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DUKEPOWER

' January' 17, 1990

'D'ocument' Control Desk-'

-

.U. S. Nuclear Regulatory CommissionWashington, D.-C.c -20555-

Subject:> CatawbaLNuclear.Stati'onDocket No. 50-4131 .

.LER'413/89-16, Rev. 1

Gentlemen:

Attached is-Licensee Event Report 413/8D-16,' Revision?1,- concerning'

TECHNICAL SPECIFICATION.3'O.3 ENTERED DUE'.TO FOUR~ CHANNELS OF POWER.RANGE' INSTRUMENTATION BEING DECLARED INOPERABLE:FOLLOWING UNIT' RUNBACK.AS.A RESULT 0F FAILURE.OF,A GENERATOR' BREAKER AIR PRESSURE GAUGE..

This event was considered to beTof no significance |with respect'to the,health and' safety of the,public.

Very truly.yours,

[Tony . Owen."

Station Manager 1

keb\LER-NRC.TBO

xc: Mr.-S.'D. Ebneter American^ Nuclear. InsurersRegional Administrator,-Region II' _c/o Dottie.Sherman,'ANI. Library |U. S.1 Nuclear Regulator Commission The Exchange, Suite ~245101LMarietta Street, NW, Suite 2900- -270 Farmington~AvenuelAtlanta. GA -30323 Farmington, OT 06032

M &'M Nuclear. Consultants Mr. K. Jabbour1221 Avenues of tho' Americas U'. S. Nuclear' Regulatory Commission-Nek York, NY 10020 Office of Nuclear Reactor'. Regulation

. J.Washingtoni D. C. L205S5 .; i

- INPO Records Center: Suite'1500 Mr. W.-T. Orders~1100 circle 75 Parkway NRC Resident Inspector.

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Cttawba Nuclear Station, Unit 1 o |5 | o | 0 | o 1411 13 1 |OF| 0|8Four Channels of Power Range Instrumentation' Inoperable Following Unit-* ' ' ' * '

Runback As A Result of Failure of a Cencrator Breaker Air Pressure GaugeEVENT OATI 161 LER NUMeER 18) REPORT DATE (7) OTHER F ACitfTIES INVOLVED fel

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On September 13, 1989, at 0541' hours Unit i was in Mode 1, 100% PowerOperation. Generator 1B Power Circuit Breaker (PCB) opened causing Unit runback

!'to 54% Power. Four out of four channels of Power Range Nuclear Instrumentation(PRNI) displayed greater than the 5% allowable mismatch between Rated Thermal |Power (RTP) and Nuclear Power, in the non-conservative direction. At 0550-hours,

|

| Technical Specification 3.0.3 was entered and Work Request 4099 SWR was issued-l to complete calibration of the PRNIs. The Unit was stable at 54% Power at 0630 '

hours and the calibrations were performed. Following the required calibrationsof the PRNIs, the Unit exited Technical Specification 3.0.3. The pneumaticgauge was subsequently replaced, and Generator PCB 1B was restored.to service.Unit Power increases commenced at 1003 hours'on September 13, 1939. Allrequired PRNI calibrations were completed to within 2% of RTP by 1525 hours.Unit Power reached 97% Power at 1815 hours. At 2100 hours, Unit Reactor Powerreached 100%. The Power Range mismatch was considered to be an expectedphenomenon following e Unit runback. This incident has been attributed toEquipment Failure due to the failure of the pressure gauge on the PCB whichcaused the Unit runback.

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! BACKGR0VND |Tj ~ The purpose of the Out of Core Instrumentation [EIIS:JG] (ENB) System is to 4

s monitor. Reactor-[EIIS:VSL] Core leakage neutron flux and generate appropriate t

< trips and alarms for various phases of. Reactor [EIIS:VSL], operations. The three i

2 ' separate overlappi.ng ranges' of Source Range, Intermediate Range, and Power Rangealso provide control functions and indicate Reactor status during Mode 2,, -

; :Startup and Mode 1, Power Operation _ Technical Specification;4.3.1.1 requires . Sthat channel calibration ~be performed daily on;the Power Range Neutron Flux High'

Setpoint. This is to be. performed by-comparison-of. calorimetric (reactor . .

, thermal power best estimate, based on; actual plant indicator temperatures). to*,

) excore' power (based upon nuclear'powernlevels from detector instrumentation)i indication when the Unit is above 15% Rated Thermal Power.(RTP). Excore channel !

