CNS-16-043, Additional Information Regarding Flood Hazard Reevaluation Report, Response to Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Forc

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Additional Information Regarding Flood Hazard Reevaluation Report, Response to Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force
ML16179A196
Person / Time
Site: Catawba  Duke Energy icon.png
Issue date: 06/23/2016
From: Henderson K
Duke Energy Carolinas
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
CNS-16-043
Download: ML16179A196 (5)
v • d • e


Text

,*

~:

Kelvin Henderson

~~DUKE Vice President

~ ENERGY~ Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 o: 803. 701.4251 f: 803.7013221 10 CFR 50.4 10 CFR 50.54(f)

CNS-16-043 June 23, 2016 Attention: Document Control Desk U. S. Nuclear Regulatory Commission Washington, D. C. 20555-001 Duke Energy Carolinas, LLC (Duke Energy)

Catawba Nuclear Station (CNS), Units 1 and 2 Docket Numbers 50-413 and 50-414 Renewed License Nos. NPF-35 and NPF-52

Subject:

Additional Information Regarding Flood Hazard Reevaluation Report, Response to Request for Information Pursuant to Title 10 of the Code of Federal Regulations .

50.54(f) regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012

References:

1. NRC Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 20,12 (ADAMS Accession No. ML12053A340)
2. NRC Letter, Prioritization of Response Due Dates for Request For Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Flooding Hazard Reevaluations for Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated May 11, 2012 (ADAMS Accession No. ML12097A509)
3. Duke Energy Letter, Flood Hazard Reevaluation Report, Response to NRC 10 CFR 50.54(f) Request for Additional Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, Dated March 12, 2014 (ADAMS Accession No. ML14077A054)
4. NRC Letter, Revised Interim Staff Response to Reevaluated Flood Hazards Submitted in Response to 10 CFR 50.54(f) Information Request - Flood-Causing Mechanism Reevaluation, dated December 21, 2015 (ADAMS Accession No. ML15352A192)

United States Nuclear Regulatory Commission Page 2 June 23, 2016

' 5. NUREG/CR-7046 (PNNL-20091 ), Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, Date Published: November 2011 (ADAMS Accession No. ML11321A195)

6. Nuclear Energy Institute (NEI), "Diverse and Flexible Coping Strategies (FLEX)

Implementation Guide," NEI 12-06, Revision 2, December 2015 (ADAMS Accession No. ML15348A015)

7. NRC Order EA-12-049*, "Issuance of Order to Modify Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events",

dated March 12, 2012 (ADAMS Accession No. ML12054A735)

Ladies and Gentlemen:

On March 12, 2012, the NRC issued Reference 1 to all power reactor licensees and holders of construction permits in active or deferred status. Enclosure 2 of Reference 1 requested that each licensee perform a reevaluation of external flooding sources and report the results in accordance with the NRC's prioritization plan (Reference 2). The Flooding Hazard Reevaluation Report (FHRR) for Catawba was provided by Reference 3. The FHRR shows that some flood levels exceed the Current Design Basis (COB) levels for Catawba. The increased levels are the result of newer methodologies and guidance which are applicable to new reactor reviews and typically exceed the methodologies and guidance used to establish the COB for existing plants.

By letter dated December 21, 2015 (Reference 4), the NRC provided a revised summary of the interim staff response to the reevaluated flood-causing mechanisms described in the FHRR for Catawba, as well as supplemental information resulting from requests for additional information and audits. The staff summary of the results from the review were provided in tables as an enclosure to the letter. Table 1 provides the COB flood hazard mechanisms flood levels. The reevaluated flood hazard mechanisms that exceed COB results are provided in Table 2. The NRC concluded that the reevaluated flood hazards information is suitable for assessments associated with Near-Term Task Force (NTTF) Recommendation 2.1 "Flooding" for Catawba, as well as the Mitigating Strategies Assessment (MSA) of the impact of the reevaluated flood hazard information on the mitigating strategies developed in respo.nse to NRC Order EA-12-049 (Reference 7).

NUREG/CR-7046 (Reference 5) defines a deterministic process for the evaluation of flooding impacts at a nuclear site as the Hierarchical Hazard Assessment (HHA) approach. This approach allows for a progressively refined stepwise estimation of site-specific flood hazards.

The HHA process allows licensees the option to refine simplified flooding evaluations, based on varying degrees of conservatism, to assess susceptibility to flooding.

