ML080100595

Response to Request for Additional Information (RAI) Regarding Unit 2 Technical Specification Change 06-06, Probability of Prior Cycle Detection (Popcd)

ML080100595
Person / Time
Site:	Sequoyah
Issue date:	01/08/2008
From:	James Smith Tennessee Valley Authority
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
TAC MD4110
Download: ML080100595 (47)

Text

January 8, 2008 10 CFR 50.90 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk

Washington, D.C. 20555 Gentlemen:

In the Matter of ) Docket No. 50-328 Tennessee Valley Authority )

SEQUOYAH NUCLEAR PLANT (SQN) RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI) REGARDING UNIT 2 TECHNICAL

SPECIFICATION CHANGE 06-06, PROBABILITY OF PRIOR CYCLE

DETECTION (POPCD) (TAC NO. MD4110)

Reference:

NRC letter to TVA dated November 20, 2007, Sequoyah Nuclear Plant, Unit 2 - Request for

Additional Information Regarding Revised

Probability of Prior Cycle Detection Model (TAC

No. MD4110)

Enclosed are the TVA responses to the staffs request for additional information from the reference letter. TVAs

responses were discussed with your staff during telephone

conference calls on November 27 and December 18, 2007. TVAs

responses support staff review of the subject TS change for

SQN Unit 2. provides the TVA responses to the staffs questions. Enclosure 2 provides reformatted TS pages for TS

Change 06-06 that support TVAs response to NRC question

No. 1. Please note that the TS pages provided by Enclosure 2

supersede the TS pages previously provided by TVAs January

12, 2007 letter. Enclosure 3 provides a TVA commitment

associated with implementation of the subject TS change.

U.S. Nuclear Regulatory Commission Page 2 January 8, 2008 Please direct questions concerning this issue to J. D. Smith at (423) 843-7170.

I declare under penalty of perjury that the foregoing is true and correct. Executed on this 8th day of January, 2008. - Sincerely, n Manager, Site Licensing and Industry Affairs Enclosures

1. TVA Reponses to NRC's Request for Additional Information

2. Reformatted TS and Bases page markups for TSC 06-06 3. TVA Commitment cc (Enclosures)

Mr. Brendan T. Moroney, Project Manager U.S. Nuclear Regulatory Commission Mail Stop 08G-9a One White Flint North 11555 Rockville Pike Rockville, Maryland 20852-2739 Mr. Lawrence E. Nanney, Director Division of Radiological Health Third Floor L&C Annex 401 Church Street Nashville, Tennessee 37243-1532 E1-1 ENCLOSURE 1 TENNESSEE VALLEY AUTHORITY (TVA)

SEQUOYAH NUCLEAR PLANT (SQN)

UNIT 2 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION (RAI) FOR SQN TECHNICAL SPECIFICATION (TS) CHANGE 06-06, PROBABILITY OF PRIOR CYCLE DETECTION (POPCD)

NRC Question 1 Regarding your proposed reporting requirements for implementation of the POPCD methodology, please update your proposal to reflect

your new SG technical specification format. In addition, please

discuss your plans to clarify when the report would be submitted

since as currently written, you would be required to submit a

report 90-days after the SGs were returned to service regardless

of whether SG tube inspections were performed. For example, you

could specify that consistent with Technical Specification 6.9.1.16.1 the report would be submitted 90-days after the

initial entry into MODE 4 following completion of an inspection

performed in accordance with Specification 6.8.4.k, Steam

Generator (SG) Program.

Please note that the discussion in Section 2.0 of Enclosure 1 to your January 12, 2007, submittal does not match the wording in

your proposed Technical Specifications in Enclosure 2. The staff

assumed that the proposed wording in the Technical Specifications

is what you intended to propose.

TVA response of this submittal provides reformatted TS and Bases markup pages that supersede the markups previously provided in

TVAs January 12, 2007 submittal. It may be noted that the

wording in Section 2.0 of TVAs January 12, 2007, submittal did

contain typographical errors that resulted in a mismatch with the

wording provided in Enclosure 2. The proposed TS wording

provided in Enclosure 2 was the intended wording.

NRC Question 2 Regarding the changes you intend to make to your Bases, the NRC does not have a copy of the Westinghouse letter that is

referenced. As a result, it can not comment on whether this

change is appropriate. The NRC expects that if the POPCD

methodology is approved that it would be implemented consistent E1-2 with the methodology provided to the staff to support its approval. The methodology in the referenced Westinghouse letter

may have been modified as a result of responses to the NRC

staffs request for additional information. Please discuss your

plans to ensure that the Bases reflect the actual POPCD

methodology that is approved by the NRC staff.

TVA Response TVA has revised the Bases pages to reflect the actual POPCD methodology approved by the NRC staff. (Note: Enclosure 2 of

this submittal contains the Bases page markups with the

references that include the NRC letter that approves the POPCD

methodology for SQN Unit 2.)

NRC Question 3 On pages E1-5 and E4-14 of Enclosure 1 to your January 12, 2007, submittal, you indicated that if an indication grows by an

extreme amount (i.e., an outlier) that you will implement a

methodology intended to address this issue. Given the text on

these two pages are different, it is not clear whether the

methodology would be submitted for NRC approval. Please confirm

that this outlier methodology would be submitted for NRC approval

prior to implementation. The NRC staff notes that its previous

approval of POPCD relied on (1) modifications to the inspection

and repair criteria to limit the potential for indications with

high voltage growth; (2) other calculations performed by the

licensee; and (3) additional reporting requirements that

essentially require an assessment if the under predictions were

significant (as discussed in the technical specifications).

TVA Response The outlier method would be submitted for NRC approval prior to implementation consistent with page E4-14 of Enclosure 4

.NRC Question 4 On pages E1-5 and E4-15 of Enclosure 1 to your January 12, 2007, submittal, you indicated that you performed rotating probe

inspections of bobbin indications greater than 1.5 volts and no

indications exceeded the 1.9 volt threshold for preventive

repair. Since the actual practices in prior inspections may

affect the potential for large voltage growth rates, please

discuss whether any indications were preventively repaired as a

result of these inspections (i.e., regardless of whether they

exceeded the 1.9 volt threshold). If indications were repaired (to address the potential for large voltage growth rates),

E1-3 discuss whether similar practices will be employed in all future inspections.

TVA Response During the end-of-cycles (EOCs) 12 and 13 inspections, 13 indications were preventively plugged at least in part as a

result of the rotating pancake coil (RPC) inspection of

indications over 1.5 volts. These indications were the largest

RPC confirmed indications less than two bobbin volts. During the

EOC-14 inspection, the indications above 1 volt were RPC tested.

A small number of tubes (five indications) were preventively

plugged. No specific guideline for preventive tube plugging was

applied. The considerations for plugging included RPC volts, bobbin growth rates, number of RPC indications, etc.

TVA will continue to review large bobbin voltage, RPC confirmed indications for preventive tube plugging that do not exceed the 1.9-volt RPC volt threshold for repair

. The option for preventive tube plugging will continue to be judgmental based on the overall NDE responses.

NRC Question 5 You indicated that the number of high voltage indications in the POPCD database for SQN-2 does not satisfy the minimum

requirements specified by the industry. As a result, you

compared the SQN-2 database to the industry database. Please

discuss what the effect would be on the SQN-2 POPCD curve if the

SQN-1 [Sequoyah Nuclear Plant, Unit 1] and SQN-2 POPCD databases

were combined. Although there may be differences in the noise

levels (e.g., from denting) between the two units, there may be

some insights gained on potential performance for higher voltage

level indications.

In addition, please provide an enlarged view of the data above 1.0 volt in Figure 5.

