ML15111A449
| ML15111A449 | |
| Person / Time | |
|---|---|
| Site: | Millstone  |
| Issue date: | 04/15/2015 |
| From: | Daugherty J R Dominion Nuclear Connecticut |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 15-164, GL-08-001 | |
| Download: ML15111A449 (10) | |
Text
F&Dominion Nuclear Connecticut, Inc. DominionRope Ferry Rd., Waterford, CT 06385Mailing Address:
P.O. Box 128Waterford, CT 06385dom.comAPR 15 2015U. S. Nuclear Regulatory Commission Serial No.: 15-164Attention:
Document Control Desk NL&OS/TFO:
R3Washington, DC 20555-0001 Docket Nos.: 50-33650-423License Nos.: DPR-65NPF-49DOMINION NUCLEAR CONNECTICUT, INC.MILLSTONE POWER STATION UNITS 2 AND 3SUPPLEMENT TO LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523, REVISION 2, GENERIC LETTER 2008-01, MANAGING GAS ACCUMULATION By letter dated January 15, 2015, Dominion Nuclear Connecticut, Inc. (DNC) submitted a license amendment request (LAR) for Millstone Power Station Unit 2 (MPS2) andMillstone Power Station Unit 3 (MPS3). The proposed amendment would modifyTechnical Specification (TS) requirements to address Generic Letter 2008-01,"Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, andContainment Spray Systems,"
as described in Technical Specifications Task Force(TSTF)-523, Revision 2, "Generic Letter 2008-01, Managing Gas Accumulation."
TSTF-532, Revision 2 was approved for use by the Nuclear Regulatory Commission (NRC) aspublished in the Federal Register on January 15, 2014 (79 FR 2700).During a telephone conference on March 26, 2015, the NRC provided DNC anopportunity to supplement the LAR submitted under DNC Letter 15-012 (ADAMsAccession No. ML15021A128).
This was based on the NRC staff's acceptance reviewwhich identified that the basis provided for exceptions from TSTF-523 did not providesufficient detail to support the exception.
Attachment 1 provides supplemental information related to the MPS2 requested testingfrequency of 92 days versus the testing frequency of 31 days specified in TSTF-523.
This supplement expands upon a previous discussion provided in DNC Letter 09-970(ADAMS Accession No. ML100190064).
Attachment 1 also provides supplemental information related to the requested exemption of the MPS3 Quench Spray System andthe Recirculation Spray System from this (gas accumulation) testing.
The supplement likewise expands upon a previous discussion provided in DNC Letter 08-0013C(ADAMS Accession No. ML082890266).
In accordance with 10 CFR 50.91, a copy of this letter, with attachment, is beingprovided to the State of Connecticut.
Serial No. 15-164Docket Nos. 50-336/423 Page 2 of 3If you should have any questions regarding this submittal, please contact Wanda Craftat (804) 273-4687.
Sincerely, Jo R. Daugherty Site Vice President
-Millstone STATE OF CONNECTICUT
))COUNTY OF NEW LONDON )The foregoing document was acknowledged before me, in and for the County aforesaid, today by Mr. John R. Daugherty, who is Site Vice President
-Millstone, of DominionNuclear Connecticut, Inc. He has affirmed before me that he is duly authorized toexecute and file the foregoing document in behalf of that company, and that thestatements in the document are true to the best of his knowledge and belief.Acknowledged before me this t! day of J L 2015.My Commission Expires:
AAjL-e& Ali (-N y\Notary/ :WM. E. BROWNNOTARYPULILIC MY COMMISSION EXPIRES MAR 31. 201, 6 Serial No. 15-164Docket Nos. 50-336/423 Page 3 of 3
Attachment:
Supplement to License Amendment Request to Adopt TSTF-523Commitments contained in this letter: None\cc: U.S. Nuclear Regulatory Commission Region I2100 Renaissance BlvdSuite 100King of Prussia, PA 19406-2713 Richard V. GuzmanNRC Senior Project ManagerU.S. Nuclear Regulatory Commission One White Flint North, Mail Stop 08 C211555 Rockville PikeRockville, MD 20852-2738 NRC Senior Resident Inspector Millstone Power StationDirector, Radiation DivisionDepartment of Energy and Environmental Protection 79 Elm StreetHartford, CT 06106-5127 Serial No. 15-164Docket Nos. 50-336/423 ATTACHMENT 1SUPPLEMENT TO LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523DOMINION NUCLEAR CONNECTICUT, INC.MILLSTONE POWER STATION UNIT 2 AND 3 Serial No. 15-164Docket Nos. 50-336/423 Attachment 1, Page 1 of 6SUPPLEMENT TO LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523By letter dated January 15, 2015, Dominion Nuclear Connecticut, Inc. (DNC) submitted a license amendment request (LAR) for Millstone Power Station Unit 2 (MPS2) andMillstone Power Station Unit 3 (MPS3). The proposed amendment would modifyTechnical Specification (TS) requirements to address Generic Letter (GL) 2008-01,"Managing Gas Accumulation in Emergency Core Cooling, Decay Heat Removal, andContainment Spray Systems,"
as described in Technical Specifications Task Force(TSTF)-523, Revision 2, "Generic Letter 2008-01, Managing Gas Accumulation."
