ML15202A125
| ML15202A125 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 07/16/2015 |
| From: | Mark D. Sartain Dominion, Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 15-288, TAC MF5715, TAC MF5716 | |
| Download: ML15202A125 (7) | |
Text
iDomi nion Dominion Nuclear Connecticut, Inc.
5000 Dominion Boulevard, Glen Allen, VA 23060 Web Address: www.dom.com U. S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 July 16, 2015 Serial No.
NLOS/WDC Docket Nos.
License Nos.15-288 R0 50-336/423 DPR-65 NPF-49 DOMINION NUCLEAR CONNECTICUT. INC.
MILLSTONE POWER STATION UNITS 2 AND 3 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523. REVISION 2, GENERIC LETTER 2008-01. MANAGING GAS ACCUMULATION (TAC NO. MF5715 & MF5716)
By letter dated January 15, 2015, and supplemented by letter dated April 15, 2015, Dominion Nuclear Connecticut, Inc. (DNC) submitted a license amendment request (LAR) for Millstone Power Station Unit 2 (MPS2) and Millstone Power Station Unit 3 (MPS3). The proposed amendment would modify technical specification requirements to address Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," as described in Technical Specifications Task Force (TSTF)-523, Revision 2, "Generic Letter 2008-01, Managing Gas Accumulation."
TSTF-523, Revision 2 is approved for use by the Nuclear Regulatory Commission (NRC) and was announced in the Federal Register on January 15, 2014 (79 FR 2700). In an email dated June 1, 2015, the NRC transmitted a request for additional information (RAI) related to the LAR. DNC agreed to respond to the RAI by July 17, 2015.
The attachment to this letter provides DNC's response to the NRC's RAI Questions 2, 3, 4, 5, and 6. The responses to RAI Questions 1, 7, 8, and 9 will be submitted by July 31, 2015.
If you should have any questions regarding this submittal, please contact Wanda Craft at (804) 273-4687.
Sincerely, Mark D. Sartain Vice President - Nuclear Engineering COMMONWEALTH OF VIRGINIA COUNTY OF HENRICO
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The foregoing document was acknowledged before me, in and for the County aforesaid, today by Mr. Mark D. Sartain, who is Vice President - Nuclear Engineering, of Dominion Nuclear Connecticut.
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 I*'P day of 2015.
My Commission Expires:
'*UraO.ao j '31,O ~.IC I
WANDA D. CRAFT No tary Publi I
Notary Public Notay Pbli v
Commonwealth of Virginia My Reg. # 7520495 2 1 Mycommission Expires January 31, 2t.* i4rr~*
Serial No.15-288 Docket Nos. 50-336/423 Page 2 of 2
Attachment:
Response to Request for Additional Information Regarding License Amendment Request to Adopt TSTF-523 - Questions 2, 3, 4, 5, and 6 Commitments contained in this letter: None cc:
U.S. Nuclear Regulatory Commission Region I 2100 Renaissance Blvd Suite 100 King of Prussia, PA 19406-2713 Richard V. Guzman NRC Senior Project Manager U.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C2 11555 Rockville Pike Rockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power Station Director, Radiation Division Department of Energy and Environmental Protection 79 Elm Street Hartford, CT 06106-5127
Serial No.15-288 Docket Nos. 50-336/423 ATTACHMENT RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523 -
QUESTIONS 2, 3, 4, 5, AND 6 DOMINION NUCLEAR CONNECTICUT, INC.
MILLSTONE POWER STATION UNITS 2 AND 3
Serial No.15-288 Docket Nos. 50-336/423 Attachment, Page 1 of 4 By letter dated January 15, 2015, and supplemented by letter dated April 15, 2015, Dominion Nuclear Connecticut, Inc. (DNC) submitted a license amendment request (LAR) for Millstone Power Station Unit 2 (MPS2) and Millstone Power Station Unit 3 (MPS3).
The proposed amendment would modify Technical Specification (TS) requirements to address Generic Letter 2008-01, "Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," as described in Technical Specifications Task Force (TSTF)-523, Revision 2, "Generic Letter 2008-01, Managing Gas Accumulation." TSTF-523, Revision 2 is approved for use by the Nuclear Regulatory Commission (NRC) and was announced in the Federal Register on January 15, 2014 (79 FR 2700). In an email dated June 1, 2015, the NRC transmitted a request for additional information (RAI) related to the LAR.
This attachment provides DNC's response to the NRC's RAI Questions 2, 3, 4, 5, and 6.
RAI 2
The Millstone Power Station Unit 3 (MPS3) Containment Quench Spray System (QSS) is stated to be excluded from surveillance requirements (SRs), in part, because there are no identified gas intrusion mechanisms. Please explain how potential operator error during initial filling is not a gas intrusion mechanism for this system.
DNC Response The QSS suction and discharge piping is filled by gravity from the head of water supplied by the Refueling Water Storage Tank (RWST).
Suction piping is properly sloped such that it is either self-venting back to the RWST or self-venting to the QSS pump where it can be vented locally. Once filled, each train is dynamically vented by running its QSS pump on recirculation at rated flow back to the RWST.
Quarterly operability surveillances are also performed for each pump train by operating the pump at rated flow (approximately 4000 gpm) with flow from the RWST outlet through the pumps to the discharge recirculation line back to the RWST. The flow rate through this piping is sufficient to ensure that the suction lines and the discharge lines up to the recirculation line are full of water and adequately swept of any accumulated gases (14" schedule 40 suction line, Froude number = 1.60, 12" schedule 40 discharge line, Froude No. = 2.00). Thus, any potential air in the system piping, regardless of the cause, would be dynamically removed following any system maintenance and on a quarterly basis thereafter.
