ML20100P143

Requests That EPRI ARC Database for 3/4 Inch & 7/8 Inch Diameter Tubes & Updated ARC Correlation for 7/8 Inch Diameter Tubes Be Withheld Per 10CFR2.790(b)(4)

ML20100P143
Person / Time
Site:	Sequoyah
Issue date:	02/28/1996
From:	Liparulo N WESTINGHOUSE ELECTRIC COMPANY, DIV OF CBS CORP.
To:	Russell W NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM)
Shared Package
ML19355C727	List: ML20100P131 ML20100P143
References
CAW-96-934, NUDOCS 9603110061
Download: ML20100P143 (55)

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Westinghouse EnergySystems Nelear Semes DNidon Electric Corporation l

80x 355 Pittsbutgh Pennsylvania 15230 0355 1

February 28,1996 CAW-96-934 Document Control Desk US Nuclear Regulatory Commission Washington, DC 20555 Attention: Mr. William T. Russell, Director APPLICATION FOR WITHHOLDING PROPRIETARY INFORMATION FROM PUBLIC DISCLOSURE

Subject:

"EPRI ARC Database for 3/4" and 7/8" Diameter Tubes and Updated ARC Correlation for 7/8" Diameter Tubes" (Proprietary)

The proprietary information for which withholding is being requested is further identified in Affidavit CAW-96-934 signed by the owner of the proprietary information, Westinghouse Electric Corporation.

The affidavit, which accompanies this letter, sets forth the basis on which the information may be withheld from public disclosure by the Commission and addresses with specificity the considerations listed in paragraph (b)(4) of 10 CFR Section 2.790 of the Commission's regulations.

Accordingly, this letter authorizes the utilization of the accompanying Affidavit by Tennessee Valley i

Authority.

Correspondence with respect to the proprietary aspects of the application for withholding or the Westinghouse affidavit should reference this letter, CAW-96-934, and should be addressed to the undersigned.

Very truly yours,

)

g J

N.9. Liparulo, Manager JJM/bbp Regulatory & Engineering Networks Enclosures Kevin Bohrer/NRC(12H5) cc:

camwsoon 9603110061 960304 PDR ADOCK 05000328 P

PDR

I CAW-96-934 l

AFFIDAVIT 1

COMMONWEALTH OF PENNSYLVANIA:

ss l

COUNTY OF ALLEGHENY:

l Before me, the undersigned authority, personally appeared Nicholas J. Liparulo, who, being by me duly sworn according to law, deposes and says that he is authorized to execute this Affidavit on behalf of Westinghouse Electric Corporation (" Westinghouse") and that the averments of fact set forth in this Affidavit are true and correct to the best of his knowledge, information, and belief:

Nicholas J. Lip lo, Manager Regulatory & Engineering Networks Sworn to and subscribed before me this 2/

day of 4/ - - % /

,1996 Y 0h u

/

Notary Public NotartalSeal Rose Myle Payne, Notary Public Monroovllo Doro, A!'agheny County My Commocion Egres Nov 4,1996 Member,PennsjtrarnaAssoasconof Notanos 192eC-JWF 19228%

.. CAW-%-934 (1)

I am Manager, Regulatory & Engineering Networks, in the Nuclear Services Division, of the Westinghouse Electric Corporation and as such, I have been specifically delegated the function of reviewing the proprietary information sought to be withheld from public disclosure in connection with nuclear power plant licensing and rulemaking proceedings, and am authorized to apply for its withholding on behalf of the Westinghouse Energy Systems

. Business Unit.

j (2)

I am making this Affidavit in conformance with the provisions of 10CFR Section 2.790 of the Commission's regulations and in conjunction with the Westinghouse application for withholding accompanying this Affidavit.

(3)

I have personal knowledge of the criteria and procedures utilized by the Westinghouse Energy Systems Business Unit in designating information as a trade secret, privileged or as confidential commercial or financial information.

(4)

Pursuant to the provisions of paragraph (b)(4) of Section 2.790 of the Commission's regulations, the following is furnished for consideration by the Commission in determining whether the information sought to be withheld from public disclosure should be withheld.

(i)

The information sought to be withheld from public disclosure is owned and has been held in confidence by Westinghouse.

(ii)

The information is of a type customarily held in confidence by Westinghouse and not customarily disclosed to the public. Westinghouse has a rational basis for determining the types of information customarily held in confidence by it and, in that connection, utilizes a system to determine when and whether to hold certain types of information in confidence. The application of that system and the substance of that system

- constitutes Westinghouse policy and provides the rational basis required.

)

i Under that system, information is held in confidence if it falls in one or more of several types, the release of which might result in the loss of an existing or potential competitive advantage, as follows:

192eC-JWF-2:022996

. CAW-96-934 (a)

The information reveals the distinguishing aspects of a process (or component, structure, tool, method, etc.) where prevention of its use by any of Westinghouse's competitors without license from Westinghouse constitutes a competitive economic advantage over other companies.

(b)

It consists of supporting data, including test data, relative to a process (or component, structure, tool, method, etc.), the application of which data secures a competitive economic advantage, e.g., by optimization or improved marketability.

(c)

Its use by a competitor would reduce his expenditure of resources or improve his competitive position in the design, manufacture, shipment, installation, assurance of quality, or licensing a similar product.

(d)

It reveals cost or price information, production capacities, budget levels, or commercial strategies of Westinghouse, its customers or suppliers.

(e)

It reveals aspects of past, present, or future Westinghouse or customer funded development plans and programs of potential commercial value to Westinghouse.

(f)

It contains patentable ideas, for which patent protection may be desirable.

(g)

It is not the property of Westinghouse, but must be treated as proprietary by Westinghouse according to agreements with the owner.

+

There are sound policy reasons behind the Westinghouse system which include the following:

(a)

The use of such information by Westinghouse gives Westinghouse a competitive advantage over its competitors, it is, therefore, withheld from disclosure to protect the Westinghouse competitive position.

1926C-JWF 3:02:s96

j CAW-96-934 l

l I

(b)

It is information which is marketable in many ways. The extent to which such information is available to competitors diminishes the Westinghouse ability to sell products and services involving the use of the information.

