ML032880104

Revised Technical Specifications, Reactor Coolant System (RCS) Flow Rate Measurement Using Elbow Tap Methodology

ML032880104
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Site:	Watts Bar
Issue date:	10/03/2003
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RTS Instrumentation 3.3.1 Table 3.3.1-1 (page 3 of 9)

Reactor Trip System Instrumentation APPLICABLE MODES NOMINAL OR OTHER SPECIFIED REQUIRED SURVEILLANCE ALLOWABLE TRIP FUNCTION CONDITIONS CHANNELS CONDITIONS REQUIREMENTS VALUE SETPOINT

9. Pressurizer Water If 3 X SR 3.3.1.1 :592.7% 92% span Level-High SR 3.3.1.7 span SR 3.3.1.10

10. Reactor Coolant Flow-Low

a. Single Loop 1 (g) 3 per N SR 3.3.1.1 2 89.7% 90% flow loop SR 3.3.1.7 flow SR 3.3.1.10 SR 3.3.1.15

b. Two Loops 1 (h) 3 per X SR 3.3.1.1 289.7% 90% flow loop SR 3.3.1.7 flow SR 3.3.1.10 SR 3.3.1.15

11. Undervoltage If I perbus M SR 3.3.1.9 24734V 4830 V RCPs SR3.3.1.10 SR 3.3.1.15

12. Underfrequency I I per bus M SR 3.3.1.9 256.9 Hz 57.5 Hz RCPs SR 3.3. 1.1 SR 3.3.1.15 (continued)

(f) Above the P-7 (Low Power Reactor Trips Block) interlock.

(g) Above the P-8 (Power Range Neutron Flux) interlock.

(h) Above the P-7 (Low Power Reactor Trips Block) interlock and below the P-8 (Power Range Neutron Flux) interlock.

Watts Bar-Unit 1 3. 3-17 Amendment 47

RCS Pressure, Temperature, and Flow DNB Limits 3.4.1 SURVEILLANCE REQUIREMENTS SURVEILLANCE FREQUENCY SR 3.4.1.1 Verify pressurizer pressure is 2 2214 psig. 12 hours0.5 days <br />0.0714 weeks <br />0.0164 months <br /> SR 3.4.1.2 Verify RCS average temperature is 12 hours0.5 days <br />0.0714 weeks <br />0.0164 months <br />

< 593.2 0 F.

SR 3.4.1.3 Verify RCS total flow rate is 2 380,000 gpm 12 hours0.5 days <br />0.0714 weeks <br />0.0164 months <br /> (process computer or control board indication).

SR 3.4.1.4 ------------------NOTE------------------

Required to be performed within 24 hours1 days <br />0.143 weeks <br />0.0329 months <br /> after 2 90% RTP.

Verify by precision heat balance or elbow 18 months I tap Ap method that RCS total flow rate is 2 380,000 gpm.

Watts Bar-Unit 1 3.4-2 Amendment 7, 47

RTS Instrumentation B 3.3.1 BASES BACKGROUND Signal Process Control and Protection System (continued) input failure to the control system, which may then require the protection function actuation, and a single failure in the other channels providing the protection function actuation. Again, a single failure will neither cause nor prevent the protection function actuation. These requirements are described in IEEE-279-1971 (Ref. 4). The actual number of channels required for each unit parameter is specified in Reference 2.

Two logic trains are required to ensure no single random failure of a logic train will disable the RTS. The logic trains are designed such that testing required while the reactor is at power may be accomplished without causing trip.

Trip Setpoints and Allowable Values The Trip Setpoints are the nominal values at which the bistables, setpoint comparators, or contact trip outputs are set. Any bistable or trip output is considered to be properly adjusted when the "as left" value is within the band for CHANNEL CALIBRATION accuracy.

The Trip Setpoints used in the bistables, setpoint comparators, or contact trip outputs are based on the analytical limits stated in Reference 6. The selection of these Trip Setpoints is such that adequate protection is provided when all sensor and processing time delays are taken into account. To allow for calibration tolerances, instrumentation uncertainties, instrument drift, and severe environment errors for those RTS channels that must function in harsh environments as defined by 10 CFR 50.49 (Ref. 5), the Trip Setpoints specified in Table 3.3.1-1 in the accompanying LCO are conservatively adjusted with respect to the analytical limits. A detailed description of the methodology used to calculate the Trip Setpoints, including their explicit uncertainties, is provided in the "Westinghouse Setpoint Methodology for Protection Systems, Watts Bar 1 and 2" (Ref. 6). The uncertainties for Reactor Coolant Flow - Low function using the elbow tap Ap flow measurement methodology are provided in Reference 13. The Source Range and Intermediate Range Neutron detector setpoints are based on the requirements and recommendations of ISA 67.04 (Reference 10) standard and recommended practice. The actual nominal (continued)

Watts Bar-Unit 1 B 3.3-4 Amendment 47

RTS Instrumentation B 3.3.1 BASES BACKGROUND Trip Setpoints and Allowable Values (continued)

Trip Setpoint entered into the bistable/comparator is more conservative than that specified by the Allowable Value to account for changes in random measurement errors detectable by a COT. One example of such a change in measurement error is drift during the surveillance interval. If the measured setpoint does not exceed the Allowable Value, the bistable is considered OPERABLE.

