ML24008A248

NAC International, Response to Apparent Violations (a and B) in NRC Inspection Report 72-1031/2023-201; EA-2023-069

ML24008A248
Person / Time
Site:	07201031
Issue date:	01/08/2024
From:	Cole K NAC International
To:	Office of Nuclear Material Safety and Safeguards, Document Control Desk
References
EA-2023-069, IR 2023201
Download: ML24008A248 (19)

Text

Atlanta Corporate Headquarters 2 Sun Court, Suite 220 Peachtree Corners, GA 30092 Phone 770-447-1144 www.nacintl.com January 8, 2024 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Response to Apparent Violations (A and B) in NRC Inspection Report 72-1031/2023-201; EA-2023-069

References:

1) U.S. Nuclear Regulatory Commission (NRC) Letter to NAC International Inc., NAC International Inc - The U.S. Nuclear Regulatory Commission Inspection Report No. 72-1031/2023-201, (ADAMS Accession No. ML23283A238), dated December 7, 2023, which includes Enclosure 1 (Apparent Violations Being Considered for Escalated Enforcement) and Enclosure 2 (NRC Inspection Report 721031/2023201)

2) NAC International Inc. Letter to NRC, ED20230029: 10 CFR 72.242 Reportable Licensing Basis Non-Mechanistic Tip-over Evaluation Deficiency for the NAC-UMS and MAGNASTOR Dry Cask Storage Systems, Docket Numbers 72-1015 and 72-1031, dated March 10, 2023.

Dear Ms. Helton,

In Enclosure A to this letter, NAC International Inc. (NAC) hereby submits its responses to Apparent Violations A and B identified in Reference 1, Enclosure 1 (Apparent Violations Being Considered for Escalated Enforcement) and Reference 1, Enclosure 2 (Inspection Report 72-1031/2023-201).

As requested in Reference 1, NACs response for each of the Apparent Violations contains (1) the reason for the apparent violation, (2) the corrective steps that have been taken and the results achieved, (3) the corrective steps that will be taken, and (4) the date when full compliance will be achieved. Reference 2, included as Enclosure B to this letter, provided NACs docketed notification of the self-identified deficiencies that we are using as additional information for addressing our response to Apparent Violation A. In sum, in view of the low safety significance of the violations, as well as the comprehensive corrective actions taken to address the root cause and prevent recurrence of such conditions in our design controls, NAC does not believe that escalated enforcement is warranted for the Apparent Violations.

Should you have any questions or require additional information, I am available to discuss.

Alternatively, please contact Joyce Hamman, NACs Vice President of Quality at jhamman@nacintl.com or 678.328.1215 or Heath Baldner, NACs Director of Licensing at hbaldner@nacintl.com or 678.328.1252.

Sincerely, Digitally signed by Kent S.

Kent S. Cole Cole Date: 2024.01.08 15:54:30

-05'00' Kent S. Cole President and CEO cc: Shana Helton, Director Division of Fuel Management Office of Nuclear Material Safety and Safeguards Page 1 of 19

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Enclosures:

A. Response to Apparent Violations in NRC Inspection Report 72-1031/2023-201; EA-2023-069 B. NAC Letter to NRC, ED20230029, dated March 10, 2023 Page 2 of 19

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ENCLOSURE A NAC International Inc.

Response to Apparent Violations in NRC Inspection Report 72-1031/2023-201; EA-2023-069 Introduction and Summary NAC International Inc. (NAC) accepts Apparent Violations A and B identified in Reference 1, which involved NACs self-identification of a calculation error that occurred in 2007. NAC has conducted a root cause evaluation and a safety significance determination, which found that the condition identified had no impact on the ability of the affected NAC storage and transportation systems to perform their intended safety function. NAC has nevertheless taken comprehensive corrective actions to address the root cause and prevent recurrence of such conditions in our design controls.

In view of the low safety significance of the violations, as well as the comprehensive corrective actions taken, NAC does not believe that escalated enforcement is warranted for the Apparent Violations.

While NAC does not contest Apparent Violation A, as we have discussed with the NRC staff, NAC does not agree with certain language in Apparent Violation A and the Inspection Report that could give the impression that there has been a longstanding deficiency in NACs design controls (specifically from September 2007 through March 2023). Such a conclusion is not supported by the facts. NAC urges the NRC to clarify this language in Apparent Violation A and the Inspection Report (section 1.5.2 at page 10) to ensure a representative characterization of the underlying deficiency.

NACs Quality Assurance program and adherence to design controls are active and robust as evidenced by regular NRC and industry inspections that have found acceptable results.

Apparent Violation A (as stated in Reference 1):

Title 10 of the Code of Federal Regulations (10 CFR) Part 72.146 (b), Design Control, requires, in part, that design control measures must provide for verifying or checking the adequacy of design by methods such as design reviews, alternate or simplified calculational methods, or by a suitable testing program.

From September 2007 through March 2023, NAC International, Inc. (NAC) failed to establish adequate design control measures for verifying or checking the adequacy of design by methods such as design reviews or simplified calculational methods. Specifically, NAC failed to provide adequate design control measures for verifying input parameters to a finite element analysis used in a fuel rod structural calculation for their storage and transportation systems (i.e., NAC-UMS, MAGNASTOR, NAC-STC and MAGNATRAN). NACs computational model, calculation 71160-2025, had a value of 0.215 inches for a fuel rod diameter when the value should have been 0.431 inches. This error resulted in the stress demands on the fuel rod being reported as half of its actual value and once corrected the safety margin was negative, which indicated that the stresses induced in the fuel rod cladding exceeded the NRC approved design bases values.