(c)

Use by our competitor would put Westinghouse at a competitive disadvantage by reducing his expenditure of resources at our expense.

(d)

Each component of proprietary information pertinent to a particular i

competitive advantage is potentially as valuable as the total competitive advantage. if competitors acquire components of proprietary information, any one component may be the key to the entire puzzle, thereby depriving Westinghouse of a competitive advantage.

(e)

Unrestricted disclosure would jeopardize the position of prominence of Westinghouse in the world market, and thereby give a market advantage to the competition of those countries.

(f)

The Westinghouse capacity to invest corporate assets in research and development depends upon the success in obtaining and maintaining a competitive advantage.

(iii)

The information is being transmitted to the Commission in confidence and, under the 1

l provisions of 10CFR Section 2.790, it is to be received in confidence by the Commission.

(iv)

The information sought to be protected is not available in public sources or available information has not been previously employed in the same original manner or method to the best of our knowledge and belief.

1 (v)

The proprietary information sought to be withheld in this submittal is that which is appropriately marked in letter NSD-SGD-1212, "EPRI ARC Databases for 3/4" and 7/8" Diameter Tubes and Updated ARC Correlation for 7/8" Diameter Tubes", dated February 26,1996 (Proprietary), being transmitted by the Tennessee Valley Authority Company letter and Application for Withholding Proprietary Information from Public 1926C JWF-4422996

'l

, CAW-96-934 i

Disclosure, to the Document Control Desk, Attention Mr. William T. Russell. The proprietary information as submitted for use by the Tennessee Valley Authority Company for the Sequoyah Units 1 and 2 is expected to be applicable in other licensee submittals in response to certain NRC requirements for justification of steam generator tube integrity evaluations.

This information is part of that which will enable Westinghouse to:

(a)

Perform steam generator tube integrity evaluations.

Further this information has substantial commercial value as follows:

(a)

Westinghouse plans to sell the use of similar information to its customers for purposes of meeting requirements for licensing documentation.

(b)

Westinghouse can sell support and defense of the technology to its customers in the licensing process.

Public disclosure of this proprietary information is likely to cause substantial harm to the competitive position of Westinghouse because it would enhance the ability of i

competitors to provide similar methodologies and licensing defense services for commercial power reactors without commensurate expenses. Also, public disclosure of the information would enable others to use the information to meet NRC requirements for licensing documentation without purchasing the right to use the information.

The development of the technology described in part by the information is the result of applying the results of many years of experience in an intensive Westinghouse effort and the expenditure of a considerable sum of money.

1936C-JWF-5:Or896

. CAW-96-934

~

i In order for competitors of Westinghouse to duplicate this information, similar technical programs would have to be performed and a significant manpower effort, having the requisite talent and experience, would have to be expended for developing testing and analytical methods and performing testing.

1 Further the deponent sayeth not, l

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I 1.0 Updated ARC Correlations for 7/8" Tubes This section reports on the evaluations performed which utilized the results ofleak rate and burst testing of tube sections removed from SGs at utility sites in the United States after the publication of the original EPRI database for 7/8" diameter SG tubes (NP-7480-L, Volume 1). The results of the destructive examinations of the tube sections were reported in utility specific reports, and will be summarized in the complete data update report to follow. The additional pulled tube data ger-mane to the APC correlations, and the bobbin amplitudes for APC applications, will be contained in a table in the complete update report to be issued at a later date.

The additional data consist of results from pulled tube sections from Beaver Val-ley 1 (SG-95-06-006, May 1995), Farley 2 (SG-95-07-010, July 1995), Sequoyah 1 (SG-96-01-007, January 1996), and Farley 1 (SG-96-01-003, January 1996).

The results of the leak and burst tests are compared herein to the database of similar test results for 7/8" outside diameter SG tubes, and the effect ofincluding u

the new test data in the reference database is evaluated. In summary, the applica-ble test data are consistent with the database relative to the burst pressure, the probability ofleak, and the leak rate as function of bobbin amplitude correlations for 7/8" diameter tubes. The comparisons and evaluations follow.

4 Suitability for Inclusion in the Database The morphology of the degradation of each indication considered herein was reviewed relative to the EPRI guidelines for inclusion / exclusion of tube specimen data in the alternate plugging criteria (APC) database. The findings of the reviews were recorded in documents prepared for each utility as the data were obtained.

The details of the reviews will be included in a comprehensive report to be issued at a later date dealing with multiple tube sizes. None of the reviews revealed information that would lead to a conclusion that the data considered in this section should not be included in the database. Therefore, the correlations reported herein should be considered applicable to the use of APC for indications in 7/8" diameter tubes in Westinghouse SGs and constitute the analyses of the updated database.

1.1 Free Span Burst Correlation The burst pressure database used in this report for 7/8" tubes consists of the EPRI recommended database, plus test results from tube R11060-1 removed from D.C.

Cook Unit 1. The 'results for this tube section were abnormally high, but the degradation morphology did not meet all of the exclusion criteria developed for degradation with abnormally high burst pressures, hence it was retained in the correlation database. The results from ten (10) burst tests, performed on tube specimens which exhibited a non-zero bobbin amplitude at a TSP elevation location, were considered for evaluation. A plot of the burst pressures of the additional specimens is depicted on Figure 1-1 relative to the burst pressure correlation devel-oupestrai 7s.2ee 1-1 02/24/9s

l oped using the reference database and relative to a 95% confidence band to contain 90% of the population of burst pressures.

1.

A visual examination of the data relative to the EPRI database indicates that the burst pressures measured fall within the scatter band of the refer-ence data, i

2.

Nine, i.e.,90%, of the data points fall within a 95%/90% tolerance interval (approximate) about the regression line (95% confident to contain 90% of j

the underlying normal population).

3.

One, i.e.,10%, of the data points falls outside of the 95%/90% tolerance band about the regression line.