*

:: ' gains are to be adjusted to make indicated.excore power consistent with? indicated calorimetric power whenever- this comparison . reveals an absolute !

'j difference of more than 2% between the two..<

|' Technical Specification 3.3.1, Table 3.3-1, requires-that three out of 1our-channels of PRNI must be operable during. Modes 1 and 2. ;

During power operation, a power.. range channel must be considered INOPERABLE i..

whenever a mismatch exists-between calorimetric; power and~excore power- >i1

indication that is-greater than 5.0% in the non-conservative direction''(calorimetric power greater'than:excore power). If the mismatch is between 2.0%

L and'5.0% in the'non-conservative direction, the channel is OPERABLE as long as i. the calibration process has been ' initiated. ;When the Unit is engaged in a= power

maneuver which results in a mismatch between . calorimetric and excore power in 1

excess of 2%, 'excore adjustment may be delayed.until the Unit reaches a steadystate power level, provided the mismatch does not exceed 5.0% in thenon-conservative direction, as specified by the Technical; Specification' Interpretation, dated June 2,'1989.

'

Technical Specification 3.0.3 is required to be entered when the Unit.is-

'

operating in a condition prohibited by Technical Specifications. This condition.

exists when a Limiting Condition for Operation-is not met except as provided inthe associated Action Requirements. It requires'that within one hour-action- -

shall be initiated to place the Unit in a Mode-in which the' specification d m s {not apply by placing:it, as applicable, in:

a. At least HOT STANDBY within'the next 6_ hours,b. At least HOT SHUTDOWN-within the following 6 hours, andc. At least COLD SHUTDOWN within'the subsequent 24' hours.

-

The Unit Main Power [EIIS:EA]-(EPA)' System's primary function is to generate andtransmit power '.o Duke's Transmission. System while-simultaneously supplying the

-

6.9KV Normal' Auxiliary Power-[EIIS:EA]-(EPB) System. 'If the generator,

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e Transmission System to the Unit Auxiliary Power System. The EPA ~ System is5 divided into non-safety trains, connected to the 230KV switchyard through a ;

h step-up transformer [EIIS:XFMR] and two power circuit breakers [EIIS:BRK] (PCBs) 1

K located in the switchyard. A generator breaker is provided on each train. The|- generator breaker and step-up transformer combination on each train is capable

of carrying approximately fifty percent (750MVA) of the rated generator output.

EVENT DESCRIPTION

On September 13, 1989, at 0541 hours,'with Unit 1 at 100% Power Operation,i Generator PCB 1B tripped open, causing an unexpected Unit runback. OperationsQ entered AP/0/A/5500/03, Load Rejection. At 0550 hours, the PRNI:versus Thermal'f Power (TP) was observed to be greater than 5% non-conservative on all four(- channels. Technical Specification 3.0.3 was entered'at 0550 hours, and Work . ' i

Request 4009 SWR was issued to direct the Instrumentaion and Electrical (IAE)section to calibrate the PRNI. The-determination was made at 0600 hours,'thatGenerator PCB 1B tripped on low air pressure as a result of a failed pressuregauge at the PCB, Phase X. The Unit was stablized'at 54% Power at'0630' hours.

- The Control Room Operator (CRO) exited Technical Specification 3.0.3 at 0640;

g hours, due to the acceptable power mismatch on three of the four channels. '

Operations determined-that the failed pressure gauge would be replaced by 0930;

hours, by the Transmission Department; therefore, adjustment of the remaining.power range channel per Technical Specifications was unnecessary as powerescalation was expected to correct the mismatch problem.

,

!

' Generator PCB 1B was restored to service at 0952 hours, following the-

i

replacement of the pneumatic pressure gauge. No problems were encounteredfollowing this action.

At 1003 hours on September 13, 1989, Unit 1 Power increase began to establish '

100% Power Operation. Power was increased from 54% at a rate.of 10% per hour.At 1340 hours, Reactor power was at 90% and holding to perform Main Steam[EIIS:SB] (SM) System control valve _[EIIS:V] movement tests and to completefinal PRNI calibrations. All four channels of the PRNI registered Quadrant

,

Power Tilt Ratios of less than 1.02%. The control valve movement test and PRNI 1calibrations were complete at 1525 hours. Power _ increases continued to 100% at '

,

3% per hour. Unit power reached 97% thermal power at 1815 hours and by 2100hours, the Unit reached 100% Power Operation.

