ML20245G505
| ML20245G505 | |
| Person / Time | |
|---|---|
| Site: | Beaver Valley |
| Issue date: | 12/31/1988 |
| From: | Jen Y, Rice W WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP. |
| To: | |
| Shared Package | |
| ML19297H613 | List: |
| References | |
| WCAP-12097, NUDOCS 8905030164 | |
| Download: ML20245G505 (56) | |
Text
_
4-WESTINGHOUSE CLASS 3
- 9 1
g.6 l
l RTD BYPASS ELIMINATION' LICENSING REPORT FOR BEAVER VALLEY UNIT 1 1
W. R. RICE Y. A. JEN DECEMBER, 1988 i
1 L
I 1
l.
l
{-
Westinghouse Electric Corporation
~Pittsburgh, PA~
~
s 8905030164^890421 PDR.- ADOCK 05000334
-4 P.
PDC-
- fi 1701v
- 1D/122288 l
1 4
WESTINGHOUSE CLASS 3 y-ACKNOWLEDGEMENT l
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The authors wish to recognize contributions by the'following individuals:
-l l
W. G. Lyman i
l C. R. Tuley l
]
- l G. E. Lang
_j
(
)
C. E. Leach J. P. Kutz R. M. Waters I
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1701v;1D/122288 i
4 WESTINGHOUSE CLASS 3
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F TABLE OF CONTENTS Page Section a
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List of Tables iii List of Figures iv 1.0 Introduction 1.1 Historical Background 1.
1.2 Mechanical Modifications 2
1.3 Electrical Modifications 4
2.0 Testing 2.1 Response Time Test 9
2.2 Streasing Test 9
3.0' Uncertainty Considerations 3.1 Calorimetric Flow Measurement. Uncertainty 12 3.2 Hot Leg Temperature Streaming Uncertainty 12 3.3 Control and Protection Function Uncertainties 14 4.0 Safety Evaluation 4.1 Response Time 30 4.2 RTD Uncertainty 30 4.3 Non-LOCA Evaluation 31 4.4 LOCA Evaluation 33 4.5 Instrumentation and Control Safety Evaluation 33 4.6 Mechanical Safety Evaluation 36 l
4.7 Technical Specification Evaluation 38 1701v;1D/122288 i
WESTINGHOUSE CLASS 3 TABLE OF CONTENTS (Cont)
Section M
5.0 Control System Evaluation 39 1
1 6.0 Conclusions 40 7.0 References 41 Appendix A - Definition of An Operable Channel And 42 Hot Leg RTD Failure Compensation Procedure i
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+
WESTINGHOUSE CLASS 3-I e
1 LIST OF TABLES I
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Table Title Page 2.1-1 Response Time Parameters for RCS Temperature Measurement 11
.I 3.1-1 Rod Control System Accuracy 16-I l
3.1-2 Flow Calorimetric Instrumentation Uncertainties 17 3.1-3 Flow Calorimetric Sensitivities 18 3.1-4 Calorimetric RCS Flow Measurement Uncertainties 19 3.1-5 Cold Leg Elbow Tap Flow Uncertainty 21 3.1-6 Overtemperature Delta-T Reactor Trip 22 3.1-7 Overtemperature Delta-T Gain Calculations 24 3.1-8 Overpower Delta-T-25 3.1-9 Overpower Delta-T Gain Calculations 27 3.1-10 Loss of Flow 28 3.1-11 Technical Specification Modification 29 1701v:lo/122288 iii
o
' WESTINGHOUSE CLASS 3 v
LIST OF FIGURES Figure-Title Pm 1.2-l' Hot Leg RTD Scoop Modification for Fast-Response-6 RTD Installation 1.2-2 Cold Leg Pipe Nozzle Modification Fast-Response 7-RTD Installation 1.3-1 RTD' Averaging Block Diagram, Typical'for Each of 3 8
Channels l
d 1701v:1D/122288 iv
WESTINGHOUSE CLASS 3 v
1.0 INTRODUCTION
Westinghouse Electric Corporation has been contracted by Duquesne Light to remove the existing Resistance Temperature Detector (RTD) Bypass System and replace this hot leg and cold leg temperature measurement method with fast response thermowell mounted RTDs installed in the reactor coolant loop piping. This report is submitted for the purpose of supporting operation of Beaver Valley Unit 1 utilizing the new thermowell mounted RTDs.
l l
I 1.1 HISTORICAL BACKGROUND Prior to 1968, PWR designs had been based on the assumption that the hot leg temperature was uniform across the pipe. Therefore, placement of the temperature instruments was not considered to be a factor affecting the accuracy of the measurement. The hot leg temperature was measured with direct immersion RTDs extending a short distance into the pipe at one location. By the late 1960s, as a result of accumulated operating experience at several plants, the following problems associated with direct immersion RTDs were identified:
o Temperature streaming conditions; the incomplete mixing of the coolant leaving regions of the reactor core at different temperatures produces significant temperature gradients within the pipe.
o The reactor coolant loops required cooling and draining before the RTDs could be replaced.
The RTD bypass system was designed to resolve these problems; however, operating plant experience has now shown that operation with the RTD bypass loops has created it's own obstacles such as:
o Plant shutdowns caused by excessive primary leakage through valves, flanges, etc., or by interruptions of bypass flow due to valve stem failure.
1701v:1o/122288 1
o WESTINGHOUSE CLASS 3 o
Increased radiation exposure due to maintenance on the bypass line and to crud traps which increase radiation exposure throughout the loop compartments.
i' The proposed temperature measurement modification has been developed in response to both sets of problems encountered in the past. Specifically:
l o
Removal of the bypass lines eliminates.the components which have been a major source of plant outages as well as Occupational Radiation
]
Exposure (ORE).
o Three thermowell mounted hot leg RTDs provide an average measurement (equivalent to the temperature measured by the bypass system) to j
account for temperature streaming.
1 o
Use of thermowells permits RTD replacement without draining the reactor coolant loops.
F311owing is a detailed description of the effort required to perform this modification.
1.2 HECHANICAL MODIFICATIONS The individual loop temperature signals required for input to the Reactor Control and Protection System will be obtained using RTDs installed in each reactor coolant loop.
1.2.1 Hot Leg a) The hot leg temperature measurement on each loop will be accomplished with three fast response, narrow range, single element RTDs mounted in thermowells. To actw:lish tne sampling function of the RTD bypass manifold system and ndnimin the need for additional hot leg piping penetrations, the thernrweils wi'l be located within the three existing 1701v:1 D/122288 2
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WESTINGHOUSE CLASS 3 i
RTD bypass manifold scoops. A hole will be made through the end of each scoop so that water will flow in through the existing holes in the leading
)
~
edge of the scoop, past the RTD, and out through the new hole (Figure 1.2-1).
These three RTDs will measure the hot leg temperature which is used to calculate the reactor coolant loop differential temperature (AT) and average temperature (T,yg).
b) This modification will not affect the single wide range RTD currently installed near the entrance of each steam generator.