TSTF-532, Revision 2 was approved for use by the Nuclear Regulatory Commission (NRC) aspublished in the Federal Register on January 15, 2014 (79 FR 2700).During acceptance review of the proposed LAR, the NRC requested additional information to support exceptions from TSTF-523 for MPS2 related to testing frequency and for MPS3 for exempting certain plant systems from testing.
This attachment provides the supplemental information to support the NRC's review of the LAR.Additional Information for MPS2 Exception to TSTF-523 Testing Frequency:
In a letter dated January 15, 2015, DNC took exception to the recommended 31-daygas void monitoring surveillance frequency for Emergency Core Cooling System(ECCS), Shutdown Cooling (SDC), and Containment Spray (CS) piping by proposing a92-day (or quarterly) surveillance frequency for MPS2.In DNC letter dated October 14, 2008 (Serial No. 08-0013C),
as part of the nine-month response to GL 2008-01, DNC noted that MPS2 did not conduct periodic UT or ventingof in-scope
- systems, but identified that the potential for small voids, believed to bewithin acceptance
- criteria, could form, and credited an action plan to develop a quarterly monitoring and trending program to periodically monitor piping locations susceptible togas intrusion using ultrasonic testing (UT), venting, or other means every 92 days.In DNC letter dated January 14, 2010 (Serial No.09-790),
DNC discussed use of aquarterly frequency for void monitoring at MPS2 for in-scope piping. DNC noted thatthe quarterly monitoring frequency was based on operating experience at MPS2 withthe requirement that the monitoring frequency would be increased if trending of theissue identified a need. In the March 2, 2011 NRC closeout to GL 2008-01 (ADAMSAccession No. ML110540393),
the NRC concluded that the detection, monitoring, andtrending of voids in the discharge piping of MPS2 was acceptable.
At MPS2, the High Pressure Safety Injection (HPSI), Low Pressure Safety Injection (LPSI) and CS pumps are located a significant distance below the Refueling WaterStorage Tank (RWST) and discharge into containment or the Reactor Coolant System(RCS) which is at an elevation above the pumps. This configuration tends to impedegas void build-up near the pumps.
Serial No. 15-164Docket Nos. 50-336/423 Attachment 1, Page 2 of 6MPS2 has been performing gas monitoring on the ECCS, CS, and SDC piping on aquarterly basis for five years. Monitoring results are tabulated in a Microsoft EXCEL filefor trending purposes.
Should trending identify a problem point, the monitoring frequency of that point would be increased.
The monitoring presently includes eightpoints in the pump(s) suction piping and nineteen points in the pump(s) discharge piping. The gas void accumulation issues identified over the last five years have beenprimarily limited to the CS and LPSI pump discharge high point piping. With theexception of a one-time operating experience in which Safety Injection Tank (SIT)leakage occurred through three isolation valves, gas accumulation issues at MPS2 havebeen limited to improper fill and vent restoration activities during refueling outages oron-line maintenance.
Review of the past five years of gas monitoring datademonstrates that MPS2 operating experience justifies a 92-day monitoring frequency.
Gas void experience identified in the last five years since the 92-day monitoring hasbeen in place are described below:* HPSI Pump On-Line Maintenance Monitoring results indicate one instance of gas voiding in the suction pipingduring and after restoration (same day) from HPSI pump on-line maintenance.
This condition was entered into the corrective action program on December 18,2012. Prior to the void being vented, additional UT was performed tocharacterize the actual size of the void by UT measurement of the actual voidlength. The measurement confirmed the actual void volume was within theacceptance criteria.
