ML071160067

Request for Additional Information (RAI) Extended Power Uprate Application Probabilistic Risk Assessment Licensing Review

ML071160067
Person / Time
Site:	Susquehanna
Issue date:	04/27/2007
From:	Richard Guzman NRC/NRR/ADRO/DORL/LPLI-1
To:	Mckinney B Susquehanna
Guzman R, NRR/DORL, 415-1030
References
TAC MD3309, TAC MD3310
Download: ML071160067 (7)

Text

April 27, 2007 Mr. Britt T. McKinney Sr. Vice President and Chief Nuclear Officer PPL Susquehanna, LLC 769 Salem Blvd., NUCSB3 Berwick, PA 18603-0467

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION (RAI) - SUSQUEHANNA STEAM ELECTRIC STATION, UNITS 1 AND 2 (SSES 1 AND 2) - EXTENDED POWER UPRATE APPLICATION RE: PROBABILISTIC RISK ASSESSMENT LICENSING REVIEW (TAC NOS. MD3309 AND MD3310)

Dear Mr. McKinney:

In reviewing your letter dated October 11, 2006, concerning the request to increase the maximum steady-state power level at the SSES 1 and 2 from 3489 megawatts thermal (MWt) to 3952 MWt, the Nuclear Regulatory Commission staff has determined that additional information contained in the enclosure to this letter is needed to complete its review. These questions were discussed with your staff during a teleconference on April 19, 2007. As agreed to by your staff, we request you respond by May 31, 2007.

If you have any questions, please contact me at 301-415-1030.

Sincerely,

/RA/

Richard V. Guzman, Senior Project Manager Plant Licensing Branch I-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-387 and 50-388

Enclosure:

RAI cc w/encl: See next page

April 27, 2007 Mr. Britt T. McKinney Sr. Vice President and Chief Nuclear Officer PPL Susquehanna, LLC 769 Salem Blvd., NUCSB3 Berwick, PA 18603-0467

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION (RAI) - SUSQUEHANNA STEAM ELECTRIC STATION, UNITS 1 AND 2 (SSES 1 AND 2) - EXTENDED POWER UPRATE APPLICATION RE: PROBABILISTIC RISK ASSESSMENT LICENSING REVIEW (TAC NOS. MD3309 AND MD3310)

Dear Mr. McKinney:

In reviewing your letter dated October 11, 2006, concerning the request to increase the maximum steady-state power level at the SSES 1 and 2 from 3489 megawatts thermal (MWt) to 3952 MWt, the Nuclear Regulatory Commission staff has determined that additional information contained in the enclosure to this letter is needed to complete its review. These questions were discussed with your staff during a teleconference on April 19, 2007. As agreed to by your staff, we request you respond by May 31, 2007.

If you have any questions, please contact me at 301-415-1030.

Sincerely,

/RA/

Richard V. Guzman, Senior Project Manager Plant Licensing Branch I-1 Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket Nos. 50-387 and 50-388

Enclosure:

RAI cc w/encl: See next page DISTRIBUTION:

Public RidsOgcMailCenter RidsNrrPmRGuzman RidsNrrAplaBC DHarrison LPLI-1 R/F RidsNrrDorlLpl1-1 RidsAcrsAcnwMailCenter RidsNrrLaSLittle Accession Number:

• RAI provided by memo. No substantive changes made.

OFFICE NRR/LPLI-1/PM NRR/LPLI-1/LA NRR/EICA/BC NRR/LPLI-1/BC NAME RGuzman SLittle MRubin* MKowal DATE 4/26/07 4/26/07 4/9/07 4/27/07 OFFICIAL RECORD COPY

REQUEST FOR ADDITIONAL INFORMATION RELATING TO THE APPLICATION FOR EXTENDED POWER UPRATE (EPU)

PROBABILISTIC RISK ASSESSMENT (PRA) LICENSING REVIEW SUSQUEHANNA STEAM ELECTRIC STATION, UNITS 1 AND 2 (SSES 1 AND 2)

PPL SUSQUEHANNA, LLC DOCKET NOS. 50-387 AND 50-388 The Nuclear Regulatory Commission (NRC) staff is reviewing the request from PPL Susquehanna, LLC (PPL, the licensee) to support the application of the EPU for SSES 1 and 2.

The NRC staff has determined that additional information requested below will be needed to complete its review.

1. Constant Pressure Power Uprate (CPPU) Safety Analysis Report (SAR) Section 10.5, Page 10-10: The section indicates that the changes to emergency operating plans/

severe accident management guides as a result of the CPPU were not available prior to completion of the PRA evaluation and it is assumed that the procedural changes have a minor impact on the PRA results. Please describe the status of these procedural changes and if they have been developed sufficiently (e.g., in draft form) to confirm that the PRA results would only be minimally impacted.

2. CPPU SAR Section 10.5.3, Page 10-14: The section discusses the operator response evaluation, but does not explicitly identify the human reliability analysis (HRA) methods used. Please describe the SSES HRA methods employed in these analyses.