(1) Reason for the Apparent Violation:

NAC agrees that in 2007 NAC failed to provide adequate design control verification of certain input parameters to a finite element analysis used in a fuel rod structural calculation for MAGNASTOR storage and transportation systems, and that this same calculation error was propagated during Page 3 of 19

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2019 and 2020 and remained undetected until NAC self-identified the issue during review of a 2022 calculation. Specifically, a parameter used in the computation of bending stress in the finite element model used to structurally evaluate a fuel rod under the non-mechanistic tip-over accident condition was incorrectly specified resulting in the non-conservative calculation of stresses in calculation 71160-2025, revision 1. The calculation uses an ANSYS 2-D elastic beam element, BEAM3, to represent a single fuel rod. The BEAM3 element requires the input of various "real constants" that define physical properties of the element such as cross-sectional area, area moment of inertia, and height. The so-called HEIGHT real constant is used by ANSYS in the computation of bending stress in the element and is defined in ANSYS documentation to be the total height of the beam (i.e., rod outer diameter in this case). NAC personnel in 2007 failed to confirm that all real constant inputs (i.e., area, area moment of inertia, height) used in the calculations were correct. The corresponding input code thus incorrectly set the HEIGHT real constant using a parameter equal to the outer radius of the rod, which is half of the correct value. Use of the correct value effectively doubles the ANSYS computed bending stress.

NAC performed a Root Cause Evaluation to determine the cause(s), as further described below in item (2) paragraph number 4.

(2) Corrective Steps Taken and Results Achieved:

NAC has taken comprehensive corrective actions to address the condition and prevent recurrence of such calculation errors. The corrective actions and results achieved are summarized here.

NAC issued Corrective Action Report (CAR) 23-01 to address the identified issue on February 28, 2023. The CAR required 1) an extent of condition investigation, 2) a safety significance determination - evaluating the ability of the affected components to perform their intended safety function, 3) a determination of impacted customer facilities, 4) a root cause investigation and determination, and 5) implementation of corrective actions to prevent recurrence. In response to the CAR:

1. NAC performed an extent of condition investigation, initially completed on March 10, 2023. NAC determined, as documented in its Reference 2 notification letter to NRC (see Enclosure B), that the calculation error originated in 2007 in an ANSYS calculation (71160-2025, Rev 1, Fuel Assembly Structural Evaluation, NEWGEN) that was utilized in the original MAGNASTOR [Docket 72-1031] and MAGNATRAN system [Docket 71-9356] certification basis. This same error was subsequently propagated into other ANSYS calculations:

• 71160-2139 Rev. 0, PWR and BWR Fuel Fatigue Evaluation for MAGNATRAN (2020)

• EA790-2520 Rev. 0 BWR Fuel Assembly Structural Evaluation, UMS (2019)

• 423-2020 Rev. 0 PWR High Burnup Fuel Rod 30-ft Side Drop and Fatigue Evaluation for NAC-STC (2022) (issue found in this calculation)

The calculational error was introduced into the certification basis for the UMS Storage system [Docket 72-1015] at Certificate of Compliance (CoC) Amendment 5 (in 2020),

which permitted the storage of high burnup fuel, and impacts those users that adopted Amendment 5 and beyond. The calculational error was introduced into the certification basis for the NAC-STC Transport system [Docket 71-9235] at the submittal for CoC Revision 21, dated May 9, 2022.

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NAC subsequently issued Finding Report (FR)23-008 on March 27, 2023, after some discrepancies were identified in additional fuel parameters. The discrepancies originated from prior efforts to build bounding models, which in some cases used worst case attributes from different fuel designs that did not reflect a specific actual fuel design.

When coupled with limited documentation on analytic assumptions on the source or basis of an input, the engineers basis of conservative intent was not clear. These discrepancies were relatively small in magnitude but were brought into the scope of NACs root cause evaluation and were part of NACs comprehensive actions to revise and/or issue new calculations to address the discovered deficiencies. See below, item (4) of this section, for a current and comprehensive summary of the actions taken to correct the deficient calculations and amend the certification basis.

2. NAC documented its determination that there was no Impact to Safety, identified the impacted components, and concluded that they maintained their ability to perform their intended safety function, in its March 10, 2023, Reference 2 notification to the NRC.

NACs subsequent calculations (described in paragraph number 4 below) affirmed this determination of no Impact to Safety.

3. The impacted facilities and models are as documented in NACs March 10, 2023, Reference 2 notification to the NRC. On March 2, 2023, NAC notified potentially impacted facilities in advance of the NRC notification, addressed concerns and questions (in support of these facilities corrective action / notification programs), and notified them of the impending CAR 23-01, NACs assessment of Impact to Safety, and the potential for reportability.

4. NAC performed a root cause evaluation and issued a Root Cause Analysis Report for CAR 23-01 on March 30, 2023. The root cause evaluation determined a human performance error occurred because of the following contributing factors:

• Failure to adequately confirm input. The ANSYS-required input of full height for a symmetric beam element is counterintuitive to the classical formula for stress in a beam under simple bending. Bending stress in a beam is classically calculated as Mc/I, (where M = moment, c = distance from neutral axis to extreme fiber and I = area moment of inertia). Note that c in beam theory is total height / 2. Based on the expectation and assumption that ANSYS input would follow this classical formulation, the input data to the original calculation used radius (distance from the neutral axis to the extreme fiber). But as defined in the ANSYS Element Reference, the HEIGHT real constant for the BEAM3 element requires the total height (outside diameter).

