NG-16-0076, Response to Request for Additional Information. License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency

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Response to Request for Additional Information. License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency
ML16106A303
Person / Time
Site: Duane Arnold NextEra Energy icon.png
Issue date: 04/14/2016
From: Vehec T
NextEra Energy Duane Arnold
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
NG-16-0076
Download: ML16106A303 (15)
v • d • e


Text

NEXTeraM ENERGY~

DUANE ARNOLD April 14, 2016 NG-16-0076.

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 Op. License No. DPR-49 Response to Request for Additional Information. License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency

References:

1) License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency, NG-15-0234. dated August 18. 2015(ML15246A445)
2) Electronic Communication. Request for Additional Information -

Extension of the 10 CFR 50 Appendix J Containment Type A &

Type C Test Intervals. dated December 15. 2015

3) Letter. T. A. Vehec (NextEra) to U.S. NRC. "Response to Request for Additional Information. License Amendment Request (TSCR-
  • 143) to Extend Containment Leakage Test Frequency, NG 0029. dated January 29. 2016
4) Electronic Communication. Request to Additional Information -

Extension of the 10 CFR 50 Appendix J Containment Type A &

Type C Test Intervals. dated March 14. 2016 In the Reference 1 letter, NextEra Energy Duane Arnold; LLC (hereafter NextEra Energy Duane Arnold) submitted a License Amendment Request for the Duane Arnold Energy Center (DAEC) pursuant to 10 CFR 50.90. The NRC Staff requested, via Reference 2, additional information regarding that application.

NextEra Energy Duane Arnold submitted that additional information via Reference 3. Subsequently, the NRC Staff requested, via Reference 4, additional information regarding that application.

The Enclosure to this letter contains the requested information.

NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324

Document Control Desk NG-16-0076 Page 2 of 2 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 does not contain any new or revised commitments.

If you have any questions or require additional information, please contact J. Michael Davis at 319-851-7032.

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

E~eli.l:.d on April.14, 2016 (f;L __/

T.A.~

Vice President, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC Enclosure cc: NRC Regional Administrator NRC Resident Inspector NRC Project Manager A. Leek (State of Iowa)

Enclosure to NG-16-0076 Response to Request for Additional Information. License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency 12 pages follow

NRC RAI In a letter dated August 18, 2015, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15246A445), as supplemented by lett(f]r dated January 29, 2016 (ADAMS Accession No. ML16034A031 ), NextEra Energy Duane Arnold, LLC requested an amendment to Duane Arnold Energy Center (DAEC) Technical Specifications (TS). The proposed amendment will revise DAEC TS Section 5. 5. 12, "Primary Containment Leakage Rate Testing Program," to allow extension of the Type A test interval up to one test in 15 years and extension of the Type C test interval up to 75 months.

The Probabilistic Risk Assessment Licensing Branch issued Request for Additional Information (RA/) by letter dated November 24, 2015 (ADAMS Accession No. ML15327A476) and the licensee provided responses to the RA/ in letter dated January 29, 2016. The NRG staff has reviewed the responses and has determined that additional information is needed for the staff to complete its evaluation. The request for additional information is provided as below:

Second Round of Request for Additional Information Regarding Duane Arnold Energy Center Request to Permanently Extend the Integrated Leak Rate Test Frequency to 15 Years In an electronic communication dated December 15, 2015, the NRG staff requested a list of all findings from the past peer reviews and self-assessments relevant to the Integrated Leak Rate Test (ILRT) extension submittal, dated August 18, 2015, for which the internal events probabilistic risk assessment (PRA) did not meet the American Society of Mechanical Engineers (ASME) PRA Standard Capability Category (CC) I supporting requirements (SRs) and

  • requested the licensee to summarize why not meeting each CC I requirement would have no impact on this application (PRA request for additional information (RAl)-1.b). In response to PRA RA/-1.b, the licensee identified five SRs, IE-83, IE-C6, HR-A1, HR-A2 and HR-C1, Which were assessed as not meeting CC I. The licensee further discussed the impact of findings associated with those SRs on the Duane Arnold Energy Center (DAEC) containment leakage test frequency extension request in Table 1 of the response.

In discussing the impact of not meeting SRs IE-83 and IE-C6, the licensee stated, in part, that:

Substantial margin to the guidelines contained in Regulatory Guide 1. 174 have been demonstrated for this ILRT test interval extension request with respect to acceptable changes in

[large early release frequency) LERF. ... Change in the Type A ILRT test interval from the three in ten years to one in fifteen years is conservatively estimated to represent a 2. 57E-08/yr increase in LERF. Postulated increase in baseline values of [core damage frequency) GDF and LERF result in approximately the same fractional increase in the calculated delta-LERF for this application. For example, a large increase in baseline GDF and LERF, such as 10 percent, would translate into an increase in delta-LERF of about 10 percent, resulting in a final delta-LERF that is still well below the 1E-07 criteria for which the impact of the requested /LRT testing extension is considered to be very small. As such, these criteria would also not be exceeded by inclusion of additional initiators in the PRA as required for closure of this Peer Review item.

Jn discussing the impact of not meeting SR HR-C1, the licensee stated that:

The impact of evaluating pre- initiators at the train level instead of the system level, or at the system level instead of the train level, is judged to have little or no impact on baseline values of GDF and LERF. Even if the actual impact of addressing this gap is more than minor, the Enclosure to NG-16-0076 Page 1 of 1Z

change translates into only a small reduction in margin to criteria established for the ILRT testing interval extension application as described earlier with respect to finding IE-83-01A. As such, the conclusions of the risk evaluation performed for this application are not changed by this variance from the standard.

The estimated increase in LERF of 2. 57E-08/yr does not include the risk from external events.

