ML24108A181
| ML24108A181 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 04/15/2024 |
| From: | James Holloway Virginia Electric & Power Co (VEPCO) |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| 24-072 | |
| Download: ML24108A181 (1) | |
Text
April 15, 2024 VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNITS 1 AND 2 PROPOSED LICENSE AMENDMENT REQUEST 10 CFR 50.90 Serial No.:
24-072 NRA/GDM:
RO Docket Nos.:
50-280/281 License Nos.: DPR-32/37 RECLASSIFICATION OF LOW HEAD SAFETY INJECTION FLOW INDICATION REGULATORY GUIDE 1.97 VARIABLE SUPPLEMENTAL INFORMATION By letter dated August 10, 2023 (ADAMS Accession No. ML23226A186), Virginia Electric and Power Company (Dominion Energy Virginia) submitted a license amendment request (LAR) for Surry Power Station (SPS) Units 1 and 2 to revise the SPS Technical Specifications (TS) to add Low Head Safety Injection (LHSI) flow indication as required accident monitoring instrumentation. The addition of LHSI flow indication to the TS is due to reclassification of the Regulatory Guide (RG) 1.97, Revision 3, "Criteria for Accident Monitoring Instrumentation for Nuclear Power Plants," Type D Category 2 variable to a Type A Category 1 variable. The reclassification of the LHSI flow instrumentation resulted from a reanalysis of the LHSI pumps' net positive suction head (NPSH) requirements that was performed to obtain additional operating margin. The reanalysis identified the need for manual operator action to throttle LHSI pump flow when only a single pump is in operation for a brief period of time under certain operating conditions. This operating scenario identified the commensurate need to reclassify the existing RG 1.97 LHSI flow instrumentation and to incorporate the instrumentation into the Accident Monitoring TS.
During a conference call on March 14, 2024, between Dominion Energy Virginia and the NRC review staff, Dominion Energy Virginia clarified the manual operator actions required for throttling LHSI pump flow to ensure adequate net positive suction head available.
During a subsequent conference call on March 21, 2024, Dominion Energy provided an overview of the LHSI subsystem and its redundant trains, as well as its operation during initial operation and following Recirculation Mode Transfer (RMT). At the conclusion of the calls, Dominion Energy Virginia stated it would provide the following supplemental information in support of the LAR: 1) a discussion of the required manual operator actions for throttling a LHSI pump discharge valve, 2) a description of the LHSI system and its operation, and 3) a discussion of the qualification of the LHSI RG 1.97 flow instrumentation. The supplemental information is provided in the attachment.
Serial No.24-072 Docket Nos. 50-280/281 Page 2 of 3 If you should have any questions regarding this submittat please contact Mr. Gary D.
Miller at (804) 273-2771.
Respectfully, James E. Holloway Vice President - Nuclear Engineering and Fleet Support
Attachment:
Supplemental Information in Support of License Amendment Request -
Addition of Low Head Safety Injection Flow Instrumentation to the RG 1.97 TS Instrumentation Table Commitment contained in this correspondence:
- 1. The time-critical operator actions to throttle and unthrottle the LHSI pump discharge valve will be controlled in the SPS time-critical operator action program.
COMMONWEAL TH OF VIRGINIA
)
)
COUNTY OF HENRICO
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The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mr. James E. Holloway, who is Vice President - Nuclear Engineering and Fleet Support, of Virginia Electric and Power Company. He has affirmed before me that he is duly authorized to execute and file the foregoing document in behalf of that company, and that the statements in the document are true to the best of his knowledge and belief.
Acknowledged before me this
\\ S +" day of A:v-<, \\
, 2024.
My Commission Expires: :TamJ~v~ "31, 2.028.
