ML20211K669

Proposed Tech Spec Changes Re Measurement Uncertainty for RCS Flow Rate & Allowable Power Levels for RCS Flow Rate Less than 100% of Thermal Design Flow

ML20211K669
Person / Time
Site:	Summer
Issue date:	06/27/1986
From:	SOUTH CAROLINA ELECTRIC & GAS CO.
To:
Shared Package
ML20211K665	List: ML20211K660 ML20211K669
References
NUDOCS 8606300214
Download: ML20211K669 (13)

Text

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POWER OISTRIBUTION LIMITS 3/4.2.3 RCS FLOW RNTE AND NUCLEAR ENTHALPY RISE HOT CHANNEL FACTOR LIMITING CONDITION FOR OPERATION 3.2.3 The co'mbination of indicated Reactor Coolant System (RCS) total flow rate and R shall be maintained within the region of allowable operation shown on Figure 3.2-3 for 3 loop operation.

Where:

N a*

R

= 1.49 [1.0 + 0.2 (1.0 - P)]

THERMAL POWER b*

P = RATED THERMAL POWER N

Fh=MeasuredvaluesofF obtained by using the movable incore c.

detectorstgobtaingHpower distribution map.

The measured values of F shall be used to calculate R since Figure 3.2-3 includes me$$urement ungertainties of 2.1% for flow and 4% for l

incore measurement of Fg.

APPLICABILITY:

MODE 1.

ACTION:

With the combination of RCS total flow rate and R outside the region of acceptable operation shown on Figure 3.2-3:

a.

Within 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br /> either:

1.

Restore the combination of RCS total flow rate and R to within the above limits, or 2.

Reduce THERMAL POWER to less than 50% of RATED THERMAL POWER and reduce the Power Range Neutron Flux - High trip setpoint to less than or equal to 55% of RATED THERMAL POWER within the next 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br />.

b.

Within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> of initially being outside the above limits, verify through incore flux mapping and RCS total flow rate comparison that the combination of R and RCS total flow rate are restored to within.

the above limits, or reduce THERMAL POWER to less than 5% of RATED l

THERMAL POWER within the next 2 hours2.314815e-5 days <br />5.555556e-4 hours <br />3.306878e-6 weeks <br />7.61e-7 months <br />.

I

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l Identify and correct the cause of the out-of-limit condition prior c.

/

to increasing THERMAL POWER above the reduced THERMAL POWER limit required by ACTION items a.2. and/or b. above; subsequent POWER -

l OPERATION may proceed provided that the combination of R and indicated RCS total flow rate are demonstrated, through incore flux mapping and RCS total flow rate comparison, to be within the region.of acceptable operation shown on Figure 3.2-3 prior to exceeding the following THERMAL POWER levels:

SUMMF860[$0I)214 860627 3/4 2-8 PDR ADOCK 0500 5

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MEASUREMENT UNCERTAINTIES OF 2.1*i FOR FLOW l

AND 4.0% FOR INCORE MEASUREMENT OF Fj ARE INCLUDED.IN THIS FIGURE 38 36 ACCEPTABLE UNACCEPTABLE OPERATION REGION OPERATION REGION 34 t:

-2 s

j 3

6 9

y 32 e

3 3

u.

J ho 30 (1.00,29.47)

U yg, y7p (1.00,29.17) m

,y y,,

SEE NOTE

% "/ W l

8 (1.00,28.29) 40v RTp 28 (1.00,27.99) w

=.

26 l

I 24 0.90 0.95 1.00 1.05 1.10 R = F /1.49 (1.0 + 0.2(1.0 - P3 N

l FIGURE 3.2-3 RCS TOTAL FLOW RATE VS. R THREE LOOP OPERATION l

f NOTE: When operating in this region the restricted power levels shall be considered to be 100% of rated thermal power IRTP) for Figure 2.11.

l l

SUMMER - UNIT 1 3/4 2-10

POWER DISTRIBUTION LIMIT BASES HEAT FLUX HOT CHANNEL FACTOR and RCS FLOWRATE and NUCLEAR ENTHALPY RISE i

HOT CHANNEL FACTOR (Continued)

F limit for, Rated Thermal Power (FRTP) as provided in the Radial Peaking xy x

Factor Limit Report per specification 6.9.1.11 was determined from expected power control maneuvers over the full range of burnup conditions in the core.

