ML15313A024

Millstone, Units 2 and 3 - Response to Second Request for Additional Information Regarding License Amendment Request to Adopt TSTF-523, Revision 2, Generic Letter 2008-01, Managing Gas Accumulation

ML15313A024
Person / Time
Site:	Millstone
Issue date:	11/02/2015
From:	Sartain M D Dominion, Dominion Nuclear Connecticut
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
15-497, GL-08-001, TAC MF5715, TAC MF5716
Download: ML15313A024 (9)

Text

~~Dominion~Dominion Nuclear Connecticut, Inc.5000 Dominion Boulevard, Glen Allen, VA 23060Web Address: www.dom.comNovember 2, 2015U. S. Nuclear Regulatory CommissionAttention: Document Control DeskWashington, DC 20555-0001Serial No.N LOS/WDCDocket Nos.License Nos.15-497R050-336/423DPR-65NPF-49DOMINION NUCLEAR CONNECTICUT. INC.MILLSTONE POWER STATION UNITS 2 AND 3RESPONSE TO SECOND REQUEST FOR ADDITIONAL INFORMATIONREGARDING LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523, REVISION2. 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 requirementsto address Generic Letter 2008-01, "Managing Gas ,Accumulation in Emergency CoreCooling, Decay Heat Removal, and Containment Spray Systems," as described inTechnical Specifications Task Force (TSTF)-523, Revision 2, "Generic Letter 2008-01,Managing Gas Accumulation." TSTF-523, Revision 2 is approved for use by theNuclear Regulatory Commission (NRC) and was announced in the Federal Register onJanuary 15, 2014 (79 FR 2700). In an email dated June 1, 2015, the NRC transmitted arequest for additional information (RAI) containing nine questions related to the LAR. Ina letter dated July 16, 2015, DNC responded to RAI Questions 2, 3, 4, 5, and 6. In aletter dated July 30, 2015,rDNC responded to RAI Questions 1, 7, 8, and 9. In an emaildated October 2, 2015, the NRC transmitted a second RAI. The attachment to thisletter provides DNC's response to the NRC's second RAI.If you should have any questions regarding this submittal, please contact Wanda Craftat (804) 273-4687.Sincerely,Mark D. SartainVice President -Nuclear EngineeringCOMMONWEALTH OF VIRGINIACOUNTY OF H-ENRICO)))The foregoing document was acknowledged before me, in and for the County and Commonwealth aforesaid, today by Mr. Mark D. Sartain, who is VicePresident -Nuclear Engineering, of Dominion Nuclear Connecticut. He has affirmed before me that he is duly authorized to execute and file theforegoing 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 day of A//PV'A'f.lI , 2015.My Commission Expires:/,,'t 31//( ' IONt~ Com owaOR=AIG b ~,s'LYVrir,lic 11Rea. # 751 8653aMy Commission'Expires December 31,............. T V Serial No. 15-497Docket Nos. 50-336/423Page 2 of 2Attachment:Response to Second Request for Additional Information Regarding LicenseAmendment Request to Adopt TSTF-523Commitments contained in this letter: .Nonecc: U.S. Nuclear Regulatory CommissionRegion I2100 Renaissance BlvdSuite 100King of Prussia, PA 19406-2713Richard V. GuzmanNRC Senior Project ManagerU.S. Nuclear Regulatory CommissionOne White Flint North, Mail Stop 08 C211555 Rockville PikeRockville, MD 20852-2738NRC Senior Resident InspectorMillstone Power StationDirector, Radiation DivisionDepartment of Energy and Environmental Protection79 Elm StreetHartford, CT 06106-5127 Serial No. 15-497Docket Nos. 50-336/423ATTACHMENTRESPONSE TO SECOND REQUEST FOR ADDITIONAL INFORMATIONREGARDING LICENSE AMENDMENT REQUEST TO ADOPT TSTF-523DOMINION NUCLEAR CONNECTICUT, INC.MILLSTONE POWER STATION UNITS 2 AND 3 Serial No. 15-497Docket Nos. 50-336/423Attachment, Page 1 of 6By 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 inEmergency Core Cooling, Decay Heat Removal, and Containment Spray Systems," asdescribed in Technical Specifications Task Force (TSTF)-523, Revision 2, "GenericLetter 2008-01, Managing Gas Accumulation." TSTF-523, Revision 2 is approved foruse by the Nuclear Regulatory Commission (NRC) and was announced in the FederalRegister on January 15, 2014 (79 FR 2700). In an email dated June 1, 2015, the NRCtransmitted a request for additional information (RAI) related to the LAR. In a letterdated July 16, 2015, DNC responded to Questions 2, 3, 4, 5, and 6 of the RAI. In aletter dated July 30, 2015, DNC responded to RAI Questions 1, 7, 8, and 9. In an emaildated October 2, 2015, the NRC transmitted a second RAI. This attachment providesDNC's response to the NRC's second RAI.RAI 4-1RAI 4 requested a description of "the monitoring of system parameters that couldidentify a change that could introduce gas into piping between surveillance intervals."The July 16, 2015, DNC response addressed accumulators but did not address otherpotential sources of gas. Please provide the monitoring frequency and the response toa malfunction that could introduce gas into a system that is important to safety for thefollowing systems/equipment during power operation:a. Reactor coolant systemb. Chemical sampling systemc. Any other equipment where a malfunction could introduce gas into a system thatis important to safetyDNC Response 4-1a. The response and monitoring frequency for oft-gassing due to Reactor CoolantSystem (RCS) leakage is not pre-defined. RCS operational leakage is aparameter controlled by Technical Specification (TS) 3.4.6.2 and includes limitsfor identified leakage of 10 gpm and unidentified leakage of 1 gpm. TSSurveillance 4.4.6.2.1 requires verification that RCS operational leakage is withinthese limits by the performance of an RCS water inventory balance at least onceper 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br />. Early leak detection is the goal of the RCS leakage monitoringprogram. Trending and investigating unidentified RCS leakage is procedurallycontrolled with actions for specified unidentified RCS leakage