KATHRYN HILL BARRET NOTARY PUBLIC COMMONWEALTH OF VIRGINIA MY COMMISSION EXPIRES JANUARY 31, 2028 otary Public
cc:
U.S. Nuclear Regulatory Commission - Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, GA 30303-1257 NRC Senior Resident Inspector Surry Power Station Mr. L. John Klos NRC Project Manager - Surry U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738 Mr. G. Edward Miller NRC Senior Project Manager - North Anna U.S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, MD 20852-2738 State Health Commissioner Virginia Department of Health James Madison Building - 7th floor 109 Governor Street Suite 730 Richmond, VA 23219 Serial No.24-072 Docket Nos. 50-280/281 Page 3 of 3
Attachment Serial No.24-072 Docket Nos. 50-280/281 SUPPLEMENTAL INFORMATION IN SUPPORT OF LICENSE AMENDMENT REQUEST ADDITION OF LOW HEAD SAFETY INJECTION FLOW INSTRUMENTATION TO THE RG 1.97 TS INSTRUMENTATION TABLE Virginia Electric and Power Company (Dominion Energy Virginia)
Surry Power Station Units 1 and 2
SUPPLEMENTAL INFORMATION Serial No.24-072 Docket Nos. 50-280/281 Attachment LICENSE AMENDMENT REQUEST - ADDITION OF LOW HEAD SAFETY INJECTION FLOW INSTRUMENTATION TO THE RG 1.97 TS INSTRUMENTATION TABLE SURRY POWER STATION UNITS 1 AND 2 BACKGROUND By letter dated August 10, 2023 (ADAMS Accession No. ML23226A186), Virginia Electric and Power Company (Dominion Energy Virginia) submitted a license amendment request (LAR) for Surry Power Station (SPS) Units 1 and 2 to revise the SPS Technical Specifications (TS) to add Low Head Safety Injection (LHSI) flow indication as required accident monitoring instrumentation. The addition of LHSI flow indication to the TS is due to reclassification of the Regulatory Guide (RG) 1.97, Revision 3, 11Criteria for Accident Monitoring Instrumentation for Nuclear Power Plants," Type D Category 2 variable to a Type A Category 1 variable. The reclassification of the LHSI flow instrumentation resulted from a reanalysis of the LHSI pumps' net positive suction head (NPSH) requirements that was performed to obtain additional operating margin. The reanalysis identified the need for manual operator action to throttle LHSI pump flow when only a single pump is in operation for a brief period of time under certain operating conditions. This operating scenario identified the commensurate need to reclassify the existing RG 1.97 LHSI flow instrumentation and to incorporate the instrumentation into the Accident Monitoring TS.
During a conference call on March 14, 2024, between Dominion Energy Virginia and the NRC review staff, Dominion Energy Virginia clarified the manual operator actions required for throttling LHSI pump flow to ensure adequate net positive suction head available.
During a subsequent conference call on March 21, 2024, Dominion Energy provided an overview of the LHSI subsystem and its redundant trains, as well as its operation during initial operation and following Recirculation Mode Transfer (RMT). At the conclusion of the calls, Dominion Energy Virginia stated it would provide the following supplemental information in support of the LAR: 1) a discussion of the required manual operator actions for throttling a LHSI pump discharge valve, 2) a description of the LHSI system and its operation, and 3) a discussion of the qualification of LHSI RG 1.97 flow instrumentation.
The supplemental information is provided below.
Required Manual Operator Actions for Throttling a LHSI Pump Discharge Valve As stated in the LAR, a reanalysis of the LHSI pumps' performance was performed to obtain additional NPSH margin for a brief period when RMT actuates if only one LHSI pump is running. With only one pump running, when RMT occurs, pump flow increases to a point where the NPSH required is equal to or slightly exceeds NPSH available based on the conservative NRG-approved methodology used in the reanalysis. With two pumps Page 1 of 8
Serial No.24-072 Docket Nos. 50-280/281 Attachment running, total Safety Injection (SI) flow is greater, but individual LHSI pump flow is lower, so the NPSH margin issue does not exist.
To resolve this issue, operator actions were developed to throttle the running LHSI pump's discharge valve prior to RMT. This action increases the NPSH margin during the most limiting time period. To perform this action, LHSI pump flow indication is required since the operator would throttle to a pre-designated flow band. After verification that recirculation has been properly established, the LHSI discharge valve would be restored to its fully open position thus providing full pump flow to the core. It is important to note that the manual operator action to throttle LHSI pump flow is being used to increase NPSH margin; however, failure to complete the throttling action would not result in failure of the LHSI pump. The manual-remote operator action to throttle LHSI flow by throttling the operating LHSI pump discharge valve is performed in the Main Control Room (MCR). No field operator actions are required. The LHSI pump discharge valve switches are located on the MCR Benchboard, and LHSI flow indication is located on the MCR Vertical Board (See Figure 1).