CONCLUSION.

This incident has'been attributed to Equipment Failure. The pneumatic gauge,manufactured by Protais (France), normally displays _a pressure of 500 lbf/sq.in. !on Phase X, Y, and Z of the Generator B PCB. The failure of the gauge occurred '

at the connection of the bourdon tube and the linkage of the meter. Thepneumatic pressure that resulted from the break of the soldered connectioncaused the gauge to be separated from its housing on the breaker. The immediate

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drop in pressure caused the Generator 1B PCB to tr'ip open. During the fourteen !'

year use history of the Protais. gauges, there have.been no failures reported.

The mismatches reported.on the PRNI channels after Unit power reduction wereconsidered to be-an expected phenonmenon. Within the past twelve months, one-

previous Problem Investigation Report (PIR)-2-C88-0335 was-initiated as a. resultof entering Tech Spec 3.0.3 due to all four channels of PRNI being declared'

.

-inoperable. This occurred during a power manuever of Unit 2 from 96% to 51%' ' power. All channels were' inoperable due to the allowable non-conservative

mismatch between calorimetric power and excore power. The cause of thatincident was attributed,to Defective Procedures. The procedure OP/2/A/6100/03,. -

Controlling Procedure'For Power Operation,.did not contain a Caution or other'

L information concerning the Power Range mismatch that normally occurs on a power( decrease. The procedures-for both Units were revised. A Technical .

F Specification Interpretation revision was issued June 9, 1989. Since thisprevious incident was not. caused by Equipment Failure,- the current incident isnot considered to be a recurring event. ;

The Protais' gauge is not NPRDS reportable.

CORRECTIVE ACTION

|| SUBSEQUENT

t

| 1) Work Request 4099 SWR was issued to recalibrate the PRNI.|

| 2) The Protais pneumatic gauge was replaced for? Generator IB PCB. !

,

! 3) Recalibration of PRNI was completed, per IP/1/A/3240/11.

4) Safety Analysis was revised based upon review.

5) The' failed Protais pneumatic gauge was sent to the Duke Poweri Standards Laboratory for' failure analysis and testing.

L SAFETY ANALYSIS

! The excore power range neutron detectors [EIIS:XT]'are arranged and located such |''l that one detector measures core leakage neutron flux for one quadrant. Each

detector and its associated circuitry comprise one channel, for a total of fourPRNI channels. The Power Range High Neutron Flux Trip (High Setpoint) functionutilizes a 2-out-of-4 trip logic. |

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Catawba Technical Specification 4.3.1.1 requires that channel calibration be-performed daily on the Power Range Neutron Flux High Setpoint. This is to beperformed by comparison of calorimetric (thermal.best estimate) to excore. power

..1 indication when the Unit is above 15% rated thermal power-(RTP). Excore. channel[ gains are to be adjusted to make' indicated excore (NIS) power consistent with .; ' indicated calorimetric power whenever this comparison reveals an absolute

difference of more than 2% between the two..

~ During power operation, a power range channel must be considered IN0PERABLE;whenever a mismatch exists between calorimetric power and excore power -

-

indication that is greater than 5.0% in the non-conservative direction.

i (calorimetric power greater than excore power). If_the mismatch is between 2.0%f.I and 5.0% in the non-conservative direction, the channel is OPERABLE as long as

'

the calibration process has been initiated. When the-Unit is engaged inLa power-'

maneuver which results in a mismatch between calorimetric and excore power in.

excess of 2%, excore adjustment may be delayed until-the Unit reaches,a steady: |state power level, provided the mismatch does not exceed 5.0% in- the non-

iconservative direction, as specified by the Technical Specification '

Interpretation, dated June 2, 1989. The justification for the increased'

allowable mismatch is based upon the existing margins in the Steam Generator ;,

,, [EIIS:HX] (S/G) low-low level and power range high flux (high and low) setpoint !i calculations, power range response during specific transient analyses, and the- i'

conservatisms inherent in the Catawba FSAR analyses.