This RTD will continue to provide the hot leg temperature used to monitor reactor coolant temperature during startup, shutdown, and post accident conditions.
c)
The present Reactor Vessel Level Instrumentation System (RVLIS) has pressure taps located in the RTD bypass piping hot leg branch lines.
In order to retain the hot leg connection for the RVLIS a new boss will be j
mounted at the same elevation as the existing connections on the same two hot legs.
l 1.2.2 Cold Leg a) One fast response, narrow range, dual-element RTD will be located in each j
cold leg at the discharge of the reactor coolant pump (as replacements for the cold leg RTDs located in the bypass manifold). Temperature streaming in the co1d leg is not a concern due to the mixing action of the RCP. For this reason, only one RTD is required.
This RTD will measure the cold leg temperature which is used to calculate reactor coolant loop AT and T
The existing cold leg RTD bypass penetration nozzle will be avg.
modified (Figure 1.2-2) to accept the RTD thermowell.
One element of the RTD will be considered active and the other element will be held in reserve as a spare.
b) Tnis modification will not affect the single wide range RTD in each co'ad leg current.ly installed at the discharge of the reactor coolant pump.
This RTD will continue to provide the cold leg temperature used to monitor reactor coolant temperature during startup, shutdown, and post accident conditions.
1701v:1o/122288 3
WESTINGHOUSE CLASS 3 5
1.2.3 Crossover Leg
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The RTD bypass manifold return line will be capped at the nozzle on the crossover leg.
1.3 ELECTRICAL N0 DEIFICATIONS l
)
1.3.1 Control & Protection System l
Figure 1.3-1 shows a block diagram of the modified protection system electronics. The hot leg RTD measurements (three per loop) will be electronically averaged in the process protection system.
The averaged Thot signal will then be used with the T signal to calculate reactor coolant cold loop AT and T,yg which are used in the reactor control and protection system.
This will be accomplished by additions to the existing process protection system equipment.
The present RCS loop temperature measurement system uses dedicated direct immersion RTDs for the control and protection systems.
This was done largely to satisfy the IEEE Standard 279-1971 which applied single failure criteria to control and protection system interaction.
The new thermowell mounted RTDs will be used for both control and protection.
In order to continue to satisfy the requirements of IEEE ?.79-1971, the T,yg and AT signals used in the control grade logic will be input into a median signal selector, which will select the signal which is in between the highest and lowest values of the three loop inputs.
This will avoid any adverse plant response that could be caused by a single signal failure.
1.3.2 Qualification 1
The 7100 Process Electronics modifications will be qualified to the same level as the existing 7100 electronics.
RTD qualification will be verified to support, Duquesne Light's compliance to 10CFR50.49.
1701v:1o/122288 4
d
i WESTINGHOUSE CLASS 3' 4
1.3.3 RTD Operability Indication
~
Existing control board AT and T,yg indicators and alarms will provide the means of identifying RTD failurcs, although the now redundant indication for the T,yg and AT signals will be removed. The spare cold leg RTD element provides sufficient spare capacity to accommodate a single cold leg RTD failure per loop. Failure of a hot leg RTD is addressed via manual action as the plant I&C personnel would defeat the failed signal and rescale the electronics to average the remaining two hot leg signals-(see Figure 1.3-1 and Section4.5).
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4 1701v:10/122288 5
1
WESTINGHOUSE CLASS 3 5
)
a., c.
,('
1 l
I s
i
,1 1
l l
i Figure 1.2-1 Hot Leg RTD Scoop Modification for Fast Response RTD Installation 1701v:1 D/122288 6
WESTINGHOUSE CLASS 3 l
b l
I J
O., C l
i 1
)
i 1
l l
1
)
1 l
1 1
Figure 1.2-2 Cold Leg Pipe Nozzle Modification for Fast Response RTO Installation 1701v:10/122288 7
WESTINGHOUSE CLASS 3 4
0., C i
l l
l l
1 i
l t
~
l 1
l l
l 1
Figure 1.3-1 RTD Averaging Block Diagram.
Typical for Each of 3 Channels 1701v:10/122288 8
WESTINGHOUSE CLASS 3 o
2.0 TESTING I
There are two specific types of tests which are performed to support the installation of the thermowell mounted fast-response RTDs in the reactor coolant piping:
RTD response time tests and a hot leg temperature streaming test.
The response time for the Beaver Valley Unit 1 application will be verified by testing at the RTD manufacturer and by in-situ testing. Data from thermowell/RTD performance at operating plants provide additional support for the system.
4 2.1 RESPONSE TIME TEST The RTD manufacturer, WEED Instruments Inc., will perform time response testing of each RTD and thermcwell prior to installation at Beaver Valley Unit 1.
These RTD/thermowells must exhibit a response time bounded by the values shown in Table 2.1-1.
The revised response time has been factored into the transient analyses discussed in Section 4.0.
In addition, response time testing of the WEED RTDs will be performed in-situ at Beaver Valley Unit 1.
This testing will demonstrate that the WEED RTDs can satisfy the response time requirement when installed in the plant.
2.2 STREAMING TEST Past testing at Westinghouse PWRs has established that temperature stratification exists in the hot leg pipe with a temperature gradient from maximum +o minimum of [
]b,c.e A test program was implemented at an operating plant to confirm the temperature streaming magnitude and stability with measurements of the RTD bypass branch line temperatures on two adjacent hot leg pipes. Specifically, it was intended to determine the l
magnitude of the differences between branch line temperatures, confirm the short-term and long-term stability of the temperature streaming patterns and evaluate the impact on the indicated temperature if only 2 of the 3 branch line temperatures are used to determine an average temperature.
This plant specific data is used in conjunction with data taken from other Westinghouse designed plants to determine an appropriate temperature error for use in the 1701v:10/122288 9
WESTlNCHDUSE CLASS 3 safety analysis and calorimetric flow calculations.
Section 3 will discuss the specifics of these uncertainty considerations.
The test data was reduced and characterized to answer the three objectives of the test program. First, it is conservative to state that the streaming pattern [
]b,c.e Steady state data taken at 100% power for a period of four months indicated that the streaming pattern
[
]b,c.e In other words, the temperature
.b,c e l
gradient [
This is inferred by [
]b,c.e 4
obso.ed between branch lines. Since the [
]b,c.e into the RTD averaging j
circuit if a hot leg RTD fails and only 2 RTDs are used to obtain en average hot leg temperature. The operator can review temperatures recorded prior to the RTD failure and determine an [
]b,c,e into the "two RTD" average to obtain the "three RTD" expected reading. A generic procedure has been provided to Duquesne Light which specifies how these [
]b,c e are to be determined.
(Appendix A) This significantly reduces the error introduced by a failed RTD.
l Both the test data and the operating data support previous calculations of streaming errors determined from tests at other Westinghouse plants.