Setpoints in accordance with the Allowable Value ensure that SLs are not violated during AOOs (and that the consequences of DBAs will be acceptable, providing the unit is operated from within the LCOs at the onset of the AOO or DBA and the equipment functions as designed). Note that in the accompanying LCO 3.3.1, the Trip Setpoints of Table 3.3.1-1 are the LSSS.

Each channel of the process control equipment can be tested on line to verify that the signal or setpoint accuracy is within the specified allowance requirements of Reference 2.

Once a designated channel is taken out of service for testing, a simulated signal is injected in place of the field instrument signal. The process equipment for the channel in test is then tested, verified, and calibrated.

SRs for the channels are specified in the SRs section.

The Process Protection System is designed to permit any one channel to be tested and maintained at power in a bypassed mode. If a channel has been bypassed for any purpose, the bypass is continuously indicated in the control room.

The Trip Setpoints and Allowable Values listed in Table 3.3.1-1 are based on the methodology described in References 6 and 13, and ISA 67.04 (Ref. 10), which incorporates all of the known uncertainties applicable for each channel. The magnitudes of these uncertainties are factored into the determination of each Trip Setpoint. All field sensors and signal processing equipment for these channels are assumed to operate within the allowances of these uncertainty magnitudes.

(continued)

Watts Bar-Unit 1 B 3.3-5 Amendment 47

RTS Instrumentation B 3.3.1 BASES APPLICABLE a. Reactor Coolant Flow-Low (Single Loop)

SAFETY ANALYSES, (continued)

LCO, and APPLICABILITY in the core. In MODE 1 below the P-8 setpoint, a loss of flow in two or more loops is required to actuate a reactor trip (Function 10.b) because of the lower power level and the greater margin to the design limit DNBR.

The Reactor Coolant Flow-Low Trip Setpoint and Allowable Value are specified in % indicated loop flow, however, the. Eagle-21m values entered through the MMI are specified in an equivalent % differential pressure.

b. Reactor Coolant Flow-Low (Two Loops)

The Reactor Coolant Flow-Low (Two Loops) trip Function ensures that protection is provided against violating the DNBR limit due to low flow in two or more RCS loops while avoiding reactor trips due to normal variations in loop flow.

Above the P-7 setpoint and below the P-8 setpoint, a loss of flow in two or more loops will initiate a reactor trip. Each loop has three flow detectors to monitor flow. The flow signals are not used for any control system input.

The LCO requires three Reactor Coolant Flow-Low channels per loop to be OPERABLE.

In MODE 1 above the P-7 setpoint and below the P-8 setpoint, the Reactor Coolant Flow-Low (Two Loops) trip must be OPERABLE. Below the P-7 setpoint, all reactor trips on low flow are automatically blocked since no conceivable power distributions could occur that would cause a DNB concern at this low power level.

Above the P-7 setpoint, the reactor trip on low flow in two or more RCS loops is automatically enabled. Above the P-8 setpoint, a loss of flow in any one loop will actuate a reactor trip because of the higher power level and the reduced margin to the design limit DNBR.

(continued)

Watts Bar-Unit 1 B 3.3-24 Revision 13, Amendment 7, 47

RTS Instrumentation B 3.3.1 BASES APPLICABLE b. Reactor Coolant Flow-Low (Two Loops) (continued)

SAFETY ANALYSES, LCO, and The Reactor Coolant Flow-Low Trip Setpoint and APPLICABILITY Allowable Value are specified in % indicated loop flow, however, the Eagle-21> values entered through the MMI are specified in an equivalent %

differential pressure.

11. Undervoltage Reactor Coolant Pumps The Undervoltage RCPs reactor trip Function ensures that protection is provided against violating the DNBR limit due to a loss of flow in two or more RCS loops. The voltage to each RCP is monitored. Above the P-7 setpoint, a loss of voltage detected on two or more RCP buses will initiate a reactor trip. This trip Function will generate a reactor trip before the Reactor Coolant Flow-Low (Two Loops) Trip Setpoint is reached, The loss of voltage in two loops must be sustained for a length of time equal to or greater than that set in the time delay. Time delays are incorporated into the Undervoltage RCPs channels to prevent reactor trips due to momentary electrical power transients.

