SBK-L-16073, Re-Evaluated Bounding Flood Elevation for Riverine Flooding
| ML16137A504 | |
| Person / Time | |
|---|---|
| Site: | Seabrook  |
| Issue date: | 05/10/2016 |
| From: | Ossing M NextEra Energy Seabrook |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| SBK-L-16073 | |
| Download: ML16137A504 (2) | |
Text
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Seabrook Station NEXTera.
ENERGYe SEABROOK May 10, 2016 SBK-L-16073 Docket No. 50-443 Re-evaluated Bounding Flood Elevation for Riverine Flooding By letter dated September 25, 2015, NextEra Energy, LLC (NextEra) provided its Flood Hazard Reevaluation Report (FHRR) for Seabrook Station in response to Enclosure 2 of the U.S.
Nuclear Regulatory Commission (NRC) request for information pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.54(f) (hereafter referred to as the 50.54(f) letter) dated March 12, 2012. The NextEra response contained information related to each re-evaluated flood-causing mechanism that is currently being reviewed by the NRC.
Due to ongoing audit discussions between the NRC staff and NextEra, it is necessary to provide the re-evaluated flood elevations associated with the Riverine (Streams and Rivers) flood-causing mechanism.
The re-evaluated bounding flood elevation for Riverine Flooding is a stillwater elevation of
+5.32 feet Plant Datum (ft-Plant Datum) (+4.55 feet North American Vertical Datum of 1988
[ft-NAVD88]), as determined in Calculation FPL-081-CALC-016, Revision 1, "Probable Maximum Storm Surge (PMSS), Wave Runup, Combined Effects, and Low Water Calculation."
Review of Figure 7.2 of the calculation suggests that peak Probable Maximum Flood (PMF) water surface elevation (WSEL) was insensitive to higher PMF flow contributions. Two physical reasons were identified for the insensitivity: 1) the small PMF flow contribution relative to the tidal flow through Hampton Harbor inlet and 2) the hypsometry of the Harbor and contributing channels, especially at high tide levels. Given the large available physical margin between the peak PMF WSEL and site grade at +20.0 ft-Plant Datum(+ 19.2 ft_NAVD88), the conservatisms in the evaluation, and the insensitivity in peak PMF WSELs to increased flow rates, it can be concluded that adjusting various PMF flood model parameters (i.e., sensitivity analysis) likely would yield no adverse impact with respect to site flooding.
NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874
'""tJ.S. Nuclear Regulatory Commission SBK-L-16073/Page 2 If you have any questions or require additional information, please contact me at (603) 773-7512.
Sincerely, NextE a Energy Sefbrook, LLC cc:
NRC Region I Administrator NRC Project Manager, Project Directorate 1-2, NRC Senior Resident Inspector
U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001 Seabrook Station NEXTera.
ENERGYe SEABROOK May 10, 2016 SBK-L-16073 Docket No. 50-443 Re-evaluated Bounding Flood Elevation for Riverine Flooding By letter dated September 25, 2015, NextEra Energy, LLC (NextEra) provided its Flood Hazard Reevaluation Report (FHRR) for Seabrook Station in response to Enclosure 2 of the U.S.
Nuclear Regulatory Commission (NRC) request for information pursuant to Title 10 of the Code of Federal Regulations (10 CFR), Part 50, Section 50.54(f) (hereafter referred to as the 50.54(f) letter) dated March 12, 2012. The NextEra response contained information related to each re-evaluated flood-causing mechanism that is currently being reviewed by the NRC.
Due to ongoing audit discussions between the NRC staff and NextEra, it is necessary to provide the re-evaluated flood elevations associated with the Riverine (Streams and Rivers) flood-causing mechanism.
The re-evaluated bounding flood elevation for Riverine Flooding is a stillwater elevation of
+5.32 feet Plant Datum (ft-Plant Datum) (+4.55 feet North American Vertical Datum of 1988
[ft-NAVD88]), as determined in Calculation FPL-081-CALC-016, Revision 1, "Probable Maximum Storm Surge (PMSS), Wave Runup, Combined Effects, and Low Water Calculation."
Review of Figure 7.2 of the calculation suggests that peak Probable Maximum Flood (PMF) water surface elevation (WSEL) was insensitive to higher PMF flow contributions. Two physical reasons were identified for the insensitivity: 1) the small PMF flow contribution relative to the tidal flow through Hampton Harbor inlet and 2) the hypsometry of the Harbor and contributing channels, especially at high tide levels. Given the large available physical margin between the peak PMF WSEL and site grade at +20.0 ft-Plant Datum(+ 19.2 ft_NAVD88), the conservatisms in the evaluation, and the insensitivity in peak PMF WSELs to increased flow rates, it can be concluded that adjusting various PMF flood model parameters (i.e., sensitivity analysis) likely would yield no adverse impact with respect to site flooding.
NextEra Energy Seabrook, LLC, P.O. Box 300, Lafayette Road, Seabrook, NH 03874
'""tJ.S. Nuclear Regulatory Commission SBK-L-16073/Page 2 If you have any questions or require additional information, please contact me at (603) 773-7512.
Sincerely, NextE a Energy Sefbrook, LLC cc:
NRC Region I Administrator NRC Project Manager, Project Directorate 1-2, NRC Senior Resident Inspector