Your justification for using the SQN-2 POPCD curve instead of the more limiting of the composite POPCD or SQN-2 POPCD curve is

largely qualitative and relies on the small differences between

the curves. Since the POPCD curve is used to calculate the

probability of burst under steam line break conditions and the

amount of leakage under steam line break conditions, it would

appear that a more appropriate comparison would be to evaluate

the effects of the different POPCD curves on the structural and

leakage integrity of the SG tubes. Please provide this

assessment.

E1-4 Since this is a one-time assessment, please discuss your plans to submit a similar analysis until a sufficient number of high

voltage data points are present at SQN-2. Alternatively, discuss

your plans for using the most limiting of the POPCD curves.

TVA Response The large number of dents and high dent voltages at SQN-1 preclude meaningful combination of data from SQN-1into POPCD for

SQN-2. The addition of the SQN-1 data would not contribute

meaningful data for application of POPCD and would significantly

degrade the SQN-2 POPCD.

An enlarged view above 1.0 volt in Figure 5 is provided as Figure 5-1 (see page E1-30). The SQN-2 POPCD curve at the lower

95 percent is conservative relative to the industry curve while

the nominal regression curves are nearly identical. The smaller

number of data points in the SQN-2 POPCD data compared to the

industry data lead to the larger uncertainties for the SQN-2

POPCD. However, the differences are small and have negligible

influence on burst probability and leakage analyses.

The conclusion that small changes in POPCD have a negligible influence on burst and leakage is based on prior experience with

POPCD analyses rather than qualitative judgment. See response

to RAI-19 for examples of burst and leakage sensitivity to small

changes in POPCD. In Table 19-1 (see page E1-24), the

probability of burst and leakage are compared for the Addendum 5

POPCD and the SQN-2 POPCD. All other inputs are identical. The

computation considered 250,000 Monte Carlo Trials. In both

cases, the results are conservative relative to the as-found

indications at end of cycle (EOC)-13. Although the probability

of burst (POB) values are small, there are significant

differences between the POB values computed using the two

different POPCD functions. A test was run to determine if this

difference was a consequence of the small number of Monte Carlo

trials relative to the POB values. Table 19-1A (see page E1-25)

shows the comparable results using 1 million Monte Carlo trials.

Table 19-1B (see page E1-25) shows that the percent difference

between the POB using the two different POPCD curves is

significantly less when a larger number of trials is used. This

is because the Monte Carlo results are more reliable when more

bursts are predicted. Similarly, it is expected that for cases

where the probability of burst is greater, the difference in POB

for slightly different POPCD curves will be small.

A sufficient number of high voltage data points to satisfy the criteria for a plant-specific POPCD is expected to be present

when the EOC-14 POPCD is evaluated at the EOC-15 inspection. The

earliest that POPCD can be implemented is the EOC-15 inspection.

Accordingly, implementation of POPCD on SQN-2 will be based on E1-5 plant specific data with no need to assess the more limiting of the plant specific and industry POPCD distributions.

NRC Question 6 On page E4-6 (1 st bullet), you indicate that the end of cycle (EOC) inspection EOC n bobbin voltages are generally based on the inspection records for the EOC

n. Please discuss your plans to report (in the 90-day report) any instances in which sizing is

based on a reanalysis of the voltages previously reported. The

staff notes that detection will always be based on past

inspection records (as indicated in the first bullet).

TVA Response In any instance for which sizing is based on a reanalysis of the voltages previously reported, a description of the change and the

basis for the change would be discussed in the 90-day report. No

reanalyses have been applied to the POPCD data through the

EOC-12 evaluations reported in the submittal. The option for

reanalysis is included primarily to permit review of a EOC n missed indication with a very high EOC n+1 voltage for use in growth rate assessments.

NRC Question 7 On page E4-6 (2 nd bullet), you indicate that the EOC n voltage for new EOC n+1 indications will be based on lookback analyses when the EOC n voltages are not available from the inspection record.

Please clarify when an EOC n voltage would be available for a flaw not reported in EOC n (or should the when in this sentence really be since). In addition (if when is the correct word

in this sentence), please discuss why it is acceptable (in this

case) not to confirm that the reported EOC n voltage actually corresponds to the flaw reported at EOC n+1.TVA Response The word when in the sentence should be changed to the word since. The use of the word since will provide improved

clarity for the 2 nd bullet on page E4-6.

NRC Question 8 On page E4-7, you indicated that data supporting the adequacy of using the square root sum of the squares method for determining

the inferred bobbin voltage from multiple rotating probe

indications at a tube support plate was provided by another

utility (in an August 18, 2004 letter). Since this information E1-6 was specific to this utility, please provide a similar plot demonstrating that the approach is currently adequate for SQN-2 (future assessments will be provided in the 90-day report).

TVA Response Figure 8-1 (see page E1-31) shows the inferred bobbin voltage from multiple +Point indications compared to the measured bobbin

voltages. The inferred bobbin volts are obtained as the square

root of the sum of squares of the bobbin volts obtained for each

+Point indication from the correlation of bobbin volts to +Point

volts. It is seen that the inferred bobbin volts are

conservative compared to the measured bobbin volts for nearly all

measurements. The conservatism results from the relatively high

bobbin volts obtained from the correlation with +Point volts as

shown in Figure 8-2 (see page E1-31), which represents the

correlation updated to include EOC-14 data. The polynomial fit

to the 95 percent confidence on the mean regression line is used

to infer the bobbin volts. It is seen that the bobbin volts

inferred from the +Point volts is always greater than unity such

that the multiple +Point indication correlation leads to bobbin

volts greater than 1.5. Figure 8-2 is further discussed in

RAI-9.NRC Question 9 Figure 2 provides a correlation for assigning an inferred bobbin voltage to indications detected only with a rotating probe. A

similar curve is provided in Figure 3-13 of your March 20, 2007

letter, which submitted the SQN-2 Cycle 14 90-day SG report.

Please discuss the differences in these curves. Please discuss

if there have been significant changes in this correlation with

time. If so, discuss whether a composite curve is more

appropriate or whether a conservative lower bound to any single

cycle data is appropriate. In addition, please confirm that

there are no data from axially oriented outside diameter stress

corrosion cracking indications not detectable by bobbin (AONDBs)

such that an assessment of the adequacy of this correlation can

currently be assessed. The staff notes that it appears that the

prior practice was to plug AONDBs on detection (page E4-17).

TVA Response Figure 2 applies bobbin voltages inferred from the 95 percent confidence on the mean regression correlation of bobbin with

+Point volts. This is consistent with Section 10.1 of Addendum 6

to the alternate repair criteria (ARC) database (Reference 1) and

prior licensed POPCD applications. Figure 3-13 of the 90-day

report infers bobbin voltages from the 95 percent prediction E1-7 interval of the correlation, which yields more conservative bobbin voltage predictions.

Figure 8-2 (see page E1-31) shows a revision of the submittals Figure 2 bobbin to +Point volt correlation for SQN-2 EOC-14 data.

The +Point data for this correlation includes the single axial

indication (SAI) data from the EOC-14 inspection.

Upon approval for POPCD implementation, the 95 percent confidence on the mean bobbin to +Point voltage correlation will be applied

to obtain inferred bobbin voltages consistent with Figure 2 of

the transmittal and Figure 8-2 (see page E1-31) of this response.

The adequacy of the correlation cannot be assessed since the

prior practice was to plug the indications.

If/once an AONDB becomes detectable by bobbin, a comparison of the actual bobbin voltage to what would be expected based on the

inferred bobbin voltage from the prior inspection and typical

voltage growth will be included in the 90-day report.

NRC Question 10 On page E4-9, you indicated that if the p-value is greater than 5 percent, you will propose an alternate probability of detection (POD) model and submit the recommendation to the NRC for

approval. Given that it may take time for the NRC to review any

changes to the POD model, please discuss the model to be used in

the interim pending staff review of the alternate model. The NRC

staff notes that it previously accepted the use of a default

value of 0.6 for POD as an acceptable alternative.