In the original submittal, the licensee estimated the total increase in LERF from both internal and external events as 8. 14E-08/yr. Furthermore, this impact estimate (from both external hazards and internal events) provided in the original submittal does not include the new seismic hazard GDF and LERF estimates, which were provided in response to PRA RAl-2. The new seismic GDF estimate in response to PRA RAl-2 is larger than the seismic GDF estimate in the original submittal by more than a factor of 8. Although the licensee provided an estimate change in LERF of 6. 80E-08/yr in response to PRA RAl-2 when providing the new seismic GDF estimate, this change in LERF estimate does not appear to include the risk from other external hazards or internal events.

The NRG staff believes that the change in LERF could increase to a value greater than 1E-07/yr when the impact from external events is considered, the new seismic GDF and LERF estimates from response to PRA RAl-2 are used, and the findings related to IE-83, IE-G6, and HR-G1 are resolved. For a change in LERFgreaterthan 1E-07/yr, the licensee should provide total LERF and demonstrate that the RG 1. 174 guidelines are met. The licensee provided total LERF estimate of 9. 79E-06/yr in the original submittal. Again, this estimate could exceed the guideline value of 1E-05/yr once the new seismic risk estimates are considered and the findings associated with the above SRs are resolved.

In summary, the NRG staff does not find the information provided by the licensee in the original submittal and in response to PRA RAls to be sufficient for determining that the change in LERF is less than 1E-07/yr (to meet the guidelines of RG 1. 174 Region Ill) or the total LERF is less than 1E-05/yr (to meet the guidelines of RG 1. 174 Region II).

  • Show that the change in LERF does not exceed 1E-07/yr by including the impact of external hazards, using updated seismic risk estimates and providing a sensitivity analysis that estimates the impact of not meeting SRs IE-83, IE-G6 and HR-G1. Alternatively, show that the total LERF does not exceed 1E-05/yr when external hazards are considered, updated seismic risk estimates are used, and a sensitivity analysis is performed to estimate the impact of not meeting SRs listed above.

Enclosure to NG-16-0076 Page 2of12

NextEra Energy Response:

This response is provided in three parts:

  • Part 1 - Impact of All External Hazards to the Change in LERF - provides all of the information previously provided in RAl-2. It includes:

o An estimate of DAEC Seismic CDF and Seismic LERF using the most up to date seismic hazard estimate o A discussion of the internal and external events total CDF, total LERF, and LiLERF for the ILRT application, updated for the new seismic hazard.

o A sensitivity case examining a lower bound for seismic LERF value.

  • Part 2 - Sensitivity Analysis for the impact of SRs IE-83, IE-C6 and HR C1 -It includes:

o The impact of SRs IE-83, IE-C6 and HR C1 on internal events and fire CDF and LERF o The delta LERF determination for internal events o The delta LERF determination for external events o The assessment of the combined results against the RG 1.174 LiLERF Acceptance Guideline

  • Part 3: RAI Response Summary - provides a summary table of all analysis results.

Part 1: Impact of All External Hazards to the Change in LERF External Events Total GDF, Total LERF, and LJ.LERF for ILRT Application Table 1 summarizes the conservative Duane Arnold external hazard CDF estimates used for the ILRT application.

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0~.~E~Rfr~flYsr)f~~

,~:::::~~~:~::i~S~~i{~,;:,~,~,:.x:;!:~, ~:;.*/;

Seismic 5.71E-06 5.71E-06 Internal Fire 1.20E-05 7.49E-06 Not External Flood < 1E-06 calculated High Winds 1.41 E-07 < 1.41 E-07 Enclosure to NG-16-0076 Page 3of12

Transportation and not not Nearby Facilities significant significant Judged Judged included in included in Other Plant-Unique IPE for IPE for External External Events Events Total < 1.89E-05 < 1.33E-05 The value of Seismic CDF and LERF, External Flood, Transportation and Nearby Facilities, and Other Plant-Unique hazards have'been updated from the values presented in Table 7-2 of Reference 4. The information in Table 1 differs somewhat from what was provided in the response contained in Reference 10, however it more accurately characterizes the external events risk for DAEC and its use does not change any ILRT conclusions for DAEC.

The value of seismic LERF is assumed to be equal to seismic CDF. The values presented above are taken from Reference 5.

The External Flooding CDF and LERF were not calculated. In section 5.2.5 of the DAEC IPEEE (Reference 6) it was concluded that the DAEC design basis has been determined to meet the 1975 SRP criteria related to external floods. Based on the conformance to the 1975 SRP, the contribution to core damage frequency from external flood initiated accident sequences is judged to be less than 1E-6/yr. Furthermore, Reference 7, in the reevaluation of the flooding hazard for the Duane Arnold Energy Center site, concluded that the Current Licensing and Design Basis (CLB) bounds the updated results.

For the CDF and LERF due to Transportation and Nearby Facilities Hazards, section 5.3.5 of Reference 6 concluded that the "design of the DAEC plant is appropriate for its siting such that the contribution to overall plant risk from transportation and nearby facility hazards is not significant." For the Other Plant-Unique Hazards, Reference 6, section 5.4.6 stated "No quantitative evaluation was judged necessary for external events not already included in the internal IPE or the NRG-specified external events of the IPEEE."

An alternate estimate of the wind hazard LERF can be made assuming the ratio CDF to LERF for these hazards is similar to the ratio for internal events. The internal events CDF is 4.24E-06/yr (per Section 5.2.1 of Reference 4, and the internal events LERF is 1.46E-06/yr (per high early release frequency specified in Table 5-1 of Reference 1). The internal event ratio of LERF to CDF is:

Enclosure to NG-16-0076 Page 4 of 12

LERF1E I CDF1E =1.46E-06/yr I 4.24E-06/yr =0.34 The total external events LERF contribution for DAEC is therefore approximated as:

LERFEE = {LERFseismic) + {CDFwind

  • 0.34) + {LERFfire)

=(5.71E-06) + (1.41E-07

  • 0.34) + (7.49E-06)

=1.32E-05/yr Note that the above LERF estimate does not consider internal events and any LERF contribution due to non-detected containment flaws as assessed in the ILRT methodology.