• Lack of commenting within the ANSYS calculation. The original calculation had no comments or annotations inserted for the consideration of other users that identified calculated values/variables/constants that needed to be verified/checked.

5. NAC performed two Corrective Actions to prevent recurrence of the issue:

1) NAC Standard Practice 222 (SP-222) Analysis Guideline - Methods to Ensure Accurate Modeling and Durable Interpretation of Results was issued on June 1, 2023. SP-222 provides guidance for clear documentation of inputs, assumptions, and the nature of the models developed. Comments are now added by NAC Page 5 of 19

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within all calculations to provide explanation and clarification based on ANSYS definitions.

2) Training of engineering staff to CAR 23-01 and the resultant root cause analysis was conducted April 20, 2023. Emphasis was placed on use of the simple BEAM function within ANSYS and for the NAC technical staff to be aware of the discrepancy between engineering beam theory and the required element inputs, as defined in the ANSYS Elements Reference, and to more generally assure that design inputs are consistent with applicable modelling software definitions and guidance. Additionally, the training discussed the risks of building a hybrid model using worst case inputs from several different (fuel) designs as opposed to building representative, more realistic models of the bounding (fuel) design for that particular analysis. Such representative models that reflect real designs are easier to document and verify. The training also emphasized the need to thoroughly document key assumptions and basis with comments so that a qualified performer with no prior involvement or access to the original performer could understand the analysis previously performed.

(3) Corrective Steps That Will Be Taken:

As corrective steps to comprehensively and systematically bring all licensed hardware into compliance, each affected systems CoC will be updated. Much of that work is already completed (but shown in this section for ease of reviewing the status) or in progress. All impacted calculations have been revised, and several new calculations prepared. All analyses supporting these calculations were performed in accordance with the training noted in Corrective Action 2 above, and included comments as noted in Corrective Action 1, above.

NAC has been systematically preparing CoC amendment requests to bring these new and revised calculations into its certification basis for each affected system. The outline below shows the actual schedule of the calculation completion and actual and projected dates for CoC amendment/revision for the affected systems/CoCs:

NAC-STC Docket 71-9235 Calculation: PWR High Burnup Fuel Rod 30-ft Side Drop and Fatigue Evaluation for NAC-STC

• Completed 3/27/23 - 423-2020-R1 Addresses error, performed during Transport Amendment RAI process, and submitted to the NRC.

CoC:

• Submitted CoC revision request to the NRC 04/10/2023.

• CoC revision issued 11/30/23.

NAC-MPC Docket 72-1025 CoC basis is not impacted by the error.

UMS Transport Docket 71-9270 Calculation: Fuel Rod Evaluation for the UMS Transport Cask 30-ft Side Drop Accident

• Completed 11/20/23 - EA790-2524-R0 New Calculation addresses error, fuel assembly performance with 60 unsupported length.

CoC:

• Pending CoC revision submittal to the NRC in 2024.

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UMS Storage Docket 72-1015 Calculation: PWR Fuel Rod Evaluation for the UMS Storage Tip-Over Accident

• Completed 6/2/23 - EA790-2519-R0 New UMS PWR specific Calculation replaces 71160-2025-R1 addresses error, fuel assembly performance with 60 unsupported length.

Calculation: Fuel Assembly Structural Evaluation for the MAGNASTOR And UMS Storage End Drop Condition

• Completed 5/11/23 - 71160-2026-R1 (Appendix C) Addresses error, UMS fuel buckling.

Calculation: BWR Fuel Assembly Structural Evaluation

• Completed 7/7/23 - EA790-2520 R1 - Addresses error, Storage tip-over BWR assemblies.

CoC:

• Submitted CoC Amendment request to the NRC on 10/10/23.

MAGNATRAN Docket 71-9356 Calculation: PWR and BWR Fuel Assembly Fatigue Evaluation for MAGNATRAN (includes 30 Side Drop)

• Completed 8/10/23 - 71160-2139-R1 Addresses error.

CoC:

• Pending CoC revision submittal to the NRC in 2024.

MAGNASTOR Docket 72-1031 Calculation: Fuel Rod Evaluation for the MAGNASTOR Storage Tip-Over Accident

• Completed 3/15/23 - 71160-2049-R0 New Calculation addressing error.

• Completed 4/14/23 - 71160-2049-R1 (Appendix E) Addresses PWR fuel assemblies.

• Completed 5/10/23 - 71160-2049-R2 (Appendix F) Addresses BWR fuel assemblies.

• Completed 7/10/23 - 71160-2049-R3 Addresses MSO tip-over.

Calculation: Fuel Assembly Structural Evaluation for the MAGNASTOR and UMS Storage End Drop Condition

• Completed 5/11/23 - 71160-2026-R1 (Appendix C) Addresses MAGNASTOR and UMS PWR and BWR fuel assemblies; included M5 material properties.

CoC:

• Submitted a CoC Amendment package (A14) to the NRC 07/24/23.