In summary, the visual examination doesn't indicate any significant departures from the reference database. Although the burst pressure is less than would have been expected for one of the indications, the appearance of one such indication in the additional ten data points is not significantly improbable Moreover, the bobbin l

amplitude for this indication increased from 4 volts before removal to 12 volts after, thus, the burst pressure could have been reduced as a consequence of mechanical deformation from the tube removal activities. Since the regression line for this analysis represents the mean and median burst pressure to be expected from the

)

parent population, it would be expected that additional data should fall about half -

l above and half below the line. For the additional data analyzed, six (6) values' were -

above the line and four (4) values below the line. For ten values drawn at random from the population of bursts, the probability that the split would be five above and five below is about 25%, and the probability that the results would'be split six/four in either direction is 41%. Thus, distribution relative to above or below the regression line is not unusual. In addition, the average difference in the observed burst pressure relative to the predicted burst pressures is only 1.1%. Finally, al-though the tube data are from SGs at multiple plant sites, an examination of the normalized residuals relative to the predictions of the reference correlation equa-tion was performed. The results of this analysis are shown on Figure 1-2 where the distribution of observed deviates is compared to those expected from a normal distribution. There doesn't appear to be any significant systematic departure from normality.

Since the additional burst pressure data were not indicated to be from a separate population from the reference data, the regression analysis of the burst pressure on the common logarithm of the bobbin amplitude was repeated with the additional data included. A comparison of the regression results obtained by including these data in the regression analysis is provided in Table 1-1. Regression predictions ob-D:\\APc\\EPR148.29s 1-2 02/24/96

tained by including these data in the regression analysis are shown on Figure 1-3.

The appropriate regression equation for future ARC analyses is,-

P3 - 7.592 - 2.370 log (Volts),

(1-1) with a SLB structural limit of 8.6 volts. The changes to the correlation are:

1.

The intercept of the burst pressure, P, as a linear function of the common 3

logarithm of the bobbin amplitude regression line is increased by 0.48%.

This has the effect ofincreasing the predicted burst pressure as a function of the bobbin amplitude.

2.

The absolute slope of the regression line is increased by 2.19%, i.e., the slope is more steep. This has the effect of decreasing the burst pressure as a function of bobbin amplitude for indications greater than about 3 volts.

3.

There is an increase in the standard error of the residuals of 1.38%. The effect of this change would be reflected in a slightly larger deviation of the 95% prediction line from the regression line.

The net effect of the changes on the SLB structural limit (1.43 APSLB ), using 95%/95% lower tolerance limit material properties, is to decrease it by 0.2 volts, i.e.,

from 8.8 volts to 8.6 volts. The increase in the slope relative to the increase in the intercept, and the increase in the standard error coupled with the fact that the structural limit is also decreased indicates that the probability of burst would also increase for bobbin indications over the structural range ofinterest. Based on the relatively small change in the structural limit, the change in the probability of burst would also be expected to be small.

1.2 Probability of Leak Correlation As for the burst pressure correlation, there are ten (10) additional data pairs that were considered relative to the reference database and the probability ofleak (POL) correlation to the common logarithm of the bobbin amplitude. Figure 1-4 illus-trates the additional data relative to the reference correlation. All of the specimens except one exhibited POL behavior commensurate with expectations indicated by the reference database and regression curve. The single exception was an indica-tion with a bobbin amplitude of 4.03 volts that exhibited leakage, thus becoming the indication with the second lowest voltage of the indications that leaked in the database.

Based on the reference curve, the POL for the leaking indication is 0.133, thus, roughly 1 in 7 indications with an amplitude of 4.03 volts would be expected to leak. Had the expectation been 1 in 20, statistically anomalous behavior could have been suspected. The indication that leaked was the same indication that nurcszentas nos 1-3 02/W96

exhibited a lower than expected burst pressure. It is strongly suspected that this indication experienced ligament tearing during the tube pull as indicated by the maximum 96% corrosion depth resulting in post-pull Argon leakage at 200 psid and the increase in bobbin amplitude from 4.03 to 12.2 volts. However, since it is difficult to prove that the wall thickness ligament would not have torn during postulated SLB conditions, the indication is to be retained in the EPRI database.

In conclusion, data exathinations revealed no significant evidence ofirregular results, i.e., outlying behavior is not indicated.

In order to assess the quantitative effect of the new data on the correlation curve, the database was expanded to include the additional data points and a Generalized Linear Model regression of the POL on the common logarithm of the bobbin ampli-tude was repeated. A comparison of the correlation parameters with those for the reference database is shown'in Table 1-2. These results indicate:

1.

A 9.7% increase (smaller negative value) in the logistic intercept parame-ter.

2.

A 6.2% decrease in the logistic slope parameter.

3.

The absolute values of the parameters' covariance matrix changed by 26.5% to 34.5%. These changes may have a significant impact on the POL values used during the Monte Carlo Simulations, but may not have a significant impact on the 95% confidence bound on the total estimated leak rate from a single SG.

4.

The Pearson standard error decreased by 7.2% from 0.640 to 0.594. This is a negative indicator since the ideal value would be 1.0, but is not judged to j

be significant.

An additional evaluation was performed which demonstrated that most of the changes in the distribution parameters are a result ofincluding the 4.03 V indica-tion that leaked. In order to assess whether or not these changes are significant, the reference correlation and the new correlation were also plotted on Figure 1-4.

An examination of Figure 1-4 reveals a moderate change in the correlation up to about 5 V, with a 31% increase at 4.03 V. A tabular summary of POL predictions before and after including the additional data pomt is provided as Table 1-3. For indications with amplitudes less than 1.0 volt, the POL increases by a factor of 2 to

4. The POL for indications of 3 volts increases by about 50%, while the change in the POL is not significant for indications of 8 volts and greater.

When the total leak rate is determined using the leak rate to bobbin volts correla-tion, the resulting value can be quite insensitive to the form of the POL function.

