ML19325C640

LER 89-016-00:on 890913,four Channels of Power Range Instrumentation Showed Greater than 5% Allowable Mismatch Between Rated Thermal Power & Nuclear Power.Caused by Equipment Failure.Pneumatic Gauge replaced.W/891011 Ltr

ML19325C640
Person / Time
Site:	Catawba
Issue date:	10/11/1989
From:	Glover R, Owen T DUKE POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
LER-89-016-02, LER-89-16-2, NUDOCS 8910170127
Download: ML19325C640 (8)

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Catawba' Nuclear Station Docket No. 50-413-

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LER 413/89-16:

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4:- ' Attached-is Licensee Event Report 413/89-16, concerning Technical il . Specification.3.0.31being entered-due-to'four= channels of power-range-

[# -instrumentation being declared inoperable following unit runback as a>

' result of: failure:of a generator breaker air pressure gauge.

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This eveht was considered to be of no significance with respect to the

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Tony )Ouen' iStation' Manager

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'~] Yts n,,. c.y. excretic suewssioN od tri ] No 111 1 15 81 9 Aesn.ACT rum,e M mo an < e neo. -ere, surm one ma tvm-re osmo us, On September 13, 1989, at 0541 hours0.00626 days <br />0.15 hours <br />8.945106e-4 weeks <br />2.058505e-4 months <br />, Unit I was in Mode 1, 100% Power Operation. ' Generator 1B Power Circuit Breaker (PCB) opened causing Unit runback to 55% 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 hours0.00637 days <br />0.153 hours <br />9.093915e-4 weeks <br />2.09275e-4 months <br />, Technical Specification 3.0.3 was entered and Work Request 4099 SWR was issued to complete calibration of the PRNIs. The Unit was stable at 55% Power at 0630 i

hours and the calibrations were performed. Following the required calibrations of'the PRNI, the Unit exited Technical Specification 3.0.3. The pneumatic gauge

.

was subsequently replaced, and Generator PCB 1B was restored to service. Unit

[ Power increases commenced at 1003 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.816415e-4 months <br /> on September 13, 1989. All required L PRNI calibrations were completed to within 2% of RTP by 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br />. Unit Power reached 97% Power at'1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br />. At 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />, Unit Reactor Power reached 100%. The Power Range mismatch was considered to be an expected phenomenon following a Unit runback. This incident has been attributed to Equipment Failure due to the failure of the pressure gauge on the PCB which caused the

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-BACKGROUND F

The purpose of the Out of Core Instrumentation [EIIS:JG} (ENB) System is to monitor Reactor [EIIS:VSL) Core leakage neutron flux and generate appropriate trips and alarms for various phases of Reactor [EIIS:VSL] operations. The three separate overlapping ranges of Source Range, Intermediate Range, and Power Range also provide control functions and indicate Reactor status during Mode 2, Startup and Mcde 1. Power Operation. Technical Specification 4.3.1.1 requires

-that channel calibration be performed daily on the Power Eange Neutron Flux High Setpoint. This is to be performed by comparison of calorimetric (reactor-thermal power best estimate, based on actual plant indicatar temperatures) to excore power (based upon nuclear power levels from detector instrumentation) indication when the Unit is above 15% Pated 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 difference of more than 2% betueen the two.

Technical Specification ~3.3.1, Table 3.3-1, requires that three out of four channels of PRNI must be operable during Modes 1 and 2.

During-power operation, a power range channel must be considered INOPERABLE whenever a mismatch exists between calorimetric power and excore power 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%

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 in a 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-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 in the associated Action Requirements. It requires that within one hour action shall be initiated to place the Unit in a Mode in which the specification does not apply by placing it, as applicable, in:

a. At least HOT STANDBY within the next 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />,

b. At least HOT SHUTDOWN within the following 6 hours6.944444e-5 days <br />0.00167 hours <br />9.920635e-6 weeks <br />2.283e-6 months <br />, and

c. At least COLD SHUTDOWN within the subsequent 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />.

The Unit Main Power [EIIS:EA] (EPA) dystem's primary fanction is to generate and transmit power to Duke's Transmission System while simultaneously supplying the 6.9KV Normal Auxiliary Power [EIIS:EA] (EPB) System. If the generator I

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Transmission System to the Unit Auxiliary Power System. The EPA System is divided into non-safety trains, connected to the 230KV switchyard through a step-up transformer [EIIS XFMR] and two power circuit' breakers [EIIStBRK] (PCBs) located in the switchyard. A generator breaker is provided on each train. The generator breaker r.nd step-up transformer combination on each train is capable -

- of carrying approximately fli'ty percent (750MVA) of the rated generator output.

