ML17058A127
| ML17058A127 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 02/24/2017 |
| From: | Ed Miller Plant Licensing Branch II |
| To: | Pierce C Southern Nuclear Operating Co |
| References | |
| ME9555, ME9556 | |
| Download: ML17058A127 (9) | |
Text
NRR-PMDAPEm Resource From: Miller, Ed Sent: Friday, February 24, 2017 8:53 AM To: 'CRPIERCE (CRPIERCE@southernco.com)'
Cc: 'McElroy, G. Ken'
Subject:
VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION (CAC NOS. ME9555 AND ME9556)
Attachments: Vogtle 4b RAI Feb 24 2017.docx Mr. Pierce, Subsequent to my sending the questions, I received some additional edits to RAIs 6 and 11. The changes have been included in the attached file and well plan on using this version at the public meeting on 2/28/17.
Please let me know if you have any questions. Thanks!
Ed Miller 415-2481 From: Miller, Ed Sent: Thursday, February 23, 2017 8:52 AM To: 'CRPIERCE (CRPIERCE@southernco.com)'
Cc: 'McElroy, G. Ken'
Subject:
FW: VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION (CAC NOS. ME9555 AND ME9556)
Mr. Pierce:
By letters dated September 13, 2012, as supplemented by letters dated August 2, 2013, July 17, 2014, November 11, 2014, December 12, 2014, March 16, 2015, and May 5, 2015, February 17, 2016, April 18, 2016, and July 13, 2016, Southern Nuclear Operating Company, Inc. (SNC), submitted a license amendment request to modify the Vogtle Electric Generating Plant Technical Specifications requirements to permit the use of Risk Informed Completion Times in accordance with Nuclear Energy Institute (NEI) Report NEI-06-09, Revision 0, Risk Informed Technical Specifications Initiative 4b, Risk-Managed Technical Specifications (RMTS). The U.S. Nuclear Regulatory Commission (NRC) staff finds that additional information is needed as set forth in the attached document.
The NRC staff has held public meetings with SNC to discuss these RAIs on January 26, 2015, February 2, 2017, and February 7, 2017. Currently, the NRC staff has another public meeting with SNC scheduled for February 28, 2017, to discuss the information needs. In addition to ensuring the questions are clear, we also intend to discuss what would be an appropriate response schedule at the meeting. If you have any questions prior to the meeting, please let me know.
Ed Miller, Project Manager Special Projects and Process Branch Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation (301) 415-2481 1
Hearing Identifier: NRR_PMDA Email Number: 3371 Mail Envelope Properties (7a772365f5dd4b739d99c3f8bd3e155e)
Subject:
VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 - REQUEST FOR ADDITIONAL INFORMATION (CAC NOS. ME9555 AND ME9556)
Sent Date: 2/24/2017 8:52:38 AM Received Date: 2/24/2017 8:52:00 AM From: Miller, Ed Created By: Ed.Miller@nrc.gov Recipients:
"'McElroy, G. Ken'" <GKMCELRO@southernco.com>
Tracking Status: None
"'CRPIERCE (CRPIERCE@southernco.com)'" <CRPIERCE@southernco.com>
Tracking Status: None Post Office: HQPWMSMRS03.nrc.gov Files Size Date & Time MESSAGE 1989 2/24/2017 8:52:00 AM Vogtle 4b RAI Feb 24 2017.docx 35352 Options Priority: Standard Return Notification: No Reply Requested: No Sensitivity: Normal Expiration Date:
Recipients Received:
REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION SOUTHERN NUCLEAR OPERATING COMPANY, INC.
VOGTLE ELECTRIC GENERATING PLANT, UNITS 1 AND 2 DOCKET NOS. 50-424 AND 50-425 By letter dated September 13, 2012, as supplemented by letters dated August 2, 2013, July 17, 2014, November 11, 2014, December 12, 2014, March 16, 2015, and May 5, 2015, February 17, 2016, April 18, 2016, and July 13, 2016 (ADAMS Accession Nos. ML12258A055, ML13217A072, ML14198A574, ML14315A051, ML14346A643, ML15075A479, ML15125A446, ML16048A096, ML16109A338, and ML16195A503, respectively), Southern Nuclear Company, Inc. (SNC), proposed changes to the Technical Specifications (TSs) for the Vogtle Electric Generating Plant (VEGP or Vogtle). The proposed amendment would modify TS requirements to permit the use of Risk Informed Completion Times (RICTs) in accordance with Topical Report (TR) Nuclear Energy Institute (NEI) 06-09, Revision 0-A, Risk Informed Technical Specifications Initiative 4b, Risk-Managed Technical Specifications (RMTS) Guidelines.
