ML23227A250

Attachment 1: Summary of Clarification Call Action Items (non-proprietary)

ML23227A250
Person / Time
Site:	07201032
Issue date:	08/15/2023
From:	Holtec
To:	Office of Nuclear Material Safety and Safeguards
Shared Package
ML23227A248	List: ML23227A249 ML23227A250 ML23227A252
References
5018108, CAC 001028, EPID L-2021-LLA-0053
Download: ML23227A250 (1)

Text

Holtec Responses to Action Items listed in Meeting Minutes [1] on HI-STORM FW Amendment 7 RAI 3-10 Response Clarification Call

Docket No.72-1032 Holtec International HI-STORM FW Multipurpose Canister Storage System Certificate of Compliance No. 1032 Amendment No. 7

Action 1

Holtec will provide supplemental information on the analysis at higher temperature that bounds the fuel basket, show its correlation to ultimate strength, and the safety margin using 90%

ultimate strength.

Holtec Response:

Holtec has revised Position Paper DS-331 to include additional results for Metamic-HT fuel baskets at higher temperatures (up to 400°C) that bound the thermal analysis results in Chapter 4 of the HI-STORM FW FSAR. The maximum stress in the Metamic-HT basket panels remains below 90% of the materials ultimate strength for all analyzed temperatures (from 275°C to 400°C). A copy of Position Paper DS-331 Rev. 3 is attached.

Action 2

Holtec will provide additional information related to Metamic-HT material property.

Holtec Response:

Holtecs Metamic-HT was first used in the HI-STAR 180 system. A Metamic-HT Qualification Sourcebook [2] was created to support the approval of this material for use in the HI-STAR 180 system. The Summary of Changes for Revision 1 (June 2009) and Revision 2 (August 2009) of the Metamic-HT Sourcebook states that the revisions were made as the result of RAIs and technical interactions with the NRC Staff under Docket No. 71-9325 (HI-STAR 180).

Per the Metamic-HT Sourcebook, To determine its suitability in dry storage applications, Metamic-HTs properties listed in Table 1.2 have been quantified by a testing program that emulates the qualification regimen of an ASTM material. Using the test data, the minimum values of the mechanical and thermo-physical properties are determined in the test program.

Values of properties that are equal to or less than the minimum values are set down as Minimum Guaranteed Values (MGV). Holtecs responses to the HI-STAR 180 Initial Application RAIs [3] explain that the Minimum Guaranteed Value (MGV) is required to be less than the Minimum Measured Value of the property from the entire batch of data in the database. For structural qualification of fuel basket Holtec deploys an approach that is more conservative than the ASME Code. The approach is based on limiting the maximum panel displacement under design basis events. This approach is evaluated in Holtec Position Paper DS-331. Further information can be found in Holtecs responses to the Materials RAIs [3]

Page 1 of 3 The NRCs SER for 71-9325 CoC Revision 0 [4] describes the basis for approval of Metamic-HT for use in the HI-STAR 180 system.

From 180 SER Section 2.9: The applicant provided data to quantify the performance and characteristics of Metamic-HT in a manner somewhat emulating that of an ASTM/ASME material, but with several deviations from normal ASME Code practice (which the staff uses as a benchmark). One deviation is the establishment of the "minimum guaranteed value" (MGV) for various properties. The MGV values adopted by the applicant differ from the "stress allowable" used by the ASME Code. The Code "stress allowable" is directly used for stress-based design calculations. The applicant's MGV data is primarily used as the Metamic-HT material production QA/QC acceptance criteria. Consequently, a direct comparison of "stress allowable" with MGV's is not valid.

Furthermore, The applicant provided Revision No.2 to the Qualification Sourcebook incorporating major changes largely prompted by the staff's review. In particular, additional coupons tested were added to the respective data tables to broaden the data base for all properties; the coupons data includes separate data sets of up to 30 coupons each for as-extruded as well as thermally aged and irradiated coupons at different temperatures; the use of the statistical approach (mean minus two sigma) has been discontinued in favor of a more conservative approach. Now, the MGV is required to be less than the "Minimum Measured Value" of the property from the entire batch of data in the database to eliminate concerns of data scatter and lot-to-Iot variability; design criteria for structural reliance of Metamic-HT in fuel basket applications have been added to the Sourcebook and a justification provided for the dimensionless maximum lateral deflection in fuel baskets utilizing Metamic-HT panels in lieu of ASME based code stress limits; the production sampling plan has been expanded to establish the link between in-production testing and the required level of reliability of the material's property;

Metamic-HT was eventually also approved for use in the HI-STORM FW system, where it was used in a dry storage system for the first time. The NRCs SER for 72-1032 Amendment 0 [5]

describes the basis for approval of Metamic-HT for use in the HI-STORM FW system in the Chapter 8 Materials Evaluation.