(4) Date When Full Compliance Will Be Achieved:

As noted above in item (3) above, there is a CoC revision that is complete and there are four remaining CoC revisions needed to bring the certification basis for all affected storage and transportation systems into full compliance. NAC-STC Docket 71-9235 is in compliance with a revised CoC issued. UMS Docket 72-1015 and MAGNASTOR Docket 72-1031 have CoC amendment requests submitted to NRC for review. UMS Transport Docket 71-9270 and MAGNATRAN Docket 71-9356 are pending, and NAC will make these submittals coincident with other requested changes to the UMS Transport and MAGNATRAN CoC. Since there are currently no UMS Transport and MAGNATRAN casks fabricated or in use, it is our view that the benefits of regulatory efficiency of a complementary submittal / review of UMS Transport and a complementary Page 7 of 19

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submittal / review of MAGNATRAN is more beneficial than an expedited unitized submittal/reviews; however, we intend to coordinate with NRC technical staff on the preferred approach. Based on NACs CoC amendment request plans outlined above, and typical timelines for CoC issuance, NAC expects full compliance by the end of 2025.

Additional Information NAC notified the NRC of this self-identified issue via letter ED20230029, dated March 10, 2023 (Reference 2 and Enclosure B to this letter). The notification letter included those elements required by 10 CFR 72.242, including date and time of discovery, method of discovery, affected systems/casks and owners, intended corrective actions, and an assessment of safety consequences and implications. As stated in Reference 2, NAC has completed an impact to safety evaluation and determined there is no Impact to Safety or concerns relative to the ability of the components to perform their intended safety function based on the error identified. The calculational error is specific to the non-mechanistic tip-over analysis. Both the MAGNASTOR FSAR and UMS FSAR provide evaluations which determined the loaded systems on the ISFSI pad do not tip-over within licensed conditions. The safety functions of the VCC and TSC (e.g., passive heat rejection, environmental protection, TSC confinement, fuel assembly geometry control) are unaffected by the error in fuel rod modeling.

No change in design is (or was) required to bring NACs systems into compliance. The calculations with the error were for assumed-to-be damaged fuel (specifically with a missing fuel grid resulting in a 60-inch unsupported span for the fuel rods instead of a more typical 30-inch span for intact assemblies). NAC considers this a very conservative condition as an analytical basis for assemblies with damaged or partially missing grids. This supports NACs determination that there was no safety impact as a result of the calculation error.

As noted previously, NAC agrees that in 2007 NAC failed to provide adequate design control for verification of certain input parameters to a finite element analysis used in a fuel rod structural calculation for MAGNASTOR storage systems and that instances of this same calculation error were propagated during 2019 and 2020 and remained undetected until NAC self-identification in 2022.

NAC acknowledges the underlying deficiencies as explained above; however, we are concerned with certain wording used in the Apparent Violation A and the accompanying Inspection Report (section 1.5.2).

Specifically, the Apparent Violation and Inspection Report use a broad statement that From September 2007 through March 2023, [NAC] failed to establish adequate design control measures

. The actual condition of the violation is an error in a single calculation that was propagated twice by reuse once in 2019 and once in 2020. Our concern is the NRCs description of Apparent Violation A could be read to mean that NAC failed to establish adequate design control from 2007 to 2023. This characterization is overly broad given that the 2007 calculational error was isolated and was not susceptible to being detected by routine Quality Assurance activities, although as NAC acknowledges it was repeated more than once. The NRCs statement, as written, extrapolates and implies incorrectly that an error in 2007 in a single calculation is indicative of a continuous systemic failure of NACs design control program since 2007 (i.e., suggesting a potential for multiple different kinds of calculational errors of a continuing nature).

NAC believes that, given the original 2007 calculational error, the Apparent Violation A statement is not supported by the facts. We are concerned a literal reading of the statement does not convey the NRCs intention and could be misleading to or misinterpreted by stakeholders, which would be extremely adverse to NACs noteworthy reputation. NAC has a robust design control program, as evidenced by repeated NRC and customer inspections with no recognized finding of failure to Page 8 of 19

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establish design control over the period identified. We understand and can appreciate the NRC staff members acknowledged that they did not intend to imply that NAC has a long-standing design control deficiency, and that the statement should not be read in isolation. However, overall, we believe the public and stakeholder interest is best served if statements that could be misleading and misinterpreted are revised and corrected, and we respectfully request that the NRC staff consider clarifying this statement in Apparent Violation A and the Inspection Report (at section 1.5.2) in making a final determination with respect to the Apparent Violations.

Apparent Violation B (as stated in Reference 1):

The 10 CFR 72.242(d), Record Keeping and Reports requires, in part, that each certificate holder shall submit a written report to the NRC within 30 days of discovery of a design or fabrication deficiency, for any spent fuel storage cask which has been delivered to a licensee, when the design or fabrication deficiency affects the ability of structures, systems, and components important to safety to perform their intended safety function.

Contrary to the above, from March 29, 2022, to March 10, 2023, NAC failed to submit a written report to the NRC within 30 days of discovery of a design or fabrication deficiency, for any spent fuel storage cask which has been delivered to a licensee, when the design or fabrication deficiency affects the ability of structures, systems, and components important to safety to perform their intended safety function. Specifically, NAC failed to submit a written report to the NRC within 30 days of discovery of a design error in a fuel rod structural calculation for normal and accident conditions that exceeded design bases limits; this design error impacted the NAC-UMS and MAGNASTOR storage systems which had been delivered to general licensees (i.e., Palo Verde, McGuire, Catawba, Zion, Kewaunee, and Three Mile Island). NAC discovered the design deficiency in calculation 71160-2025 on March 29, 2022, which adversely impacted the licensees computation for bending stresses on fuel rod cladding (i.e., negative margins). Eventually, NAC submitted the required report to the NRC on March 10, 2023, updated the report on March 28, 2023, (Agencywide Documents Access and Management System Accession No. ML23069A215 and ML23087A062), this was approximately 11 months after NAC identified the issue.

