ML11305A091

Response to Request for Additional Information Long-Term Questions - Restart Readiness Determination Plan

ML11305A091
Person / Time
Site:	North Anna
Issue date:	10/28/2011
From:	Grecheck E Virginia Electric & Power Co (VEPCO)
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
11-577B
Download: ML11305A091 (14)

Text

VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 October 28, 2011 10 CFR 100, Appendix A U.S. Nuclear Regulatory Commission Serial No.: 11-577B Attention: Document Control Desk NL&OS/GDM RO Washington, DC 20555 Docket Nos.: 50-338/339 License Nos.: NPF-4/7 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)

NORTH ANNA POWER STATION UNITS 1 AND 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI)

LONG-TERM QUESTIONS - RESTART READINESS DETERMINATION PLAN By letters dated September 28, October 6 and October 13, 2011, and by email dated October 12, 2011, the NRC requested additional information regarding Dominion's Restart Readiness Determination Plan for North Anna Power Station following the August 23, 2011 Central Virginia earthquake. These documents included requests for information associated with both prior-to-restart and post-restart (i.e., long-term) actions.

The purpose of this letter is to address the remaining NRC questions associated with post-restart actions that have not been addressed in Dominion's previous submittals.

Dominion's responses to these questions are provided in the attachment. The specific NRC RAI letter/conference call date, the associated NRC technical review branch, and the corresponding questions being answered are listed below for reference.

NRC Technical NRC RAI Letter Date Rev Review Bnch Branch RAI Questions NRC Letter dated September 28, 2011 EMCB (Snubbers) Q1 NRC Letter dated October 6, 2011 EMCB (Structures) Qs 36 and 37 Licensing Q3 NRC Letter dated October 13, 2011 EMCB (Piping) Qs 2 and 3 EMCB (Pumps and Q Valves)

NRC Conference Call on October 20, 2011 EMCB (Seismic Q1 Instrumentation) 4kcoD

Serial No. 11-577B Docket Nos. 50-338/339 Page 2 of 3 If you have any questions or require additional information, please contact Mr. Gary D.

Miller at (804) 273-2771 or Mr. Thomas Shaub at (804) 273-2763.

Sincerely, E. S. Grecheck Vice President - Nuclear Development Attachments:

1. Response to NRC Request for Additional Information (RAI), Long-Term Questions - Restart Readiness Determination Plan

2. Commitments contained in this letter VIK L.HULL Notary Public Conumonwlth of Virginia [

140542 COMMONWEALTH OF VIRGINIA ) JMy Commision Expires May 31, 2014 COUNTY OF HENRICO )

The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by E. S. Grecheck who is Vice President - Nuclear Development, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that Company, and that the statements in the document are true to the best of his knowledge and belief.

Acknowledged before me this 6 2 8"day of 2011.

My Commission Expires:. 31, oJ&O/4*

Notary Public

Serial No. 11-577B Docket Nos. 50-338/339 Page 3 of 3 cc: Regional Administrator U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave. NE Suite 1200 Atlanta, Georgia 30303-1257 NRC Senior Resident Inspector North Anna Power Station M. Khanna NRC Branch Chief- Mechanical and Civil Engineering U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9E3 11555 Rockville Pike Rockville, MD 20852-2738 R. E. Martin NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 P. G. Boyle NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G-9A 11555 Rockville Pike Rockville, MD 20852-2738 J. E. Reasor, Jr.

Old Dominion Electric Cooperative Innsbrook Corporate Center 4201 Dominion Blvd.

Suite 300 Glen Allen, Virginia 23060

Serial No. 11-577B Docket Nos. 50-338/339 Attachment I Response to NRC Request for Additional Information (RAI)

Long-Term Questions - Restart Readiness Determination Plan Virginia Electric and Power Company (Dominion)

North Anna Power Station Units 1 and 2

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 1 of 8 Response to NRC Request for Additional Information (RAI)

Long-Term Questions - Restart Readiness Determination Plan

Background

By letters dated September 28, October 6, and October 13, 2011, and by email dated October 12, 2011, the NRC requested additional information regarding Dominion's Restart Readiness Determination Plan for North Anna Power Station following the August 23, 2011 Central Virginia earthquake. These documents included requests for information associated with both prior-to-restart and post-restart (i.e., long-term) actions.