An additional flood-hazard assessment of the combined effects flood-causing mechanism is warranted based on the initial estimated impacts of the simplified conservative analysis.

Although the FHRR has been submitted in response to the March 12, 2012, NRC request for information pursuant to the10 CFR 50.54(f) letter, Duke Energy intends to perform a more representative evaluation of the combined effects flooding mechanism, consistent with the HHA process.

United States Nuclear Regulatory Commission Page 3 June 23, 2016 The evaluation of this flooding mechanism is being refined using updated and site specific parameters to achieve a more accurate physics-based, but conservative, analysis of flooding.

Applied Weather Associates (AWA) was employed to reevaluate the Site Specific Probable Maximum Precipitation (SSPMP). Data used to determine rainfall values reported in Hydro-meteorological Report (HMR) 51 and 52 is more than 40 years old. The site specific study includes the analyses of storms, considering the unique characteristics of the watershed/site, and updates the storm database that were not included in these HMRs. The initial stage of the HHA process refined the generalized Probable Maximum Precipitation (PMP) found in HMR 51 with a site-specific study directly applicable to the Catawba-Wateree watershed. The SSPMP was used to develop and evaluate the Site Specific Probable Maximum Flood (SSPMF) for the Catawba-Wateree River Basin identified with the Cowans Ford and Wylie Dams. This PMP reanalysis has been completed and provides an updated PMP Catawba-Wateree River Basin specific analysis.

A second refinement involves using a more appropriate method to model precipitation losses to compute runoff in conjunction with Combined Effects, Appendix H, Section H.1 of NUREG 7046.

The precipitation losses used in computing the runoff in the Catawba FHRR are based on a common industry, empirical runoff infiltration method (Curve Number) developed by the Soil Conservation Service (SGS) for single precipitation events. The results reported in the 2014 FHRR allows for initial abstraction during the antecedent event but, as applied, did not allow abstraction during the second PMF event. This limitation leads to overly conservative results at Catawba. The SSPMF Constant Loss Rate (CLR) method allows for initial abstractions during back-to-back events leading to conservative but realistic and more accurate results at Catawba.

  • The second refinement will involve re-evaluating the infiltration losses on the Catawba-Wateree River Basin by applying the CLR method in lieu of the SGS method in the existing hydrologic model. This second refinement effort is currently underway. Based upon preliminary results from this refinement, it is expected that Section H.2 of NUREG 7046 Floods Caused by Seismic Dam Failures will now be the controlling Combined Effects scenario. Re-evaluation of this controlling scenario is also underway.

Nuclear Energy Institute (NEI) guidance document NEI 12-06, "Diverse and Flexible Coping Strategies (FLEX) Implementation Guide", Revision 2 (Reference 6), Appendix G, includes a methodology to perform a MSA with respect to the reevaluated flood hazards. The methodology provided by Appendix G will be employed to assess the impact of the flooding hazard reevaluations with respect to the guidance and strategies required by Order EA-12-049 (Reference 7). For the combined effects flooding mechanism, the updated combined effects flooding analysis will be included in the MSA submittal.

Duke Energy anticipates completing and submitting the MSA for Catawba by the end of the first quarter of 2017. The summary results of the SSPMF CLR method for the combined effects flooding mechanism will be included with the MSA submittal.

There are no regulatory commitments associated with this letter. Please address any comments or questions regarding this matter to Sherry Andrews at 803-701-3424.

United States Nuclear Regulatory Commission Page4 June 23, 2016 I declare under penalty of perjury that the foregoing is true and correct. Executed on June 23, 2016.

Sincerely, Kelvin Henderson, Vice President, Catawba Nuclear Station

United States Nuclear Regulatory Commission Page 5 June 23, 2016 xc:

C. Haney, Regional Administrator U.S. Nuclear Regulatory Commission, Region II Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, GA 30303-1257 W. M. Dean, Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 13 H16M 11555 Rockville Pike Rockville, MD 20852-2738 Michael D. Orenak, Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 0-8G9A 11555 Rockville Pike Rockville, MD 20852-2738 P.J. Bamford, Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 13 F_15 11555 Rockville Pike Rockville, MD 20852-2738 G.A. Hutto, Ill NRC Senior Resident Catawba Nuclear Station Justin Folkwein American Nuclear Insurers 95 Glastonbury Blvd., Suite 300 Glastonbury, CT 06033-4453

~:

