ML20237A411
| ML20237A411 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 08/10/1998 |
| From: | Bajestani M TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| TAC-MA0630, TAC-MA630, NUDOCS 9808140037 | |
| Download: ML20237A411 (5) | |
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Tennessee VaHey Authority, Post Office Box 2000, Soddy Daisy. Tennessee 37379-2000 Masoud Bajestani Site _Vice President Sequoyah Nuclear Plant Augusi-10, 1998 U.S. Nuclear Regulatory Commission ATTN:
Document Control Desk Washington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket No. 50-327 Tennessee Valley Authority
)
SEQUOYAH NUCLEAR PLANT (SON) - RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING UNIT 1. CYCLE 8 STEAM s
'. GENERATOR (S/G) REPORT (TAC NO. MA0630)
%ference: NRC letter to TVA dated July 2, 1998, "Sequoyah Unit'l: Request for Additional Information Regarding the Review of Steam Generator Tube Inspection Special Report (TAC No. MA0630)"
The enclosure to this letter provides the additional information requested by the referenced letter.
The additional information contains the input-parameters used in the analysis to predict S/G tube burst probability and end-of-cycle (EOC-9) leakage values.
Please direct questions concerning this issue to me a' (423) 843-7001 or Pedro Salas at (423) 843-7170.
Sincerely, p
d Masoudi estani QCPj l
Enclosure i
cc:
See page 2 i
9908140037 990810 PDR ADOCK 05000327
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O U.S. Nuclear Regulatory Commission Page 2 August 10, 1998 cc (Enclosure):
Mr. R.
W.
Hernan, Project Manager Nuclear Regulatory Commission One White. Flint, North 11555 Rockville Pike Rockville, Maryland 20852-2739 NRC Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy-Daisy, Tennessee 37379-3624 Regional Administ: ' tor U.S. Nuclear Regul ory Commission Region II 61 Forsythe St.,
SW, Suite 23T85 Atlanta, Georgia 30303-3415 i
4 i
I
o ENCLOSURE RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE ALTERNATE REPAIR CRITERIA 90-DAY REPORT FOR SEQUOYAH UNIT 1 CYCLE 8 STEAM GENERATOR (S/G) TUBE INSPECTION
Background
By letter dated August 8, 1997, TVA submitted for staff review the special report on S/G activities completed during the Sequoyah Unit 1 Cycle 8 refueling outage.
TVA submitted the report to satisfy a commitment as a part of implementing the voltage-based alternate repair criteria in the Sequoyah Unit 1 technical specifications.
The alternate repair criteria were implemented based on Generic Letter 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected By Outside Diameter Stress Corrosion Cracking."
By letter dated July 2, 1998, the staff requested additional information regarding input parameters used in calculations provided by TVA's August 8, 1997 letter.
The requested input parameters are associated with the analysis for EOC-9 steam line break (SLB) leak rate and tube burst probability correlations.
As stated in the report, the correlations used in the EOC-9 leak rate and tube burst probability analyses are based on a database pre'Jiously transmitted to NRC (see Reference 8.5 contained in,
to TVA's August 8, 1997 letter).
Details requested by NRC on the leakage and burst correlations i
are provided below.
~
NRC Question No. 1 "For calculations to obtain the tube burst probability on page 7-4 of the submittal, provide the following input parameters: (1) the i
mean, standard deviation, and normalized value of the material property distribution for stean generator tubing; (2) slope and intercept of the burst pressura vs. voltage correlation; (3) the number of burst pressure data points; and (4) sum of (X-X bar) *
- 2, mean of X and sum of X* *2, where X is the log of the bobbin voltage of the burst pressure vs. voltage correlation."
TVA Response The tube burst probability-results shown on page 7-4 of the 90-day report were obtained Osing a correlation between the burst pressure and the common logarithm of the bobbin amplitude.
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The following material properties were used:
1 (1)
Mean 68.78 ksi*
=
3.172 ksi l
Standard Deviation
=
Normalization value 68.78 ksi
=
No. of data points 360
=
The following regression parameters were used:
(2)
Intercept 7.5920
=
Slope
-2.3700
=
l Standard Error 0.8285
=
(3)
No. of data points 80
=
(4)
Mean of X 0.3666
=
Sum of (X-Xbar)2 42.9441 2
Sum of X is not calculated.
NRC Question No. 2 "For calculations to obtain the tube leakage on page 7-4 of the submittal, provide the following input parameters:
(1) intercept of the leak rate vs. voltage correlation; (2) total number of leak i
rate data points; (3) sum of (X-X-bar)**2, mean of X, and sum of X**2, where X is the log of individual bobbin voltage in the leak rate vs. voltage correlation; (4) slope, intercept, mean square
- error, and number of data points of probability of-leak vs.
voltage correlation; and (5) coefficients, Vn, V12, and V22 of.the covariance matrix of the regression equation."
TVA Response At.the time of preparation of the Sequoyah Unit 1 EOC-8 90-day report, a two-sided test was applied to check the p value from the regression for the slope parameter for acceptability of a leak rate vs. bobbin amplitude correlation.
The p value, based on the database cited in the 90-day report, exceeded the 5% limit specified.in Generic Letter 95-05.
Therefore, leak rate was considered independent of the bobbin amplitude in the EOC-9 leak rate analysis.
Since the correlation functional form considered appropriate is logarithm of leak rate vs. logarithm of bobbin voltage, the common logarithm of the leak rate is assumed
- constant, i.e.,
a
+a Q
=
where Q'is the common logarithm of leak rate, a is the mean of the logarithm of the leak rates, and a is the estimated error about E-2
,s the mean of the logarithm of the leak rates.
The mean and standard deviation of the population of log leak rates used for EOC-9 leak rate projections shown on page 7-4 are as follows:
(1)
Mean (log of leak rates) 0.5696
=
Standard Error (log of leak rates) 0.1576
=
(2)
No. of data points 27
=
Estimates for the mean and standard deviation of leak rates from simulation of log leak rate are as follows:
Estimate of mean 21.9559 1ph**
=
Estimate of standard deviation 127.9976 1ph
=
Probability of Leakage EOC-9 SLB leak rates were estimated using a correlation between probability of leakage expressed as a logistic function and the I
common logarithm of the bobbin amplitude.
The following tegression parameters were used:
(3)
Intercept
-6.2269
=
Slope 7.7739
=
Standard Error 0.594
=
(4)
No. of data points 109
=
(5)
Vil 2.2911
=
V12
-2.6004
=
V22 3.2995
=
NRC Question No. 3 "For the burst probability and leakage calculations, provide the number of Monte Carlo simulations that were performed to obtain the results on page 7-4 of the submittal."
i TVA Response The Monte Carlo analyses for the EOC-9 SLB leak rate and tube burst probability results shown on page 7-4 of the 90-day report are based on 250,000 simulations.
- ksi = 1000 pounds per square inch
- 1ph = liters per hour E-3 L__-________-___-_-____-__-______--__-_--------_______.---_
-.