TVA Response A default value of 0.6 for POD would be used as an alternative POD in the event that the p-value for a POPCD analysis is greater

than five percent. However, the likelihood of the p-value

increasing from less than 2.9 x 10

-7 to 0.05 as more data is accumulated in the database is extremely low.

NRC Question 11 On page E4-15, you indicate that an assessment for the onset of voltage dependent growth should be performed and the methods of

Reference 1 applied when growth rates show a dependence on the

beginning of cycle voltage. Please confirm that this assessment

will be performed. In addition, discuss whether there are any

differences in the voltage dependent growth methodology discussed

in Reference 1 and the methodology approved by the NRC staff in

prior POPCD approvals. If there are any differences, please

justify them.

E1-8 TVA Response Assessments for the onset of voltage dependent growth (VDG) will be performed and documented in each 90-day report. There are no

differences between the VDG methods of Section 10.3 of

Reference 1 and the methodology approved by the NRC staff in

prior POPCD approvals. It can be noted that Section 10.3

includes examples based on applying the methods to the plant

having a previously approved POPCD.

NRC Question 12 On page E4-16, you indicated that a rotating probe (+Point) inspection would be performed for +Point confirmed indications at

EOC n that are not detected by bobbin at EOC n+1. Please confirm that this is Note 1 in Table 1 (rather than Note 3 in Table 1 as

indicated in the text).

TVA Response It is correct that Note 1 in Table 1 should have been referenced on page E4-16 rather than Note 3.

NRC Question 13 On page E4-17, you indicate that you assign a through-wall depth (i.e., a percent code) to bobbinindications confirmed with a

rotating probe to be volumetric indications. Please confirm that

this applies only to volumetric wear indications and

thinning/wastage indications rather than to volumetric

indications attributed to intergranular attack or closely spaced

cracks. Please confirm that the voltage based repair criteria

are applied to volumetric outside diameter cracking indications (including intergranular attack). If not, please confirm that these indications are plugged on detection.

TVA Response It is correct that depth assignments for volumetric indications are only made for indications attributed to wear and

thinning/wastage indications. The voltage based repair criteria

are applied to intergranular attack or volumetric interpretations

for outside diameter cracking indications.

E1-9 NRC Question 14 On page E4-18, you indicated that no reevaluation was performed of the EOC 9 data for a 2.03 volt indication that was detected at

EOC 10. Please confirm that future assessments of POPCD that use

previous data will be re-evaluated to determine the voltage of

the potentially missed indication. In addition, please discuss

what growth rate was assigned to this indication if the previous

data were not reviewed (this is important from a benchmarking

standpoint).

TVA Response A review of the EOC-10 90-day report showed no 2.03 volt indication at SG 3, R32C17 H01 as stated on page E4-18.

Supporting documentation for that report noted that the 2.03 volt

indication at SG 3, R32C17 H01 which was originally reported as a

distorted support indication (DSI) was RPC tested and determined

to be an ID flaw, and thus it was eliminated from the axial

outer-diameter stress corrosion cracking (ODSCC) analysis.

Therefore, no look back to determine an ODSCC growth rate was

performed. This information however was not received by the

person developing the POPCD. As described on page E4-18, the

average growth rate of 0.1 volt was assigned to this indication

to obtain a 1.93 volt missed indication at EOC-9, which is the

largest undetected indication in the POPCD database. This

remains as a small conservatism in the SQN-2 POPCD. The

benchmark predictive calculations for EOC-11 in Table 8 consider

the 0.1 volt growth rate for this indication. The largest growth

in the EOC-11 predictive analysis is 0.7 volts/effective full-

power year.

TVA confirms that future assessments of POPCD that use previous data will be reevaluated to determine the voltage of the

potentially missed indication.

NRC Question 15 On page E4-18, you indicate the composite POPCD data contains 11 indications found only with a rotating probe (Column F of

Table 4) although there were only six occurrences. You further

indicate that the rotating probe only detections are counted as

missed indications in two successive cycle POPCD evaluations even

though they were repaired on detection. Please clarify this

discussion. If an indication was initially detected at EOC n+1 and subsequently plugged, it does not appear (to the staff) that the

indications should be counted twice based on a review of Table 1.

E1-10 TVA Response When the indication is found only by RPC at Cycle n+1, the indication is included as a missed bobbin indication at Cycle n (e.g., most frequently bobbin no degredation detected [NDD]

indication bobbin NDD intersection [BND]w/o RPC in Table 1) and

entered in Column F in Table 4. When Cycle n+2 is completed, the

indication is included as a missed bobbin indication at Cycle n+1 (Cycle n BND w/RPC detected [RDD] in Table 1). In most cases, the indication remains bobbin NDDand RPC detected at EOC n+2 (column F of Table 4) although the indication could be a new

indication in Column E or D of Table 4. Since these indications

were preventively plugged when found at SQN-2, the indication is

missed at Cycle n+1 based on BND w/RDD and plugged as shown in

Table 2 for Cycle n.

NRC Question 16 Please provide an enlarged view of the data above 1.0 volt in Figure 4. In addition, please discuss what POPCD curve is

required to be used in the assessments given that the POD above

1.0 volt for the cycle 12 data is less than the corresponding POD

for the composite dataset.

TVA Response Figure 16-1 (see page E1-32) provides the requested data above 1.0 volt from Figure 4 of the transmittal. On page E4-19 of TVAs January 12,2007 transmittal, it is noted that the multi-cycle POPCD is considered more appropriate for

future operational assessments than any one cycle of POPCD data.

On page E4-23, first bullet, it is noted that differences between

the multi-cycle POPCD and the last cycle should be assessed in

the 90-day report relative to the potential for significant

changes in detection capability. Recognizing the number of data

points for any one cycle of POPCD is considered to be too small

to control the expected POPCD for the next cycle, if there are

significant negative trends in POPCD, appropriate adjustments

will be made to POPCD to ensure reliable projections continue to

be made. If there are significant negative trends in POPCD, other corrective actions may also be necessary (e.g., chemical

cleaning to reduce noise, other actions to reduce noise in the

ECT, . . .).

NRC Question 17 Regarding Table 7, please confirm that the number of data points in the POPCD curve for EOC 7 through 12 is only slightly greater

than the number of datapoints from EOC 12. Since a number of

datapoints should be present from year to year, the staff would E1-11 have expected a large number of data points for the EOC 7 through 12 composite curve and a significantly less number of datapoints

for any one cycle (unless a significant number of new indications

were identified in EOC 13).

TVA Response As noted in the following paragraph, there is a large difference in the number of data points between EOC-7 to EOC-12 and only

EOC-12. However, Table 7 has erroneously entered the POPCD

parameters for EOC-8 to EOC-12 for EOC-12 parameters. The

Corrected Table 7 is attached (see page E1-24) and shows the

correct differences in the number of points as discussed below.

The POPCD plot for EOC-12 in Figure 4 of the submittal is

correct.The number of data points for EOC-7 to EOC-12 (Table 4 of submittal) is 4524 for detection at EOC n and 1869 for no detection at EOC n where the corresponding values for only EOC-12 (Table 6 of submittal) are 1494 and 361. These data represent a

large number of data points for the EOC-7 to EOC-12 data and a

significantly smaller number of data points for Cycle 12 alone.

NRC Question 18 Please confirm that no adjustment to the voltage growth rate distribution is performed when the average growth rate decreases

from one cycle to the next.

TVA Response As noted in Section 4.2, page E4-15 of the POPCD submittal, the incremental increase in average growth rate will be implemented

when the average growth rate shows an increase for the just

completed cycle. The intent of this statement is that the

adjustment is made only when the average growth rate increases

from one cycle to the next, and no adjustment is performed when

the average growth rate decreases. This is further noted in the

step-by-step description of developing growth rates given in the

response to RAI-22.