rates. Exceedingspecified unidentified leakage rates result in a Condition Report (CR), a request Serial No. 15-497Docket Nos. 50-336/423Attachment, Page 2 of 6for cognizant system engineering support, and a troubleshooting plan dependingupon the actual leakage rate. If internal RCS leakage across system boundariesis suspected, the CR corrective action plan and/or troubleshooting plan mayinvoke ultrasonic testing (UT) for gas accumulation monitoring in lower pressurepiping areas as a method to determine the RCS leak path(s). A gas monitoringfrequency would then be developed for problem areas until the condition iscorrected.b. The response and monitoring frequency for off-gassing due to a malfunctionassociated with chemical sampling is not pre-defined. Establishing andmaintaining primary water chemistry is procedurally controlled. The procedureidentifies the parameters, minimum sampling frequencies, and appropriate limitsand action levels necessary to implement the MPS2 primary water chemistrycontrol program. The procedure includes a list of possible causes and correctiveactions to take when a chemical parameter is discovered outside specified limitsand exceeds an action level. Abnormal test results are documented in a CR. Atechnical evaluation of the abnormal chemistry condition, including implicationsfor plant equipment and components, is performed if the parameter is notrestored below the action level within seven days. The CR and technicalevaluation processes would be instrumental in determining if the abnormalchemistry condition could cause gas voiding elsewhere in the system. If so, theCR corrective action plan may invoke ultrasonic testing (UT) for gasaccumulation monitoring as an early gas void detection method. A gasmonitoring frequency would be developed for problem areas until the condition iscorrected.c. Equipment malfunctions would be documented in a CR. The CR processrequires investigation of an adverse condition and establishes the necessarycorrective actions to correct the condition and any consequential conditions. If,during the CR investigation, concerns with either gas voiding and/or gasaccumulation became evident, corrective actions would prompt furtherinvestigation (e.g., gas monitoring troubleshooting) and resolution.RAI 9-1RAI 9 requested specified detail regarding the void surveillance history of MillstonePower Station, Unit 2 (MPS2). Please address the following:a. DNC identified a void discovery on August 13, 2013, but there is no entry in thetable of void discoveries for this date.b. 92-day surveillances were identified on May 21, 2013 and May 16, 2014 wherethe measured void volumes of 6.557 ft3 and 5.286 ft3 exceeded the volume thatwas predicted to exceed the operable limit of 2.57 ft3.The first was attributed toaccumulator leakage and the second to an improper fill and vent after a refuelingoutage (RFO). Why were these not identified earlier by daily monitoring of Serial No. 15-497Docket Nos. 50-336/423Attachment, Page 3 of 6accumulator level and immediate follow-up after an outage, respectively? HaveDNC procedures been changed to correct these occurrences?c. A void volume of 0. 122 ft3 was measured versus a 0. 129 ft3 criterion during a 92-day surveillance on July 28, 2014. This was attributed to outgassing aftershutdown coollng termination following an RFO. All other similar occurrencesresulted in smaller volumes. Please provide information to substantiate this largeoutgassing volume.RAI 9e requested the MPS2 void surveillance history related to "Monitoring ofequipment such as accumulators or reactor coolant system leakage and follow-up fromoutages with respect to void assessment." Please describe the surveillances that havebeen conducted when exiting an outage and the surveillances that have beenconducted prior to a return to power operation.DNC Response 9-1a. The void discovered on August 13, 2013 was initially provided in the July 30,2015, DNC response on page 15 of 18 as part of a group of repeat occurrencesat UT location 26 during the date period from May 22, 2013 through March 31,2014. The discovery of this void occurred during the scheduled 92-daysurveillance which coincided with weekly surveillances that were also required atthat same location. Specific details of the August 13, 2013 void have beenadded. Refer to the Cycle 22 table below.b. On November 11, 2012, daily monitoring of the Safety Injection Tank (SIT)identified decreasing level in the tank. The response to an unknown drop in SITtank level is procedurally controlled and includes steps to perform gasaccumulation UTs at the containment penetrations for the High Pressure SafetyInjection (HPSI)/Low Pressure Safety Injection (LPSI) loop injection lines only. Atthis time, SIT leakage into the Containment Spray (CS) discharge header viamultiple normally closed manual valves was not considered a credible gasintrusion leak path. Surveillance at the CS discharge header on December 4,2012 indicated no void and the next surveillance of the CS discharge header onFebruary 26, 2013 indicated a void volume of 0.341 ft3, which was within theacceptance criteria. Operations concluded the leakage from the SIT was goingto the refueling water storage tank. This was a missed opportunity to recognizeSIT leakage into the CS discharge header as a gas intrusion leakage path. Itwas not until the next 92-day scheduled surveillance on May 21, 2013 identified avoid volume at the CS header that SIT leakage into the CS discharge headeracross three normally closed valves was identified as a credible gas intrusionleakage path. The procedure for SIT level monitoring was revised to require theperformance of UTs for potential gas accumulation at the containmentpenetrations for the CS discharge headers.

