ML20134P296

Documents TVA Request for Discretionary Enforcement for Plant TS 3.8.1.1,Action B for DG 2A-A

ML20134P296
Person / Time
Site:	Sequoyah
Issue date:	02/14/1997
From:	Shell R TENNESSEE VALLEY AUTHORITY
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML20134P285	List: ML20134P282 ML20134P296
References
NUDOCS 9702250328
Download: ML20134P296 (11)

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Tennessee Varey Authenty. Scst ONe Ben 2000 Soddy.Da;sy. Tennessee 37379 2oCO February 14,1997 i

U.S. Nuclear Regulatory Commission A7N: Document Control Desk Washington, D.C. 20555 Gentlemen:

In the Matter of

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Docket Nos. 50-327 Tennessee Valley Authority

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50 328 SEQUOYAH NUCl. EAR PLANT (SON)- REQUEST FOR DISCRETIONARY ENFORCEMENT FOR FOR UNITS 1 AND 2 TECHNICAL. SPECIFICATION (TS) 3.8.1.1 ACTION 8 FOR DIESEL GENERATOR (DIG) 2A A This letter serves to document TVA's request for discretionary enforcement for Units 1 and 2 TS 3.8.1.1 for D/G 2A A.

During planned testing on the 2A-A D/G, the D/G 'C' phase winding was i

determined to have an inadequate polarization index level. During subsequent i

troubleshooting, the generator pigtallInsulation was identified as the source of the dielectric breakdown. Replacement and testing of the generator pigtails has been completed. At the end of the post maintenance testing for the generator pigtail repairs, a degraded performance of the 2A2 engine govemor was noted.

The remaining time required to replace the governor actuator and perform the subsequent testing to ensure DIG operability is expected to exceed the allowed outage time govemed by TS Action 3.8.1.1.b by approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />, in order to allow adequate time to comp!ete the testing of the 2A-A D/G, discretionary enforcement is being requested for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> (~36 hour margin),

which is in addition to the 72-hours allowed outage time provided by TS Action 3.8.1.1.b. Without this additional time, both units will be shut down as required by TSs at approximately 1725 hours0.02 days <br />0.479 hours <br />0.00285 weeks <br />6.563625e-4 months <br /> Eastern Standard Time on February 14, 1997. Note that an allowed outage time of 7 days has been justifled for a planned D/G maintenance outage once per 18. months per D/G in TS Change Request 96-08 (submitted to NRC August 22,1996).

Enclosure

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U. S. Nuclear Regulatory Commission Page 2 February 14,1997 Please direct questions concerning this issue to me at (423) 843 7170.

Sincerely, krY l

R. H. Shell Site Licensing and Industry Affairs Manager Enclosure cc: See page 3

U.S. Nuclear Regulatory Commission Page 3 February 14.1997 cc (Enclosure):

Mr. R. W. Hernan, Project Manager U.S. Nuclear Regulatory Commission One Whhe Flint, North-11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident inspector Sequoyah Nuclear Plant 2600 loou Ferry Road Soddy-Daisy. Tennessee 37379 3624 Regional Administrator U.S. Nuclear Regulatory Commission Region 11 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323-2711 p

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U.S. Nuclear Regulatory Commission Page 3 February 14,1997 JDS:EAM cc (Enclosure):

Mr. R. W. Hernan, Project Manager U.S. Nuclear Regulatory Commission One White Flint, North 11555 Rockville Pike Rockville. Maryland 20852-2739 NRC Resident inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administrator U.S. Nuclear Regulatory Commission i

Region il 101 Merletta Street, NW, Suite 2900 Atlanta, Georgio 30323-2711 R. J. Adney, OPS 4A SON R. R. Baron, BR 4J-C E. S. Christenbury, ET 11H K M. J. Fecht, OPS 4A-SON K. N. Harris, LP 6A C J. T. Harron, POB 28 SON T J. McGrath, LP 38-C Vice President Engineering and Technical Services, LP GA.C J. R. Rupert, OPS 4A-SON E. W. Whitaker, BR 4J-C K. W. Whittenburg. BR 4F.C O. J. Zeringue, LP 6AC RIMS, WT 3B-K

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B LICENSING TRANSMITTAL TO NRC

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SUMMARY

AND CONCURRENCE SHEET THE PURPOSE OF THIS CONCURRENCE SHEET IS TO ASSURE THE ACCURACY AND COMPLETENESS OF TVA SUBMITTALS TO THE NRC.

