ML20280A743
| ML20280A743 | |
| Person / Time | |
|---|---|
| Site: | 07201032 |
| Issue date: | 11/06/2020 |
| From: | Boyce T, Garcia-Santos N, Patrick Koch, John Mckirgan, David Tarantino Division of Fuel Management |
| To: | O'Mullane C Holtec |
| NGSantos NMSS/DFM/FFL 301.415.6999 | |
| Shared Package | |
| ML20280A740 | List: |
| References | |
| EPID L-2019-LLA-0231 | |
| Download: ML20280A743 (6) | |
Text
Final Staggered Request for Additional Information HOLTEC International LLC Docket No. 72-1032 Certificate of Compliance No. 1032 Model No. HI-STORM FW Amendment No. 6 By letter dated October 2, 2019 [Agencywide Documents Access and Management System (ADAMS) Package Accession No. ML19282C357], and as supplemented on June 30, 2020 (ADAMS Package Accession No. ML20182A860), Holtec International (the applicant) requested to amend Certificate of Compliance (CoC) No. 1032, Model No. HI-STORM FW Storage System.
This request for additional information (RAI) identifies information needed by the U.S. Nuclear Regulatory Commission (NRC) staff (the staff) in connection with its review of the application.
Each individual RAI describes information needed by the staff to complete its review of the application and to determine whether the applicant has demonstrated compliance with the regulatory requirements of Title 10 of the Code of Federal Regulations (10 CFR) Part 72.
STRUCTURAL EVALUATION RAI-3-1 Provide the following information:
- a. an evaluation of a drop accident in all credible bounding orientations (e.g., a side drop or corner drop orientation) for assessing the handling accident conditions for the HI-STORM FW cask and the HI-TRAC VW transfer cask, and a justification of why the analyzed orientations are bounding; or
- b. a justification for how other drop orientations are bounded by the existing end drop analysis.
As discussed in NUREG-2215, Standard Review Plan for Spent Fuel Dry Storage Systems and Facilities, the review of a safety analysis report (SAR) should ensure that an applicant evaluated all credible potential orientations of the cask during cask transfer and handling drops. It is not clear to the staff how the vertical end drop analyzed in Holtec Report HI-2200647, Analysis of the Postulated Drop and Missile Impact Events for the Loaded HI-STORM FW, Version E, Cask and the Loaded HI-TRAC VW System, considers all credible potential orientations of the cask for a handling accident.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236 (b), (c), and (l).
RAI-3-2 Provide an evaluation of the fuel basket, including deflections, to determine if the fuel basket maintains the spent nuclear fuel in a subcritical arrangement under handling accident conditions (considering all credible bounding orientations), and include such evaluation in the design criteria for the handling accident condition.
Enclosure
2 The structural evaluation of the handling accident condition detailed in Holtec Report HI-2200647 provides a structural analysis of the plastic strains of the fuel basket.
However, the evaluation in Holtec Report HI-2200647 does not consider all the design criteria defined for the spent fuel basket defined in Chapter 2 of the SAR (e.g., the maximum deflection defined in the structural design criteria for the fuel basket listed in Table 2.2.11 of the SAR). Additionally, the acceptance criteria for the handling accident condition described in Section 2.2.3(a) of the SAR does not include any criteria for the fuel basket or subcritical arrangement of the spent nuclear fuel.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(b) and (c).
RAI-3-3 Provide the following information:
- a. mechanical property data based on physical testing for the materials evaluated using a strain-based approach for the drop accident conditions presented in Holtec Report HI-2200647;
- b. failure strains and material flow curves based on this physical testing that consider strain-rate effects, uniform elongation, and triaxiality effects for use in the finite element analysis and structural evaluation of the drop accident conditions presented in Holtec Report HI-2200647; and
- c. an updated finite element analysis and structural evaluation of the drop accident conditions presented in Holtec Report HI-2200647 using failure strains and material flow curves based on mechanical property data obtained from physical testing.
Holtec Report HI-2200647 includes a description of the structural evaluation of HI-STORM FW components from the drop accident conditions. This evaluation used a strain-based methodology with strain-based acceptance criteria to determine the structural integrity of important to safety (ITS) components subjected to an 11-inch drop. The applicant calculated true-stress-true-strain data in Appendix B to Holtec Report HI-2200647 and used this data in the analysis of the drop accident for the following materials:
- Metamic,
- Alloy X,
- SA350-LF2,
- SA193-B7,
- SA53,
- SA516-70,
- 304 type stainless steel,
- SA350-LF3,
- SB-637,
- SA-336 f 11,
- SA-240 304 type stainless steel, and
- SA106 grade C.