Serial No. 15-497Docket Nos. 50-336/423Attachment, Page 4 of 6Prior to restart from the spring 2014 refueling outage (2R22), the quarterly gasaccumulation surveillance procedure was due, was performed, and gasaccumulation in the CS header from improper fill and vent during restart wasidentified. The quarterly gas accumulation surveillance procedure was notperformed as a refueling outage restoration verification activity, but it wasrecognized that performance of the procedure prior to restart from a refuelingoutage could have prevented the inoperable CS header situation that occurredduring plant heat up from 2R22. As a result of the lessons learned, the quarterlygas accumulation surveillance procedure was added to the outage surveillancechecklist. The quarterly gas accumulation surveillance procedure is required tobe performed prior to plant heat up from a refueling outage and prior to plant heatup from a forced outage if any portion of the emergency core cooling system isdrained for maintenance.c. During the quarterly gas accumulation surveillances following the 2R22 outage,the void volumes found in the LPSI loop injection high points at containmentpenetration UT locations 20, 21, 22, and 23 were consistently between 0.000 ft3and 0.069 ft3 with the exception of July 28, 2014 where a larger void of 0.122 ft3was discovered. The nominal void volumes are attributed to outgassing as aresult of improper fill and vent activities near the end of the refueling outage. Apossible contributor to the large void volume was identified to be the LPSI pump.A LPSI pump is run once a quarter on minimum flow recirculation for 5 to 10minutes. During the quarterly LPSI pump run, there is no flow in the maindischarge header, but the header is pressurized and then depressurized.Because the larger void volume on July 28, 2014 was a one-time occurrence,DNC has concluded that a portion of the total void on this date was due to aresidual air void that migrated to this high point over time by itself or was aidedduring the quarterly LPSI pump run.The horizontal run of pipe at the loop injection high points is approximately 2 feetin length. The actual void volume acceptance criteria at the high points (1.5 ft3)exceed the void volume an empty horizontal pipe would indicate. Therefore,DNC has conservatively chosen 50% of the horizontal pipe volume (0.128 ft3,0.244 ft3, 0.129 ft3, and 0.147 ft3) as the acceptance criteria for the high points.The larger void volume of July 28, 2014 was still within the conservativeacceptance criteria.e. At MPS2 when exiting an outage, system specific fill and vent procedures for theHPSI, LPSI and CS piping systems are performed to verify systems are full ofwater. These procedures include UT inspection points at various vulnerablesystem high points to ensure systems have been properly filled and vented. Ifgas voids are present, the fill and vent process is repeated or alternate methods(i.e., dynamic venting) of void removal is pursued. The UT validations associatedwith these fill and vent procedures have historically been relied upon to supportplant restarts following refueling outages. The quarterly gas accumulationsurveillance procedures were not routinely performed prior to startup after a Serial No. 15-497Docket Nos. 50-336/423Attachment, Page 5 of 6refueling outage. Three refueling outages have occurred since gas monitoringwas first established at MPS2 in March of 2010. The scheduling date of thequarterly gas accumulation surveillance procedure coincided with the date ofplant restart for two of the three refueling outages but was not formally tied toplant restart activity. As noted in the response above, the quarterly gasaccumulation surveillance procedure is now included on the outage surveillancechecklist and is required to be performed prior to plant heat up.

Serial No. 15-497Docket Nos. 50-336/423Attachment, Page 6 of 6Cycle 22Date Location Void Vol. Allowable Notes Surveillance Reason for Disposition(ft3) Vol. (ft3) Frequency Discovery withRespect toImpact onOperability8/13/13 UT Point 26 -CS 0.161 2.57 Mode 1. Source is SIT back 92 days Routine Voiddischarge leakage across multiple surveillance volumevalves into the B Train CS withindischarge header -Location operabilityis restored to water filled limitscondition each instance