Kelvin Henderson

~~DUKE Vice President

~ ENERGY~ Catawba Nuclear Station Duke Energy CN01VP I 4800 Concord Road York, SC 29745 o: 803. 701.4251 f: 803.7013221 10 CFR 50.4 10 CFR 50.54(f)

CNS-16-043 June 23, 2016 Attention: Document Control Desk U. S. Nuclear Regulatory Commission Washington, D. C. 20555-001 Duke Energy Carolinas, LLC (Duke Energy)

Catawba Nuclear Station (CNS), Units 1 and 2 Docket Numbers 50-413 and 50-414 Renewed License Nos. NPF-35 and NPF-52

Subject:

Additional Information Regarding Flood Hazard Reevaluation Report, Response to Request for Information Pursuant to Title 10 of the Code of Federal Regulations .

50.54(f) regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 2012

References:

1. NRC Letter, Request for Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Recommendations 2.1, 2.3, and 9.3, of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated March 12, 20,12 (ADAMS Accession No. ML12053A340)
2. NRC Letter, Prioritization of Response Due Dates for Request For Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) Regarding Flooding Hazard Reevaluations for Recommendation 2.1 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, dated May 11, 2012 (ADAMS Accession No. ML12097A509)
3. Duke Energy Letter, Flood Hazard Reevaluation Report, Response to NRC 10 CFR 50.54(f) Request for Additional Information Pursuant to Title 10 of the Code of Federal Regulations 50.54(f) regarding Recommendations 2.1, 2.3, and 9.3 of the Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, Dated March 12, 2014 (ADAMS Accession No. ML14077A054)
4. NRC Letter, Revised Interim Staff Response to Reevaluated Flood Hazards Submitted in Response to 10 CFR 50.54(f) Information Request - Flood-Causing Mechanism Reevaluation, dated December 21, 2015 (ADAMS Accession No. ML15352A192)

United States Nuclear Regulatory Commission Page 2 June 23, 2016

' 5. NUREG/CR-7046 (PNNL-20091 ), Design-Basis Flood Estimation for Site Characterization at Nuclear Power Plants in the United States of America, Date Published: November 2011 (ADAMS Accession No. ML11321A195)

6. Nuclear Energy Institute (NEI), "Diverse and Flexible Coping Strategies (FLEX)

Implementation Guide," NEI 12-06, Revision 2, December 2015 (ADAMS Accession No. ML15348A015)

7. NRC Order EA-12-049*, "Issuance of Order to Modify Licenses with Regard to Requirements for Mitigation Strategies for Beyond-Design-Basis External Events",

dated March 12, 2012 (ADAMS Accession No. ML12054A735)

Ladies and Gentlemen:

On March 12, 2012, the NRC issued Reference 1 to all power reactor licensees and holders of construction permits in active or deferred status. Enclosure 2 of Reference 1 requested that each licensee perform a reevaluation of external flooding sources and report the results in accordance with the NRC's prioritization plan (Reference 2). The Flooding Hazard Reevaluation Report (FHRR) for Catawba was provided by Reference 3. The FHRR shows that some flood levels exceed the Current Design Basis (COB) levels for Catawba. The increased levels are the result of newer methodologies and guidance which are applicable to new reactor reviews and typically exceed the methodologies and guidance used to establish the COB for existing plants.

By letter dated December 21, 2015 (Reference 4), the NRC provided a revised summary of the interim staff response to the reevaluated flood-causing mechanisms described in the FHRR for Catawba, as well as supplemental information resulting from requests for additional information and audits. The staff summary of the results from the review were provided in tables as an enclosure to the letter. Table 1 provides the COB flood hazard mechanisms flood levels. The reevaluated flood hazard mechanisms that exceed COB results are provided in Table 2. The NRC concluded that the reevaluated flood hazards information is suitable for assessments associated with Near-Term Task Force (NTTF) Recommendation 2.1 "Flooding" for Catawba, as well as the Mitigating Strategies Assessment (MSA) of the impact of the reevaluated flood hazard information on the mitigating strategies developed in respo.nse to NRC Order EA-12-049 (Reference 7).

NUREG/CR-7046 (Reference 5) defines a deterministic process for the evaluation of flooding impacts at a nuclear site as the Hierarchical Hazard Assessment (HHA) approach. This approach allows for a progressively refined stepwise estimation of site-specific flood hazards.

The HHA process allows licensees the option to refine simplified flooding evaluations, based on varying degrees of conservatism, to assess susceptibility to flooding.