Bank D Rod Cluster Control Assemblies (RCCAs) are located in the core such that-.

jone RCCA is inserted in the middle of the core along.the vertical axis, with one '

: 'RCCA inserted in each of the four quadrants (for a total of 5 RCCAs in ControlBank D). -The RCCAs in control Bank D are positioned more closely to the excoreneutron flux seen by these detectors to a greater degres than the other controlbanks. This phenomenon commonly _ occurs during power reductions in which ControlBank D is partially inserted. ~

Core quadrant 1 (channel N43) mismatch exceeded 5% from 0555 hours to.0643hours; core quadrant 2 (channel N42) mismatch exceeded 5%'from 0555 hours to0630 hours; core quadrant 3 (channel N44) mismatch exceeded 5% from 0555 hoursto 0640 hours; core quadrant 4-(channel N41) mismatch exceeded 5% from 0552s

hours to 0623 hours. Therefore, all four NIS channels were technicallyinoperable from 0555 hours to 0623 hours, a total of 28 minutes. The maximummismatch errors were 8.1%, 7.8%, 6.95%, and 8.2% for quadrants 1, 2, 3, and 4,respectively. During this short period of multiple channel inoperability, thechannels were not functionally inoperable, as they would have still_providedinput to the SSPS Reactor trip function. The NIS channels were only 3.1%, 2.8%, j

'

1.95%, and 3.2% non-conservative beyond.the allowable mismatch, for quadrants 1 !

through-4, respectively,i

-The following'is a list of Catawba FSAR Chapter 15 transients in which credit isassumed for the Power Range High Neutron Flux Trip (High Setpoint):

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j 1)- Startup of an-Inacti.ve Reactor Coolant Pump [E!IS:P] at an Incorrect !1 Temperature (discussed in Section 15.4.4).S- .

. 12) Feedwater System Malfunctions that Result in a Reduction in Feedwater-

b Temperature (discussed in Section 15.1.1).b

L 3) . Excessive Increase in Secondary Steam Flow (discussed in Section. <

[.. -15.1.3).

4) Inadvertent Opening of a Steam _ Generator Relief or Safety Valve '

(discussed in Section'15.1.4).;fI

j 5) Steam System. Piping Failure (discussed in Sectionf15.1.5). .

|s

|| 6) Uncontrolled Rod [EIIS: ROD] Cluster Control Assembly Bank Withdrawal[; From a Suberitical or Low Power Startup. Condition (discussed inL Section 15.4.1), r

( .

[ 7) Uncontroll'ed Rod Cluster Control Assembly Bank Withdrawal.at Powerp (discussed in Section'15.4.2).h

,

'

8) . Spectrum of Rod Cluster Control Assembly Ejection- Accidents (discussedin Section 15.4.8).

'The following discussion outlines the protective features'which existed for theabove scenarios other than the Power Range High Neutron Flux Trip Function (HighSetpoint): -

'

1) The "Startup of an Inactive Reactor' Coolant Pump at an IncorrectTemperature" scenario.is not applicable. All.four Reactor Coolantloops were in operation during this incident. However .if the Unit-had been operating in'a three loop configuration, any. postulated powerexcursion would have been terminated.at the P-8 setpoint (2-out-of-4power range indications > 49% full. power). '

L 2) The Unit would be protected against a "Feedwater System Malfunctionsthat Result in a Reduction in Feedwater Temperatures "' scenario by theOvertemperature and Overpower Delta-T trip functions.

3) The Unit would be protected against the " Excessive Increase-inSecondary Steam Flow" scenario by the Overtemperature and Overpower-Delta-T trip functions. -;

L 4) The Unit would be protected against the " Inadvertent Opening of a-' ,

Steam Generator Relief or Safety Valve" scenario.by initiation of a '

Safety Injection signal (due to steamline pressure) which initiates a'.

Reactor Trip signal. The~0vertemperature and Overpower Delta-T tripfunctions also provide Reactor protection in this scenario. j

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d 5) The Unit would be protected against a " Steam System Piping Failure"-J' scenario by initiation of a Safety Injection signal (due to steamline>e' pressure) which initiates a Reactor Trip signal. The Overtemperature[ and Overpower Delta-T trip functions also provide Reactor' protection =D' in this scenario.- .

:-

? 6) The " Uncontrolled Rod Cluster Control Assembly. Bank Withdrawal From ai Subcritical-~or. Low Power.Startup Condition" scenario,is not) applicable, as this. incident involved a load: follow power reduction:

~

2 (Unit runback).,

.