(1) Reason for the Apparent Violation:

NAC personnel failed to adequately evaluate the potential safety significance of the calculational error (see CAR 23-01 information above) and escalate the issue within the NAC QA Program.

Specifically, the personnel involved failed to follow NAC QA Manual Section 16.0, NAC Program procedures, including QP 16-1, Corrective Action Reports, and QP 16-2, Potential Significant Deficiencies and Defects and Regulatory Reporting, requiring in part that personnel report significant issues to the Vice President, Quality. Instead, the NAC personnel utilized NACs Self-Identification Report (SIR) process specified in NACs Standard Practice SP-116, Self-Identification Report, which was subsequently determined via root cause evaluation to have weaknesses that contributed to the lack of visibility to the SIR, and the SIR languished without timely evaluation of the safety significance and formal reporting in NACs QA Program. Reliance on the SIR process may have contributed to some personnel believing that the issue they identified was properly evaluated and considered for reporting despite that it effectively fell into an inactive status and was not properly processed, reviewed, and escalated.

The root cause investigation determined that NAC personnel failed to adhere to the requirements of the NAC QA Program for notifying / escalating an identified noncompliance in a timely manner due to two contributing factors:

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1) Training/education to the NAC Quality Assurance Manual, Quality Procedures, and Standard Practices related to reporting of deficiencies was weak. Personnel interviewed were generally aware of the commitments, responsibilities, and timeliness for identifying and reporting deficiencies and non-compliances, but not the process as a whole. Personnel identified that guidance on reporting issues is found in the QA Manual and procedures.

However, personnel interviewed were unsure of specifics such as which procedure provided guidance or the difference in reporting issues under 10 CFR Part 21 and 10 CFR 72.48.

There was a general lack of understanding of an individual's reporting responsibility once they learn of a possible defect or failure to comply.

2) NACs Standard Practice SP-116, Self-Identification Report, was inadequate for the intended purpose. It contained some instances of ambiguous language relative to documenting and identifying errors or deficiencies. Additionally, SP-116 lacked defined timelines/durations for review and actions within the self-identifying process and no method for follow-up and tracking to closure. Self-Identification Reports also had limited visibility to NAC management until NAC QA was notified after a safety significance determination.

(2) Corrective Steps Taken and Results Achieved:

NAC initiated Corrective Action Report (CAR) 23-02, dated April 4, 2023, to address the identified issue. The CAR required 1) an extent of condition investigation, 2) a root cause investigation and determination, and 3) implementation of corrective actions to prevent recurrence. In response to the CAR:

1) NAC performed an extent of condition investigation, which was completed on April 3, 2023. This extent of condition review was initiated on March 3, 2023, as part of NACs recognition of its delayed reporting. This review resulted in the issuance of NAC Finding Report FR 23-006, which documented NACs findings with respect to the SP-116 Self-Identification Report process, and was the impetus to escalate the FR 23-006 to CAR 23-02.

2) NAC performed and issued a Root Cause Analysis Report for CAR 23-02 on May 3, 2023. The root and contributing causes are noted above in item (1) Reason for the Apparent Violation.

3) NAC performed the following corrective actions to prevent recurrence of the delays in reporting to NRC.

1) The Self Identification Report process was implemented and released into NACs workflow system on October 13, 2023, to provide appropriate visibility, automatic routing, timely processing, and easy status awareness of SIRs. Over the past 1.5 years, NAC has implemented a secure electronic workflow system utilizing Microsoft PowerApps. The electronic system provides automatic email notification to the responsible parties of necessary review and approval for proposals, purchase requisitions, drawings, customer documentation, and corrective action documents (CARs, FRs, and Nonconformance Reports (NCRs)). NAC has added the self-identification process to the workflow system.

All SIRs must be entered into the workflow. The Business Unit Vice President and the Vice President of Quality are alerted for a review within a specified time.

The revised procedure (and workflow) provides each reviewer with the authority to elevate the issue to the appropriate corrective action category (CAR, NCR, FR),

as necessary.

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2) A revision to SP-116 was issued on October 12, 2023, to address the issues noted in the RCA. SP-116 has been revised to clarify the applicability and purpose of the self-identification process, including ownership. The revision also better defines the processing requirements and tracking of SIRs in the workflow system.

Including SIRs in the workflow system ensures SIRs maintain visibility company-wide and are processed in accordance with SP-116 timelines.

3) Training of personnel was completed by October 12, 2023. Training of all appropriate personnel to the revised SP-116 to re-emphasize NACs commitment for timely deficiency or defect reporting was accomplished. This training provided a demonstration of how SIRs will move through the workflow system.

Additionally, NACs President and CEO, Kent Cole, reinforced the corrective action process and the importance of entering issues into the corrective action program during a recent employee all-hands meeting. Training on the specifics of CAR 23-01, and the resulting CAR 23-02, as it relates to the workflow system, was also conducted with appropriate personnel.

