ELV-02942, Responds to Request for Addl Info for Changes for Tech Spec Re Removal of Resistance Temp Detector Bypass Loops

Responds to Request for Addl Info for Changes for Tech Spec Re Removal of Resistance Temp Detector Bypass Loops

ML20082D125
Person / Time
Site:	Vogtle
Issue date:	07/16/1991
From:	Hairston W GEORGIA POWER CO.
To:	NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
References
ELV-02942, ELV-2942, NUDOCS 9107230207
Download: ML20082D125 (5)

Text

- - _ _ _ - - - _ _ _ - _ . _ _ _ _ _ _

1. T

6

'I]L] ^) 4- 3 ,j9 i_4 i 5 ; yt A,

. .i c. 2 1:

. w .- .

!.* ;1i

?I  :. i s. - i' , ,

.i< e, e

i i 1 , 4 r <

3

.. C. Hoh stan. El ELV-02942 1039 Docket Nos. 50-424 50-425 U. S. Nuclear Regulatory Commissian ATIN: Document Conti01 tiesk Washington, D. C. 20555 Gentlemen:

V0GTLE ELECTRIC GENERAT!t1G PLANT RESPONSE TO REQUES1 FOR ADDITIONAL INFORMATION EllLEY_P33SE!fMAL Enclosure 2 of the NRC's letter dated June 21, 1991, requested additional information relative to our request for Technical Specificattor.s changes associated with removal of resistance temperature detector (RTD) bypass loops. The responses to these questions ire attached.

Sincerely, v .L_ - .-

,d/.}b:n~Ludu- b W. G. Hairston, 111 WGH,Ill/HWM/gmb Encicsure xc: Georoia Power Company Mr. C. K. McCoy Mr. W. B. Shipman Mr. P. D. Rushton Mr. M. Sheibani NORMS U. S. Nuclear Reaulatory Commission Mr. S. D. Ebneter, Regional Administrator Mr. D. S. Hood, Licensing Project Manager, NRR Mr. B. R. Bonser, Senior Resident Inspector, Vogtle 9107230207 910716 P

PDR ADOCK 05000424 FDR @fl I

g

O ENCLOSL'RE RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RTD BYPASS REMOVtl

1. Who is responsible fcr the engineering and construction?

Respontg Westinghouse Electric Corporation has been contracted by Georgia Power Company to perform the engineering and plant modifications 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 RIDS installed in the reactor coolant loop piping.

2. Will the new RTDs be located at the same locations as the existing scoops?

BasDonse Yes.

3. Will there be a channel check performed every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> to detect a failed RTD?

B11!LoJ111 A channel check of the overpower delta T (OPDT) and overtemperature delta T (0 TDT) instruments will continue to be performed once per 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> in accordance with Technical Specification 3/4.3.1.

4. a. What methad will be used to predict the RTD response time?

Response

In order to minimize the effects of bypass loop elimination on safety analyses, s. RTD with a response time no greater than 4 seconds was chosen. The RTD manufacturer, Weed Instruments, Inc.,

will perferr. response time testing of each RTD and thermowell prior to installation of the RTDs. These RTD/thermowells must exhibit a response time bounded by the value (4 seconds) given in table 2.1-1 of WCAP-12788.

At least once per 18 months in accordance with Technical Specification 4.3.1.2, the response time of each reactor trip function using these RTDs will be demonstrated to be within its limit. The response times that will be evaluated are as follows:

(1) longest narrow range reactor coolant system (RCS) RTD response time, (normally measured by the loop current step response (LCSR) method).

i e

i ENCLOSURE (CONTINVED)

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RID BYPASS _ REMOVAL (2) Signal processing time (time from " RID output at OPDT or 010T trip setpoint" to " loss of voltage at the undervoltage (UV) coil" for the rcactor trip breaker). ir.cluding time for averaging the three temperature signals.

(3) longest response time of the UV coil and the reactor trip breaker for either reactor trip breaker,

,4) Control rod stationary gripper coil response time (time fr:n " voltage loss to the stationary gripper coil" to "beginning of control rod movement into the core").

b. Has the impact of the response time due to the additional electronics associated with the new RTDs been taken into consideration in the analysis?

