Forwards LER 80-009/01T-0. · report date: march 10,1980 reportable occurrence 80-09 issue o occurrence date: feb ruary 25, 1980 page 1 of 12 fort st vrain nuclear generating station

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7 - public Service Company ? Cc3 cede16805 Weld County Road 191/2, Platteville, Colorado 80651

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March 10, 19s0Fort S t. VrainUnit No. 1P-80044

Mr. Karl V. Seyfrit, DirectorNuclear Regulatory Cot:: missionRegion IVOffice of Inspection and Enforcement611 Ryan Plaza DriveSuite 1000Arlington, Texas 76012

Reference: Facility Operating LicenseNo. DPR-34

Docket No: 50-267

Dear Mr. Seyfrit:

Enclosed please find a copy of Reportable Occurrence Report No. 50-267/80-09, Pinal, sub:::itted per the requirements of Technical SpecificationAC 7.5.2(a)9.

Also, plesse find enclosed one copy of the Licensee Event Report forReportable Occurrence Report No. 50-267/80-09.

Very truly yours,

$ WR.4.6Don Warembourg

, Manager, Nuclear Production

DV/c1s

Enclosure

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REPORT DATE: March 10,1980 REPORTABLE OCCURRENCE 80-09ISSUE O

OCCURRENCE DATE: Feb ruary 25, 1980 Page 1 of 12

FORT ST VRAIN NUCLEAR GENERATING STATIONPUBLIC SERVICE COMPANY OF COLORADO

16805 WELD COUNTY ROAD 19 1/ 4PLATTEVILLE, COLORADO 80651

REPORT NO. 50-267/ 80-09 /01-T-0

FINAL

IDENTIFICATION OFOCCURRENCE:

While the plant was in a shutdown condition, a test was performed to evalu-ate the fixed low feedwater flow, fixed circulator speed high, and programmedcirculator speed /feedwater flow trips. As a result, it was determinedthat the design of the bistable trip module when used with the module testunit for calibration of process trip (bistable) functions of the plantprotective system induced a calibration off-set which could have possiblyallowed the trips to occur outside Technical Specification limits.

This is reportable per Fort St. Vrain Technical Specification AC 7.5.2(a)9.

CONDITIONS PRIORTO OCCURRENCE:

Steady State Power _ Routine Shutdown

Hot Shutdown Routine Load Change

X Cold Shutdown Other (specify)_

Refueling Shutdown

Routine Startup

The major plant parameters at the time of the event were as follows:

Reactor Power -0- Wth

Electrical Power N/A We

Secondary Coolant Pressure N/A psig

Secondary Coolant Temperature N/A *F

Secondary Coolant Flow N/A #/hr..

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Primary Coolant Pressure 83 psia

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 2 of 12

CONDITIONS PRIORTO OCCURRENCE: (Cont' d)

Primary Coolant Core Inlet Temperature N/A 'F

Primary Coolant Core Outlet Temperature 212 *F *

Primary Coolant Flow N/A f/hr.

Circulator lA N/A RPM

Circulator 13 N/A RPM

Circulator 1C N/A RPM

Circulator ID N/A RPM

DESCRIPTION OFOCCURRENCE:

Test T-137 was performed to collect data on the plant protective system (PPS),ff,xed low feedwater flow, fixed circulator speed high, and programmed circu-lator speed /feedwater flow trips. The test was conducted while the reactor*

was in a shutdown condition and the circulator under test was shutdown.

Channel A, one of the three channels of Loop I, was selected for obtaining"as found" data, calibrating the instrumentation and obtaining "as lef t"data. When the data were evaluated, it was found that a calibration off-set existed in the process trip (bistable) modules, model PT-3D and modelPT-3S. This was determined to be due to the signal from the module testunit (MU) not using the same input point as the measured signal.