External events LERF attributed specifically to non-detected containment failures is conservatively estimated as follows, using the probabilities of a non-detected containment failure (PNocF) described in Section 5.3 of Reference 4:

LERFNDCF = PNDCF, /j. * (CDFEE - LERFEE)

Where, PNocF,s110 =0.0023 PNDCF,1/10 =0.0023

  • 3.33 PNDCF,1/15 = 0.0023
  • 5.00

=1.89E-05/yr (from Table 1)

=1.32E-05/yr

[CDFEE and LERFEE are the core damage and large early release frequencies, respectively, associated with external hazard sequences only]

Note in the above equation, LERF is subtracted from GDF because only the_ non-LERF portion of GDF is applicable to the ILRT Class 3b evaluation. This properly excludes sequences that are already LERF arid independent of Class 3b such as containment isolation failure. The results of the ILRT Class 3b calculation of LlLERF are presented in Table 2.

Table 2 summarizes the External Events LERF and LlLERF values attributed specifically to non-detected containment failures. Reported LlLERF values are relative to the 3 per 1O year surveillance interval.

3.00E-08 5.15E-08 Enclosure to NG-16-0076 Page 5 of 12

Assessment of internal and external events against the RG 1.174 f1LERF Acceptance Guideline The 6LERF for the 1/10 and 1/15 ILRT intervals (combining the contributions from internal and external events), relative to the base 3/10 interval, are as follows:

LlLERF1110 =6LERF1E,1110 (Table 6-8 of Reference 4) + 6LERFEE,1110

=1.50E-08/yr + 3.00E-08/yr

=4.50E-08/yr 6LERF 111 s =6LERF1E, 1115 (Table 6-8 of Reference 4) + 6LERFEE,111s

=2.57E-08/yr + 5.15E-08/yr

=7.72E-08/yr Sensitivity Analysis An additional sensitivity analysis was performed on the fraction of seismic core damage frequency expected to lead to LERF. The results of this sensitivity analysis demonstrate that the 6LERF value remains below 1E-07/year for all seismic LERF contributions when the fraction of seismic core damage frequency expected to lead to LE_RF exceeds 60%. This 60% value is considered reasonable, given that industry experience indicates that plants with full scope seismic PRAs notice a LERF/CDF in general higher than the ratio noticed in internal events.

Conclusion For the updated estimate of seismic CDF of 5.71 E-06/yr, the 6LERF for the 1/15 interval falls within RG 1.174 Region Ill (Reference 8), where 6LERF is less than 1.0E-07/yr. In this region, the 6LERF contribution due to the ILRT interval extension is considered very small.

Part 2: Sensitivity Analysis for the impact of SRs IE-83, IE-C6 and HR C1.

The RAI requests that the licensee provide a sensitivity analysis that estimates the impact of SRs IE-83, IE-C6 and HR C1.

Reference 9 contains the results of the evaluation of the impact of the unresolved peer review findings. The evaluation concludes that the fire PRA is impacted only by peer review finding HR-C1-01A, causing both the value of Fire PRA CDF and LERF to increase by approximately 3%. The internal events PRA is impacted by peer review findings IE-B3-01A and finding HR-C1-01A. The estimated combined impact from these findings causes internal events CDF to increase by approximately 16.9% and internal events LERF to increase by approximately 18.6%.

Enclosure to NG-16-0076 Page 6 of 12

Incorporating results of the previously unresolved peer review comments results in the following updated values of CDF and LERF for the internal and external events PRAs (including the seismic PRA contribution determined by Part 1 above):

Internal Events PRA CDF =4.96E-06/yr (from Reference 9, Table 6)

Internal Events PRA LERF = 1.73E-06/yr (from Reference 9, Table 6)

Seismic Hazard CDF =5.71E-06/yr (unchanged from above)

Seismic Hazard LERF =5.71 E-06/yr (unchanged from above)

Fire PRA CDF =1.24E-05/yr (from Reference 9, Table 5)

Fire PRA LERF = 7.72E-06/yr (from Reference 9, Table 5)

High Winds CDF =1.41 E-07/yr (unchanged from above)

High Winds LERF =4.86E-08/yr (unchanged from above)

External Flood CDF = 1.00E-6/yr (unchc:mged from above)

Integrating these changes into the plant CDF/LERF contribution table (see Table 3) results in the following:

Enclosure to NG-16-0076 Page 7of12

Internal Events 4.96E-06 1.73E-06 Seismicity 5.71E-06 5.71 E-06 Internal Fire 1.24E-05 7.72E-06 not External Flood < 1E-06 calculated High Winds 1.41 E-07 4.86E-08 Transportation and not not Nearby Facilities significant significant Judged Judged included in included in Other Plant-Unique IPE for IPE for External External Events Events Total for External 1.93E-05 1.35E-'05 Events Delta LERF Determination for Internal Events (impact of SRs)

In order to determine the impact of the sensitivity values of Internal Events CDF and LERF, these values are used as input to a sensitivity calculation of the impact of the ILRT extension risk assessment. Changes to the values of internal events CDF and LERF also result in modifications to the class frequency distributions used for the ILRT analysis. The results of this calculation are contained in Table 4.

