9.6 ksi.

" Dimensions for the components are taken as the nominal. This is acceptable as this is a comparative analysis.

" The evaluated paths for which the stress results are extracted and used for comparison (flawed vs unflawed) are shown in Figure 13.

4.0 CALCULATIONS The determination of the SARF, as a function of weld quality (number and density of postulated flaws),

is performed using two load cases. The pressure load is the primary normal and off normal load for these weldments and consists of internal pressure applied to the inner top cover and outer top cover. The specific definition and modeling details are described below for the pressure load case.

The drop load cases consist of a canister end drop, a canister corner drop, and a canister side drop. For this comparative analysis the canister side drop load case is utilized as it best represents the behavior of the drop event (an event that is germane to the MNGP ISFSI DSC hardware configuration) and is a more easily evaluated/modeled condition. The side drop load case develops localized stresses along a line of contact similar to the corner drop. The specific details for the side drop load case are described below.

4.1 Pressure Loading The pressure loading consists of a nominal 100 psig internal pressure applied to the top cover plates. For evaluation of the ITCP (the nominal pressure boundary) weldment quality, the pressure is applied to the inside surface of the ITCP and the DSC shell, and the contacting surfaces between the ITCP and OTCP are bonded with sliding capability using ANSYS contact elements to allow for load transfer from the ITCP to the OTCP. For the ITCP pressure analysis, CONTA174 and TARGE170 contact elements were used to prevent the ITCP from penetrating the OTCP. In these cases the OTCP acts as a non-pressure retaining structural support for the ITCP. Figure 11 shows the displaced shape for the ITCP pressure load case.

For evaluation of the OTCP weldment quality, the pressure is applied only to the inside surface of the OTCP and the inside surface of the DSC. The ITCP and the weldment to the shell are both contained within this model and are not modeled as containing flaws, nor are they loaded by pressure. The intent of applying the pressure loading to the OTCP alone is to maximize the response of the OTCP-to-DSC shell weldment, as a result of postulated flaws within the weld. Applying the pressure to the ITCP, which in turn will load the OTCP, will diminish the response of the OTCP, as there exists supplemental stiffness from the ITCP. Figure 10 shows the displaced shape for the OTCP pressure load case.

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VANwOWutpfy - f 4.2 Side Drop Loading The side drop loading case is evaluated as a static 75G load case in which the FEM of the DSC shell is oriented with the symmetry plane in the direction of the drop. For the side drop analysis, the same contact element types (CONTA 174 and TARGE 170) were used to prevent the ITCP from penetrating the DSC outer cylinder. These are not used for the OTCP weld prep-to-DSC shell potential contact region, as the area of potential contact is small relative to the OTCP weld size.

To simulate the support of the transfer cask, the lower 200 of the DSC model is supported by a material which represents the stiffness of the transfer cask given that there is a difference in diameter between the DSC and the transfer cask. In the transfer condition, the DSC is supported within the Transfer Cask on thin guide rails, and the use of a lessor stiffness support in the lower 200 degree region is representative.

Again this is a comparative analysis and the intent is to show the effect of weld quality in the weldments in the most highly stressed area of contact, which is at bottom dead center. Radial displacement couples between the DSC and support block are used. Figure 12 shows the geometry of this load case.

5.0 RESULTS OF ANALYSIS The determination of the SARF for a given postulated flaw population is performed by extracting the stress results from the unflawed geometry, and the flawed geometry for the specific load case. These stresses are extracted and linearized along identical paths to capture the change in stresses due to the missing/flawed elements.

The comparison to determine the change in stress results, as a result of the postulated flaw population, typically compares the linearized membrane (Pm) and membrane plus bending (Pm + Pb) stress intensities for a path adjacent to the postulated flaw and at other regular spacings between the postulated flaws.

These discrete ratios are then combined to produce a weighted SARF for the weld flaw pattern.

Figure 13 shows the path locations and orientations for the three types of flaws for which stresses are extracted.

In general the comparison of stress results is done by comparing linearized membrane (Pm) and membrane plus bending (Pm + Pb) stress intensities. However, in the case of the side drop event for the radial and laminar flaws, the high compressive stresses in all three principal stresses make the use of stress intensity not representative. In these cases, where all three principal stresses are compressive, and the resultant stress intensity is of lesser magnitude than the principal stresses, the resulting SARF's are unrealistic. In these cases the greater stress values of the three principal stresses are combined by SRSS and compared for the flawed and unflawed configuration.

An initial set of postulated flaw populations for the radial, circumferential and laminar flaw were developed and analyzed. Subsequent to initial runs, additional flaw populations for the radial and circumferential flaw cases were run. The specific geometry of the flaw populations are shown in Tables 1 through 4, along with the resulting SARF's.