APPARENT CAUSEOF OCCURRENCE:

I Design Unusual Service Condition,Including Environment

Manufacture Component Failure

Installation / Cons t. Other (specify)

Operator

Procedure

Test signal from module test unit (EU) not using the same input path as themeasured signal to the bistable trip was the cauw.

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 3 of 12

ANALYSIS OFOCCURRENCE:

The circulator speed and feedwater flow instrument channels are shownschematically on Figure 1.

The signal from the circulato speed probe 01 1 cr a =1etea to a eveeamodifier (SM) pre-amplifier 2 which is a pulse output and from the SMto a speed transmitter (ST) w ere the signal is c reed f rom a pulsea a voltage signal. The output of the a=plifier is smi tedthe s eed switches low (SSL), speed switches high . H), 5, , ,

and 7 and to the feedwater setpoint programmer 8 .as t e measured s g-nal. e measured signal is coc: pared to fixed setpoints which, dependingon the function required, either provide a permissive to set the circulatorbr 9 , or to initiate a circul r trip on high water turbine speed

or high steam turbine speed .

Circulator overspeed is an indication of speed control or other failurenecessitating rapid shutdown of the circulator. The speed sensing systemresponse and trip setting are chosen so that under the maximum overspeedsituation possible (loss of restraining torque), the circulator will remainwithin design capabilities.

Th feedwater flow differential pressure across he flow element (FE)is sensed by the f transmitter (Fr), , and transmitted to

th flow modifier (FM), The output of t FM is tr mit ted.

the setpoint programmers and flow switches low (FSL) 16 and 1/as the measured signal. e measured signal is co red to a fixed set-point to provide a fixed low feedwater flow trip, 8 , to avoid unstablesteam generator flow conditions.

The SSL 07 is grost ==ea hF che feeaw ter f1ow distaste seevoint prest ==erh . Low circulator speed indicates speed control or equipment failure

necessitating a circulator shutdown. Too low a circulator speed causesa mismatch between thermal power input and heat removal (feedwater flow)in a steam generator. This may result in flooding of the superheatersection of a steam generator.

The P3L 16 is programaed by the circulator speed bistable setpoint prog-rammer 8 Low feedwater flow indicates control or equipment failures.

and res ts in an increase in superheater outlet temperature and/or unstableflow conditions in the steam generator. As a circulator speed controllerfailure can lead to higher than normal circulator speeds and a correspondingincrease in superheater steam outlet temperature, a programmed low-feedvater-flow trip prevents prolonged operation in the region of speed versus flowwhich may cause excessive superheat steam tec:peratures.

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 5 of 12

ANALYSIS OFOCCURRENCE: (Cont' d)

In accordance with SR 5.4.1, Reactor Protective System and Other CriticalInstrumentation and Control Checks, Calibrations, and Tests, Table 5.4-3,Channel Descriptions 1 and 2, a monthly test is performed on the circulatorspeed-steam and water and the feedwater flow instrumentation. The test,Method b of the table, specifies an internal test signal to verify tripsetting and indicators. The internal test signal is from a module testunit (MIU) module one of which is installed in each bay (channel) of thePlant Protective System (PPS) .

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Testing is accomplished by injecting a signal at a point in the analogportion of the measurement channel prior to the bistable and noting thetrip point against the input value as displayed on the meter indicatorfor the channel.

When the data from the circulator speed /feedwater flow calibration test,T-137, were analyzed, it was found that a calibration off-set existed inthe process trip (bistable) modules. The off-set was determined to bedue to the test signal from the MTU not using the sa=e input point asthe measured signal. Refer to Figure 2.

MIU Input0 to IV Test

ks

%S1> Output

Op erateProcess aputR1O to 10V

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FIGURE 2

During normal operation, the r. ode switch, S1, on the process trip (bistable)is in the OPERATE position and a O to 10 volt signal proportional to themeasured process is transmitted through a 10 to 1 voltage divider network,R1, to an operational amplifier, A1, and also through a variable resistor,

REPORTABLE OCCURRENCE 80-09ISSUE OPage 6 of 12

ANALYSIS OF0CCURRENCE: (Cont ' d)

R2, to the module meter indicator, M. When the input reaches a predetermineds etp oint, the bistable trips, the output of Al changes state, and therequired protective or permissive action is initiated to a 2 of 3 logiccircuit.

