ML16308A226
| ML16308A226 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 12/21/2016 |
| From: | Lauren Gibson Japan Lessons-Learned Division |
| To: | Heacock D Dominion Nuclear |
| Gibson L, NRR/JLD, 415-1056 | |
| Shared Package | |
| ML16308A234 | List: |
| References | |
| CAC MF6109, CAC MF6110 | |
| Download: ML16308A226 (4) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. David A. Heacock President and Chief Nuclear Officer Dominion Nuclear Innsbrook Technical Center 5000 Dominion Boulevard Glen Allen, VA 23060-6711 December 21, 2016
SUBJECT:
MILLSTONE POWER STATION, UNITS 2 AND 3 - INTERIM STAFF RESPONSE TO REEVALUATED FLOOD HAZARDS SUBMITTED IN RESPONSE TO 10 CFR 50.54(f) INFORMATION REQUEST-FLOOD-CAUSING MECHANISM REEVALUATION (CAC NOS. MF6109 AND MF6110)
Dear Mr. Heacock:
The purpose of this letter is to provide a summary of the U.S. Nuclear Regulatory Commission (NRC) staff's assessment of the reevaluated flood-causing mechanisms described in the March 12, 2015, flood hazard reevaluation report (FHRR) submitted by Dominion Nuclear Connecticut, Inc. (the licensee) for Millstone Power Station, Units 2 and 3 (MPS2 and MPS3)
(Agencywide Document Access and Management System (ADAMS) Accession No. ML15078A203), as well as supplemental information resulting from audits.
This letter and the enclosed tables supersede the NRC's partial interim staff response letter dated October 13, 2016 (ADAMS Accession No. ML16267A131). This letter includes a correction to the tables provided in that letter. Specifically, in the October 13, 2016, letter, a design-basis flood evaluation for tsunami hazards was given incorrectly for each unit. In fact, tsunami hazards were not considered in the design basis for MPS2 and MPS3. The enclosed tables supersede the tables in the October 13, 2016, letter with the change being the replacement of the tsunami hazard design-basis flood elevation level with a note that tsunami hazards are not included in the design basis. In addition, the design basis for storm surge in both Tables 1 was corrected. This letter also includes a discussion of the path forward in light of the licensee's decision to use a probabilistic storm surge analysis as part of its flood hazard reevaluation.
By letter dated March 12, 2012, the 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)
(ADAMS Accession No. ML12053A340). 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. Concurrent with the reevaluation of flooding hazards, licensees were required to develop and implement mitigating strategies in accordance
with NRC Order EA-12-049, "Requirements for Mitigation Strategies for Beyond-Design-Basis External Events" (ADAMS Accession No. ML12054A735). On March 30, 2015, the Commission provided staff requirements memorandum (SRM) (ADAMS Accession No. ML15089A236) to COMSECY-14-0037, "Integration of Mitigating Strategies for Beyond-Design-Basis External Events and the Reevaluation of Flooding Hazards," dated November 21, 2014 (ADAMS Accession No. ML14309A256), affirming that licensees need to address the reevaluated flooding hazards within their mitigating strategies for beyond-design-basis external events.
Revision 2 of Nuclear Energy Institute (NEI) guidance document NEI 12-06, dated December 2015, includes a methodology for performing a mitigating strategies assessment (MSA) with respect to the reevaluated flood hazards. On February 29, 2016, the NRC staff published Japan Lessons-Learned Division (JLD) Interim Staff Guidance (ISG)
JLD-ISG-2012-01, Revision 1, "Compliance with Order EA-12-049, 'Order Modifying Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events"' (ADAMS Accession No. ML15357A142), in the Federal Register (81 FR 10283). This ISG endorses Revision 2 of NEI 12-06 (ADAMS Accession No. ML16005A625). Based on the guidance provided in Revision 2 of NEI 12-06, flood event duration parameters and applicable flood associated effects should be considered as part of the MPS2 and MPS3 MSA. The NRC staff will evaluate the flood event duration parameters (including warning time and period of inundation) and flood-related associated effects developed by the licensee during the NRC staff's review of the MSA.
In addition to the MSA, in order to complete its response to the information requested by 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, "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 SRM to COMSECY-15-0019, "Closure Plan for the Reevaluation of Flooding Hazards for Operating Nuclear Power Plants" (ADAMS Accession No. ML15209A682).
The NRC staff has reviewed the information submitted by the licensee in its FHRR and has summarized the results of the 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 included. Because of the difference in the licensing basis and the elevations for MPS2 and MPS3, there is a Table 1 and Table 2 for each site.
The attached tables do not include the staff's assessment of flooding due to storm surge. In its FHRR, the licensee submitted both deterministic and probabilistic storm surge analyses. The NRC staff had been focusing its review on the deterministic methodology. During a November 3, 2016, teleconference held as part of the audit, 1 the licensee informed the NRC staff that it intends to use the probabilistic storm surge analysis in its flood hazard reevaluation.