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It should be noted that the intent of the calculation is to show a flaw population that is severe and thus demonstrate that large flaw populations (size, length, and density) can be tolerated, as the calculated SARF is acceptable. In the selection of the flaw population parameters, the depth of the flaws is typically set as a through-wall flaw. Obviously, such a flaw would have been unacceptable, and would have been identified by leak test examination. However, the intent of this calculation is to address structural capacity of the weldment, not confinement.' Thus the use of the through-wall flaw allows for a conservative determination of the SARF.

Table 1 documents the calculated SARF's for the OTCP weldment subjected to pressure loading.

Table 2 documents the calculated SARF's for the OTCP weldment subjected to the side drop loading.

Table 3 documents the calculated SARF's for the ITCP weldment subjected to pressure loading.

Table 4 documents the calculated SARF's for the ITCP weldment subjected to the side drop loading.

Table 5 presents the axial deflection at the centerline of the OTCP for the various flaw configurations analyzed for the pressure load case. The intent is to show that, as expected, the stiffness of the combined OTCP and ITCP is greater (less deflection) than the OTCP alone. This is the reason that the pressure loading was applied to the OTCP alone, so as to maximize the deflection of the OTCP, and therefore challenge to the OTCP weldment. A review of the table shows that the change in deflection of the OTCP as a result of the introduction of postulated flaws, in either the OTCP or ITCP weldment, is relatively low (< 15% in the worst case). Thus the evaluation of flaws does not require the explicit evaluation of concurrent flaws in the OTCP and ITCP, as their responses (unflawed/flawed) are basically similar, and this is a comparative evaluation.

In addition, a comparisons of the deflections of the OTCP in the unflawed and postulated flawed cases shows that for the less severe, but still significant flaw populations (Radial 2, Laminar, Circ 3, and Circ 4), the change in response (OTCP deflection) is small, typically 1% or less. It can therefore be presumed that a mix of flaw types would produce similar results as that for a single flaw type, e.g. a mix of radial, laminar, and circumferential flaws would have similar results as that for the bounding single flaw type. The worst case SARF for the selected flaw types will be utilized, thus any substitution of lesser SARF flaws (e.g. laminar) for greater SARF flaws (Circ) would be bounded.

Finally, the postulated 50% circumferential flaw for Circ 4 is positioned in the upper half of the weldment. The change in SARF values (Tables 3 and 4) between the Circ 3 and Circ 4 cases is an increase of -4% for the pressure case, and -14% for the side drop case. A 50% through-wall flaw, located in the lower portion of the weldment, would have an SARF no worse than the Circ 3 case, and the Circ 3 case SARF, for both pressure and side drop, is greater than 0.80. The placement of the 50%

through-wall flaw in the lower half of the weldment would thus not change the results to a point where the Circ 3 case would not be bounding.

1The results demonstrate that the remaining ligaments of the DSC weldments have sufficient structural capacity, even with very severe and conservative penalties (postulated flaws) for nonconforming PT examinations, to perform their design function of restraining the OTCP and ITCP's, and additionally maintaining the confinement function during all service level load cases.

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Caw" MM My AuAK W.0

6.0 CONCLUSION

S AND DISCUSSION The OTCP and ITCP weldments are made using both materials and processes, and in conditions which would result in high quality (very small flaw distribution). Specifically it is a stainless steel weldment made with argon cover gas in a flat position using a machine GTAW process. As such, concerns over weld porosity are minimized and the machine welding process will produce a very uniform and consistent weldment. Report 1301415.405 [1, See Appendix B] details the expected flaw distribution for this type of weldment.

A review of Tables 1 through 4 documents the calculated SARF for the selected flaw populations. The question of which flaw population to consider representative or typical, or bounding is based not on these analytical results but on the separate Reference I report. This report is based on the actual elements of the OTCP and ITCP welding, and considers industry experience and ISFSI Vendor experience [1, See Appendix B].

Reference 1 states in the conclusion that:

It is suggested a bounding subsurface defect condition is conservativelyrepresentedas an intermittent lack offusion (LOF)defect evenly distributedalong the canisterweld. Further, the total length for LOF is conservatively estimatedat 25% of the canistercover plate weld circumference. The estimated through thickness dimension is 1/8 inch, because this dimension representsa maximum weld bead thickness. One eighth inch is consideredto be a conservative assumption, because it is recognized that most weld beads will be thinner especially as the weld cavity begins to fill. No credit is being taken for remelting even though remelting is normally associatedwith multipass welding. "

Comparing this to the analyzed flaw populations:

OTCP: Both the radial and laminar flaws are not representative of the circumferentially oriented flaw described above. However, in both cases, the postulated flaws for these types are full thickness and full width, and thus would be considered more severe than a 1/8" thick, 25% total weld length flaw, with a width of one weld bead. As an example, the laminar flaw is the full width of the weld, and covers 72% of the circumferential arc. The radial Configuration 2 flaw (more limiting), shown in Figure 3, is a full height (through-wall) flaw, spanning the full weldment width, and occurring less than 2" apart.