The purpose of this letter is to address the remaining NRC questions associated with post-restart actions that have not been addressed in Dominion's previous responses, as well as subsequent questions that arose during clarifying conference calls. Dominion's response to these questions is provided below.

NRC LETTER DATED SEPTEMBER 28, 2011 EMCB - Snubbers

1. Please confirm that analyses will be performed to ensure the snubbers are designed (with appropriatefactors of safety) to withstand loads comparable to or greater than that observed during the August 23, 2011 earthquake.

Dominion Response Snubber load acceptance criteria are based on allowable design load criteria. For small bore hydraulic snubbers used at North Anna Power Station, the allowable design load is typically 30% to 50% less than the faulted allowable loading provided by the manufacturer. Even if the assumption is made that the August 23, 2011 earthquake fully developed design type loading conditions in the piping systems, and assuming that those loads were 20% above the design basis earthquake loading, there is still substantial margin available to snubber failure. Furthermore, snubbers are available in discrete sizes, with discrete allowable loads. It is Dominion's practice to select the next larger size snubber based on the calculated design load. The difference between the calculated design load and load rating of the next largest size snubber provides additional margin to the maximum capability of a snubber. Based on the above, no additional analysis is required to ensure snubber design is adequate.

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 2 of 8 NRC LETTER DATED OCTOBER 6, 2011

36. In order to better define site-specific ground motion or Ground Motion Response Spectrum, the licensee is to confirm its understanding of the seismic source characteristicsof the August 23, Mineral, Virginia earthquake in terms of its faulting mechanism, geometry, recurrence intervaland maximum magnitude.

Dominion Response The following information is taken from the USGS Earthquake Hazards Program website (http://earthquake.usqs.qov/) to develop an understanding of the August 23, 2011 seismic event. The quake epicenter was located at 37.9360 N, 77.933' W, approximately 18 km (11 miles) from.the North Anna Power Station. In the tectonic summary, the USGS indicates that the earthquake could not be causally associated with a currently mapped fault, but that it originated from a reverse or compression fault with a north or northeast striking plane. Earthquake magnitude estimates for the August 23, 2011 event range from 5.7 to 5.8, depending upon the calculation methodology used.

According to the USGS, accurate estimates of the probable fault rupture geometry will not be understood until longer term studies have been completed. The recurrence interval for this event cannot be stated with any degree of certainty at this time.

37.Because of the closeness of the August 23 earthquake to the NAPS site, and possible reverse faulting mechanism for the earthquake, the licensee is to confirm if there is any potential special ground motion effect due to the relative locations of the fault and the site (for example, a hanging wall effect from a reverse fault).

Dominion Response The scientific community has not yet completed a full evaluation of the August 23, 2011 earthquake as of this time. We have been consulting with the Department of Geosciences at Virginia Polytechnic Institute and State University on this issue and will provide an update regarding any special ground motion effects by March 31, 2012.

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 3 of 8 NRC LETTER DATED OCTOBER 13, 2011 Licensing Question

3. The staff requests that the licensee describe its long term plans for revaluating its design/licensingbasis and updating the Final Safety Analysis Report for NAPS, Units I and 2. Further, the staff requests that the licensee provide a schedule for completion of these items and a justification for the proposed schedule.

Dominion Response Dominion will not be re-evaluating the design basis. Consistent with EPRI NP-6695, Dominion plans to perform ,a seismic analysis of the recorded August 23, 2011 seismic event, which includes: (1) developing floor response spectra at various building levels based on recorded input motion, (2) assessing new floor spectra for exceedances with the design base floor spectra, and (3) evaluating selected equipment based on exceedances identified with the new floor spectra. These evaluations are intended to confirm that no undetected damage was sustained.

Dominion also plans to revise the North Anna Power Station Updated Final Safety Analysis Report (UFSAR) to document: 1) the recorded August 23, 2011 seismic event,

2) a summary of the evaluation and results of the seismic analysis of the recorded event completed per RG. 1.1.67/EPRI NP-6695, 3) design controls on the seismic margin management plan, and 4) incorporation of Regulatory Guide (RG)'1.166, "Pre-Earthquake Planning and Immediate Nuclear Power Plant Operator Post-Earthquake Actions," and 1.167, "Restart of a Nuclear Power Plant Shut Down by a Seismic Event,"

into the North Anna licensing basis. These actions will be completed as indicated in to this letter.

