ML16248A003

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

ML16248A003
Person / Time
Site:	Monticello
Issue date:	09/16/2016
From:	Lauren Gibson Japan Lessons-Learned Division
To:	Gardner P Northern States Power Company, Minnesota
Shared Package
ML16248A004	List: ML16245A720 ML16248A003
References
CAC MF7712
Download: ML16248A003 (7)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 September 16, 2016 Mr. Peter A. Gardner Site Vice President Northern States Power Company - Minnesota Monticello Nuclear Generating Plant 2807 West County Road 75 Monticello, MN 55362-9637

SUBJECT:

MONTICELLO NUCLEAR GENERATING PLANT - INTERIM STAFF RESPONSE TO REEVALUATED FLOOD HAZARDS SUBMITTED IN RESPONSE TO 10 CFR 50.54(f) INFORMATION REQUEST- FLOOD-CAUSING MECHANISM REEVALUATION (CAC NO. MF7712)

Dear Mr. Gardner:

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 May 12, 2016 (Agencywide Document Access and Management System (ADAMS) Accession No. ML16145A233), flood hazard reevaluation report (FHRR) submitted by Northern States Power Company, a Minnesota corporation (the licensee), doing business as Xcel Energy, for Monticello Nuclear Generating Plant (Monticello), as well as supplemental information resulting from the NRC's audit of the FHRR.

By letter dated March 12, 2012, the NRC issued a request for information pursuant to Title 1O 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 the staff requirements memoranda (SAM) (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.

The NRC staff has reviewed the information submitted by the licensee and has summarized the results of the NRC's review in the tables provided as an enclosure to this letter. Table 1 provides the current design-basis flood hazard mechanisms. Table 2 provides reevaluated

P. Gardner flood hazard mechanisms; however, reevaluated hazard mechanisms bounded by the current design-basis (Table 1) are not included.

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 guidance documents currently being finalized by the industry and NRC staff) for Monticello. Further, the NRC staff has concluded that the licensee's reevaluated flood hazard information is a suitable input for other assessments associated with Near-Term Task Force Recommendation 2.1 , "Flooding." The NRC staff plans to issue a staff assessment documenting the basis for these conclusions at a later time.

Revision 2 of Nuclear Energy Institute (NEI) 12-06 includes a methodology to perform 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), dated December 2015. 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 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's review of the MSA.

As stated above, Table 2 of the enclosure to this letter describes the reevaluated flood hazards that exceed the current design-basis. 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 these reevaluated flood hazards, 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).

P. Gardner If you have any questions, please contact me at (301) 415-1056 or e-mail at Lauren .Gibson@nrc.gov.

Sincerely, Lauren K. Gibson, Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket No. 50-263

Enclosure:

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

ENCLOSURE:

SUMMARY

TABLES OF REEVALUATED FLOOD HAZARD LEVELS

Monticello Nuclea r Generating Plant, Un it 1 Table 1. Current Design Basis Flood Hazards for Use in the MSA Mechanism Stillwater Waves/ Design Basis I Reference Elevation Run up Hazard Elevation Local Intense Precipitation Not included Not included Not included FHRR Section 1.5, 2.1.3 & Table 5 in DB in DB in DB Streams and Rivers Mississippi River Probable 939.2 ft Not 939.2 ft FHRR Section 1.5.1 Maximum Precipitation NGVD29 applicable NGVD29 Failure of Dams and Onsite Water Control/Storage Structures I

Not included ; Not included Not included FHRR Section 1.5 in DB in DB in DB Storm Surge Not included Not included Not included FHRR Section 1.5 in DB in DB in DB Seiche Not included Not included Not included FHRR Section 1.5 in DB in DB in DB Tsunam i Not included

• Not included Not included FHRR Section 1.5 in DB in DB in DB Ice-Induced Flooding No Impact No Impact No Impact FHRR Section 1.5.2 on the Site on the Site on the Site Identified Identified Identified Channel Migrations/Diversions Not included ! Not included Not included FHRR Section 1.5 in DB ' in DB in DB Note 1: Reported values are rounded to the nearest one-tenth of a foot.

Monticello Nuclear Generating Plant, Un it 1 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms for Use in the MSA Mechanism Stillwater Waves! Reevaluated Reference Elevation Run up Hazard Elevation Local Intense Precipitation 935.8 ft Minimal 935.8 ft FHRR Section 2.1.2 & Tables 5 and 6 NGVD29 NGVD29 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.

PKG ML16248A004; LTR: ML16248A003; ENCL: ML16245A720 *via email OFFICE NRR/JLD/JHMB/PM NRR/JLD/LA NRO/DSEA/RHM2/TR* NRO/DSEA/RHM2/BC*

NAME LKGibson Slent PChaput AR iveraVarona DATE 09/13/2016 09/ 9 /2016 09/1/2016 09/1/2016 OFFICE NRR/JLD/JHMB/BC (A) NRR/JLD/JHMB/PM NAME GBowman LKGibson DATE 09/ 15/2016 09/1612016