The circumferential flaw, Configuration 3, shown in Figure 7, is a full height (through-wall) flaw, 1" long and occurring every 5". The 1" in 5" spacing is a 20% occurrence of postulated flaws, which although less than 25%, is tempered by the fact that the analyzed flaw is full height, not the expected one bead thickness dimension (- 1/8") described above. With this consideration, the Configuration 3 circumferential flaw bounds the "conservatively assumed" flaw stated in Reference 1.

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Can" MWf MuWi hWO ITCP: The 360 degree embedded flaw postulated and evaluated (Figure 9), is much more adverse than the expected flaw of Reference 1 described above.

In both the OTCP and the ITCP weldments, the weld is a multi-layer weldment, and both received multi-level VT and PT examinations. Although the PT cannot be credited, the VT can be assumed to have seen large surface breaking flaws. As a further argument that the postulated and analyzed flaws are bounding for flaws that would have not have been identified by the VT exams, the likelihood that multiple through-layer thickness flaws of the postulated percentage of arc length (e.g. the Circ 3 case flaw covers 20% of the total arc length) would occur in every layer, and would also line up with flaws below and above to create a through-wall combined flaw, and not be detected by the multiple VT's, is highly unlikely and not realistic.

Again the use of through-wall flaws is done to evaluate the structural integrity of the weldments. The validation of confinement of the weldments was separately confirmed by successful leak testing.

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7.0 REFERENCES

1. SI Report No. 1301415.405, Revision 0, "Expectations for Field Closure Welds on the AREVA-TN NUHOMS 61BTH Type I & 2 Transportable Canister for BWR Dry Fuel Storage," October 2014, SI File No. 1301415.405. [Appendix B]

2. ANSYS Mechanical APDL and PrepPost, Release 14.5 (w/ Service Pack 1), ANSYS, Inc.,

September 2012.

3. AREVA Design Drawings for the 61BTH, Type I and 2, NUH61BTH-3000, Rev 1, "NUHOMS 61 BTH Type I DSC Main Assembly," and NUH61 BTH-4008, Rev 1, NUHOMS 61 BTH Type I & 2 Transportable Canister for BWR Fuel Field Welding, PROPRIETARY SI File No. 1301415.201P.

4. ASME Boiler and Pressure Vessel Code, Section 11, Part D, Material Properties, 2004 Edition.

5. ASME Boiler and Pressure Code, Section III, Division 1, Rules for Construction of Nuclear Facility Components, 2004 Edition.

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Table 1: OTCP Stress Reduction Factor Results - Pressure Loading PRESSURE IAADING Radial Radila#2 Jania

_____#1____ I I CliTU 3 Ji Cr#4 Pm PmI-Pb(I Pm+P(O) Pm Pm+Pb() Pm+Pb(O) Pm Pm+Pb(I) Pm+Pb(O) Pm Pm+I'b(l) Pm+Pb(O) PM Pmn+Pb(l) IPm+/-Pb(O) PM I Pm+Pb(1) IPM+Pb(O) Pm Pm+PbM ) Pm+Pb(O)

Average 0.908 0.762 0.900 0.955 0.879 0.973 0.911 0.911 0.950 0.515 0.534 0.436 0.759 0.771 0.703 0.924 0.920 0.888 0.940 0.956 0.919 MN 0.762 0.879 0.911 0.436 0.703 0.888 0.919 Through Wall Flaw Through Wall Flaw Through Wall Flaw Through Wall Flaw Through Wall Flaw Through Wall Flaw 50% Part Through Wall Flaw Pattern Arc .16 Pattern Arc 1.734 Pattern Arc Pattern Arc 5194 Pallem Arc 5184 Pattern Arc 5atte5,1A4 Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) 0.144 Flaw Arc Flaw Arr360c 2016 Flaw Arc 1012 Flaw Arc 1.012 laWidthg(in) 0.144 FlawWidh(in) (in) Length (in) Lengthe(in) Length (in) Length (in)

Un-Flawed Arc Un-Flawed Ar .59 Un-Flawed Arc 1.584 Un-Flawed Arc 1.584 Un-Flawed Arc 3169 Un-Flawed Arc 4172 Un-FlawedAm 4.172 Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in)