ORIGINAL EXTENDED DATE_

DATE DUE NRC -

DATE DUE NRC SUBMITTAL PREPARED BY Keith Weller and Jim Smith ACTION NO.

FEES REQUIRED YES _ NO PROJECT /DDCUMENT l.D.,Scquoyah Nuclear Plant (SONI Request for Discletionary Enforcement for Units 1 and 2 Technical specification (TS) 3.8.1.1, Action B for D/G 2A-A PURPOSE /

SUMMARY

To avoid dual un'rt shutdown RESPONDS TO,

(RIMS NO.) COMPLETE RESPONSE YES NO__

PROBLEM OR DEFICIENCY DESCRIPTlDN _ Discretionary enforcement request to allow time to repair and test the D/G.

CORRECTIVE ACTION / COMMITMENT INDEPENDENT REVIEW DATE 1"l% W2~ N O.T.TI M*, O 3=% T D, N '* * **'* * " ~

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CONCURRENCE NAME ORGANIZATION SIGNATURE DATE Pedro Salas Corp. L&lA Manager J. T. Herron SON Plant Manager J. R. Rupert SON Engtg and Support Manager M. J. Burzynski SON Engra and Material Manager E. J. Vigluicci Office of the General Council i: disc-enf.wd.eam

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__ Site Licensino Concurrence Sheet

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ORIGINAL EXTENDED DATE DATE DUE NRC DATE DUE NRC PROJECT /DDCUMENT l.D. _ Sequoyah Nuclear Plant (SON)- Recuest for Discretionary Enforcernent for Units 1 and 2 Technical specification (TS) 3.8.1.1. Action B for D/G 2A-A U

incident Investigation No.

^

Cross Reference Documents (PER, CAQR.etc.)

Verification by CONCURRENCE 1

SIGNATURE DR l

NAME ORGANIZATION LETTER REFERENCE DATE J. D. Smith SON Site Licensing Supv.

l J. S. Smith SON Site LicensinD.

J. R. Reynolds SON OPS Supt i

M. J. Lorek SON Mech /Neir Engr.

C. R. Butcher SQN Lead Electrical Enar.

NRC response or approval required? _

Yes No 1:dg2aa.jds: cam 1

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l ENCLOSURE 4

Request for Discretionary Enforcement for D/G 2A-A

Background

in February of 1996, during planned surveillance testing, the polarization index and megger readings were found to be low on the "C" phase of the 2A-A D/G and cleaning of the cables was required to achieve an ecceptable reading. Corrective actions were established to perform additional megger checks and polarization index measurements. The results of previous readings were evaluated to determine adverse trends associated with the D/G 2A-A stator and further corrective actions.

On February 11 and 12,1997, while performing the additional tests, low megger

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readings and unacceptable polarization index readings were identified on the "C" Phase D/G stator winding. Cleaning of cables and connections could not return the readings to an acceptable value. The generator pigtallinsulation was identified as the l

source of the d' electric breakdown. Replacement and testing of the generator pigtails was completed with ~24 hours left in the allowed outage time. At the end of the post maintenance testing for the generator pigtail repairs, a degreded performance of the 2A2 engine governor actuator was noted. As a conservative measure, TVA is replacing the degraded actuator and the actuator on the other tandem engine.

The root cause of the 2A2 actuator degradation is being investigated. A preliminary investigation has not identified additional failures of this actuator at Sequoyeh. A failure analysis of this actuator will be conducted as a part of our investigation.

The remaining time required to replace the engine actuators and complete required testing is expected to excied the allowed outage time (AOT) governed by Technical i

Specification (TS) 3.8.1.1, Action "b" by approximately 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />. This will require a i

total D/G allowed outage time of 84 hours9.722222e-4 days <br />0.0233 hours <br />1.388889e-4 weeks <br />3.1962e-5 months <br />.

TS Compliance TS 3.8.1.1, Action "b", allows a D/G to be inoperable for up to 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> before proceeding to a shutdown condition. The 72-hour period will expire at 1725 hours0.02 days <br />0.479 hours <br />0.00285 weeks <br />6.563625e-4 months <br /> Eastern Standard Time on February 1t,1997. Installation, testing and return to operation activities for the 2A A D/G are estimated to be completed by 0500 hours0.00579 days <br />0.139 hours <br />8.267196e-4 weeks <br />1.9025e-4 months <br /> on February 15,1997.