So, the effect of the changes in the parameter values and variances would be expected to be small or insignificant relative to the calculation of the 95% confi-dence bound of the total leak rate from a SG. However, when the leak rate is D-\\APC\\EPRI 78.296 1-4 02/24/96

~;.

considered as independent of the voltage, as for the current APC database, the increase in POL will more directly affect the estimated total leak rate.

i l

1.3 Free Span SLB Leak Rate Correlation for 7/8" Tubes As previously noted, only one of the specimens exhibited leakage at SLB operating conditions. The test leak rate value corresponded to 2.19 lph at the SLB tempera-ture and pressure difference conditions. The correlation ofleak rate to bobbin voltage exhibits a p-value of 6.5% for the slope parameter using the reference database, and a value of 6.4% with the additional data point. Based on the require-ments stipulated in NRC Generic Letter 95-05 for voltage based plugging criteria, the use of the correlation in performing Monte Carlo simulations to estimate the total leak rate from a SG is not considered to be justified. Figure 1-5 illustrates the new data point relative to the distribution predicted mean using the reference database and relative to a lower 95% confidence limit for a predicted leak rate from the distribution. Also illustrated on Figure 1-5, is the relation of the data point to the regression fit (median of the log-normal distribution) and to the expected leak rate (mean of the log-normal distribution) based on the regression analysis of the leak rate on the bobbin amplitude.

The common logarithm (log) of the test leak rate,0.340, is lower than the mean log l

leak rate for the reference database,0.576, but is well within one standard devia-

. tion of that value. The effects ofincluding the data point in the database on the estimated parameters of the leak rate distribution are tabulated in Table 1-4. The estimated mean and standard deviation of the population ofleak rates are de-creased, hence, predicted leak rates from Monte Carlo simulations and the 95%

confidence bound on the total leak' rate from a single SG will be reduced. For clarification, the values listed in Table 1-4 for the mean, p, and standard deviation, o, of the population ofleak rates are derived from the sample values of the log leak rate. These are the expected leak rate parameters to result from a simulation of l

the log leak rates using the NRC accepted leak rate simulation method as described in WCAP-14277.

]

1.4 Summary / Conclusions r

The review of the effect of the additional data indicates that the SLB structural limit burst pressure 'will not be significantly changed by the inclusion of the data.

l Therefore, it is likely that the conclusions relative to EOC probability of burst and l

based on the correlation obtained using the reference database would not be signifi-I cantly affected.

The probability ofleak correlation to the common logarithm of the bobbin ampli-tude is moderately changed by the inclusion of the data, leading to the expectation i

of predicting slightly larger 95% confidence bound leak rates. At the same time, the mean and standard deviation of the leak rate distribution are decreased, l

leading to the expectation oflower 95% confidence bound leak rates. It may be l

D:\\APC\\EPRI 78.29s 1-5 c2/24/9s

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expected that the increase in the POL will be at least partially offset by the l

decrease in the predicted leak rates.

D:\\APC\\EPRI 78.296 16 025 W96

l Table 1-1: Effect of Additional Data on the 7/8" Tube Burst Pressure vs. Bobbin Amplitude Correlation P3 = ai + a2 og(Volts) l Reference Database with New / Old Database Value additional Ratio ai 7.5557 7.5920 1.0048 a2

-2.3194

-2.3700 1.0219 2

r 82.7%

81.84 %

0.9900 og,,,,

0.817 0.828 1.0138 N (data pairs) 70 80 hp q

p Value for a2 51027 1 10'3 9 10'4 Reference o 68.78 ksim g

, y,; yf 7

r Notes: (1) This is the flow stress value to which all data was normalized i

prior to performing the regression analysis. This affects the coefficient and standard error values. The corresponding values for a flow stress of 75.0 ksi can be obtained from the above values by multiplying by 1.0904.

DMPc\\EPRI 78.296 1-7 OMM6

Table 1-2: Effect of Additional Data on the 7/8" Tube Probability of Leak Correlation

-[0'

• E2 ogw 1

Pr(Leak) =

1+e Reference Database with Pa e er Change Database additional

-6.8974

-6.2269

-9.7%

i 8.3507 7.7739

-6.9%

2 V U) 3.4998 2.2911

-34.5%

11

~

V

-3.8456

-2.6004

-32.4%

12 V

4.5821 3.2955

-26.1%

22 DoF*

97 107 th 9 "

Deviance 25.09 28.90 15.2 %

~

Pearson SD 64.0%

59.4%

-7.2%

Notes: (1) Parameters V are elements of the covariance matrix of jj the coefficients, g, of the regression equation.

(2) Degrees of freedom.

D.\\APC\\EPRI 78.296 1-8 02/24/96

l I

l l

l Table 1-3: Effect of Additional Data on 7/8" Tube Probability of Leak Predictions Bobbin EPRI/NRC w/ additional

• • # Old l

Amplitude Database Database ah.o l

(Volts)

POL POL 0.10I) 2.39 10-7 8.31 10'7 3.48 0.250 2.95 10~6 8.63 10'6 2.93 0.300 1.28 10'5 3.39 10'6 2.64

~~

0.500 8.18 10'5 1.90 10'4 2.33

~

~

~

4 0.600 1.58 10 3.52 10'4 2.22 0.800 4.50 10'4 9.29 10-4 2.07 1.000 1.01 10 1.97 10'3 1.95 4

~

2.000 0.0123 0.0201 1.63 4

3.000 0.0515 0.0746 1.45 4.030 0.1367 0.1793 1.31 5.000 0.2572 0.3115 1.21 8.000 0.6557 0.6886 1.05 10.000 0.8105 0.8245 1.02 15.000 0.9490 0.9486 1.00 20.000 0.9814 0.9799 1.00 30.000 0.9957 0.9948 1.00

~

40.000 0.9985 0.9980 1.00 50.000 0.9993 0.9991 1.00 i

I D:\\APC\\EPRI-78.296 1-9 02 aves

~ _ _.. -.

e Table 1-4: Effect ofInclusion of Additional Data

.on the Reference Leak Rate Database for 7/8" Tube APC Applications Leak Rate (lph)

Log ( Leak Rate )l-Parameter Reference w/ additional Reference w/ additional Database Database Database Database Sample Size 26 27 26 27 Sample p 13.74 13.32 0.5764 0.5696 Sample a 21.13 20.84 0.8338 0.8188

,, V lt :%sgj$N:n 6.5%

6.4%

p Value 4

The following are based on the lognormel distribution sample parameters.