(3) Corrective Steps That Will Be Taken:

Refresher training on the NAC Quality Assurance functions and responsibilities is scheduled for January 24, 2024. Training will include requirements of the NAC corrective action program including what issues are appropriate for each element of the corrective action program, i.e., classifying the issue/deficiency as a CAR, an NCR, or FR, etc. It will also include refresher training for 10 CFR Part 21 and other defect/deficiency reporting obligations and related NAC Quality Program requirements and procedures to supplement and reinforce training already completed as noted above. This training will be required for all NAC employees performing work under the NAC Quality Program.

(4) Date When Full Compliance Will Be Achieved:

Full compliance with the required actions resulting from CAR 23-02 is expected to be completed by January 31, 2024, after completion of the QA refresher training.

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ENCLOSURE B Reference 2

[NAC Letter to NRC, ED20230029, dated March 10, 2023]

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R-255979 ANAC Atlanta Corporate Headquarters 3930 East Jones Bridge Road, Suite 200 ii INTERNATIONAL Peachtree Corners, GA 30092 Phone: 770-447-1144 Fax: 770-44 7 1- 797 March 10, 2023 U.S. Nuclear Regulatory Commission 11555 Rockville Pike Rockville, MD 20852-2738 Attn: Document Control Desk Director, Division of Spent Fuel Management, Office of Nuclear Material Safety and Safeguards

Subject:

10 CFR 72.242 Reportable Licensing Basis Non-Mechanistic Tip-over Evaluation Deficiency for the NAC-UMS and MAGNASTOR Dry Cask Storage Systems Docket Numbers. 72-1015 and 72-1031 72.242(d)(J) -Abstract Overview NAC has internally identified a licensing basis deficiency for the NAC-UMS and MAGNASTOR dry cask storage systems. Specifically, a parameter used in the computation of bending stress in the finite element model used to structurally evaluate a fuel rod under the non-mechanistic tip-over accident condition was incorrectly specified resulting in the non-conservative calculation of stresses. More specifically, the calculation uses an ANSYS 2-D elastic beam element, BEAM3, to represent a single fuel rod. The BEAM3 element requires the input of various "real constants" that define physical properties of the element such as cross-sectional area, area moment of inertia, and height. The height real constant is used by ANSYS in the computation of bending stress in the element and is defined in ANSYS documentation to be the total height of the beam (i.e., rod outer diameter in this case). The input code in question incorrectly set the height real constant using a parameter equal to the outer radius of the rod, which is half of the correct value. Use of the correct value effectively doubles the computed bending stress.

NAC has completed an impact to safety evaluation and determined there is no Impact to Safety or concerns relative to the ability of the components to perform their intended safety function based on the error identified. The calculational error is specific to the non-mechanistic tip-over analysis. Both the MAGNASTOR FSAR and UMS FSAR provide evaluations which determined the loaded systems on the ISFSI pad do not tip-over within licensed conditions. Additionally, the safety functions of the VCC and TSC (e.g., passive heat rejection, environmental protection, TSC confinement, fuel assembly geometry control) are unaffected by the error in fuel rod modeling.

ED2821882'J D .,Zo,t3 COC\

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U.S. Nuclear Regulatory Commission March I 0, 2023 Page 2 This condition is repo1iable since the deficiency when corrected results in the non-conservative calculation offuel rod bending stresses exceeding the licensing basis limits for the NAC-UMS and MAGNASTOR. However, NAC has determined there is no safety consequence.

NAC's other dry cask storage system, which is the NAC-MPC system, was determined to not have been affected by this issue.

72.247(c/J(2)

Description:

Fuel rod side drop analyses are presented in UMS FSAR Sections 11.2.16. l (PWR) and 11.2.16.2 (BWR) and MAGNASTOR FSAR Section 3.8.4 as bounding evaluations for the lateral accelerations experienced by the fuel during a non-mechanistic tip-over event. The 60g uniform lateral acceleration applied in these evaluations significantly bounded the maximum accelerations reported for the tip-over event of 33.4g and 26.6g at the top of the basket for UMS and MAGNASTOR, respectively. As noted above, correction of the input error doubled the bending stress and resulted in the storage tip-over evaluation margins being negative.

The calculational error presented is specific to the non-mechanistic tip-over analysis. Both the UMS and MAGNASTOR FSAR provide evaluations which determine the loaded systems on the ISFSI pad do not tip-over within licensed conditions. It is also important to note that the analyses performed are on fuel assemblies with up to 60" of unsuppo1ied fuel rod length (simulating a missing fuel grid). This analysis provides the basis for treating assemblies with partially damaged grid straps (corners missing, side damage, etc.) as undamaged and not requiring canning in damaged fuel cans. Because this missing fuel grid evaluation met the yield stress acceptance criteria, undamaged fuel is considered bounded.

Updated fuel rod structural analyses associated with the non-mechanistic tip-over, are in process. The updated analyses apply a revised method of evaluation (MOE) utilizing an acceleration load and a dynamic load factor (DLF) determination developed from the LS-DYNA cask tip-over time history.

These updated analyses will be provided in amendments to the affected system FSAR's. Preliminary results of the updated analyses demonstrate stress in the fuel rod cladding remains below allowable yield stress under the non-mechanistic tip-over conditions and supports the existing criteria of less than or equal to 60" of unsupported rod length i.e., loss of grid strap suppoti, allowing fuel assemblies with grid damage to not require placement into damaged fuel cans.