A detailed discussion of the long term Seismic Margin Management Plan is provided in the response to EMCB Question 3 below.

Mechanical and Civil Engineering Branch Questions

2. Discuss the method which will be used to identify welds for inspections and identify the type of inspections that will be performed for pre-restartand post-restart.

Dominion Response Pre-restart Weld Inspections - As noted in the response to the NRC's questions associated with plant piping systems, as well as the subsequent clarifications to those responses, contained in Dominion letters dated October 10 and 18, 2011 (Serial Nos.

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 4 of 8 11-577 and 11-577A, respectively), piping welds were visually inspected as part of the system detailed inspections that were performed on the accessible portions of the safety related and non-safety related plant piping systems. No indication of weld leaks or earthquake related damage was identified during these comprehensive inspections.

In addition, as discussed in Dominion letter dated September 27, 2011 (Serial No.

11-520A), to provide further assurance that safety related pipe welds had not sustained earthquake induced damage, a sample of system piping welds that were considered to be susceptible to damage from a seismic event were selected and inspected using nondestructive examination (NDE). To select the pipe welds for inspection, a review of industry earthquake experience was performed to identify piping vulnerabilities (Reference EPRI LR-2008-008, EPRI-1019199). Pipe welds were selected in areas that had potential for strong anchor movements. As a result, pipe welds were selected in reactor coolant system (RCS) loop drain piping, containment penetration area piping, and service water (SW) tie-in vault piping. A number of safety related piping welds and supports in these areas were selected for NDE. The welds were examined using liquid penetrant or magnetic particle examination techniques. The examinations were completed with satisfactory results, i.e., no earthquake induced flaws were identified. A table of the specific welds examined, examination method used, examination results and the associated ASME Code Category is provided in the September 27, 2011 letter (Serial No. 11-520A).

Post-restart Weld Inspections - As required by ASME Section XI, and in accordance with North Anna's Risk-Informed Inservice Inspection Program, a certain number of welds are inspected each inspection period, to ensure that piping and component integrity is being maintained. The need for additional post-restart weld inspections, if any, will be determined by a sampling review that will be conducted in accordance with RG 1.167 and EPRI NP-6695, "Guidelines for Nuclear Plant Response to an Earthquake." Specifically, Dominion will follow the guidance of EPRI NP-6695, Section 6.3, in conducting analytical evaluations of the effects of the August 23, 2011 earthquake on piping systems and components. These evaluations will provide additional assurance that North Anna can operate safely in the long-term and is capable of withstanding a second earthquake. Any corrective measures, such as additional weld inspections/examinations that may be considered necessary as a result of these additional evaluations, would be implemented on a case by case basis. As discussed in the EPRI NP-6695 guidance, inspections would be performed if the analytical evaluations for piping and supports predict that faulted level stresses would have been exceeded because of the August 23, 2011 earthquake. The type of inspection performed would be based on the specifics of the predicted exceedance.

3. Discuss the post-restart(i.e., long-term) actions in place (i.e., those included within the corrective action program) to evaluate seismically qualified piping and pipe supports, including those SSCs discussed on pages 4 and 5 of the September 17, 2011, submittal, to demonstrate compliance with the licensing and design basis

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 5 of 8 and/or applicable design basis code criteria/requirements,when these evaluations consider seismic loadings, (OBE and DBE) derived from the August 23, 2011, seismic event, combined with all other applicable load cases.

Dominion Response As noted above, Dominion will follow the guidance of EPRI NP-6695, Section 6.3 in conducting analytical evaluations of the effects of the August 23, 2011 earthquake on piping systems and components. These evaluations will provide additional assurance that North Anna can operate safely in the long-term and is capable of withstanding a second earthquake. Any corrective measures, such as additional focused inspections that are considered necessary as a result of these additional evaluations, would be implemented on a case by case basis.