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, TSbbl e 2 OT u fte h ba Table 2: OTCP Stress Reduction Factor Results - Side Drop Loading SIDE DROP Radial Laminar Circ#1 Cire#2 Cite#3 Cire#4 PrI Pm+Pb(l) Pm+Pb(O) Pm Pm+Pb(l) Pm+Pb(O) PmI Pm+Pb(l) Pm+Pb(O) PmI Pm+Pb(l) Pm+Pb(O) IPro Pm+Pb(l) Pm+Pb(O) Pm Pm+Pb(I) Pm+Pb(O)

Average 0.976 0.921 0.912 0.882 0.957 1.000 0.542 0.606 0.762 0.720 0.756 0.903 0.846 0.861 0.972 0.979 0.974 0.974 MIN 0.912 0.882 0.542 0.720 0.846 0.974 Through Wall Flaw Through Wall Flaw Through Wall Flaw Through Wall Flaw Through Wall Flaw 50% Part Through Wall Flaw Pattern Arc 0864 Pattern Arc 5760 Pattern Arc Pattern Arc Pattern Arc 5184 Pattern Arc Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in)

Flaw Width (in) 0.144 Flaw Arc 4176 Flaw Arc Flaw Arc 2.016 Flaw Arc 1012 Flaw Arc 1.012 Length (in) Length (in) Length (in) Length (in) Length (in)

Un-Flawed Arc 0720 Un-Flawed Arc 1594 Un-Flawed Arc Un-Flawed Arc 3.168 Un-Flawed Arc 4172 Un-Flawed Arc 4.172 Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in) Spacing (in)

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Table 3: ITCP Stress Reduction Factor Results - Pressure Loading ITCP Pressure Pm Pm+Pb(I) Pm+Pb(O) 0.964 1.000 0.954 0.954 Flaw Cross Section 0.006 in2 Area Pattern Arc Spacing (in)

Flaw Arc Length (in)

Flaw Arc Spacing (in)

File No.: 1301415.301 Page 15 of 30 Revision: 0 F0306-01 R2

Table 4: ITCP Stress Reduction Factor Results - Side Drop Loading ITCP Side Drop Pm Pm+Pb(I) Pm+Pb(O) 1.000 0.931 1.000 0.931 Flaw Cross 0.006 in2 Section Area Pattern Arc Spacing (in)

Flaw Arc Length (in)

Flaw Arc Spacing (in)

File No.: 1301415.301 Page 16 of 30 Revision: 0 F0306-01R2

Table 5: OTCP and ITCP Deflection Load Cases - Pressure Load Case Axial Axial Deflection - Deflection - Ratio of Increase Component Flaw Type Unflawed Flawed (Percent change)

Configuration Configuration Flawed/Unflawed (inches)(') (inches)()

Radial 1 0.9089 0.921 1.3%

Radial 2 0.9089 0.9149 0.7%

Laminar 0.9089 0.918 1.0%

OTCP Circ 1 0.9089 1.0391 14.3%

Circ 2 0.9089 0.9507 4.6%

Circ 3 0.9089 0.9208 1.3%

Circ 4 0.9089 0.9169 0.9%

ITCP Circ 0.629 0.6314 0.4%

Note:

1) The deflection value was taken at the center top of each plate.

File No.: 1301415.301 Page 17 of 30 Revision: 0 F0306-01R2

!Vnnw M~bpfyAuOWKs W

- OTCP WELD ITCP WELD

- Inner

\-Outer Top Top Cover Cover Plate Plate (ITCP)

(OTCP)

BAS~EM Figure 1. Finite Element Model and OTCP and ITCP Details File No.: 1301415.301 Page 18 of 30 Revision: 0 F0306-01R2

!Vftw"MWukffyAuMII WW~k Figure 2. OTCP Postulated Flaw Configuration - Radial #1 File No.: 1301415.301 Page 19 of 30 Revision: 0 F0306-0 1R2

~SVuawuhfpAWOUNAdNs kO Pressure: Radial #2 Figure 3. OTCP Postulated Flaw Configuration - Radial #2 File No.: 1301415.301 Page 20 of 30 Revision: 0 F0306-01R2

cobv1wzuhbpy A=XaiL kn Pressure: laminar Flaw Figure 4. OTCP Postulated Flaw Configuration - Laminar File No.: 1301415.301 Page 21 of 30 Revision: 0 F0306-01R2

~SbbabwhIhbpE~MuohiWIL Ac~

Postulated Flaw Irc MAL cutaway view Pressure:Circ#1 Figure 5. OTCP Postulated Flaw Configuration - Circumferential #1 File No.: 1301415.301 Page 22 of 30 Revision: 0 F0306-0 1R2

