NG-11-0407, Response to Second Request for Additional Information Related to an Amendment to Adopt Technical Specifications Task Force Traveler TSTF-425, Revision 3, to Relocate Specific Surveillance Frequencies to a Licensee Controlled Program

Response to Second Request for Additional Information Related to an Amendment to Adopt Technical Specifications Task Force Traveler TSTF-425, Revision 3, to Relocate Specific Surveillance Frequencies to a Licensee Controlled Program

ML113050120
Person / Time
Site:	Duane Arnold
Issue date:	11/01/2011
From:	Wells P NextEra Energy Duane Arnold
To:	Office of Nuclear Reactor Regulation, Document Control Desk
References
NG-11-0407, TSTF-425, Rev 3
Download: ML113050120 (5)

Text

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DUANE ARNOLD November 1, 2011 NG-11-0407 10 CFR 50.90 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001 Duane Arnold Energy Center Docket No. 50-331 Renewed Gp. License No. DPR-49 Response to Second Request for Additional Information Related to an Amendment to Adopt Technical Specifications Task Force Traveler TSTF-425, Revision 3, to Relocate Specific Surveillance Frequencies to a Licensee Controlled Program

References:

1) License Amendment Request (TSCR-120): Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program (TSTF-425, Rev.

ID, NG-11-0037, dated February 23,2011

2) Clarification of Information Contained in License Amendment Request (TSCR-120): Application for Technical Specification Change Regarding Risk-Informed Justification for the Relocation of Specific Surveillance Frequency Requirements to a Licensee Controlled Program (TSTF-425, Rev. 3), NG 0135, dated April 20,2011

3) Response to Request for Additional Information Related to an Amendment to Adopt Technical Specifications Task Force Traveler TSTF-425, Revision 3, to Relocate Specific Surveillance Frequencies to a Licensee Controlled Program, NG-11-0299, dated August 15, 2011 In the Reference 1 letter, as clarified by Reference 2, NextEra Energy Duane Arnold, LLC (hereafter NextEra Energy Duane Arnold) requested a revision to the Technical Specifications (TS) for the Duane Arnold Energy Center (DAEC) pursuant to 10 CFR 50.90. Subsequently, the NRC Staff requested, via facsimile and electronic mail, NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324

Document Control Desk NG-11-0407 Page 2 of 2 additional information regarding that application. Reference 3 provided the originally requested information.

As a result of discussions with the Staff held on September 15, 2011, the NRC has requested additional information regarding the Reference 3 responses, transmitted via email (ADAMS Accession Number ML11279A024). The Attachment to this letter contains that requested information.

This additional information does not impact the 10 CFR 50.92 evaluation of "No Significant Hazards Consideration" previously provided in the referenced application.

This letter makes no new commitments or changes to any existing commitments.

If you have any questions or require additional information, please contact Steve Catron at 319-851-7234.

I d clare under penalty of perjury that the foregoing is true and correct.

xe uted on November 1, 2011.

Pe ells Vice President, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC

Attachment:

Response to Second Request for Additional Information Related to an Amendment to Adopt Technical Specifications Task Force Traveler TSTF-425, Revision 3, to Relocate Specific Surveillance Frequencies to a Licensee Controlled Program cc: M. Rasmusson (State of Iowa)

Attachment to NG-11-0407 Page 1 of 3 RESPONSE TO SECOND REQUEST FOR ADDITIONAL INFORMATION RELATED TO AN AMENDMENT TO ADOPT TECHNICAL SPECIFICATIONS TASK FORCE TRAVELLER TSTF-425, REVISION 3, TO RELOCATE SPECIFIC SURVEILLANCE FREQUENCIES TO A LICENSEE CONTROLLED PROGRAM DUANE ARNOLD ENERGY CENTER DOCKET NO. 50-331 By letter dated February 24, 2011, NextEra Energy Duane Arnold, LLC, requested an amendment to the Duane Arnold Energy Center Renewed Facility Operating License to adopt TSTF-425, by which a risk-informed relocation to a licensee controlled program would be applied to Technical Specification surveillance frequency requirements.

On June 10, 2011 the NRC sought further information, which was provided by NextEra Energy Duane Arnold, LLC in a supplement dated August 15, 2011. A clarification conference call took place on September 15, 2011, to discuss the responses in the August 15, 2011 supplement. At that time, NRC informed NextEra Energy Duane Arnold, LLC that the NRC would assess what further information might be required.

Subsequently, the NRC issued three follow-up questions. The questions and NextEra Energy Duane Arnold, LLCs responses to the questions are as follows:

1. Expand the discussion on your sensitivity analysis for the loss-of-bus initiators 1A1, 1A2, 1A3, and1A4 in response to Question number 5 (referring to the text of your supplement dated August 15, 2011), including important assumptions, what was varied in the sensitivity analysis, and the insights gained related to the importance of these buses as initiators for TSTF-425 application. Discuss how these initiators, as well as the other initiators discussed in the gap description for IE-B3-01A, will be addressed for TSTF-425 application.

Response

A sensitivity study was performed to assess the significance of subsuming loss of 4160 VAC bus initiating events into the Turbine Trip (TT) initiating event. This study was a preliminary best estimate of expected increases in CDF when 4160 VAC bus failures are treated as initiating events separate from the TT initiator.

