ML20077K624

License Amendment Request - Request for Additional Information

ML20077K624
Person / Time
Site:	Prairie Island
Issue date:	04/13/2020
From:	William Allen Storage and Transportation Licensing Branch
To:	Sharp S Northern States Power Company, Minnesota
Allen W
References
EPID L-2019-LLA-0169
Download: ML20077K624 (7)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 13, 2020 Mr. Scott Sharp, Site Vice President Prairie Island Nuclear Generating Company Northern States Power Company - Minnesota 1717 Wakonade Drive East Welch, Minnesota 55089-9642

SUBJECT:

PRAIRIE ISLAND LICENSE AMENDMENT REQUEST - REQUEST FOR ADDITIONAL INFORMATION (EPID NO. L-2019-LLA-0169)

Dear Mr. Sharp:

By letter dated July 26, 2019, Northern States Power Company submitted to the U.S. Nuclear Regulatory Commission (NRC) an amendment request to the Special Nuclear Materials (SNM) license number SNM-2506 for the Prairie Island Independent Spent Fuel Storage Installation.

The proposed amendment request seeks to increase the storage capacity of the Prairie Island Independent Spent Fuel Storage Installation and to approve the design of a new storage pad to be built at the existing facility.

NRC staff has determined that additional information is required to complete its technical review of your application. The request for additional information is identified in the enclosure to this letter anD was discussed with your staff in a conference call on April 7, 2020. We request that you provide the requested information by May 12, 2020. Inform us at your earliest convenience, but no later than May 5, 2020, if you are not able to provide the information by that date. If you are unable to provide a response by May 12, 2020, please propose a new submittal date with the reasons for the delay.

Please reference Docket No. 72-10 and EPID No. L-2019-LLA-0169 in future correspondence related to this licensing action. The staff is available to discuss these questions as well as your proposed responses. If you have any questions, please contact me at (301) 415-6877.

Sincerely, Digitally signed by William C.

Allen Chris Allen, Project Manager Storage and Transportation Licensing Branch Division of Spent Fuel Management Office of Nuclear Material Safety and Safeguards Docket No.: 72-10 EPID NO. L-2019-LLA-0169

Enclosure:

Request for Additional Information

ML20077K624 OFFICE: NMSS\DFM NMSS\DFM NMSS\DFM NAME: WAllen WWheatley JMcKirgan DATE: 4/1/20 4/2/20 4/10/20 Request for Additional Information Northern States Power Company Docket No. 72-10 Proposed Amendment to Special Nuclear Materials License No. SNM-2506 STRUCTURAL 2.1 In Section 3.2 Soil Liquefaction Analysis, of Enclosure 1 of the Prairie Island Independent Spent Fuel Storage Installation (ISFSI) license amendment request, the applicant discusses design inputs, acceptance criteria and conclusions related to the liquefaction analysis of the proposed pad. For the staff to ascertain that the current licensing basis is maintained, and that sufficient data is provided to make a safety finding, the following information needs to be included:

a. Provide the logs and locations of the Cone Penetrometer Testing (CPT) performed for the proposed ISFSI pad.

Insert S-1 of Enclosure 2 states that To support the ISFSI expansion, additional field investigations at the ISFSI site were made in July 2018. The field program consisted of performing four soundings (CPT-1 through CPT-4) located directly south of the eastern original pad as shown in Appendix 2C. The staff cannot determine from the submittal if appendix 2C was updated with the information.

b. Identify locations of potentially liquefiable soil pockets relative to the proposed ISFSI pad.

In Section 3.2.2 of the submittal, the applicant states that For the PI ISFSI project site, the screening determined that potentially liquefiable soil types were present and that they could become saturated at some future date. The staff cannot determine from the submittal the location and the depth of these liquefiable deposits in relation to the proposed ISFSI pad.

c. Provide the values of Cyclic Resistance Ratio (CRR) and Cyclic Stress Ratio (CSR) and/or Factors of Safety (FS) in graphical or tabular form for the depths of study as related to the proposed ISFSI pad. Also provide a calculation package or sample calculations describing the efforts made for this analysis. In Section 3.2.2 of the submittal, the applicant states the ratio of the shear resistance (CRR) of the soil under repetitive loading to earthquake-induced shear stresses (CSR) at various depths was calculated using both the CPT and SPT data. The staff cannot determine how the current CPT and SPT data correlate.