~#Van" MWO~ AUoDabK hic Pressure: Circ #2 Figure 6. OTCP Postulated Flaw Configuration - Circumferential #2 File No.: 1301415.301 Page 23 of 30 Revision: 0 F0306-01R2

Van" W91 hpfAUaDOu WO Pressure: Circ #3 Figure 7. OTCP Postulated Flaw Configuration - Circumferential #3 File No.: 1301415.301 Page 24 of 30 Revision: 0 F0306-01R2

VOs"MMM ANOUN -NW Figure 8. OTCP Postulated Flaw Configuration - Circumferential #4 File No.: 1301415.301 Page 25 of 30 Revision: 0 F0306-0 1R2

Cabbw" &&I* -NOWRe Pressuru:Circ Crack - 1tCP Figure 9. ITCP Postulated Flaw Configuration - Circumferential File No.: 1301415.301 Page 26 of 30 Revision: 0 F0306-01R2

~SVaow Mpg hobpfy Mut Figure 10. OTCP Pressure Load Case - Displaced Shape (Exaggerated)

File No.: 1301415.301 Page 27 of 30 Revision: 0 F0306-01R2

Vonuw"WNI hbdEAW&

Figure 11. ITCP Pressure Load Case - Displaced Shape (Exaggerated)

File No.: 1301415.301 Page 28 of 30 Revision: 0 F0306-01R2

bVAsb NWhbEA=GWzi tW-Figure 12. Side Drop Model File No.: 1301415.301 Page 29 of 30 Revision: 0 F0306-01R2

~UVan" vw hbfAUao hCO Ni OTCP Radial Flaw OTCP Laminar Flaw Stress Path Stress Path OTCP Circumferential ITCP Flaw Stress Path Stress Path Figure 13. OTCP and ITCP Stress Path Definitions File No.: 1301415.301 Page 30 of 30 Revision: 0 F0306-01R2

Vmw"Mbff1AM~hftfte APPENDIX A ANSYS INPUT FILES File No.: 1301415.301 Page A- I of A-2 Revision: 0 F0306-01R2

Vago"MwW M~y ANaWOK knO File Name Description BaseModel.INP ANSYS mdl input file to construct the 3-dimensional

- model.

ANSYS input file to perform OTCP flawed stress analyses C*_$_%.INP * = 1-4 (Case Number)

$ = Side, Pressure (Loading)

%= Radial, Circ, Lam (Flaw Direction)

ANSYS input file to perform ITCP flawed stress I1_$_CIRC.INP analyses

$ = Side, Pressure (Loading)

Pressure.1NP ANSYS input file to perform OTCP non-flawed pressure stress analyses.

ANSYS input file to perform OTCP non-flawed side drop stress analyses.

1IPressure.INP ANSYS input file to perform ITCP non-flawed pressure stress analyses.

11 Side.fNP ANSYS input file to perform ITCP non-flawed side

-__drop stress analyses.

Genstress.mac Macro to perform linearized path stress extraction.

Macro to perform linearized path stress extraction i ousing the native ANSYS PRSECT command.

GETPATH.TXT Path listing for stress extraction.

Data.xlsm Excel file to compile stresses and compute ratios.

File No.: 1301415.301 Page A-2 of A-2 Revision: 0 F0306-01 R2

APPENDIX B SI REPORT 1301415.405, REVISION 0, "EXPECTATIONS FOR FIELD CLOSURE WELDS ON THE AREVA-TN NUHOMS 61BTH TYPE 1 & 2 TRANSPORTABLE CANISTER FOR BWR DRY FUEL STORAGE,"

File No.: 1301415.301 Page B- 1 of B-7 Revision: 0 F0306-01R2

Stnctural Integrty Assotes, Inc 11sis Ve""ly Drie Sut. 125 Huftpw., NC 291 ww.S tu corn

.mm(*odrtcm October 23, 2014 Report No. 130141$.405.R0 Quality Prwogru 9 Nuclear JCotmndid

)k. lames F. Back&

Xce! Energy Projec Supervisor -2013 DoIS Loading Campaign Montioclo Nuclear Generating Plat 2807 W. Cojoy Road 75 Monticello. MN 53362

Subject:

Expectations for FHld Closure Welds oa Ow AREVA-TN NUHOMS 61BTH Type I & 2 Tmr t Cnister for BWR Dry Fed Stoarp

References:

1. Xc! Energy Conurct No. 1005, Release 41, Amendment 6.

2. SI Report 1301413.402 R0, "Review ofTRIVIS C Welding Procedures used for Field Welds on the Tramnuclear NUHOM 61BTH Type I & 2 Tranportable Canister for BWR Fuel". January 30,2014

3. SI Report 1301415.403 R2, "Assesment of Monticello Spent Fuel Canister Closure Plate Welds based on Welding Video Records", May 2014

4. E-mail tran on Questons Regarding Postulated DCS Welding Flaw Dirubutions.pdf, from Peter Quinlan to Dick Smith October 10, 2014, Sl File No. 1301415.203.