Enclosure to NG-16-0076 Page 8 of 12

3a 3.45E+04 2.97E-08 1.03E-03 9.89E-08 3.41E-03 1.49E-07 5.13E-03 3b 3.45E+05 7.45E-09 2.57E-03 2.48E-08 8.57E-03 3.73E-08 1.29E-02 7 3.67E+05 4.72E-06 1.73E+OO 4.72E-06 1.73E+OO 4.72E-06 1.73E+OO 8 5.19E+05 1.89E-08 9.80E-03 1.89E-08 9.80E-03 1.89E-08 9.80E-03 Total N/A 4.96E-06 1.75E+OO 4.96E-06 1.76E+OO 4.96E-06 1.77E+OO ILRT Dose Rate from 3.60E-03 1.20E-02 1.80E-02 3a and 3b Delta From 3 N/A 8.08E-03 1.39E-02 Total in 10 yr Dose From 1 Rate N/A N/A 5.79E-03 in 10 yr change From 3 N/A 0.46% 0.79%

in dose in 10 yr rate from From 1 N/A N/A 0.33%

base in 10 yr 3b Frequency 7.45E-09 2.48E-08 3.73E-08 (LERF)

From 3 N/A 1.74E-08 2.98E-08 Delta in 10 yr LERF From 1 N/A N/A 1.24E-08 in 10 yr CCFP% 95.80% 96.15% 96.40%

From 3 N/A 0.35% 0.60%

Delta in 10 yr CCFP% From 1 N/A N/A 0.25%

in 10 yr The results of this sensitivity analysis are summarized in Table 5.

Enclosure to NG-16-0076 Page 9 of 12

1.74E-08 2.98E-08 Delta LERF Determination for External Events (impact from SRs)

External events LERF attributed specifically to non-detected containment failures is conservatively estimated as follows, using the probabilities of a non-detected containment failure (PNocF) described in Section 5.3 of Reference 4:

LERFNDCF =PNDCF, h. * (CDFEE - LERFEE)

Where, PNocF,s110 =0.0023 PNDCF,1/10 =0.0023

  • 3.33 PNDCF,1/15 = 0.0023
  • 5.00 CDFEE =1.94E-05/yr (from Table 3 above)

LERFEE =1.36E-05/yr (from Table 3 above)

CDFEE - LE RF EE =5. 77E-06 Table 6 summarizes the External Events LERF and LlLERF values attributed specifically to non-detected containment failures. Reported LlLERF values are relative to the 3 per 1O year surveillance interval.

3.09E-08 5.31E-08

  • Assessment against the RG 1.174 aLERF Acceptance Guideline The LlLERF for the 1/10 and 1/15 ILRT intervals, relative to the base 3/10 interval, are as follows:

Enclosure to NG-16-0076 Page 10of12

bLERF1110 =bLERF1E,1/10 (from Table 5) + bLERFEE,1/10 (from Table 6)

=1. 74E-08/yr + 3. 09E-08/yr

=4.83E-08/yr bLERF1115 =bLERF1E,1/15 (from Table 5) + bLERFEE,1/15 (from Table 6)

=2.98E-08/yr + 5.31 E-08/yr

=8.29E-08/yr Conclusion In this sensitivity case, the values of internal events CDF, internal events LERF, fire events CDF and fire events LERF have been raised to reflect the impact of the unresolved peer review comments. When these impacts are included, the bLERF forthe 1/15 interval rises from 7.72E-08/yr to 8.29E-08/yr. This higher value falls within RG 1.174 Region 111 (Reference 8) for very small increases, where bLERF is less than 1.0E-07/yr.

Part 3: RAI Response Summary Table 7 provides a summary of the results of the analyses performed for this RAI response.

Updated Seismic Hazard 4.50E-08 7.72E-08 (CDFseismic e uals LERFseismic Updated Seismic Hazard plus 4.83E-08 8.29E-08 impact of SRs (CDFseismic equals LERFseismic)

The results of these analysis cases demonstrate that the bLERF value remains below 1E-07 /year when the impact of the updated seismic hazard and unmet supporting requirements are included.

Enclosure to NG-16-0076 Page 11 of 12

RAI Response References

1. NRC Document, "Results of Safety/Risk Assessment of Generic Issue (GI) 199,

'Implications of Updated Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing Plants,"' (ADAMS Accession No. ML100270582).

2. EPRI Document, "Seismic Probabilistic Risk Assessment Implementation Guide," EPRI, Palo Alto, CA: 2013. 3002000709.
3. NextEra Energy document, NG-14-0092, "NextEra Energy Duane Arnold, LLC Seismic Hazard and Screening Report (CEUS Sites), Response to NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding Recommendation 2.1 of the Near-Term Task Force Review of Insights .from the Fukushima Dai-ichi Accident," March 2014 (ADAMS Accession No. ML14092A331).
4. NextEra Energy Document, NG-15-0234 "License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency," dated 18 August 2015, (ADAMS Accession No. ML15246A445), Attachment 4.
5. NextEra Energy Document, DAEC-BFJR-14-015, Revision 0, "Duane Arnold Seismic CDF Estimate."
6. NextEra Energy Document, "Duane Arnold Energy Center Individual Plant Examinations
  • of External Events (IPEEE)," November 1995.
7. NextEra Energy Document, FPL070-PR~002, Rev. 0, "NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding."
8. Regulatory Guide 1.174, Revision 2, "An Approach for Using Probabilistic Risk Assessment in Risk"-lnformed Decisions on Plant Specific Changes to the Licensing Basis," May 2011.
9. NextEra Energy document, Assessment of PRA Peer Review Findings with Respect to

/LRT Testing Interval Extension, as transmitted by EC 284252 DIT-08, PDA Transition to NE/ 94-01 R-3A, dated 30 March 2016.

10. NextEra Energy Document, NG-16-0029 "Response to Request for Additional Information; License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency, dated 29 January 2016.

EnClosure to NG-16-0076 Page 12of12

NEXTeraM ENERGY~

DUANE ARNOLD April 14, 2016 NG-16-0076.

