ML15229A148
| ML15229A148 | |
| Person / Time | |
|---|---|
| Site: | Byron  |
| Issue date: | 09/03/2015 |
| From: | Tekia Govan Japan Lessons-Learned Division |
| To: | Bryan Hanson Exelon Generation Co, Exelon Nuclear |
| Govan, Tekia NRR/JLD 415-6197 | |
| References | |
| TAC MF3893, TAC MF3894 | |
| Download: ML15229A148 (6) | |
Text
UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 Mr. Bryan C. Hanson Senior Vice President Exelon Generation Company, LLC President and Chief Nuclear Officer Exelon Nuclear 4300 Winfield Road Warrenville, IL 60555 September 3, 2015
SUBJECT:
BYRON 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. MF3893 AND MF3894)
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 Documents Access and Management System (ADAMS) Accession No. ML14079A416), flood hazard reevaluation report (FHRR) submitted by Exelon Generation Company, LLC (Exelon, the licensee) for Byron Station, Units 1 and 2 (Byron), 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 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 review in the table provided as an Enclosure to this letter. Table 1 provides the current design-basis flood hazard mechanisms. All the reevaluated flood hazard mechanisms at Byron are bounded by the current design-basis.
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 Byron. 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 Byron 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.
Because the reevaluated flood hazard mechanisms at Byron are bounded by the current design-basis, it is unnecessary for the licensee to perform an integrated assessment or focused evaluation, 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). Therefore, the NRC staff confirms that the licensee responded appropriately to Enclosure 2, of the 50.54(f) letter.
If you have any questions, please contact me at (301) 415-6197 or e-mail at Tekia.Govan@nrc.gov.
Docket Nos. 50-454 and 50-455
Enclosure:
Summary of Results of Flooding Hazard Re-Evaluation Report - ML15226A598 cc w/encl: Distribution via Listserv Tekia V. Govan, Project Manager Hazards Management Branch Japan Lessons-Learned Division Office of Nuclear Reactor Regulation
ENCLOSURE:
SUMMARY
TABLES OF REEVALUATED FLOOD HAZARD LEVELS
Byron Station, Units 1 & 2 Table 1. Current Design Basis Flood Hazards for Use in the MSA Mechanism Stillwater Waves/
Design Basis Reference I
Elevation Run up Hazard I
i Elevation I
Local Intense Precipitation 870.9 ft Not 870.9 ft FHRR Section 2.2.1 I
NGVD29 applicable NGVD29 Streams and Rivers 708.3 ft Not 708.3 ft FHRR Section 2.2.2 NGVD29 applicable NGVD29 Failure of Dams and Onsite Water Control/Storage Structures No impact on No impact on No impact on FHRR Section 2.2.3 the site the site the site identified identified identified Storm Surge Not included Not included Not included FHRR Section 2.2.4 in DB in DB in DB I
I Seiche
! I I
Not included Not included Not included FHRR Section 2.2.4 in DB in DB in DB Tsunami Not included Not included Not included FHRR Section 2.2.5 I
I
~-------
1 Ice-Induced Flooding I
No Impact No Impact I No Impact FHRR Section 2.2.6 I
Identified Identified Identified I
Channel Migrations/Diversions Not included Not included Not included FHRR Section 2.2.7 in DB in DB in DB i
I Note: Reported values are rounded to the nearest one-tenth of a foot.
PKG ML15243A462; LTR: ML15229A148; ENCL: ML15226A598 *via email OFFICE NRR/JLD/JHMB NRR/JLD NRO/DSEA/RHM2/TR*
NRO/DSEA/RHM2*
NAME TGovan Slent SBreithaupt ARivera-Vaona DATE 8/18/2015 8/18/2015 8/17/2015 8/17/2015 OFFICE NRR/JLD/JHMB NRR/JLD/JHMB/PM NAME MShams TGovan DATE 8/28/2015 9/ 3 /2015