The above information is necessary to comply with Title 10 of the Code of Federal Regulations (10 CFR) 72.102(c) and 10 CFR 72.102(d).

Enclosure

2.2 In Section 3.3, Soil Structure Interaction Analysis, of the PI ISFSI license amendment request, the applicant discusses design inputs, acceptance criteria, analyses and conclusions related to soil structure interaction (SSI). For the staff to ascertain that the current licensing basis is maintained, and that sufficient data is provided to make a safety finding, the following information needs to be included:

a. Provide the Acceleration Input Motions generated per Approach 2, Option 1 of NUREG 0800, Chapter 3.7.1.

b. Provide the Upper Bound, Best estimate and Lower Bound strain compatible soil properties (shear modulus and damping) data per depth generated for the SSI analysis in graphical or tabular form.

c. Justify why Model 3 for the single cask on the corner of the pad is the governing loading case.

d. Provide a schematic of the ISFSI pad model used for SASSI2010 analysis including mesh distribution and sizes.

e. Provide results of the 36 SSI analysis cases analyzed in tabular format, as appropriate.

The above information is necessary to comply with 10 CFR 72.102(c) and 10 CFR 72.102(d).

2.3 Provide additional structural analysis details.

In Section 3.4 Structural Analysis, of enclosure 1 of the PI ISFSI LAR, the licensee discusses design inputs, acceptance criteria and conclusions related to the structural analysis of the proposed pad. In order for the staff to ascertain that the current licensing basis is maintained, and that sufficient data is provided to make a safety finding, additional details on the structural analysis need to be provided. Structural analyses or calculation packages that include the following information need to be included:

a. Details on calculation of subgrade modulus for the SAFE analysis.

b. Pad settlement and differential settlement evaluations

c. Schematic of finite element mesh generated by SAFE for ISFSI pad.

d. Results of load combination permutations used in SAFE design models as stated in the last paragraph of Section of 3.4.2.2.

e. Final pad reinforcement details resulting from shear and flexure design for the various cask load configurations and combinations.

f. Results of maximum soil bearing pressure evaluation The above information is necessary to comply with 10 CFR 72.102(c), 10 CFR 72.102(d) and 72.24(d) 2

2.4 Clarify cask load configurations used in structural analysis.

Section 3.4.2, Supporting Analysis and Acceptance Criteria, of enclosure 1 of the PI ISFSI LAR states that A total of four different cask load configurations were considered in order to envelope the worst-case moment, shear, and settlement in the new pad. In section 3.4.4, Results and Conditions of the same document, it is stated that The pad was analyzed using three cask configurations. Additionally, Section 2.4, Cask Loading Pattern of Soil Structure Interaction Analysis of the ISFSI Expansion Pad also discusses the use of three cask loading patterns. Because an apparent inconsistency in the licensees assessment of cask load configurations exists, the following information is requested:

a. Specify the cask load configurations referenced in Section 3.4.2, and

b. Confirm that the analyzed cask load patterns are conservative and bound all other possible scenarios.

The above information is necessary to comply with 10 CFR 72.102(c), 10 CFR 72.102(d) and 72.24(c)(3).

THERMAL 6.1 Provide a detailed discussion of the method of evaluation (MOE) used to demonstrate that the thermal performance of the TN40HT casks currently in place on the existing ISFSI pads are not adversely affected by the deployment of the proposed ISFSI pad expansion.

The applicant has provided a high-level summary of the evaluations performed, including some calculations, to demonstrate that the addition of a third ISFSI pad at the Prairie Island ISFSI will have minimal impact on the thermal performance of the casks on the existing ISFSI pads. This information was provided to support a request that the NRC review and approve an alternate methodology for demonstrating thermal performance of the spent fuel storage cask system in this license amendment request.

The differences in the alternate methodology, when compared to the existing methodology, are primarily related to the numerical modeling software used to perform the thermal analysis. In lieu of reviewing input and output parameters of the actual analysis files developed by the applicant, the NRC staff is requesting that a more thorough and complete narrative of the MOE, consistent with the guidance in NEI 12-04, draft NUREG 2215, and NUREG 2152, be included in the FSAR, such that the staff could perform appropriate inspection and oversight activities.

