ML15211A363

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

ML15211A363
Person / Time
Site:	Braidwood
Issue date:	09/03/2015
From:	Tekia Govan Japan Lessons-Learned Division
To:	Bryan Hanson Exelon Generation Co
Minarik A, NRR/JLD, 415-6185
Shared Package
ML15230A303	List: ML15211A363
References
TAC MF3895, TAC MF3896
Download: ML15211A363 (8)

Text

UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 September 3, 2015 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555

SUBJECT:

BRAIDWOOD STATION, UNITS 1 AND 2 - INTERIM STAFF RESPONSE TO REEVALUATED FLOOD HAZARDS SUBMITTED IN RESPONSE TO 10 CFR 50.54(f) INFORMATION REQUEST- FLOOD-CAUSING MECHANISM REEVALUATION (TAC NOS. MF3895 AND MF3896)

Dear Mr. Hanson:

The purpose of this letter is to provide a summary of the U.S. Nuclear Regulatory Commission (NRC) staff's assessment of the re-evaluated flood-causing mechanisms described in the March 12, 2014 (Agencywide Document Access and Management System (ADAMS) Accession No. ML14079A418), flood hazard reevaluation report (FHRR) submitted by Exelon Generation Company, LLC (Exelon, the licensee ) for Braidwood Station, Units 1 and 2 (Braidwood), as well as supplemental information resulting from requests for additional information and audits.

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 re-evaluate flood-causing mechanisms using present-day methodologies and guidance. Concurrently, 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 M.arch 30, 2015, the Commission provided Staff Requirements Memoranda (SRM) (ADAMS Accession No. ML15089A236) to COM-SECY-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 flood hazard information submitted by the licensee 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

B. Hanson reevaluated flood hazard mechanisms; however, the 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 Enclosure 1, 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 Braidwood. 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.

In addition, NEI 12-06 "Diverse and Flexible Coping Strategies (FLEX) Implementation Guide" is currently being revised. This revision will include a methodology to perform a Mitigating Strategies Assessment (MSA) with respect to the reevaluated flood hazards. Once this methodology is endorsed by the NRC, flood event duration parameters and applicable flood associated effects should be considered as part of the Braidwood 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.

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 NRC letter, "Coordination of Request for Information Regarding Flooding Hazard Reevaluation and Mitigating Strategies for Beyond Design Bases 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).

B. Hanson If you have any questions, please contact me at (301) 415-6197 or e-mail at Tekia.Govan@nrc.gov.

Sincerely,

~*~~~

Tekia Govan, Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket Nos. 50-456 and 50-457

Enclosure:

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

ENCLOSURE:

SUMMARY

TABLES OF REEVALUATED FLOOD HAZARD LEVELS

Braidwood Station, Units 1 and 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA i Mechanism Stillwater Waves/ Design Basis Reference Elevation Run up Hazard I

Elevation I Local-!;;tense Pre~ipitation 601.9 ft MSL Not 601.9 ft MSL FHRR Section 2.2.2 applicable Streams and Rivers PMF on Mazon River 582.0 ft MSL 2.0 ft 584.0 ft MSL FHRR Section 2.2.2 PMF on Cooling Pond 598.2 ft MSL 4.1 ft 602.3 ft MSL FHRR Section 2.2.4 Failure of Dams and Onsite Water Control/Storage Structures No impact on No impact on No impact on the site the site the site FHRR Section 2.2.3 identified identified identified Storm Surge No impact on No impact on No impact on the site the site the site FHRR Section 2.2.5 identified identified identified I i

I Seiche No impact on No impact on No impact on the site the site the site FHRR Section 2.2.5 identified identified identified L----

Tsunami No impact on No impact on No impact on the site the site the site FHRR Section 2.2.6 identified identified identified Ice-Induced Flooding Ice jam flooding - Near Intake 555.0 ft MSL Not 555.0 ft MSL FHRR Section 2.2.7 i applicable I I  !

Braidwood Station, Units 1 and 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA

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Mechanism Stillwater Waves/ Design Basis Reference Elevation Run up Hazard Elevation Channel Migrations/Diversions No impact on No impact on No impact on the site the site the site FHRR Section 2.2.8 identified identified identified Note: Reported values are rounded to the nearest one-tenth of a foot.

Braidwood Station, Units 1 and 2 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms for Use in the MSA 1----------~---

Mechanism Stillwater Waves/ Reevaluated Reference '

Elevation Run up Hazard Elevation Streams and Rivers I PMF on Cooling Pond 599.4 ft MSL 2.5 ft 601.9 ft MSL FHRR Table 4.4 I

I .

[ PMF on Mazon River 594.3 ft MSL 1.5 ft 595.8 ft MSL FHRR Table 4.3 I

I 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 ML15230A523; LTR: ML15211A363; ENCL: ML15230A236 *via email OFFICE NRR/JLD/JHMB/PM NRR/JLD/LA NRO/DSENRHM2/TR* NRO/DSENRHM2/BC*

NAME AMinarik Slent PChaput ARivera-Varona DATE 8126 /15 07/31/15 08/18/15 08/18/15 OFFICE NRR/JLD/JHMB/BC OGC** NRR/JLD/JHMB/PM NAME MShams SClark TGovan DATE 8 / 28 /15 08/14/15 9 / 3 /15