The NRC's review of this complex methodology may extend beyo.nd the expected submittal 1 The audit plan, dated June 15, 2015, is available at ADAMS Accession No. ML15153A077.
dates for the MSA and the additional flooding evaluations related to the 50.54(f) letter.
Therefore, the licensee proposed using its results for the probabilistic storm surge analysis as an input for the additional assessments while the NRC staff's review is ongoing. The NRC staff agreed with this approach. The MSA is expected to be submitted in June 2017 and a focused evaluation is expected to be submitted in December 2017. The staff's evaluation of the probabilistic storm surge analysis is continuing and future correspondence documenting the results of the staff's review will be forthcoming. The licensee acknowledged that these submittals may need to be revised based on the results of the NRC's review of this mechanism.
For other flood-causing mechanisms, the NRC staff has concluded that the licensee's reevaluated flood hazards information, as summarized in the enclosure, is suitable for the assessment of mitigating strategies developed in response to Order EA-12-049 (i.e., defines the mitigating strategies flood hazard information described in Nuclear Energy Institute (NEI) guidance document NEI 12-06, "Diverse and Flexible Coping Strategies (FLEX) Implementation Guide") for MPS2 and MPS3. Further, the NRC staff has concluded that the licensee's reevaluated flood hazard information is a suitable input for other flooding assessments associated with the 50.54(f) letter. The NRC staff plans to issue a staff assessment documenting the basis for these conclusions at a later time.
If you have any questions, please contact me at (301) 415-1056 or e-mail at Lauren.Gibson@nrc.gov.
Docket Nos. 50-336 and 50-423
Enclosure:
Summary of Results of Flooding Hazard Re-Evaluation Report cc w/encl: Distribution via Listserv Sincerely, Lauren Gibson, Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation
Millstone Power Station, Unit 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA Mechanism Local Intense Precipitation Streams and Rivers Failure of Dams and Onsite Water Control/Storage Structures Storm Surge Storm Surge (standing wave) within the Intake Structure for Unit 2 Storm Surge at the Powerblock Seiche Tsunami Ice-Induced Flooding Stillwater Elevation 14.5ft NGVD29 No Impact on the Site Identified Not included in DB 26.5 ft NGVD29 18.1 ft NGVD29 No Impact on the Site Identified Not included in DB No Impact on the Site Identified Waves/
!Design Basis Run up Hazard Elevation Reference Minimal 14.5 ft FHRR Table 1.2-1 NGVD29 No Impact No Impact FHRR Table 1.2-1 on the Site on the Site Identified Identified Not included Not included FHRR Sections 2.3.3 & 3.3 in DB in DB
- ---~
Not 26.5 ft FHRR Sections 1.5 and 3.4 applicable NGVD29 7.0 ft 25.1 ft FHRR Section 3.9 and FHRR Table NGVD29 3.0-1 FHRR Table 1.2-1 No Impact No Impact FHRR Table 1.2-1 on the Site on the Site Identified Identified Not included Not included FHRR Table 1.2-1 in DB in DB No Impact No Impact FHRR Table 1.2-1 on the Site on the Site Identified Identified
Millstone Power Station, Unit 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA I
Mechanism Stillwater Waves/
Design Basis 1 Reference Elevation Run up
~7::::~:!!_ --- ~-~
Channel Migrations/Diversi.;-n~ I No Impact No Impact No Impact FHRR Table 1.2-1 on the Site on the Site on the Site Identified Identified Identified Note 1: Reported values are rounded to the nearest one-tenth of a foot.
Millstone Power Station, Unit 2 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms for Use in the MSA Mechanism Stillwater Elevation Local Intense Precipitation 17.5 ft NGVD29 Streams and Rivers 11.2 ft NGVD29 Storm Surge Under Review Tsunami I
14.7 ft I NGVD29 Waves/
Run up Minimal Not applicable Under Review Not applicable Reevaluated Hazard Elevation 17.5 ft NGVD29 11.2 ft NGVD29 Under Review 14.7ft NGVD29 Reference FHRR Section 3.1 FHRR Section 2.2 FHRR Section 2.6 Note 1: The licensee is expected to develop flood event duration parameters and applicable flood associated effects to conduct the MSA. The staff will evaluate the flood event duration parameters (including warning time and period of inundation) and flood associated effects during its review of the MSA.
Note 2: Reevaluated hazard mechanisms bounded by the current design basis (see Table 1) are not included in this table.
Note 3: Reported values are rounded to the nearest one-tenth of a foot.