A thorough description of the MOE is important because it will demonstrate that the design basis functions will protect the integrity of important shielding or fission product barriers, and thus those features that protect against dose to the public or release of radioactive material. It will also control the analyses and assessment process through control of the methods and will assure that the required response of the shielding or barriers as previously established by NRC review will be maintained.

This narrative may include:

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1. Comparison tables of input parameters used for the existing finite element analysis of the ISFSI and those used in the CFD analysis for the alternate MOE.

2.

The approach taken by the applicant was to use a previously approved modeling approach to validate the alternate modeling approach. Since a method of evaluation includes inputs and other modeling choices, it is appropriate to provide a clear representation of similarities between the existing analyses and the proposed MOE, for each of the elements relied upon to make the proposed MOE complete.

3. A thorough discussion of the following:

a. mesh generation, including appropriate plots, and applicable sensitivity studies.

b. treatment of boundary conditions.

c. the final thermal radiation model used.

d. how the heat transfer out of the top of the casks is treated.

As with item (1), a reasoned and orderly presentation of specific modeling choices is important to fully evaluate whether an element of a method of evaluation is appropriate and complete.

4. Any additional relevant information related to the numerical modeling aspects of the MOE that might be revealed during an audit of actual input and output files.

The applicant is responsible for a complete discussion of all elements of an MOE on which they rely to illustrate that said MOE is sufficient to demonstrate the performance of that design in light of the requirements presented in 10 CFR Part 72. If the essential elements of the MOE are not adequately identified in the application, the staff cannot make a finding of reasonable assurance of adequate protection. This may result in the MOE not being approved for use beyond the existing licensing action.

This information is needed to assess compliance with 10 CFR 72.122(h)(1), 10 CFR 72.128(a)(2,3,4).

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MATERIALS 8.1 Include the use of ACI 201.2R in the safety analysis report (SAR) description of the new ISFSI pad design or provide justification for how the durability of the concrete will be ensured without SAR requirements to follow this ACI guidance.

The SAR Section A4.2.1 states that the new concrete pad is designed to the requirements of ACI 349-13, Code Requirements for Nuclear Safety-Related Concrete Structures. An exception is being taken to reduce the minimum compressive strength of the concrete from the 4,500 psi requirement of this ACI code. The staff notes that ACI 349-13 establishes the 4,500 psi minimum strength to meet durability requirements for concrete that is exposed to freezing and thawing cycles.

Enclosure 1 of the license amendment request (evaluation of the proposed change) states that the guidance in ACI 201.2R-16, Guide to Durable Concrete, will be followed to ensure the durability of the concrete with the reduced minimum compressive strength.

However, the use of ACI 201.2R-16 is not discussed in the SAR. It is unclear to the staff how the durability of the concrete will be achieved without a SAR specification for the use of ACI 201.2R-16.

This information is needed to demonstrate compliance with 10 CFR 72.24(c)(4) and 72.122(b)(1).

8.2 Clarify apparent discrepancies between the temperature values and footnotes in SAR Table A3.3-7.

The SAR Table A3.3-7 includes new footnotes that describe revisions made to the maximum component temperatures for buried casks. However, the temperature values in the table have not been revised from the prior version of the SAR in accordance with the new footnotes.

This information is needed to demonstrate compliance with 10 CFR 72.24(c) and 72.120(d).

8.3 In the SAR, clarify if the existing aging management programs are to be implemented for the new pad and casks immediately upon placing them into service or sometime afterward (e.g., after 20 years of service).

The SAR Sections 9.8 and A9.8 describe the aging management activities associated with Prairie Islands renewed ISFSI license. Enclosure 1 of the license amendment request states that the new SSCs will be included in the ISFSI aging management programs (AMPs). The SAR does not specifically address the inclusion of the new SSCs in the AMPs. To provide clarity for the staffs review of the amendment request (and for subsequent NRC AMP inspection activities) the SAR should state the timing for the implementation of the AMPs for the new pad and casks.

This information is needed to demonstrate compliance with 10 CFR 72.120(a).

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