3. CPPU SAR Section 10.5.3, Page 10-14, and Table 10-5, Pages 10 10-46, and Table 10-6, Page 10-47: This section states that about 100 independent and 20 dependent operator actions were not impacted by the CPPU, and lists in Tables 10-5 and 10-6, those actions that were impacted. Please identify the operator actions (including the values) that have a risk achievement worth greater than 2.0 or Fussel-Vessely importance greater than 0.005, as determined from the CPPU CDF calculation. (Note: The NRC staff will use this information to support the appropriate amount of review to perform in accordance with NUREG/CR-1764, Guidance for the Review of Changes to Human Actions.)

4. CPPU SAR Section 10.5.3, Page 10-14, and Table 10-5, Pages 10 10-46, and Table 10-6, Page 10-47: Please confirm that, as a result of the CPPU, all previously modeled operator actions can be physically achieved within their CPPU times and Enclosure

describe the basis for this determination (e.g., procedural walk-throughs, simulator exercises).

5. CPPU SAR Section 10.5.3, Page 10-14, and Table 10-5, Pages 10 10-46, and Table 10-6, Page 10-47: There are numerous human error probabilities (HEP) for similar actions with very slight differences in timing. For example, the failure of the operate to initiate standby liquid control system (SLCS) after an anticipated transient without scram (ATWS) has five different HEPs, addressing CPPU times of 3.2 minutes, 5 minutes, 6 minutes, 9.5 minutes, and 16 minutes. The NRC staff is aware that there are success criteria considerations (e.g., ability to use one SLCS pump as opposed to two), that might warrant different operator actions, but this is typically limited to two HEPs (in the SLCS example, an early initiation is the latest time at which one SLCS pump provides success, while a late initiation establishes the latest time at which two SLCS pumps provide success). For each of the multiple HEP operator actions, please explain why multiple HEPs are necessary.

6. CPPU SAR Section 10.5.3, Page 10-14 and Table 10-11, Pages 10 10-52: Two of the facts and observations (F&Os) identified are related to missing pre-initiator HEPs.

Please describe the type of pre-initiators not included (the subject of the F&O) and the rationale for why these events would not appreciably impact risk.

7. CPPU SAR Section 10.5.4, Pages 10 10-17: The discussion on success criteria does not identify if a specific unit was used in determining the appropriate success criteria for both units or if there are any differences in the plant designs that might impact success criteria. Please identify any significant plant differences and how these differences are addressed within the CPPU PRA.

8. CPPU SAR Section 10.5.4, Page 10-15: The inventory makeup success criteria discussion states that control rod drive (CRD) injection as an independent makeup source during the initial stages of an accident is deemed marginal for both pre-CPPU and CPPU conditions, but that it is viable as a late injection source. Please describe the scenarios/sequences and timing in which CRD is modeled as a sufficient injection source in the pre-CPPU PRA and the CPPU PRA.

9. CPPU SAR Section 10.5.4, Page 10-15: The pool heat load discussion addresses non-ATWS scenarios, but does not address ATWS scenarios. Please describe the impact of ATWS scenarios on pool heat load.

10. CPPU SAR Section 10.5.4, Page 10-16: The overpressure margin discussion states that for an isolation ATWS scenario having four safety relief valves (SRVs) out of service is acceptable to prevent over-pressurizing the reactor pressure vessel (RPV) for CPPU conditions. Please clarify for the pre-CPPU and CPPU conditions, what is the success criteria for SRVs for these isolation ATWS scenarios and what is the success criteria for non-isolation ATWS scenarios.

11. CPPU SAR Section 10.5.4, Page 10-16: The SRV actuation discussion does not identify the number of SRVs expected to open following the various initiating events that must subsequently reclose and if this number increases with the CPPU (or if this aspect is conservatively modeled in the SSES PRA). Please clarify how the pre-CPPU and

CPPU PRA models address the number of SRVs that open (and must subsequently reclose) for each of the initiating event groups.

12. CPPU SAR Section 10.5.4, Pages 10 10-21: The Level 2 PRA discussion states that release categories are defined based on the percentage of cesium iodine (CsI) released to the environment, but does not identify the percentage used to define a large release. Please provide the percentage of CsI used to define a large release, in the context of the large early release frequency (LERF) metric.

13. CPPU SAR Section 10.5.5, Pages 10 10-24: The NRC staff understands that the fire and other external events were evaluated using the analyses of the SSES Individual Plant Examination of External Events (IPEEE). Please confirm that the changes made to the internal events PRA logic model since the IPEEE was submitted would not significantly affect the IPEEE conclusions concerning internal fire and other external event risks. Specifically, please confirm for the internal fires assessment that no previously screened areas would be unscreened at the pre-CPPU or CPPU conditions.

14. CPPU SAR Section 10.5.5, Pages 10 10-23: The IPEEE staff evaluation indicated that SSES fire analysis contained a significant weakness involving the assumption that the severity of a fire and probability of failure of fire suppression were independent, resulting in low core damage frequencies (CDFs). It does not appear that the SSES fire analysis has been updated since the IPEEE. Please address this specifically identified weakness in the SSES fire analysis and, if necessary, supplement the internal fire analyses to address this issue.

