ML20217J465

Requests Addl Info on Proposed License Amend Re Reactor Coolant Sys Flow Monitoring for Plant,Units 1 & 2

ML20217J465
Person / Time
Site:	South Texas
Issue date:	08/11/1997
From:	Alexion T NRC (Affiliation Not Assigned)
To:	Cottle W HOUSTON LIGHTING & POWER CO.
References
TAC-M99245, TAC-M99246, NUDOCS 9708140266
Download: ML20217J465 (11)

Text

_. _ - __ __ _ _ . . _ _ _ . _ . . _. -

August 11, 1997 Mr. William T. Cottle Group-.Vice-President, Nuclear Houston Lighting & Power Company

. South Texas Project Electric-Generating Station

-P.O. Box 289

=Wadsworth,-TX 77483 ,

SUBJECT:

-REQUEST FOR ADDITIONAL INFORMATION ON THE PROPOSED LICENSE AMENDMENT REGARDING REACTOR COOLANT SYSTEM FLOW MONITORING SOUTH TEXAS PROJECT, UNITS 1 AND 2 (STP) (TAC NOS. M99245-AND M99246)

Dear Mr.1Cottle:

The staff has reviewed your application for amendment dated August 6,1997, to allow the use of elbow taps to measure reactor coolant system (RCS) flow rate at the STP, The staff has identified a need for additional information as  !

requested in the enclosed request for additional information (RAI).

-If you have any questions regarding this request, please contact me at (301) 415-1326.

Sincerely, Orig signed by Thomas W.-Alexion, Project Manager Project Directorate IV-1 >

Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation )

Docket Nos.-50-498 and 50-499

Enclosure:

Request for Additional Information

=cc w/ enc 1: -See next page /

DISTRIBUTION: /

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,1 NUCLEAR REGULATORY COMMISSION

• P WASHINGTON D.C. speeHoot

• • • • • /j August 11, 1997 i

Mr. William T. Cottle Group Vice-President, Nuclear Houston Lighting & Power Company South Texas Project Electric Generating Station P.O. Box 289 Wadsworth, TX 77483

SUBJECT:

REQUEST FOR ADDITIONAL INFORMATION ON THE PROPOSED LICENSE AMENDMENT REGARDING REACTOR COOLANT SYSTEM FLOW MONITORING - SOUTH TEXAS PROJECT, UNITS 1 AND 2 (STP) (TAC NOS. M99245 AND M99246)

Dear Mr. Cottle:

The staff has reviewed your application for amendment dated Auguit 6, 1997, to allow the use of elbow taps to measure reactor coolant system (R S) flow rate at the STP. The staff has identified a need for additional infc1 nation as-requested in the enclosed request for additional information (RA').

If you Save any questions regarding this request, please contact me at (301) 415-136.

, Sincerely, n

rJ m n .Jhpu Thomas W. Alexion, Project planager Project Directorate IV ,

Division of Reactor Projects III/IV Office of Nuclear Reactor Regulation Docket Nos. 50-498 and 50-499

Enclosure:

Request for Additional Information cc w/ encl: See next page

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• 4e, u - -* --

Mr. William T. Cottle Houston Lighting & Power Company South Texas, Units 1 & 2 Cc:

Mr. David P. Loveless Jack R. Newman, Esq.

Senior Resident inspector Morgan, Lewis & Bockius U.S. Nuclear Regulatory Commission 1800 M Street, N.W.

P. O. Box 910 Washington, DC 20036-5869 Bay City TX 77414 Mr. Lawrence E. Martin Mr. J. C. Lanier/M. B. Lee General Manager, Nuclear Assurance Licensing City of Austin Houston Lighting and Power Company Electric Utility Department P. O. Box 289 721 Barton Springs Road Wadsworth, TX 77483 Austin, TX 78704 Rufus S. Scott Mr. M. T. Hardt Associate General Counsel Mr. W. C. Gunst Houston Lighting and Power Company City Public Service Board P. O. Box 61867 P. O. Box 1771 Houston, TX 77208 San Antonio, TX 78296 Joseph R. Egan, Esq.

Mr. G. E. Vaughn/C. A. Johnson Egan & Associates, P.C.

Central Power and Light Company 2300 N Street, N.W.

