ML20080F329
| ML20080F329 | |
| Person / Time | |
|---|---|
| Site: | McGuire, Mcguire  |
| Issue date: | 01/12/1995 |
| From: | Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML20080F327 | List: |
| References | |
| NUDOCS 9501200033 | |
| Download: ML20080F329 (16) | |
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UNITED STATES
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NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20666 4 001
,o SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION o
RELATED TO AMENDMENT NO. 153 TO FACILITY OPERATING LICENSE NPF-9 AND AMENDMENT NO. 135 TO FACILITY OPERATING LICENSE NPF-17 DUKE POWER COMPANY t
MCGUIRE NUCLEAR STATION. UNITS 1 AND 2 DOCKET NOS. 50-369 AND 50-370 Since a single request was made by Duke Power Company for changes to the McGuire and Catawba Nuclear Stations, Units 1 and 2, Technical Specifications, a single safety evaluation was prepared to cover the request.
1.0 INTRODUCTION
By letter dated January 10, 1994 (Ref.1), as supplemented September 15 and March 21, 1994, and January 5 and 10, 1995, Duke Power Company (DPC or the licensee) requested changes to the Technical Specifications (TSs) for the Catawba and McGuire Nuclear Stations, Units 1 and 2.
These changes were related to a change in the method for measuring reactor coolant system (RCS) flow rate. The minimum RCS flow rate requirement is related to Departure from j
Nucleate Boiling (DNB) parameters for steady-state operation and also impacts the TS for reactor trip on low reactor coolant flow (Table 2.2-1).
The September 15, 1994, January 5 and 10, 1995, letters provided clarifying i
information that did not change the scope of the January 10, 1994, i
application, the Federal Register Notice, or the initial proposed no significant han rds consideration determination.
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The method of measuring the RCS flow rate proposed by DPC depends on data from past historical calorimetric heat balances (CHBs) used for calibrating the
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cold leg elbow taps. The proposed method results in a higher RCS flow rate as the effect from an overly conservative hot leg streaming bias is reduced.
Based upon the CHB method, the Catawba TS allows for a tradeoff of 2% power for each 1% reduction in RCS flow rate up to a 10% reduction in RCS flow rate.
Catawba Unit I was operating at 98% of full power as it could not meet the full power RCS flow rate requirements of TS 4.2.5.3.
Therefore, the proposed method was initially revietod for Catawba Unit 1 only as a short-term solution to enable operation at full power for the remainder of the current cycle 8 operation. The short-term solution was evaluated and was found to be acceptable for the remainder of the cycle 8 (Ref.11).
Subsequent to the short-term approval, the review continued in order to determine the acceptability as a permanent solution. Additional information was supplied by DPC in the meeting summaries of February 10,1994 (Ref. 2) and March 16,1994 (Ref. 3) and letters of March 21, 1994 (Ref. 9), September 15, 1994 (Ref. 10), January 5, 1995 (Ref. 12), and January 10, 1995 (Ref. 13).
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9501200033 950112 PDR ADOCK 05000369 P
PDR.
'1 The licen.cee requested that the following TSs be modified to reflect the changes required from the proposed method of measuring RCS flow:
A.
Catawba,. Units 1 and 2:
1)
Table 2.2-1, Reactor Trip System Instrumentation Trip Setpoints, Functional Unit 11: The trip setpoint for the minimum measured flow rate limit per loop was changed from equal or greater than 90% to equal or greater than 91%. The allowable value was changed from equal or greater than 88.9% to equal or greater than 89.7%.
2)
TS 3/4.2.5 DNB Parameters: for 4.2.5.3.
For the method of i
measuring RCS flow rate, the " precision heat balance" requirement was removed.
3)
Figure 3.2-1, Reactor Coolant System Total Flow Rate Versus Rated Thermal Power - Four Loops in Operation. The flow measurement uncertainty value was changed from 2.2% to 1.9%.
4)
TS B 3/4.2.5 DNB Parameters:
Remove " measurement error of 2.1%" and add " measurement uncertainty, greater than or equal to the value stated on Figure 3.2-1".