The temperature gradients defined by the recent plant operating data are well within the upper bound temperature gradients that characterize the previous data. Differences observed in the operating data compared with the previous data indicate that the temperature gradients are smaller, so the measurement uncertainties are conservative. The measurements at the operating plants, I
obtained from thermowell RTDs installed inside the bypass scoops, were expected to be, and were found to be, consistent with the measurements j
obtained previously from the bypass loop RTDs.
l 1-1 1701v:1 D/122288 10 i
l
WESTINGHOUSE CLASS 3 a
TABLE 2.1-1 RESPONSE TIME PARAMETERS FOR RCS TEMPERATURE MEASUREMENT RTD Fast Response Bypass System Thermowell RTD System
~ ~
RTD Bypass Piping and Thermal Lag (sec) f~
RTD Re ponse Time (sec)
Electronics Delay (sec)-
Total Response Time-(sec) 6.0 sec 6.0 see 4
I 1701v;1D/122288 11
WESTINGHOUSE CLASS 3 i
1 3.0 UNCERTAINTY CONSIDERATIONS This method of hot leg temperature measurement has been analyzed to determine the magnitude of the two uncertainties included in the Safety Analysis:
l Calorimetric Flow Measurement Uncertainty and Hot Leg Temperature Streaming j
l Uncertainty.
3.1 CALORIMETRIC FLOW MEASUREMENT UNCERTAINTY i
Reactor coolant flow is verified with a calorimetric measurement performed l
after the return to power operation following a refueling shutdown.
The two I
most important instrument parameters for the calorimetric measurement of RCS flow are the narrow range hot leg and cold leg coolant temperatures.
The accuracy of the RTDs has, therefore, a major impact on the accuracy of the flow measurement.
1 With the use of three T RTDs (resulting from the elimination of the RTD hot Bypass lines) and the latest Westinghouse RTD cross-calibration procedure I
(resulting in low RTD calibration uncertainties at the beginning of a fuel cycle), the Beaver Valley 1 RCS Flow Calorimetric uncertainty is determined to be (
Ja,c including use of cold leg Elben Taps (see Tables 3.1-2, 3, 4 and 5).
This calculation is based on the standard Westinghouse methodology previously approved on earlier submittals of other plants associated with RTD Bypass Elimination or the use of the Westinghouse Improved 1
Thermal Design Procedure.
Tables 3.1-1 through 3.1-11 were generated specifically for Beaver Valley Unit 1 and reflect plant specific measurement uncertainties and operating conditions.
3.2 HOT LEG TEMPERATURE STREAMING UNCERTAINTY The safety analyses incorporate an uncertainty to account for the difference between the actual hot leg temperature and the measured hot leg temperature caused by the incomplete mixing of coolant leaving regions of the reactor core at different temperatures. This temperature streaming uncertainty is based on an analysis of test data from other Westinghouse plants, and on calculations l
l'f 01 v.10/122288 12
WESTINGHOUSE CLASS 3 to evaluate the impact on temperature measurement accuracy of numerous possible temperature distributions within the hot leg pipe. The test data has shown that the circumferential temperature variation is no more than [
]b,c.e, and l'
that th-inferred temperature gradient within the pipe is limited to about
[
]b,c,e The calculations for numerous temperature distributions have shown that, even with margins applied to the observed j
temperature gradients, the three point temperature measurement (scoops or ther:nowell RTDs) is very effective in determining the average hot leg temperature.
The most recent calculations for the thermowell RTD system have established an overall streaming uncertainty of (
]b,c,e for a hot leg measurement. Of this total, [
] b, c., e This overall temperature streaming uncertainty provides additional margin when applied to the 3-loop Beaver Valley Unit 1 plant, since the 3-loop temperature distributions are not similar, so more of the total streaming uncertainty would be random.
The new method of measuring hot leg temperatures, with the three hot leg thermowell RTDs, is at least as effective as the existing RTD bypass system,
[
]a,c Although the new method measures temperature at one point at the RTD/thermowell tip, compared to the five sample points in a 5-inch span of the scoop measurement, the thermowell measurement point is opposite the center hole of the scoop and therefore measures the equivalent of the average scoop sample if a linear radial temperature gradient exists in the pipe.
The thermowell measurement may have a small error relative to the scoop measurement if the temperature gradient over the 5-inch scoop span is nonlinear. Assuming that the maximum inferrea temperature gradient of (
]b,c.e exists from the center to the end of the scoop, the difference between the thermowell and scoop measurement is limited to
{
]b,c,e Since three RTD measurements are averaged, and the nonlinearities at each scoco are random, the effect of this error on the hot leg temperature measurement i: limited to (
]b,c,e On the other 1701v:1o/122288 13
WEST!NGHOUSE CLASS 3 l
hand, imbalanced scoop flows can introduce temperature measurement j
uncertainties of up to [
3a,c,
In all cases, the flow imbalance uncertainty will equal or exceed the
{
]b,c,e sampling uncertainty for the thermowell RTDs, so the new measurement system tends to be a more accurate measurement with respect to streaming uncertainties.
Temperature streaming measurements have been obtained from tests at 2, 3 and 4-loop plants and from thermowell RTD installations at 4-loop plants.
Although there have been some differences observed in the orientation of the individual loop temperature distributions from plant to plant, the magnitude of the differences have been [
b3,c e.
)
Over the testing and operating periods, there were only minor variations of less than [
]b,c e in the temperature differentials between scoops, and I
smaller variations in the average value of the temperature differentials.
[
b3,c.e,
Provisions were made in the RTD electronics for operation with only two hot leg RTDs in service.
The two-RTD measurement will be biased to correct for the difference compared with the three-RTD average. Based on test data, the bias value would be expected to range between [
]b,c,e Data j
comparisons show that the magnitude of this bias varied less than b
[
l,c e over the test period. Appendix A provides a procedure for utilizing the actual plant bias data. Note that this procedure only allows the use of positive (or zero) bias values.
3.3 CONTROL AND PROTECTION FUNCTION UNCERTAINTIES Calculations were performed te determine or verify the instrument uncertainties for the control and protection functions affected by the RTD 1
,I 1701v:10/122288 14
WESTINGHOUSE CLASS 3 Bypass Elimination.
Table 3.1-1, Rod Control System Accuracy, notes that the calculated uncertainty is the same as previously assumed in the Safety
~
Analyses. Table 3.1-6 provides the uncertainty breakdown for Overtemperature Delta-T. A comparison of the Channel Statistical Allowance with the Total Allowance noted on Table 3.1-7 results in the conclusion that sufficient margin exists for the uncertainties.
Table 3.1-8 documents the breakdown for Overpower Delta-T. Comparing the Channel Statistical Allowance for this function with the Total Allowance noted on Table 3.1-9 will conclude that this function is acceptable. Table 3.1-10 provides the Loss of Flow breakdown.
Table 3.1-11 notes that the Total Allowance (TA) for this function is larger than the Channel Statistical Allowance, thus the uncertainties are provided for. Table 3.1-11 lists the affected protection function Technical Specification values, some modifications are necessary, as noted.