BR1MaLQ The analyses used 4 seconds for the RTD response time and a 2-second allowance for electronics delay, which includes the averaging of the three temperature signals. The addition of the averaging process is not expected to be significant relative to the amount of time allowed for the electronics delay. Experience indicates that 2 seconds for signal processing time is conservative.

c. What is the margin between the response time used in the analysis and the response time to be addressed in the Technical Specification surveillance?

Response

There is no margin between the response time used in the analyses and the Technical Specification surveillance limit. It is not the current practice to apply margins to response time acceptance criteria,

d. What margin exists to account for inaccuracies in the method of measuring of response time?

Resnonse The acceptance criteria for response time testing will be the same as the value of the response time used in the safety analyses. No specific cllowance was made in the safety analyses to account for any inaccuracy in the measurement of response time. The measured value of the RTD response time will be increased in a manner consistent with NUREG-CR 5560 to account for the uncertainty in the LCSR method. Permanent records of response time test results are maintained such that a drift in measured response time could be identified.

ENCLOSURE (CONTINUED) l ,

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RTD BYPASS REMOVAL

e. What margin is available for drift response time?

Response

No specific allowance is made for response time drift. The res)onse time is periodically verified, in accordance with the Tecinical Specifications, to be within the valees used in the safety analyses.

5. Discuss whether:

a. Existing overall channel functional checks and calibration accuracy requirements will be maintained.

Resoonse The existing overall channel functional checks and calibration accuracy requirements will remain the same.

b. The impact of rack drift has been considered in the evaluation.

Response

The effect of rack drift has been included in the uncertainty analyses presented in section 3 of WCAP-12788, Rev 1. The rack drift is identified as "RD" in the tables that are included in section 3 of the WCAP.

c. There is any improvement in the accuracy of temperature readings.

Response

Temperature uncertainties for RTD bypass loops are described in WCAP-12460. Temperature uncertainties for RTD bypass loops eiiminated are described in WCAP-12462 and are consistent with those contained in WCAP-12788. The difference in the uncertainties is small, about 0.10F. The more limiting of the two values was used in the safety analyses in order to bound operation with either form of temperature measurement.

6. Discuss streaming relative to RCS flow measurement uncertainty for low leakage cores. Also indicate whether this has been included in the 2.5 percent flow measurement uncertainty tiiscussed in your submittal.

Resoonse Westinghouse has determined that the effects of low leakage core designs on hot leg streaming are conservative; i.e., it results in a bias such tha+ the flow determined by the heat balance is less than the actual flow. Therefore, the current flow uncertainty is sufficient I.

I , .

ENCLOSURE (CONTINVED)

RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION RTD BYPASS REMOVA1 even though no explicit allowance has been made for low leakage core designs. The effects of streaming on RCS flow measurement have been observed in plants with bypass loops and plants without bypass loops.

Elimination of the bypass loops and the use of thermowell mounted RTDs in the reactor coolant loops is not expected to significantly change the observed effects of streaming on RCS flow teasurement.

7. Indicate the method used to calibrate the RTr> and to detect long term drift. Also indicate the frequency of calibration.

Response

The RTDs are laboratory calibrated following manufacture. Accuracy requirements are confirmed through cross calibration testing after installation and at subsequent refueling outages. Cross calibration

-testing is performed in accordance with the Westinghouse methodology, which provides correction of random drift. Although cross calibration testing is not sensitive to unidirectional (systematic) drift, such drift is not expected based on Westinghouse experience and based on the results of a study published in NUREG/CR-5560 (section 23.1, page 144).

8. Discuss your plans to compare data at full power conditions for before and after implementation of RTD bypass removal.

Response

Reactor coolant system flow is determined following each refueling, in accordance with Technical Specification 4.2.5.3. The records of these measurements are maintained as part of the plant records. The measurements taken during the previous cycle are available for comparison if required. There are no plans to perform special tests before and af ter RTD bypass loop removal since the modification will be made in conjunction with a refueling outage. Data will be taken following installation to assure that the thermowell RTDs are performing as expected.

9. At what deviation in loop temperature will the delta T and delta lavg.

alarms be initii.ted?

Resoonse The delta T deviation alarm is set at 30F. The Tavg deviation alarm is set at f 20F.

_ _ _ _ _ - _ _ _ _ _ __