Remove discussion on obtaining RCS total flow rate from precision heat balance.
i Insert the following:
"The measurement error for RCS total flow rate is based upon the performance of past heat balances. Sets of elbow tap coefficients, as determined during these heat balances, were averaged for each elbow tap to provide a single set of elbow tap coefficients for use in calculating RCS flow. This set of coefficients establishes the calibration of the RCS flow rate indicators and becomes the set of elbow tap coefficients used for RCS flow measurement. Potential fouling of the feedwater venturi, which might not be detected, could bias the result from these heat balances in a non-conservative manner."
B.
McGuire, Units 1 and 2:
1)
Table 2.2-1, Reactor Trip System Instrumentation Trip Setpoints, functional Unit 11: The trip setpoint for minimum measurcq flow limit per loop was changed from equal or greater than 90% to equal or greater than 91%. The allowable value was changed from equal or greater than 88.8% to equal or greater than 90%.
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TS 3/4.2.5 DNB Parameters:
for 4.2.5.3.
For the method of measuring RCS flow rate, the " precision heat balance" requirement was removed. Also removed were the phrases, "of Surveillance 4.2.3.5" and "in connection with Surveillance 4.2.3.5" under Table Notation in Table 4.3-1.
3)
Figure 3.2 -1, Reactor Coolant System Total Flow Rate Versus Rated Thermal Power - Four Loops in Operation. The flow measurement uncertainty value was changed from 1.7% to 1.8%.
4)
TS B 3/4.2.5 DNB Parameters:
Remove "measurament error of 1.7%" and add " measurement uncertainty, greater than or equal to the value stated on Figure 3.2-1".
Remove discussion on obtaining RCS total flow rate from precision heat balance.
Insert the following:
"The measurement error for dCS total flow rate is based upon the performance of past heat balances. Sets of elbow tap coefficients, as determined during these heat balances, were averaged for each elbow tap to provide a single set of elbow tap coefficients for use in calculating RCS flow. This set of coefficients establishes the calibration of the RCS flow rate indicators and becomes the set of elbow tap coefficients used for RCS flow measurement.
Potential fouling of the feedwater venturi, which might not be detected, could bias the result from these heat balances in a non-conservative manner."
2.0 BACKGROUND
Because of the effect of the current use of low leakage core loading in the DPC plants, there is increased hot leg temperature streaming. The lower leakage core designs have a higher percentage of the core power produced in the inner core regions. This leads to an increased temperature distribution (skewing) within the hot leg due to incomplete mixing in the upper plenum.
Therefore, the CHB method for obtaining RCS flow rate now has more uncertainty.
Because of the dewing of the temperature profile from the increased hot leg streaming, the three resistance temperature devices (RTDs) in each hot leg have ovnstated the average bulk temperature, resulting in an overly conservative temperature bias. This results in a reduced RCS flow rate value.
This problem from increased hot leg temperature streaming is common in various degrees to other plants using low leakage core loading. Therefore DPC has proposed another method using the cold leg elbow taps to measure the RCS flow rate.
In addition to the added conservatism from hot leg temperature streaming, there are other effects that are adversely affecting the RCS flow rate, such
! as the degradation of the stcam generator (SG) tubes. This necessitates that tubes be plugged or sleeved, which increases the pressure drop in the steam generators and consequently reduces flow rate through the core. Other changes that can affect the RCS flow rate are changes in fuel design and possibly pump wear. As a result of these effects it is more difficult to ensure meeting the Technical Specification (TS) minimum flow requirements. These effects contributed to the inability of Catawba Unit 1 to meet the TS minimum RCS flow requirement using the CHB method.
The evaluation of the proposed method includes the following topics below: (1) introduction, (2) current method of RCS flow rate measurement, (3)
DPC-proposed new method for RCS flow measurement, (4) assessment of the long-term solution for DPC RCS flow rate measurement, (5) the flow measurement uncertainty, and (6) changes to the reactor trip setpoints.
3.0 EVALUATION 3.1 Introduction The RCS flow rate is one of the inputs for calculation of the Departure from Nucleate Boiling Ratio (DNBR). The transient and accident analyses include as inputs initial conditions of RCS thermal design flow. The minimum RCS flow rate requirement in the Technical Specifications is consistent with the assumed RCS thermal design flow.