NRC Question 19 In the benchmark analysis, you used the composite POPCD curve from Cycle 7 through 12. This does not appear to be appropriate

since some of the data was not present at the time of the

inspections (and using future data to predict past trends would

normally be expected to provide reasonable results). As a

result, please repeat the benchmark analysis with POPCD data E1-12 available at the time the inspections were performed (use of the latest burst and leakage correlations and actual cycle lengths is

acceptable). In addition, this benchmarking should not include

the datapoint that exhibited extreme voltage growth since

actions were taken to limit the possibility of such extreme

voltage growths and inclusion of this datapoint can skew the

results. This datapoint should not be included in the beginning

of cycle voltage distribution or the growth rate data (i.e., the

average growth rate or the distribution of growth rates). As

part of this benchmarking analysis, please include an analysis of

the EOC 14 inspection data completed in Fall 2006. Please

include in this response the database used for assessing the

integrity of the tubes, the actual cycle length, and the cycle

length assumed in the benchmarking analysis. Lastly, discuss

whether there has been any significant preventive plugging of

tubes such that the benchmarking analysis (or growth rate

distributions) may have been skewed.

TVA Response As discussed in page E4-20 of the submittal, the SQN-2 composite POPCD was used for all prior cycles since the industry POPCD for

these cycles (required per Section 3.3, pages E4-10 and E4-11

when inadequate plant specific data are available) is essentially

the same as the Sequoyah POPCD. Figure 19-1 (see page E1-33)

shows the comparison of the industry Addendum 5 POPCD with the

SQN-2 POPCD. It is seen that these two distributions are

essentially the same with the larger uncertainties in the SQN-2

POPCD leading to a lower 95 percent POPCD slightly smaller than

the industry POPCD below about 0.2 volt and a slightly higher

POPCD above about 0.3 volt. Page E4-39, Figure 5 compares the

SQN-2 POPCD with the industry POPCD updated to the time of the

SQN-2 POPCD submittal. In this case, the lower 95 percent SQN-2

POPCD is in excellent agreement with the industry POPCD. It is

noted in Table 7-4 of the January 12, 2007 TVA submittal that

there is essentially no change in the industry POPCD data between

Addenda 4 and 5. Since the industry POPCDs for Addenda 4 to 6

and the SQN-2 POPCD are essentially the same and burst pressures

or leak rates are not sensitive to small changes in POD, there

was no need to change the POPCD distribution between the

projected EOC-11 to EOC-13 predictions in Table 9, page E4-33.

To numerically demonstrate the negligible influence of small differences in POD, the EOC-13 projections were repeated using

the Addendum 5 POPCD. The results are shown in the lower part of

Table 19-1 (see page E1-33), where the projected leak rates, number of indications, and maximum volts are essentially

unchanged by the change in POPCD. Small differences are seen in

the burst probabilities with the SQN-2 POPCD yielding slightly

lower burst probabilities, which is likely due to the modest E1-13 increase in the SQN-2 POPCD above about 0.3 volt. For benchmarking, the objective is to demonstrate margins over the

as-found conditions. This objective is satisfied by both the

SQN-2 and Addendum 5 POPCD distributions. The use of the SQN-2

POPCD is thus more realistic than using the Addendum 5 POPCD

since it yields slightly smaller burst probability margins. The

Addendum 5 POPCD would be the required benchmarking POD for

EOC-13 projections if there were significant differences from the

SQN-2 POPCD. The Addenda 4 and 5 industry POPCDs would have been

the required POPCD distributions for projecting Cycles 11 and 12, respectively. The negligible differences in burst pressures and

leak rates between applying the Addendum 5 POPCD and the SQN-2

Cycles 7-12 POPCD together with the negligible differences in

POPCD between Addendum 4 and Cycles 7-12 support the use of the

Cycles 7-12 POPCD for all benchmarking analyses in Table 8 of the

submittal. The actual cycle length in EFPD is compared to the

length of time in the analyses in Table 19-5 (see page E1-27).

EOC-11 used the actual time, and the other cases used the times

that were used in the predictions in the respective 90-day

reports.The benchmarking analyses for Cycles 13 and 14 are performed including and not including the one large growth rate of 5.67

volts/effective full power year found for Cycle 12 for a

comparison of the resulting POB and leakage. It is appropriate

to exclude the large growth rate because of the preventive

measures discussed in RAI-4. In this case, the bobbin voltages

grew at modest rates from 1.06 volts at EOC-7 to 1.98 volts at

EOC-11. The indication was not +Point inspected prior to the

large 9.76 volts found at EOC-12. The indication would have been

+Point inspected at EOC-11 based on the preventive repair

guideline currently being applied to inspect all bobbin DSI

indications greater than 1.7 volts. It is not clear that a

+Point inspection at EOC-11 would have led to a +Point amplitude

greater than 1.9 volts that would have required repair. The

results are shown at the bottom of Table 19-1 (see page E1-24).

It is seen that exclusion of the high growth rate value reduces

the burst probabilities and leak rates although the EOC-13

projections remain conservative compared to the as-found results.

Table 19-2 (see page E1-26) provides the EOC-14 projections and as-found results at EOC-14 for projections with and without the

large growth rate found in Cycle 12. The columns in the table

identify the ARC burst and leak rate correlations, the growth

rate used, and the POPCD used in the analyses. The EOC-14

projections with the large growth rate included are the

projections given in Table 9 of the submittal. The projections

are based on a Cycle 14 length of 545 days where the actual cycle

length was 537.1 days. The observations from the comparison are

as follows:

E1-14 1) The number of indications is underpredicted when POPCD is used. The extent of the underprediction is shown in

Table 19-3A (see page E1-26).

2) Using POPCD, leakage is conservatively predicted for all SGs. The results using the reduced growth rate are

much closer to the as-found results.

3) Using POPCD and the large growth rate due to the large indication at EOC-12, POB is conservatively predicted

for all SGs.

4) Using POPCD and the growth rate obtained by ignoring the large indication at EOC-12, POB is conservatively

predicted for SGs 1, 2, and 3, and is underpredicted by

1.11 x 10-4 using the reportedDSIs. This is an underprediction of one tenth of the value for

considering method revision (0.001) in the Diablo

Canyon TS as approved by NRC.

Based on these observations, the underprediction of the number of indications was investigated. It was noted that the definition

of what would be called a DSI was changed in the EOC-14

inspection from the definition used previously. In EOC-14, a

bobbin indication that appeared to be inside diameter (ID), and

was either RPC inspected and found to be NDD or was reviewed by

history to be unchanged and previously RPC tested as NDD, that

indication was considered to be a DSI and included in the

indication count and the integrity and leakage analysis. Table

19-3B (see page E1-26) shows what the indication count at EOC 14

would have been if the definition of a DSI were unchanged from

EOC-13. This table shows that the underprediction would be

significantly less, and within the limits specified (15 percent

or 150 indications) in the Diablo Canyon TS as approved by NRC.

The probability of burst and leakage were recomputed for EOC-14

results using the revised indication population. It is seen in

Table 19-4 (see page E1-27) that the results are slightly but not

significantly more favorable. This is because the probability of

burst and leakage are very dependent on the largest indications

which were not affected by the revision.

It is expected that this change in definition will result in a one-time step change in the number of indications so the

predictions for EOC-16 and beyond will not continue to show this

level of underprediction. The projections of record for EOC-15

were made in the 90-day report using the approved POD of 0.6.

Projections are planned to be made for EOC-15 for benchmarking

purposes using the approved POPCD prior to EOC-15. It is

expected that POPCD may be used for the projections of record

from EOC-16 forward.

E1-15 There were only 13 tubes preventively plugged at EOC-12 and EOC-

13. These are properly treated as plugged tubes in the benchmark

projections and the EOC actuals include the influence of all

plugging at the prior EOC. The growth rate from EOC n-1 to EOC n includes the growth for all tubes plugged at EOC

n. The growth rate from EOC n to EOC n+1 would not include the growth for any tubes plugged at EOC n.NRC Question 20 Regarding your continuing assessment of the inspection results, please confirm that an assessment will be performed for any

underpredictions in order to assess the probable cause. As

currently written, it is not clear to the staff whether the

assessments would only be performed when the quantitative

criteria listed in Section 7.0 of your submittal are exceeded.