Population p -

23.9 lph

- 22.01ph These values are biassed to Population a 149.1 lph 128.0 lph be higher than expected.

Upper 95% Pred.

100.6 lph 92.51ph.

These ranges are biassed to

~

Lower 95% Pred.

0.143lph 0.1491ph be wider than expected.

Notes: 1. It has been previously shown that a log-normal distribution can be used to describe the population ofleak rates.

o n ecssrai-7s.nes 1-10 omas

.l Figure 1-1: Burst Pressure vs Volts for 7/8" Alloy 600 SG Tubes Additional Data, Reference o = 68.8 ksi @ 650 F r

12.0

~~.....

EPRI/NRC Database

~

10.0 Additional Data

__i Regression Curve N

---

95%/90% Tol. Band 8.0 s

x 5

g N

=

60 N

-N

...]-

g N

p.,

~.,

54 N

m 4.0 I

l

. E':.'

N 4I.

2.0 l, l L.

l 0.0 0.1 1.

10.

100.

Bobbin Amplitude (Volts) l-11 RFK: 2/24/96. 3 24 PM

[7ssv_296.xts] Tol Band

Figure 1-2: Burst Pressure for 7/8" Diameter Tubes Deviate Analysis of Additional Data 2.5 l

. Observed Data 2.0 Normal Distribution

_ /[

'~'

/_ _Z L

g 1.0 f

5

/

> 0.5 g

.o o

1 2

/,.

-0.5 "8

/

7

-1.5

-2.0

/

-2.5

-2.5

-2.0

-1.5

-1.0

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 Observed Deviate Values 1-12 RFK: 2/24/96. 3 23 PM

[788V_296 xis] New Devs

i l

Figure 1-3: Burst Pressure vs Volts for 7/8" OD Alloy 600 SG Tubes NRC/EPRI Database, Reference c = 68.8 ksi @ 650 F r

12.0 EPRI/NRC Database Additional Data 10.0 -

Regression Curve g.

--- 95% Prediction @ LTL New Regression

+

-N+

g 8.0 :

w x

New 95% Pred @ LTL t,x

_N 6

~x g_

K N

y sx, ' f

\\

m

- w g

6.0

.,q m

A N

w g

xx 4__A~'A w ~x.

m u

4U

---

~ --

- - ~

• d Ad

_ _ _. 3.657 ksi - - -- - L---J-i

_. -. 1s '*' %

b l

m 1

Xs

... -.. -.. u. y,, 'x ~.

... ~ 2_sgo y,; -.

l il i

2.0 m

M kd'I s

l i

y 8.8 V -

- 28.5 V il

'~

0.0 O.1 1.

10.

100.

Bobbin Amplitude (Volts) 1-13 RFK: 2/24/96. 3 25 PM

[78BV_296 xis] BysV.NRC

,3 i

Figure 1-4: Probability of Leak for 7/8" SG Tubes Effect ofInclusion of Additional Data 1.0 t

0.9

[

EPRI/NRC Database Additional Data i

0.8 -

--- POL EPRI/NRC Data m

d

.7 w/ Additional Data I

0 E

al c

50.6 O

'i t

.i 3 00

['

t h,

D 0.4

/

5 I

l i

g 0.3 ll K

l 0.2 r/

0.1 tj

/

x 0.0 0.01 0.1 1.0 10.0 100.0 Bobbin Amplitude (Volts)

[78 pol _6 xis] Pouog(V) l-14 RFK: 2/24/96,3 26 PM

Figure 1-5: Leak Rate vs Bobbin Amplitude 7/8" Tube Data, All Data, NRC Correlation t

1000.0 Test Database Additional Data 7_T Z

Distribution Mean

- - - 95% Confidence 100.0 -

7

-Regression Exp(Q)

Regression Median (Q) p'

-p-.s

.n.

/

2 10.0 W

R.

s g

/

10 A

/

^

/

e

/

/

~

0.1 0.01 1.0 10.0 100.0 Bobbin Amplitude (Volts)

~

1-15 ark 2r249s, a 27 eu F8qv_nrc.xis] NRC.Pkt

4 Relevant information from TVA Letter Dated February 9,1996, "Special Report On Steam Generator (SG) Activities Completed During The Unit 1 Cycle 7 Refueling Outage'"

5 I

l l

l TABLE 3 l

SQN Unit 1 Cycle 7 PWSCC SAls AND MAls AT DENTED TUBE SUPPORT PLATES

< 5 VOLT DENTS All Tubes will be plugged Dent Size Detected

"+ POINT

• l l

EG EQW fdd

>= 5 VoMs 1.EXgh wRtkia

% WAl.L AXIAL EXT

[N,$1DE TSP i

1 9

92 2.89 NDD 27 0.42 YES l

3 11 71 2.02 YES 99 1.10 NO l

3 21 33 3.3 NDD 34 0.36 YES l

3 13 37 3.51 NDD 20 0.22 YES 1

3 14 71 3.74 YES 70 0.86 NO l

4 1

18 2.96 YES 45 0.63 YES 4

3 53 2.9, 5 YES 87*

YES 4

5 64 1.78 YES 94*

YES 4

9 32 4.98 YES 81*

YES l

<5 VOLT DENT EXPANSION 3

4 63 4 l.