3 The methodology used in Appendix B to Holtec Report HI-2200647 to compute material flow curves for the finite element structural analysis and strain-based evaluations follows the Holtec Position Paper DS-307, Construction of True-Stress-True-Strain Curves for LS-DYNA Simulations. The staff notes that the use of the methodology outlined in this position paper has previously been found inadequate to provide material data for strain-based evaluations, in particular for an evaluation of the ATB 1T transportation package. Specifically, constants used to develop material flow curves have been determined analytically (e.g., constants K and n) without the support of material testing. As discussed in the summary of the November 13, 2018, meeting with Holtec International (ADAMS Accession No. ML18331A184), the staffs position is that these constants should be based on mean test values obtained from material testing. In addition, the applicant needs to supply material flow curves that consider strain-rate effects, uniform elongation, and triaxiality effects if the material is challenged beyond the uniform elongation limit.
The staff notes that strain-based acceptance criteria are specified in the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Non-mandatory Appendices EE and FF. The criteria specified by the applicant is not based on an industry code or standard, but rather a reference that was used in the development of Non-mandatory Appendices EE and FF. In addition, Non-mandatory Appendices EE and FF provide some of the physical data that the applicant needs to provide for 304 type stainless steel.
As the mechanical property data is essential to the validity of the structural analysis of the drop accident condition, the staff requests that the material models used in the LS-DYNA simulations described in Holtec Report HI-2200647 be based on sufficient physical testing and any results be updated.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(l).
RAI-3-4 Clarify the discrepancy between the depictions of the anchorage for the HI-STORM FW, Version E, in Drawing No. 11695, HI-STORM FW Version E Anchored Cask, and Holtec Report HI-2188720, Structural Calculation Package for HI-STORM FW Anchor System and revise the SAR, drawings, and calculations as necessary.
The structural evaluation of the anchored HI-STORM FW system relies on finite element analysis and hand calculations presented in Holtec Report HI-2188720.
However, the anchorage configuration evaluated in Holtec Report HI-2188720 differs from the anchorage configuration depicted in the drawings and SAR description of the HI-STORM FW anchorage. Specifically, the anchorage evaluated in Holtec Report HI-2188720 is comprised of several anchorage components that are not depicted in the SAR Drawings, such as an embedment plate, compression block, and anchor rod. As this anchorage hardware is designated as ITS and relied on to resist accident loads (e.g., loads associated with the earthquake and tornado accident conditions), the staff requests clarification of the components and configuration of the anchorage hardware and that the SAR, drawings, and calculations be updated as necessary.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(b) and (l).
4 RAI-3-5 Provide structural qualification for the components and welds comprising the anchorage housing and the welds connecting the radially extended baseplate to the cask for the HI-STORM FW, Version E, anchored variant.
Drawing No. 11695 depicts the components of the anchored HI-STORM FW cask.
The drawing includes Item No. 2 described as Plate, Anchor Housing and is categorized as ITS; Item No. 5 described as Plate, Radial Bottom and is categorized as ITS; and three welds connecting these components and the cask baseplate to the body of the cask. It appears that these components and welds are a part of the structural load path resisting certain loads (e.g., loads associated with the earthquake and tornado accident conditions) on the cask and, therefore, require structural evaluation. However, the structural analyses for the earthquake and tornado accident conditions detailed in Holtec Report HI-2188720 and Holtec Report HI-2200647, respectively, do not appear to contain structural evaluations of these components or welds.
This information is needed to determine compliance with regulatory requirements in 10 CFR 72.236(b) and (l).
RAI-3-6 Specify the preload or pre-tension required of the anchor studs for the HI-STORM FW Version E anchored variant.
As discussed throughout Holtec Report HI-2188720, the structural evaluation of the anchored HI-STORM FW system relies on the friction contact between the top surface of the independent spent fuel storage installation (ISFSI) pad embedded plate and the bottom surface of the baseplate of the anchored cask. An important step of the seismic evaluation described in HI-2188720 is determining that the friction force is greater than the seismic lateral force, and thus, the seismic lateral force on the cask does not impart shear loading directly on the anchorage in the ISFSI pad.