During testing, S1 is placed in the TEST position and a 0 to 1 volt signalwhich allows simulating variations in the measured process is transmittedfrom the MTU to Al, R2, and M to verify or to set the bistable trip point.Using the MrU causes a calibration off-set of the bistable due to R1,R2, and M. The off-set is variable depending on the position (resistancevalue) of R2, and is greater at some points than the allowable tclerancesderived from the instrument error analysis used for establishing setpointswhich are conservative based on the Technical Specification limits ofLCO 4.4.1 for circulator speed and feedvater flow calibration.

As a result of the calibration off-set discovered in T-137, scheduled andspecial surveillance testing was performed on all bistable trip modules,and the results were evaluated to determine the scope of the problem.

Evaluation determined that of the forty-three (43)model PT-3D bistabletrips in the plant protective system, thirteen (13)are not affected bythe off-set, and of the thirty-nine (39) model PT-35 bistable trips inthe plant protective system, twenty-one (21) were not affected by theoff-set. Since the tesc sigm'1 from the MTU does not go directly to thebistable but to an amplifier module in the plant protective system, boththe measured signal and the test signal to the bistables use the same in-put point, and no off-set is encountered.

The PT-3D bistables which were not affected are for the primary coolantpressure scram. The PT-3S bistables which were not affected are for thehigh reheat steam temperature scram, reactor building high teuperaturescram, and low superheat header temperature which is a loop shutdown para-meter.

Table 1 listo the thirty (30) PT-3D bistables which were affected and thefunction of each. -

NOTE: The D on the rodel number defines a double, i.e. two b1 stables,so that SSH-21XXX and SSH-21XXX-1 are in one module and SSL-21XXX-1and SSL-21XXX-2 are in one module .1nd FSL-22XX-1 and FSL-22XX-2are in one module.

REPORTABLE OCCURRENCE 80-09ISSUE OPage 7 of 12

ANALYSIS OFOCCURRENCE: (Cont' d)

Table 2 lists the eighteen PT-3S bistables which were affected and thefunction of each.

TABLE 1

PT-3D BISTABLES

Instrument No. Function

SSH-21161 Circulator 1A Steam Turbine Overspeed (Channel A)SSH-21161-1 Circulator 1A Water Turbine Overspeed (Channel A)SSL-21161-1 Circulator 1A Program Speed Low (Channel A)SSL-21161-2 Circulator 1A Fixed Speed Low (Channel A)SSH-21162 Circulator 1C Steam Turbine Overspeed (Channel A)SSH-2H6 2-1 Cir tor 1C Water Turbine Overspeed (Channel A)SSL-21162-1 Cir.. :or 1C Program Speed Low (Channel A)SSL-21162-2 Ciretaator 1C Fixed Speed Low (Channel A)SSH-21163 Circulator 1A Steam Turbine Overspeed (Channel B)SSH-2H63-1 Circulgtor 1A Water Turbine Overspeed (Channel B)SSL-21163-1 Circulator 1A Program Speed Low (Channel B)SSL-21163-2 Circulator lA Fixed Speed Low (Channel B)SSH-21164 Circulator 1C Steam Turbine Overspeed (Channel B)SSH-2n64-1 Circulator 1C Water Turbine Overspeed (Channel B)SSL-21164-1 Circulator 1C Program Speed Low (Channel B)SSL-2n64-2 Circulator 1C Fixed Speed Low (Channel B)SSH-21165 Circulator lA Steam Turbine Overspeed (Channel C)SSH-21165-1 Circulator 1A Water Turbine Overspeed (Channel C)SSL-21165-1 Circulator 1A Program Speed Low (Channel C)SSL-2n65-2 Circulator 1A Fixed Speed Low (Channel C)SSH-21166 Circulator 1C Steam Turbine Overspeed (Channel C)SSH-21166-1 Circulator 1C Water Turbine Overspeed (Channel C)SSL-21166-1 Circulator 1C Program Speed Low (Channel C)SSL-21166-2 Circulator 1C Fixed Speed Low (Channel C)SSH-2H67 Circulator 1B Steam Turbine Overspeed (Channel A)SSH-2H67-1 Circulator 13 Water Turbine Overspeed (Channel A)SSL-2H6 7-1 Circulator 1B Program Speed Low (Channel A)SSL-21167-2 Circulator 13 Fixed Speed Low (Channel A)SSH-21168 Circulator ID Steam Turbine Overspeed (Channel A)SSH-21168-1 Circulator ID Water Turbine Overspeed (Channel A)SSL-2n68-1 Circulator ID Program Speed Low (Channel A)SSL-21168-2 Circulator ID Fixed Speed Low (Channel A)SSH-2H69 Circulator 1B Steam Turbine Overspeed (Channel B)SSH-21169-1 Circulator 1B Water Turbine Overspeed (Channel B)SSL-21169-1 Circulator 1B Program Speed Low (Channel B)

