ML19070A217

Supplement to Interim Staff Response to Reevaluated Flood Hazards Submitted in Response to 10 CFR 50.54(f) Information Request - Flood - Causing Mechanism Reevaluation

ML19070A217
Person / Time
Site:	Millstone
Issue date:	04/03/2019
From:	Juan Uribe Beyond-Design-Basis Management Branch
To:	Stoddard D Dominion Nuclear Connecticut
Uribe J, NRR/DLP/PBMB, 415-3809
References
EPID L-2015-JLD-0011, EPID L-2015-JLD-0012
Download: ML19070A217 (10)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 April 3, 2019 Mr. Daniel G. Stoddard Senior Vice President and Chief Nuclear Officer Dominion Nuclear Connecticut, Inc.

Millstone Power Station Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 230601

SUBJECT:

.MILLSTONE POWER STATION, UNITS 2 AND 3 - SUPPLEMENT TO INTERIM STAFF RESPONSE TO REEVALUATED FLOOD HAZARDS SUBMITTED IN RESPONSE TO 10 CFR 50.54(f) INFORMATION REQUEST- FLOOD-CAUSING MECHANISM REEVALUATION (EPID NOS. L-2015-JLD-0011 AND L-2015-JLD-0012)

Dear Mr. Stoddard:

The purpose of this letter is to provide a summary of the NRC staff's assessment of the storm surge reevaluated flood-causing mechanism and supplement the NRC's December 21, 2016, letter.

By letter dated March 12, 2012 (Agencywide Document Access and Management System (ADAMS) No. ML12053A340), the U.S. Nuclear Regulatory Commission (NRC) issued a request for information pursuant to Title 10 of the Code of Federal Regulations, Section 50.54(f)

(hereafter referred to as the 50.54{f) letter). The request was issued as part of implementing lessons learned from the accident at the Fukushima Dai-ichi nuclear power plant. Enclosure 2 to the 50.54(f) letter requested licensees to reevaluate flood-causing mechanisms using present-day methodologies and guidance.

By letter dated December 21, 2016 (ADAMS Accession No.ML16308A226), the NRC staff provided to you a summary assessment of the reevaluated flood-causing mechanisms described in the March 12, 2015, flood hazard reevaluation report (FHRR) submitted by Dominion Nuclear Connecticut, Inc. (Dominion, the licensee) for Millstone Power Station, Units 2 and 3 (MPS2 and MPS3) (ADAMS Accession No. ML15078A203). This letter did not include the staff's conclusions associated with the storm surge flood-causing mechanism, and stated that the staff's evaluation of the probabilistic storm surge analysis was ongoing and that future correspondence documenting the results of the staff's review would follow. By letter dated January 4, 2019 (ADAMS Accession No. ML19011A110), Dominion supplemented the FHRR report with additional information related to the probabilistic storm surge flood hazard.

The NRC staff has reviewed the information submitted by the licensee in its FHRR and January 4, 2019. letter, and has summarized the results of the probabilistic storm surge review in the tables provided as an enclosure to this letter. Table 1 provides the current design-basis flood hazard mechanisms. Table 2 provides the reevaluated flood hazard mechanisms; however, the reevaluated flood hazard mechanisms bounded by the current design basis {Table 1) are not

D. Stoddard included. Because of the difference in the licensing basis and the reevaluated hazard elevations for MPS2 and MPS3, there is a Table 1 and Table 2 for each site. The NRC staff also notes that the values for mechanisms in Table 2 considered to be not bounded by the current design basis, other than storm surge, remain unchanged from the NRC's December 21, 2016, letter.

As stated in its December 21, 2016, letter, the licensee submitted both deterministic and probabilistic storm surge analyses in its FHRR, but proposed using its results for the probabilistic storm surge analysis as an input for the additional assessments. The NRC staff agreed with this approach. The NRC staff reviewed the storm surge analysis and notes that the storm surge values reflected in Table 2 of this letter are representative of an annual exceedance probability that supports decision-making, which is typically 10-3 (with margin) to 10-4 _ This approach is consistent the performance of an integrated assessment as described in Nuclear Energy Institute (NEI) 16-05, Revision 1, "External Flooding Assessment Guidelines" (ADAMS Accession No. ML16165A178). Guidance document NEI 16-05, Revision 1, has been endorsed by Japan Lessons-Learned Division (JLD) interim staff guidance (ISG) JLD-ISG-2016-01, "Guidance for Activities Related to Near-Term Task Force Recommendation 2.1, Flood Hazard Reevaluation" (ADAMS Accession No. ML16162A301 ). The application of the storm surge values presented in Table 2 for methods other than those described in JLD-ISG-2016-01 should be closely coordinated with the NRC staff to ensure adequate communication.