The system maintains this friction contact partially by the preload of the anchor studs. As the preloading of the anchor studs is necessary to validate the seismic analysis, the staff requests that the preload of the anchor studs be specified and that the SAR be updated as needed.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(b).
RAI-3-7 Provide an evaluation of the effects of differential thermal expansion and thermal fatigue on the anchorage components and required preload of anchor studs for the HI-STORM FW system.
Holtec Report HI-2188720 presents the structural evaluation of the components of the HI-STORM FW anchorage and the consideration of the effects of the preload in the seismic analysis. The analysis does not contain a discussion or evaluation of the differential thermal expansion of the anchorage components. The staff recognizes the potential for changing temperatures of the anchorage components to result in differential expansion. This differential thermal expansion could affect the stresses of the anchorage components evaluated in the report and the necessary preload evaluated in the report. The significance of the preload of the anchor studs is discussed in RAI-3-5. As the stresses and anchor stud preload evaluated in the
5 report are necessary for ensuring structural integrity of the anchorage, the staff requests that the applicant provides an evaluation of the effects of differential thermal expansion on the anchorage components and the preload of the anchor studs.
Holtec Report HI-2188720 also presents an evaluation of the effects of mechanical fatigue from the earthquake accident condition on the HI-STORM FW anchorage.
The staff recognizes the potential for changing temperatures to result in cyclic thermal expansion and thermal fatigue of the anchorage components. As the analysis of fatigue in the anchorage is necessary for ensuring structural integrity, the staff requests that an evaluation of thermal fatigue be provided.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(b) and (l).
RAI-3-8 Demonstrate that the HI-STORM FW design will maintain a safe configuration under the following conditions:
- a. the earthquake accident conditions for the proposed anchored HI-STORM FW configuration, and
- b. the drop accident conditions for the proposed changed to the technical specification to allow non-single failure proof lifting equipment.
As part of your response, provide the input and output files of the finite element analysis models used to perform structural evaluations of the drop and earthquake accident conditions for the HI-STORM FW storage system.
The applicant is seeking approval of an anchored configuration for the HI-STORM FW for use in high seismic regions and adding to the technical specifications the option to use non-single failure proof lifting equipment when handling the storage system up to a specified maximum height, among a few other changes. To support these changes, the applicant provided Holtec Report Nos. HI-2188720 and HI-2200647 to describe the finite element analyses and structural evaluations for the anchored HI-STORM FW earthquake accident condition and the HI-STORM FW drop accident condition, respectively. The evaluations presented in these reports rely on analyses from finite element modeling to determine the adequacy of certain ITS components to maintain confinement integrity and perform a shielding function.
Given that the models may be complex (i.e., highly non-linear), the staff needs to verify the modeling conditions of the ITS confinement and shielding components such as:
- material model assignment,
- material density,
- overall model weight,
- post yield material behavior,
- element erosion,
- dimensions,
- element type and function,
- overall model behavior (animation files),
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- hour glassing effects,
- lock-up effects,
- boundary conditions,
- contacts,
- velocity assignment,
- processor output specification,
- stress distribution, and
- effective plastic strain distribution, among others.
The staff needs the input and output files to efficiently verify the validity and accuracy of the finite element models used by the applicant to conclude that the cask maintains the integrity of the confinement boundary and its shielding function under earthquake and drop accident conditions.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(d) and (l).
MATERIALS EVALUATION RAI-4-1 Clarify the standards used for the construction of the Independent Spent Fuel Storage Installation (ISFSI) pad.
The staff wanted to confirm the standards applicable to the design of the concrete structures and their ability to withstand outdoor conditions. The applicant noted the following:
- 1. Section 2 of the application includes information regarding the applicability of the code.
- 2. ACI 318-05 is used for the strength analysis of the ISFSI pad.
- 3. the analysis considers concrete behavior due to outdoor exposure.
- 4. the maximum concrete compression is assumed to be 7,000 psi.
For the pad, the assumptions and analyses allow to construct the pad in any place in the U.S.
The staff pointed out that the question was mainly about the fabrication requirements of the storage system. The staff noted that the safety analysis report does not contain specific requirements for the pad to be designed and constructed in accordance with ACI durability requirements to account for outdoor exposures. The applicant noted that the applicable code was ACI-318 for fabrication and that it intended to follow the durability requirements in that code. The applicant will be adding information in the safety analysis report (SAR) to clarify the applicable code for outdoor durability considerations.
This information is needed to determine compliance with the regulatory requirements in 10 CFR 72.236(b).