NDD 55 0.40 YES 3

26 63 4.6 '

NDD 20 0.27 YES j

3 26 68 3.54 NDD 35 0.36 YES 3

26 77 2.49 NDD 30 0.31 YES 3

38 66 2.94,

NDD 20 0.31 YES

<5 VOLT DENT EXPANSION

~

4 8

48 3.52 NDD 20 0.27 YES 4

11 73 2.43 NDD 20 0.27 YES 4

17 63 4.5 NDD 35 0.27 YES 4

19 49 3.5 YES 20 0.31 YES 4

28 15 2.26 NDD 35 0.31 YES 4

30 15 2.4 NDD 20 0.27 YES 4

42 32 4.2 YES 30 0.27 YES

>5 VOLT DENTS 1

12 51 5.6 NDD 48 0.42 YES 2

10 31 7.8 NDD 38 0.36 YES 3

8 11 5

NDO 22 0.72 YES 3

14 61 10.8 NDD 35 0.62 NO 3

14 80 15.6 NDD 50 0.36 YES 3

17 64 6.9 NDD 35 0.63 YES 3

18 61 10.5 NDD 55 0.49 NO 3

21 68 8.6 NDD 40 0.36 NO 3

33 70 6.6 NDD 25 0.22 YES 4

16 45 50.7 NDO 45 0.27 NO 4

17 46 22.7 YES 80 0.80 NO 4

26 20 5.3 YES 45 0.63 YES l

4 32 20 5.2 YES 35 0.54 YES 4

34 16 5.48 NDD 44 0.27 YES 4

35 25 13.3 YES 40 0.49 YES 4

36 53 6.89 NDD 80 0.27 YES 4

36 57 5.92 NDO 65 0.31 YES

• Bobbin Coil % Throughwall l

l:\\sharedu1c7Wic7saLxis l

l l

21 l

l l

).

J ALTERNATE PLUGGING CRITERIA RESULTS A report in accordance with Technical Specification Change 95-15 commitment for Alternate Plugging Criteria was prepared by Westinghouse Electric Corp. to.

provide results, distributions, and evaluations within 90 days of unit restart for the implementation of Alternate Plugging Criteria at SON Unit 1. The Westinghouse report is Attachment 1.

I I

e

)

4 N RC C 3 RT.D OC 22

\\

j*

I DAMAGE MECHANISM ASSESSMENT AND TUBE PULL a

The damage mechanism occurring on the inside diameter at the TTS transition and 4

dented tube support plate intersections is Primary Water Stress Corrosion Cracking (PWSCC). Alloy 600 PWSCC is influenced by tensile stress, operational temperature, i

and a susceptible metallurgical structure in the presence of normal primary coolant water.

The metallurgical condition of all tubes with PWSCC detected at the WEXTEX expansion transitions was evaluated for the mechanical properties (tensile, yield, percent elongation, and Rockwell B hardness) relative to the average of all tubes in the SG. Generally, higher carbon contents in Alloy 600 imply a higher susceptibility to PWSCC.

Comparison of Carbon Content and Mechanical Properties Carbon Tensile Yield Elongation Hardness

(%)

(KSI)

(KSI)

(%)

(B)

Average of All SQN SGs 0.034 102.26 56.35 38.40 87 Average of all tubes with 0.03 101.90 56.04 39.00 87 TTS PWSCC Tube with TTS expansion zone PWSCC in the SQN Unit 1 SGs do not have 4

significantly different mechanical properties than the average tubes in the SQN SGs.

An assessment of the location of TTS PWSCC cracks was obtained by evaluating, by zones, the distribution of cracks (axial and circumferential) within the SGs and is listed below:

Number of Cracks in Zones Zone 1 Zone 2 Zone 3 Zone 4 Totalin SG SG Axial Circ.

Axial Circ.

Axial Cire.

Axial Cire.

Axial Circ.

1 4

0 4

2 2

1 2

5 4

33 6

41 3

18 0

18 4

1 3

19 4

19 Total 1

2 1

2 5

7 74 10 82 Total /

zone 3

1 7

81 92 Percent 3.3%

1.1%

7.6 88.0 %

j Results of the SQN U1C7 examinations show zone 3 and 4 contained 95.6% of all axial and circumferevial expansion zone PWSCC. Zone 3 and 4, being located in the center section of the SG, would operate at a higher temperature and be insulated by the sludge pile further raising the tube temperatures and driving the kinetics of TTS PWSCC.

NRCC3RT. Doc 23

i i.

l A sample of tubes from each SG with TTS PWSCC were reviewed for internal diameter tubesheet expansion transition profiles. Evaluations of the expansion transition profiling plots identified the majority of the circumferential PWSCC detected was associated with oversized tubesheet hole conditions that produce transitions with changes in diameter of greater than 15 mits and/or irregularly shaped (sharp or uneven) transitions. The table below is a sample of tubes from each SG with circumferential PWGCC.

Irregular Tubesheet Profile Evaluation Percent of Tubes l

Tubes with Tubes with Oversized with Oversized holes PWSCC and holes and/or irregular and/or irregular l

SG Profile data Expansions Expansions 1-OH 1 of 2 1

2 0-IR 50 %

l 17-OH 18 of 21 2

21 1-lR 86 %

3-OH 3 of 9 l

3 9

0-IR 33 %

5-OH 5 of 6

~

4 6

0-IR 83 %

26-OH 27 of 38 Totals 38 1-IR 71 %

The tube pulled for top of tubesheet Primary Water Stress Corrosion Cracking will be discussed in this section. Tubes pulled for alternate plugging criteria will be discussed in the section on Alternate Plugging Criteria.

One tube (R15 C23) was pulled from Steam Generator 2 for a top of tubesheet inside diameter (ID) circumferential indication. The TTS region fractured during the tube pulling process. Field eddy current data (3 coil RPC) for the TTS region of R15 C23 determined an ID circumferential indication measuring 336*

circumferential extent. The + Point probe measured the same location to have i

multiple circumferential indications with a total circumferential involvement of 316*. Figure 3 is the crack profile by blind NDE (3 coil RPC) verses actual destructive examination results. NDE results show good correlation with metallurgical Scanning Electron Microscopy (SEM) results.

Due to the fracturing of the tube during the pulling process, leak and burst testing were not able to be performed.

i The calculated burst pressure from the destructive analysis results is approximately 7800 psi, which is well within the structural integrity requirements of Regulatory Guide 1.121.