By electronic correspondence dated January 24, 2017 (ADAMS Accession No. ML17027A018),
the NRC staff provided a draft request for additional information to SNC for discussion at a public meeting. Subsequently at public meetings dated January 26 and February 2, 2017, the NRC staff discussed these information needs with SNC. By electronic correspondence dated February 3, 2017 (ADAMS Accession No. ML17037A175), the NRC staff provided an updated request for additional information that addressed issues discussed at the meetings. Another public meeting was held on February 7, 2017, to continue discussions. As a result of these discussions, the NRC staff has further modified RAI questions 6, 10, and 11 to provide additional clarity and regulatory basis. RAIs 6 and 11 have been modified to more clearly convey what information a complete response would contain. RAI 10 was originally written as a broad question applied to multiple TS actions, however, it has been modified to more specific individual questions for each specification. The other questions from the February 3, 2017, correspondence remain valid.
RAI 6
According to Section A-1.3.2.1 of Appendix A of RG 1.177, when a component fails, the CCF probability for the remaining redundant components should be increased to represent the conditional failure probability due to CCF of these components, in order to account for the possibility that the first failure was caused by a CCF mechanism. When a component fails, the calculation of the plant risk, assuming that there is no increase in CCF potential in the redundant components before any extent of condition evaluation is completed, could lead to a non-conservative extended completion time calculation, as illustrated by inclusion of the guidance in Appendix A of RG 1.177. Much of the discussion in Appendix A describes how configuration specific risk calculations should be performed.
In Section 3.2 of the NRC safety evaluation for NEI 06-09, the NRC staff stated that compliance
with the guidance of RG 1.174 and RG 1.177, is achieved by evaluation using a comprehensive risk analysis, which assesses the configuration-specific risk by including contributions from human errors and common cause failures.
The limitations and conditions in Section 4.0 of the safety evaluation for NEI 06-09 state that:
The [NRC] staff interprets TR NEI 06-09, Revision 0, as requiring consideration of [additional] RMAs [due to the potential for increased risks from common cause failure of similar equipment] whenever the redundant components are considered to remain operable, but the licensee has not completed the extent of condition evaluations [such that a CCF mechanism can be confirmed or excluded].
The requirement to consider additional RMAs prior to the determination that a CCF mechanism exists or does not exist was included by the NRC staff in the safety evaluation for NEI 06-09 as an additional measure to account for the potential that the first failure was caused by a CCF mechanism. However no exception to the RG 1.177 guidance was taken in the LAR for the calculation of the RICT with regards to the quantification of CCF before a CCF can be confirmed or excluded.
Please confirm and describe how that treatment of CCF, in the case of an emergent failure, either meets the guidance in RG 1.177 or meets the intent of this guidance when quantifying a RICT. Addressing CCF in this case could adjust the RICT calculation to numerically account for the increased possibility of CC. Alternatively, prior to exceeding the front stop, implement RMAs that are not credited in the RICT calculation sufficient to ensure that any safety function of the remaining train would not be lost if a CCF condition did exist and the remaining train failed to function upon demand.
Either option would need to remain in effect until the possibility of CCF was excluded at which point, a new RICT could be calculated or appropriate RMAs reconsidered.
RAI 10
The Commissions Policy on Probabilistic Risk Assessment (Use of Probabilistic Risk Assessment Methods in Nuclear Regulatory Activities, dated August 16, 1995) identifies five key safety principles required for risk-informed decision-making applied to changes to TSs as delineated in Regulatory Guides 1.177 and 1.174. They are:
- The proposed change meets current regulations;
- The proposed change is consistent with defense-in-depth philosophy;
- The proposed change maintains sufficient safety margins;
- Increases in risk resulting from the proposed change are small and consistent with the Commissions Safety Goal Policy Statement; and
- The impact of the proposed change is monitored with performance measurement strategies.