EVENT DESCRIPTION On September 13, 1989, at 0541 hours0.00626 days <br />0.15 hours <br />8.945106e-4 weeks <br />2.058505e-4 months <br />, with Unit 1 at 100% Power Operation,

Generator PCB 1B tripped open, causing an unexpected Unit runback. Operations entered AP/0/A/5500/03, Load Rejection. At 0550 hours0.00637 days <br />0.153 hours <br />9.093915e-4 weeks <br />2.09275e-4 months <br />, the PRNI versus Thermal Power (TP) was observed to be greater than 5% non-conservative on all four channels. Technical Specification 3.0.3 was entered at 0550 hours0.00637 days <br />0.153 hours <br />9.093915e-4 weeks <br />2.09275e-4 months <br />, and Work Request 4099 SWR was issued to direct the Instrumentaion and Electrical (IAE) section to calibrate the PRNI. The determination was made at 0600 hours0.00694 days <br />0.167 hours <br />9.920635e-4 weeks <br />2.283e-4 months <br />, that Generator PCB 1B tripped on low air pressure as a result of a failed pressure gauge at the PCB, Phase X. Tha Unit was stablized at 55% Power at 0630 hours0.00729 days <br />0.175 hours <br />0.00104 weeks <br />2.39715e-4 months <br />.

The Control Room Operator (CRO) exited Technical Specification 3.0.3 at 0640 hours0.00741 days <br />0.178 hours <br />0.00106 weeks <br />2.4352e-4 months <br />, due to the acceptable power mismatch on three of the four channels.

Operations determined that the failed pressure gauge would bn replaced by 0930 hours0.0108 days <br />0.258 hours <br />0.00154 weeks <br />3.53865e-4 months <br />, by the Transmission Department; therefore, adjustament of the remaining power range channel per Technical Specifications was unnecessary as power escalation was expected to correct the mismatch problem.

Generator PCB IB was restored to service at 0952 hours0.011 days <br />0.264 hours <br />0.00157 weeks <br />3.62236e-4 months <br />, follcwing the replacement of the pneumatic pressure gauge. No problems were encountered following this action.

At 1003 hours0.0116 days <br />0.279 hours <br />0.00166 weeks <br />3.816415e-4 months <br /> on September 13, 1989, Unit 1 Power increase began to establish

!. 100% Power Operation. . Power was increased from 55% at a rate of 10% per hour.

At 1340 hours0.0155 days <br />0.372 hours <br />0.00222 weeks <br />5.0987e-4 months <br />,-Reactor power was at 90% and holding to perform Main Steam

[EIIS:SB]'(SM) System control valve [EIIS:V) movement tests and to complete final PRNI calibrations. All four channels of the PRNI registered Quadrant Power Tilt Ratios of less than 2%. The control valve movement test and PRNI calibrations were complete at 1525 hours0.0177 days <br />0.424 hours <br />0.00252 weeks <br />5.802625e-4 months <br />. Power increases continued to 100% at 3% per hour. Unit' power reached 97% thermal power at 1815 hours0.021 days <br />0.504 hours <br />0.003 weeks <br />6.906075e-4 months <br /> and by 2100 hours0.0243 days <br />0.583 hours <br />0.00347 weeks <br />7.9905e-4 months <br />,:the Unit reached 100% Power Operation.

CONCLUSION l

This incident has been attributed to Equipment Failure. The pneumatic gauge, manufactured by Protais (France), normally displays a pressure of 500 lbf/sq.in, i

on Phase X, Y, and Z of the Generator B PCB. The failure of the gauge occurred l

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

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drop in pressure caused the Generator 1B PCB to trip 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 were considered to be an expected phenonmenon. Within the past twelve months, one previous Problem Investigation Report (PIR) 2-C88-0335 was initiated as a result of 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 that incident was attributed to Defective Procedures. The procedure OP/2/A/6100/03, Controlling Procedure For Power Operation, did not contain a Caution or other

.information concerning the Power Range mismatch that normally occurs on a power decraase.__ The procedures for both Units were revised. A Technical Specification Interpretation revision was issued June 9, 1989. Since thin previous incident was not caused by Equipment Failure, the current incident is not- considered to be a recurring event.

The Protals gauge is not NPRDS reportable.

CORRECTIVE ACTION ,

SUBSEQUENT-

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

2) The Protais pneumatic gauge was replaced for Generator 1B PCB.

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

PLANNED

1) The Protais pneumatic gauge will be sent to the Duke Power Standards Laboratory for failure analysis and testing.

2) Further review of the Safety Analysis of this Report will be performed and this report will be revised if necessary, following completion of Planned Item #1.

SAFETY ANALYSIS The excore power range neutron detectors are arranged and located such that one detector measures core leakage neutron flux for one quandrant. Each detector and its associated circuitry comprise one channel, for a total of four PRNI channels. The Power Range High Neutron Flux Trip (High Setpoint) function utilizes a 2-out-of-4 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 be.

, performed by comparison of calorimetric (thermal best estimate) to excore power indication when the Unit is above 15% kTP. Excore channel gains are to be adjusted to make indicated excore power consistent with indicated calorimetric power whenever-this comparison reveals an absoluto difference of more than 2%

between the two.