The LCO requires one Undervoltage RCP channel per bus to be OPERABLE.

In MODE 1 above the P-7 setpoint, the Undervoltage RCP trip must be OPERABLE. Below the P-7 setpoint, all reactor trips on loss of flow are automatically blocked since no conceivable power distributions could occur that would cause a DNB concern at this low power level. Above the P-7 setpoint, the reactor trip on loss of flow in two or more RCS loops is automatically enabled.

12. Underfrequency Reactor Coolant Pumps The Underfrequency RCPs reactor trip Function ensures that protection is provided against violating the DNBR limit due to a loss of flow in two or more RCS loops from a major network frequency disturbance. An underfrequency condition will slow down the pumps, (continued)

Watts Bar-Unit 1 B 3.3-25 Revision 13, Amendment 7, 47

RTS Instrumentation B 3.3.1 BASES REFERENCES 1. Watts Bar FSAR, Section 6.0, Engineered Safety Features."

2. Watts Bar FSAR, Section 7.0, "Instrumentation and Controls."

3. Watts Bar FSAR, Section 15.0, Accident Analysis."

4. Institute of Electrical and Electronic Engineers, IEEE-279-1971, "Criteria for Protection Systems for Nuclear Power Generating Stations," April 5, 1972.

5. 10 CFR Part 50.49, "Environmental Qualifications of Electric Equipment Important to Safety for Nuclear Power Plants."

6. WCAP-12096, Rev. 7, "Westinghouse Setpoint Methodology for Protection System, Watts Bar 1 and 2," March 1997.

7. WCAP-10271-P-A, Supplement 1, and Supplement 2, Rev.

1, "Evaluation of Surveillance Frequencies and Out of Service Times for the Reactor Protection Instrumentation System," May 1986 and June 1990.

8. Watts Bar Technical Requirements Manual, Section 3.3.1, "Reactor Trip System Response Times."

9. Evaluation of the applicability of WCAP-10271-P-A, Supplement 1, and Supplement 2, Revision 1, to Watts Bar.

10. ISA-DS-67.04, 1982, "Setpoint for Nuclear Safety Related Instrumentation Used in Nuclear Power Plants."

11. WCAP-13632-P-A Revision 2, "Elimination of Pressure Sensor Response Time Testing Requirements," January 1996

12. WCAP-14036-P-A, Revision 1, "Elimination of Periodic Protection Channel Response Time Tests,' October 1998.

13. WCAP-16067-P, Rev. 0, "RCS Flow Measurement Using Elbow Tap Methodology at Watts Bar Unit 1," April 2003.

Watts Bar-Unit 1 B 3.3-63 Revision 13, 34, Amendment 24, 47

RCS Pressure, Temperature, and Flow DNB Limits B 3.4.1 BASES APPLICABLE result in meeting the DNBR criterion. This is the SAFETY ANALYSES acceptance limit for the RCS DNB parameters. Changes to the (continued) unit that could impact these parameters must be assessed for their impact on the DNBR criteria. The transients analyzed for include loss of coolant flow events and dropped or stuck rod events. A key assumption for the analysis of these events is that the core power distribution is within the limits of LCO 3.1.7, "Control Bank Insertion Limits;'

LCO 3.2.3, -AXIAL FLUX DIFFERENCE (AFD);" and LCO 3.2.4,

'QUADRANT POWER TILT RATIO (QPTR).-

The pressurizer pressure limit of 2214 psig and the RCS average temperature limit of 593.2 0 F correspond to analytical limits of 2185 psig and 594.2 0 F used in the safety analyses, with allowance for measurement uncertainty.

The RCS DNB parameters satisfy Criterion 2 of the NRC Policy Statement.

LCO This LCO specifies limits on the monitored process variables -

pressurizer pressure, RCS average temperature, and RCS total flow rate - to ensure the core operates within the limits assumed in the safety analyses. Operating within these limits will result in meeting the DNBR criterion in the event of a DNB limited transient.

RCS total flow rate contains a measurement error of 1.6%

(process computer) or 1.8% (control board indication) based on performing a precision heat balance and using the result to calibrate the RCS flow rate indicators. Potential fouling of the feedwater venturi, which might not be detected, could bias the result from the precision heat balance in a nonconservative manner. Therefore, a penalty of 0.1% for undetected fouling of the feedwater venturi raises the nominal flow measurement allowance to 1.7% (process computer) or 1.9% (control board indication).