On-line pump maintenance procedures were revised toinclude post vent UTs and an engineering evaluation for any point not found full.No other pump suction-side gas voids have been detected to date.* 'B' LPSI pump cavitation On April 6, 2014, during a planned refueling outage shutdown, the 'B' LPSI pumpbegan to cavitate when the pump was started in preparation for SDC. Asrequired by procedure, preparation for SDC requires a LPSI pump to be run atapproximately 400 gpm through a 2" warm-up line to verify system integrity.
The'A' and 'B' LPSI pumps share a common discharge line.Initial conditions included a known gas void in the 'A' LPSI pump discharge piping. The void was the result of on-line pump maintenance that occurred twomonths prior. This gas void had been determined to be well within its established acceptance criteria for pump discharge-side void volumes and could not bevented or swept out until the next refueling outage..The procedure also required isolation from the RWST. This step effectively removes the surge tank in a closed piping system. Operating a closed systemwithout surge protection for short periods of time is acceptable if the closedsystem is water solid. However, the system was not water solid due to theexisting void. As a result, this caused the 'B' LPSI pump to cavitate as the pump Serial No. 15-164Docket Nos. 50-336/423 Attachment 1, Page 3 of 6began to move volume from the pump suction to fill volume in the pumpdischarge.
The procedure was revised to require the RWST isolation valve to beopen prior to starting the LPSI pump, remain open until the system stabilized, and then the RWST would be re-isolated.
This issue is considered resolved.
Having a monitoring frequency of less than 92 days would not have resulted inidentifying this issue sooner.* Small Gas Voids at Containment Penetrations Small void volumes have been found in the high point of four individual LPSI loopinjection lines upstream of their respective isolation valve near the containment penetrations.
These voids have been small enough to pass the monitoring acceptance criteria with significant margin. Once removed, these pointsgenerally remain 100% full. Subsequent trending has not identified an on-goinggas intrusion mechanism.
Based on operating experience to date, identification and removal of this condition was not affected due to the present 92-day testingfrequency.
Gas Void in 'B' CS discharge headerOn May 21, 2013, while operating in mid-cycle, gas monitoring identified a gasvoid in the 'B' CS header upstream of the containment penetration.
The void waslarge enough to initially declare the 'B' train of CS inoperable.
Prior to venting,additional UT measurements were taken to determine the actual void size. Afollow-up evaluation determined that the 'B' train header had additional marginsuch that the system would have performed its safety function.
The cause of thevoid was determined to be SIT leakage through three closed isolation valves inseries in small intersecting piping that provided return flow to the RWST. As thehigher pressure SIT water volume began to leak into the low pressure
'B' CSdischarge header, dissolved nitrogen gas came out of solution.
It was noted thatthe operating procedure required action to inspect for gas accumulation in theECCS injection header when SIT levels decrease for an unknown reason, but didnot include inspection of the CS headers.
The procedure was revised to includeinspection of the CS headers when the cause of a decrease in SIT level isunknown.
Once the gas intrusion mechanism was identified, the monitoring frequency at this point was increased as needed until the event was fullyresolved.
The gas intrusion mechanism was resolved during the next refueling outage with the replacement of the isolation valves. It is noted that this gasintrusion event may have been discovered earlier with a gas monitoring frequency of less than 92 days. The event may also have been prevented if theSIT level monitoring procedure had appropriately included a provision to inspectthe CS headers.
In addition, a recent calculation determined additional voidmargin is available for this location.
Thus, with the corrections applied(procedure provision to inspect CS headers and calculation establishing addedmargin),
the present 92-day gas monitoring frequency is considered to remainappropriate.
Serial No. 15-164Docket Nos. 50-336/423 Attachment 1, Page 4 of 6* Gas Void in 'A' CS discharge headerOn May 16, 2014, during plant start-up (Mode 3) following a refueling outage,gas monitoring identified a gas void in the 'A' CS discharge header upstream ofthe containment penetration.
The void was large enough to declare the 'A' trainof CS inoperable.
The cause of the void was determined to be inadequate venting of the 'A' CS header following outage maintenance.
The 'A' CS header isinterconnected with the 'B' CS header. Maintenance had been performed on the'B' CS header which was properly filled and vented following maintenance.
- However, the 'A' CS header was not included in the maintenance recovery effortsand, therefore, was not verified filled and vented. This event could have beenprevented if the gas monitoring procedure had been performed prior to enteringMode 4 during plant start-up activities.
The gas monitoring procedure is nowrequired to be performed as a Mode 4 hold for future plant shutdowns andrestarts.
This issue is considered resolved.
Having a monitoring frequency ofless than 92 days would not have resulted in identifying the issue sooner.