The non-safety related 4160 VAC buses at DAEC are 1A1 (Division 1) and 1A2 (Division 2). These supply power to the main condenser circulating water pumps in addition to feedwater and condensate pumps. Typically the plant will experience an automatic scram on low vessel water level when 1A1 or 1A2 is lost. If the outdoor temperature is high, a turbine trip due to exceeding a condenser vacuum setpoint may occur.

The safety related 4160 VAC buses are 1A3 (Division 1) and 1A4 (Division 2). These support operation of emergency core cooling systems and of safety related containment heat removal systems. An automatic reactor scram is not expected upon loss of 1A3 or

Attachment to NG-11-0407 Page 2 of 3 1A4. However, if the loss is known to be the result of an electrical fault, control room operators are directed by procedure to manually scram the plant. A turbine trip has a higher consequence than a manual shutdown. The sensitivity study assumed a turbine trip would result from the loss of a safety related 4160 VAC bus.

Risk associated with loss of 4160 VAC buses was determined by calculating the conditional core damage probability (CCDP) of Turbine Trip with 1A1, 1A2, 1A3 or 1A4 out of service. The result for each case was then multiplied with the annual failure rate of a single bus to obtain an estimate of the core damage frequency (CDF) associated with loss of 1A1, 1A2, 1A3 or 1A4 as an initiator. A major insight gained from reviewing the results of the sensitivity analysis is that joint failure probabilities for operator actions that reflect the degree of dependence dominate the loss of bus consequences.

Although the total increase in core damage frequency by adding the 4160 VAC loss of bus initiators was found to be very small (per the Regulatory Guide 1.174 Criteria), the sensitivity analysis did suggest that certain impacts for subsuming these events into the Turbine Trip initiator do not conform to the PRA Standard. Because these events may have unique plant response aspects, especially on the effect of operator performance, the gap identified by the focused peer review is valid. Surveillance control frequency changes implemented through the TSTF-425 application would require determining the impact of the change in surveillance frequency using a sensitivity analysis, qualitative analysis, bounding analysis or explicit modeling in accordance with the NEI 04-10 guidance. This analysis would include an understanding of the impact of all the initiators identified in the finding for support system initiators (IE-B3-01A).

2. Expand upon your response to Question number 9e (referring to the text of your supplement dated August 15, 2011). Discuss the scope of the focused peer review against the ASME/ANS Standard RA-Sa-2009 Supporting Requirements (SRs) for the new PRA methods. For example, did the review scope focus on only open gap items or did it address SRs for the entire element associated with the new PRA method?

Response

The purpose of the DAEC Focused Peer Review conducted in March 2011 was to review the technical elements of the internal events, at-power PRA with a focus on DAECs disposition of findings and suggestions as a result of a Full Scope Peer Review conducted in 2007. The review was conducted in accordance with NEI 05-04, Revision 2 Process for Performing Follow-on PRA Peer Reviews Using the ASME PRA Standard, as endorsed and clarified by the NRC in Regulatory Guide 1.200, Revision 2.

The peer review team determined that a review of all supporting requirements for the Human Reliability Analysis technical element was needed since it involved a broad based change in methodology for calculating human error probabilities. Other upgrades received enhanced attention by the review team, but did not require re-review of all

Attachment to NG-11-0407 Page 3 of 3 supporting requirements within the respective technical element category. These included use of the Alpha Factor Method for calculating common cause factors, use of convolution methods for calculating AC power recovery terms, incorporation of revised LOCA frequency data to differentiate between steam line breaks and water line breaks, and incorporation of new internal flood frequency data. The set of supporting requirements that needed to be reviewed for each technical element was determined by the peer review team consistent with ASME/ANS Standard RA-Sa-2009.

Qualifications of peer review team members were consistent with Section 1-6.2 of the ASME standard. The team consisted of personnel with knowledge of plant and containment design, and of plant operation. Individually, each team member was familiar with the requirements of the standard for his or her area of review and experienced in performing activities related to the technical elements for which he or she was assigned. Collectively, they had the capability to assess all of the PRA technical elements. None of the team members performed nor directly supervised any work on the Duane Arnold PRA. One team member serves on the Joint Committee on Nuclear Risk Management main committee, which approves changes to the Standard. Each of the team members participated in at least two previous peer reviews and each has nearly twenty or more years of experience in the development and maintenance of nuclear plant PRAs.

In summary, the 2011 Focused Peer Review entailed a comprehensive review of all PRA upgrades, updates and previous F&Os and is considered to be the Internal Events PRA Peer Review of record.

3. For the Duane Arnold TSTF-425 acceptance review, the NRC Staff also seeks a clarification of an apparent typo observed in your (DAEC) answer within your August 15, 2011 supplement. Question No. 2 was related to Supporting Requirement SC-A6. However, your response cited only reference to IE-A4a.

Please confirm that a typo occurred and provide replacement text as part of your response to this RAI.

Response

Yes, it is a typographical error. The citation should have been to Supporting Requirement SC-A6, not IE-A4a. All the other information in that response was correct. The corrected response reads:

Supporting Requirement SC-A6 was assessed as Not Met in the December 2007 PRA Peer Review, but was re-assessed as Met: Capability Category I/II/III in the subsequent Focused PRA Peer Review of March 2011. Although our discussion in Table 2-1 regarding disposition of the 2007 gap focuses on use of MAAP for evaluating success criteria, other analytical tools were also employed for the Rev 6 PRA update.