Millstone Power Station, Unit 3 Table 1. Current Design Basis Flood Hazards for Use in the MSA Mechanism Local Intense Precipitation RWST/SIL Valve Enclosure Demineralized Water Storage Tank Block House Fuel Building Auxiliary Building Door A-24-6 Engineered Safety Features Building Hydrogen Recombiner Building Main Steam Valve Building Emergency Generator Enclosure Auxiliary Building Door A-24-1 Control Building Streams and Rivers Stillwater Elevation 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.3 ft NGVD29 24.9 ft NGVD29 24.3 ft NGVD29 No Impact on the Site Identified i
Waves/
Run up Minimal Minimal Minimal Minimal Minimal Minimal Minimal Minimal Minimal Minimal No Impact on the Site Identified Design Basis Hazard Elevation 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.9 ft NGVD29 24.3 ft NGVD29 24.9 ft NGVD29 24.3 ft NGVD29 No Impact on the Site Identified Reference FHRR Table 1.2-3 and Table 3.0-3 FHRR Table 1.2-3 FHRR Table 1.2-3 FHRR Table 3.0-3 FHRR Table 1.2-3 FHRR Table 1.2-3 FHRR Table 1.2-3 FHRR Table 1.2-3 FHRR Table 3.0-3 FHRR Table 1.2-3 FHRR Table 1.2-2
Millstone Power Station, Unit 3 Table 1. Current Design Basis Flood Hazards for Use in the MSA Mechanism Stillwater Waves/
Design Basis Reference Elevation Run up Hazard Elevation Failure of Dams and Onsite -T Water Control/Storage I
Structures Not included Not included Not included FHRR Sections 2.3.3 & 3.3 in DB in DB in DB Storm Surge Storm Surge at Seaward Wall of
- 19. 7 ft 21.5 ft 41.2 ft FHRR Section 3.9 Intake Structure for Unit 3 NGVD29 NGVD29 Storm Surge at Powerblock 19.7 ft 4.1 ft 23.8 ft FHRR Section 1.5 NGVD29 NGVD29 FHRR Table 1.2-2 Seiche No Impact No Impact No Impact FHRR Table 1.2-2 on the Site on the Site on the Site Identified Identified Identified Tsunami Not included Not included Not included FHRR Table 1.2-2 in DB in DB in DB Ice-Induced Flooding No Impact No Impact No Impact FHRR Table 1.2-2 on the Site on the Site on the Site Identified Identified Identified I
Channel Migratlons/Dlversio~s I ~
No Impact No Impact No Impact FHRR Table 1.2-2 on the Site on the Site on the Site I
Identified Identified Identified Note 1: Reported values are rounded to the nearest one-tenth of a foot.
Millstone Power Station, Unit 3 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms for Use in the MSA Mechanism Streams and Rivers Storm Surge Tsunami Stillwater Elevation 11.2 ft NGVD29 Under Review 14.?ft NGVD29 Waves/
Run up Not applicable Under Review Not applicable Reevaluated Hazard Elevation 11.2 ft NGVD29 Under Review 14.7 ft NGVD29 Reference FHRR Section 2.2 FHRR Section 2.6 Note 1: The licensee is expected to develop flood event duration parameters and applicable flood associated effects to conduct the MSA. The staff will evaluate the flood event duration parameters (including warning time and period of inundation) and flood associated effects during its review of the MSA.
Note 2: Reevaluated hazard mechanisms bounded by the current design basis (see Table 1) are not included in this table.
Note 3: Reported values are rounded to the nearest one-tenth of a foot.
Therefore, the licensee proposed using its results for the probabilistic storm surge analysis as an input for the additional assessments while the NRC staff's review is ongoing. The NRC staff agreed with this approach. The MSA is expected to be submitted in June 2017 and a focused evaluation is expected to be submitted in December 2017. The staff's evaluation of the probabilistic storm surge analysis is continuing and future correspondence documenting the results of the staff's review will be forthcoming. The licensee acknowledged that these submittals may need to be revised based on the results of the NRC's review of this mechanism.
For other flood-causing mechanisms, the NRC staff has concluded that the licensee's reevaluated flood hazards information, as summarized in the enclosure, is suitable for the assessment of mitigating strategies developed in response to Order EA-12-049 (i.e., defines the mitigating strategies flood hazard information described in Nuclear Energy Institute (NEI) guidance document NEI 12-06, "Diverse and Flexible Coping Strategies (FLEX) Implementation Guide") for MPS2 and MPS3. Further, the NRC staff has concluded that the licensee's reevaluated flood hazard information is a suitable input for other flooding assessments associated with the 50.54(f) letter. The NRC staff plans to issue a staff assessment documenting the basis for these conclusions at a later time.
If you have any questions, please contact me at (301) 415-1056 or e-mail at Lauren.Gibson@nrc.gov.
Sincerely, IRA/
Lauren Gibson, Project Manager Hazards Management Branch Japan Lessons-Learned 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 DISTRIBUTION:
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