- However, based on the calculations performed, the changes in uncertainties are acceptable with minimal modifications to the plant Technical Specifications, primarily Allowable Values.
l J
1701v:10/122288 15
WESTINGHOUSE CLASS 3' TABLE 3.1-1 R0D CONTROL SYSTEM ACCURACY Tavg TURB PRES
+
__ a,c PM =
SCA =
M&TE=
STE =
i SD
=
BIAS =
RCA =
~
M&TE=
M&TE=
RTE =
RD
=
CA
=
BIAS =
_ +a,c ELECTRONICS CSA
=
ELECTRONICS SIGMA =
CONTROLLER SIGMA
=
CONTROLLER BIAS
=
CONTROLLER CSA
=
1701v:10/122288 16
l WESTINGHOUSE CLASS 3-TABLE 3.1-2
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FLOW CALORIMETRIC. INSTRUMENTATION UNCERTAINTIES
~
(% SPAN)
FW TEMP FW PRES FW DP STM PRESS'..TH TC PRZ PRESS
+a,c SCA =
M&TE=
SPE =
STE =
l I
=
R/E =
RDOT=
4 BIAS =
~
CSA =
- OF INST USED 3
1 1
DEG F PSIA
% DP PSIA DEG F DEG F
' PSIA INST SPAN = 500.
2000.
120.
1400.
100.
.100.
800.
+a,c INST UNC.
(RAND 0M) =
INST UNC.
(BIAS)
=
NOMINAL
= 437.
890.
790.
605.0 545.0
'2250.
1701v:10/122288 17
WESTINGHOUSE CLASS 3 TABLE 3.1-3
[
~
FLOW CALORIMETRIC SENSITIVITIES I
FEEDWATER FLOW 1
~
]
+a,c TEMPERATURE
=
MATERIAL
=
DENSITY TEMPERATURE
=
PRESSURE
=
DELTA P
=
l FEEDWATER ENTHALPY i
TEMPERATURE
=
PRESSURE
=
h5 1199.7 BTU /LBM
=
hF 416.6 BTV/LBM
=
Dh(SG) 783.0 BTV/LBM
=
1 STEAM ENTHALPY
.l I
PRESSURE
_+a,c l
=
MOISTURE
=
HOT LEG ENTHALPY TEMPERATURE
=
PRESSURE
=
hH 620.4 BTU /LBM-
=
hC 541.0 BTU /LBM
=
Dh(VESS) 79.4 BTV/LBM
=
Cp(TH) 1.454 BTU /LBM-DEGF i
=
1-COLD LEG ENTHALPY TEMPERATURE'
=
PRESSURE
=
l Cp(TC) 1.231 BTU /LBM-DEGF COLD LEG SPECIFIC VOLUME
+a,c
' TEMPER /.TURE
=
PRESSURE
=
1701v:10/122223 18
I WESTINGHOUSE CLASS 3 TABLE L1-4
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CALORIMETRIC RCS FLOW MEASUREMENT UNCERTAINTIES COMPONENT INSTRUMENT ERROR FLOW UNCERTAINTY
+a,c l
FEEDWATER FLOW 1
VENTURI
' THERMAL EXPANSION COEFFICIENT TEMPERATURE MATERIAL-DENSITY TEMPERATURE PRESSURE i
. DELTA P i
FEEDWATER ENTHALPY TEMPERATURE l
PRESSURE l
STEAM ENTHALPY PRESSURE MOISTURE NET PUMP HEAT ADDITION HOT LEG ENTHALPY TEMPERATURE STREAMING, RANDOM STREAMING, SYSTEMATIC PRESSURE COLD LEG ENTHALPY l
TEMPERATURE PRESSURE COLD LEG SPECIFIC VOLUME i
TEMPERATURE PRESSURE d
a 1701v:1D/122288 19
_ _ _ _ = _ _ _ _ _ _ _ _ _ _ _ _ _ -._- _
WEST 1NGH0VSE CLASS 3 TABLE 3.1-4 (continued)
~
CALORIMETRIC RCS FLOW MEASUREMENT UNCERTAINTIES
~
BIAS VALUES
+a,c FEEDWATER PRESSURE DENSITY.
ENTHALPY STEAM PRESSURE ENTHALPY PRESSURIZER PRESSURE ENTHALPY - HOT LEG ENTHALPY - COLD LEG SPECIFIC VOLUME - COLD LEG FLOW BIAS TOTAL VALUE
- ** +,++ INDICATE SETS OF DEPENDENT. PARAMETERS
+a,c SINGLE LOOP UNCERTAINTY (WITHOUT BIAS VALUES)
N LOOP UNCERTAINTY (WITHOUT BIAS VALUES)
N LOOP UNCERTAINTY (WITH BIAS VALUES) l l
I*
O 1701v;1 D/122288 20
WEST!NGHOUSE CLASS 3 o
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TABLE 3.1'5 1
l 1
COLD LEG ELBOW TAP FLOW UNCERTAINTY
]
l INSTRUMENT UNCERTAINTIES i
% DP SPAN
% FLOW
_ +a,c PMA =
PEA =
SCA =
l SPE -
STE =
=
RCA =
~
M&TE=
RTE =
RD
=
ID
=
A/D =
RDOT=
BIAS =
FLOW CALORIM. BIAS 0.0
=
FLOW CALORIMETRIC 1.7
=
INSTRUMENT SPAN 120.
=
SINGLE LOOP ELBOW TAP FLOW UNC =
N LOOP ELB0W TAP FLOW UNC
=
N LOOP RCS FLOW UNCERTAINTY (WITHOUT BIAS VALUES)
=
o N LOOP RCS FLOW UNCERTAINTY (WITH BIAS VALUES)
=
1701v:1D/122288 21
WESTINGHOUSE CLASS 3 1
1 l
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)
TABLE 3.1-6 l
4 OVERTEMPERATURE AT l
l i
Parameter Allowance
- Process Measurement Accuracy i
_ +a,c
+a. c 1
PrimaryElementAccuracy Sensor Calibration
+a,c j
Sensor Pressure Effects
\\
Sen or Temperature Effects i
3+a,c Sensor Drift
_ +a,c Bias Environmental Allowance Rack Calibration
+a,c e
1701v:10/122288 22
WESTINGHOUSE CLASS 3 TABLE 3.1-6 (continued)
OVERTEMPERATURE AT Parameter Allowance
- Measurement &. Test Equipment Accuracy
+a,c
]
+a,c Rack Accuracy
+a,c I
~
Rack Comparator Setting Accuracy Two inputs Rack Temperature Effects Rack Drift AT Tavg In % span (Tavg - 100 'F, pressure - 800 psi, power - 150 % RTP, AT - 90.0 'F = 150 % RTP, DI - + 30 % DI)
See Table 3.1-7 for gain and conversion calculation 4a,c
- [
)
Channel Statistical Allowance =
+a,c e
1701v:10/122288 23
WESTINGHOUSE CLASS 3 TABLE 3.1-7 OVERTEMPERATURE AT GAIN CALCULATIONS The equation for Overtemperature AT is:
' f AT[(1)/(1+14 )] 5 S
S )] - T'] + K (P - P') - f (AI)3 2 ))[T[(1)/(1 + t S
S
- K [(1 + ty )/(1 + t AT [K S
3 1
2 g y y ((max)nal) 1.180 Technical Specifjcgtion value K
nomi
=
[
.]