The In-Structure Response Spectra (ISRS) for the August 23, 2011 earthquake for the Containment, Auxiliary Building, and other safety related structures, will be developed based on actual time-histories recorded during this event. The ISRS will be used both in analytical evaluations performed pursuant to EPRI NP-6695, Section 6.3 and in evaluating any subsequent modifications as described below. It is expected that the development of the ISRS for the August 23, 2011 earthquake will be completed within about one year. In the interim, current design practices, which have provided significant seismic margins to the station as demonstrated by the extensive inspections and testing of the station to date, will be followed. For plant modifications made after August 23, 2011, relevant information (e.g., the existing margins in pipe stress and support capability in the analyses of record, or existing margins in shake-table testing, and available recorded seismic data) will be used to evaluate if the August 23, 2011 earthquake could be accommodated by the proposed modified system and equipment, or if additional analysis or modification is warranted. Modifications of the type described below will be tracked and checked against the location specific ISRS for the August 23, 2011 earthquake as the location specified ISRS become available.

Desiqn Changes Dominion will revise the design change process for North Anna Power Station to require an assessment of seismic margins based on the August 23, 2011 earthquake. The applicable codes, standards and other criteria for such evaluations will be the same as those being used for the design basis; with the exception that when evaluating SSCs for the August 23, 2011 earthquake, an appropriate damping value, such as 5% of critical damping, can be used for analyzing piping systems, supports and equipment anchorage. This approach is in accordance with the industry guidance provided in EPRI Report NP 6041-SL and the Seismic Qualification Utility Group (SQUG) Generic Implementation Procedure (GIP).

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 6 of 8 As an example, piping systems and supports will be evaluated as follows:

(1) For a minor modification (e.g., change of a valve or components, piping supported by chart method, or other minor changes which can be reviewed with the design basis analysis) the consideration of the August 23, 2011 earthquake will be evaluated by comparing with the available margins in the design basis analysis for the design basis earthquake (DBE) case only. This evaluation will be documented as an attachment to the calculation revision or addendum that documents the modified piping system.

(2) For a major modification involving a piping system, when a new analysis of record is required, the analysis will be performed using the design basis ISRS. The following additional evaluations options will be used to appropriately consider the August 23, 2011 earthquake:

• The analysis will be reviewed with respect to the ISRS generated for the August 23, 2011 earthquake. If there is sufficient margin by inspection and judgment that considers the natural frequencies of the piping system and the entire frequency range of the ISRS from the August 23, 2011 earthquake, then explicit analysis using the August 23, 2011 ISRS may not be needed.

• Depending upon the available margin in the design base analysis, an additional analysis may be performed using the ISRS for the August 23, 2011 earthquake to augment the DBE case.

" Alternatively, an analysis may be performed using the enveloped DBE and the ISRS from the August 23, 2011 earthquake.

The engineering basis for selecting an option and the evaluated results will be documented.

New and Replacement Equipment New and replacement safety related equipment will be seismically qualified as follows:

(1) For equipment qualified by shake-table testing, the DBE required response spectra (RRS) will be based on the envelope of the design basis ISRS and the ISRS developed from the August 23, 2011 event. Additionally, the test response spectra (TRS) will envelop this. new RRS by a margin of 10% as required by IEEE Std. 323-1974.

(2) For equipment qualified by analysis, the analysis will be performed using the design basis ISRS. The analysis will also be reviewed with respect to the ISRS generated for the August 23, 2011 earthquake. Depending upon the available margin, a

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 7 of 8 separate analysis may be performed using the ISRS from the August 23, 2011 earthquake. Alternatively, an analysis may be performed using the enveloped DBE and the August 23, 2011 event spectra. If there is sufficient margin by inspection and judgment that considers the natural frequencies of the equipment and the spectral values in the entire frequency range of the ISRS from the August 23, 2011 earthquake, explicit analysis using these ISRS may not be needed. In this case, the engineering basis of such judgment will be documented.

(3) For items that use seismic experienced based evaluations, the SQUG Generic GIP, Revision 3 with exceptions as noted in the North Anna UFSAR and applicable Dominion Standard will be used. Since the containment basemat spectra from the August 23, 2011 earthquake are enveloped by the SQUG bounding spectra, there is no impact of this earthquake on the 20 equipment classes of the GIP. However, the anchorage and load path calculations will be done as outlined in step (2) above. The same methodology is planned to be used for conduit, cable trays and raceways.

(4) For equivalency evaluations involving like-for-like replacement or evaluation of seismically insensitive or rugged items, no additional evaluation from the ISRS based on the August 23, 2011 earthquake is required.

