ONS-2014-014, Oconee, Units 1, 2, and 3 - Response to Request for Additional Information Regarding Near-Term Task Force (NTTF) Recommendation 2.3, Flooding Walkdowns - Review of Available Physical Margin (APM) Assessments

Oconee, Units 1, 2, and 3 - Response to Request for Additional Information Regarding Near-Term Task Force (NTTF) Recommendation 2.3, Flooding Walkdowns - Review of Available Physical Margin (APM) Assessments

ML14034A105
Person / Time
Site:	Oconee
Issue date:	01/30/2014
From:	Batson S L Duke Energy Carolinas
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ONS-2014-014
Download: ML14034A105 (7)

Text

I Scott L. Batson bDUKE Vice President Oconee Nuclear Station ENERGY. Duke Energy ONOIVP 1 7800 Rochester lHy Seneca, SC 29672 o: 864.873.3274 ONS-2014-014

f. 864.873.4208 Scott. Batson@duke-energy.com January 30, 2014 ATTN: Document Control Desk 10 CFR 50.54 (f)U.S. Nuclear Regulatory Commission Washington, DC 20555 Duke Energy Carolinas, LLC (Duke Energy)Oconee Nuclear Station (ONS), Unit Nos. 1, 2, and 3 Docket Nos. 50-269, 50-270, and 50-287 Renewed License Nos. DPR-38, DPR-47, and DPR-55

Subject:

Response to Request for Additional Information Regarding Near-Term Task Force (NTTF) Recommendation 2.3, Flooding Walkdowns

-Review of Available Physical Margin (APM) Assessments

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-lchi Accident; dated March 12, 2012, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML12053A340).

2. NEI 12-07, Guidelines for Performing Verification Walkdown of Plant Flood Protection Features, Revision 0-A, dated May 2012.3. NRC Letter to Nuclear Energy Institute (NEI), Endorsement of Nuclear Energy Institute (NEI) 12-07, Guidelines for Performing Verification Walkdowns of Plant Flood Protection Features, dated May 31, 2012, (ADAMS Accession No. ML12144A142).

4. Duke Energy Letter, Flooding Walkdown Information Requested by 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 November 27, 2012.5. NRC letter, Request for Additional Information associated with Near-Term Task Force Recommendation 2.3, Flooding Walkdowns; dated December 23, 2013 (ADAMS Accession No. ML13325A891).

Ladies and Gentlemen:

On March 12, 2012, the Nuclear Regulatory Commission (NRC) issued Reference 1 requesting information pursuant to 10 CFR 50.54(f).

Enclosure 4 of that letter requested information associated with NTTF Recommendation 2.3 for Flooding Walkdowns.

Nuclear Energy Institute (NEI) 12-07 (Reference

2) provided walkdown guidance which was endorsed by NRC via letter dated May 31, 2012 (Reference 3). Oconee submitted its flooding walkdown report (Reference

4) modeled after Appendix D of the NEI 12-07 guidance document.Following the initial review of walkdown reports, the NRC staff conducted audits at a sampling of plant sites, These reviews and site audits, determined that additional information was necessary for the NRC to complete its assessments.

United States Nuclear Regulatory Commission Flood Walkdown APM RAI January 30, 2014 Page 2 By letter dated December 23, 2013 (Reference 5), the NRC requested additional information regarding the determination and documentation of Available Physical Margin (APM) during flooding walkdowns.

This letter requests that the response be provided no later than January 31, 2013.The response for Oconee Nuclear Site is enclosed.This letter contains no new, or revised, Regulatory Commitments.

If you have any questions regarding this submittal, please contact David Haile, Oconee Regulatory Affairs at 864-873-4742.

I declare under penalty of perjury that the foregoing is true and correct. Executed on January 30, 2014.Sincerely, Scott L. Batson Vice President Oconee Nuclear Station

Enclosure:

Oconee Nuclear Station Units 1, 2 and 3, Response to the NRC Request for Additional Information (RAI) Regarding Available Physical Margin (APM) during Flooding Walkdowns United States Nuclear Regulatory Commission Flood Walkdown APM RAI January 30, 2014 Page 3 cc: Mr. Victor McCree, Regional Administrator U.S. Nuclear Regulatory Commission

-Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303-1257 Mr. Eric Leeds, 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 Mr. Richard Guzman, Project Manager (ONS)(by electronic mail only)U.S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop O-8C2 Rockville, MD 20852 Mr. Eddy Crowe NRC Senior Resident Inspector Oconee Nuclear Station Enclosure Oconee Nuclear Station Units 1, 2 and 3 Response to the NRC Request for Additional Information (RAI)Regarding Available Physical Margin (APM) during Flooding Walkdowns E1 Enclosure Oconee Nuclear Station Units 1, 2, and 3 Response to the NRC Request for Additional Information Regarding Seismic Walkdowns Determination and documentation of available Physical margin (APM)

Background:

The NRC staff observed that several licensees did not consistently determine and/or document available physical margin (APM) in a manner that met the expected interpretation of NEI 12-07 during audits associated with review of the NTTF Recommendation

2.3 report

submittals.

APM is defined in Section 3.13 of NEI 12-07 and the process for obtaining and evaluating APM values is described in Section 5.8 of NEI 12-07. Consistent with NEI 12-07, a numerical value for APM should be determined and documented for every applicable flood protection feature (e.g., wall, penetration, berm, door, etc.). This would normally be a numerical value reflecting the difference between the licensing basis flood height at the location of the feature and the point at which the function of the flood protection feature is compromised (e.g., the top of a barrier or the height of the first unsealed penetration in a barrier) such that the resulting flood can affect a structures, systems, and components important to safety. Next, in accordance with Section 5.8 of NEI 12-07, if the APM appears to be small and the consequences of flooding appear to be significant, the licensee should enter the condition into the CAP and appropriate action be taken.While NEI 12-07 does not require that a specific numerical threshold value for "small" APM be defined for each site, doing so establishes a consistent basis for determining what instances need to be entered into the CAP. If a numerical APM value cannot be determined for any flood protection feature, the licensee should perform an assessment of the ability of the barrier to withstand the licensing basis flood plus the contribution of the additional water corresponding to the pre-established small-margin threshold value. If the barrier can withstand this flood, the APM for the feature is "not small" and further evaluation in accordance with Section 5.8 of NEI 12-07 is not required.