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 Op. License No. DPR-49 Response to Request for Additional Information. License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency

References:

1) License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency, NG-15-0234. dated August 18. 2015(ML15246A445)
2) Electronic Communication. Request for Additional Information -

Extension of the 10 CFR 50 Appendix J Containment Type A &

Type C Test Intervals. dated December 15. 2015

3) Letter. T. A. Vehec (NextEra) to U.S. NRC. "Response to Request for Additional Information. License Amendment Request (TSCR-
  • 143) to Extend Containment Leakage Test Frequency, NG 0029. dated January 29. 2016
4) Electronic Communication. Request to Additional Information -

Extension of the 10 CFR 50 Appendix J Containment Type A &

Type C Test Intervals. dated March 14. 2016 In the Reference 1 letter, NextEra Energy Duane Arnold; LLC (hereafter NextEra Energy Duane Arnold) submitted a License Amendment Request for the Duane Arnold Energy Center (DAEC) pursuant to 10 CFR 50.90. The NRC Staff requested, via Reference 2, additional information regarding that application.

NextEra Energy Duane Arnold submitted that additional information via Reference 3. Subsequently, the NRC Staff requested, via Reference 4, additional information regarding that application.

The Enclosure to this letter contains the requested information.

NextEra Energy Duane Arnold, LLC, 3277 DAEC Road, Palo, IA 52324

Document Control Desk NG-16-0076 Page 2 of 2 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 does not contain any new or revised commitments.

If you have any questions or require additional information, please contact J. Michael Davis at 319-851-7032.

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

E~eli.l:.d on April.14, 2016 (f;L __/

T.A.~

Vice President, Duane Arnold Energy Center NextEra Energy Duane Arnold, LLC Enclosure cc: NRC Regional Administrator NRC Resident Inspector NRC Project Manager A. Leek (State of Iowa)

Enclosure to NG-16-0076 Response to Request for Additional Information. License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency 12 pages follow

NRC RAI In a letter dated August 18, 2015, (Agencywide Documents Access and Management System (ADAMS) Accession No. ML15246A445), as supplemented by lett(f]r dated January 29, 2016 (ADAMS Accession No. ML16034A031 ), NextEra Energy Duane Arnold, LLC requested an amendment to Duane Arnold Energy Center (DAEC) Technical Specifications (TS). The proposed amendment will revise DAEC TS Section 5. 5. 12, "Primary Containment Leakage Rate Testing Program," to allow extension of the Type A test interval up to one test in 15 years and extension of the Type C test interval up to 75 months.

The Probabilistic Risk Assessment Licensing Branch issued Request for Additional Information (RA/) by letter dated November 24, 2015 (ADAMS Accession No. ML15327A476) and the licensee provided responses to the RA/ in letter dated January 29, 2016. The NRG staff has reviewed the responses and has determined that additional information is needed for the staff to complete its evaluation. The request for additional information is provided as below:

Second Round of Request for Additional Information Regarding Duane Arnold Energy Center Request to Permanently Extend the Integrated Leak Rate Test Frequency to 15 Years In an electronic communication dated December 15, 2015, the NRG staff requested a list of all findings from the past peer reviews and self-assessments relevant to the Integrated Leak Rate Test (ILRT) extension submittal, dated August 18, 2015, for which the internal events probabilistic risk assessment (PRA) did not meet the American Society of Mechanical Engineers (ASME) PRA Standard Capability Category (CC) I supporting requirements (SRs) and

  • requested the licensee to summarize why not meeting each CC I requirement would have no impact on this application (PRA request for additional information (RAl)-1.b). In response to PRA RA/-1.b, the licensee identified five SRs, IE-83, IE-C6, HR-A1, HR-A2 and HR-C1, Which were assessed as not meeting CC I. The licensee further discussed the impact of findings associated with those SRs on the Duane Arnold Energy Center (DAEC) containment leakage test frequency extension request in Table 1 of the response.

In discussing the impact of not meeting SRs IE-83 and IE-C6, the licensee stated, in part, that:

Substantial margin to the guidelines contained in Regulatory Guide 1. 174 have been demonstrated for this ILRT test interval extension request with respect to acceptable changes in

[large early release frequency) LERF. ... Change in the Type A ILRT test interval from the three in ten years to one in fifteen years is conservatively estimated to represent a 2. 57E-08/yr increase in LERF. Postulated increase in baseline values of [core damage frequency) GDF and LERF result in approximately the same fractional increase in the calculated delta-LERF for this application. For example, a large increase in baseline GDF and LERF, such as 10 percent, would translate into an increase in delta-LERF of about 10 percent, resulting in a final delta-LERF that is still well below the 1E-07 criteria for which the impact of the requested /LRT testing extension is considered to be very small. As such, these criteria would also not be exceeded by inclusion of additional initiators in the PRA as required for closure of this Peer Review item.

Jn discussing the impact of not meeting SR HR-C1, the licensee stated that:

The impact of evaluating pre- initiators at the train level instead of the system level, or at the system level instead of the train level, is judged to have little or no impact on baseline values of GDF and LERF. Even if the actual impact of addressing this gap is more than minor, the Enclosure to NG-16-0076 Page 1 of 1Z

change translates into only a small reduction in margin to criteria established for the ILRT testing interval extension application as described earlier with respect to finding IE-83-01A. As such, the conclusions of the risk evaluation performed for this application are not changed by this variance from the standard.

The estimated increase in LERF of 2. 57E-08/yr does not include the risk from external events.

In the original submittal, the licensee estimated the total increase in LERF from both internal and external events as 8. 14E-08/yr. Furthermore, this impact estimate (from both external hazards and internal events) provided in the original submittal does not include the new seismic hazard GDF and LERF estimates, which were provided in response to PRA RAl-2. The new seismic GDF estimate in response to PRA RAl-2 is larger than the seismic GDF estimate in the original submittal by more than a factor of 8. Although the licensee provided an estimate change in LERF of 6. 80E-08/yr in response to PRA RAl-2 when providing the new seismic GDF estimate, this change in LERF estimate does not appear to include the risk from other external hazards or internal events.