The criteria established in 10 CFR 50, Appendix A, require a high degree of assurance that specified acceptable fuel design limits (SAFDL) are not exceeded. The SAFDLs for anticipated operational occurrences (A00) are that neither DNB nor melting at the fuel centerline occurs. The results of the safety analyses calculation are used to assure that the SAFDLs are met. The nuclear industry has developed Limiting Safety System Settings (LSSS) methodologies which combine uncertainties statistically. The validity of such methodologies requires that input uncertainties be statistically valid.
The various aspects of RCS flow rate measurement using both the DPC current and proposed methodology are discussed below.
3.2 Aspects of Current DPC Method of RCS Flow Rate Measurement 3.2.1 Current Method for RCS Flow Rate Measurement In the current method, the RCS flow rate is obtained from a calorimetric heat balance (CHB) which is taken on each side of the steam generator. The flow rate on the secondary side is measured by the laboratory calibrated feedwater venturi meters. The primary side heat balance in conjunction with the secondary side heat balance is used to derive the RCS flow rate.
The accuracy of this method of obtaining the RCS flow rate is based on a detailed flow measurement uncertainty (FMU) analysis for the plant-specific instrumentation which requires evaluation and approval by the NRC. Originally most plants used a FMU of 3.5% which was considered to be a very conservative value. Currently, most plants have a FMU uncertainty value less that 3.5%
based on approved methods for combining uncertainties, such as related to
i setpoint methodology (Ref. 4, 5, 6 and 7) and other guidance for assessing uncertainties provided by NRC (Ref. 8). The RCS flow rate is measured witim.
the desired probability and confidence level. The errors in parameters for htaining flow measurement include errors classified as precision (random) rors and bias (fixed) errors. These are combined to obtain the overall uncertainty. The FMU value is documented in the Technical Specifications and is needed to assure that the minimum RCS measured flow rate is above the RCS thermal design flow.
3.2.2 Elbow Tao Confiouration The DPC cold leg elbow tap configuration for RCS flow rate measurement is not calibrated in advance in a laboratory. However, the cold leg elbow pressure drop is benchmarked (normalized) against the established RCS flow rate for each cycle based on the single full power data point calculated from the precision calorimetric heat balance (CHB) at each refueling.
Although DPC benchmarked RCS flow at 100% power to flow, a benchmark at 90% power to flow to coincide with the Low Flow Trip would provide more conservatism. However, the impact of this change would be minimal.
The purpose of the elbow tap reading for the CHB method is to ascertain that the full-power steady-state flow rate has not decreased during the cycle. The elbow tap pressure drop is also used to measure the reduced RCS flow rate for the low flow reactor trip. This is accomplished by using the relationship between pressure drop and flow rate from the full-power calorimetric heat balance data point to obtain an elbow tap flow correlation coefficient from which to extrapolate a flow rate value.
The licensee provided information (Ref. 3) regarding the use of the cold leg elbow taps for the Catawba and McGuire plants. The pressure drops are obtained from three sets of pressure taps in each of the cold leg elbows.
After a short pipe run from the steam generator exit, the RCS flow from the steam generator flows through a 31" inside diameter pipe in a relatively short pipe run to the RCS pump. This pipe run includes two 90 degree pipe bends separated by a short straight pipe run. The elbow taps are located in a plane 22 degrees and 30 seconds after the start of the first 90 degree elbow turn.
One tap is located on the outside pipe radius. This tap is used as a common tap to obtain three sets of pressure drop data in connection with three other taps located close to each other on the inside pipe radius.
3.3 DPC Proposed New Method for RCS Flow Rate Measurement 3.3.1 RCS Flow Rate Compared to Hydraulic Calculations The licensee presented the results of a study relating to their proposed new method for RCS flow rate measurement. This study included pertinent data compiled from the past refuelings that related to the RCS flow rate measurement. The data and information for each cycle included:
1.
the FMU value, 2.