WhenRCSflowrateandFharemeasured,noadditionalallowancesare necessary prior to comparison with the limits of Figure 3.2-3.

Measurement errors of 2.1% for RCS total flow rate and 4% for Fh have been allowed forl in determining the limits of Figure 3.2-3.

The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> periodic surveillance of indicated RCS flow is sufficient to detect only flow degradation which could lead to operation outside the acceptable region of operation shown on Figure 3.2-3.

3/4.2.4 QUADRANT POWER TILT RATIO The quadrant power tilt ratio limit assures that the radial power distribution satisfies the design values used in the power capability

~

analysis.

Radial power distribution measurements are made during startup testing and periodically during power operation.

The limit of 1.02, at which corrective action is required, provides DNB and linear heat generation rate protection with x y plane power tilts.

A limiting tilt of 1.025 can be tolerated before the margin for uncertainty in F is depleted.

The limit of 1.02,was selected to provide an allowance for q

the uncertainty associated with the indicated power tilt.

The two hour time allowance for operation with a tilt condition greater than 1.02 but less than 1.09 is provided to allow identification and cor-rection of a dropped or misaligned control rod.

In the event such action does not correct the tilt, the margin for uncertainty on F is reinstated by q

i reducing the maximum allowed power by 3 percent for each percent of tilt in j

excess of 1.0.

For purposes,of monitoring QUADRANT POWER TILT RATIO when one excore detector is inoperable, the movable incore detectors are used to confirm that i

the normalized symmetric power distribution is consistent with the QUADRANT POWER TILT RATIO.

The incore detector monitoring is done with a full incore flux map or two sets of 4 symmetric thimbels.

These locations are C-8, E-5, E-11, H-3, H-13, L-5, 2-11, N-8.

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3/4.2.5 DNB PARAMETERS The limits on the DNB related parameters assure that each of the parameters are maintained within the normal steady state envelope of operation assumed in the transient and accident analyses.

The limits are consistent with the initial FSAR assumptions and have been analytically demonstrated adequate to maintain a minimum DNBR of 1.30 throughout each analyzed transient.

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The 12 hour1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> periodic surveillance of these parameters through instrument readout is sufficient to ensure that the parameters are restored within their limits following load changes and other expected transient operation.

SUMMER - UNIT 1 B 3/4 2-5 y

17+

+

y 3--

yy

+ - -,-

e-

-u 7-i---

-e+ - - -

r ATTACHMENT 2 REACTOR COOLANT SYSTEM (RCS) FLOW RATE MEASUREMENT The RCS flow rate measurement is required by Technical Specification 4.2.3.2 at least once every thirty-one (31) effective full power days. This is accomplished with elbow tap flow instrumentation using the process computer display after normalizing the elbow tap flow measurement with a precision heat balance across the steam generators.

The elbow tap flow measurement is presently the basis for the Technical Specification total flow measurement uncertainty. Normalizing the elbow tap flow measurement with the initial precision heat balance reduces the uncertainty by eliminating errors due to the transmitter calibration and temperature and pressure effects. Thus, with a more accurate determination of RCS flowrate, the required measured flow rate can be reduced.

Whenever the process computer display is unavailable, the RCS flow rate will be determined using digital voltmeter (DVM) readings from the elbow tap process racks.

Specification 3.2.3, RCS Flow Rate and Nuclear Enthalpy Rise Hot Channel Factor,in the Standard Technical Specifications requires that total reactor flow (total flow through the vessel from all loops) be above some minimum value. The minimum flow value is Thermal Design flow corrected for the total flow measurement uncertainties. Historically, the uncertainty has been specified as 3.5%. Flow measurement uncertainties much less than this can be achieved by using modern statistical error analyses and normalizing elbow tap flow indications with a precision calorimetric flow measurement. The accuracy achieved by this technique depends primarily on the measurement procedure employed and how well the instrument errors are understood and controlled by plant personnel. The normalization of the elbow tap flow measurement with the precision calorimetric flow calculation, the measurements required, and the measurement uncertainty analyses are described in the following paragraphs and tables.