In addition, please confirm that the assessment of the

underprediction of the number of indications will include the

potential need to increase the number of indications regardless

of whether the indications that need to be increased are low or

high voltage. Lastly, please confirm that you will provide an

update (based on the results of your inspection) to Table 7 for

the composite and one-cycle POPCD curve for SQN-2 in your 90-day

report.TVA Response As noted in the first bullet of Section 7.0, page E4-22, an assessment of the probable cause for any underpredictions, including potential corrective actions and potential changes to

probability of detection and or growth methodology, will be

included in the 90-day report. This assessment is expected to be

qualitative and no changes in ARC analysis methods are expected

to be immediately implemented in operational assessments. An

assessment of the potential need to revise the ARC analysis

methods will be performed if the underpredictions in burst

probability or leak rate exceed the values given in the second

bullet in Section 7.0. This assessment is expected to include

quantitative evaluations of proposed changes to the analysis

methods that might be immediately implemented in the operational

assessment.

As noted in the third bullet of Section 7.0, an assessment will be made of the need to increase the number of predicted low

voltage indications if the total number of as-found indications

is underestimated by greater the 15 percent or by greater than

150 indications. This guidance is based on the small influence

of low voltage indications on burst probability and leak rates.

An underprediction of high voltage indications leading to an

underprediction of burst probability or leak rate would lead to E1-16 the assessments of growth rates and POD required by the first or second bullet of Section 7.0.

TVA will provide an update (based on the results of each inspection) to Table 7 for the composite and one-cycle POPCD

curve for SQN-2 in the 90-day report.

NRC Question 21 On page E1-5, you indicate that upon approval of the POPCD methodology the growth ratesused in the operational assessments

will be obtained as the bounding growth rate of the SGs and the

composite average growth over the last two cycles of operation.

Please clarify this statement. For example, is the composite

average growth, the composite from all SGs over one cycle (or two

cycles)? If the composite is from all SGs, discuss whether it is

necessary to assess whether the average growth rate from one SG

is increasing at a rate greater than the other SGs (implying that

this SG may need a larger increase in the average growth rate

than the composite growth rate would suggest).

TVA Response The average growth rates for each SG for the past three cycles are shown in Table 21-1 (see page E1-28). Several observations

can be made. First, the average growth rates are small, with one

exception below 0.1 volt/EFPY; second, growth rates increase and

decrease for each SG; and third, the SG with the largest average

growth in one cycle is not the one with the largest average

growth in the next cycle. The increase in average growth rate

for each SG based on Table 21-1 is shown in Table 21-2 (see page

E1-28). It is seen that the increase in average growth rate

between Cycles 12 and 13 is negative for three of the four SGs.

The increase in average growth rate between Cycles 13 and 14 is

positive, but less than 0.1 volts/EFPY, for all four SGs. It may

also be noted that SG 3 that had the highest increase in average

growth in Cycle 13 had the lowest increase in growth in Cycle 14.

The benchmark cases run for RAI-19 did not add a growth rate adjustment (Delta Volts Adjustment) because the average

increase in growth rate was so small. In order to evaluate the

impact of a small growth rate adjustment, the prediction for SG 4

EOC-14 was recalculated with a growth rate adjustment of

0.1 volts/EFPY which bounds the increases in Table 21-2. The

comparison of the results reported in Table 19-2 (see page E1-26)

and those with the growth rate adjustment is shown in Table 21-3 (see page E1-28). The POB for this case has increased with this

adjustment to a conservative prediction relative to the as-found

results.

E1-17 Because the average growth rates are small, but variable, the bounding approach to developing the growth rate distribution to

be used for predictive analyses is considered appropriate for

SQN-2. An approach which will increase the likelihood of a

conservative prediction is to add the growth rate adjustment

prior to determining the bounding growth rate distribution.

The SQN-2 guidelines for developing growth rates are changed from those given in Section 4-2 (page E4-15). Upon implementation of

POPCD, if the average growth rate for any SG shows an increase

for the just completed cycle compared to the prior cycle, the

incremental increase in average growth per EFPY will be added to

each point in the growth rate distribution for that SG.

A bounding curve that envelopes the adjusted growth rate distributions for each SG for the last two cycles is the bounding

growth rate distribution to be used for the operational

assessment predictions. As discussed in RAI-22, voltage dependent growth (VDG)will be appliedon a SG specific basis for

the SGs showing VDG (only when it is conservative) with the

bounding growth distribution (determined from SGs without VDG)

applied for the other SGs. Similarly, if one SG develops a

significantly greater growth rate than the others, a SG specific

growth rate distribution will be used for this SG with the

bounding growth rate distribution of the other SGs applied to the

other SGs. This approach will provide a conservative growth rate

distribution, without the excessive conservatism of applying the

bounding growth rate adjustment to the bounding growth rate

distribution.

NRC Question 22 Please provide a step-by-step description of the rationale that will be used for selecting the growth rate distribution and the

POPCD curve used in the EOC projections. Please confirm that

this methodology was used in performing the benchmarking

analysis. If not, please justify any differences. Please

confirm that voltage dependent growth is assessed on a SG basis

rather than just a composite of all SGs.

TVA Response The step-by-step process to be applied for developing the growth rate distribution used in EOC projections upon NRC approval for

implementing POPCD is given below: 1.Prepare cumulative probability distribution function (CPDF) curves for each SG for each of the last two cycles.

When POPCD is applied, then either steps 1a or 1b are

applicable:

E1-18a.If the NRC has not approved the extreme growth modeling, then all growth rate data from the last two

cycles will be included in the assessment. b.If the NRC has approved the extreme growth modeling, than any growth rates greater than 5 volts/EFPY are to

be excluded from these distributions and included in

the extreme growth distribution, subject to possible

future NRC limitations on the extreme growth methods. 2.For each curve selected from Step 1, analyze the growth curve for signs of VDG. In general, only the last cycle

growth rates need to be evaluated for VDG since the prior

cycle would have previously been evaluated for VDG. a.Plot the individual growth data on a scatter chart with beginning of cycle (BOC) voltages on the x-axis

and voltage growth rates on the y-axis. Perform a

simple linear regression on these data. If the slope is

greater than about 0.1, then VDG should be considered

in the operational assessment projection for the next

cycle. If the slope is less than or equal to zero, then there is no evidence of VDG. If the slope is only

slightly positive (between 0.0 and 0.1), then

engineering judgment should be used to determine if VDG

needs to be included in the analyses. Engineering

judgment decisions should consider the results of the

previous POB and leak rate predictions to determine

appropriate actions if underpredictions occur, and

should consider the affects of potential preventative plugging below the repair limit. In some cases, it may

be necessary to perform POB and leak rate sensitivity

calculations to determine which growth curve is

limiting (voltage dependent or independent). b.For each curve in which VDG is apparent, determine how many growth bins to use and the appropriate breakpoints

by performing piecewise regression analysis in

accordance with Section 10.3 of the ARC database

Addendum 6 (Reference 1). 3.When POPCD is applied, determine the need for a growth rate adjustment (Delta Volts Adjustment) to account for

potentially increasing growth rates, per the following

steps:a.Determine the average growth rate for each SG. If there is VDG, the average growth rate for each cycle on

VDG growth bin should be determined. This process is E1-19 applied for the last two cycles (Cycles n and n-1).

