ML19327C070

LER 89-018-00:on 891012,notification Given of Potential Single Failure of Diesel Generator Voltage Regulator That Could Result in Loss of All But One ECCS Loop.Caused by Design Deficiency.New Procedure developed.W/891109 Ltr

ML19327C070
Person / Time
Site:	Quad Cities
Issue date:	11/09/1989
From:	Bax R, Maclennan M COMMONWEALTH EDISON CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-018-02, LER-89-18-2, RLB-89-255, NUDOCS 8911150204
Download: ML19327C070 (6)

Text

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7 Commonwealth Edison ouad CitIs Nuclear Power Statui

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% . 22710 206 Avenue North -

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.. RLB-89-255 November 9, 1989 U. S. Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 o ,

Reference:

Quad Cities Nuclear Power Station i Docket Number 50-254, DPR-29, Unit One Enclosed is Licensee Event Report (LER)89-018, Revision 00, for Quad Cities Nuclear ,

Power Station.

This report is submitted as a voluntary report.

i.

Raspectfully, COMMONNEALTH EDISON COMPANY ,

QUAD CITIES NUCLEAR POWER STATION l

R. L.

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g e l: Station Manager '

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RLB/MJB/eb l

l' Enclosure cc: R. Stols '

R. Higgins INPO Records Center

i. NRC Region III ,

8911150204 891109 PDR ADOCK 05000254 / M@ -

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s.!cENstt EVENT REPORT (LER g Facility Name (1) Docket Number (2) Pane f3) l Gua'd cities unit One el El of of of 21 El a 1 !of!0l1 Title (4) Potential single Failure of the Olesel Generator Voltage Regulator Which could Retult in a Lost of All But One Emeroency fore Cop 11no System Looo Event Date (1) LER Number (6) Reoort Date (7) Other Facilities Involved fa)

Month Day Year Year /// Sequential // Revision Meith Day Year Facility Namet Docket Numberftl I

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// Number /p/,

p// Number of El ol of of 21 6lE

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11 0 11 2 al 9 al 9 oI1 Ia oIo 1 11 019 al 9 of si el of of I i TH1$ REPORT !$ sV8MITTED PUR$uANT TO THE REQUIREMENTS OF 10CFR 0

f ehack one or more of the followino) (11) 2 20.402(b) 20.405(c) _ 50.73(a)(2)(iv) _ 73.71(b)

POWER 20.a05(a)(1)(1) _ 50.36(c)(1) 50.73(a)(2)(v) _ 73.71(c)

LEVEL 20.405(a)(1)(11) $0.36(c)(2) _ 50.73(a)(2)(vli) K. Other (Specify flo) ololo _, 20.405(a)(1)(iii) _ 50.73(a)(2)(1) 50.73(a)(2)(v111)(A) in Abstract

////////////////////////// _ 20.405(a)(1)(tv) __ 50.73(a)(2)(11) _ 50.73(a)(2)(viii)(B) below and in

////////////////////////// 20.405(a)(1)(v) 50.73(a)(2)(iii) _ 50.73(a)(2)(x) Text)

__ LICENSEE CONTACT FOR THIS LER f121 Name TELEPHONE NUPGER AREA CODE Michael F. MacLennan. Technical Staff Ennineer. Eyt. 2166 3 l o19 61 El 41 -l 21 21 41 1 COMPLETE ONE LINE FOR EAth,GtiP T FAILURE DESCRIBED IN THIS REPORT f13)

CAUSE SYSTEM COMPONENT MANUFAC- REPORTA8LE CAUSE SYSTEM COMPONENT MANUFAC- REPORTABLE TURER Y0 NPPE, TURER TO NPRDS B EIK I I El c cl of al o N I I l l I l l I I I I I 1 I / I I I f I i 1 SUPPLEMENTAL REPORT EXPECTED f141 Expected ttonth l Day I Year Submission lYet fff yet. comolete EXPECTE0 10BMI$510N DATE) "

X l N0 l l l AS$ TRACT (Limit to 1400 spaces i.e. approximately fifteen single-space typewritten lines) (16) l l On October 12, 1989, an Emergency Notification System (ENS) phone notification was made to the Nuclear Regulatory Commission (NRC), notifying them of a scenario

! involving the plant possibly being outside the design basis. It was determined l that during a Loss of Offsite Power (LOOP), in conjunction with a Loss of Coolant

, Accident (LOCA), it is possible that the Unit Diesel Generator (DG)[EK) voltage I regulator [RG) could fall in such a manner that the only Emergency Core Cooling i System (ECCS) available would be one loop of the Core Spray (CS) System [BM). The scenario is of minimal safety significance because of the low probability of such

! an occurrence, calculated to be on the order of lE-8/yr. Regular surveillances and l monitoring of OG parameters during operation, and a new procedure mitigate the affects of such an occurrence. Options to eliminate this design deficiency are under investigation.