72.242(d)(2)(i) Dare/Time o(Discoverv:

On March 29, 2022, an error was discovered during checking of a new calculation (423-2020 Rev. 0) being prepared for the fatigue and side drop evaluation for HBU fuel rods in an NAC-STC transportation cask. This calculation used the model (ANSYS input) from a preceding side drop analysis (71160-2139 Rev. 0, circa 12/2020) which itself references preceding ANSYS input files from calculation 71160-2025 Rev. 1, circa 8/2007.

Engineering then issued Self-Identification Report (SIR)22-002, which identified a parameter used in the computation of bending stress in the finite element model for the fuel rod 60g Side Drop analysis was incorrectly specified resulting in the non-conservative calculation of stresses.

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U.S. Nuclear Regulatory Commission March 10, 2023 Page 3 The calculation error was documented per Standard Practice (SP) SP- I 16 (not patt of the formal QA Program) as Self-Identification Report (SIR) No.22-002, Dated 03/29/2022, and remained in Engineering for resolution prior to formal QA notification on 02/28/2023. The SIR was immediately escalated to CAR 23-0 I. This process weakness is identified in Finding Report (FR 23-006).

72.242(cl)(2)(ii) ause:

The error has been traced back to calculation 71160-2025 Rev. 1 approved in 2007 and is the origin ofthe error. The error was then propagated by incorporating the incorrect ANSYS model into subsequent analyses.

72.242(d){2)0ii) Failure Mode:

The potential failure mode would be the possibility ofa beyond-design-basis event resulting in storage cask tip-over, which could cause fuel rod yielding in fuel assemblies with pa1tially damaged fuel grids creating an unanalyzed condition.

72.242(d)(2)0v) Svstems/Secondarv Fune/ions:

The safety functions of the VCC and TSC (e.g., passive heat rejection, environmental protection, TSC confinement, fuel assembly geometry control) are unaffected by the error in fuel rod modeling. There were no other NAC-UMS and MAGNASTOR systems or secondary functions affected by this deficiency.

The deficiency is specific to the fuel rod cladding evaluated for the hypothetical cask tip-over event that were calculated in the licensing basis.

72.242(d)(2)(v) Method o[Discoverv:

The error was discovered during checking of a new calculation (423-2020 Rev. 0) being prepared for the fatigue and side drop evaluation for HBU fuel rods in an NAC-STC transportation cask.

72.2.:f.2(d)(2)(vi) Model Number o[Each omponent:

There is no generic manufacturer or model number associated with the NAC-UMS or MAGNASTOR systems. Serial numbers for each of the affected TSC can be found below in response to 72.242(d)(2)(vii) 72.2-12(d)(2)(1 ii) Model/Serial Numbers CJ(Affected Casks:

The NAC-UMS dry cask storage system is affected and reportable under 10 CFR 72.242(d). The error discussed above in Section 72.242(d)(2) was introduced in Amendment 5 which permitted the storage of high burnup PWR fuel (up to 60 GWd/MTU assembly average burnup). The deficiency described, herein, is generic to the NAC-UMS FSAR PWR tip-over evaluations. Those sites that have TSCs loaded to ED20230029 Page 15 of 19

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U.S. Nuclear Regulatory Commission March I 0, 2023 Page 4 Amendment 5 or after are affected. This includes sites that have recertified their systems to Amendment 5 or any amendment thereafter. The following casks are affected:

Those sites that have TSCs loaded prior to Amendment 4 or have not rece1iified their systems to later amendments are not affected by this error and are thus not reportable under 10 CFR 72.242(d).

NAC-UMS dry cask storage systems loaded at Duke Energy (McGuire or Catawba) were loaded under Amendments 4 and have not been recertified to a later amendment, and therefore are not impacted. This encompasses the following casks:

• Duke Enenry (McGuire) - UM -T C-418-001 thru -024 and 049 thru -052

• Duke Energy (Catawba) - UMS-TSC-418-025 thru -048 NAC-UMS dry cask storage systems loaded at Maine Yankee are also not affected and also not reportable under 10 CFR 72.242(d) because they have a site-specific tip-over evaluation which demonstrates the Maine Yankee fuel rods are structurally adequate for the evaluated 60g side drop condition (FSAR Section 11.2.15.1.6).

• Maine Yankee - UMS-TSC-790-001 thru -060 The NAC-UMS cask model is not currently being manufactured for any Independent Spent Fuel Storage Installations (ISFSis) in the United States (U.S.) nor are there any casks currently available to be loaded.

The MAGNASTOR dry cask storage system is affected and reportable under IO CFR 72.242(d). The deficiency described, herein, is generic to the MAGNASTOR FSAR PWR tip-over evaluations and is associated with the following casks:

• Duke Energy (McGuire) - MAG-TSC-418-055 thru -068. -071. -072. -073. -075. -076. -098. -

099, -100 thru -114

• Duke Energy (Catawba) -MAG-TSC-418-069. -070. -074. -077 thru -097. -119. -121. -123. -124.