When determining the average growth rates, it is

acceptable to include the negative growth rates (in

lieu of setting the negative growth rates to zero). b. If an extreme voltage growth rate (greater than 5 volts/EFPY) has occurred during either cycle, it should

be included or not included as discussed in Step 1. c. If the average Cycle n growth is greater than the average Cycle n-1 growth for any SG or any VDG bin, then the difference should be added to each of the

individual growth rates in the growth rate distribution

and any VDG distributions for any VDG distribution for

that SG if found necessary from Step 2. d. If the average Cycle n growth is less than the average Cycle n-1 growth, then no adjustment is performed. 4.For SGs that do not show VDG, select a growth curve that bounds all SG curves including the Delta Volts

Adjustment for the last two cycles. Since the curve

bounds all other growth rates for the last two cycles of

operation, it will be the limiting curve relative to

projecting leakage and probability of burst for these SGs.

In some cases, however, Step 2 may show that it may be

necessary to perform analyses for voltage-dependent growth

to determine which growth curve is limiting for an SG. In

such cases with VDG, it may also be necessary to perform

POB and leak rate sensitivity calculations using the

different growth curves to determine which curve is limiting.VDG will be applied on a SG specific basis for the SGs showing VDG (only when it is conservative) and a bounding growth distribution (determined from the SGs

without VDG) applied for the other SGs as discussed in 3.c

above. Similarly, if one SG develops a significantly

greater growth rate than the others, a SG specific growth

rate distribution will be used for this SG and the

bounding growth rate distribution determined from the

other SGs applied to the other SGs. For this guideline, the conservative approach of selecting the limiting growth

curve regardless of the number of indications in the SG-

specific growth distribution is applied so ARC guidelines

on minimum numbers of indications in a growth curve do not

need to be applied. 5.If multiple calculations are performed using different growth rate distributions or POPCD distributions, then the

90-day report should specify the calculation of record.

E1-20 The above steps were considered for developing the growth rates used in the benchmarking analyses. No VDG has been experienced

on SQN-2 and the growth rate adjustments are negligible for the

benchmark cases run, except as described in RAI-21.

Since the SQN-2 POPCD database will satisfy all requirements for applying a plant-specific POPCD at the next inspection, including

EOC-14 data in the POPCD database, the multi-cycle SQN-2 POPCD

from EOC-7 to the last completed POPCD update (e.g., POPCD for

EOC-14 when the EOC-15 inspection is completed) will be used for

operational assessment projections of burst probability and SLB

leak rate except if significant trends in POPCD occur. In this

case, appropriate adjustments will be made to the POPCD to ensure

conservative projections continue to be made. The step-by-step

process for updating POPCD for operational assessments is only to

update the multi-cycle POPCD to include POPCD analyses from the

last completed inspection. As discussed in the response to RAI-

19, the SQN-2 POPCD through EOC-12 was used for EOCs-11 through

EOC-14 projections since there are negligible differences in the

industry Addenda 4 to 6 POPCDs and the SQN-2 POPCD through EOC-

12.NRC Question 23 You indicate that you will address POPCD uncertainties by either applying POPCD at the lower 95 percent confidence level or

including an uncertainty analysis for POD in the operational

assessment (Section 8.0 of your January 12, 2007 letter). Please

clarify whether the uncertainty analysis for POD in the

operational assessment is equivalent to the uncertainty analysis

approved for use at Diablo Canyon (in their approval to use

POPCD). If not, please clarify this statement.

In addition, since the POPCD curve is used to calculate the probability of burst under steam line break conditions and the

amount of leakage under steam line break conditions, it would

appear that an assessment of the adequacy of using the lower 95

percent confidence level to address uncertainty (rather than the

Monte Carlo approach approved for use at Diablo Canyon) would be

to evaluate the effects of the different approach for modeling

uncertainty in the POPCD curves on the structural and leakage

integrity of the SG tubes. Please provide this assessment.

Since this is a one-time assessment, please discuss your plans to submit a similar analysis in each of your 90-day reports. In the

event that the results using the lower 95 percent confidence

level are non-conservative, discuss your plans to use the

uncertainty modeling approach approved for Diablo Canyon.

E1-21 TVA Response The uncertainty analysis methods applied to obtain the lower 95 percent POD are identical to the uncertainty methods approved for

use at Diablo Canyon.

The requested comparison of applying directly the lower 95 percent confidence for the POD with performing the Monte Carlo

analysis allowing for variability in the POD and then selection

of the 95 percent results should never be necessary and is not

included in this RAI response or planned for future 90-day

reports. The primary purpose for performing Monte Carlo analyses

is to reduce the conservatism in applying individual lower

confidence values (deterministic analyses) in the analyses for

burst pressures and leak rates. Without this established

reduction in conservatism, Monte Carlo calculations would rarely

or never be performed. Since the POPCD uncertainties are small

due to the large number of data points, the effects of including

POPCD uncertainties on burst pressures and leak rates, even at

the conservative lower 95 percent POD, are negligible.

In order to illustrate the uncertainties in the SQN-2 POPCD, Figure 23-1 (see page E1-34) shows the POPCD curves for the

50 percent confidence, the 95 th percentile lower bound, and the 99 th percentile lower bound POPCD for volts greater than 1 volt.

It is seen that the curves are quite close. To assess the effect

of these differences on probability of burst and leakage, the SG

4 example case which was run with 1 million trials is rerun with

the 50 percent confidence and with the 99-percent lower-bound

POPCD curves. The results are shown in Table 23-1 (see page E1-

28). It is seen that compared to the 50 percent confidence

POPCD, the 95 percent confidence POPCD results in a slight

increase in the number of indications, leak rate and POB.

However, compared to the 95 percent confidence POPCD, the 99

percent confidence POPCD results in a small increase in the

number of indications, no increase in the leak rate, and a small

decrease in the POB. From these results, it is seen that the

POPCD uncertainties have a negligible effect on the burst and

leakage predictions; and therefore, a refinement in the

methodology to include the POPCD uncertainties in the Monte Carlo

process is unwarranted.

The Industry POPCD curve presented in Figure 1 and Figure 5 and expanded in Figure 5-1 (see page E1-30) is not the Addendum 5

curve used in the benchmark analyses. The Figure 1 curve is

described in the submittal as essentially the same as reported

in Addendum 6. Later, Figure 5 curve (the same as Figure 1) is

described as industry POPCD updated to the time of the Sequoyah

2 POPCD submittal. The Addendum 5 curve is shown in Figure 19-

1, and described as Figure 19-1 shows the comparison of the

industry Addendum 5 POPCD with the SQN-2 POPCD. It is seen that E1-22 these two distributions are essentially the same with the larger uncertainties in the SQN-2 POPCD leading to a lower 95 percent

POPCD slightly smaller than the industry POPCD below about 0.2

volt and a slightly higher POPCD above about 0.3 volt.

An expanded view of Figure 19-1 is shown as Figure 19-2 (see page E1-34). Figure 19-2 shows that the POPCD used in the benchmark

analyses for 95 th percentile Addendum 5 is slightly more conservative than the 95 th percentile SQN-2 specific curve. Note that in Table 19-1A, the leakage and number of indications are

very slightly more conservative for the Addendum 5 cases

indicating that the Addendum 5 curve is a slightly more

conservative POPCD.

The POB values, because they are so small, are somewhat variable because of the Monte Carlo analysis process.

Therefore, it is not inconsistent that the slightly lower POPCD curve results in a slightly more conservative result.

Compared to the PWSCC ARC that was implemented for Diablo Canyon, the application of a 95 th percentile POPCD is very different.

For example, consider a 3-volt indication and assume the

indication was plugged. As seen in Figure 23-1 (see page

E1-34), the mean POPCD is 0.97, and the 95 th percentile is 0.96.

A POD of 0.97 in the ARC analysis means that for every 100 Monte

Carlo trials of the population in the SG, there will be 3

indications that are to be included in the analysis. If

uncertainties are applied (symmetric about the mean), sometimes

the POD will be a little higher and sometimes it will be a little

lower. At the end of the analysis, the number of 3-volt

indications considered will be 3/100 times the number of Monte

Carlo trials.