N RC C 3 RT.DO C 24

\\

l' 1

1 4

SEM fractography was performed on the fracture face of tube R15 C23. The ID origin corrosion averaged 26% throughwall around the circumference with a j

maximum depth of 88%. The corrosion was comprised of 5 separate -

l macrocracks. SEM examinations showed no nearby, separately nucleated, corrosion cracks parallel to the fracture face on the tube ID surface. [.pth profiling of the indication is presented in Table 4. This simple corrosiv morphology is typical of primary water stress corrosion cracking. Then were no L

markings on the tube OD to identify the TTS relative to the fracture face and significant tube elongation prevented a precise dimensional analysis of the pre-pull fracture face elevation.

Based on the pulled tube analysis, NDE characterization of the TTS expansion transition conditions, chemistry, and metallurgical condition of the Alloy 600 tubes, it was concluded that the damage mechanism is PWSCC originating in the WEXTEX expansion transitions. In addition,95.6% of the time indications occur in zones 3 and 4, and have a higher probability in tubes with oversized diameter tubesheet hole conditions.

o I

l l

i N RC C 3 RT.D OC 25 e

v r

w i+:

e m

Sequoyah R15C23; Circumferential Crack,TTS (As-Read by Analyst) 100 %

Analysis:

-RPC. 80 mit HF

/

~ ~ "I '.

I

'I

~

90% -

12*

16'h 30 g '

~

~

30' Calibration:

~

E.

}

-Based on field l.

standard 80%

I

p e

6:;

s i::

e.

l 70 %

.t ;

/

i ;

e.

'..*>*I Od O

f.

l's j*p N g

--o--Destr. Exam e

o.

60 %

;4 A; ;'. i

- - e -.RPC,80 mit HF e

f u) 1

@ g =E 50%

f

<I; a

n o j, l

J e

. o N

e.

Average Dentti 9

Destructive Exam 0 0

• / i g "en y 40%

d l

-g Crack Lgth: 53.2%

j 360*:

25.9 %

r 4

l g

neo t

s g

e Crack Lgth: 45.1%

,0.,.

i I

360*:

40.6%

i 3

/

l TotalCrack Angfe:

20%

l' d

Destr. Exam 175*

U '

I RPC 324' l

10%

I s

0% em

,m

=

= %

>v A-

^' ~

0 40 80 120 160 200 240 280 320 360 Circumferential Extent (')

9 e

.l ljll l(Il, If I

9 G

$dm,

@3, 0o "n "o a NK el a5 T

l r C ou i

Z b

c

,J a e is tioN n,o.

Se quo 8 (7 765(4 4(3 321 U y

(

( 21 1(99 1( 1 1 1 I 1( 1 1 2

40/9/W0 6/6 000U a

0 0

0 0987N51 0

432I 1

0 0000 0 4 000l 00//1 /0DM/4m00Mf h

U 2

/2/// l /

0/466/00/02 6 0 000 0

/000m

/

00OU 1

0 0

)0 U

0000 0 0 476 0 00)0)3 0

)

)

0 0

0 n

)

)

)

<=

<=

o c

c

<=

i

(

t

=

=

=

d

=

=

=

=

=

=

e i

=

g_

M M

M M

M S

r l h

ee

/

a a

a a

e a

c c

c c

sn G

c r

r r

r r

o o

o o

/g T

t a

o h

c c

c c

%v u

c i

r r

r r

i r

a a

a a

b a

a c

c c

c t s e

s ck k

k k

k k

k h.

c r

I oD n

2 2

i i

4 3

3 ue t

T T

Ti Ti T

Ti pi gp e

T p

p p

hh r

i w

g i

p p

p r

e a

l

)l n

u lar M

ac ro c

rac k

L D

a e

p

aL t

t h

oW i

n 1

/M W

fi L

l i

e i

dy s

ths i

f i

o (n-i r

c 4 I

h D

es O

)

r ig in Co

=

=

= M r

3h h

r 1 a o

1 6

0c s

r 1

dw dw do C

io e

e c u

n r

e i

g a i

g i

w g

r s

r e c

=

r e

ek ek ek e

i a

s s

s3 2

i l

l l

s e

e e

l n

n n

g g

g t

tl t

h i

h zg3y oo g

ll

l Sequoyah Unit i S/G Tube Intergranular Macrocrack Depth I'rofiles Conunents Ductile Lg-at Tide No.,

Length vs. Depui location / Width (inches) in:alion (degrees / % tivoughwall) 4

KlX23, 904/34)

Ugso:nt I / 0.005" wide

<==

Near TIS (206/00)c= Ugament i 210/42 (211/4l}

Ligament 2 / 0.008" wide i

<==

(216/00)<== Ugament 2 Macircrack 4 length i

220/25 Ugament 3 / 0.003" wide

= 86 degrees

<==

(221/00)<= Ugament 3 230/63 240/75 o

25NT1 yy Ugament 4 / 0.012" wide

<==

(253/00)<== Ugronent 4 z

260/81 N

g0 (264/88)<= Maxinunn Crack Depth o:

2. O 270r/5 280r/2 (288/00)o== M.ueus.ck 4 lip "j$

29w00 300/00 Mouuu.i 5 length ra (308/00)c== Macrocrack 5 Tip

= 30 degrees 310/50 320/69 330/64 (338/00)c== Macrocrack 5 Tip g

340/00 o

350/00 y

(Average Macrocrack Depth = 26%

a Throughwall over 360 degrees; There were g

no 100% thnxighwall areas; Max. Crack z

Depth = 88% Throughwall at 264 degrees.)

T 4

y 3v

CIRCUMFERENTIAL GROWTH RATES To determine a circumferential crack growth rate, a review was performed of past examinations for all tubes identified at the SQN Unit 1 Cycle 6 outage where PWSCC was initiated. This review was performed with knowledge that a defect was present and to determine if the defect was present in previous examinations. The table below is comparative data for 79 tubes with circumferential indications previously examined with RFC during the prior outage. The average circumferential crack growth rate from Cycle 6 to Cycle 7 was 47.5', with a minimum of O' and a maximum of 185*.