Serial No. 15-164Docket Nos. 50-336/423 Attachment 1, Page 5 of 6Additional Information for MPS3 Exception for Plant Systems Testing:In a letter dated January 15, 2015, DNC took exception to including the Recirculation Spray System (RSS) and the Quench Spray System (QSS) in the Technical Specifications for monthly gas monitoring for MPS3.In a DNC letter dated October 14, 2008, (Serial No. 08-0013C) as part of the nine-month response to GL 2008-01, DNC provided a basis for exception from testing for theQSS and RSS systems.
The original responses regarding the QSS and RSS systemshave been supplemented with additional information and are provided in the paragraphs below.Quench Spray System (QSS):The QSS pumps are each supplied by an independent suction line from the RWST.The system piping is maintained full from the RWST to an equivalent level in the pipingheaders located inside containment.
System walkdowns verified that the suction pipingis properly sloped to prevent air traps. The quarterly pump operability surveillances ensure adequate water volume is pumped through suction and discharge piping (up tothe recirculation connection directly upstream of the containment isolation valves) at avelocity to adequately sweep the system piping. The water level in the discharge header inside containment is maintained by quarterly valve stroke of the containment isolation valves. The discharge piping beyond the containment isolation valves is self-venting to the containment atmosphere through the Quench Spray header nozzles.Consequently, there are no identified gas intrusion mechanisms for this system. This isa low pressure system with no gas overpressure so the possibility of entrained gasescoming out of solution when the piping is full of stagnant fluid is unlikely.
It is therefore concluded this system is free of potential gas voids.The design of the QSS (e.g., dedicated suction lines from the bottom of the RWST, thestandby design, isolation from potential pressurization from pressure sources withhigher pressure than the RWST, independent piping trains, quarterly dynamic venting)obviates the need for a monthly surveillance of the QSS.Containment Recirculation System (RSS):The RSS system piping is not maintained water-filled by design, excluding the ECCSpump cross-over piping. The containment sump is normally maintained in a dry (non-filled) state along with the RSS pump suction piping. The four containment recirculation pumps and motors and the containment recirculation coolers and associated piping arelocated outside the containment structure.
The pumps are vertical deep-well pumpsmounted in a separate stainless steel well casing. A portion of the pump casing that isbelow the sump suction line remains filled with water after dewatering.
The pumps areself-venting to the discharge piping and vent as the sump and suction piping is filledinside containment through the discharge of the containment recirculation spray system.The pumps are located adjacent to the containment structure at an elevation sufficiently below the containment structure sump to ensure adequate gravity filling of the suction Serial No. 15-164Docket Nos. 50-336/423 Attachment 1, Page 6 of 6piping, pump housing, and a portion of the discharge piping. Each RSS pump casinghas a 1" diameter vent line installed to aid in the filling and venting of the RSS pumpcasings.The discharge piping, which includes the containment recirculation
- coolers, is alsomaintained in a dry condition and will self-vent to containment through the containment recirculation spray header nozzles when the RSS pumps are started and discharge-side piping is filled. The system actuates based upon specific actuation signals whichensure there is adequate water available.
Following a Large Break Loss of CoolantAccident, the minimum time for the actuation to occur is 33 minutes.
Thus, the RSSsystem piping, with the exception of ECCS pump cross-over piping, does not requiremonitoring for gas voids.TS surveillance 4.5.2.b.1, which requires verification that the ECCS piping is full ofwater, identifies the RSS pump, the RSS heat exchanger, and associated piping exemptfrom the monthly surveillance.
The TS Bases provides the following reasons why theRSS is exempt from this Surveillance:
- The RSS pumps, since this equipment is partially dewatered during plantoperation.
Each RSS pump is equipped with a pump casing vent line that allowsautomatic VENTING of the pump casing prior to pump operation following anaccident.
" The RSS heat exchangers, since this equipment is laid-up dry during plantoperation.
Gas is flushed out of the heat exchangers during the initial operation of the RSS pumps following an accident.
" The RSS piping that is not maintained filled with water during plant operation.
The configuration of this piping is such that it is self VENTING upon initialoperation of the RSS pumps.The TS Bases specifically include the ECCS pump cross-over piping for testing (i.e.,downstream of valves 3RSS*MV8837A/B and 3RSS*MV8838A/B to safety injection andcharging pump suction) and likewise includes the water filled portions of the RSS pipingupstream of these valves. These water filled portions of the ECCS cross-over pipingwill continue to be included in the proposed TSTF-523 changes for MPS3.