Safety Consequences The electrical system design is described in Section 8.0, " Electrical Power," in the SON Final Safety Analysis Report IFSAR). SQN is connected to a strong offsite transmission network, in the vicinity of SQN, the lines are on right of ways which are sufficiently wide enough to preclude the likelihood of a failure of one line causing failure of tho other line. Electric power to SON is supplied by two physically and electrically independent circuits from the SON 161 kV switchyard through three

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cap: rete tr:nsf;rmtro to tha en:ite el2ctrical di2tribution syst m. Tha 161-kV i

switchytrd in d: sign d with two mtin bus eretions and is art nged so that the supply 2

to the onsite power system, as well as the connections to the generator and the S00-161-kV transformer bank, is maintained to one bus section for a failure of the other i

section. Four 161-kV lines terminate on one bus, and four other 161 kV lines i

terminate on the other bus. Two fuseless 84 MVAR 161 kV capacitor banks are tie I i

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to the 161-kV switchyard through double bus-tie breakers'. Each bank is independently switched. These capacitors provide reactive voltage support for the 161-kV offsite system.

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Several improvements to the plant / grid interfaces at SQN have been made since the i

72-hour AOT was established. They include:

1. Replacing the common station service transformers (CSSTs) with ones having automatic high speed onload voltage tap changers in order to maintain optimal l

voltages to the safety related system while connected to the preferred power l

supply (PPS) and during all modes of plant startup, shutdown, and operation. With the installation of these new transformers, the in-plant auxiliary power system can accommodate a transmission system bandwidth of + / -5 percent of nominal i

versus a 1-2 percent bandwidth before, i-

2. SON has implemented a design change which provides for the in-plant attemating current auxiliary power system to be normally fed from the PPS during all modes of plant operation, startup, and shutdown. This increases reliability by reducing l

plant transfers during a plant shutdown and provider, betar voltage regulation to the safety-related boards during all modes of plant operation.

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3. SON installed two 84 MVAR capacitor banks outside the 161-kV switchyard to.

provide reactive power support to the plant during a Unit 2 trip and shutdown.

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4. Transmission Power Systems performs comprehensive Transmission system Studies for allTVA nuclear plants on a three year cycle. These studies include load flow analyses and transient stability stucies and are performed in accordance j

with the guidelines in IEEE 7651995 for transmission system studies. This verification ensures that SON can withstand a design-basis accident with a j

preexisting problem In one of the two qualtfled offsite power lines.

Preferred power to SON is supplied by either of the 161-kV buses to three CSSTs.

l The CSSTs supply power to the four start buses (SBs), and the four SBs supply q

power to the eight unit boards. There are four unit boards per un'rt and the unit i

boards supply power to the four shutdown boards, there are two shutdown boards per unit. Each of the shutdown boards supply a single train of safe shutdown equipment g

along with some common equipment. The shutdown boards can also be supplied p

emergency power by seismio, environmentally qualified D/Gs that supply backup power to the vital 6.9-kV, and 480-kV busses in the event of a loss of normal and alternate offsite power.

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4 During powsr operction, ths D/Gs help to ensure that sufficlint powgr will b3 available to the tafety-related equipment, which is needed for the safe shutdown of the plant and for mitigation and control during accident conditions. During shutdown and refueling condition, the D/Gs help to ensure that the facility is able to maintain shutdown or refueling conditions for extended periods of time.

SON D/Gs have high availability and reliability ratings. For implementation of 10 CFR 50.83, SON established an D/G target reliability of 0.975.

SON D/G unavailability for 1998 was 0.008: for 1995. 0.015: and for 1994, 0.017 which clearly indicates

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an improving trend. These values are well below the year 2000 industry goal of 0.025.

The increase in risk for having the 2A A DIG out of service two additional days may be determined by computing the change in mean core damage probability as discussed in EPRI Report EPRI TR-105396, PSA Applications Guide (see example in l

Section 4.2.3). The change in mean core damage probability (ACDP) can be determined by multiplying the change in mean core damage frequency for the given condition by the length of time in the configuration. For the case considering one D/G out of service due to maintenance, the calculated mean core damage frequency is 4.81E 5 events per year. This results in a risk achievement worth of 1.5 (i.e.,4.81E.

5 / 3.2E-5). The core damage probability for two additional days of maintenance is calculated as follows:

oCDP= {ll.5

• 3.2x10 ) - 3.2x10*) * (2/385)= 0.875x10 4

4 The analysis was performed using the SON PSA zero maintenance model(ZMM).

j This model computes the mean core damage frequency assuming all equipment is in service. The model is used to provide insights relative to specific pieces of equiptr.ent or configurations. Removal of equipment from service is evaluated for its risk impact in accordance with plant maintenance procedures.