5. Repair Rates in Welded Construction - An Amlysis of Industry Trends, TWL CambridgeU, Wldin J Cin.. November 2012, S1 File No.

1301415.204.

Dear hr. Becks:

Details of the machine gas tungsten arc welding (OTAW) field closure welds used on the NUHOMS 61BTH transportable dry shielded canisters (DSC) located at Xc. Energy's Monticello Nuclear Generating Plant (MNGP) have been reviewed in an attempt to perform a qualitative assessment of the likelihood that the welds might contain unacceptable defects. It is known that the required NDE acceptance testng was not performed according to approved procedures. Sequential dye penetrant (PT) cxamnations were required on the inner top cover plate weld -first after the weld root and hot pass(e) were complte and again, after the final weld layer was completed. This is a relatively small weld (3/16 inch partial penetration weld) and it was not required to perform an intermediate inspection. The second weld isa 1/2 inch partial penetration weld that requires a root, intermediate, and final PT inspection due to the Toll-Free 17T-414-7163 AMMUe Mk*MM AWKU ~ SOWI ftftMI afm.J ptw DOWN Ok4ft 3MMORM U6472-M Fi.7-u

= kor Si4U* m sa 9-ww*

t-wook ft-aft-l 21WN Mwtm ISM O.14A.

MIS*I-OMI 8100.M4 14,440

• 010.0 11w44mq/ 0400*417 File No.: 1301415.301 Page B-2 ofrB-7 Revision: 0 F0306-01 R2

James F. Beck. October 23,2014 Rport No. 1301413.405.R0 Pae 2 of 6 lar ams. The probl*m ihw& was that th dwell time used for both y pistraat mid developer were loss required by prOce&c. Th PT tet wer pV41*0014 but ProCl&e were not folowd. Iis poit is beig ephauizd beca e lgp oem defCtS are SO very qikddy with PT testing and Maly would havo bean iduAe am O*ih dwell tims were too shor to meW procedere. smlenr Vg defects nfglt have been miss as the dye requir sufiant d&A frme to wick and then be pulled at via t1m developer. 11s SWm Mi is in no way ktnded to jumti the ft to flow approved PT prooe&*es, bit ratw to aptly perspectve frow a qualitative seam.

There are a mxbe ofreasons to believe tut teW doom welds 4n tWr curret onditio do not contain Jalee discontim ies that od allege the etiness of the doem* welds to meuat thmir tended desgn Action.* t is &epupose of is review, perfarmed in a0cordnce with Refrenae 1, to detW vlidrasons to supor this conclusion. A is provded that is outilined in tohelsting balmw" Reasons to eqiect the sf t spot fe canister welds are ee kmloare onfixaties:

1. Use of qmuale and prove weding procedures; and teckiqme. (Reference 21

2. Use of.aachi GTAW pcess. (R[frence, 2)

3. Application.of.a prove arid robust weding Ysysen designd specilAlyt10suIVst thes types of field welds in thiese specifi types of canisltrs. (Referenc 3)

4. Use of and easiywedble bae m*t s (SA-240 Type 304 stainles steel).

,notil (Refernce21

5. Use of soid wire Slw new desined for wddn thme base motnals and fcnistedd to elfidnate hot crackng anl oter te tof W fisas (SPA 3 .9 I m esit aftaless steel gir ealfA said weldng grad ases for shiedin the weld padufe.

[RefernceJ

6. Canisters ar odented intOw vertical potin during waing such that Ow weld is perfom in h flat welds position (the Mo foin.iin wddivg OdStati .

(Rfrenil!esu 2,3 and 41

7. Weld roots are typically about 1/8 inch or dsihtiy cka which is good practice for OTAW macln welds. (Rafernc 4)

8. Weld layers are thin (between 1/16 inch and I/8 inch) reuirong miti layers (and nuldti weld passe) to mist with developinS weld deposit =ostey via remeli.

