NL-13-1937, Pilot 10 CFR 50.69 License Amendment Request, Response to Request for Additional Information
| ML13256A306 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 09/13/2013 |
| From: | Pierce C Southern Co, Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-13-1937, TAC ME9472, TAC ME9473 | |
| Download: ML13256A306 (10) | |
Text
Charles R. Pierce Southern Nuclear Regu latory Affairs Director Operating Company, Inc.
40 Inverness Center Parkway Pos t Office Box 1295 Birmingham, Alaba ma 35201 Tel 205992.7872 Fax 2059927601 September 13, 2013 SOUTHERN ' \
COMPANY Docket Nos.: 50-424 NL-13-1937 50-425 U. S. Nuclear Regulatory Commission ATIN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant Pilot 10 CFR 50.69 License Amendment Request Response to Request for Additional Information Ladies and Gentlemen:
By letter dated August 31, 2012, Southern Nuclear Operating Company (SNC) requested amendments to the Vogtle Electric Generating Plant (VEGP) Units 1 and 2 (TAC NOS ME9472 and ME9473). The proposed amendments would revise the VEGP licenSing basis to implement 10 CFR 50.69, risk informed categorization and treatment of structures, systems, and components for nuclear power plants.
By letter dated April 17,2013, the NRC requested additional information. SNC responded to the request by letter dated May 17, 2013 and noted responses to requests for additional information (RAls) 19, 25, 26 and 27 would require additional time to develop and would be provided within 120 days from the date of the SNC letter. SNC provided the responses to RAls 19 and 27 by letter dated July 2, 2013. In the response to RAI 27, SNC identified that a Base-Case Sensitivity (BCS) model would be developed and used for the categorization process and to respond to RAls that request sensitivity analyses on NRC approved methods including RAls 25 and 26.
The enclosure to this letter provides a summary of the BCS model results and SNC's response to RAls 25 and 26.
This letter contains no NRC commitments. If you have any questions, please contact Ken McElroy at (205) 992-7369.
U. S. Nuclear Regulatory Commission NL-13-1937 Page 2 Mr. C. A. Pierce states he is Regulatory Affairs Director of Southern Nuclear Operating Company, is authorized to execute this oath on behalf of Southern Nuclear Operating Company and, to the best of his knowledge and belief, the facts set forth in this letter are true.
a" a a Respectfully submitted, C.l{ flw
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C. R. Pierce Regulatory Affairs Director ..-/
Sworn to and subscribed before me this --I'1--,3=--th
__ day of 2013.
~W6t Notary PublIc My commission expires: If* :<- z0 13
Enclosure:
cc: Southern Nuclear Operating Company Mr. S. E. Kuczynski, Chairman, President & CEO Mr. D. G. Bost, Executive Vice President & Chief Nuclear Officer Mr. T. E. Tynan, Vice President - Vogtle Mr. B. L. Ivey, Vice President - Regulatory Affairs Mr. B. J. Adams, Vice President - Fleet Operations RType: CVC7000 U. S. Nuclear Regulatory Commission Mr. V. M. McCree, Regional Administrator Mr. R. E. Martin, NRR Senior Project Manager - Vogtle Mr. L. M. Cain, Senior Resident Inspector - Vogtle State of Georgia Mr. J. H. Turner, Environmental Director Protection Division
Vogtle Electric Generating Plant Request to Revise the Licensing Basis to Implement 10 CFR 50.69 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request Enclosure Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request
Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request Base Case Sensitivity Model:
In the response to RAI #27 dated July 2, 2013, SNC identified that a Base-Case Sensitivity (BCS) model would be developed and used for the categorization process and to respond to RAls that request sensitivity analyses on NRC approved methods (including RAls 25 and 26). As identified in the RAI #27 response, the BCS model removes the three Unendorsed Analysis Methods (UAMs) used in the Vogtle fire PRA and changes the alignment factor for pump oil fires to the factor endorsed by the NRC.
Background Information:
In the July 2,2013 response to RAI #27, SNC prepared a list of fire PRA methods that have been in use in the industry and the subject of recent communications relative to Unendorsed Analysis Method (UAM) / NRC endorsement status, and identified their applicability to the Vogtle fire PRA.
As stated in the response to RAI #27, the following methods are used in the Vogtle fire PRA that can be characterized as a UAM:
- Not using 0.001 as the lowest value for failure of manual suppression (using values less than 0.001, even 0);
- Not using lower failure threshold for sensitive electronics;
- Electrical cabinet heat release rate or severity factors and cabinet to cabinet fires (one method rejected, one method commented, others exist)
In addition, SNC also identified in the response to RAI #27 that:
- Although an endorsed method was used for alignment factor for pump oil fires, the alignment factor used by SNC in the Vogtle fire PRA for pump oil fires is slightly different than the factor accepted by the NRC staff in the NRC endorsement letter dated June 21,2012 (ML 12172A06).