RAI 10.1:
NEI 06-09, Risk Informed Technical Specifications Initiative 4b: Risk Managed Technical Specifications (RMTS), Revision 0-A, states that Risk Management Actions (RMAs) and compensatory actions for significant components should be predefined to the extent practicable in plant procedures and implemented at the earliest appropriate time in order to maintain defense-in-depth.
Moreover, the NRC staffs safety evaluation for NEI 06-09, Section 4.0, Limitations and Conditions, (ADAMS No. ML12286A322) states that a licensees LAR adopting the NEI 06-09 initiative will describe the process to identify and provide compensatory measures and RMAs during extended Completion Times (CT), and provide examples of compensatory measures/RMAs.
In the LAR dated September 13, 2012, Enclosure 10, Risk Management Action Example, pages E10-3 and E10-4, the licensee provided two examples of risk management actions that are considered during a RICT for: a) inoperable diesel generator, and b) inoperable battery.
Provide similar examples of RMAs to assure a reasonable balance of defense-in-depth is maintained for the following TS actions:
Current Proposed TS Condition Description Completion Maximum Time Backstop 3.8.1 C Two required offsite circuits inoperable. 24h 30 days 3.8.1 D One required offsite circuit inoperable 12h 30 days AND One DG inoperable.
3.8.1 F One automatic load sequencer 12h 30 days inoperable.
3.8.4 C One DC electrical power source 2h 30 days inoperable for reasons other than Condition A or B.
3.8.7 A One required inverter inoperable. 24h 30 days RAI 10.2:
As summarized from the UFSAR, Vogtles TS Bases state: The AC, DC, and AC vital bus electrical power distribution systems are designed to provide sufficient capacity, capability, redundancy, and reliability to ensure the availability of necessary power to ESF systems so that the fuel, Reactor Coolant System, and containment design limits are not exceeded. When the licensee enters TS Conditions 3.8.9.A, 3.8.9.B, or 3.8.9.C, these subsystems carry the potential vulnerability to single failures that will reduce protection against the exceedance of the design limits.
Current Proposed TS Condition Description Completion Maximum Time Backstop 3.8.9 A One or more AC electrical power 8h 30 days distribution subsystems inoperable.
3.8.9 B One or more AC vital bus electrical power 2h 30 days distribution subsystems inoperable.
3.8.9 C One or more DC electrical power 2h 30 days distribution subsystems inoperable
- 1) For each TS conditions lowest estimated RICT (least amount of time available, calculated beyond the front-stop):
- a. Describe a scenario/plant configuration for this condition.
- b. Explain how each subsystem would retain the ability to defend against vulnerabilities during this scenario (e.g., examples of RMAs to assure a reasonable balance of defense-in-depth is maintained for this TS condition).
- 2) For each TS conditions highest estimated RICT (most risk significant component(s) that would result in a calculation close to the 30-day back-stop, without PRA functional consideration):
- a. Describe a scenario/plant configuration for this condition.
- b. Explain how each subsystem would retain the ability to defend against vulnerabilities during this scenario (e.g., examples of RMAs to assure a reasonable balance of defense-in-depth is maintained for this TS condition).
RAI 10.3:
The proposed changes to the TS include Condition 3.4.11.F, Two [PORV] Block Valves inoperable. The current TS require restoring one block valve to operable status within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.
The proposed change is to permit the option of calculating a RICT for this Required Action. Per the proposed RICT program, the RICT could be calculated to be any length of time between 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> and 30 days.
The TS bases state that an OPERABLE block valve may be either open and energized, or closed and energized with the capability to be opened, since the required safety function is accomplished by manual operation. Although typically open to allow PORV operation, the block valves may be OPERABLE when closed to isolate the flow path of an inoperable PORV that is capable of being manually cycled (e.g., as in the case of excessive PORV leakage).
A TS loss of function is considered to exist when two redundant SSCs are simultaneously inoperable. Voluntary entry into a condition representing a TS loss of function is prohibited throughout the proposed TSs by a Note which modifies the Condition. If emergent conditions create a TS loss of function, the RICT is limited to a maximum of 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and constraints on PRA functionality are applied.
The required position of the PORV block valves could be either open or closed, dependent on the condition of its associated PORV. If the block valves are not repositionable, then inoperability of the block valves could result in a loss of safety function.
Please provide an explanation of how PRA functionality would be applied in this Condition, why this condition would not be considered a TS loss of function, and how it would be assured that design basis success criteria would be satisfied.