K
=
y 0.01655 K
=
2 0.000801.
K
=
v$sselAT 60.0*F
=
1.91%
AI gain
=
+a,c Pressure Gain =
Pressure SCA
=
Pressure SMTE =
Pressure STE
=
Pressure SD
=
+a,c AI conversion
=
3 l
l al PHA
=
alPMAf
=
Total ' Allowance (TA) =
[
)+a,c = 8.0 % AT span i
e 1701v:10/122288 24
WESTINGHOUSE CLASS 3 o
TABLE.3.1-8
~
OVERPOWER AT
.i Parameter Allowance
- Process Measurement Accuracy
+a,c
[
]+a,c Primary Element Accuracy Sensor Calibration
._+a,c Sensor Pressure Effects Sensor Temperature. Effects Sensor Drift
[-
]+a,c Environmental Allowance Rack Calibration q+a,c
-Measurement & Test Equipment Accuracy
+a,c.
Rack Accuracy
+a,c l
~
Racii Comparator Setting. Accuracy
.Two inputs Rack Temperature Effects Rack Drift AT-Tavg 1701v:1 D/122288 25
I l
WESTINGHOUSE CLASS 3 TABLE 3.1-8' (continued) i i
~
OVERPOWER AT l
I 1
In % span (Tavg - 100 *F, AT - 90.0 'F = 150 % RTP)+a'e
- [
.)
Channel Statistical Allowance =
+a, c l
l I
l l
I' i
i 1701v:10/122288 26 I
WESTINGHOUSE CLASS 3 TABLE 3.1-9 l
OVERPOWER AT GAIN CALCULATIONS The equation for Overpower AT is:
AT((1)/(1 + 14 )] 1 S
5 )] - T"] - f (AI))
- K EE(*3 )/(1 + '3 )lI(1)/(1 + '5 )))T - K (T[(1)/(1 + 1 S
AT [K 3
3 5
2 5
6 g 4 K4 (nominal) 1.070TechnicalSpecif4gafionvalue
=
[
]
K4 (max)
=
K 0.02
=
5 K
0.00128
=
vhssel6T 60.0*F
=
Total Allowance =
(
]+a,c = 5.4 % span I
l l-I i
l l
l 1701v:1o/122288 27
WESTINGHOUSE CLASS 3 l
TABLE.3.1-10 LOSS OF FLOW Parameter Allowance
- l l
Process Measurement Accuracy
- +a,c
+a,c j
Primary Element Accuracy
)+a,c Sensor Calibration
(
3+a,c Sensor Pressure Effects
[
l+a,c Sensor Temperature Effects
(
)+a,c i
Sen or Drift
)+a,c Environmental Allowance 1
Rack Calibration Rack Accuracy (
]+a,c Measurement &' Test Equipment Accuracy (
) a,c Comparator One input [
]+a,e 1
RackTemperatureEffe$$,c Rack Drift 1.0 % AP span In % flow span (120 % Thermal Design Flow) % AP span converted to flow span via Equation 3-21.8, with F,,x = 120 % and FN = 100 %
Channel Statistical Allowance' =
~ +a,c 1701v:1o/122288 28
- ]
WESTINGHOUSE CLASS 3 TABLE 3.1 "
TECHNICAL SPECIFICATION MODIFICATIONS Overtemperature AT TA
= 8.0 % AT span Z
= 4.30 S
= 1.67 (Temperature) + 0.69 (Pressure)
Nominal values as noted on Overtemperature AT Gain Calculations Allowable Value 5 3.3 % AT span Overpower AT TA
= 5.4 % AT span Z
= 1.72*
S
= 1.67 Nominal values as noted on Overpower AT Gain Calculations-Allowable Value 5 2.9 % AT span
- Loss of Flow TA
= 2.5 % span Z
= 1.50 S
= 0.60 Nominal Trip Setpoint 3 90.0 % Loop Design Flow Allowable Value 2 88.9 % Loop Design Flow
- Indicates value changed from Westinghouse Letter NS-0PLS-88-003, 11/03/88.
/
1701v:10/122288 29
WESTINGHOUSE CLASS 3 4.0 SAFETY EVALUATION The primary impact of the RTD Bypass Elimination on the FSAR Chapter 14 (Reference 1) safety analyses are the differences in response time characteristics and instrumentation uncertainties associated with the fast response thermowell RTD system. The affects of these differ:.nces are discussed in the following sections.
4.1 RESPONSE TIME The current response time parameters of the Beaver Val. ley Unit 1 RTD bypass system assumed in the safety analyses are shown in Table 2.1-1.
For the fast response thermowell RTD system, the overal; response time will consist of [
]a,c (3, presented i 'iection 2.1 and as given in Table 2.1-1).
The new thermowell mounted RTDs have a response time equal to or better than the old bypass piping transport, thermal lag and direct immersion RTD. This j
then allows the total RCS temperature measurement response time to remain unchanged at 6.C seconds (Ref r ence Table 2.1-1).
This channel response time I
is factored into the Overtemperature Delta-T and Overpower Delta-T trip performance. Therefore, those transients that rely on the above mentioned trips must be evaluated for the modified response characteristics.
Section 4.3 includes a discussion on the evaluation for these events.
4<2 RTD UNCERTAINTY l
The proposed fast respo..se thermowell RTC system will make use of RTDs, manufactured by Weeo Instruments Inc., with a total uncertainty of
[
Ja c assumed for the analyses.
l The FSAR analyses make explicit allowances for instrumentation errors for some of the reactor protection system setpoints.
In addition, allowances are made l.
for the average reactor coolant system (RCS) temperature, pressure and power.
These allowances are made explicitly to the initial conditions.
i 1701v:1 D/122288 30 L
WEST!NGHOUSE CLASS 3 1
The following protection and control system p rameters were evaluated and determined to be unaffected (with res v t to accident analysis assumptions) by J
~
the change from one hot leg RTD to three hot leg RTDs; the Overtemperature AT (OTDT), Overpower AT (OPDT), and Low RCS Flow reactor trip functions, RCS loop T,yg measurements used for input to the rod control system, and the calculated value of the RCS flow uncertainty. System uncertainty calculations were performed for these parameters to determine the impact of the change in the number of hot leg.RTDs. The results of these calculations, noted n. 3.3, indicate sufficient margin exists to account for known instrument uncertainties.
