ML13214A384
| ML13214A384 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 07/26/2013 |
| From: | Batson S Duke Energy Carolinas |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML13214A384 (10) | |
Text
DUKE Scoft L. Baon EW E E ~M~D(~Vice President Oconee Nuclear Station Duke Energy ONOIVP 17800 Rochester Hwy Seneca, SC 29672 o: 864.873,3274 10 CFR 50.90 f 864.873.4208 Scot.Batson@duke-energy.com July 26, 2013 U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Duke Energy Carolinas, LLC Oconee Nuclear Station (ONS), Units 1, 2, and 3 Docket Numbers 50-269, 50-270, and 50-287 Additional Information Regarding License Amendment Request for Temporary Technical Specification Change to Add a Required Action Completion Time for One Keowee Hydro Unit Inoperable for Generator Field Pole Rewinds License Amendment Request (LAR) No. 2012-01, Supplement 3 On June 27, 2012, Duke Energy Carolinas, LLC (Duke Energy) submitted a License Amendment Request (LAR) requesting the Nuclear Regulatory Commission (NRC) approve a Technical Specification (TS) change that adds a temporary Completion Time to TS 3.8.1 Required Action (RA) C.2.2.5 to allow time to perform major maintenance on a Keowee Hydro Unit (KHU). By letters dated December 14, 2012, and May 28, 2013, Duke Energy responded to NRC Request for Additional Information (RAls). The NRC issued another RAI by letter dated June 26, 2013. The enclosure provides the requested information.
There are no regulatory commitments associated with this letter. If there are any additional questions, please contact Boyd Shingleton, ONS Regulatory Affairs, at (864) 873-4716.
I declare under penalty of perjury that the foregoing is true and correct. Executed on July 26, 2013.
Sincerely, Scott L. Batson Vice President Oconee Nuclear Station Enclosure Response to NRC Request for Additional Information www.duke.energy.com
Nuclear Regulatory Commission Licdnse Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 2 cc w/
Enclosure:
Mr. Victor McCree, Regional Administrator U. S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE, Suite 1200 Atlanta, GA 30303-1257 Mr. John Boska, Senior Project Manager (by electronic mail only)
Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission 11555 Rockville Pike Mail Stop O-8G9A Rockville, MD 20852 Mr. Ed Crowe Senior Resident Inspector Oconee Nuclear Site Ms. Susan E. Jenkins, Manager Radioactive & Infectious Waste Management Division of Waste Management South Carolina Department of Health and Environmental Control 2600 Bull St.
Columbia, SC 29201
ENCLOSURE Duke Energy Response to NRC Request for Additional Information (RAI)
Enclosure - Duke Energy Response to NRC RAI Licdnse Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 1 NRC Background Information By letter dated June 27, 2012, Duke Energy Carolinas, LLC (Duke), submitted an application to the Nuclear Regulatory Commission (NRC) for a proposed amendment for the Oconee Nuclear Station, Units 1, 2, and 3, which would revise the Technical Specification (TS) on the emergency power system. The application is in the NRC's Agencywide Documents Access and Management System under Accession No. ML12181A312. The revision would permit each of the two emergency power system generating units (Keowee Hydro Units) to be out of service for up to 75 days on a one-time basis for major maintenance work. The Nuclear Regulatory Commission (NRC) staff is reviewing the submittal and has the following questions:
Question 1 The LAR stated in Section 4.0, Risk Insights:
The justification for the TS Completion Time (CT) extension is based on the deterministic evaluation in Section 3.0. To supplement this evaluation and to gain insights concerning the proposed plant configuration, Duke Energy performed a risk assessment. The findings of the risk assessment confirm that the risk impact with adding an additional Completion Time of 75 days to restore an inoperable KHU due to generator pole rewind work is insignificant. The relevant criteria are Core Damage Frequency (CDF) and Large Early Release Frequency (LERF). The increase in either of these metrics resulting from the addition of a new 75-day Completion Time to restore an inoperable KHU due to major maintenance is estimated to be insignificant.
Regarding the above stated risk assessment, please respond to the following questions:
Concerning the risk assessment performed to gain insights in Section 4.0 of the Oconee LAR dated June 27, 2012, related to the proposed one-time 75-day TS CT, please discuss the basis for your conclusion(s) on risk insights (i.e., risk impact with additional 75-day CT is insignificant). Provide your key assumptions used to derive your conclusion.
Duke Energy Response:
The following key assumptions were used in the subject risk evaluation.
- 1. Average maintenance unavailability values were used for the base case numbers because of the long durations involved with the KHU refurbishments.