From FW SER Section 8.1: Since Metamic HT is a new structural material, a comprehensive test program was necessary to fully determine its physical properties and characteristics. The testing program emulated that typically employed to qualify an American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code structural material. Holtec provided extensive data from their testing program for staff review. The data and analyses were documented in the Holtec comprehensive proprietary report; Metamic HT Qualification Sourcebook. Since this document and data are proprietary, the staff summarizes the testing program and findings in lieu of excerpting detailed technical discussion from the applicants documents.

From FW SER Section 8.1.1: Using the guidance of ASME Section II, Appendix 5, Holtec determined mechanical properties (as listed previously) at room temperature and also at several temperatures ranging from minus 40 degrees C to 500 degrees C. The test data was analyzed using statistical methods and minimum, average, and mean values of the various properties were determined. Additionally, a design value for the various properties was established which is called the Minimum Guaranteed Value (MG V). The MGV is a numerical value (for any given

Page 2 of 3 property) which was chosen to be below the lowest measured value from the test data. The MGV is then demonstrated (guaranteed) to be exceeded for every manufactured lot of Metamic HT through lot testing. Any lot which fails to meet one (or more) MGV values is discarded. Lot testing sample size is controlled by a statistical sampling approach. If any lot of material fails to meet any one of the various MGVs, then an enhanced sampling plan is invoked for subsequent production lots.

The FW SER Section 8.1.10: Conclusions used the same language as was used in the HI-STAR 180 SER: The applicant has provided data to quantify the performance and characteristics of Metamic HT in a manner somewhat emulating that of an ASTM/ASME material, but with several deviations from normal ASME Code practice (the staff uses the ASME Code as a benchmark).

One deviation is the establishment of the MGV for various properties. The MGV values adopted by the applicant differ from the stress allowable used by the ASME Code. The Code stress allowable is directly used for stress-based design calculations. The applicants MGV data is primarily used as the Metamic HT material production QA/QC acceptance criteria.

The HI-STORM FW FSAR [6] lists the applicable Metamic-HT MGVs in Table 1.2.8a and the qualification tests for the material are discussed in Sections 10.1.3 and 10.1.6.2 and Tables 10.1.6 through 10.1.8. The enhanced sampling plan mentioned in the SER quote above is described in the notes to Table 10.1.7. All Metamic-HT used in all HI-STORM FW canisters, both past and present, has been subjected to these tests to provide additional assurance that the properties continue to meet the required values.

Metamic-HT was never presented as an ASME material. However, the data presented in the Metamic-HT Sourcebook, unchanged from previous NRC reviews, and the continued use of approved qualification testing provided, and should continue to provide, the same confidence level for the use of Metamic-HT in Holtec equipment as exists for any ASME qualified material, and for all prior approvals of the HI-STORM FW.

References:

[1] Clarification Call with Holtec on HI-STORM FW Amendment 7 Request for Additional Information (RAI) 3-10 Conversation Record between Holtec and NRC associates dated August 3, 2023. ADAMS Accession No. ML23216A217.

[2] HI-2084122 Revision 14 (latest revision), Metamic-HT Qualification Sourcebook

[3] Transmittal of Response to Additional Information on HI-STAR 180 Transport Cask letter from T. Morin (Holtec) to P. Saverot (NRC) dated July 13, 2009. ADAMS Accession No. ML091970336.

[4] NRCs SER for HI-STORM 180 CoC No. 71-9325 Revision 0. ADAMS Accession No. ML092890297

[5] NRCs SER for HI-STORM FW CoC No. 72-1032 Amendment 0. ADAMS Accession No. ML111950325.

[6] HI-2114830, Final Safety Analysis Report for HI-STORM FW MPC Dry Storage System, Latest Revision

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