ML13163A221
| ML13163A221 | |
| Person / Time | |
|---|---|
| Site: | Watts Bar  |
| Issue date: | 06/12/2013 |
| From: | James Shea Tennessee Valley Authority |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| TAC MF1875 | |
| Download: ML13163A221 (10) | |
Text
Tsrrflgsss* Vrer*fey fuffi*trnnri#* rf l tlt fi,tarls*lt $trrsrr*t,,Sh,*tteali*n,$n, Tenne'fi$*e 3lrltlf June 1?, 2013 r0 cFH 50.90
'!0 cFR sn.gr AlTN: Dscument Control Oesk U.$. Nuclear Regulatory Somrnlssicn Washlngton, F,C. 30555-0001 Wafts Bar Nuclear Plant, Unit 1 Facllily OBerating License No. NFF-90 NRC Docket No. 50-390
$ubject Response to Request for Additional lnformdlon Regarding Application for One-Time Ghange to tfie Tschnical Specification (TS! 3.G.flGompletion Time for an Inoperable Gontainment $prey Train Under Exigent Circumatancee to Allow for Pump Repeir (WBN-TS-Z01SOt1l, TAC No. [tiF-1875
References:
t" Leterfrom TVAto NRC, "Application for One-Time Changeto tlre Tsuhnical Specification (T$) 3.6,6 Completion Time for an fnoperabie Containment
$pray Train Under Exigent Circumstiances to Altow for Pump Repair
{WBN-TS-2013411}." dared May ZZ, 2013 7", Electranic Mailftm NRC to TVA,.Request furAdditicnal fnformation - one time change to TS 3.S.6 Completion for an Inoperable Containment $pray Train Under frxlgant f,ircumstances to allow for pump repair - TAg MF-1875,-
dated June 4, ?S13 Ey tretter dated May ?2, 2013 {fteferencs 1}, Tennessee Valley Authority WA} reqr"reet*d a change to the Watts Bar Huclear Flant ttA/BN) Unit 1 Technical $peeific*tions (TSs) proposing a ane-time change to the T$ 3,6.6 Completion Time for an inoperable Containment $pray {C$)
Train B, This proposed ch*nge was requested under exigent circumstances to allow for repair ef a leaking rnechanical seel on 0$ Pump 1B-8.
A telepho*e conference callwas held on June 3, 2013 between TVA and Nuclear Regulatory Commission {NRC) representatives to discuse draft questions the NRC reviewers had prepared regarding the requested exigent TS change. The TVA representatives responded to the NRC's questions during the call and agreed to provide formal docketed responses after the NRC transrnitted ihe fiormal questions.
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- lL"urt,# f ff" fffit S In Ref#qnffi g" d#d.lune 4, 20'N3, f}* NRC rcque*ed additbnal infurmdinn rruardlng ths exrgent T$ charg* furU\\lBN Unit 1 {Reference 1}. TVA agreed to provide the RAI rc$pon$e wilhin tpproxlffia&ly one week cf the RAI transmittal.
Th* erudu*rrm to thlx Htsr c*nt*in* WA's rusptrr*s$ to the ftaference 2 RAl. 8a*ed sn a review sf th* ennfosnd infunnalion, TVA hss Setrrrniilsd that Sris RAI ressanss dses *st eltsr the nn *$*ificnnt ftsear*s co**id*nalion enraluet{on in*hided *r tfte Refurenm 1 *ubrnif[af. A*
such, lhs originel concluslcn of no significant hazsrdp mns*deratien sssociated srith ttrc pr$ps$sd TS change rcrneins vslid.
In eccordsnce {$ith 10 CFR 50.91(bXI}, TVA is eerding a copy of ST is letter ard the cnclosure t* th* T*nns*see Separfnent of Envircnrnsnt and ffonEenratign, Thcfe sr $s nevv rcgulatnry s(ffitffiitmenb oont#ned in this b{Hr. Pbgse adcltucs any rymtkrna rugsrding this nquesttE Ed $ellrullEt {423} ?S't-&ss" I ds*lare un&r pennlty *f perjury thetthe fwegring i* true s*d s6ne*1, Hxcfft*d on thi*
tlon day of Jun* f*{S.
fd*nt. Mu*lmnr L$*eirru:i,ffiS Enclssu;e:
Rwpcn*e to NftC Reque*tfo*Addltianal Infonnat-iffi {ftAl}
cc {Enc'losur*}:
NR* R*giofiillAdrfllnkmftr - Region ll NfrC Rssideid Inspedsr - W*ttts Bar Nuclear Flant
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ENCLOSURE TENNESSEE VALLEY AUTHORTTY (n/A)
WATTS BAR NUCLEAR PLANT UNIT 1 RESPONSE TO NRC REQUEST FOR ADDTTTONAL TNFORMATTON (RAt)
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NRC Request
- 1. In your May 22, 2013 submiftal, Section 3.2, Technical Specification Change Evaluation, stated that:
"Based on sensitivity sfudies pertormed using the WEC LOTIC and WCOBRNTRAC computer codes, it is estimated that the peak containmenf pressure could reach approximately 16.8 - 25.3 psig during a design-based accident DBA LOCA with no CS cooling available or credited."