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 8 of 12

ANALYSIS OF0CCURRENCE: (Con t' d)

TABLE 1 (Cont'd)

PT-3D BISTABLES

Instrument No. Function

SsL-21169-2 Circulator 1B Fixed Speed Low (Channel B)SSH-21170 circulator 1D Steam Turbine Overspeed (Channel B)SSH-21170-1 Circulator ID Water Turbine Overspeed (Channel B)SSL-21170-1 Circulator ID Program Speed Low (Channel B)SSL-21170-2 Circulator ID Fixed Speed Low (Channel B)SSH-21171 Circulator 1B Steam Turbine Overspeed (Channel C)SSH-21171-1 Circulator 1B Water Turbinc Overspeed (Channel C)SSL-21171-1 Circulator 13 Program Speed Low (Channel C)SSL-21171-2 Circulator 1B Fixed Speed Low (Channel C)SSE-21172 Circulator ID Steam Turbine Overspeed (Channel C)SSH-211''2-1 Circulator 1D Water Turbine Overspeed (Channel C)SSL-21172-1 Circulator ID Program Speed Low (Channel C)SSL-21172-2 Circulator ID Fixed Speed Low (Channel C)FSL-2209-1 Loop I Feedwater Flow . Fixed Low (Channel A)FS L-2209-2 Program Low Feedwater Trig (Channel A)FSL-2210-1 Loop II Feedwater Flow Fixed Low (Channe* 1)E L-2210-2 Program Low Feedwater Trip (Channel A)FSL-2211-1 Loop I Feedwater Flow Fixed Low (Channel B)FSL-2211-2 Program Low Feedwater Trip (Channel B)FS L-2212-1 Loop II Feedwater Flow Fixed Low (Channel B)FSL-2212-2 Program low Feedwater Trip (Channel B)FSL-2213-1 Loop I Feedvater Flow Fixed Low (Channel C)FS L-2213-2 Program Low Feedwater Trip (Channel C)FSL-2214-1 Loop II Feedwater Flow Fixed Low (Channel C)FS L-221.' -2 Program low Feedwater Trip (Channel C)

TABLE 2,

PT-3S BISTABLES

Instrument No. Function

ISH-93454A Pipe Rupture North WallXSH-93454B Pipe Rupture North WallISH-93454C Pipe Rupture North WallXSE-93455A Pipe Rupture North WallISR-93455B Pipe Rupture North WallISE-93455C Pipe Rupture North WallXSH-93456A Pipe Rupture South Wall