RCS flow rate obtained from the calorimetric heat balance, 3.
elbow tap pressure drop (inches of water),
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the cold leg water density 5.
calculated elbow tap flow coefficient from the CHB, 6.
amount of steam generator tube plugging, 7.
hot leg temperature for each RTD in each of the three loops, 8.
delta T temperature (Thot-Tcold),
9.
modifications (such as, steam generator tube plugging, changes in fuel type, upflow modifications, elbow tap transmitters replaced),
The licensee made hydraulic calculations to deconstrate their ability to accurately obtain the estimated RCS flow rate for each cycle using the initial i
RCS pump flow rate test data. The RCS pump test data was used with pressure drop calculations of the primary loop to predict the best estimate RCS flow rate for each cycle. The calculations included those for the primary system in its original condition during the first cycle and then for succeeding cycles. The calculations for each cycle included the cumulative effects of changes from modifications such as steam generator tube plugging, fuel type, upflow modifications, etc.
The licensee compared the RCS flow rates for the previous cycles from three methods: (1) predictions from hydraulic calculations, (2) the current CHB method, and (3) a proposed elbow tap method explained in Section 3.3.2.
t As an example, the results from the first two methods applied to Catawba Unit 1 (the methods are also applicable to McGuire) are shown in Figure 1 and indicate that when the plant was initially started there was a relatively close agreement between the RCS flow rate predicted from the hydraulic calculation and the RCS flow rate calculated from the CHB. This relatively close agreement (except for the data point between 1988 and 1990) follows until 1991. In succeeding cycles after 1991, the two methods deviate, with the CHB method showing less RCS flow rate than that from the hydraulic calculation I
method, The difference is understood to be due to the overly conservative effects on the CHB method from hot leg streaming introduced with low leakage core loading.
Figure 1 indicates that the RCS flow rate for Catawba Unit 1 for the current cycle 8 using the CHB method for RCS flow rate is less than the TS limit of 382,000 gpm for full power operation.
Figure 1 also indicates that the flow rate obtained by the use of the proposed elbow tap method has a value that is greater than the TS limit.
3.3.2 Proposed New Method for RCS Flow Measurement Usino Elbow Taos In the new method proposed by DPC, the RCS flow rate is measured by using the elbow tap APs and the cold leg density to calculate the flow rate. The flow rate is proportional to the square root of the AP as measured by the elbow taps.
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f In the new method proposed by DPC, the flow correlation coefficient is first obtained from the equation below for each elbow tap using data from past calorimetric heat balances.
K, - m,/J(AP,)(p,)
l the elbow tap flow correlation coefficient, where:
K, m,
the RCS flow rate measured with the precision CHB, AP, - the elbow tap pressure drop measurement, and the cold leg density.
p, This past data is used as a standard to obtain a flow correlation coefficient for the elbow tap readings. The final flow coefficient value for each elbow tap is based on the average value from past cycles.
i The flow rate is calculated for each of the three elbow taps in a loop. Then the three flows are averaged to obtain the loop flow. The loop flows are then added to obtain the total RCS flow rate.
The flow coefficients (per loop elbow tap) as obtained from the above method are proposed to be " frozen" for all future cycles. The selection of the
" frozen" K value (elbow tap coefficient) is influenced by the number of cycles chosen on which to base the K value. The flow coefficients from the previous cycles include the early ones, which did not have the conservatism due to hot leg streaming, as well as the later flow coefficients, which have added conservatism from hot leg streaming. The flow coefficients proposed by DPC for the Catawba and McGuire plants are listed in Table 1.
3.3.3 Anoroaches for Elbow Tao Based Flow Indication 3.3.3.1 Use of Elbow Taos In using elbow taps for indication of RCS flow rate, one should assure that:
- 1. There is reasonable confirmation that the elbow tap correlation used to determine RCS flow rate is accurate to within a known uncertainty and bias or that the perceived rate (correlation determined rate including uncertainty and bias) is less than the actual flow rate.
- 2. There is reasonable confirmation to assure that the proposed method of determining RCS flow rate remains within acceptable bounds of accuracy.
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Reasonable confirmation that the originally determined RCS flow rate is accurate to within a known uncertainty and/or that it is less than the actual i
flow rate should be supported by either:
Applicable flow test data that correlates RCS flow instrumentation to flow rate, or
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a j Some other method of correlating RCS flow rate to the RCS flow instrumentation.