At the 95 th percentile level of POPCD, the POD is 0.96 which means that in the ARC analysis there will be 4 indications for

every 100 Monte Carlo trials. Since this is constant, at the

end of the analysis the number of 3-volt indications considered

will be 4/100 times the number of Monte Carlo trials. The more

3-volt indications considered in the analysis, the more likely

one will have a greater probability of burst and leakage, and the

more frequently a larger number of large indications contribute

to the total leakage. Therefore, it is apparent that using the

95 th percentile POPCD is conservative compared to using the mean with uncertainties.

Given that the bases for performing Monte Carlo analyses is to reduce projected burst and leak rate results relative to

deterministic analyses such as directly applying the lower 95

percent POPCD curve, there are no plans to include sampling of E1-23 POPCD uncertainties in operational assessments such as applied for Diablo Canyon.

Supplemental Information Since the submittal was prepared, additional data was obtained from the EOC-14 inspection enabling the construction of POPCD

which includes the latest data. This cumulative data is shown in

Table 10 (see page E1-38) for the EOC-13 POPCD with data through

EOC-14. The log-logistic data fit parameters are given in

Table 11 (see page E1-39) and the comparison of the EOC-12 POPCD

which has been used in the benchmarks and the EOC-13 POPCD are

shown in Figure 25-1 (see page E1-35) with an expanded view in

Figure 25-2 (see page E1-36). The EOC-13 POPCD is slightly lower

than the EOC-12 POPCD because of the increased number of new

indications in EOC-14 due to the change in the DSI definition.

Reference1.EPRI Report NP 7480-L, Addendum 6, 2004 Database Update, Steam Generator Tubing Outside Diameter Stress Corrosion

Cracking at Tube Support Plates Database for Alternate

Repair Limits, October 2004.

E1-24 Corrected Table 7. Sequoyah-2 and Industry POPCD Log Logistic Distribution Parameters Parameter Sequoyah-2 POPCD at EOC-7 to EOC-12 Sequoyah-2 POPCD At EOC-12 Industry POPCD 30 Inspections Number of Data Points6393 1845 46454 b 0 (Intercept) 1.9947 2.3727 1.9628 b 1 (Slope) 2.9920 2.6592 3.1433 V 113.530E-03 1.467E-02 3.742E-04 V 12 6.826E-03 2.767E-02 7.215E-04 V 22 1.728E-02 6.962E-02 2.077E-03 Table 19-1 Additions to Table 8. Sequoyah-2 Prior Cycle Benchmarking Results for POPCD Projected Results As Found Results ProjectedOutage S GPOB Leak Rate No.Ind.Max. Volts (1)POB Leak Rate No.Ind.Max. Volts (1)POB & Leak Rate CorrelationsGrowth Rate Used POD Used EOC-13 Projections Reported in Table 8 of POPCD Submittal, 250,000 trials EOC-13 1 1.05x10

-30.421 342 8.5 1.90x10

-50.0724294 1.95 2 1.02x10

-3 0.429 342 8.5 3.10x10

-5 0.0769305 1.97 3 1.23x10

-3 0.574 406 8.7 5.26x10

-5 0.224 412 2.36 4 2.78x10

-3 1.230 969 8.8 9.24x10

-5 0.285 836 1.74 Addendum 5 PSLB = 2405 psiAll SGs: Bounding Cycles 11

& 12, Fig. 3-16, Ref. 8

including largest growth rate.

Seq.-2 POPCDEOC-13 Projections Revised for Changes in Growth Rate and POPCD, 250000 Trials EOC-13 1 9.72x10

-50.222 342 3.6 1.90x10

-50.07242941.95 2 9.72x10

-5 0.240 342 3.6 3.10x10

-50.07693051.97 3 1.40x10

-4 0.355 406 3.8 5.26x10

-50.224 4122.36 4 2.26x10

-4 0.722 969 3.9 9.24x10

-50.285 8361.74 Addendum 5 PSLB = 2405 psiAll SGs: Bounding Cycles 11

& 12, Fig. 3-16, Ref. 8

without largest growth rate.

Seq.-2 POPCDEOC-13 1 1.30x10

-40.220 345 3.6 1.90x10

-50.07242941.95 2 7.28x10

-5 0.238 345 3.6 3.10x10

-50.07693051.97 3 2.17x10

-4 0.352 409 3.8 5.26x10

-50.224 4122.36 4 2.67x10

-4 0.722 978 3.9 9.24x10

-50.285 8361.74 Addendum 5 PSLB = 2405 psiAll SGs: Bounding Cycles 11

& 12, Fig. 3-16, Ref. 8

without largest growth rate.

Add. 5 POPCD Notes:1. Voltage where projected tail accumulates to 0.3 ind.

E1-25 Table 19-1A Additions to Table 8. Sequoyah-2 Prior Cycle Benchmarking Results for Additional Monte Carlo Trials Projected Results As Found Results ProjectedOutage S GPOB Leak Rate No.Ind.Max. Volts (1)POB Leak Rate No.Ind.Max. Volts (1)POB & Leak Rate CorrelationsGrowth Rate Used POD Used EOC-13 Projections Revised for 1 million trials EOC-13 1 8.65x10

-50.218 342 3.6 1.90x10

-50.07242941.95 2 7.33x10

-5 0.236 342 3.6 3.10x10

-50.07693051.97 3 1.32x10

-4 0.348 406 3.8 5.26x10

-50.224 4122.36 4 2.29x10

-4 0.715 969 3.9 9.24x10

-50.285 8361.74 Addendum 5 PSLB = 2405 psiAll SGs: Bounding Cycles 11

& 12, Fig. 3-16, Ref. 8

without largest growth rate.

Seq.-2 POPCDEOC-13 1 7.66x10

-50.220 345 3.6 1.90x10

-50.07242941.95 2 8.10x10

-5 0.236 345 3.6 3.10x10

-50.07693051.97 3 1.57x10

-4 0.352 409 3.8 5.26x10

-50.224 4122.36 4 2.16x10

-4 0.722 978 3.9 9.24x10

-50.285 8361.74 Addendum 5 PSLB = 2405 psiAll SGs: Bounding Cycles 11

& 12, Fig. 3-16, Ref. 8

without largest growth rate.

Add. 5 POPCD Notes:

1. Voltage where projected tail accumulates to 0.3 ind.

Table 19-1B Additions to Table 8. Sequoyah-2 Prior Cycle Comparison of Results for Additional Monte Carlo Trials ProjectedOutage 1 Million trials 250,000 Trials SG POB Seq-2 POPCD POB Add 5 POPCD Difference as % of Seq 2 POPCD POB POB Seq-2 POPCD POB Add 5 POPCD Difference as % of Seq 2 POPCD POB EOC-13 1 8.65x10

-5 7.66x10-5 11.4% 9.72x10

-5 1.30x10-4-33.7% 2 7.33x10

-5 8.10x10-5-10.5% 9.72x10

-5 7.28x10-5 25.1% 3 1.32x10

-4 1.57x10-4-18.9% 1.40x10

-4 2.17x10-4 -55% 4 2.29x10

-4 2.16x10-4 5.7% 2.26x10

-4 2.67x10-4 -18.1%

E1-26 Table 19-2 Additions to Table 9. Sequoyah-2 EOC-14 Benchmarking Results for POPCD Projected Outage S GProjected Results As Found Results POB & Leak Rate Correlations Growth Rate Used POD Used POB Leak Rate No. Ind Max.Volts POB Leak Rate No. Ind. Max.Volts EOC-14 Projections Reported in Table 9 of POPCD Submittal EOC-14 1 1.73x10