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REPORTABLE OCCURRENCE 80-09ISSUE OFage 9 of 12

ANALYSIS OFOCCURRENCE: (Cont' d)

TABLE 2 (Cont'd)

PT-3S BISTABLES

Instrument No. Function

XSH-93456B Pipe Rupture South WallXSH-93456C Pipe Rupture South WallXSH-93457A Pipe Rupture South WallXSH-934573 Pipe Rupture South WallXSH-93457C Pipe Rupture South WallXSH-93470A Pipe Rupture Under PCRVXSH-93470B Pipe Ruptdre Under PCRVXSH-03470C Pipe Rupture Under PCRVXSH-93471A Pipe Rupture Under PCRVXSH-934713 Pipe Rupture Under PCRVXSH-93471C Pipe Rupture Under PCRV

Testing of the affected bistables listed in Table 1 disclosed that a totalof nine (9) would have tripped outside the limits of LCO 4.4.1, Table 4.4-3,Items No.1, No. 6, and No. 9. Those bistables are listed below in Tables3, 4, and 5 respectively.

TABLE 3

Item No.1FUNCTIONAL UNIT: Circulator Speed - LowLCO TRIP SETTING: 1910 rpm Below Normal as Programmed by W flow

Instrument Circulator "As Found" Trip (rpm)

SSL-21161-1 1A 1940SSL-21162-1 1C 19 25SSL-21163-1 1A 1940SSL-21165-1 1A 19 25SS L-2116 7-1 la 1940SSL-21170-1 1D 1925SSL-21172-1 1D 1925

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 10 of 12

MIALYSIS OFOCCURRENCE : (Cont' d)

TABLE 4

Item No. 6FTICTIONAL ETIT: Circulator Speed - High SteamLCO TRIP SETTING: < 11,000 rpm

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Instrument Circulator "As Found" Trip (rpm)

SSH-21170 1D 11,310

TABLE 5

Item No. 9FUNCTIONAL UNIT: Circulator Speed - High WaterLCO TRIP SETTING: < 8,800 rpm

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Instrument Circulator "As Found" Trio (rpm)

SSH-21170-1 1D 8,910

Although the trip settings were found to be less conservative than thoseestablished by the Technical Specifications, they did not prevent the ful -fillment of the functional requirements of the affected systems.

Testing of the affected bistables listed in Table 2 disclosed that alltrips were within LCO 4.4.1, Table 4.4-2 limits.

CORRECTIVEACTION:

1. Surveillance testing was performed and the results evaluated to determinewhich bistable trips were affected.

2. As found trip points were determined and :: hose bistables listed inTables 3, 4, and 5 which were not in tolerance were recalibrated tothe proper setpoints.

3. Recalibration was accomplished by use of a modified MTU and e.cenderboard which will also be used for testing until permanent change isimplemented. Refer back to Figure 2. The modified MrU and extenderboard use the Process Input line and a 0 to 10V MrU signal so that S1remains in the OPERATE position during test. In this manner, no cali-bratien off-set exists, and compliance with test, Method b, of Table 5.4-3of SR 5.4.1 is maintained.

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 11 of 12

CORRECIIVEACIION: (Con t' d)

4. Change Notices have been initiated to modify affected bistable modulesand bay wiring to utilize the same input point for both test and processsignals.

No further corrective action is anticipated or required.

FAILURE DATA /SIMILARREFORTED OCCURRENCES:

N/A

PROGRAMMATIC IMPACT:

N/A

CODE IMPACT:

N/A

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REPORTABLE OCCURRENCE 80-09ISSUE OPage 12 of 12

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Prepared By:Mic ael J. Ferris ( |Tech (itical Services htgineer

'Reviewed By: ._.

/ Technical Services Supervisor. W Gahn

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Reviewed By:Frank M. MathieOperations Manager

Approved By: MLu4-

Don Warerbourg [Manager, Nuclear Production

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