3.3.3.2 Assurance to Show that Correlation Remains Viable With an elbow tap correlation and an acceptance bound established, there is need is to assure that the correlation remains viable. A reasonable approach is to provide an analysis program that correlates all phpical changes in the i
RCS flow path to the RCS flow rate and use this for confiriation of the elbow j
tap measurements of flow rate.
1 To confirm this, one should demonstrate that the elbow tap-based flow rate t
indication is within the uncertainty bound that was established for.the elbow tap correlation when compared to an analysis prediction. Primary emphasis upon the analysis is acceptable since no change in elbow tap correlation is anticipated when physical changes are made in the plant.
An acceptable analysis program is one that accurately calculates plant changes in pump performance, core bundle changes, SG tube plugging, SG tube sleeving, l
SG replacement, and any other physical changes in the RCS that affect the RCS flow rate (the same criteria as applied to the above confirmation process).
Acceptability is established by comparing analysis results with available plant data.
1.
If the proposed elbow tap correlation-is "best-estimate," then the staff will expect a direct comparison of elbow tap determined flow rate based upon the proposed elbow tap correlation.
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2.
If the elbow tap correlation is conservative, then the staff will expect two comparisons - one with a best-estimate correlation
.t coefficient that provides the best fit to the analysis and the other with the proposed correlation.
I 3.
If the elbow tap determined flow rate crosses over and becomes less conservative than the analytically determined flow rate, the NRC should be contacted for further review of acceptability.
3.4 Assessment of the DPC Proposed Method for RCS Flow Rate Measurement The staff believes that the most important potential safety need directly i
associated with RCS flow rate is maintenance of an adequate margin to prenent departure from nucleate boiling. The next safety need is providing reacterr trip due to a low RCS flow rate, with the concerns being departure from nucleate boiling and an overtemperature condition. However, the importance of RCS flow rate to reactor trip is diminished by other trip parameters, such as
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loss of pump power, too large a temperature difference between the hot and cold legs, or high pressure; trip parameters that will often cause trip prior I
to a flow rate trip.
j The inaccuracy of the current method of obtaining RCS flow rate by a CHB is due to. hot leg streaming.
In regard to this, DPC stated (Ref. 10) that the
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only information available regarding the temperature distribution in the hot l
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1eg is from the hot leg RTDs themselves. This.information does not provide enough data points to give an accurate temperature profile.
i The DPC-proposed method uses the cold leg elbow taps to measure the RCS flow i
rate as an equivalent but more accurate method than the CHB method. This is the basis on which the staff evaluation is made. The DPC method uses a number of previous determinations of elbow tap correlation coefficients, K, to i
" freeze" the value of K.
It uses the K to obtain RCS loop flow rates without further calorimetric calibration,s. These elbow tap coefficients are
. listed in Table 1 and are based on 6 cycles of data for Catawba Units 1 and 2, i
and 5 and 8 cycles of data for McGuire Units 1 and 2, respectively (Ref. 13).
i 3.4.1 Review of Possible Detrimental Effects in the Use of Elbow Taos
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The licensee presented information (Ref.10) to support the conclusion that a
the components exposed to water in the elbow tap differential pressure instrumentation do not change. over the life of the plant. Deposits in the RCS from impurities in the reactor coolant are expected to be small or j
nonexistent. Most deposits of impurities in the reactor coolant are expected I
to occur in the hottest portions of the RCS and in regions experiencing the lowest flow.
If preferential deposits were to occur in the region of the
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taps, the reduction in pipe diameter would be extremely small in comparison to the diameter of the cold leg (31"). Fouling or deposits within the instrument i
tubing between the elbow tap and the differential pressure instrument is not a concern since no flow is transmitted within the tubing.
l In addition, DPC stated (Ref.10) that erosion (flow accelerated corrosion) is not a concern since the velocity of the RCS fluid is small relative to velocities known to cause erosion in stainless steel. Erosion of the RCS piping will be small or nonexistent during plant life.
I The licensee stated (Ref.10) that the elbow taps have been putioned on the elbow in such a manner that velocity pressure components and turpulence effects are minimized while not impacting the differential pressure indications.