In summary, changes hsve been made in the Reactor' Protection System response times only to account for the new thermowell mounted RTDs.
l s
4.3 NON-LOCA EVALUATION 4
l The changes in the RTD response time discussed in Section 2.1 and the instrumentation uncertainties discussed in Section 3.3 have been considered for the Beaver Valley Unit i non-LOCA safety analysis design basis. Only those transients which assume OTDT/0PDT protection are potentially affected by changes in the RTD response time.
Instrumentation uncertainties can affect j
the non-LOCA transient initial condition assumptions and those transients which assume protection from low primary coolant flow reactor trip.
As noted in Section 3.0, the RTD bypass elimination can potentially affect the rod control system accuracies and flow calorimetric instrumentation uncertainties.
The calculations documented in Section 3.0 support the continued validity of the non-LOCA safety analysis initial condition RCS temperature and flow assumptions. On thir basis, the FSAR non-LOCA safety analysis initial condition assumptions are appropriate and conservative for the proposed RTD Bypass Elimination and no revision of accident analysis initial condition assumptions is required.
The RTD respor,se time and instrumentation uncertainties associated with the RTD Bypass Elimination can potentially affect protection systems assumed to be 1701v;1o/122288 31
WESTINGHOUSE CLASS 3 availabie for mitigation of design basis non-LOCA transients.
The protection system setpoints evaluated in Section 3.0 are OTDT, OPDT and Low Primary Coolant Loop Flow (Loss of Flow) reactor trip.
The transients which assume protection from these functions are listed below.
Assumed Protection Reference Accident Function FSAR Section Loss of External Electrical 14.1.7 Load / Turbine Trip OTDT FSAR Section Uncontrolled RCCA Bank With-14.1.2 drawal at Power OTDT FSAR Section Accidental Depressurization 14.1.15 of the RCS OTDT FSAR Section Partial Loss of Forced 14.1.5 Reactor Coolant Flow Loss of Flow WCAP-10961-P Steamline Break for EQ (Reference 2)
Outside Containment OPDT As noted in Section 4.1, the new thermowell mounted RTDs have a response time equal to or better than the old bypass piping transport, thermal lag and direct immersion RTD. On the basis of the informatica documented in Table 2.1-1, it is concluded that the safety analysis assumption for total OTDT/0PDT channel response time of i.0 seconds remains valid.
Evaluation of the effects of the RTD Bypass Elimint ion on the uncertainties associated with these setpoints, as well as the Loss of Flow setpoint, supports the continuing validity of the current non-LOCA safety analysis assumptions for the above transients.
In conclusion, the Reference 1 and 2 non-LOCA safety analysis assumptions applicable to Beaver Valley Unit i remain valid for the replacement of the l
existing RTD Bypass System with fast response thermowell mounted RTDs 1701v:10/122288 32
WESTINGHOUSE CLASS 3 installed in the reactor coolant loop piping.
Therefore, the conclusions presented in FSAR Chapter 14 remain valid and all applicable non-LOCA safety analysis acceptance criteria continue to be met.
l
~
4.4 LOCA Evaluation The elimination of the RTD bypass system impacts the uncertainties associated with RCS temperature and flow measurement.
The magnitude of the uncertainties are such that RCS inlet and outlet temperatures, thermal design flow rate and the steam generator performance data used in the LOCA analyses will not be j
affected. Past sensitivity studies have shown that the variation of the core inlet temperature (Tin) used in the LOCA analyses affects the predicted core flow during the blowdown period of the transient.
The amount of flow into the core is influenced by the two phase vessel-side break flow, and the core cooling is affected by the quality of the fluid. These sensitivity studies concluded that the inlet temperature effect on peak clad temperature is dependent on break size. As a result of these studies, the LOCA analyses are performed at a nominal value of T without consideration of small in uncertainties. The RCS flow rate and steam generator secondary side i
temperature and pressure are also determined using the loop average temperature (T,yg) output. These nominal values used as inputs to the analyses are not affected due to the RTD bypass elimination.
It is concluded that the elimination of the RTD bypass piping will not affect the LOCA analyses input and hence, the results of the analyses for Beaver Valley Unit i remain unaffected.
Therefore, the plant design changes due to the RTD bypass elimination are acceptable from a LOCA analysis standpoint without requiring any reanalysis.
4.5 INSTRUMENTATION AND CONTROL (I&C) SAFETY EVALUATION The RTD Bypass Elimination modification for Beaver Valley Unit 1 does not functionally change the AT/T,yg protection channels.
The implementation i.
of the fast response RTDs in the reactor coolant piping will change the inputs into the AT/T,yg Protection Sets I, II, and III, as follows:
1701v;1D/122288 33
WESTINGHOUSE CLASS 3 C'
l 1.
The Narrow Range (NR) cold leg RTD in the cold leg manifold will be replaced with a fast response NR dual element well mounted RTD in the RCP pump discharge pipe. The signal from this fast response NR RTD will signal. One element perform the same function as the existing RTD Tcold of the RTD will be held in reserve as a spare.
2.
The NR hot leg RTD in the bypass manifold will be replaced with 3 fast response NR single element well mounted RTDs in the hot leg that are electronically averaged in the process protection system.
3.
Identification of failed signals will be by the sami means as before the modifications, i.e., existing control board alarms and indications.
i 4.
Signal process and the added circuitry to the Protection Set racks will be accomplished by additions to the process control (Westinghouse Model 7100) racks using 7100 technology. When one T signal is removed from the hot averaging process, the electronics will allow a bias to be manually added to a 2-RTD average Thot (as opposed to a 3-RTD average Thot) in rder to obtain e value comparable with the 3-RTD average Thot pri r to the failed RTD.
In the event of a cold leg RTD failure, the spare cold leg RTD element will be manually connected'to the 7100 circuitry in place of the failed RTD.
Existing control board AT and Tavg indicators and alarms will provide the means of identifying RTD failures.
Upon identification of a failed RTD, the operator would place that protection channel in trip (consistent with the time requirements specified in the Technical Specifications),
identify and disconnect the failed P.TD, and rescale the summing amplifier for a two RTD input condition.
The channel would then be returned to service. During this process the plant will be in a partial trip mode and will therefore be in a safe condition.
The conversion to thermowell mounted PTDs will result in elimination of the control grade RTDs and their associated control board indicators.
The protection grade channels will now be used to provide inputs to the control 1
1701v:10/122288 34
WESTINGHOUSE CLASS 3 system through isolators to prohibit faults in the control rack from propagating into the protection racks.
In order to satisfy the control and protection interaction requirements of IEEE 279-1971, a Median Signal Selector (MSS) will be used in the control channels presently utilizing a high auctioneered T,yg or AT signal (there will be a separate MSS for each function).
The Median Signal Selector will use as inputs the protection grade T,yg or AT signals from all three loops, and will supply as an output the channel signal which is the median of the three signals. The effect will be that the various control grade systems will still use a valid RCS temperature in the case of.a single signal failure.