- 2. Significant Risk Management Actions (RMAs) will be in effect during the subject KHU refurbishment activities. Specifically, no discretionary maintenance or testing will be performed on the Standby Shutdown Facility (SSF), Emergency Feedwater (EFW) System, and AC Power system (e.g., Startup Transformers, CT4, and CT5) during the these activities. Therefore, two KHU analysis cases were evaluated: one assuming average maintenance unavailability on the SSF, EFW, and AC Power Systems and another case assuming zero maintenance unavailability for these systems.
Enclosure - Duke Energy Response to NRC RAI License Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 2
- 3. Annual average tornado frequency values were used (i.e., no seasonal adjustments were made).
- 4. Seismic risk is considered insensitive to unavailability of a Keowee overhead unit and was not considered further in the analysis.
The table below shows the change in risk over the entire maintenance duration for a 75 day completion time compared to the current 45 day TS (a difference of 30 days per unit). The risk metrics of interest are incremental conditional core damage probability (ICCDP) and incremental conditional large early release probability (ICLERP).
Incremental Risk for 60 Days Additional Unavailability (30 Days per KHU)
Risk Measure No Maintenance Case Average Maintenance Case ICCDP -1.6E-06 1.6E-07 ICLERP -2.6E-08 8.2E-09 These results show a risk improvement if no maintenance is performed on the SSF, EFW System and AC Power System, and only a small risk increase if average maintenance unavailability values are assumed. By limiting maintenance activities on these important systems, the actual risk is expected to be between these two ICCDP and ICLERP values and is judged to represent an insignificant impact on overall plant risk.
Question 1 (continued)
What duration was used for the single Keowee Hydro Unit (KHU) outages? Were dual KHU outages considered as part of the single KHU outage risk assessment? If dual KHU outages were considered, how many hours of dual KHU outages were considered for the risk assessment?
Duke Energy Response:
The duration used for a single KHU outage was 75 days. Dual KHU outages were not considered in the PRA risk assessment since no change to the 60-hour Completion Time of TS 3.8.1 Required Action (RA) H.2 was requested.
Question I (continued)
- When a single KHU outage is entered, how is it ensured that the other KHU will maintain its high reliability to start and run?
Enclosure - Duke Energy Response to NRC RAI License Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 3 Duke Energy Response:
ONS Operations procedures require the KHU associated with the underground emergency power path be demonstrated operable prior to taking the KHU associated with the overhead emergency power path out of service. Technical Specification (TS) 3.8.1 Required Action (RA) C.1 requires Surveillance Requirement (SR) 3.8.1.3 be performed within 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> of a KHU becoming inoperable if not performed within the previous 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> and once per 7 days thereafter. The normal SR frequency for SR 3.8.1.3 is 31 days. This SR verifies the availability of the KHU associated with the underground emergency power path to start automatically and energize the underground emergency power path. Utilization of either the auto-start or emergency start sequence assures the control function operability by verifying proper speed control and voltage. Power path verification is included to demonstrate breaker operability from the KHU onto the standby buses.
This is accomplished by closing the Keowee Feeder Breakers (SK) to energize each de-energized standby bus.
TS 3.8.1 RA C.2.2.2 requires suspending KHU generation to the grid prior to exceeding the 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> Completion Time of RA C.2.1. TS 3.8.1 RA C.2.2.3 requires verification by administrative means that the remaining KHU and its required underground emergency power path are operable.
This assures that the KHU and its required underground emergency power path are available prior to entering an extended single KHU outage (> 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />). TS 3.8.1 RA C.2.2.4 requires verifying alternate power source capability by performing SR 3.8.1.16 prior to exceeding 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. This SR verifies that both emergency power paths are operable prior to entering the extended single KHU outage.
Additionally, the ONS Risk Management Process and resulting required Critical Activity Plans implement risk mitigation actions such as a review to confirm there are no outstanding corrective work orders or equipment deficiencies on the underground emergency power path and protected equipment posting strategies. This provides further confidence in the reliability associated with the KHU and underground emergency power path remaining in service.
Question I (continued)
There may be times when a dual KHU outage is entered, for example to drain the penstock and isolate a single KHU, followed by bringing back one KHU for a period of time, and then re-entering a dual KHU outage to recover the KHU undergoing maintenance. What steps are taken to ensure that the KHU brought back to service between dual KHU outages does not have degradation in its reliability to start and run?
Duke Energy Response:
After each dual KHU outage, an operability test (SR 3.8.1.3) is performed to demonstrate operability of the KHU not undergoing maintenance prior to declaring the KHU operable.