This program will be maintained until NRC and industry efforts to determine the appropriate actions to address updated earthquake predictions and recommendations based on Fukushima Task Force and/or GI-199 have been determined and implemented.

Pumps and Valves 4 Please discuss your planned approach and evaluations to confirm that appropriate design factors of safety are maintained if safety-related pumps and valves are subjected to seismic acceleration loads comparable to those observed during the August 23, 2011 earthquake. Provide your response for each unit separately.

Dominion Response Although the question above requests separate responses for each unit, the answer for both units is the same. A significant amount of inspection and testing of plant safety related pumps and valves has been performed to ensure that they are capable of performing their intended safety functions post earthquake. Safety margins are maintained if components function within design limits after a seismic event.

Post-earthquake inspection and testing has shown that installed safety related equipment experienced no loss of margin and would be capable of withstanding a second earthquake should it occur. A detailed discussion of the testing and inspection effort for these components is provided in the responses to the Inservice Testing

Serial No. 11-577B Docket Nos. 50-338/339 Attachment Page 8 of 8 Program questions contained in Dominion's letters dated October 20 and 28, 2011 (Serial Nos. 11 -566C and 11-566D).

In addition, as noted in the response to Question 3 above, a long term Seismic Margin Management Plan has been developed to address the impact of the August 23, 2011 earthquake on the design change process and, the procurement of new and replacement equipment.

NRC CONFERENCE CALL DATED OCTOBER 20, 2011 Temporary Seismic Instrumentation

1. Describe how plant seismic instrumentation will provide the necessary earthquake information for determining whether an OBE has occurred. Provide the free field OBE response settings for the temporary seismic monitoring instrumentation and whether this equipment will be used for making plant shutdown recommendations for OBE exceedance.

Dominion Response In station Abnormal Procedure 0-AP-36, Seismic Event, the OBE is based on the containment foundation rock spectra and the readings from the Kinemetrics and Engdahl seismic instrumentation. The OBE settings for this instrumentation are:

Vertical 0.04 g Horizontal 0.06 g In station General Engineering Procedure 0-GEP-30.1, Free-Field Seismic Instrumentation Data Retrieval and Analysis, the OBE is based on soil spectra and the readings from the temporary, free-field seismic instrumentation. The OBE settings for this instrumentation are:

Vertical 0.06 g Horizontal 0.09 g Following confirmation of a seismic event, the Main Control Room operator will follow 0-AP-36 which directs the operator to the control room indication for determination of whether the OBE has been exceeded. As required by procedure, within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />, the Shift Manager or Station Emergency Manager will be provided with the free-field monitor seismic event data. Indication from any of the seismic instrumentation (i.e., Kinemetrics, Engdahl, or temporary free field seismic equipment) that the OBE has been exceeded requires both Units 1 and 2 to be shut down.

Serial No. 11-577B Docket Nos. 50-338/339 Attachment 2 Response to NRC Request for Additional Information (RAI)

Long-Term Questions - Restart Readiness Determination Plan Commitments Virginia Electric and Power Company (Dominion)

North Anna Power Station Units 1 and 2

Serial No. 11-577B Docket Nos. 50-338/339 Page 1 of 1 North Anna Power Station Commitments Commitment Completion

1. Dominion will provide an update regarding any Complete by March 31, 2012 special ground motion effects

2. Dominion will implement a long term plan to address the impact of the August 23, 2011 earthquake on procurement of new and Complete byDecember31 2011 replacement equipment and the design change process.

3. Dominion will revise the North Anna Updated Final Safety Analysis Report to document:

a. the recorded August 23, 2011 seismic Complete by April 30, 2012 event

b. a summary of the evaluation and results of Complete by April 30, 2013 the seismic analysis of the recorded event completed per RG. 1.1.67/EPRI NP-6695,

c. design controls on the seismic margin Complete by April 30, 2012 management

d. incorporation of Regulatory Guide (RG) Complete by December31, 2012 1.166, "Pre-Earthquake Planning and (subject to receipt of seismic Immediate Nuclear Power Plant Operator monitoring equipment and outage Post-Earthquake Actions," and 1.167, schedules)

"Restart of a Nuclear Power Plant Shut Down by a Seismic Event," into the North Anna licensing basis