The entry condition for Emergency Operating Procedure (EOP) ES-1.3 (TRANSFER TO COLD LEG RECIRCULATION) is currently set to 20% Refueling Water Storage Tank (RWST) level. MCR meters are the credited indication for meeting this entry condition; however, an alarm (RWST Low Level) is also set to this value for an additional operator cue. The EOP entry condition and the RWST Low Level alarm setpoints are being increased to 30% RWST level as part of this design change to provide ample time for the operator to throttle the LHSI flow via the operating pump discharge valve. EOP ES-1.3, Step 4, currently has the operators check that both LHSI pumps are running. A planned procedure change will revise the associated Response Not Obtained (RNO) Step to direct the operator to throttle the running LHSI pump flow using its respective discharge valve.
The time to throttle the LHSI flow is based on the available systems and components in service at the time of the event. Since the transition into ES-1.3 and RMT are both based on RWST level, the time to throttle the LHSI flow is dependent upon the number of systems drawing from the RWST. If a single LHSI pump fails with both ESF trains available, the throttling could occur just after the first half-hour of the event, whereas if only one ESF train is available, the throttling could occur just after the first hour of the event. Therefore, there is no specified time required since it is a parameter-based action; however, the timeliness of performing the manual throttling operator actions has been validated with worst-case conditions (quickest RWST drawdown) through several validations. Furthermore, while a parameter-based action, the action will be listed and controlled under the time-critical operator action program to ensure it continues to be met by performing periodic and/or for-cause validations as directed by the program.
In addition to the throttling action, an unthrottling action is being established. The safety analyses for containment depressurization were run at the minimum throttled flow rate and established a time-critical operator action to restore full LHSI flow, i.e., fully opening the operating LHSI pump discharge valve, within 4.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> after RMT is completed. This Page 2 of 8
Serial No.24-072 Docket Nos. 50-280/281 Attachment time critical operator action time is based on returning the containment to subatmospheric conditions within the dose consequences leakage assumption of six hours. The minimum flowrate was verified to exceed core decay heat removal requirements, so the containment pressure response is the limiting parameter. The time critical operator action to unthrottle the LHSI pump discharge valve within 4.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> of RMT completion will also be controlled in the time critical operator action program. EOP ES-1.3 will have a step for the operators to fully open the LHSI discharge valve that was throttled once the RWST is depleted (~0% RWST level); this is well before the 4.5 hours5.787037e-5 days <br />0.00139 hours <br />8.267196e-6 weeks <br />1.9025e-6 months <br /> from the completion of RMT. As a double check, a step for this unthrottling action is also placed in EOP E-1, LOSS OF REACTOR OR SECONDARY COOLANT, which is the procedure that would be transitioned back into from ES-1.3. Consequently, sufficient time is available for the MCR operators to accomplish throttling and unthrottling of the LHSI flow and will continue to be verified in accordance with the time critical operator action program. Since the manual operator actions will be proceduralized and included in the SPS operator training program, no work orders or pre-job briefs are required to successfully accomplish these actions.
In summary:
The required instruments and controls the operators need to throttle LHSI flow are located in the MCR.
The operator actions to throttle/unthrottle LHSI flow are EOP directed steps.
A conservative approach was used to ensure human actions will occur in the appropriate timeframe, including an operator cue at 30% RWST level with the action to throttle the LHSI flow by 13.5% RWST level, and the action to unthrottle the LHSI flow once the RWST has been depleted ( ~0% RWST level or after the Containment Spray pumps have been secured due to cavitation).
To validate the conservative approach and adequacy of the timing, simulator validations were successfully performed.
Since the required manual operator actions (i.e., throttling and unthrottling LHSI pump flow) are included in the EOPs and are classified as time critical operator actions, they will be included in the operator training program.