To ensure proper action by the Median Signal Selector, the present manual switches that allow for defeating of a T,yg or sT signal from a single loop will be eliminated. The MSS will automatically select a valid signal in the case of a signal failure. Warnings that a failure has occurred will be provided by loop to median T and AT deviation alarms.
avg Other than the above changes, the deactor Protection System will remain the same, as that previously utilized.
For example, two out of three voting logic continues to be utilized for the thermal overpower protection functions, with the model 7100 process control bistables continuing to operate on a "de-energize to actuate" principle. Non-safety related control signals will now be derived from protection channels via a Median Signal Selector, i
The above principles of the modification have been reviewed to evaluate conformance to the requirements of IEEE-279-1971 criteria and associated 10CFR 50 General Design Criteria (GDC), Regulatory Guides, and other applicable industry standards.
IEEE 279-1971 requires documentation. of a design basis.
Following is a discussion of design basis requirements in conformance to pertinent 1&C criteria:
a.
The single failure criterion continues to be satisfied by this chanr because the independence of redundant protection sets is maintained.
O 1701v;1o/122288 35
r
)
1 WESTINGHOUSE CLASS 3 b.
The quality of the components and modules being added is consistent with
)
use in a Nuclear Generating Station Protection' System.
For the
]
Westinghouse Quality Assurance program, refer to Appendix A of the FSAR.
c.
The changes will continue to maintain the capability of the protection system to initiate a reactor trip during and following natural phenomena credible to the plant site to the same extent as the existing system.
d.
Channel independence and electrical separation is maintained because the Protection Set circuit assignments continue to be Loop.1 circuits input to Protection Set I; Loop 2 to Protection Set II; and Loop 3 to Protection Set III, with appropriate observance of field wiring interface criteria to I
assure the independence.
e.
Due to the elimination of the dedicated control system RTD elements, temperature signals for use in the plant control systems must now be derived from the protection system RTDs.
To eliminate any degrading control and protection system interaction mechanisms introduced as a consequence of the RTD Bypass Elimination modification, a Median Signal Selector has been introduced into the control system.
The Median Signal Selector preserves the functional isolation of interfacing control and protection systems that share common instrument channels. The details of the signal selector implementation are contained in Section 1.3.1.
On the basis of the foregoing evaluation, it is concluded that the compliance of Beaver Valley Unit 1 to IEEE 279-1971, applicable GDCs, and industry standards and regulatory guides has not been changed with the.I&C modifications required for RTD bypass removal.
4.6 MECHANICAL SAFETY EVALUATION The presently installed RTD bypass system is to be replaced with fast acting narrow range RTD thermowells.
This change requires modifications to the hot leg scoops, the hot leg piping, the crossover leg bypass return nozzle, and the cold leg bypass manifold connection. All welding and NDE will be 1701v:1o/122288 36
WESTINGHOUSE CLASS 3 performed per ASME Code Section XI requirements. Each of these modifications is evaluated below.
~
i The original three scoops in the loop A, B and C hot legs, which feed the l
bypass manifold, and the bypass manifold connection must be removed'and all scoops modified to accept three fast response RTD thermowells.
[
Ja,c to provide the proper flow j
path. A thermowell design will be used such that the thermowell will be positioned to provide an average temperature reading. The thermowell will be fabricated in accordance with Section III (Class 1) of the ASME Code.
The installation of the thermowell into the scoop will be performed using GTAW for I
the root pass and finished out with either Gas Tungsten Arc Weld (GTAW) or Shielded Metal Arc Weld (SMAW). The welding will be examined by penetrant test (PT) per the ASME Code Section XI. Prior to welding, the surface of the scoop onto which welding will be performed will be examined as required by Section XI.
1~
The cold leg RTD bypass line must also be removed.
The nozzle must then be j
modified to accept the fast response RTD thermowell.
The installation of the j
thermowell into the nozzle will be performed using GTAW for the root pass and 1
finished with either GTAW or SMAW. Weld inspection by PT will be performed as required by Section XI.
The thermowells will extend approximately [
la,c inches into the flow stream. This depth has been justified based on [ flow
)
induced vibration)a,c analysis. The root weld joining the thermowells to the modified nozzles will be deposited with GTAW and the remainder of the weld 1
may be deposited with GTAW or SMAW.
Penetrant testing will be performed in i
accordance with the ASME Code Section XI.
The thermowells will be fabricated in accordance with the ASME Section III (Class 1).
The cross-over leg bypass return piping connection must be removed and the nozzles capped. The cap design, including materials, will meet the pressure boundary criteria of ASME Section III (Class 1). The cap will be root welded j-to the nozzles by GTAW and fill welded by either GTAW or SMAW.
l Non-destructive examinations (PT and radiographs) will be performed per ASME Section XI. Machining of the bypass return nozzle, as well as any machining performed during modification of the penetrations in the hot and cold legs, 1701 v:1D/122288 37
-_-__________-_-_-A
WESTINGHOUSE CLASS 3 O
shall be performed such as to minimize debris escaping into the reactor coolant system.
The present Reactor Vessel Level Instrumentation System (RVLIS) has pressure taps located on the RTD bypass piping hot leg branch lines on loops B and C.
In order to tetain the hot leg connection for the RVLIS a new boss will be mounted on these two hot legs.
The installation boss for the new RVLIS connections will be root welded by GTAM.
Finish welding can be either GTAW or SMAW. Weld inspection by PT will be performed per Section XI.
The RVLIS bosses are fabricated in accordance with Section III (Class 1) of the ASME Code.
In accordance with Article IWA-4000 of Section XI of the ASME Code, a hydrostatic test of new pressure boundary welds is required when the connection to the pressure boundary is larger than one inch in diameter.
Since the cap for the crossover leg bypass return pipe is [ ]a,c inches and the cold leg RTD connections are [ ]a,c inches, a system hydrostatic test is required after the bypass elimination modification is complete.
Paragraph IWB-5222 of Section XI defines this test pressure to be 1.02 times the normal operating pressure at a temperature of 500*F or greater.
In summary, the integrity of the reactor coolant piping as a pressure boundary component, is maintained by adhering to the applicable ASME Code sections and Nuclear Regulatory Commission General Design Criteria.
Further, the pressure retaining capability and fracture prevention characteristics of the piping is not compromised by these modifications.
4.7 TECHNICAL SPECIFICATION EVALUATION As a result of the calculations summarized in Section 3.0, several protection functions' Technical Specifications must be modified.
The affected functions and their associated Trip Setpoint information, are noted on Table 3.1-11.
1701v:1o/122288 38
WESTINGHOUSE CLASS S o
5.0 CONTROL SYSTEM EVALUATION A prime input to the various NSSS co.; trol systems is the RCS cverage temperature,T(avg).
This is calculated electronically as the average of the measured hot and cold leg temperatures in each loop.
The effect of the new RTD temperature measurement system is to potentially change the time response of the T(avg) channels in the various loops.
This in turn could impact the response of (
]a,c However, as previously noted, the new RTD system (RTD +
thermowell) will have a time response identical to that of the current system (RTD + bypass line).