P. O. Box 289 Washington, DC 20037 Mail Code: N5012 Wadsworth, TX 74483 Office of the Governor ATTN: Andy Barrett, Director INP0 Environmental Policy Records Center P. O. Box 12428 700 Galleria Parkway Austin, TX 78711 Atlanta, GA 30339-3064 Arthur C. Tate, Director Regional Administrator, Region IV Division of Compliance & Inspection

. U.S. Nuclear Regulatory Commission Bureau of Radiation Control 611 Ryan Plaza Drive, Suite 400 Texas Department of Health Arlington, TX 76011 1100 West 49th Street Austin, TX 78756 Dr. Bertram Wolfe 15453 Via Vaquero Texas Public Utility Commission Monte =Sereno, CA 95030 ATTN: Mr. Glenn W. Dishong 7800 Shoal Creek Blvd.

Judge, Matagorda County Suite 400N Matagorda County. Courthouse Austin, TX 78757-1024 1700 Seventh Street Bay City, TX 77414

1 RE0VLST FOR AD91T10NAL INFORMAT10N PROPOSED AMENDMENT TO ALLOW USE OF ELBOW TAPS TO MEASURE REACTOR COOLANT SYSTEM FLOW RATE

1. Section 2.0 states that surveil'ence requirement (SR) 4.2.5, which currently requires the performance of precision heat balance measurements every 18 months, will no longer specify the method to be used for RCS flow measurement. Explain the elimination of the reference to RCS flow measurement methodology from the SR (i.e., why not reference both the precision heat balance measurements and the specific elbow tap methodology described in the application). Additionally, the proposed SR does not provide a reference as to when the measurements are to be taken. Section 2 of the submittal references 'beginning of cycle" as does the analysis, include such a reference in the SR or justify its ommission. Also include the power level at which the surveillance is to be performed at in the proposed SR (per analysis assumption) or justify its ommission.

2. Based on the change 4 RCS flow measurement methodology, are any revisions required

• the revised thermal design procedure? Normally the RTDP references th t..lorimetric. Has streaming uncertainty increased from the assumptiuns made in the RTDP7 Are the uncertainties for the elbow tap transmitters zerced out in the South Texas RTDP7

3. Describe how the calorimetric uncertainties will be accounted for in the proposed methodology given that the proposed elbow tap correlation method relies on previous calorimetrics.

4. Section 3.4.2 states that calorimetric flows from all fuel cycles are evalcated for use in defining baseline calorimetric flow. What does the term

• evaluated" mean? Was the average for all cycles used? How many cycles of data were utilized?

5. Section 3.4.2, " Baseline Elbow Tap AP," states that the average AP from all elbow taps is used as the basis for the baseline elbow tap coefficient. Considering potential differences in installation and initvidual elbow ta) and hydraulic characteristics, explain why this approach is accepta)1e. The AP data su) plied seems to indicate that loop 4 is consistently different from the otler loops, is this measurement an indication of different flow characteristics or a sensing element installation effects? Would separate flow coefficients for each elbow tap better reflect flows? If you choose to use the proposed averaging method, provk'e a justification of this method including (but not limited to) a compe non of this method to using individual elbow tap correlation and show that your proposed method is conservative.

Identify all alaces (analyses, calculation methods, etc. that may be affected by t1is approach and specify whether this would) result in a net benefit or penalty (i.e., why are you proposing this approach in lieu of correlating each elbow tap individually?).

ENCLOSURE

2-

6. Section 3.4.2, ' Flow Verification for Future Cycles," states the average of all elbow tap & s measured at or near full power... What is considered at or near full power?

7. Section 3.4.2, ' Elbow Tap Flow Measurement Procedure," states that calorimetric flows that fell well outside the allowance (either high or low) should not be used in defining baseline flow. How was the allowance and screening criteria determined? Was this procedure used at South Texas and were any calorimetric measurements deleted from the baseline flow determination.

8. The RTDP calorimetric flow uncertainty is given as a 95/95 value. Do the elbow tap flow measurements and best estimate hydraulic analysis provide equivalent results with regard to the 95/95 value? In Section 3.4.2 of your submittal you proposed to compare R to 1.004*R'. In Section 3.5.2 of your submittal you stated that the best estimate flow analysis has an accuracy of 12%. Discuss how this uncertainty (associated with your best estiinate analytical methodology) is accounted for. Provide a more detailtd justification of your proposal to allow elbow taps to exceed the best estimate flow by as much as 0.4% and still be accepted at a valid measurement of flow. Explain this from an RTDP uncertainty assumption perspective as well as from the perspective of uncertainties assumed in other analyses that include an RCS flow assumption. Provide all places (analyses, calculation methods, etc.) that are affected by this credit.

9. Section 3.5 states that the component & accuracy for the Prairie Island measurements was established by calibrations to be within 11% of the measured op. The sum of the & s measured across the reactor and steam generator were within 1% of the pump & , confirming measurement accuracy.