15. CPPU SAR Section 10.5.5, Pages 10 10-24: The seismic discussion indicates that a number of seismic-related issues were closed out, but that there is an ongoing process to monitor seismic issues at the plant. Please describe the remaining seismic issues at the plant and the potential impact of these issues on plant seismic risk.

16. CPPU SAR Section 10.5.6, Pages 10 10-27: The section states that the time to core uncovery for CPPU conditions is 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> compared to 9.1 hours1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> at pre-CPPU conditions at 1 day into an outage with the RPV level at the flange. Please provide the time for boildown (core uncovery) at 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> and 8 hours9.259259e-5 days <br />0.00222 hours <br />1.322751e-5 weeks <br />3.044e-6 months <br /> into an outage for pre-CPPU and CPPU conditions.

17. CPPU SAR Table 10-3, Page 10-40, and Table 10-4, Page 10-41: The loss of service water and loss of instrument air initiating event frequency is set at 5E-3/year. Please provide the justification and data source for using this value for these initiating events.

18. CPPU SAR Section 10.5.8, Pages 10 10-30 and Table 10-3, Page 10-40, and Table 10-4, Page 10-41: The Sensitivity Cases use a long-term data period of 10 years to provide a projected average increase in risk as a result of the CPPU. However, the majority of the risk increase will occur within the first year after implementation of CPPU. To provide a perspective of the potential maximum risk increase in the first year following implementation of the CPPU, please re-perform the sensitivity calculations for this first year only (i.e., increase the turbine trip w/ bypass frequency from 0.894/year to 2.894/year and increase the isolation initiator frequency from 0.136/year to 1.136/year).

In addition, include a sensitivity case that incorporates into the current sensitivity case

1. 4 (the combined sensitivity cases) the inclusion of the loss of instrument air and service water initiators and reflects any changes resulting from the SSES response to the following comment.

19. CPPU SAR Section 10.5.8, Pages 10 10-30 and Table 10-3, Page 10-40, and Table 10-4, Page 10-41: The combination of individual sensitivity cases in Sensitivity Case #4 is to determine if there are synergistic effects that would not be revealed in individual sensitivity cases. However, the sum of deltas of the individual sensitivity cases is actually greater than the delta for the combined sensitivity case. Please explain why the sum of the deltas of the individual sensitivity cases is greater than the combined sensitivity case.

20. Please provide a summary of the LERF results for both the pre-CPPU and CPPU conditions similar to Table 10-12 and 10-13.

21. Please provide a parametric uncertainty analysis of the pre-CPPU and CPPU CDF and LERF.

Susquehanna Steam Electric Station, Unit Nos. 1 and 2 cc:

Robert A. Saccone Bryan A. Snapp, Esq Vice President - Nuclear Operations Assoc. General Counsel PPL Susquehanna, LLC PPL Services Corporation 769 Salem Blvd., NUCSB3 Two North Ninth Street, GENTW3 Berwick, PA 18603-0467 Allentown, PA 18101-1179 Terry L. Harpster Supervisor - Document Control Services General Manager - Plant Support PPL Susquehanna, LLC PPL Susquehanna, LLC Two North Ninth Street, GENPL4 769 Salem Blvd., NUCSA4 Allentown, PA 18101-1179 Berwick, PA 18603-0467 Richard W. Osborne Rocco R. Sgarro Allegheny Electric Cooperative, Inc.

Manager - Nuclear Regulatory Affairs 212 Locust Street PPL Susquehanna, LLC P.O. Box 1266 Two North Ninth Street, GENPL4 Harrisburg, PA 17108-1266 Allentown, PA 18101-1179 Director, Bureau of Radiation Protection Supervisor - Pennsylvania Department of Nuclear Regulatory Affairs Environmental Protection PPL Susquehanna, LLC Rachel Carson State Office Building 769 Salem Blvd., NUCSA4 P.O. Box 8469 Berwick, PA 18603-0467 Harrisburg, PA 17105-8469 Michael H. Crowthers Senior Resident Inspector Supervising Engineer U.S. Nuclear Regulatory Commission Nuclear Regulatory Affairs P.O. Box 35, NUCSA4 PPL Susquehanna, LLC Berwick, PA 18603-0035 Two North Ninth Street, GENPL4 Allentown, PA 18101-1179 Regional Administrator, Region 1 U.S. Nuclear Regulatory Commission Steven M. Cook 475 Allendale Road Manager - Quality Assurance King of Prussia, PA 19406 PPL Susquehanna, LLC 769 Salem Blvd., NUCSB2 Board of Supervisors Berwick, PA 18603-0467 Salem Township P.O. Box 405 Luis A. Ramos Berwick, PA 18603-0035 Community Relations Manager, Susquehanna Dr. Judith Johnsrud PPL Susquehanna, LLC National Energy Committee 634 Salem Blvd., SSO Sierra Club Berwick, PA 18603-0467 443 Orlando Avenue State College, PA 16803