Additionally, while in the extended single KHU outage, TS 3.8.1 RA C.1 requires SR 3.8.1.3 be performed more frequently (once per 7 days versus once per 31 days), thus providing additional assurance that the remaining KHU will start and run on demand during the extended single KHU outage. Additionally, RA C.2.2.3 requires verification that the remaining KHU and its required
Enclosure - Duke Energy Response to NRC RAI Licinse Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 4 underground emergency power path are operable and that Limiting Condition for Operation (LCO) 3.3.21 for the Emergency Power Switching Logic (EPSL) Keowee Emergency Start Function is met prior to exceeding 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. If a Keowee Emergency Start channel becomes inoperable during the extended single KHU outage, RA L.2 requires compliance be restored within 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> rather than the 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> allowed by TS 3.3.21 RA A.1.
Question I (continued)
Regarding the Safe Shutdown Facility (SSF) during a dual KHU outage and a single KHU outage, are there differences in the way the SSF is ready to be used if needed (e.g., in the deployment of the SSF)? Ifso, please discuss the differences.
Duke Energy Response:
The difference in SSF readiness per our operating procedures is that the SSF is required to be operable prior to entry into and during a dual KHU outage versus "available" prior to entry into and during single KHU outages. A component is considered available or functional prior to post maintenance testing being performed and operable after post maintenance testing is completed.
Actions required during Keowee Outages (Dual, Overhead, or Underground) that require SSF activation are directed by Operations procedures (Abnormal and Emergency Operating Procedures).
Keowee Outages (single or dual) are controlled by an Operations Procedure for removal and restoration of the Overhead and Underground Power Paths individually or concurrently. One of the initial conditions for removal of both Power Paths (Overhead and Underground) is to verify that the SSF is operable. No discretionary maintenance or testing is allowed on the SSF during the dual KHU outage. In addition the Protected Equipment Program is implemented for both KHUs and/or power paths being unavailable.
An initial condition for removal of a single KHU or its associated overhead emergency power path is to verify the SSF is "available." Whether discretionary maintenance or testing is permitted is dependent on the electronic risk assessment tool (ERAT) results. Also, Operations hangs Protected Equipment tags as required by the risk management process.
Critical Activity Plans are required for Keowee Outages that result in a PRA ORANGE electronic risk assessment tool (ERAT) risk condition or where activities result in greater than 33 percent of TS RA Completion Time being used. These plans, which are required by the Oconee risk management program, are intended to provide structure and oversight to the overall work plan and work execution and are not intended to direct work. Critical Activity Plans, which are required to be reviewed and approved by the Plant Operations Review Committee, are the second level of risk management control and require contingency plans for problems that have a reasonable chance to occur.
Enclosure - Duke Energy Response to NRC RAI License Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 5 Question 1 (continued)
- During KHU outages, are there any planned actions in the event of a heightened likelihood of a loss of offsite power and/or Lee Combustion Turbine power source (such as tornado warnings, severe weather)?
Duke Energy Response:
The ONS Operations procedure for removal and restoration of KHUs identifies specific planned actions upon notification of impending severe weather conditions, including tornado warnings.
During a dual KHU outage, the procedure requires a licensed operator to be dispatched to the SSF and restoration of the Keowee underground power path if the remaining work can be backed out of or completed and the unit restored within the expected time of the weather impact. The abnormal procedure (AP) for natural disasters is required to be entered following notification of a tornado warning, tornado watch, severe thunderstorm warning, or high wind warning in the Oconee/Pickens County area. The AP requires operators initiate restoration of the following systems to service from any in progress maintenance activities or surveillance testing if possible:
- SSF systems (SSF Diesel Generator, Reactor Coolant Makeup Pumps, SSF Auxiliary Service Water)
- Keowee Underground Power Path
- Keowee Overhead Power Path
" 4160v Power System (Main Feeder or Standby Bus)
- EFW System
- Station ASW Pump/Switchgear Critical Activity Plans are required for Keowee Outages that result in a PRA ORANGE electronic risk assessment tool (ERAT) risk condition or where activities result in greater than 33 percent of TS RA Completion Time being used. These plans, which are required by the Oconee risk management program, are intended to provide structure and oversight to the overall work plan and work execution and are not intended to direct work. Actions required during Keowee Outages (Dual, Overhead, or Underground) that require SSF activation are directed by Operations procedures (Abnormal and Emergency Operating Procedures).