' Operability requirements'of the PRNI channels are met provided the process of-

-adjusting the excore channel (s) has been initiated and the mismatch does not exceed 5.0% in the non-conservative direction.

The basis for an allowable non-conservative mismatch of up to 5.0% is the application of Technical Specification 2.2.1. Operation with setpoints less conservative than the trip setpoint but within the allowable value sinceAnan allowance has been made in the safety analysis accomodate this error.

-optional provision has been included for determining the operability of aThe channel when its trip setpoint is found to exceed the allowable value.-

methododolgy of this option utilizes the as-measured deviation from the specified calibration point for rack and sensor [EIIS:XI] components in conjunction with a statistical combination of the other uncertainties of the instrumentation to measure the process variable and the uncertainties in calibrating the instrumentation.

In Technical Specification Equation 2.2.1, Z + R + S 1 TA, the interactive effects of the errors in the rack and the sensor and the as-measured values are considered. Z, as specified in Table 2.2-1 in percent span, is the statistical

. summation of errors assumed in the analysis excluding those associated with the sensor and rack drift and the accuracy of their measurement. TA or Total Allowance is the difference in percent span, and R or Rack Error is the

. as-measured deviation, in percent span, for the affected channel from the specified trip setpoint. S or Sensor Error is either the as-measured deviation of the sensor from its calibration point or the value specified in Table 2.2-1 in percent span, from the analysis assumptions. Use of Equation 2.2.1 allows for a sensor drift factor, an increased rack drift factor, and provides a threshold-value for reportable events, as described in the Bases of Technical Specifications.

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

1) Startup c; an Inactive Reactor Coolant Pump [EIIS:P] at an Incorrect Temperati..e (discussed in Section 15.4.4),

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-3)- Excessive Increase in Secondary Steam Flow (discussed in Section 15.1.3).

x -4) Inadvertant Opening'of a Steam Generator Relief of Safety Valve ,

(discussed in Section-15.1.4). ]4

, 5)- Steam System Piping Failure (discussed in Section 15.1.5).

6) . Uncontrolled Rod [EIIS: ROD) Cluster Control Assembly Bank Withdrawal- -

' From a Subcritical or Low Power Startup Condition (discussed in Section 15.4.1).

7)- Uncontrolled Rod Cluster Control Assembly Bank Withdrawal at Power

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(discussed in Section 15.4.2).

8) Spectrum of Rod Cluster Control Assembly Ejection Accidents (discussed in Section 15.4.8).

The following discussion outlines the protective features which existed for the above scenarios other than the Power Range High Neutron Flux Trip Function (High Setpoint): ,

.' -1) The "Startup of an Inactive Reactor Coolant Pump at an Incorrect Temperature" scenario is not applicable and the 55% Power level was above the P-8 interlock. All four Reactor Coolant loops were in operation during this incident.

2)~ The Unit would be protected against a "Feedwater System Malfunctions that Result in a Reduction in Feedwater Temperatures " scenario by the Overtemperature and Overpower Delta-T trip functions.

,o 3)' The Unit would be protected against the " Excessive Increase in i Secondary Steam Flow" scenario by the Overtemperature and Overpower Delta-T trip functions.

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 Overtempcrature and Overpower Delta-T trip functions also provide Reactor protection in this scenario.

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5) 'The Unit would'be protected against a " Steam System Piping Failure" b scenario by initiation of a Safety Injection signal (due to steamline pressure) which initiates a Reactor Trip signal.. The Overtemperature

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and Overpower Delta-T trip functions'also provide Reactor protection L in this scenario, p

l6) The " Uncontrolled Rod Cluster Control Assembly Bank Withdrawal From a l Suberitical or Low Power Startup Condition" scenario is not applicable i

.as this incident involved a load follow power reduction.  ;

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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

- .Setpoint): Overtemperature.and Overpower Delta-T, pressurizer pressure, and pressurizer level. In addition to these trip functions,  ;

there are the following RCCA withdrawal blocks: i l

a) high neutron flux, b) Overtemperature Delta-T,'and c) Overpower Delta-T. For slow RCCA withdrawal accidents, thermal' time constraints on the heatup do not become a factor; the l

' plant is tripped and DNBR is maintained above the limit value.

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

'The calibration problem was one of gain setting, or overall absolute value power .1

-indication. The ability of the'PRNI to detect-axial flux difference (AFD) and 1 ihigh flux rate was unaffected. The Overtemperature Delta-T Trip Function

• -receives AFD as an-input to the setpoint equation, and the Overpower Delta-T Trip 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 the incident. The Overtemperature Delta-T Trip function protects against DNB conditions, and the Overpower Delta-T Trip L ' Function ensures that allowable heat generation rate (kw/ft) is not exceeded.

Based on the above analysis,.it can be concluded that the Reactor was protected

.at all' times, and that no postulated scenario could have occurred which would

.have challenged the Power Range High Neutron Flux Trip Function.

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Further' review of this Safety Analysis will be performed.

i; l- The health and safety of the public were unaffected by this incident.

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