Reactor coolant loop flow is determined from the steam generator thermal outp(ut, corrected for the loop's share of the net pump heat input, and the enthalpy rise Ah) of the coolant. Total reactor flow is the sum of the individual loop flows. Table 1 lists the calorimetric equations and defines the terms.

To establish the overall flow measurement uncertainty, the accuracy and relationship to RCS flow of each instrument used for the calorimetric measurements must be determined.

Instrumentation for the elbow tap flow indication is depicted in Figure 1. Table 2 provides the list of components involved in the precision calorimetric flow calculations. The overall loop flow measurement uncertainty is the statistical summation of individual uncertainties (accounting for interadive effects where necessary) and appears at the bottom of Table 2.

To establish the overall uncertainty for the process computer and DVM elbow tap flow measurement, the accuracy and relationship of all instrumentation to the RCS flow must be determined. There are several components (transducer, converter, isolator, etc.) which contribute to the overall uncertainty of the measurement. Tables 3 and 4 list and define uncertainties from the elbow tap flow transmitters to the process computer and DVM using three (3) taps (one (1) per loop). The overall loop flow measurement uncertainty is the statistical summation of individual uncertainties and appears in Table 3 and 4.

Table 5 statistically combines the overall precision calorimetric measurement uncertainty and the uncertainty of the elbow tap flow indication using three (3) taps. The total flow

ATTACHMENT 2 PAGE2 uncertainty using three (3) normalized elbow taps (1 per loop) with the process computer display is + 2.008%. The total flow uncertainty using three (3) normalized elbow taps (1 per loop) with the DVM reading is + 2.003%. Based upon this, the RCS flow measurement uncertainty included in Techiiical Specification 3/4.2.3 is chosen to be 2.1 %.

In summary,individualloop flow is determined by performance of a precision calorimetnc and these values are used to normalize elbow tap measurements. The loop flow measurements are summed to arrive at the total RCS flow. The measurement uncertainty is determined by statistically combining precision calorimetric and elbow tap flow measurement uncertainties. A precision calorimetric flow measurement must be performed to normalize the elbow taps to take credit for this particular measurement uncertainty.

This proposed change has no adverse safety implications since the Thermal Design flow rate which is utilized in various safety analyses is unchanged.

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ATTACHMENT 2 PAGE3 TABLE 1 REACTOR COOLANT LOOP FLOW CALCULATION WL = (Y){Qsc - Op + LQQ}(Vc)

N

{hH - hc}

Loop flow (gpm)

Where:

WL

=

Steam generator thermal outp(ut (Btu /hr)

QSG

=

Primary system net heat losses Btu /hr)

QL

=

Number of loops N

=

Reactor coolant mp heat added (Btu /hr)

Qp

=

hH Hotleg enthalp (Btu /lb)

=

cold leg enthal y(Btu /lb) hc

=

Cold leg specificvolume (ft3/lb)

Vc

=

0.1247 gpm/(ft3/hr)

Y

=

(hs -ht)Wf 05G

=

Steam enthalpy (Btu /lb)

Where:

hs

=

Feedwater enthalpy (Btu /lb) hF

=

Feedwater flow (Lb/hr)

Wp

=

(K)(Fa)VPF AP Wp

=

Feedwater venturi flow coefficient Where:

K

=

Feedwater venturi correction for thermal expansion Fa

=

Feedwater density (Ib/ft3)

PF

=

Feedwater venturi pressure drop (inches H2O) i AP

=

I

ATTACHMENT 2 PAGE4 TABLE 2 CALORIMETRIC FLOW MEASUREMENT UNCERTAINTIES Individual Uncertainty %

Component Instrument Error Dependent Power or %

Effects %

Flow

'Feedwater Flow DP Cell Calibration i0.5%

t 0.39 DP Cell Reading i 1.0%

t 0.78 Uncertainty Venturi K t 0.5% K t 0.5 Thermal Expansion Coefficient Temperature t 0.54'F i0.06 0.18 Material i5.0%

Density Temperature i0.54*F 0.04 Pressure 160 psi

'Feedwater Enthalpy Temperature t 0.54'F t 0.08 Pressure i60 psi

• Steam Enthalpy Calibration i 1.5 psi 0.006 Moisture Carryover 0.25%

t 0.22

' Primary Enthalpy TsRTD t0.5'F

!0.95 Ty RTD Bridge t 0.554*F

! 1.044 Ts Temperature i1.2*F t 2.27 Streaming Ts Pressure Effect 12.8 psi 0.102 i0.128 (including drift allowance)