Critical activity plans for dual KHU outages are required to address multiple risk and mitigation strategies, including severe weather. The weather forecast must be reviewed prior to entering a dual KHU outage condition and monitored during the outage window to determine whether work will continue based on changing weather conditions. As part of the Critical Activity Plan for dual KHU outages, the Work Control Center is required to notify the Transmission Control Center (TCC) and the System Operating Center (SOC) to take action to ensure grid reliability and minimize risks (e.g., minimize non-critical maintenance work affecting ONS ties in surrounding power paths and substations). This notification is a prerequisite in the Critical Activity Plan for dual KHU outages.
Enclosure - Duke Energy Response to NRC RAI License Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 6 Question 1 (continued)
During KHU outages, are there any planned actions to ensure availability and reliability of the emergency feedwater system?
Duke Energy Response:
Planned actions to ensure availability and reliability of the Emergency Feedwater (EFW) system for a KHU outage are dependent upon the results of a risk assessment using the ERAT. ERAT factors in the status of plant equipment and the plant schedule for testing and maintenance to identify whether EFW is protected equipment during KHU outages. The Operations Procedure controlling removal and restoration of the Overhead and Underground Power Paths concurrently requires, as a prerequisite for entry into a dual KHU outage, verification that all three Units EFW Systems are fully operable. This procedure also requires the Work Control Center (WCC) to be notified that no discretionary maintenance is allowed on EFW equipment during the outage and to implement the protected equipment program for both KHUs or power paths inoperable per the ONS risk management process. Through this process, the EFW system is identified as protected equipment, which means a protected equipment posting is required, a site wide communication is completed, and surveillances and intrusive work are normally not allowed. The primary purpose of protecting EFW equipment is to ensure it is available for normal operations and for mitigating abnormal or emergency conditions.
Question 2 Please provide the proposed KHU generator field pole rewind outage schedule for both KHU (MS Project or equivalent is acceptable) which includes the identification of all periods of time when one or both KHU are inoperable in accordance with TS up to completion of all work and both KHU restored to operable.
Enclosure - Duke Energy Response to NRC RAI License Amendment Request No. 2012-01, Supplement 3 July 26, 2013 Page 7 Duke Energy Response:
The refined schedule is provided below. It is generally consistent with the schedule provided in June 27, 2012, License Amendment Request as later clarified in an April 11, 2013, Duke Energy/NRC conference call. The overall outage length is the same.
10 Task Name Duration Stan Finsh Janu*y February M c ..
12/29 115 1.12 1.19 *126 212 2M9 2116 M3 3/2 39 We 3r23 130 S Dual KHU outage to late KHU for maintenance 40 hrs Wed 18/14 Thu 1V9114 2 Genrator Pole Rewind (single KHU outage) 840Mrs Thu I//14 Thu 2113/14 3 Contingency f Pole Rewind (srng KHU outage) 380 hrs Thu 2M13/14 Fn 2128114 4 Dual KHU outage to unisolate KHU undergoing maintenance 40 1rs Fn 2128/14 Sun 3r2/14 5 1st Balance Run (single KHU outage) 24hrs Sun 302/14 Mon 3/3/14 6 Duel Unit outage to Install Caicuied Balance Shot 20 hrs Mon 303/14 Tue 314/14 7 2nd Balance Run (single KHU outage) 24hrs Tue 314/14 Wed 315/14 8 Dual Unit Outage for 2nd Balance shot 20 le Wed 305/14 Thu 316/14 9 Final Balance Run (single KHU outage) 48 hrs Thu 30/14 Sat 3/8/14 10 Contingency for Addrtional Balance Shot (dual KHU outage) 20 hrs Sat 3/8/14 Sat 3/8/14 11 Contingency for Addtrbonal Balance Run (single KHU outage) 24 hrs Sat 308/14 Sun 319/14 12 Contingency for Additional Balance Shot (dual KHU outage) 20hrs Sun 319/14 Mon 3110/14 13 Contingency for Additional Balance Run (single KHU outage) 24 hrs Mon 3W10/14 Tue 3M111/14 14 Post Modification Testing (PMT) (single KHU outage) 48 rs Tue 3/11114 Thu 3/13/14 15 Contingency to Resolve Problems Found during PMT (single KHU outage) 184 hrs Thu 3/13/14 Fri 3121/14 16 Corwnissioning Run (Restore to Operability) (single KHU outage) 48 Irs Fri 3121114 Sun 3123114 17 Work order & paperwork closeout, final acceptance, exit TS (single KHU outage) 16hrs Sun 3123/14 Mon 3/24/14' Preted: Keowe Outage Tineh _07; [ Task [,Progress su"Mmry q1V EW TOWks DedPaene -
IDide:V Wed U24113 sph Milestone *Propd Sumrmay WMMM Externl Wilestonte Pop I