The additional delay resulting from the Median Signal Selector (MSS) is small in comparison with the RTD time response [
Ja,c Therefore, there will be no significant impact on the T(avg), channel response and no need, as a result of implementing the new system, to revise any of the control system setpoints. However, DLCo always has the option of making setpoint I
adjustments.
If desired, system performance can be verified by performing a series of plant tests (e.g., step load changes, load rejections, etc.)
following installation of the new RTD system.
Control system setpoints can then be adjusted based on the results of the tests.
It should be recognized that control systems do not perform any protective function in the FSAR accident analysis. With respect to accident analyses, control systems are assumed operative only in cases in which their action aggravates the consequences of an event, and/or as required to establish initial plant conditions for an analysis.
The modeling of control systems for accident l
analyses is based on nominal system parameters as presented in the Precautions, Limitations, and Setpoint document.
1701v:1D/122288 39
WEST 1 ~.100SE CLASS 3
6.0 CONCLUSION
S
.The rathod of utilizing fast response RTDs installed in the reactor coolant loop piping'as a means for RCS temp 9rature indication has undergone extensive.
analyses, evaluation and testing as described in this report. The incorporation of this system into the Beaver Valley Unit i design meets all safety, licensing and control requirements necessary for safe operation of this unit, The analytical evaluation has been. supplemented with in plant and laboratory testing to further verify system performance. The fast response RTDs installed in the reactor coolant loop piping adequately replace the '
prosent hot and cold leg temperature measurement system ar.d enhances ALARA efforts as well as improve plant reliability.
)
l 1701v:1D/122288 40
i WESTINGHOUSE CLASS 3
7.0 REFERENCES
1.
Updated Final Safety Analysis Report, Beaver Valley Power' Station Unit 1,.
Revision 5, January 1987.
2.
WCAP-10961-P, Steamline Break Mass / Energy teleases for Equipment Qualification Outside Containment, October 1985.
(Proprietary) 1
)
i i
l i
~
l I
1701v:10/122288 41
WESTINGHOUSE CLASS 3 APPENDIX A l
DEFINITION OF AN OPERABLE CHANNEL AND HOT LEG RTD FAILURE COMPENSATION PROCEDURE i
I I
I
)
i l
l i
1701v:1D/122288 42
c WESTINGHOUSE LLASS'3 1
j 1
I l
RTD BYPASS ELIMINATION '
I FOR BEAVER VALLEY 1 DEFINITION OF AN OPERABLE CHANNEL AND
^
HOT LEG RTD FAILURE COMPENSATION PROCEDURE I
l l
Westinghouse Electric Corporation Pittsburgh, PA I
l 1701v:10/12228a 43 l:
[
WESTINGHOUSE CLASS 3-s DEFINITION OF AN OPERABLE CHANNEL The RTD Bypass Elimination modification uses the average of 3.RTDs in each hot leg to provide a representative temperature measurement..In the event one or more of the RTDs fails, steps must be taken to compensate for the loss of that-RTD's input to the averaging function.
In the event of this type of RTD failure this procedure could be envoked.
Single RTD Failure Hot Leg: All three hot leg RTDs must be operable during the period following l
refueling from cold to hot zero power and from hot zero power to full power.
i During the heat cp period the plant operators will be [
i Ja,c Typically this data is recorded at initial 100% power and, thereafter, during the normal protection channel surveillance interval.
Onco [
Ja,c any hot leg can then tolerate a single RTD failure and still remain operable.
If the situation arises where a single hot leg RTD failure occurs a bias value must be applied to the average of the remaining two valid RTDs.
[
3a,c 1701v:1o/122288 44 1
1
i WESTINGHOUSE CLASS 3 4
1 The plant may operate with a failed hot leg RTD at any power level during that same fuel cycle.
It is permissible to shutdov:n and startup during the cycle without requiring that the failed RTD be replaced.
[
3a.c The Median Signal Selector will eliminate any control system concerns, the Tavg and AT signal associated with the loop containing the failed hot leg RTD will most likely not be the Median Signal chosen as the input to the control systems.
If another hot leg RTD fails in a different loop the utility should operate using manual contral. Manual control is recommended so that the operator can control the plant based on the best measurement available.
4 If automatic operation is continued the control system may choose the biased channel due to the positive (or zero) bias application.
This means the control system will perceive a higher Tavg than actually oxists at reduced power and the plant will operate at reduced temperatures.
While this is not necessarily undesirable it does reduce the total plant megawatt output. The use of automatic control can be considered based on utility power requirements.
Cold Leg:
If the active cold leg RTD fails, then that RTD should be disconnected from the 7100 cabinets.
The installed spare RTD should then be connected in the failed RTD's place.
1 I
Double RTD Failure:
Inoperable Channel Hot Leg or Cold Leg:
If two or more of the three hot leg RTDs or both cold leg RTD elements fail in the same protection channel then that channel is considered inoperable and should be placed in trip. Operation with only one valid hot leg RTD is not presently analyzed as part of the licensing basis.
1701v:1D/12220e 45
WESTINGHOUSE CLASS 3 l
i PROCEDURE FOR OPERATION WITH A HOT LEG RTD OUT OF SERVICE i
l 1
The hot leg temperature measurement is obtained by averaging the measurements,
from the three thermowell RTDs installed.on the hot leg of each loop.
(
I Ja,c In the event that one of the three RTDs fails, the failed RTD will be i
disconnected and the hot leg temperature measurement will be obtained by averaging the remaining two RTD measurements.
[
i 1
i ja,c The bias adjustment corrects for [
l I
]a,c To assure that the measured hot leg temperature is maintained at or above the true hot leg temperature, and l
thereby avoid a reduction in safety margin at reduced power, [
l 3a,c d
1701v:10/122288 46 I-
'l WESTINGHOUSE CLASS 3 a
1 i
An RTD failure will most likely result in an offscale high or low indication and will be detected through the normal means in use today (i.e., TAVG and AT deviation alarms). Although unlikely, the RTD (or its electronics channel) can fail graoually, causing a gradual change in -the loop temperature i
measurements.
[
,)a,c The detailed procedure for cerrecting for a failed hot leg RTD is presented below:
_ a,C
\\
I i
l I
f 1701v:1D/122288 47
e WESTINGHOUSE CLASS 3 a,c 4
l
.i l
l I
i i
l i
I I
l i
{
i l
l l
l l
{
1701v:10/122288 48
_______..J
1 l
l l
WESTINGHOUSE CLASS 3 i
a,c i
1
)
l l
1
{
1 1
i l
l 1
I I
i 1
l j
l l
l l
l 1
- 1701v:1D/122288 49
n.-----__
.e WESTINGHOUSE' CLASS 3 1
APPENDIX n
CALCULATION OF HOT LEG TEMPERATURE BIAS 6
8,C i
j
)
1 l
1 i
d i
1 3
e
- a 1701v:1D/122288 50 t