It is further noted that conclusions regarding "large" values of APM should be based on engineering evaluations or existing design documents.

Licensees should ensure that the process for APM determination and evaluation used during their flooding walkdowns is consistent with the guidance in NEI 12-07. The intent of this Request for Additional Information (RAI) is not to repeat the flooding walkdowns or perform an extensive revision of the walkdown record forms and other paperwork.

Instead the purpose is to verify or modify the process used to determine APM such that every site is aware of the margin at each of its flood protection features and take appropriate interim actions when the APM is small and the consequences are significant.

Instances where numerical values for APM were not determined, or where the basis for the APM was found to be questionable, should be rectified by either the documentation of a specific value or an explanation of why a non-numerical value is appropriate.

Requested Additional Information Please provide the following:

NRC RAI 1: Confirmation that the process for evaluating APM was reviewed;Response to RAI 1: A review of the process used to evaluate APMs at Oconee Nuclear Station has been completed.

E2 Enclosure Oconee Nuclear Station Units 1, 2, and 3 Response to the NRC Request for Additional Information Regarding Seismic Walkdowns NRC RAI 2: Confirmation that the APM process is now or was always consistent with the guidance in NEI 12-07 and discussed in this RAI;Response to RAI 2: The original walkdown effort did follow the guidance provided in NEI 12-07 and employed a consistent approach to evaluating if "small" margins existed. However, the approach for "small" margin was not defined and documented, as discussed in this RAI, at that time. The approach for "small" margin, as it was used to assess Available Physical Margin at Oconee Nuclear Station, has since been documented, and thus, the APM process is now consistent with both NEI 12-07 and the information discussed in this RAI.NRC RAI 3: If changes are necessary, a general description of any process changes to establish this consistency; Response to RAI 3: The change of incorporating a definition for small margin into the APM process was necessary to become consistent with the "Background" discussion in this RAI. Also, seals that were not evaluated in accordance with Approach A or B, as described in RAI 4, were entered into CAP for further evaluation of their APM. This action establishes consistency with the direction provided in RAI 4 below.It should be noted that documenting the definition of small margin did not change the assessment of margin classifications established in the original flooding walkdown report. The margin classification for seals did change, as discussed in RAI 4.NRC RAI 4: As a result of the audits and subsequent interactions with industry during public meetings, NRC staff recognized that evaluation of APM for seals (e.g., flood doors, penetrations, flood gates, etc.) was challenging for some licensees.

Generally, licensees were expected to use either Approach A or Approach B (described below) to determine the APM for seals: A. If seal pressure ratings were known, the seal ratings were used to determine APM (similar to example 2 in Section 3.13 of NEI 12-07). A numerical value for APM was documented.

No further action was performed if the APM value was greater than the pre-established small-margin threshold value. If the APM value was small, an assessment of "significant consequences" was performed and the guidance in NEI 12-07 Section 5.8 was followed.B. If the seal pressure rating was not known, the APM for seals in a flood barrier is assumed to be greater than the pre-established small-margin threshold value if the following conditions were met: (1) the APM for the barrier in which the seal is located is greater than the small-margin threshold value and (2) there is evidence that the seals were designed/procured, installed, and controlled as flooding seals in accordance with the flooding licensing basis. Note that in order to determine that the seal has been controlled as a flooding seal, it was only necessary to determine that the seal configuration has been governed by the plant's design control process since installation.

In this case, the APM for the seal could have been documented as "not small".E3 Enclosure Oconee Nuclear Station Units 1, 2, and 3 Response to the NRC Request for Additional Information Regarding Seismic Walkdowns As part of the RAI response, state if either Approach A or Approach B was used as part of the initial walkdowns or as part of actions taken in response to this RAI. No additional actions are necessary if either Approach A or B was used.If neither Approach A or B was used to determine the APM values for seals (either as part of the walkdowns or as part of actions taken in response to this RAI), then perform the following two actions: " Enter the condition into the CAP (note: it is acceptable to utilize a single CAP entry to capture this issue for multiple seals). CAP disposition of "undetermined" APM values for seals should consider the guidance provided in NEI 12-07, Section 5.8. The CAP disposition should confirm all seals can perform their intended safety function against floods up to the current licensing basis flood height. Disposition may occur as part of the Integrated Assessment.

If an Integrated Assessment is not performed, determine whether there are significant consequences associated with exceeding the capacity of the seals and take interim action(s), if necessary, via the CAP processes.

These actions do not need to be complete prior to the RAI response." Report the APM as "undetermined" and provide the CAP reference in the RAI response.Response to RAI 4: Neither Approach A nor B, as described above, were used to determine the APM values for seals and trench covers. The seals and trench covers described in the walkdown report are designed to minimize leakage but are not designed to be water tight. Also, the seals and trench covers were not specifically documented as licensing basis flood protection features for the Oconee Nuclear Station. If accessible, seals were inspected for degradation as part of the original walkdowns, and corrective actions were initiated if required.

In accordance with the RAI directions above, the seals have now been assigned an APM value of "undetermined" and entered into the CAP process (PIP 0-14-00268) for further evaluation of their available physical margin.E4