Since the piping between the elbow tap and the differential 1
pressure instrument is used to transmit the pressure signal only, any velocity component of the turbulent RCS flow which is imparted to the' tap location will result in random noise in the pressure signal. To check for effects which may affect the calibration of the elbow meter, comparisons to the analytical flow l
model prediction of flow will be used to determine the extent to which the elbow tap calculated flow reflects actual flow changes.
The staff has judged that the DPC explanations are reasonable and has therefore accepted the DPC explanations as to why the above effects, including crud buildup, fouling, erosion and turbulence, do not affect the accuracy of the flow rate values for the Catawba and McGuire plants.
3.4.2 DPC Analytic Model for Flow Rate Prediction As stated in Section 3.3.3, a reasonable analytic RCS flow model is one that accurately predicts flow meter indication changes following known changes to
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i the RCS configuration. The flow model must correctly calculate the effect of
- changes such as those from steam generator tube plugging and sleeving and from replacing fuel bundles with bundles having different flow characteristics.
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The licensee presented information (Ref.10) on their analytic RCS flow model for application to the Catawba and McGuire plants. This information included the applicable _ equations. The licensee stated (Ref.12) that the analytic model was formulated and reviewed under a quality. assurance program which meets the requirement of 10 CFR Appendix B (QA CoM ition 1). Tables of l
information were presented of: (1) detailed RCS loop pressure drops, (2) flow fractions used to adjust the APs in the downconer and the core regions, (3) i pressure drops for several types of fuel in different regions _ (botton nozzle, i
core, top nozzle) for full and partial cores, (4) steam generator input for pressure drop calculations, (5) reactor coolant pump head curves,. and-(6)
.i information on tube plugging. Duke Power provided information showing that i
the RCS flow rates from the analytic model predict the flow rate from the first cycle to the current cycle.
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The staff review of the results indicate that the analytic model has inputs l
for ' calculating RCS flow rates that account for changes in the configuration, such as changes in type of fuel and various degrees of steam generator tube plugging. Since the results of the flow rate from the analytic model compare.
reasonably well to the data, as indicated below in Section 3.4.3, the results confirm the validity of the analytic model. We, therefore, find the analytic flow model to provide an acceptable prediction of the RCS flow rate.
3.4.3 DPC Flow Calibration Process and Comparison to An21vtic Prediction I
The licensee presented the results for the RCS flow rate obtained for each of j
the 4 loops for both the Catawba and McGuire plants from two methods: (1) the elbow tap AP readings, using the proposed elbow tap coefficients shown in Table 1, and (2) the analytic model.
For example, for Catawba Unit 1, the data for individual loop flows as determined by elbow tap AP's from the period from 1985 to 1993 were presented for each of the 4 loops (Figure 14 of Ref. 10). Similar data were presented l
for the individual loop flows as determined by the analytic flow model (Figure 17 of Ref. 10). The cycles during this period included changes due to i
SG tube plugging and changes in fuel type.
j The licensee pointed out that some of the data from the elbow tap readings were bad due to excessive drifting of some of the pressure transmitters and i
therefore were eliminated. The staff understands that DPC continually i
examines the elbow ' tap data carefully in order to obtain the correct RCS flow l
values.
The licensee noted that since the startup of Catawba Unit 1, the calorimetric
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flows following the November 1987 calorimetric have basically trended downward consistent with the trend in AT, but in excess of that expected by plant geometry changes. Since plant startup, the calorimetrics have indicated that the total RCS flow has dropped approximately 21,000 gpm (Figure 13 of Ref.12), whereas the elbow tap and analytic model flow have indicated a drop
. in total flow of approximately 9,000 gpm and 5,000 gpm respectively (Figures 14 & 16 of Ref. 12). The difference between these flow indications is the
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excess elbow tap AP transmitter drift during the early calorimetrics which caused the unsubstantiated indicated flow increase. This indicates a significant impact from hot leg streaming as it shows that 12,000 to 16,000 gpa of the calorimetric flow decrease can be attributed to the hot leg i
streaming phenomenon.
j The individual loop flows varied. However, for the Catawba Unit I plant, the two methods for obtaining RCS flow (elbow tap AP and analytic model) were i
shown to agree within a band of approximately 2%. The two methods are in i
closer agreement in the early cycles when there was less effects from hot leg streaming. The method using the elbow tap flow rate provided the more conservative values. As long as the elbow tap flow rate values are more conservative than the values from the analytic method, the staff finds the use of the elbow tap method for RCS flow rate measurement to be acceptable.
l The licensee also provided results, using the same comparisons as above, for the Catawba Unit 2 and McGuire Units 1 and 2 plants.