An additional flood-hazard assessment of the combined effects flood-causing mechanism is warranted based on the initial estimated impacts of the simplified conservative analysis.

Although the FHRR has been submitted in response to the March 12, 2012, NRC request for information pursuant to the10 CFR 50.54(f) letter, Duke Energy intends to perform a more representative evaluation of the combined effects flooding mechanism, consistent with the HHA process.

United States Nuclear Regulatory Commission Page 3 June 23, 2016 The evaluation of this flooding mechanism is being refined using updated and site specific parameters to achieve a more accurate physics-based, but conservative, analysis of flooding.

Applied Weather Associates (AWA) was employed to reevaluate the Site Specific Probable Maximum Precipitation (SSPMP). Data used to determine rainfall values reported in Hydro-meteorological Report (HMR) 51 and 52 is more than 40 years old. The site specific study includes the analyses of storms, considering the unique characteristics of the watershed/site, and updates the storm database that were not included in these HMRs. The initial stage of the HHA process refined the generalized Probable Maximum Precipitation (PMP) found in HMR 51 with a site-specific study directly applicable to the Catawba-Wateree watershed. The SSPMP was used to develop and evaluate the Site Specific Probable Maximum Flood (SSPMF) for the Catawba-Wateree River Basin identified with the Cowans Ford and Wylie Dams. This PMP reanalysis has been completed and provides an updated PMP Catawba-Wateree River Basin specific analysis.

A second refinement involves using a more appropriate method to model precipitation losses to compute runoff in conjunction with Combined Effects, Appendix H, Section H.1 of NUREG 7046.

The precipitation losses used in computing the runoff in the Catawba FHRR are based on a common industry, empirical runoff infiltration method (Curve Number) developed by the Soil Conservation Service (SGS) for single precipitation events. The results reported in the 2014 FHRR allows for initial abstraction during the antecedent event but, as applied, did not allow abstraction during the second PMF event. This limitation leads to overly conservative results at Catawba. The SSPMF Constant Loss Rate (CLR) method allows for initial abstractions during back-to-back events leading to conservative but realistic and more accurate results at Catawba.

  • The second refinement will involve re-evaluating the infiltration losses on the Catawba-Wateree River Basin by applying the CLR method in lieu of the SGS method in the existing hydrologic model. This second refinement effort is currently underway. Based upon preliminary results from this refinement, it is expected that Section H.2 of NUREG 7046 Floods Caused by Seismic Dam Failures will now be the controlling Combined Effects scenario. Re-evaluation of this controlling scenario is also underway.

Nuclear Energy Institute (NEI) guidance document NEI 12-06, "Diverse and Flexible Coping Strategies (FLEX) Implementation Guide", Revision 2 (Reference 6), Appendix G, includes a methodology to perform a MSA with respect to the reevaluated flood hazards. The methodology provided by Appendix G will be employed to assess the impact of the flooding hazard reevaluations with respect to the guidance and strategies required by Order EA-12-049 (Reference 7). For the combined effects flooding mechanism, the updated combined effects flooding analysis will be included in the MSA submittal.

Duke Energy anticipates completing and submitting the MSA for Catawba by the end of the first quarter of 2017. The summary results of the SSPMF CLR method for the combined effects flooding mechanism will be included with the MSA submittal.

There are no regulatory commitments associated with this letter. Please address any comments or questions regarding this matter to Sherry Andrews at 803-701-3424.

United States Nuclear Regulatory Commission Page4 June 23, 2016 I declare under penalty of perjury that the foregoing is true and correct. Executed on June 23, 2016.

Sincerely, Kelvin Henderson, Vice President, Catawba Nuclear Station

United States Nuclear Regulatory Commission Page 5 June 23, 2016 xc:

C. Haney, Regional Administrator U.S. Nuclear Regulatory Commission, Region II Marquis One Tower 245 Peachtree Center Avenue NE, Suite 1200 Atlanta, GA 30303-1257 W. M. Dean, Director, Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 13 H16M 11555 Rockville Pike Rockville, MD 20852-2738 Michael D. Orenak, Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 0-8G9A 11555 Rockville Pike Rockville, MD 20852-2738 P.J. Bamford, Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mailstop 13 F_15 11555 Rockville Pike Rockville, MD 20852-2738 G.A. Hutto, Ill NRC Senior Resident Catawba Nuclear Station Justin Folkwein American Nuclear Insurers 95 Glastonbury Blvd., Suite 300 Glastonbury, CT 06033-4453

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