Explain how this confirms accuracy of the measured M .

10. In Section 3.6.3, " Evaluation of Calorimetric Flows," the second bullet references the " baseline calorimetric flow defined above." Where is this reference in the submittal?

11. Provide and explain plant saecific data and or exptrience of the temperature profile in the lot leg as a result of streaming and its plant specific effect on temperature readings. Provide information on this phenomenon for each cycle considered in your proposed methodology.

Explain the effect of power level on this phenomenon. In addition explain how the hot leg temperature was obtained for the calorimetrics used (i.e., wAs the high, average of each loop or average of all RTDs used?).

12. Provide plant specific configurations of hot leg RTDs and elbow taps.

With regard to RTDs, Figure 3.3-2 seems to indicate that an average of the three RTDs (assuming that they are located at 0, 120, and 2'O w ws-M6de-**'P*db w *rh4-- -a +mw- 4':

degrees) would eliminate the difference. Explain the streaming effect in this case and include a temperature profile plot for the hot leg cross section. Provide similar plots for South Texas.

13. In your cerrelations you neglect any changes in specific volume due to cold leg temperature changes. Provide a justification of this approach with regard to potential future changes in parameters that may affect the specific volume of the cold leg watet (e.g., temperature and pressure).

14. An implicit assumption in your correlation methodology is that the correlation coefficient (K) in the following equation remains constant.

How will your methodology address changes to this coefficient should they occur given that you're proposing to freeze the current coefficients.

W = K (MP)*

15. Section 3.4.1 states.

• tests have demonstrated that elbow tap flow measurements have a high degree of repeatability...." Were such tests performed for configurations similar to )lant installations - with short stretches of straight pipe upstream of tie elbow taps? Provide results and conclusions. (i.e., justify your assumption of repeatability for the plant specific configuration in light of the lack of straight pipe upstream of the elbow taps.)

16. Explain the statement " Repeatability and accuracy are improved when all elbow tap AP measurements are used" in Section 3.4.2 and discuss the benefits realized from this approach.

17. Section 1-5-4 of " Fluid Meters, Their Theory and Applications," 6th Edition, Howard S. Bean, ASME, New York, 1971; reference 1 to your

... be arithmetical mean values submittal, obtained bystates, "Letover averaging the the values wholeofsec pg, tion, A, and. if the fluid motion is not strictiv steady (laminar) but turbulent. a time averaae over the section." How was this considered / applied in your proposed methodology?

18. Sections 1-5-27 and I-5-55 of " Fluid Meters, Their Theory and Applications," 6th Edition, Howard S. Bean, ASME, New York, 1971; reference 1 to your submittal, states, that "a uniform fluid velocity was assumed, thus neglecting any effect of normal stream turbulence." In addition, " Application, Part !! of Fluid Meters, Sixth Edition 1971, Interim Supplement 19.5 on Instrument and Apparatus " ASME, New York, 1972; provides guidance on length of piping required upstream of the elbow taps to ensure uniform velocity profiles. Considering that the recommended length of pipe does not exist upstream of the elbow taps in your plant, discuss how this was addressed in your proposed methodology,

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i 19. ' Flow Messurement Engineering Handbook,' R. W. Miller, McGraw-Hill Book

, Company, New York,19831 gives an accuracy for elbow taps of 14%.

j- - Additionally, tists source states that the minimum length of piping as  !

presented in Fluid Meters (see question above) is necessary to hold  ;

t piping bias errors, due to piping influence, to less than 10.5%. It  !

, further states that an additional 10.5% should be added to the flow-  !

coefficient accuracy value for any decrease in length of pipe. Discuss  !

how each of these factors was addressed in your proposed methodology.  !

List and justify the accuracy and precision values used in your l

< methodology and explain how they were applied.  ;

20. Describe how feedwater venturt fouling and its effect on feedwater measurement uncertainty was addressed in the calorimetrics that will be ,

used to derive the elbow tap coefficients. List the uncertainties for i feedwater measurement and explain how they were used to determine the  !

overall uncertainty. In addition, discuss how feedwater venturi area  !

expansion factor uncertainties were accounted for.