Larym become thmr as th groove is filled because the width is reater. (Reference 4]

9. AREVA-TN',s Whorc record wit thme welds is wecllent havin a airficat history ofwelds med with dais system and thine wldig proedures that shows 1%r rates. [Reference 41 The weldiug procedures and welder c doauroa n were reviewed in detail and specifics oflhat revieware rpoftd in Refrence 2. The review concluded Ihat 1...tde p"ocete: dOm GTAW welds in de wAjiecmt4 Ae canisterscan reasonably be exected so b# of oodqualty m.dfree ttb#r~a defect The e hetation was basdon die wacs u ofr&, de GTAVW wel, de excellen conrlsosdhnuedfor ihe wldbgpVroam, and due fact duat O welds and ban materids atm aswsnitk soaless ste Also At weldft conmnables are compaAtble Awdsw a amn atwi sed *n **duedesign...I. frsne 2)

File No.: 1301415.301 Page B-3 of B-7 Revision: 0 F0306-01 R2

VftftWWkbr*AuQW& t JaNos F. Bec .0. October 23.2014 Repoi No. 1301413.4031WO Per 3 ot6 The wddlqt spUmouiltseis performud mtirely in Owe Lft position - &wdk&r position hut aorrph iais related to wekkig out of pouibc ar havug to mpgtiate restricted diminigaes ayony sp iet aSeem. The ressos for tise viewpoist is h*At "n of position weds have to oomeeagais Sorme ofgravity ard tte Joint desig provdes sideoptot acces *brarn mipatatmn The reult oft welaig in 1he W postionis tWat deects am kely So be Ikdodmed thmn tight be expeced with other weld orientaions or restdictIon.

1h ,wap fe miser wld system is robust aid is Wovm. m wldag had is monated on a nmmmeti shielt#bb

• ove 100 ls mid is shown ir Fiure I below.

rMowddknturdIs vl*ibh iMi biJust kte bdlinEberep. Masprmtsdby ARKVA-TN) w~a~~sftAsWWKuL AW~

File No.: 1301415.301 Page B-4 of B-7 Revision: 0 F0306-0 IR2

Mpg) AMW t James F. Becka October 23.2014 Report No. 1301415.40.10 Paoe 4of6 fIte2 Wdtg qOUem pedde,,d ed aq,w e madA, hr wddu (,bet. pete by ARVA-TN)

The entive weling system rotates uiilar to a lazy-susn" and ti weldig torb is manipulated in and out as roquied f'proper p.posit There a oer tomb a**musetts such as tiat, lead, heiab etc. Ladig and trailinl camers ae moattd to provide video oft.d t o tnd rear of dw torch ad weld puddle. Welding videos have been reviewed IRnawe 31 in an attempt to 8sseM whether or not weld quality could be assessed. One objectve of he video review was to look for key discatirmnles such as porosty end evidence a rany lack of Asior The canlusion fromthw video rview were tAt circumstances we obseved at vanous tmes duing wdn ttat O iW

• apport t geneatio ofdefts such as cadde buildup, weld root burn-dw, localized ocat* a ton an ewurhowe, weld deposit surtec i*regpasties, and taseten drit requmng realipuam . However, nodig could oda.m eiter die generat of defects or *lack ofdefects. Sine each weld is a unique atity onemust rey on tmdecies or trends if post weld inpectioms Ke W available. Ther we also obeaevatcns otgood wedig practices *awell as hoste events stated above, These included root repair, pariodc adjustment of tmagsten positiocuiSi, tungsten electrod replacement, electrod steerin as ueeded, ecu. Most of du videos were vary sagle (all havinow sam oe types of obseavatins at about 1w same fequiency). Caster No. 16 also bad te s*am types of observation; but 1w Iqumncy appeared to be about twice an oftl ootes. This was ajudgment call by dw reviews ad not quantitative. It was caeully poinud out that even so, ther. was no evideme to indicate tast any specific discontinuites were generated - only that weldin conditions were observed that sometimes lead to the vanous types of discontindies. In addition snce thu welds use multiple weld beads to comdlete the weld, there is the opportunity to "beal"conditions created by welding overtw..

HEstorical Peqc#rsptv AREVA-TN was asked to describe tdk histaxical perspective ont. weldirg oft. canisters with this system. It is recognid hat all of 1w canisters were not welded by AREVA-TN but VftiftAft limplyAewabbI File No.: 1301415.301 Page B-5 of B-7 Revision: 0 F0306-01R2

Jans F. Bahka October 23.2014 ReApt No. 1301415.405.R0 Pgesof6 mi.g.4t icude a cotractr or utlit thedvs. Hoee th ,siea welding system likely would bve bean ued (oftmnrated km AEVATN). AREVA-TN noted h0t ty"al

&ds mig9t inhd locall pOosit (e), occaSionml tumnsten "khsion usosily resutuiVn iomtorch tip ontact wthOw soh& n wdd pdmd, lack of Sizon or ovedsp.