Since the EOP actions are performed from the MCR, the actions are completed with the normal staff complement and do not add significant operator burden (i.e., there is no impact to other critical operator actions).
Finally, the manual operator action to throttle LHSI pump flow is used to increase NPSH margin. However, failure to complete the action would not result in failure of the LHSI pump.
Page 3 of 8
LHSI System Trains and Operation Serial No.24-072 Docket Nos. 50-280/281 Attachment Dominion Energy Virginia defines a train as a redundant portion of a system or subsystem. Redundancy is obtained when failure of a single train does not result in failure of the system or subsystem's overall design function. A subsystem can be used to describe either a train within a system, or a separate portion of a system that provides its own design function that is also necessary for overall system function. (For example, Inside Recirculation Spray and Outside Recirculation Spray are separate subsystems of the Recirculation Spray System, each providing a diverse means for delivering recirculation spray to cool containment in response to a design basis event.) With respect to the LAR, Dominion Energy Virginia's use of the terms "train" and "subsystem" are interchangeable and are being used to describe the LHSI 'A' and 'B' redundant trains.
To better describe the separation and redundancy of the LHSI trains, highlighted sketches are provided in Figures 2 and 3 to illustrate the major flowpaths. Figure 2 depicts the overall SI system in Injection Mode, and Figure 3 shows the SI system in Recirculation Mode. The two figures highlight the 'A' LHSI Train in Orange and the 'B' LHSI Train in Purple, which corresponds to the plant color scheme for the 'H' and 'J' emergency buses, to show that the 'A' train is powered by the 'H' emergency bus, and the 'B' train is powered by the 'J' emergency bus to ensure the availability of redundant emergency power to the LHSI system.
As noted above, a reanalysis of the LHSI pumps' performance was performed to obtain additional NPSH margin for a brief period when RMT actuates if only one LHSI pump is running. Consequently, this situation would only arise in the event a failure occurred in one of the two redundant trains. If one train of LHSI is inoperable due to maintenance or testing, the operable train is capable of performing the required safety function by manually throttling the operating LHSI pump discharge valve as discussed above. A single failure in the operable train does not have to be assumed when the redundant train is inoperable and in a TS action statement allowed outage time (i.e., Completion Time).
This NRC position is confirmed (see bold emphasis below) in NRC Generic Letter 80-30, Clarification of the Term "Operable" as It Applies to Single Failure Criterion for Safety Systems Required by TS, dated April 10, 1980, which states:
The NRC's Standard Technical Specifications (STS) were fonnulated to preserve the single failure criterion for systems that are relied upon in the safety analysis report.
By and large, the single failure criterion is preserved by specifying Limiting Conditions for Operation (LCOs) that require all redundant components of safety related systems to be OPERABLE. When the required redundancy is not maintained, either due to equipment failure or maintenance outage, action is required, within a specified time, to change the operating mode of the plant to place it in a safe condition. The specified time to take action, usually called the equipment out-of-service time, is a temporary relaxation of the single failure criterion, which, consistent with overall system reliability considerations, provides a limited time to fix equipment or otherwise make it OPERABLE. If equipment can be returned to OPERABLE status within the specified time, plant shutdown is not required.
Page 4 of 8
Serial No.24-072 Docket Nos. 50-280/281 Attachment Qualification of RG 1.97 Category 1 LHSI Flow Instrumentation The existing LHSI flow instrumentation is currently categorized as a RG 1.97 Category 2 Type D variable and is being recategorized as a Category 1 Type A variable due to the potential need for the MCR operator to throttle LHSI flow under certain operating conditions as discussed above and in the LAR. Even though the existing LHSI flow instrumentation is currently categorized as a RG 1.97 Category 2 Type D variable, it was installed as safety related instrumentation. Consequently, the LHSI flow instrumentation is seismically qualified, provides continuous display and is powered by a vital bus. Each LHSI train has its own flow instrumentation loop thus providing the necessary redundancy should one LHSI train experience a single failure rendering it inoperable. The separate trains are identified in Figures 1 through 3.
Page 5 of 8
At 30% RWST Level -
Operators begin manual actions from MCR Figure 1 Read Flow on Indicator in MCR Page 6 of 8
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