This report is being submitted as a voluntary report.

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t LICENSEE EVENT REPORT fLER) TEXT CCNT2NUATION Form Ray 2.0

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FAc!LITYNAME(1) DOCKET NupeER (2) 'ittRNuMataf6) Pana (1)

Ii Year sequential Revision g//

/ Number g/// M*r l

Guad Cities Unit One 0lE 1010 l 0 l 21 El 4 8I9 - 0l 1 18 - 0l0 Ol2 0F DIE TEXT' Energy Industry Identification system (E!!s) codes are identified in the text as (XX)

PLANT AND SYSTEM IDENTIFICATION:

General Electric - Boiling Water Reactor - 2511 MWt rated core thermal power.

EVENT IDENTIFICATION: Potential Single Failure of the Diesel Generator Voltage.

Res)ulator Which Could Result in a Loss of All But One Emergency Core Cooling System Loop l

A. CONDITIONS PRIOR TO EVENT:

Unit: One Event Date: October 12, 1989 Event Time: 1430 Reactor Mode: 2 Mode Name: REFUEL Power Level: 07.

This report was initiated by Deviation Report D-4-1-89-094.

REFUEL Mode (2) - In this position interlocks are estabitshed so that one control rod only may be withdrawn when flux amplifiers are set at the proper sensitivity level and the refueling crane is not over the reactor. Also, the trip from.the turbine control valves, turbine stop valves, main steam isolation valves, and condenser vacuum are bypassed. If the refueling crane is over the reactor, all rods must be fully inserted and none can be withdrawn.

8. DESCRIPTION OF EVENT:

On October'12, 1989, at 1430 hours0.0166 days <br />0.397 hours <br />0.00236 weeks <br />5.44115e-4 months <br /> Unit One was in the REFUEL mode and Unit Two was in the SHUTDOWN mode. At this time, a courtesy ENS phone notification was made, informing the NRC of a scenario involving the plant possibly being outside of the design basis. This condition was recently identified by Northern States Power Company.

Backup power [JX] to the 4kV Essential Service [EA] buses [BU) is supplied by the Emergency Diesel Generators (DG)[EK) as detailed on Attachment 1. The Unit One(Two) DG supplies bus 14-1(24-1), and the swing (1/2) DG can supply either bus 13-1 or 23-1 as necessary. Bus 14-1(24-1) feeds bus 19(29), while bus 13-1(23-1) feeds bus 18(28). Bus 19(29) normally feeds motor control center (MCC) [MCC]

18/19-5(28/29-5). However, if the voltage drops below approximately 50 percent of the normal voltage on bus 19(29), a relay (RLY) will deenergize to automatically transfer MCC 18/19-5(28/29-5) to bus 18(28).

It was determined that during a Loss of Offsite Power (LOOP), in conjunction with a Loss of Coolant Accioent (LOCA), it is possible that the Unit DG voltage regulator

[RG) could fall in such a manner that the DG would feed bus 14-1(24-1) at a reduced voltage somewhere between 50 percent and 80 percent of normal voltage. Below 80 percent voltage, the loads fed from MCC 18/19-5(28/29-5), as well as loads fed from bus 14-1(24-1) and bus 19(29), would not be assured of operating. In addition, above approximately 50 percent of the normal voltage, the MCC 18/19-5(28/29-5) undervoltage relay which transfers feed over to bus 18 would not actuate.

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Liffuirr EVENT REPORT f LER) TEXT comituuATION Form Rav 2.0 FAcILITE NAM (1) DOCKET NuPSER (I) LER MladRIA f 6) _ Pane (3)

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Quad cities Unit One 1 0 l 5 l 01010121 El 4 A l9 - 0 l1 lA . O l0 011 0F 011.