The NRG staff believes that the change in LERF could increase to a value greater than 1E-07/yr when the impact from external events is considered, the new seismic GDF and LERF estimates from response to PRA RAl-2 are used, and the findings related to IE-83, IE-G6, and HR-G1 are resolved. For a change in LERFgreaterthan 1E-07/yr, the licensee should provide total LERF and demonstrate that the RG 1. 174 guidelines are met. The licensee provided total LERF estimate of 9. 79E-06/yr in the original submittal. Again, this estimate could exceed the guideline value of 1E-05/yr once the new seismic risk estimates are considered and the findings associated with the above SRs are resolved.

In summary, the NRG staff does not find the information provided by the licensee in the original submittal and in response to PRA RAls to be sufficient for determining that the change in LERF is less than 1E-07/yr (to meet the guidelines of RG 1. 174 Region Ill) or the total LERF is less than 1E-05/yr (to meet the guidelines of RG 1. 174 Region II).

  • Show that the change in LERF does not exceed 1E-07/yr by including the impact of external hazards, using updated seismic risk estimates and providing a sensitivity analysis that estimates the impact of not meeting SRs IE-83, IE-G6 and HR-G1. Alternatively, show that the total LERF does not exceed 1E-05/yr when external hazards are considered, updated seismic risk estimates are used, and a sensitivity analysis is performed to estimate the impact of not meeting SRs listed above.

Enclosure to NG-16-0076 Page 2of12

NextEra Energy Response:

This response is provided in three parts:

  • Part 1 - Impact of All External Hazards to the Change in LERF - provides all of the information previously provided in RAl-2. It includes:

o An estimate of DAEC Seismic CDF and Seismic LERF using the most up to date seismic hazard estimate o A discussion of the internal and external events total CDF, total LERF, and LiLERF for the ILRT application, updated for the new seismic hazard.

o A sensitivity case examining a lower bound for seismic LERF value.

  • Part 2 - Sensitivity Analysis for the impact of SRs IE-83, IE-C6 and HR C1 -It includes:

o The impact of SRs IE-83, IE-C6 and HR C1 on internal events and fire CDF and LERF o The delta LERF determination for internal events o The delta LERF determination for external events o The assessment of the combined results against the RG 1.174 LiLERF Acceptance Guideline

  • Part 3: RAI Response Summary - provides a summary table of all analysis results.

Part 1: Impact of All External Hazards to the Change in LERF External Events Total GDF, Total LERF, and LJ.LERF for ILRT Application Table 1 summarizes the conservative Duane Arnold external hazard CDF estimates used for the ILRT application.

~t~~11~i!~t~~i~~,~¥~ **~";~~lfi1lI-~li!~~~

0~.~E~Rfr~flYsr)f~~

,~:::::~~~:~::i~S~~i{~,;:,~,~,:.x:;!:~, ~:;.*/;

Seismic 5.71E-06 5.71E-06 Internal Fire 1.20E-05 7.49E-06 Not External Flood < 1E-06 calculated High Winds 1.41 E-07 < 1.41 E-07 Enclosure to NG-16-0076 Page 3of12

Transportation and not not Nearby Facilities significant significant Judged Judged included in included in Other Plant-Unique IPE for IPE for External External Events Events Total < 1.89E-05 < 1.33E-05 The value of Seismic CDF and LERF, External Flood, Transportation and Nearby Facilities, and Other Plant-Unique hazards have'been updated from the values presented in Table 7-2 of Reference 4. The information in Table 1 differs somewhat from what was provided in the response contained in Reference 10, however it more accurately characterizes the external events risk for DAEC and its use does not change any ILRT conclusions for DAEC.

The value of seismic LERF is assumed to be equal to seismic CDF. The values presented above are taken from Reference 5.

The External Flooding CDF and LERF were not calculated. In section 5.2.5 of the DAEC IPEEE (Reference 6) it was concluded that the DAEC design basis has been determined to meet the 1975 SRP criteria related to external floods. Based on the conformance to the 1975 SRP, the contribution to core damage frequency from external flood initiated accident sequences is judged to be less than 1E-6/yr. Furthermore, Reference 7, in the reevaluation of the flooding hazard for the Duane Arnold Energy Center site, concluded that the Current Licensing and Design Basis (CLB) bounds the updated results.

For the CDF and LERF due to Transportation and Nearby Facilities Hazards, section 5.3.5 of Reference 6 concluded that the "design of the DAEC plant is appropriate for its siting such that the contribution to overall plant risk from transportation and nearby facility hazards is not significant." For the Other Plant-Unique Hazards, Reference 6, section 5.4.6 stated "No quantitative evaluation was judged necessary for external events not already included in the internal IPE or the NRG-specified external events of the IPEEE."

An alternate estimate of the wind hazard LERF can be made assuming the ratio CDF to LERF for these hazards is similar to the ratio for internal events. The internal events CDF is 4.24E-06/yr (per Section 5.2.1 of Reference 4, and the internal events LERF is 1.46E-06/yr (per high early release frequency specified in Table 5-1 of Reference 1). The internal event ratio of LERF to CDF is:

Enclosure to NG-16-0076 Page 4 of 12

LERF1E I CDF1E =1.46E-06/yr I 4.24E-06/yr =0.34 The total external events LERF contribution for DAEC is therefore approximated as:

LERFEE = {LERFseismic) + {CDFwind

  • 0.34) + {LERFfire)

=(5.71E-06) + (1.41E-07

  • 0.34) + (7.49E-06)

=1.32E-05/yr Note that the above LERF estimate does not consider internal events and any LERF contribution due to non-detected containment flaws as assessed in the ILRT methodology.