In our response to RAI #27, SNC stated that SNC would remove the three unendorsed methods from the Vogtle fire PRA and change the alignment factor for pump oil fires to the factor endorsed by the NRC, and refine the resulting model as necessary using the approved/ endorsed methods. The model so generated would be designated as the Base-Case Sensitivity model (BCS model).
SNC stated it would use the BCS model to respond to other RAls that request sensitivity analyses on NRC approved methods (e.g., RAls # 25 and # 26). Each sensitivity study would be performed individually.
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Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request Results:
SNC has removed these three UAMs from the Vogtle fire PRA and changed the alignment factor for pump oil fires to the factor endorsed by the NRC. In addition, further refinement was performed to remove conservatisms that were revealed following removal of the UAMs. After completion of these model adjustments:
These sensitivity estimates are approximately 8% higher for CDF and approximately 16% lower for LERF.
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Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request NRC RAI # 25 UNC-A2-01 noted that ignition frequencies from Section 10 of NUREG/CR-6850 were used. Supplement 1 states that a sensitivity analysis should be performed when using the fire ignition frequencies in the Supplement instead of the fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850. Provide the sensitivity analysis of the impact on using the Supplement 1 frequencies instead of the Table 6-1 frequencies on the importance measures and therefore the safety significance of SSCs for all of those bins that are characterized by an alpha that is less than or equal to one.
SNC Response Using the Base-Case Sensitivity (BCS) model, a sensitivity analysis was performed using fire ignition frequencies provided in Table 6-1 of NUREG/CR 6850. The CDF and LERF for the BCS model and for this sensitivity run are summarized in the following table for comparison.
CDF and LERF comparison for a sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 CDF LERF wi Fire Base wi Fire Base Case Ignition Ignition 0/0 Case 0/0 Sensitivity Frequencies Frequencies Unit Sensitivity (BCS) from Table 6-1 Change from Table 6-1 Change (BCS)
Model of NUREG/CR of NUREG/CR Model 6850 6850 Unit 1 5.30E-05 6.71 E-05 27% 1.76E-06 2.75E-06 56%
Unit 2 6.00E-05 7.46E-05 24% 1.99E-06 3.01 E-06 51%
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Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request In order to evaluate the impact on the 10 CFR 50.69 categorization process importance measures, the metrics of interest and associated thresholds are summarized below. These thresholds are in accordance with the NEI 00-04 methodology. If a component exceeds one of these thresholds, it is categorized as High Safety Significant (HSS):
Fussell-Vesely (F-V) > 5.0E-03 Risk Achievement Worth (RAW) > 2.0 for single event Risk Achievement Worth (RAW) > 20.0 for common cause event The following information summarizes the impact on the 10 CFR 50.69 categorization process importance measures for Unit 1.
- The Unit 1 CDF sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 did not identify additional components meeting the above HSS criteria compared to Unit 1 BCS run for CDF.
- The Unit 1 LERF sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 did not identify additional components meeting the above HSS criteria compared to Unit 1 BCS run for LERF.
In conclusion, when CDF and LERF results are combined, the Unit 1 sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 did not identify additional components meeting the NEI-00-04 HSS criteria compared to the Unit 1 BCS run.
The following information summarizes the impact on the 10 CFR 50.69 categorization process importance measures for Unit 2.
- The Unit 2 CDF sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 identified only one additional component (11204U6083) as meeting the NEI-00-04 criteria for HSS compared to the Unit 2 BCS run for CDF. This component was identified as high through the associated common cause basic event. The same common cause basic event was not high in the Unit 2 BCS run; however, 3 out of 4 of the components (11204U6083, 11204U6084, 11204U6085, and 11204U6086) that make up this common cause event were HSS in the Unit 2 BCS run. Therefore, the expectation is that during the categorization review of this system by the Integrated Decision-making Panel (IDP), the prudent IDP decision would be to categorize 11204U6083 as HSS along with the other 3 components in this group.
Considering this expectation, the NUREG/CR-6850 sensitivity run would not have identified new additional HSS components.
- The Unit 2 LERF sensitivity run using 'fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 identified one components meeting the NEI-00-04 HSS criteria compared to the Unit 2 BCS run for LERF.
