ML15211A482

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

ML15211A482
Person / Time
Site:	LaSalle
Issue date:	09/03/2015
From:	Tekia Govan Japan Lessons-Learned Division
To:	Bryan Hanson Exelon Generation Co, Exelon Nuclear
Minarik A, NRR/JLD, 415-6185
References
TAC MF3655, TAC MF3656
Download: ML15211A482 (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:

LASALLE COUNTY 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. MF3655 AND MF3656)

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. ML14079A417), flood hazard reevaluation report (FHRR) submitted by Exelon Generation Company, LLC (Exelon, the licensee) for LaSalle County, Units 1 and 2 (LaSalle), 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 March 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 reevaluated flood hazard Mechanisms; however, the reevaluated flood hazard mechanisms bounded by the current design basis (Table 1) are not included.

B. Hanson 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 LaSalle. 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 LaSalle 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 forthe 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.

Tekia Govan, Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-37 4

Enclosure:

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

ENCLOSURE:

SUMMARY

TABLES OF REEVALUATED FLOOD HAZARD LEVELS

LaSalle, Units 1 & 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA Mechanism Stillwater Waves/ Design Basis Reference Elevation Run up Hazard Elevation Local Intense Precipitation LIP Zone 1 (North portion of site) 710.1 ft MSL Not 710.1 ft MSL FHRR Section 2.2.1 applicable LIP Zone 2 (South portion of site) 710.3 ft MSL Not 710.3 ft MSL FHRR Section 2.2.1 applicable Streams and Rivers Riverine 521.8 ft MSL 0.7 ft 522.5 ft MSL USFAR Revision 19 Section 2.4.3 FHRR Section 2.2.2 Failure of Dams and Onsite I 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 PMF on Lake at Dike 704.3 ft MSL 2.9 ft 707.2 ft MSL FHRR Section 2.2.4 PMF on Cooling Lake at Plant 704.3 ft MSL 1.3 ft 705.6 ft MSL FHRR Section 2.2.4 PMF on Cooling Lake at Lake 704.3 ft MSL 1.8 ft 706.1 ft MSL FHRR Section 2.2.4 Screen House Seiche Not included Not included Not included FHRR Section 2.2.5 in DB in DB in DB Tsunami Not included Not included Not included FHRR Section 2.2.6 in DB in DB in DB

LaSalle, Units 1 & 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA r-- * * * * - - - - - - - - - - - - - - - - - - - - - - -----**--*~------------*------- --------**** ---- ---* "

! Mechanism Stillwater Waves/ Design Basis Reference i Elevation Run up Hazard I Elevation Ice-Induced Flooding No impact on No impact on No impact on the site the site the site FHRR Section 2.2.7 identified identified identified i

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.

LaSalle, Units 1 & 2 Table 2. Reevaluated Flood Hazards for Flood-Causing Mechanisms for Use in the MSA

---

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Stillv,;,-a-te_r_~*-***-w-a_v_e_s_/----~1-R_e_e-va_l_u._a te-d~--- _____R___e

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'1 Mechanism

! Elevation Run up Hazard

• , Elevation i---------------t------+------+-------+-------------~-~

I Local Intense Precipitation  !

I I

! LIP for entire site 710.8 MSL Minimal 710.8 MSL FHRR Section 3.1

! Storm Surge j Lake screen house 701.0 MSL 9.6 ft 710.6 MSL FHRR Section 3.4.4 I

i I Inlet structure 701.0 MSL 11.0 ft 712.0 MSL FHRR Section 3.4.4 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.

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

Sincerely,

/RN Tekia Govan, Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation Docket Nos. 50-373 and 50-374

Enclosure:

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

PUBLIC JLD R/F RidsNRRJLD Resource TGovan, NRR LQuinn-Willingham, NRO RidsNroDsea Resource RidsNrrDorllpl3-2 Resource RidsNrrDorl Resource RidsNrrPMLaSalle Resource RidsRgn3MailCenter Resource RidsN rrLASLent RidsOgcMailCenter Resource RidsOpaMail Resource RidsAcrsAcnw_MailCtr Resource CCook, NRO ARivera-Varona, NRO KErwin, NRO ACampbell, NRO MWillingham, NRO RRivera-Lugo, NRO BHarvey, NRO MShams, NRR ADAMS A ccess1on Nos.: Pklg. ML15232A190 LTR ML15211A482 ENCL ML15219A661 *via

. ema1*1 OFFICE NRR/JLD/JHMB/PM NRR/JLD/LA NRO/DSEA/RHM2/TR NRO/DSEA/RHM2/BC*

NAME AMinarik SLent PChaput ARivera-Varona DATE 8 / 25 /15 7/31/15 08/18/15 08/18/15 OFFICE OGG* NRR/JLD/JHMB/BC NRR/JLD/JHMB/PM NAME SClark MShams TGovan DATE 08/14/15 8 / 28 /15 9 / 3 /15 OFFICIAL RECORD COPY