Based on Figure 4.3 of the PSA Applications Guide, this change in mean core damage probability is well below the threshold for potentially risk significant changes (1.0E-5).

In fact, the determined ACDP is at the lower range of non risk significant category (1.0E-7 ).

Compensatory Measures The proposed compensatory measure is to perform Surveillance Requirement 4.8.1.1.a avery four hours (eight hour frecuency is required by TSs). In addition, in accordance with TS Action 3.8.1.1.b, the remaining DGs will be tested per SR 4.8.1.1.2.a.4. SON is protecting B-train components while the 2A train D/G is out of service. Further, the switchyard will be protected to ensure effsite power supply reliability. The remaining emergency D/Gs (1 A,1B and 28) are operable.

The duration of the requested enforcement discretion (i.e.,48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />)is based upon the anticipated additional time, plus margin, needed to replace the DIGS governor actuator and perform the required functional testing.

The basis for the conclusion that a USO does not exist is as follows:

1. The prebr.bility cf occurrance or the c nsequsnces of an cccidsnt or malfunction cf cquipm:nt importent to saf2ty prcviously evclusted in the safsty analysis report may be increased; or j

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The probability of occurrence of an accident of malfunction of equipment important to safety is not increased as the D/G performs a function of accident 4

mitigation only and cannot cause an accident. Similarly, the DlG itsetf is out of service and cannot cause other equipment to malfunction. The consequences of an accident are not increased as the increase in core damage frequency as a i

result of the additional ACT is judged to be insignificant and the offsite dose i

would not increase.

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2. A possibility for an accident or malfunction of a different type than any

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evaluated previously in the safety analysis report may be created; or The possibility for an accident or malfunction to be created does not exist as a result of the increase in AOT for the DIG. as the D/G performs a function of i

accident mitigation only and cannot result in the malfunction of other equipment.

3. The margin of safety as defined in the basis for any TS is reduced.

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- The calculated increase in the AOT for one D/G out of service shows a '

non risk signtficant increase in the predicted core damage frequency (CDF). That l

calculation did not provide credit for the additional compensatory measures Imposed by TVA. When considered together, TVA concludes that the margin of safety has not been reduced, in addition, the configuration that the plant will be In for this additional period of time (one D/G inoperable) has previously been evaluated.

l TVA has evaluated the enforcement discretion request and has determined that it I

j does not represent a significant hazards consideration based on criteria established in 10 CFR 50.92. Operation of SON in accordance with the proposed amendment will not:

1. Involve a significant increase in the pr'obability or consequences of an accident previously evaluated.

The D/Gs supply backup power to the essential safety systems in the event of a loss of-offsite (normal) power. The D/Gs cannot initiate an accident. The requested relief wl!! not impact the plant design or operation. The increased out of service time does not invalidate assumptions used in evaluating the radiological consequences of an accident and does not provide a new or altered release path. Therefore, this relief does not involve an increase in the probability of any accident previously evaluated.

An increase in the AOT would not change the conditions, operating configuration, or minimum amount of operable equipment assumed in the plant FSAR for accident mitigation. The longer AOT would provide a longer time window for maintenance. Based on the smallincrease in plant risk during maintenance, this change will not result in a significant e

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Incr :ce in the con:equ;nc:a of an cecidInt.

2. Create the possibility of a new or different kind of accident from any previously analyzed.

The proposed relief to extend the AOT for the D/Gs does not alter the physical design, or configuration of the plant. The D/G operation remains unchanged, therefore, this change does not create the possibility of a new or different kind of accident from any previously analyzed.

3. Involve a significant reduction in a margin of safety.

The calculated increase in the ACT for one D/G out of service shows a non risk significant increase in the predicted core damage frequency (CDF). That calculation did not provide credit for the additional compensatory measures imposed by TVA. When considered together, TVA concludes that the margin of safety has not been reduced. in addition, the configurat!cn that the plant will be in for this additional period of time (one D/G inoperable) has previously been evaluated.

Also, the action does not involve an unreviewed environmental question because it does not increase any adverse environmentalimpacts, change effluents or power levels, or result in unreviewed environmental matters. In addition, the proposed request has been approved by the Plant Operations Review Committee.

This enforcement discretion meets criterion lla) of Section B of Inspection Manual, Part 9900. This criteria is satisfied in that a dual unit shutdown and associated undesirable transients would be avoided.

i Prior adoption of an approved line item improvement to the TSs or the improved TSs (ITS) would not have obviated the need for this notice of enforcement discretion (NOED) request.

Disc-ent.w.e sm TOTAL P.12