Tc Pressure Effect t 12.8 psi 0.026 (including drift allowance)

Tc RTD t 0.5'F 0.775 Tc RTD Bridge t 0.554'F 0.868

• Net Pump Heat Addition 20 %

0.085

' Total Loop Flow Uncertainty vee 2 3.101

' Total Reactor Flow 1.790 Uncertainty

ATTACHMENT 2 PAGE5 FIGURE 1 FLOW INDICATION INSTRUMENTATION Reactor Coolant System Flow 0 - 120,000 gpm Elbow Tap Differential Pressure 0 - 400 INWC Flow Transmitters 9 total /3 per loop Barton 752 4 - 20 MADC Westinghouse 7300 Process Control Cabinets 0 - 10 VDC Process Computer DVM 0 - 120 % Digital 0 - 10 VDC Digital Display Display

..-,.._.--.n._

ATTACHMENT 2 PAGE6 TABLE 3 PROCESS COMPUTER ELBOW TAP RCS FLOW INDICATION UNCERTAINTY Parameter

% RCS Flow Uncertainty PMA 1 0.30 %

PEA 1 0.36 %

SCA 1 0.00 %

SPE t 0.00%

STE t 0.00%

SD i 0.72 %

RCA 1 0.50 %

RTE 1 0.00 %

RD 1 0.72 %

ID O.36 %

RO 1 0.36 %

CU = [(PMA)2 + (PEA)2 + (SCA + SD)2 + (STE)2 + (SPE)2 +

(RCA + RD)2 + (RTE)2 + (ID)2 + (RO)2]t/2 Where:

Channel Uncertainty CU

=

PMA =

Process Measurement Accuracy Primary Element Accuracy PEA

=

SensorCalibration Accuracy SCA

=

Sensor Pressure Effects SPE

=

Sensor Drift SD

=

Sensor Temperature Effects STE

=

RCA =

Rack Calibration Accuracy Rack Drift RD

=

Computer Isolator Drift ID

=

Allowance for Noisy Signal RO

=

Rack Temperature Effects RTE

=

Total Loop Channel Uncertainty with 1 tap =

1.577 %

Total RCS Channel Uncertainty w/3 loops

= 10.910%

A'ITACHMENI 2 PAGE7 TABLE 4 DVM ELBOWTAP RCS FLOW INDICATION UNCERTAINTY Parameter

% RCS Flow Uncertainty PMA 0.30 %

PEA 0.36%

SCA 0.00 %

SPE 0.00 %

STE 0.00 %

SD 1 0.72 %

RCA 0.50 %

RTE 1 0.00 %

RD 10.72 %

RO 0.36 %

DVM i 0.25 %

CU = [(PMA)2 + (PEA)2 + (SCA + SD)2 + (STE)2 + (SPE)2 +

(RCA + RD)2 + (RTE)2 + (RO)2 + (DVM)2]1/2 Where:

Channel Uncertainty CU

=

PMA =

Process Measurement Accuracy Primary Element Accuracy PEA

=

Sensor Calibration Accuracy SCA

=

Sensor Pressure Effects SPE

=

Sensor Drift SD

=

Sensor Temperature Effects STE

=

RCA =

Rack Calibration Accuracy Rack Drift RD

=

Allowance for Noisy Signal RO

=

DVM =

Digital Voltmeter Uncertainty Rack Temperature Effects RTE

=

Total Loop Channel Uncertainty with 1 tap = 11.555%

Total RCS Channel Uncertainty w/3 loops

= 10.898%

ATTACHMENT 2 PAGE 8 TABLE 5 TOTAL RCS FLOW UNCERTAINTY Total Precision Calorimetric RCS 1.790 %

Flow Uncertainty

=

(Table 2)

Total RCS Elbow Tap Channel Uncertainty utilizing process t 0.910%

computer display

=

(Table 3)

Total RCS Elbow Tap Channel 0.898 Uncertainty utilizing DVM readings

=

(Table 4)

By Sum of Squares Method:

Total RCS Uncertainty using process

+ 2.008%

computer display

=

Total RCS Uncertainty using

+ 2.003%

DVM readings

=

Based on the above:

Total RCS Uncertainty included

+ 2.1 %

in Specification 3/4.2.3

=

l l

l

{

l l

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a ATTACHMENT 3 SIGNIFICANT HAZARDS CONSIDERATION 4

i i

Description of amendment request:

i The proposed amendment would modify Technical Specification 3.2.3, "RCS Flow Rate and Nuclear Enthalpy Rise Hot Channel Factor," the associated Bases, and 4

Figure 3.2-3 to reflect a flow measurement uncertainty of 2.1% instead of 3.5% as i

currently listed in Technical Specifications. The proposed change to Figure 3.2-3 would allow continued operation at lower indicated RCS flow rates due a reduced i

RCS flow measurement uncertainty of 2.1% while ensuring the Thermal Design flow requirement.

Basis for no sianificant hazards consideration determination:

Specification 3.2.3 in the Standard Technical Specifications requires that total i

reactor flow (total flow through the vessel from all loops) be above some minimum i

value. The minimum flow value is Thermal Design flow corrected for the total flow measurement uncertainties. Historically, the uncertainty has been specified as 3.5%

due to uncertainties associated with feedwater venturi fouling. Flow measurement uncertainties much less than this can be achieved by using modern statistical error analyses and normalizing elbow tap flow indications with a precision calorimetric flow measurement.

i The RCS flow rate measurement is required by Technical Specification 4.2.3.2 at i

least once every thirty-one (31) effective full power days. The elbow tap flow measurement is presently the basis for the Technical Specification total flow measurement uncertainty. Normalizing the elbow tap flow measurement with the initial precision heat balance reduces the uncertainty by eliminating errors due to the transmitters calibration, feedwater venturi fouling, and temperature and l

pressure effects. Thus, with a more accurate determination of RCS flowrate, the i

required measured flow rate can be reduced. Whenever the process computer display is unavailable, the RCS flow rate will be determined using digital voltmeter (DVM) readings from the process racks.

To establish the overall flow measurement uncertainty, the accuracy and relationship to RCS flow of each instrument used for the calorimetric measurements and elbow tap flow measurement (using either the process computer or the DVM) has been determined. The overall loop flow measurement uncertainty is the statistical sun mation of individual uncertainties (accounting for interactive effects l

where necessa. y).

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in summary, individual loop flow is determined by performance of a precision calorimetnc and these values are used to normalize elbow tap measurements. The j

loop flow measurements are summed to arrive at the total RCS flow. The measurement uncertainty is determined by statistically combining precision l

calorimetric and elbow tap flow measurement uncertainties. A precision calorimetric flow measurement must be performed to normalize the elbow taps to take credit for this particular measurement uncertainty.

The Commission has provided certain examples (48 FR 14870) of actions likely to i

involve no significant hazards considerations. The request involved in this case does l

not match any of those examples. However, the proposed amendment has been 1

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i

reviewed and determined not to involve a significant hazards consideration for the following reasons:

(1)

The probability of occurrence or the consequences of an accident or malfunction of equipment important to safety previously evaluated in the safety analysis report is not increased.

The proposed change to Figure 3.2-3 to account for a reduction in measurement uncertainties (3.5% to 2.1%) for RCS flow has no effect on the Thermal Design flow. Since the Thermal Design flow remains unchanged, the results of the previously analyzed accidents in the safety analysis report have not been affected.

(2)

The possibility for an accident or malfunction of a different type than any evaluated previously in the safety analysis report is not created.

The refinement of RCS flow uncertainty from 3.5% to 2.1% using modern statistical error analyses and normalizing elbow tap flow indications with a precision calorimetric flow measurement does not involve a change to any plant equipment. The results of the previously postulated accidents remain unchanged, and a possibility of a different accident or malfunction other than previously arialyzed has not been introduced.

(3)

The margin of safety as defined in the basis for any Technical Specification is not reduced.

The Thermal Design flow is not changed as a resuit of the proposed change to the RCS flow measurement uncertainties. The previously evaluated accidents or malfunctions have not been changed; thus, the margin of safety as defined in Technical Specifications remains unchanged.

Therefore, based on the above consideration, SCE&G has determined that this change does not involve a significant hazards consideration.

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