Reardig the potental Ox any huwKr biications (hcidays or breaks), erac typically does not ocow with austenitic stauiesm welds. Maximum sin ofindimai typ~ialy would be less thint l"to 2". Ireglarifies at strts a stops cm occur, and rollover has been seen in soame cam.

AREVA-TN also was sked ix dt hitorical expermec repain canister lowns weld aceptance mats (e.s.firt time Trate). The response idicaed that a beet estimate would be less Othn I UNSAT PT per 10 canisters, with an averane of 10 PT mminations per canmstr

('ircudes root and fina layr onirmar top cover, vet port cove, ui n pt cover and test pot%

with root mid ad fin layer on outer top cover (Or catain DSC modds. Therefor, the historical exeience su8est amra of about 1%UNSAT PTs for fe clostdre welds. Fher, t reent eddexpie*e weddn proe maturee d no wd pai at a - on eod 30+ cuis the fndin were I PT irnction fromstarts and stops was *mnd to hold developer, bit light nding was performed to smooth th surface and eliminated Oh bidication.

That, dite mwar indcons rwred no weld repais.

ARIEVA-TN wa alsos ed regari how many stailesssteel canisters hve been loaded and dosed by welding to date. The estimate was O&x nma y 750 lode*dosedNU*lOMS misters, with clows pafmWeby AREVA-TN, end user or oer cotractor. This repreents an extmive saml tht Indicamtat indiati t*ae of less dhn 1%and tOtate appeared to eagi antd y improve over th last 0 dthathve beat wlded.

Ther wer no applicae mockups W had been used to examine fo discontaities or defcots, so thainformato was unavailable. The -istorical evidence seenm to paint &hvaraie picture lending a degree ofcomfoxr hat the canisters in question at MNGP are not liky to have idicatiom of asigrficait size.

Finally, literature was examined to An infontma on regrding geeation ofdefeots in staiess steel waldmrnts. The best yer bundis hicated in Reference S. Thi papr wtitt by The Wddin Institute in CambridIM UK was pul*se in Q w Novewo 2012.

Thei pae tited "Repair Rates in Welded Cautruction - An Analysis of Inh&iy Trens" prvid good uigi_ More tdhn W0 professiouns were munated with about 10% resparonig.

There wer different kinds ofresponses such as % ofwelds requiring repair or % weld tlengts reqri repair being dte most prevalen The following applicable colusions wer noted.

OTAW staless steel welds returned under 2%repair raft. The impact o*dir-fret welding factors were parsed and s the following impacts: root repairs at 22.50, fill layers 7.5%,

hested joint type 150, access limitations 26%, and oher welding factors 11%. Most of thse are not preset in the canister welds as pointed out previously. It appers ihat tde AREVA-TN canister weld repair expeiene are slightly lower, but neertheless ae considered consistert with indus expectations fo a variety of mam.Aacured and histalled owqonxxint. Since all weldirg is in the fiat position usig a proven welding system, the 1% defect raft appears to be reasonable. In addition it was pointed out that experice with the past 30 canisters has been even better.

File No.: 1301415.301 Page B-6 of B-7 Revision: 0 F0306-01R2

!V~ftWy - bNW~ft James F. Becka October 23, 2014 Report No. 1301415.405.RO Page 6 of 6 CA~ectuSla Based on the sum of the information reviewed, it can be said that the likelihood for the occurrence of large defects Is not supported by historical evidence. While there remains the potential for long lack of fusion defects either hitetiead or sidewall, the thin multilayer design and potential for subsequent bead healing by remelting would significantly limit the through-thickness dimension of any long defect. in fact, the most likely lack of fusion indication(s) would be intermittent In nature and not expected to have a through-thickness dimension greater than one weld bead. While a quantitative estimate ofa limiting flaw size cannot be produced, the qualitative likelihood that larg defects would not be present is assuring.

It is suggest a bounding subsurface defect condition is conservatively represented as an Intermittent lack of fusion (LOF) defect evenly distributed along the canister weld. Further, the total length for LOF is conservatively estimated at 2S% of the canister cover plate weld circumference. The estimated through thickness dimension is If/ inch, because this dimension represents a maximum weld bead thickness. One eighth inch is considered to be a conservative assumption, because it is recognized that most weld beads will be tinner especially as the weld cavity begins to fill. No credit is being taken for remelting even though remelting is normally associated with multipass welding."

Very truly yours, Richard E. Smith, PhD. FAWS Senior Associate res V~xWbhv*AdM*W~h-File No.: 1301415.301 Page B-7 of B-7 Revision: 0 F0306-01R2