Any fouling that might bias the flow rate measurement greater than 0.1% can be detected by monitoring and trending various plant performance parameters. If detected, either the effect of the fouling shall be quantified and compensated for in the RCS flow rate measurement or the venturi shall be cleaned to eliminate the fouling. The LCO numerical values for pressure, temperature, and flow rate are given for the measurement location and have been adjusted for instrument error.

Use of the elbow tap Ap methodology to measure RCS flow rate results in a measurement uncertainty of *1.7% flow (process computer) or +/-1.9% flow (control board indication)

(continued)

Watts Bar-Unit 1 B 3.4-2 Revision 13, Amendment 7, 47

RCS Pressure, Temperature, and Flow DNB Limits B 3.4.1 BASES LCO (continued) based on the utilization of eight elbow taps correlated to the three baseline precision heat balance measurements of Cycles 1, 2, and 3. Correlation of the flow indication channels with this previously performed heat balance measurement is documented in Reference 3. Use of this elbow tap Ap method provides an alternative to performance of a precision RCS flow calorimetric.

APPLICABILITY In MODE 1, the limits on pressurizer pressure, RCS coolant average temperature, and RCS flow rate must be maintained during steady state operation in order to ensure DNBR criteria will be met in the event of an unplanned loss of forced coolant flow or other DNB limited transient. In all other MODES, the power level is low enough that DNB is not a concern.

A Note has been added to indicate the limit on pressurizer pressure is not applicable during short term operational transients such as a THERMAL POWER ramp increase > 5% RTP per minute or a THERMAL POWER step increase > 10% RTP. These conditions represent short term perturbations where actions to control pressure variations might be counterproductive.

Also, since they represent transients initiated from power levels < 100% RTP, an increased DNBR margin exists to offset the temporary pressure variations.

Another set of limits on DNB related parameters is provided in SL 2.1.1, "Reactor Core SLs.' Those limits are less restrictive than the limits of this LCO, but violation of a Safety Limit (SL) merits a stricter, more severe Required Action. Should a violation of this LCO occur, the operator must check whether or not an SL may have been exceeded.

ACTIONS A.1 RCS pressure and RCS average temperature are controllable and measurable parameters. With one or both of these parameters not within LCO limits, action must be taken to restore parameter~s).

RCS total flow rate is not a controllable parameter and is not expected to vary during steady state operation. If the indicated RCS total flow rate is bqlow the LCO limit, power must be reduced, as required by Required Action B.1, to restore DNB margin and eliminate the potential for violation of the accident analysis bounds.

The 2 hour2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> Completion Time for restoration of the parameters provides sufficient time to adjust plant parameters, to determine the cause for the off normal condition, and to restore the readings within limits, and is based on plant operating experience.

(continued)

. Watts Bar-Unit 1 B 3.4-3 Amendment 47

RCS Pressure, Temperature, and Flow DNB Limits B 3.4.1 BASES SURVEILLANCE SR 3.4.1.4

• REQUIREMENTS (continued) Measurement of RCS total flow rate by performance of a precision calorimetric heat balance or by using the elbow tap Ap method described in Reference 3 once every 18 months allows the installed RCS flow instrumentation to be calibrated and verifies the actual RCS flow rate is greater than or equal to the minimum required RCS flow rate.

The Frequency of 18 months reflects the importance of verifying flow after a refueling outage when the core has been altered, which may have caused an alteration of flow resistance.

This SR is modified by a Note that allows entry into MODE 1, without having performed the SR, and placement of the unit in the best condition for performing the SR. The Note states that the SR is not required to be performed until 24 hours1 days <br />0.143 weeks <br />0.0329 months <br /> after 2 90% RTP. This exception is appropriate since the heat balance or elbow tap Ap method requires the plant to be at a minimum of 90% RTP to obtain the stated RCS flow I

accuracies. The Surveillance shall be performed within 24 hours1 days <br />0.143 weeks <br />0.0329 months <br /> after reaching 90% RTP.

• Note: The accuracy of the instruments used for monitoring RCS pressure, temperature and flow rate is discussed in this Bases section under LCO (Ref. 2).

REFERENCES 1. Watts Bar FSAR, Section 15.0, 'Accident Analysis,'

Section 15.2, "Condition II - Faults of Moderate Frequency," and Section 15.3.4, "Complete Loss Of Forced I Reactor Coolant Flow.'

2. Watts Bar Drawing 1-47W605-243, "Electrical Tech Spec Compliance Tables.,

3. WCAP-16067-P, Rev. 0, "RCS Flow Measurement Using Elbow Tap Methodology at Watts Bar Unit 1,' April 2003.

Watts Bar-Unit 1 B 3.4-5 Revision 29, Amendment 47