5 21. Discuss the type of quality assurance review performed on the analytical F model. How does this meet the requirements of 10 CFR Part 50 Appendix B7 i In addition, provide data relating to changes in the slant (steam 4 i generator tube plugging, fuel des'gn changes, etc.) t1at have affected flow condition and confim that the model was able to predict these l

i changes accurately. What confirmatory checks were perfomed to ensure t accuracy of the analytical model at South Texast $1nce the RCS loops 4

experience changes at different rates (e.g., steam generator tube plugging) provide this data on a loop specific basis, i '

22. Periodic confirmation of elbow tap characteristics is important in i ensuring reliability. How will you do this? In the proposed methodology you are proposing to use-the best estimate model to confira your elbow

. tap readings. The best estimate methodology is used to confirm that your ,

" measured" flow is in agreement with your expected (predicted) flow.

Discuss the actions that you intend to take (evaluation, recalibrations, n etc.) should the elbow taps read higher / lower than your best estimate ^

predictions to ensure that flow ' measurements" are obtained in an

acceptable manner and that they are not replaced by the unconfirmed analytical' method. The use of 'unconfimed analytical method" in this question refers to a prediction of. flow without confirmation through

. actual measurement. The staff requests that the licensee also commit to 5

= 1)~ notify the NRC of any changes to the hydraulic flow model in a scnner which~affects the results of the model and 2) contact the NRC for further 8

review of the methodology if the elbow tap-determined flow rate exceeds (becomes less conservat' ve than) the analytically determined flow rate.

< 23. Discuss the effect of vibration and turbulence induced noise on elbow tap -

measurement and how this was accounted for in your proposed methodology. '

Address erosion and deposit fomation with respect to the elbow tap f

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1 5-instrument tube connection to the RCS legs. For exam)1e, if the throughwall penetration initially terminates with a starp edge at the leg inner wall surface, does this sharp edpe change with time due to flow impingement? If it changes, what is t!)e effect on indicated behavior?

If it does not change, wiat is the basis for that conclusion?

24. In Section 3.4.2 of ou stated, "If a known hydraulic

change (e.g.,tubepfoursubmittal uggint was made before a cycle, calorimetric flow L

for the cycle should be ad;u)sted so all flows have a common hydraulic

baseline." Was this approach used in your proposed methodology? If so,

discuss how this was done and justify this approach.

l 25. Section 3.6.1 states, 'Considering all of the above, the overall impact i of the hydraulic changes was expected to be 0.3 to 0.9% flow over seven cycles of operation ..." However, Section 3.5.2 states that the best  !

estimate flow analysis has an accuracy of 12%. Exslain how you were able  !

l to predict the flow changes to a better accuracy tian that of the l analytical model. Similar statements were also made for Unit 2.

26. Section 3.6.2 states that AP measurements were obtained at 70% power for some of the cycles. Additionally, this section states that a decrease of 1.2% flow from zero to 100% power and 0.4% from 70% power to 100% power ,

exists. Justify these statements. How was this data obtained? Are you assuming a linear relationship between flow and power? If so, why?

Section 3.6.3 further states that in addition to the calorimetrics at 70%

power, calorimetric data was al:,o obtained shortly after full power was attained. Why was this data not used instead of the 70% data? Also .'

explain the statement, "Another adjustment was made in normalizing flows to the baseline flow to account for the decrease in cold Itg temperature

-in Cycles 6 and 7..."

27. Explain the statement in Section 3.6.4 that less precision was used when averaging cibow tap data during early cycles and how this was accounted i for in uncertainty tems. Also explain the statement that the difference l between elbow tap and best estimate flows would be about 1% if impeller smoothing sctually occurred before Cycle 1 (i.e., What was asaused for -

impeller smoothing and when did it occur? Justify this assumption).

Explain the statement for Unit 2 that if Cycle I had been used to define baseline calorimetric flow, the flow difference in Cycles 5 and 6 would be larger and would be a mNe representative indication of low leakage loading pattern impact. With regard to the statement that based on comparisons of adjusted calorimetric flows in Table 3.6-3, the Cycle 6 -

- flow is almost 25 below the Cycle 1 flow,-it appears that a large portion

, of that difference-is attributable to impeller smoothing and tube L plugging. Present your understanding of what this 2% reduction is j attributable to.  !

L 28. The first plots of Figures 3.6-1 and 3.6-2 show that the elbow tap flows L are higher than the best estimate flows whereas the second plots show the l

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l <everse is true. Explain this difference. Pro' vide a plot which includes

11 of the following (on the same plot) for comparison and/or the data ror such a plot 1) elbow tap flows (per your proposed methodology), 2) calorimetric flows, and 3) best estimate flows.

29. Please address each of the items in Attachment 1, " Staff Guidelines for Use of Elbow Taps for RCS Flow Rate Measurement," Item 1.0, "Use of Elbow Taps " and 2.0, " Assurance to Show that the Elbow Tap Correlation Remains Viable." Explain how your proposed method to measure RCS flow rate addresses each of the items of the above guidelines. Some specific questions pertaining to these items are given below.