RAI 3
The MPS3 operating centrifugal charging pump (CCP), associated pump piping, the recirculation spray system (RSS) pump, the RSS heat exchanger, and associated RSS piping are excluded from SRs.
This appears to be inconsistent with TSTF-523, Revision 2, "Generic Letter 2008-0 1, Managing Gas Accumulation." Please provide an
Serial No.15-288 Docket Nos. 50-336/423 Attachment, Page 2 of 4 explanation for this apparent inconsistency. Include a discussion of dormant piping that may accumulate gas associated with operating CCP flow such as a tee with no flow in the vertical connection, but with flow entering and leaving through the horizontal connections.
Also, address the potential for gas generation associated with flow through bypass orifices.
DNC Response An explanation for exclusion of the RSS from SRs was provided in the April 15, 2015 supplement to the LAR.
MPS3's current TS 4.5.2.b.1 does not require verification that the operating charging pump is full of water.
No revision to the exception of surveillance related to the operating charging pump was proposed in the LAR. The charging system at MPS3 has one pump per train plus a swing pump. With one charging pump normally in operation, the suction lines of the other two charging pumps are stagnant.
Due to the close proximity of the inter-connecting pump suction lines, the vibration from a running charging pump was discovered to cause too much chatter to verify the full-of-water status via the Ultrasonic-Test (UT) method. Therefore, the associated suction piping for the two non-operating charging pumps is manually vented every 31 days. Venting of the operating charging pump's associated suction piping is not required by the TS since a system in operation is considered self-venting and cannot develop voids and pockets of entrained gases.
The concern that gas may accumulate in dormant CCP suction piping during normal plant operation has been addressed. The configuration of the CCP suction header does in fact contain stagnant piping in both horizontal and vertical orientations. Each train of charging can be aligned to a Boric Acid Storage Tank (BAST) via a 3-inch vertical take-off from its associated suction header. These stagnant lines are known to be gas collectors due to their vertical orientation.
Thus, a separate UT gas monitoring surveillance, controlled by Technical Requirements Manual (TRM), is performed on the gravity boration piping to ensure the BAST system remains available.
The common suction header from the RWST also contains a 4-inch vertical take-off that aligns the charging pumps to a hydro test pump that was used during original plant start-up testing.
Although this piping is susceptible to gas accumulation, the test pump and associated piping is retired in place and therefore is not monitored for gas accumulation.
There is a 6-inch horizontal line that connects each train of charging to the swing pump.
With one charging pump normally in operation, the two non-operating charging pump suction lines become stagnant. As stated above, the associated suction piping for the two non-operating charging pumps is manually vented every 31 days to address the potential to accumulate gas while dormant.
The concern that gas may be generated in CCP piping due to flow through bypass orifices has also been addressed.
Each CCP contains a multi-stage pressure break-down orifice in the pump's minimum recirculation flow line.
The original restriction
Serial No.15-288 Docket Nos. 50-336/423 Attachment, Page 3 of 4 orifices allowed gas (hydrogen or nitrogen) from the Volume Control Tank (VCT) to come out of solution and collect in the BAST gravity boration lines due to wear of the last stage of the restriction orifice.
A design modification (circa 2001) replaced each restriction orifice with a new design to eliminate the concern. Post-modification testing included a range of VCT pressures to verify that gas was no longer being generated and collected in the BAST gravity boration lines. At that time, a surveillance procedure was developed to monitor gas accumulation in the BAST gravity boration lines.
RAI 4
Please describe the monitoring of system parameters that could identify a change that could introduce gas into piping between surveillance intervals.
DNC Response The Safety Injection Tanks (SIT) at MPS2 are monitored daily by the Operations staff for changes in tank level. The SITs have a minimum nitrogen gas cover pressure of 200 psig which is known to cause off-gassing in lower pressure zones of interconnected piping due to back leakage across multiple check or isolation valves. Upon a decrease in SIT level with an unknown cause, procedure steps direct operators to UT inspect vulnerable low pressure high point piping for off-gassing (e.g., the High Pressure Safety Injection/Low Pressure Safety Injection loop injection lines at the containment penetrations, and the Containment Spray (CS) discharge headers). These steps aid the operators during troubleshooting activities to identify the leakage flow path and provide early indication of gas accumulation in Emergency Core Cooling System (ECCS) and CS piping.
Identification of gas accumulation or off-gassing would be entered in the corrective action program to determine if an increase in UT inspection frequency at vulnerable locations is necessary.
The accumulator tanks at MPS3 are also monitored daily for changes in tank level.
These tanks have a nitrogen gas cover pressure of approximately 650 psig and have also been known to cause off-gassing in the safety injection lines due to back leakage.
Upon a decrease in level, the accumulator fill procedure includes actions to vent various safety injection high points where gas accumulation due to back leakage could occur.
RAI 5
What are representative surveillance frequencies that exist under the MPS3 Surveillance Frequency Control Program that differ from the TSTF-523 example of 31 days and what is the basis for those changes?
Serial No.15-288 Docket Nos. 50-336/423 Attachment, Page 4 of 4 DNC Response There are no differences.
The MPS3 ECCS/CS/Shutdown Cooling (SDC) gas monitoring surveillance frequencies are currently based on 31 days.
RAI 6
The licensee states in its application, "Monitoring is not required for susceptible locations where the maximum potential accumulated gas void volume has been evaluated and determined to not challenge system OPERABILITY." Explain how this is consistent with the design basis requirement that the subject systems be water-solid.
DNC Response This statement in the LAR was taken directly from TSTF-523, Rev. 2.
However, no locations at MPS2 and MPS3 are currently credited under this statement.