In order to complete its response to the information requested by Enclosure 2 to the 50.54(f) letter, the licensee is expected to submit an integrated assessment or a focused evaluation, as appropriate, to address the reevaluated flood hazards that exceed the current design basis, as described in the NRC letter dated September 1, 2015, "Coordination of Request for Information Regarding Flooding Hazard Reevaluation and Mitigating Strategies for Beyond-Design-Basis External Events" (ADAMS Accession No. ML15174A257). This letter describes the changes in the NRC's approach to the flood hazard reevaluations that were approved by the Commission in its Staff Requirements Memorandum to COMSECY-15-0019, "Closure Plan for the Reevaluation of Flooding Hazards for Operating Nuclear Power Plants" (ADAMS Accession No. ML15209A682).

Further, the NRC staff has concluded that the licensee's reevaluated flood hazard information reflected in Table 2 is a suitable input for the remaining flooding assessments associated with the 50.54(f) letter. The NRC staff issued a staff assessment by letter dated October 3, 2018 (ADAMS Accession No. ML18256A200), that provides the documentation supporting the NRC staff's conclusions summarized in the December 21, 2016, letter, and plans to issue a staff assessment documenting the basis for the storm surge conclusions at a later time.

D. Stoddard If you have any questions, please contact me at (301) 415-3809 or e-mail at Juan.Uribe@nrc.gov.

~I Sinperely, ( r ~ / L'

~ Jv_)v1 I I I

w/ I 10 \

Juan Uribe, Project Manager Beyond-Design-Basis Management Branch Division Office of Nuclear Reactor Regulation Docket Nos. 50-336 and 50-423

Enclosure:

Summary of Results of Flooding Hazard Re-Evaluation Report cc w/encl: Distribution via Listserv

Millstone Power Station, Unit 2 Table 1. Current Design Basis Flood Hazards 1 Mechanism Stillwater Waves/Runup Design Reference Elevation Basis Flood Hazard Elevation Local Intense 14.5 feet (ft.) Minimal 14.5 ft. FHRR Table 1.2-1 Precipitation Mean sea level MSL (MSL)

Streams and Rivers No Impact No Impact No Impact FHRR Section 1.2-on the Site on the Site on the Site 1 Identified Identified Identified Failure of Dams and Not Included in Not Included in Not Included FHRR Sections Onsite Water DB DB in DB 2.3.3 and 3.3 Control/Storage Structures Storm Surge Storm Surge (standing 26.5 ft. MSL NA 26.5 ft. MSL FHRR Sections 3.4 wave) within the and 3.9. FHRR Intake Structure for Table 3.0-1.

Unit 2 Updated from Interim Staff Response (ISR) letter ML16308A234.

See FHRR supplement ML19011A110, Att.

A Table 6 Storm Surge at the 18.2 ft. MSL 6.9ft. 25.1 ft. MSL FHRR Sections 3.4 Unit 2 Powerblock and 3.9. FHRR Table 3.0-1.

Updated from ISR letter ML16308A234.

See FHRR supplement ML19011A110, Att.

A Table 6 1

In the December 21, 2016, ISR letter (ML16308A234), the staff presented elevations in National Geodetic Vertical Datum of 1929 (NGVD29) datum. For this ISR table, which includes storm surge, the staff is using MSL to be consistent with previous licensee submittals which equated MSL with NGVD29.

As a result, no numeric values previously presented in this set of tables for Units 2 and 3 were affected by this datum change.

Enclosure

Seiche No Impact on No Impact on No Impact on FHRR Table 1.2-1 the Site the Site the Site Identified Identified Identified Tsunami Not included Not included Not included FHRR Table 1.2-1 in DB in DB in DB Ice-Induced No Impact on No Impact on No Impact on FHRR Table 1.2-1 Flooding the Site the Site the Site Identified Identified Identified Channel No Impact on No Impact on No Impact on FHRR Table 1.2-1 Migrations/Diversion the Site the Site the Site Identified Identified Identified

Millstone Power Station, Unit 2 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms Mechanism Stillwater Waves/Run up Reevaluated Reference Elevation Hazard Elevation Local Intense 17.5 ft. MSL Minimal 17.5ft. MSL FHRR Section Precipitation 3.1 Streams and 11.2 ft. MSL Not applicable 11.2 ft. MSL FHRR Section Rivers 2.2 Storm Surge Storm Surge 16.92 ft. MSL NA 27.56 ft. MSL3 Updated from (standing wave) ISR letter within the Intake ML16308A234.

Structure for See calculation Unit 2 package NAI-1996-001 referenced by FHRR supplement ML19011A110.

Storm Surge at 17.5ft. MSL Negligible at 17.5 ft. MSL at Updated from the Unit 2 east.side of east side of ISR letter Powerblock MPS2. MPS2 ML16308A234.

See FHRR 2.3 ft. at west 19.8 ft. MSL at supplement side of MPS2. west side of ML19011A110, MPS2 Att. A, Table 6.

Tsunami 14.7 ft. MSL Not applicable 14.7 ft. MSL FHRR Section 2.6 2

External reevaluated water levels at the Unit 2 intake structure were reported as 16.9 ft. for stillwater and 37.2 ft. for the external total water level (including wave runup of 20.3 ft.). However, the COB is for service water pumps within the Unit 2 intake structure.