RAI 10.4:
The proposed changes to the TS include Condition 3.5.1.B, One Accumulator Inoperable (for reasons other than Boron Concentration).
The current TS require restoring the accumulator to operable status within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />. The proposed change is to permit the option of calculating a RICT for this Required Action. Per the proposed RICT program, the RICT could be calculated to be any length of time between 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> and 30 days.
Section 6.3.2 of the Vogtle FSAR states that ECCS components are designed such that a minimum of three accumulators, one charging pump, one safety injection pump, one residual heat removal pump, one RHR heat exchanger, together with their associated valves and piping will ensure adequate core cooling in the event of a design basis accident.
The Vogtle TS Bases states that the need to ensure that three accumulators are adequate for this function is consistent with the LOCA assumption that the entire contents of one accumulator will be lost via the RCS pipe break during the blowdown phase of the LOCA.
It is not clear to the staff how the assumptions in the accident analysis would be satisfied for a LOCA in which the contents of one accumulator is lost through the break, and a second accumulator is inoperable at the time of the event.
Please provide an explanation of how PRA functionality would be applied in this Condition, why this condition would not be considered a TS loss of function, and how it would be assured that design basis success criteria would be satisfied.
RAI 10-5:
The proposed changes to the TS include Condition 3.6.3.B, Containment Penetrations with more than one inoperable containment isolation valve, and Condition 3.6.3.C, Containment Penetrations with Purge Valves Leakage outside limits.
The Required Action for Condition B is to isolate the affected penetration flow path by use of at least one closed and de-activated automatic valve, closed manual valve, or blind flange. The current Completion Time to isolate the penetration flow path is one hour, which is consistent with the time specified to restore containment leakage to within its limits in TS LCO 3.6.1. Additionally, there is a requirement to verify the affected penetration flow path is isolated once per 31 days for devices outside containment.
Condition C applies when one or more penetration flow paths have one or more containment purge valves not within purge valve leakage limits. The required action is to isolate the affected penetration flow path by use of at least one closed and de-activated automatic valve, closed manual valve, or blind flange.
The proposed change is to permit the option of calculating a RICT for these Required Actions.
Per the proposed RICT program, the RICT could be calculated to be any length of time between 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br />, for Condition B, and 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> for Condition C and 30 days. During this period, no actions would be required to isolate the affected penetration pathway(s); and automatic actions to isolate the pathway may not be assured.
The containment isolation valves form part of the containment pressure boundary and provide a means for fluid penetrations not serving accident consequence limiting systems to be provided with two isolation barriers that are closed on a containment isolation signal. The containment penetrations covered under conditions 3.6.3.B and C include those penetrations that are connected directly to the RCS or to the containment atmosphere, and are typically isolated using two isolation devices in series. If both of the isolation devices are inoperable in the open position, the safety function of minimizing the loss of reactor coolant inventory and maintaining the containment pressure boundary would not be assured.
Please provide justification to support extension of the Completion Time up to a maximum of 30 days or remove these conditions from the scope of the RICT program. Please include an explanation of how PRA functionality would be applied in this Condition, why this condition would not be considered a TS loss of function, and how it would be assured that design basis success criteria would be satisfied.
RAI 11
In section 4.0 Limitations and Conditions of the NRC Staff SE to NEI 06-09, the staff stated:
As part of its review and approval of a licensees application requesting to implement the RMTS, the NRC staff intends to impose a license condition that will explicitly address the scope of the PRA and non-PRA methods approved by the NRC staff for use in the plant-specific RMTS program. If a licensee wishes to change its methods, and the change is outside the bounds of the license condition, the licensee will need NRC approval, via a license amendment, of the implementation of the new method in its RMTS program.
Please propose a license condition limiting the scope of the PRA and non-PRA methods to what is approved by the NRC staff for use in the plant-specific RMTS program. An example is provided below.
The risk assessment approach, methods, and data shall be acceptable to the NRC, be based on the as-built, as-operated, and maintained plant; and reflect the operating experience at the plant. Acceptable methods to assess the risk from extending the completion times may include methods that have been accepted for use in the RICT program, or methods generically accepted for use by NRC. If a licensee wishes to change its methods, and the change is outside the bounds of the license condition, the licensee
will need NRC approval, via a license amendment, of the implementation of the new method in its RMTS program.