CircumferentialIndications @ HTS Extents measured in degrees -

S/G Row Column Location U1C7-deg U1C6-dog DELTA 1

15 64 HTS-79 46 33 1

15 66 HTS 89 63 26 1

25 42 HTS 89 88 1

1 28 43 HTS 63 33 30

~

2 4

39 HTS 74 NDD 74 2

7 22 HTS 80 74 6

2 9

72 HTS 106 69 37 2

10 36 HTS 141 123 18 2

10 37 HTS 79 50 29 2

12 19 HTS 78 50 38 2

12 19 HTS 64 42 22 2

12 34 HTS 87 NDD 87 2

13 26 HTS 101 NDD 101

-2 13 32 HTS 114 NDD 114 2

15 22 HTS 75 NDD 75 2

15 23 HTS 336 284 52 2

15 38 HTS 93 NDD 93 2

16 38 HTS 162 60 62 2

17 21 HTS 80 66 14 2

17 26 HTS 75 NDD 75 2

18 26 HTS 117 63 54 2

18 28 HTS 76 57 19 2

18 36 HTS 88 NDD 88 2

19 23 HTS 60 NDD 60 2

19 25 HTS 100 56 44 2

19 26 HTS 80 73 7

2 19 49 HTS 185 NDD 185 2

19 51 HTS 112 NDD 112 2

21 27 HTS 59 NDD 59 2

21 30 HTS 160 144 16 NRCC3RT. DOC 29

l Circumferential Indications @ HTS Extents measured in degrees S/G Row Column Location U1C7-deg U1C6-deg DELTA 2

22 29 HTS 87 63 24 2

23 30 HTS 68 48 20 t

l 2

24 40 HTS 71 NDD 71 2

25 34 HTS 93 67 26 2

25 66 HTS 91 71 20 1

l 2

28 52 HTS 85 NDD 85 l

2 28 54 HTS 162 NDD 162 l

2 29 38 HTS 92 NDD 92 l

2 29 49 HTS 74 NDD 74 i

2 29 54 HTS 101 27 24 2

29 59 HTS 70 NDD 70 3

4 53 HTS 114 NDD 114 3

4 54 HTS 45 40 5

3 6

53 HTS 63 NDD 63 3

6 53 HTS 66 NDD 66 3

6 57 HTS 63 NDD 63 3

7 49 HTS 173 NDD 173 3,

7 73 HTS 80 NDD 80 3

8 18 HTS 70 65 5

3 8

52 HTS 113 105 8

3 8

58 HTS 39 NDD 39 3

8 75 HTS 154 162 0

3 9

76 HTS 74 71 3

3 11 61 HTS 51 52 0

3 15 66 HTS 70 NDD 70 3

16 45 HTS 171 55 116 3

18 50 HTS 58 NDD 58 3

26 48 HTS 50 51 0

3 26 63 HTS 49 NDD 49 3-30 58 HTS 51 40 9

4 7

77 HTS 76 66 10 4

8 30 HTS 70 63 7

4 12 26 HTS 35 37 0

4 12 28 HTS 67 61 6

4 12 31 HTS 61 NDD 61 4

13 39 HTS 93 84 9

4 13 47 HTS 96 NDD 96 4-14 41 HTS 281 271 10 4

14 52 HTS 51 70 0

4 15 38 HTS 105 NDD 105 4

15 48 HTS 55 NDD 55 l

4 16 32 HTS 67 58 9

l 4

18 27 HTS 68 56 12 NRCC3RT. doc 30

r.

Circumferential Indications @ HTS Extents measured in degrees SIG Row Column Location U1C7-deg U1C6-deg DELTA 4

18 41 HTS 205 201 4

4 18 46 HTS 76 73 3

4 19 38 HTS 92 NDD 92 4

19 39 HTS 45 NDD 45 4

19 61 HTS 50 41 9

4 20 46 HTS 64 67 0

Avg.=

47.50633 e

b e

NRCC3RT. Doc 31

u CORRECTIVE ACTIONS TO PREVENT REOCCURRENCE OF PWSCC RELATED TO TUBESHEET EXPANSION The corrective actions that have been implemented to address top of tubesheet PWSCC was shotpeening. Shotpeening was implemented in the Unit 1 Cycle 5 outage on all non plugged tubes from the tube end throughout the explosive expansion region to 2 inches above the top of the tubesheet. Shotpeening applies compressive stresses on the inside surface with an effective depth of 4 to 7 mils. The expansion region internal surface stresses were changed from 40-45 ksi tensile stresses to 60 ksi compressive stresses. The change in stress state to compressive will provide margin against initiation of future PWSCC.

Pre-existing cracks with depths greater than 4 mils will not be ameliorated by shotpeening and will have a reasonable probability of progressing to detectable flaws in future fuel cycles. Based on SON Unit 1 and industry experience, it is projected that less than 5 percent of the tubes in SON Unit 1 will be affected over the life of the plant, by expansion transition PWSCC. TVA's SQN Unit 1 SGs were the first explosively expanded tubesheet transitions in the world to be shotpeened. WA has taken a aggressive approach by implementing shotpeening to prevent long-term SG tube degradation of SON SGs due to PWSCC in the tubesheet expansion region. A number of tubes that experience expansion transition PWSCC during the U1C7 outage resulted from preexisting indications that were most probability greater than 4 mils during the initial shotpeening. The number of tube presently affected by expansion transition PWSCC is significantly below the 5 percent projection over the plant life.

During the U1C7 refueling outage SON implemented SG chemical cleaning to address outside diameter stress corrosion cracking (ODSCC). TVA predicted that circumferential cracking would occur at dented tube support plates based on SON Unit 1 and other plant experience. Chemical cleaning was implemented as a preventative measure to address circumferential cracking at dented tube support plates. The process that was used is the Westinghouse pressure pulse chemical cleaning which used the EPRl/SGOG chemical formulations.

Qualification of the process was performed by Westinghouse and TVA to verify effectiveness in cleaning tube support plate crevices. TVA has taken an aggressive approach to ODSCC at the top of tubesheet and at both dented and non dented tube support plate intersections. TVA had the foresight to implement chemical cleaning based nn a predictive model of ODSCC and to prevent early SG replacement.

NRCC3RT. DOC 32