External events LERF attributed specifically to non-detected containment failures is conservatively estimated as follows, using the probabilities of a non-detected containment failure (PNocF) described in Section 5.3 of Reference 4:

LERFNDCF = PNDCF, /j. * (CDFEE - LERFEE)

Where, PNocF,s110 =0.0023 PNDCF,1/10 =0.0023

  • 3.33 PNDCF,1/15 = 0.0023
  • 5.00

=1.89E-05/yr (from Table 1)

=1.32E-05/yr

[CDFEE and LERFEE are the core damage and large early release frequencies, respectively, associated with external hazard sequences only]

Note in the above equation, LERF is subtracted from GDF because only the_ non-LERF portion of GDF is applicable to the ILRT Class 3b evaluation. This properly excludes sequences that are already LERF arid independent of Class 3b such as containment isolation failure. The results of the ILRT Class 3b calculation of LlLERF are presented in Table 2.

Table 2 summarizes the External Events LERF and LlLERF values attributed specifically to non-detected containment failures. Reported LlLERF values are relative to the 3 per 1O year surveillance interval.

3.00E-08 5.15E-08 Enclosure to NG-16-0076 Page 5 of 12

Assessment of internal and external events against the RG 1.174 f1LERF Acceptance Guideline The 6LERF for the 1/10 and 1/15 ILRT intervals (combining the contributions from internal and external events), relative to the base 3/10 interval, are as follows:

LlLERF1110 =6LERF1E,1110 (Table 6-8 of Reference 4) + 6LERFEE,1110

=1.50E-08/yr + 3.00E-08/yr

=4.50E-08/yr 6LERF 111 s =6LERF1E, 1115 (Table 6-8 of Reference 4) + 6LERFEE,111s

=2.57E-08/yr + 5.15E-08/yr

=7.72E-08/yr Sensitivity Analysis An additional sensitivity analysis was performed on the fraction of seismic core damage frequency expected to lead to LERF. The results of this sensitivity analysis demonstrate that the 6LERF value remains below 1E-07/year for all seismic LERF contributions when the fraction of seismic core damage frequency expected to lead to LE_RF exceeds 60%. This 60% value is considered reasonable, given that industry experience indicates that plants with full scope seismic PRAs notice a LERF/CDF in general higher than the ratio noticed in internal events.

Conclusion For the updated estimate of seismic CDF of 5.71 E-06/yr, the 6LERF for the 1/15 interval falls within RG 1.174 Region Ill (Reference 8), where 6LERF is less than 1.0E-07/yr. In this region, the 6LERF contribution due to the ILRT interval extension is considered very small.

Part 2: Sensitivity Analysis for the impact of SRs IE-83, IE-C6 and HR C1.

The RAI requests that the licensee provide a sensitivity analysis that estimates the impact of SRs IE-83, IE-C6 and HR C1.

Reference 9 contains the results of the evaluation of the impact of the unresolved peer review findings. The evaluation concludes that the fire PRA is impacted only by peer review finding HR-C1-01A, causing both the value of Fire PRA CDF and LERF to increase by approximately 3%. The internal events PRA is impacted by peer review findings IE-B3-01A and finding HR-C1-01A. The estimated combined impact from these findings causes internal events CDF to increase by approximately 16.9% and internal events LERF to increase by approximately 18.6%.

Enclosure to NG-16-0076 Page 6 of 12

Incorporating results of the previously unresolved peer review comments results in the following updated values of CDF and LERF for the internal and external events PRAs (including the seismic PRA contribution determined by Part 1 above):

Internal Events PRA CDF =4.96E-06/yr (from Reference 9, Table 6)

Internal Events PRA LERF = 1.73E-06/yr (from Reference 9, Table 6)

Seismic Hazard CDF =5.71E-06/yr (unchanged from above)

Seismic Hazard LERF =5.71 E-06/yr (unchanged from above)

Fire PRA CDF =1.24E-05/yr (from Reference 9, Table 5)

Fire PRA LERF = 7.72E-06/yr (from Reference 9, Table 5)

High Winds CDF =1.41 E-07/yr (unchanged from above)

High Winds LERF =4.86E-08/yr (unchanged from above)

External Flood CDF = 1.00E-6/yr (unchc:mged from above)

Integrating these changes into the plant CDF/LERF contribution table (see Table 3) results in the following:

Enclosure to NG-16-0076 Page 7of12

Internal Events 4.96E-06 1.73E-06 Seismicity 5.71E-06 5.71 E-06 Internal Fire 1.24E-05 7.72E-06 not External Flood < 1E-06 calculated High Winds 1.41 E-07 4.86E-08 Transportation and not not Nearby Facilities significant significant Judged Judged included in included in Other Plant-Unique IPE for IPE for External External Events Events Total for External 1.93E-05 1.35E-'05 Events Delta LERF Determination for Internal Events (impact of SRs)

In order to determine the impact of the sensitivity values of Internal Events CDF and LERF, these values are used as input to a sensitivity calculation of the impact of the ILRT extension risk assessment. Changes to the values of internal events CDF and LERF also result in modifications to the class frequency distributions used for the ILRT analysis. The results of this calculation are contained in Table 4.