'

1 7) The " Uncontrolled. Rod: Cluster: Control- Assembly Withdrawal at Power"~i scenario is. assumed to be terminated by the following trip functions

in addition to the Power Range High Neutron Flux Trip Function (High:r^ *Setpoint): . 0vertemperature and'0verpower Delta-T, pressurizer. pressure, and pressurizer level. In, addition to these trip functions, .

there are the following RCCA withdrawal blocks: '

[ a) high-neutron flux, b) Overtemperature Delta-T, andF c) Overpower Delta-T. For slow RCCA withdrawal accidents,[ thermal-time constraints on the heatup do not become'a| factor; thei Unit is tripped and DNBR-is maintained above the limit.value. ' <

E-

8) The " Spectrum of Rod Cluster Control Assembly Ejection Accidents"b scenario assumes credit for the High Neutron: Flux Rate. Trip Function.

! Furthermore, in any postulated rod withdrawal accident, the out-of-calibrationL condition would have corrected itself during the transient-due to the absence of1 the cause of the deviation, i.e., insertion of Control Bank D.~ Also, theI conservative effects of moderator and doppler feedback would tend to limit any! postulated power excursion.

~'

:

; The calibration problem was one of gain setting, or overall absolute value power'

indication. The ability of the NIS to detect axial flux difference (AFD) and- i

high flux rate was unaffected. The Overtemperature Delta-T and the OverpowerDelta-T Trip Function receives AFD as an input _to the setpoint equation, and the-

Overpower Delta-T Tr.ip Function is unaffected by neutron flux, .Therefore, the-high flux rate, Overtemperature Delta-T, and Overpower Delta-T Trip Functions ' ;-

remained intact and functional ~throughout this event. -The Overtempe'rature,

Delta-T Trip function protects against DNB conditions, and the Overpower Delta-T I

Trip Function ensures that allowable heat generation rate-(kw/ft)=is not. exceeded.

The Unit 1 0-3 S/Gs utilize a ramped operating level based on NIS indicationinput to the feedwater control valve position. ~Hence, during this transient, it - 1

is likely that the control system was " searching", causing oscillations in-

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j feedwater flow and S/G level. For example, at the minimum achieved power level )of 54% RTP (thermal best estimate), the feedwater control valves would have been-'

L throttling to maintain approximately 48% power based on NIS input. However,these oscillations were apparently minor, as S/G low-low level Reactor trip and. j'!

|high-high level signals-did not occur.-

7\ .

.;

F Addition' ally, power mismatch signal, based on the difference between Turbine I

impulse pressure (correlative thermal power level) and NIS indication, is acontrol input to the Rod Control System program. However, this program does notutilize absolute power mismatch, but rather, rate of change of power. mismatch ;

(i.e., it is an anticipatory function). Therefore, the out-of-calibration- i-

condition of the NIS did not affect automatic rod control. j.

After recovery of the NIS from the out-of-calibration condition, core quadrant 2 1

Quadrant Power Tilt Ratio (QPTR) exceeded the value (1.02) allowed by Technical |_

Specifications (from 0800 hours to 1150 hours). Because of fuel loading ipatterns and other factors, one quadrant may see a higher burnup rate as '

compared to other quadrants. Upon RCCA insertion, the Xenon transient induced isin part related to burnup; it may also be driven by secondary side phenomena.The indicated QPTR was perhaps slightly exacerbated _by the out-of-calibration

. condition of the NIS. However, for the most-part, the indicated quadrant power" tilt was real and not merely indicate'd,-being driven by Xenon production /burnup

;

and other factors.

The QPTR Limiting Condition for Operation (LCO) states that thermal power must,

be decreased at least 3% from RTP for each 1% of indicated QPTR in excess of 1 '

,

and that the Power Range Neutron Flux-High Trip Setpoints-must.be decreasedi

!- similarly within the next four hours. This LC0 ensures that peaking factors j

| (heat flux hot channel- factor and enthalpy rise hot channel factor) remain |

| within permissible limits. The maximum value of QPTR measured was 1.0266, j

.approximately 3% in excess of 1 (one). Thus, the maximum permissible RTP during |'

| this period was 91%. Due to the Unit runback, power did not exceed j

approximately 74% (thermal best estimate) during this period of time. Also,_,

| since the QPTR was only in excess of 1.02 for 3 hours and 50 minutes, the NISadjustments were not required to be performed. Catawba Unit 1 was in compliancewith the LCO. I

The health and safety of the public were unaffected by this incident. 1

,

i

Neh4 ,CFOs 1980*520 589-60070 |.

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