-126. -128

• Zion - MAG-TSC-215555-00 I thru -030. MAG-TSCDF-215555-00 I lhru -30 and MAG-TSC-418-053 and -054

• Kewaunee - MAG-TSC-30026-089-0 I thru -12 and MAG-TSCDF-30026-184-13 thru -24

• Three Mile Island Unit 1 (TMl-1)- MAG-TSC-30076-280-001 thru -023 and MAG-TSCDF-30076-265-00 I thru -023

• Arizona Public Service {A PS-Palo Verde)- MAG-TSC-30032-280 -172 thru -174 and MAG-T CDF-30032-265-153 thru-166. -168. -170. -171 The MAGNASTOR cask model is currently being manufactured for ISFSls in the U.S. at Duke McGuire, Duke Catawba, and Palo Verde, and there are casks currently available to be loaded Duke McGuire, Duke Catawba and Palo Verde. The following cask have been delivered and are available to be loaded:

• Duke Energy (McGuire)- MAG-TSC-418-115 thru -118 ED20230029 Page 16 of 19

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U.S. Nuclear Regulatory Commission March I 0, 2023 Page 5

• Arizona Public Service (A PS-Palo Verde)- MAG-TSC-30032-280-175 and MAG-TSCDF-30032-265-167. -169 72.242(d)(2)(viii) List oflicensees Affected:

With regards to the NAC-UMS system, the affected users are:

• APS - Palo Verde None of these sites are currently loading or plan to load additional NAC-UMS systems.

With regards to the MAGNASTOR system, the affected users are:

• Duke - McGuire,

• Duke - Catawba

• APS - Palo Verde

• ZionSolutions - Zion

• KewauneeSolutions - Kewaunee

• Constellation - Three Mile Island Unit 1 (TMl-1)

Duke McGuire, Duke Catawba and APS Palo Verde are currently loading or plan to load additional MAGNASTOR systems.

72.242(d)(3) Assessment ofSa[etv Consequences and Implications NAC has completed an impact to safety evaluation and determined there is no Impact to Safety or concerns relative to the ability of the components to perform their intended safety function based on the error identified. The calculational error is specific to the non-mechanistic tip-over analysis. Both the MAGNASTOR FSAR and UMS FSAR provide evaluations which determined the loaded systems on the ISFSI pad do not tip-over within licensed conditions. The safety functions of the VCC and TSC (e.g.,

passive heat rejection, environmental protection, TSC confinement, fuel assembly geometry control) are unaffected by the error in fuel rod modeling.

Additionally, NAC has reviewed this issue against the rep011ing requirements of 10 CFR Part 21 and has determined it is not formally reportable under that regulation since there are no substantial safety hazards associated with this issue. However, NAC is always engaged with our system users and has already notified the user group of the current situation.

There are no operability implications for those NAC-UMS or MAGNASTOR casks currently in service.

Current NRC guidance on operability determinations allows the use of alternate methods of evaluations to those currently licensed (e.g., Inspection Manual Chapter (IMC) 0326, Section 08.04). NAC considers this analytical approach consistent with the NRC guidance on implementing operability determinations.

NAC will take final corrective action on this issue by obtaining an NRC amendment to the NAC-UMS and MAGNASTOR systems.

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U.S. Nuclear Regulatory Commission March I 0, 2023 Page 6 72.2.:/2(d)(4) Correc1ive Ac/ions This issue is documented and being tracked under NAC's Quality Assurance Program (QAP) via CAR 23-0 I. The CAR contains the following corrective actions:

• Perform extent of condition review;

• Determine safety significance, evaluate the ability of the components to perform their intended safety functions, and determine regulatory reportability;

• Determine impacted customer facilities and identification of components delivered; and determine customer notification protocol;

• Perform root cause analysis RCA; and

• Identify and implement corrective actions to prevent recurrence.

As noted above, NAC will bring the systems into compliance with the CoC by obtaining an NRC CoC amendment to the NAC-UMS and MAGNASTOR systems.

The RCA will also include assessment and appropriate corrective and preventative actions for the NAC SIR process and the apparent weakness in timely follow-through and tracking of SIR 22-002.

NAC's extent of condition review will also consider transportation casks, and we wil I address any related 1 0CFR71 reportability under separate communication.

72.242(d)(5) Previous Similar Evem.

• NAC identified a similar event relative to an error in modeling the fuel rod assembly effective thermal properties in which the incorrect fuel pellet diameter was used in calculating peak clad temperatures in 2021 affecting the NAC-UMS system.

72.2./2(dJ(6) Contact Mr. Heath Baldner Director, Licensing Phone: 678-328-1252 Email: hbaldner@nacintl.com ED20230029 Page 18 of 19

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U.S. Nuclear Regulatory Commission March 10, 2023 Page 7 Conclusion NAC is committed to nuclear safety and keeping the NRC informed on such matters. This reportable issue pertains to an error for calculating the bending stresses in fuel rods during a non-mechanistic tip over event. NAC has provided pertinent information relative to NAC-UMS and MAGNASTOR to keep the NRC fully informed on the scope of this error. NAC is continuing to work through the issue via NAC's QAP and CAR 23-01. Should the Commission require further details regarding the condition described herein, please contact me.

Sincerely, Heath M. Ba Id n er Digitally signed by Heath M. Baldner Date: 2023.03.1 O 14:55:42 -05'00' Mr. Heath Baldner Director, Licensing Engineering cc. Shana Helton, Director, Division of Fuel Management Jacob Zimmerman, Deputy Director, Division of Fuel Management Carrie Safford - Deputy Director, Division of Fuel Management Yoira Diaz Sanabria, Branch Chief, Storage and Transportation Licensing Branch Nishka Devaser, Project Manager, Division of Fuel Management, Licensing Branch ED20230029 Page 19 of 19

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