Sufficient detail to explain the range of peak containmenf pressures rs reguesfed as follow:
c Were these sensitivity sfudies performed with the analysis of record (AOR) computer models?
TVA Response The sensitivity studies were not performed with the AOR computer models. The sensitivity studies required a code to calculate the loss of coolant accident (LOCA) mass and energy releases and another for the corresponding containment responses. The WCOBRA/TRAC code was used to calculate the LOCA mass and energy releases. This methodology is documented in topical report WCAP-17721, "Westinghouse Containment Analysis Methodology - PWR LOCA Mass and Energy Release Calculation Methodology," dated April 2013, and was recently submitted to the Nuclear Regulatory Commission (NRC) for review and approval (ADAMS Accession No. ML131334064). The LOTICI code was used to calculate containment responses. This code and methodology are documented in the NRC approved topical report WCAP-8354-P-A, "Long Term lce Condenser Containment Code - LOTIC Code." The LOTICI code was modified for this sensitivity study to allow it to calculate a containment pressure greater than 40 pounds per square inch absolute (psia). As such, the modified LOTIC1 code is not considered to be the approved AOR (WCAP-8354-P-A) methodology.
What are the input parameter changes from the desrgn-base-accident (DBA) /oss-of-coolant-accident (LOCA) AOR modelthat result in the 16.8 and 25.3 psig values?
TVA Response The Westinghouse AOR for Watts Bar Nuclear Plant (WBN) Unit 1 is based on methodology described in WCAP-10325-P-A, "Westinghouse LOCA Mass and Energy Release Modelfor Containment Design March 1979 Version," and WCAP-8354. The sensitivity studies are based on the methodology described in WCAP-17721and WCAP-8354. See Table 1 below for input parameter changes between the AOR and this sensitivity study. The range of 16.8 pounds per square inch gauge (psig) to 25.3 psig was the result of preliminary scoping runs. The LOTIC1 AOR modelwas modified to eliminate flow from the Containment Spray Pumps (CSPs),
and preliminary SCOBRA/TRAC mass and energy releases were used as input.
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The final results of the sensitivity studies provided by Westinghouse indicate that peak containment pressure is approximately 32 psig. The higher calculated peak pressure is due to revised mass and energy releases from WCOBRA/TRAC that were then used as input into the LOTICI model. The WCOBRA/TRAC modelwas updated to include safety injection flow changes consistent with residual heat removal (RHR) spray actuation. The previous scoping WCOBRA/TRAC mass and energy releases did not modelthese flow changes.
At what time in the event is the containment peak pressure reached and how long does it remain above 15 psig pressure?
TVA Response The calculated containment pressure response is shown in Figure 1 (below). Peak pressure was reached at approximately 18000 seconds. Containment pressure will remain elevated until additional heat removalfrom containment is established via operation of a CSP and spray heat exchanger. As shown in Figure 2 (below), in all cases, containment pressure fell below the 15 psig design pressure within approximately 300 seconds or less after a train of containment spray was activated.
o Please provide graphs of fhese press ure transienfs, TVA Response i:ffi P$Y5
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?0000 Ftigure 2: Pump Suctian llreak Coxtainment Pressure -.tipray Acfuation fiensitivity Please provide a table of the input values from the AOR model and the changes for the 16.8 and 25.3 psrg resu/fs.
TVA Resoonse The WBN Unit 1 AOR LOCA mass and energy release and containment response calculations use the WCAP-10325 (mass and energy) and WGAP-8354 (LOTlCl) methodologies. Loss of offsite power and loss of an emergency diesel generator are assumed, and these assumptions were carried into the WCOBRA/TRAC and LOTIC1 sensitivity studies. Table 1 contains parameters that were updated between the AOR and the sensitivity studies.
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Table 1: Analysis of Record and Sensitivity Study Parameter Comparison Parameter Analysis of Record Sensitivities Mass and energy release methodology wcAP-10325 wcAP-17721 Mass and energy code(s)
SATANTS REFLOOD 10325 EPITOME WCOBRA/TRAC Containment response methodology wcAP-8354 WCAP-8354, see LOTIC1 note below*
Containment response code LOTlCl LOTlCl
- modified to allow calculations beyond 40 psia Containment Spray Flow from one active train of containment spray is modeled Both trains of containment spray are inactive RHR Spray RHR spray is actuated at 3600 seconds, based on containment pressure.
Flow changes are modeled in the mass and energy codes and LOTlCl.
RHR spray is actuated at 8600 seconds, based on containment pressure. Flow changes are modeled in WCOBRA/TRAC and LOTIC1.
Assumed failures Loss of offsite power, one emergency diesel generator failure.
Loss of offsite power, one emergency diesel generator failure. Failed diesel generator is assumed to power operable spray pump.