30. Provide the correlation used to measure RCS flow rate by the use of elbow taps. If you use a correlation for the elbow taps that is in the form oft m K V(3PT(4J where: m - the RCS flow rate K - the elbow tap flow correlation coefficient AP= the elbow tap pressure drop, and p - the cold leg density please provide the values of correlation coefficient K for each of the 3 taps in each loop of the celd legs and information on determined, including background of the data used,(2)and(1) what how they were conservatism has been applied for these values. It is noted that because the elbow taps are not calibrated in a laboratory environment, as the feedwater venturi meters are, but only normalized against the

! calorimetric heat balance, we expect that a conservative margin will be I applied in this method.

31. Regarding the confirmation of the correlation coefficient K, a hydraulic i analytic prediction method is needed to confirm that the elbow tap-based flow rate indication is within the uncertainty bounds.

Please describe your hydraulic analysis program for estimating RCS flow rate including the inputs needed and the breakdown of items used in the calculations such as: RCS 100) pressure drops, flow fractions used to adjust the pressure drops in tie downcomer and the core regions, pressure drops for fuel, steam generator (SG) pressure drops, reactor coolant pump head, RCS pump wear, and tube plugging. Provide the results of using

this program and also provide its accuracy in predicting RCS flow rate.

The results should show that the analysis program can predict past physical changes, such as from SG tube plugging and sleeving, core bundle changes, etc., within acceptable bounds of accuracy.

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2. '2 7-~~ "~77~

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i Staff Guidelines for Use of Elbow Tans for RCS Flow Rate Measur-- nt i The RCS flow rate is one of the inputs for calculation of the Departure from Nucleate Boiling Ratio fDNBR). The transient and accident analyses include as inputs the initial condition of RCS thermal design flow. The minimum RCS flow

- rate requirement in the Technical Specifications (TS) is consistent with the 1 assumed RCS thermal design flow.

The criteria established in 10 CFR 50. Appendix A require a high degree of are not assurancethatspecifiedacceptablefueldesignlletts(SAFDL)(A00)arethat exceeded. The SAFDLs for anticipated operational occurrences i 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 (LS$$).  !

- methodologies which combine uncertaint' es statistically. The validity of such  !

methodologies requires that input uncertainties be statistically valid. _

1 The staff believes that the most important potential safety need directly <

associated with RCS flow rate is maintenance of an adequate margin to prevent  :

departure from nucleate boiling. The next safety need is providing a reactor i 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 -

loss of pump power, too large a temperature difference between the hot and -

cold legs, or high pressure; trip parameters that will often cause a trip prior-to a flow rate trip. ,

The staff has reviewed ine use of elbow taps for RCS flow measurement previously for another nuclear power plant and has developed guidelines for the acceptability of the use of cold leg elbow taps to measure RCS flow rate.

This guidance follows. ,

1.0 Use of Elbow Tans  ;

In using elbow taps for indication of RCS flow rate, one should assure that:

1.1 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.

.l.2 There is reasonable confimation to assure that the proposed method of i determining RCS flow rate remains within acceptable bounds of accuracy. l 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 flow rate should be supported by either:

ATTACMENT 1-

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(1) App 11able flow test data that correlates RCS flow instrumentation to flow rate, or (2) Some other method of correlating RCS flow rate to the RCS flow instrumentation.

2.0 Assurance to. Show that the Elbow Tan Correlation Remains Viable 2.1 'With an elbow tap correlation and an acceptance bound established, there is need to assure that the correlation remains viable. A reasonable a)proach is to provide an analysis program that correlates all physical c1anges in the RCS flow path to the RCS flow rate and use this for confirmation of the elbow tap measurements of flow rate.

(1) To confirm this, one should demonstrate that the elbow tap-based flow rate indication is within the uncertainty bound that was established-for the elbow tap correlation when compared to an analysis prediction. Primary em)hasis upon the analysis is acceptable since no change in el)ow tap correlation is anticipated when physical changes are made in the plant.

(2) An acce) table analysis program is one that accurately calculates plant c1anges in pump performance, core bundle changes, SG tube SG tube sleeving, SG replacement, and any other physical pluggingIntheRCSthataffecttheRCSflowrate(thesamecriteria changes as applied to the above confirmation process)..

2.2 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.

(2) If the elbow tap correlation is conservative, then the staff will expect two comparisons - one with a best-estimate correlation coefficient that provides the best fit to the analysis and the other with the proposed correlation.

(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.

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