3 This reported value is the maximum water level from 4 cases evaluated for Unit 2 internal water levels using the GOTHIC code as presented in calculation package NAl-1996-001, which is referenced as "Zachry, 2018c" in the supplement to the FHRR. Based on a high-level review, staff found the use of the GOTHIC code, model development and water level and wave inputs reasonable. While the review of NAl-1996-001 did not include verification of elevations, areas and volumes included in the model, staff recognize that the licensee's documentation indicates these inputs were verified in accordance with a quality assurance plan that conforms to 10CFRSO, Appendix B.

Millstone Power Station, Unit 3 Table 1. Current Design Basis Flood Hazards Mechanism Stillwater Waves/Run up Design Reference Elevation Basis Flood Hazard Elevation Local Intense Precipitation RWST/SIL Enclosure 24.9 ft. MSL Minimal 24.9 ft. FHRR Table 1.2-3 MSL and Table 3.0-3 Demineralized Water 24.9 ft. MSL Minimal FHRR Table 1.2-3 Storage Tank Block 24.9 ft.

House MSL Fuel Building 24.9 ft. MSL Minimal FHRR Table 1.2-3 24.9 ft.

Auxiliary Building Door 24.9 ft. MSL Minimal MSL FHRR Table 3.0-3 A-24-6 Engineered Safety 24.9 ft. MSL Minimal 24.9 ft. FHRR Table 1.2-3 Features Building MSL Hydrogen Recombiner 24.9 ft. MSL Minimal FHRR Table 1.2-3 Building 24.9 ft.

MSL Main Steam Valve 24.9 ft. MSL Minimal FHRR Table 1.2-3 Building 24.9 ft.

Emergency Generator 24.3 ft. MSL Minimal MSL FHRR Table 1.2-3 Enclosure Auxiliary Building Door 24.9 ft. MSL Minimal 24.9 ft. FHRR Table 3.0-3 A-24-1 MSL Control Building 24.3 ft. MSL Minimal FHRR Table 1.2-2 24.3 ft

.MSL 24.9 ft.

MSL 24.3 ft.

MSL

Streams and Rivers No Impact No Impact No Impact FHRR Section 1.2-2 on the Site on the Site on the Site Identified Identified Identified Failure of Dams and Not Included Not Included in Not FHRR Sections Onsite Water in DB DB Included in 2.3.3 and 3.3 Control/Storage DB Structures Storm Surge Storm Surge at 19.7 ft. MSL 21.5 ft. 41.2 ft. FHRR Section 3.9 Seaward Wall of Intake MSL and Table 3.0-2.

Structure for Unit 3 Updated from ISR letter ML16308A234. See FHRR supplement ML19011A110, Att.

A Table 7 Storm Surge at the Unit 19.7ft. MSL 4.1 ft. 23.8 ft. FHRR Sections 1.5 3 Powerblock MSL and 3.9. FHRR Tables 1.2-2 and 3.0-2.

Updated from ISR letter ML16308A234. See FHRR supplement ML19011A110, Att.

A Table 7.

Seiche No Impact on No Impact on No Impact FHRR Table 1.2-2 the Site the Site on the Site Identified Identified Identified Tsunami Not included Not included in Not FHRR Table 1.2-2 in DB DB included in DB Ice-Induced Flooding No Impact on No Impact on No Impact FHRR Table 1.2-2 the Site the Site on the Site Identified Identified Identified Channel No Impact on No Impact on No Impact FHRR Table 1.2-2 Migrations/Diversion the Site the Site on the Site Identified Identified Identified

Millstone Power Station, Unit 3 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms Mechanism Stillwater Waves/Run up Reevaluated Reference Elevation Hazard Elevation Streams and 11.2 ft. MSL Not applicable 11.2 ft. MSL FHRR Section Rivers 2.2 Storm Surge Storm Surge at 17.1 ft. MSL 25.5 ft. 42.6 ft. MSL Updated from Seaward Wall of ISR letter Intake Structure ML16308A234.

for Unit 3 See FHRR supplement ML19011A110, Att. A Table 7 Storm Surge at 17.7 ft. MSL 4.5 ft. 22.2 ft. MSL4 Updated from the Unit 3 ISR letter Powerblock ML16308A234.

See FHRR supplement ML19011A110, Att. A Table 7.

Tsunami 14.7ft. MSL Not applicable 14.7 ft. MSL FHRR Section 2.6 4

The reevaluated total water level for the Unit 3 powerblock is below the site grade of 24 ft. MSL.

D. Stoddard

SUBJECT:

MILLSTONE POWER STATION, UNITS 2 AND 3 - SUPPLEMENT TO INTERIM STAFF RESPONSE TO REEVALUATED FLOOD HAZARDS SUBMITTED IN RESPONSE TO 10 CFR 50.54(f) INFORMATION REQUEST- FLOOD-CAUSING MECHANISM REEVALUATION (EPID NOS. L-2015-JLD-0011 AND L-2015-JLD-0012) DATED: April 3, 2019 DISTRIBUTION:

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