Enclosure to NG-16-0076 Page 8 of 12

3a 3.45E+04 2.97E-08 1.03E-03 9.89E-08 3.41E-03 1.49E-07 5.13E-03 3b 3.45E+05 7.45E-09 2.57E-03 2.48E-08 8.57E-03 3.73E-08 1.29E-02 7 3.67E+05 4.72E-06 1.73E+OO 4.72E-06 1.73E+OO 4.72E-06 1.73E+OO 8 5.19E+05 1.89E-08 9.80E-03 1.89E-08 9.80E-03 1.89E-08 9.80E-03 Total N/A 4.96E-06 1.75E+OO 4.96E-06 1.76E+OO 4.96E-06 1.77E+OO ILRT Dose Rate from 3.60E-03 1.20E-02 1.80E-02 3a and 3b Delta From 3 N/A 8.08E-03 1.39E-02 Total in 10 yr Dose From 1 Rate N/A N/A 5.79E-03 in 10 yr change From 3 N/A 0.46% 0.79%

in dose in 10 yr rate from From 1 N/A N/A 0.33%

base in 10 yr 3b Frequency 7.45E-09 2.48E-08 3.73E-08 (LERF)

From 3 N/A 1.74E-08 2.98E-08 Delta in 10 yr LERF From 1 N/A N/A 1.24E-08 in 10 yr CCFP% 95.80% 96.15% 96.40%

From 3 N/A 0.35% 0.60%

Delta in 10 yr CCFP% From 1 N/A N/A 0.25%

in 10 yr The results of this sensitivity analysis are summarized in Table 5.

Enclosure to NG-16-0076 Page 9 of 12

1.74E-08 2.98E-08 Delta LERF Determination for External Events (impact from SRs)

External events LERF attributed specifically to non-detected containment failures is conservatively estimated as follows, using the probabilities of a non-detected containment failure (PNocF) described in Section 5.3 of Reference 4:

LERFNDCF =PNDCF, h. * (CDFEE - LERFEE)

Where, PNocF,s110 =0.0023 PNDCF,1/10 =0.0023

  • 3.33 PNDCF,1/15 = 0.0023
  • 5.00 CDFEE =1.94E-05/yr (from Table 3 above)

LERFEE =1.36E-05/yr (from Table 3 above)

CDFEE - LE RF EE =5. 77E-06 Table 6 summarizes the External Events LERF and LlLERF values attributed specifically to non-detected containment failures. Reported LlLERF values are relative to the 3 per 1O year surveillance interval.

3.09E-08 5.31E-08

  • Assessment against the RG 1.174 aLERF Acceptance Guideline The LlLERF for the 1/10 and 1/15 ILRT intervals, relative to the base 3/10 interval, are as follows:

Enclosure to NG-16-0076 Page 10of12

bLERF1110 =bLERF1E,1/10 (from Table 5) + bLERFEE,1/10 (from Table 6)

=1. 74E-08/yr + 3. 09E-08/yr

=4.83E-08/yr bLERF1115 =bLERF1E,1/15 (from Table 5) + bLERFEE,1/15 (from Table 6)

=2.98E-08/yr + 5.31 E-08/yr

=8.29E-08/yr Conclusion In this sensitivity case, the values of internal events CDF, internal events LERF, fire events CDF and fire events LERF have been raised to reflect the impact of the unresolved peer review comments. When these impacts are included, the bLERF forthe 1/15 interval rises from 7.72E-08/yr to 8.29E-08/yr. This higher value falls within RG 1.174 Region 111 (Reference 8) for very small increases, where bLERF is less than 1.0E-07/yr.

Part 3: RAI Response Summary Table 7 provides a summary of the results of the analyses performed for this RAI response.

Updated Seismic Hazard 4.50E-08 7.72E-08 (CDFseismic e uals LERFseismic Updated Seismic Hazard plus 4.83E-08 8.29E-08 impact of SRs (CDFseismic equals LERFseismic)

The results of these analysis cases demonstrate that the bLERF value remains below 1E-07 /year when the impact of the updated seismic hazard and unmet supporting requirements are included.

Enclosure to NG-16-0076 Page 11 of 12

RAI Response References

1. NRC Document, "Results of Safety/Risk Assessment of Generic Issue (GI) 199,

'Implications of Updated Probabilistic Seismic Hazard Estimates in Central and Eastern United States on Existing Plants,"' (ADAMS Accession No. ML100270582).

2. EPRI Document, "Seismic Probabilistic Risk Assessment Implementation Guide," EPRI, Palo Alto, CA: 2013. 3002000709.
3. NextEra Energy document, NG-14-0092, "NextEra Energy Duane Arnold, LLC Seismic Hazard and Screening Report (CEUS Sites), Response to NRC Request for Information Pursuant to 10 CFR 50.54(f) Regarding Recommendation 2.1 of the Near-Term Task Force Review of Insights .from the Fukushima Dai-ichi Accident," March 2014 (ADAMS Accession No. ML14092A331).
4. NextEra Energy Document, NG-15-0234 "License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency," dated 18 August 2015, (ADAMS Accession No. ML15246A445), Attachment 4.
5. NextEra Energy Document, DAEC-BFJR-14-015, Revision 0, "Duane Arnold Seismic CDF Estimate."
6. NextEra Energy Document, "Duane Arnold Energy Center Individual Plant Examinations
  • of External Events (IPEEE)," November 1995.
7. NextEra Energy Document, FPL070-PR~002, Rev. 0, "NTTF Recommendation 2.1 (Hazard Reevaluations): Flooding."
8. Regulatory Guide 1.174, Revision 2, "An Approach for Using Probabilistic Risk Assessment in Risk"-lnformed Decisions on Plant Specific Changes to the Licensing Basis," May 2011.
9. NextEra Energy document, Assessment of PRA Peer Review Findings with Respect to

/LRT Testing Interval Extension, as transmitted by EC 284252 DIT-08, PDA Transition to NE/ 94-01 R-3A, dated 30 March 2016.

10. NextEra Energy Document, NG-16-0029 "Response to Request for Additional Information; License Amendment Request (TSCR-143) to Extend Containment Leakage Test Frequency, dated 29 January 2016.

EnClosure to NG-16-0076 Page 12of12

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