I With respect to the calorimetric heat balance (CHB) test, the staff agrees that its usage for calibration of elbow tap instrumentation can be i
discontinued. However, DPC committed (Ref. 12) to continue the CHB. This is used for other needs and it can be used as part of the program to assure discovery of unexpected behavior.
3.4.4 Conclusions on Use of Elbow Taos for RCS Flow Measurement The staff has reviewed the DPC proposed method for measuring RCS flow rate by means of the cold leg elbow taps for the Catawba and McGuire plants. Both plants use the elbow tap coefficients shown in Table 1 of this evaluation which were obtained from Reference 1.
The licensee is to submit for NRC i
review and approval any future changes for the elbow tap coefficients as i
documented in Table 1.
In general, the licensee should follow the approaches listed in Section 3.3.3.
This includes the need for an analytic program which correlates all physical changes in the RCS flow path to the RCS flow rate in advance and which will be i
used for the confirmation of the elbow tap measurements of flow rate. Also, if the elbow tap-determined flow rate approaches crossing over and becoming less conservative than the analytically determined flow rate, the NRC must be 5
contacted for further review of the methodology. The licensee committed to this action and also committed to the following:
continue to perform calorimetric heat balance testing as before, a
notify the NRC of any changes to the hydraulic flow model in a e
manner which affects the results of the model, t
notify the NRC of any change in the use of the calorimetrics and l
e fuel cycles data.
These committments were documented in letters from DPC dated January 5 (Ref. 12) and January 10, 1995 (Ref. 13).
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._ The elbow taps provide a pressure of several hundred inches of water. The elbow tap configuration makes it less precise over a range of flow conditions than a venturi, but the restricted usage to the small range of Reynold's Numbers associated with variation within normal power operations should help alleviate such concerns. Once calibrated, and provided uncertainty and any potential hardware changes are correctly considered, the staff finds the elbow tap method of obtaining RCS flow rate to be acceptable.
3.5 Flow Measurement Uncertainty The DPC request for a change in the flow measurement uncertainty (FMU) value was not reviewed by the staff. The licensee withdrew the request for this change (Ref.12). Therefore, it is not necessary to address any changes to Figure 3.2-1 related to flow measurement uncertainty.
3.6 Chanaes to Reactor Trio Setooints The staff also reviewed the changes in the reactor trip setpoints in Table 2.2-1 for both the Catawba and McGuire plants. These changes were to account for the new method of measuring the RCS flow rate. These changes account for an increase in the channel statistical allowance for the low flow trip signal attributable to the inclusion of allowances for elbow tap uncertainties since these will no longer be normalized each 18 months by the CHB process. Based on the review of the reactor trip measurement uncertainties, the staff finds the proposed low flow trip setpoints and allowable values to be acceptable.
4.0 Technical Specification Chanaes The Technical Specifications changes proposH by DPC are noted in Section 1.0.
Except for the TS on Figure 3.2-1 relating to the FMU, which DPC withdrew as noted in Section 3.5, all were found to be acceptable based on the above evaluations by the staff.
Based on the evaluation in Section 3.0, the staff has found the TS changes to be acceptable for the Catawba and McGuire plants.
5.0 STATE CONSVLTATION In accordance with the Commission's regulations, the North Carolina State i
official was notified of the proposed issuance of the amendments. The State official had no comments.
6.0 ENVIRONMENTAL CONSIDERATION
The amendments change requirements with respect to installation or use of a facility component located within the restricted area as defined in 10 CFR Part 20 and change surveillance requirements. The NRC staff has determined that the amendments involve no significant increase in the amounts, and no i
significant change in the types, of any effluents that may be released offsite, and that there is no significant increase in individual or cumulative occupational radiation exposure. The Commission has previously issued a proposed finding that the amendments invo!ve no significant hazards
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I consideration, and there has been no public comment on such finding (59 FR 7688 dated February 16,1994). Accordingly, the amendments meet the eligibility criteria for categorical exclusion set forth in 10 CFR i
51.22(c)(9).