However, this component is HSS for Unit 2 CDF sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 and the E1-4
Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request Unit 2 BCS run for CDF. Therefore, it is not counted as a net increase for the purpose of reporting net results for this sensitivity study.
In conclusion, when CDF and LERF results are combined, the Unit 2 sensitivity run using fire ignition frequencies provided in Table 6-1 of NUREG/CR-6850 identified only one (1) additional component meeting the NEI-OO-04 HSS criteria compared to the Unit 2 BCS run. As mentioned earlier, when allowing for the lOP process to apply the expected prudence, this sensitivity would not have identified new additional HSS components.
Based on the results presented above for Units 1 and 2, it is judged that the impact of using the NUREG/CR-6850 Supplement 1 fire ignition frequencies instead of the Table 6-1 frequencies on the importance measures has minimal effect and therefore the safety significance of SSCs is minimal.
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Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request NRC RAI # 26 It was recently stated at the industry fire forum that the Phenomena Identification and Ranking Table Panel being conducted for the circuit failure tests from the DESIREEFIRE and CAROL-FIRE tests may be eliminating the credit for Control Power Transformers (CPTs) (about a factor 2 reduction) currently allowed by Tables 10-1 and 10-3 of NUREG/CR-6850, Vol. 2, as being invalid when estimating circuit failure probabilities. Please perform a sensitivity study to quantify the impact of CPT credit on SSC categorization.
SNC Response Using the Base-Case Sensitivity (BCS) model, a sensitivity analysis was performed by reducing Control Power Transformers (CPTs) credit by a factor of
- 2. The CDF and LERF for the BCS model and for this sensitivity run are summarized in the following table for comparison.
CDF and LERF summary for a sensitivity run associated with reducing Control Power Transformers (CPTs) credit by a factor of 2 CDF LERF Control Power Base Control Power Base Case Transformers % Case Transformers %
Unit Sensitivity (CPTs) Change Sensitivity (CPTs) Change (8CS)
Sensitivity (BCS) Sensitivity Unit 1 5.30E-OS 6.19E-OS 17% 1.76E-06 1.99E-06 13%
Unit 2 6.00E-OS 6.84E-OS 14% 1.99E-06 2.29E-06 1S%
In order to evaluate the impact on the 10 CFR SO.69 categorization process importance measures, the metrics of interest and associated thresholds are summarized below. These thresholds are in accordance with the NEI 00-04 methodology. If a component exceeds one of these thresholds, it is categorized as high Safety Significant (HSS).
Fussell-Vesely (F-V) > S.OE-03 Risk Achievement Worth (RAW) > 2.0 for single event Risk Achievement Worth (RAW) > 20.0 for common cause event E1-6
Enclosure to NL-13-1937 Response to Request for Additional Information Regarding Pilot 10 CFR 50.69 License Amendment Request The following information summarizes impact on the 10 CFR 50.69 categorization process importance measures for Unit 1.
- The Unit 1 CPT sensitivity run for CDF identified 15 additional High Safety Significant (HSS) components compared to the Unit 1 BCS run for CDF.
- The Unit 1 CPT sensitivity run for LERF did not identify addition HSS components compared to the Unit 1 BCS run for LERF.
In conclusion, when CDF and LERF results are combined, the Unit 1 CPT Sensitivity run identified 15 additional components as HSS compared to the Unit 1 BCS run.
The following information summarizes impact on the 10 CFR 50.69 categorization process importance measures for Unit 2.
- The Unit 2 CPT sensitivity run for CDF identified nine (9) additional components meeting the HSS criteria compared to the Unit 2 BCS run for CDF.
- The Unit 2 CPT sensitivity run for LERF did not identify additional components meeting the HSS criteria compared to the Unit 2 BCS run for LERF.
In conclusion, when CDF and LERF results are combined, the Unit 2 CPT Sensitivity run identified nine (9) additional components as HSS compared to the Unit 2 BCS run.
When comparing the Unit 1 results with the Unit 2 results for CPT sensitivity run, it was noted that four (4) HSS components were unit equivalent, i.e., the corresponding component in Unit 1 and in Unit 2 met the HSS criteria. For the purpose of reporting net results for this sensitivity study, if a component meets the HSS criteria in one unit and the corresponding component in the opposite unit also meets the HSS criteria, it is counted only once rather than one per unit.
Thus, the incremental count is reduced by four (4). Therefore, the CPT sensitivity run adds a total of 20 (= 15 in Unit 1 + 9 in Unit 2 - 4 unit equivalent) HSS components compared to the BCS run.
Based on insights obtained from Units 1 and 2 results, it is anticipated that eliminating the CPT credit would identify approximately 20 more components as HSS.
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