The range of 16.8 psig to 25.3 psig was estimated based on the results of preliminary scoping runs, as discussed in the conference call held on June 3,2013 regarding this RAl. The sensitivity study transmitted to TVA indicates that the peak pressure is approximately 32 psig. The WCOBRA/TRAC modelwhich produced the mass and energy releases for the 32 psig sensitivity modeled the safety injection flow changes associated with residual heat removal spray operation, as indicated in Table 1. The WCOBRA/TRAC mass and energy release calculation is based on the methodology described in WCAP-17721. Section 4.1 of WCAP-17721 further describes biases applied to the LOCA mass and energy WCOBRA/TRAC calculation (e.9., conservatively high safety injection temperatures, 1979 + 2 sigma decay heat).
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It also stated that:
"Therefore, even without crediting CS cooling, the predicted increase in peak containmenf pressure should not significantly challenge the containment integity or result in increased leakage."
Please provide the last Integrated Leak Rate Test and combined TYPE B & C Local Leak Rate lesf resu/fs (as a percent of allowable leakage -L").
TVA Response The WBN Unit 1 Containment Leak Rate Limits are as follows:
L" L"
0.75L" 0.60L" 0.25L" 0.25 percent (%) / day @ greater than or equal to (>) P" = 1 5 psig 246 standard cubic feet per hour (scfh) 184.5 scfh 147.6 scfh 61.5 scftr The last Type A Containment lntegrated Leak Rate Test (CILRT) results (obtained on October 12,2012 during Cycle 11 refueling outage) are:
As-found CILRT = 105.1 scfl'r Acceptance Criteria (L"): less than or equal to (<) 246 scfh Percent of L" = (105.1 scfh / 246 scfh) x 100 = 42.7o/o As-left CILRT = 91.90 scfh Acceptance Criteria (0.75L"): s184.5 scfh Percent of 0.75L" = (91.90 scfh / 184.5 scftr) x 100 = 49.8o/o Percent of L" based on last CILRT as-left test results of 91.90 scfkr (91.90 scfh l 246 scfh) x 100 = 37.4%
The last combined Type B and C Local Leak Rate Test results (as of May 23, 2013) are:
Mode 1 - 4 Criteria: Total Minimum Path Leak Rate = 7.44 scfh Acceptance Criteria (0.60L"): less than (<) 147.6 scfh Percent of 0.60L" = (7.44 scfh / 147.6 scfh) x 100 = 5.1%
Mode 1 - 4 Criteria: Total Minimum Bypass Leak Rate = 5.75 scfh Acceptance Criteria (0.25L"): s 61.5 scfh Percent of 0.25L" = (5.75 scfh / 61.5 scftr) x 100 = 9,4o/o Restart Criteria: Total Maximum Path Leak Rate = 23.17 scfh Acceptance Criteria (0.60L"): < 147.6 scfh Percent of 0.60L" = (23.17 scftr / 147.6 scfh) x 1OO = 15.7Yo Restart Criteria: Total Maximum Bypass Leak Rate = 19.71 scfh Acceptance Criteria (0.25L"): s 61.5 scfh Percent of 0.25L" = (19.71 scfh / 61.5 scfh) x 100 = 32.1o/o E-6
- 2. ln your submiftal, Secfion 2.1, Basis for Exigent Reguesf, does not explain the reason for selecting specifically the week of June 24. 2013, to repair the pump sea/. P/ease explain how that week was chosen and the adverse impacts of conducting the repair after the normal 30-day notice for public comments and 60-day request for hearing peiod under 10cFR50.91.
WA Response As described in the enclosure to the May 22,2013 letter from TVA to the NRC, WBN observed a significant temporary increase in mechanical seal leakage in April 2013 associated with CSP 1B-B. As a result of this event, TVA made the decision to replace the CSP 1B-B mechanical seal at the first available opportunity. The week of June 24,2013 is the first available Train B work week. Performing this work in a planned Train B work week minimizes the risk significance and simplifies the planning process.
The adverse effect of rescheduling this work lies in the risk of another unanticipated spike in mechanical seal leakage and the associated risk of an unplanned transient that could result in a plant shutdown.
In Section 2.3, Justification for the Change, TVA sfafed "The preliminary estimate for the seal replacement activityis 68 hourg not including potential discovery rssues which may be encountered." Please provide following clarifications:
o What are the bases of the 68 hours7.87037e-4 days <br />0.0189 hours <br />1.124339e-4 weeks <br />2.5874e-5 months <br /> estimated to cover the seal repair items outlined in this section?
TVA Response The 68 hours7.87037e-4 days <br />0.0189 hours <br />1.124339e-4 weeks <br />2.5874e-5 months <br /> that was estimated for replacing the mechanical seal is based on previous experience performing similar work on other plant components.
What are the potential rssues may be encountered during the seal replacement and TVA's contingency plans for these potentialissues, including time estimates?
TVA Resoonse As part of planning the work associated with the replacement of the mechanical seal on the CSP 1B-8, TVA identified several areas which have the potential to affect the current mechanical seal replacement schedule. The activity and associated effects on the schedule are provided in the following table.
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Activity Schedule Effect (Hours)
Removal of potentially damaged/corroded pump casing bolts 18 Removal and replacement of pump shaft sleeve 12 Removal and replacement of shaft bearings 48 Replacement of the rotating element (includes additional 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to transport replacement rotating element from WBN Unit 2) 48 E-8