Pursuant to 10 CFR 51.22(b) no environmental impact statement or environmental assessment need be prepared in connection with the issuance of the amendments.
7.0 CONCLUSION
The Commission has concluded, based on the considerations discussed above, that:
(1) there is reasonable assurance that the health and safety of the public will not be endangered by operation in the proposed manner, (2) such activities will be conducted in compliance with the Commission's regulations, and (3) the issuance of the amendments will not be inimical to the common defense and security or to the health and safety of the public.
Principal Contributor:
H. Balukjian Date: January 12, 1995 i
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8.0 REFERENCES
1.
Letter from M. S. Tuckman, DPC, to USNRC, dated January 10, 1994.
2.
NRC Summary of February 10, 1994, meeting with Duke Power Company on RCS Flow Measurement Methodology, dated April 13, 1994 (includes DPC answers to request for additional information).
3.
NRC Summary of March 16, 1994, meeting with Duke Power Company on RCS Flow Measurement Methodology, dated April 6,1994 (includes DPC responses to request for additional information, dated March 7,1994).
4.
USNRC Regulatory Guide 1.105, " Instrument Setpoints for Safety-Related Systems."
5.
Criterion 13, " Instrumentation and Control," of Appendix A, " General Design Criteria for Nuclear Power Plants," to 10 CFR Part 50.
6.
Criterion 20, " Protection System Function," of Appendix A to 10 CFR 50.
7.
ISA-S67.04-1982, "Setpoints for Nuclear Safety-Related Instrumentation Used in Nuclear Power Plants."
8.
NUREG/CR-3659, A Mathematical Model for Assessing the Uncertainties of Instrumentation Measurements for Power and Flow of PWR Reactors,1984.
9.
Letter from M. S. Tuckman, DPC, to USNRC, dated March 21, 1994, t
10.
Letter from M. S. Tuckman, DPC, to USNRC, dated September 15, 1994.
11.
Letter from R. E. Martin, NRC, to D. Rehn, DPC, dated March 30, 1994, transmitting Amendments 110 and 116 to licenses NPF-35 and NPF-52 for Catawba Units 1 and 2, respectively.
1 i
h
~
CNS-1 Flow Comparison Between Analyt' col Flow Prediction, Proposed Elbow Top Method And Colorimetric Flow dO
~
B&W fuel l
,3 2
y'
~,
/
.,'.,' e I
f g
395000 --
's s, s s E
%s
-'As a
sg_
s s
T 390000 -
' 'n 32 u.
385000
- -*- - Proposed Elbow 100 itow TS Limit - 38,200 gpm
- - - * - Andyficd flow Prodcfon 380000 0
Colonmetric Flow 375000 l
l l
l
- ~ ~ "
Nov-84 Mar-86 Aug-87 Dec-88 May-90 Sep-91 Jan-93 Jun-94 Date Figure - !
V. ~
le
.i
- s TA B L E - i Elbow Tap Coefficients Taps McGuire Unit 1 McGuire Unit 2 Catawba Unit 1 Catawba Unit 2 Imp A, Tap I 0.30695 0.30174 0.29773 0.30365 140p A, Tap II 0.29821 0.29183 0.29348 0.29183 loop A, Tap III 0.30203 0.29781 0.29515 0.30020 Imp B, Tap I 0.28441 0.29909 0.30410 0.30021 Imp B, Tap II 0.28409 0.29163 0.30803 0.28332 Imp B, Tap III 0.28722 0.29173 0.30444 0.30258 Loop C, Tap I 0.28624 0.29155 0.28915 0.31370 Loop C, Tap II 0.31312 0.29399 0.28489-0.29362 Loop C, Tap III 0.29923 0.29250 0.29097 0.30150 Imp D. Tap i 0.30704 0.30037 0.30331 0.29698 Loop D, Tap II 0.29401 0.29755 0.29932 0.2 % 85 Loop D. Tap III 0.30174 0.29844 0.31051 0.29886 l
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