TEXT Energy Industry Identification system (E!!s) codes are identified in the text as (Xx]

Since the "B" loop of both the Residual Heat Removal (RHR) System (B0] and the Core Spray (CS) System [BM) are fed from Bus 14-1(24-1), the undervoltage condition could render them inoperable. Further, the injection valves (INV) for the Low

• Pressure Cooling Injection (LPCI) mode of RHR are fed from HCC 18/19-5(28/29-5),

.which under these circumstances would still be tied to bus 14-1(24-1). Thus, the LPCI mode of RHR could also be made inoperable. In this scenario, the only operable low pressure Emergency Core Cooling System (ECCS) would be "A" loop of Core Spray.

C. APPARENT CAUSE OF EVENT:

-This report is provided to document that Quad Cities Station has a similar plant configuration, such that the scenario identified by another utility, could occur at Quad Cities Station. . This voluntary LER is being submitted in accordance with -

correspondence between Commonwealth Edison Company (CECO) and NRC Regior. III personnel.

The cause of this concern is based on the potential for a single failure of a unit DG voltage regulator in conjunction with a LOOP and LOCA to adversely impact the low pressure ECCS system availability.

D. SAFETY ANALYSIS OF EVENT:

This scenario is of minimal safety significance for the following reasons:

1. The sequence of events postulated is unique and extremely remote. First, a design basis LOCA must occur; second, a loss of offsite power (LOOP) must occur; and finally, the unit diesel generator output must degrade to a point where equipment function is affected, and the voltage must remain above the dropout point for the contactor in the Low Pressure Coolant Injection l- (LPCI)[B0] swing bus transfer circuit. To be of concern, this degradation l must occur after the unit diesel generator is powering the emergency bus. The degradation must also occur before the LPCI injection valve is open. This '

l time window is less than 40 seconds for the bounding case. Not only is the probability of these conditions occurring individually over the life of the plant low, the probability of them occurring simultaneously within the short

, time window necessary for diesel degradation to be of concern is l conservatively judged to be extremely low - upper bound of 1.2E-8/yr. to 3E-8/yr.

l 2. Surveillances are performed monthly per the Technical Specifications to assure

1. diesel generator operability. Surveillance on the diesel auto start and load L circuitry, including the LPCI swing bus transfer, is performed each refueling outage.

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3. The diesel generators are monitored continuously during diesel operation.

Significant degradation in the DG output will result in a Control Room alarm .

to alert the operator. Monitored parameters include both voltage and frequency. In addition, bus undervoltage is alarmed separately in the Control Room.

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J LitEMtEE EVENT REPORT (LER) TEXT c0MTtht14 TION Form Rev,1 A

' FACILITY'NAMd-(1)- 00cKET NuMetR (2) lea huMata fs) Pana fil

-3 Year p/j//p sequential // Revision

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nuai cities w t one ol t I o I e I o l 21 si a aIe - oI1 Ia - oIo 014 or ois

'} TEXTS Energy Industry identification system (E!!s) codes are identified in the text as (XXI In summary, the postulated accident scenario is of minimal safety consequence due to:

a The extremely unlikely sequence of events which must occur in a very narrow I time period'- probability on the order of IE-8/yr.

Regular surveillances which would detect diesel generator voltage / frequency degradation.

• Continuous monitoring of key diesel generator parameters via Control Room alarms during diesel operation.

Due to these mitigating factors, reasonable assurance of safety exists for'the Quad Cities LPCI/RHR swing bus.

E. CORRECTIVE ACTIONS:  ;

On October 17, 1989, a temporary procedure, Unit Diesel Generator Voltage Regulator I Failure with a LOCA and LOOP was implemented. This procedure, which will be made permanent, provides the operators with symptoms by which to recognize the failure of the LPCI injection valve swing bus to transfer when required. Immediate and subsequent operator actions to diagnose the condition and effect a transfer from the degraded source are provided to mitigate the effects of such a failure (NTS 2542008909401).

-Based on an evaluation of possible options, it is apparent that it will not be possible to install hardware changes during the current Quad Cities Unit One reload i ten refuel outage. A schedule will be developed when the corrective actions are j identified (NTS 2542008909402). "

l F. PREVIOUS EVENTS:

There have been no previous events of this type at this station. As this event was not a component failure, a Nuclear Plant Reliability Data System (NPRDS) search was not performed.

1 G. COMPONENT FAILURE DATA:

This event does not involve an actual component failure.

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