-30.400 401 9.3 8.76x10

-50.108 438 2.36 2 1.80x10

-3 0.409 412 9.3 6.28x10

-5 0.127 507 1.81 3 2.23x10

-3 0.667 531 9.6 1.35x10

-4 0.266 574 2.27 4 4.57x10

-3 1.12 1116 9.6 3.55x10

-4 0.484 1228 4.74 Addendum 6 PSLB = 2405 psi All SGs: Bounding Cycle 12, Fig. 3-16, Ref. 8 including largest growth rate. Sequoyah-2 POPCD EOC-14 Projections Revised for Changes in Growth Rate EOC-14 1 1.35x10

-40.160 401 3.7 8.76x10

-50.108 438 2.36 2 9.24x10

-5 0.161 412 3.6 6.28x10

-5 0.127 507 1.81 3 2.31x10

-4 0.352 531 4.0 1.35x10

-4 0.266 574 2.27 4 2.44x10

-4 0.509 1116 4.0 3.55x10

-4 0.484 1228 4.74 Addendum 6 PSLB = 2405 psi All SGs: Bounding Cycle 12, Fig. 3-16, Ref. 8 without largest growth rate. Sequoyah-2 POPCD Table 19-3A EOC-14 DSI Indications as Reported in 90 Day Report SG Reported DSI Predictions with POD = 0.6

( 90 Day Report)

Predictions with POPCD (Table 19-2)

Underpredicted by POPCD Percent Underpredicted1 438 489 401 37 8% 2 507 501 412 95 19% 3 574 680 531 43 7% 4 1228 1387 1116 112 9%

Table 19-3B EOC 14 DSI Indications if EOC

-13 Definition of DSI is Used SG Revised DSI Predictions with POPCD Under/ Over predicted by

POPCD Percent Under/Over

predicted1 403 401 2 under <1% under 2 455 412 33 under 7% under 3 512 531 19 over 4% over 4 1161 1116 45 under 4% under E1-27 Table 19-4 EOC-14 As Found Results for SG 4 POB Leak RateNo. Ind. Max. Volts EOC-14 As Reported in 90 Day Report 3.55x10-4 0.484 1228 4.74 EOC-14 Revised to EOC 13 Definition of DSI 3.24x10-4 0.451 1161 4.74 Table 19-5 Cycle Length for Benchmark Analyses EOC Number Actual Cycle length, EFPD Analysis Cycle Length, EFPDEOC-11 510.35 510.35 EOC-12 501.6 515 EOC-13 470.9 498 EOC-14 537.1 545 E1-28 Table 21-1 Average Growth Volts/ EFPY SG Cycle 12 Cycle 13 Cycle 14 1 0.0466 0.0456 0.0736 2 0.0699 0.0191 0.0893 3 0.0326* 0.0851 0.097 4 0.0517 0.0358 0.1179 Average 0.0501* 0.0451 0.1012

• Large growth indication removed Table 21-2 Increase in Average Growth Volts/ EFPY SG Cy12-13 Cy13-14 1 -0.001 0.028 2 -0.0508 0.0702 3 0.0525 0.0119 4 -0.0159 0.0821 Average -0.005 0.0561 Table 21-3 Effect of Average Growth Addition Projected Outage S GProjected Results As Found Results POB & Leak Rate Correlations Growth Rate Used POD Used POB Leak Rate No. Ind Max.Volts POB Leak Rate No. Ind. Max.Volts EOC-14 Projection From Table 19-2 EOC-14 4 2.44x10

-4 0.509 1116 4.0 3.55x10

-4 0.484 1228 4.74 Addendum 6 PSLB = 2405 psi All SGs: Bounding Cycle 12, Fig. 3-16, Ref. 8 without largest

growth rate. Sequoyah-2 POPCD EOC-14 Projection with 0.1V/EFPY adjustment EOC-14 4 3.99x10

-4 0.687 1116 4.1 3.55x10

-4 0.484 1228 4.74 Addendum 6 PSLB = 2405 psi All SGs: Bounding Cycle 12, Fig. 3-16, Ref. 8 without largest growth rate, with 0.1V/EFPY adjustmentSequoyah-2 POPCD E1-29 Table 23-1 Sensitivity of POPCD Uncertainties on Results 1 Million Trials Projected Outage S GProjected Results As Found Results POB & Leak Rate Correlations Growth Rate Used POD Used POB Leak Rate No. Ind Max.Volts POB Leak Rate No. Ind. Max.Volts EOC-13 Projections, 50% CL POPCD EOC-13 4 2.09x10

-40.701 954 3.9 9.24x10

-5 0.285 836 1.74 Addendum 5 PSLB = 2405 psi All SGs: Bounding Cycles 11 & 12, Fig.

3-16, Ref. 8 without

largest growth rate. Sequoyah-2 POPCD, 50%

confidenceEOC-13 Projections, 95% CL POPCD From Figure 19-1A EOC-13 4 2.29x10

-4 0.715 969 3.9 9.24x10

-50.285 836 1.74 Addendum 5 PSLB = 2405 psi All SGs: Bounding Cycles 11 & 12, Fig. 3-

16, Ref. 8 without largest growth rate. Sequoyah-2 POPCD, 95%

lower bound EOC-13 Projections, 99% CL POPCDEOC-13 4 2.05x10

-40.715 975 3.9 9.24x10

-50.285 836 1.74 Addendum 5 PSLB = 2405 psi All SGs: Bounding Cycles 11 & 12, Fig.

3-16, Ref. 8 without largest growth rate. Sequoyah-2 POPCD, 99% lower

bound E1-30Figure 5-1. Sequoyah-2 and Industry 7/8 POPCD above 1.0 Volt Comparison of Sequoyah-2 and Industry 7/8" Tubing POPCD Weighted Generalized Linear Model Loglogistic Solution 80%90%100%1 10Bobbin Amplitude (Volts)Probability of Detection Sequoyah-2 POPCD RegressionSequoyah-2 POPCD at Lower 95%Industry 7/8 POPCD RegressionIndustry POPCD at Lower 95%

E1-31 Figure 8-1.Sequoyah 2 EOC-14: RMS Inferred Bobbin Volts from Multiple SAIs 00.5 11.5 22.5 33.5 44.5 55.5 600.511.522.533.544.55Measured Bobbin VoltsBobbin Volts Inferred from Multiple SAIsRMS Inferred BobbinVoltsIdeal Equivalent Volts Figure 8-2. Sequoyah Unit 2 EOC-14 Plus Point Volts to Bobbin Volts Correlationy = 0.0174x 2 + 1.0398x + 0.92760.000.501.001.50 2.00 2.503.003.50 4.004.505.000.000.501.001.502.002.503.003.50Plus Point SAI VoltsBobbin DSI VoltsSAI Data (no DNTs) Mean Regression LineUpper 95% Confidence of MeanPoly. (Upper 95% Confidence of Mean)

E1-32Figure 16-1. POPCD for Sequoyah-2 Cycles 7-12 and Cycle 12 above 1.0 Volt Comparison of Sequoyah-2 EOC 7-12 and EOC 12 POPCD above 1.0 Volt Weighted Generalized Linear Model Loglogistic Solution 80%90%100%1 10Bobbin Amplitude (Volts)Probability of Detection Sequoyah-2 EOC 7-12 POPCDSequoyah-2 EOC 12 POPCDSequoyah-2 EOC 7-12 POPCD at Lower 95%Sequoyah-2 EOC 12 POPCD at Lower 95%

E1-33 Figure 19-1 Comparison of Generic POPCD for 7/8" Add. 5 & Sequoyah-2 POPCD of Fig. 3(Weighted Generalized Linear Model Loglogistic Solution - Fractional POD Data Shown for Information Only) 0%10%20%30%

40%50%

60%

70%80%90%100%0.010.1110Bobbin Amplitude (Volts)Probability of Detection POPCD for Addendum 5 DatabasePOPCD at Lower 95% for Addendum 5POPCD for Seq. 2, Fig. 3POPCD for Seq. 2, Fig. 3 Lower 95%

E1-34 Figure 19-2 Expanded View of Figure 19-1 Comparison of Sequoyah-2 and ADD 5 7/8" Tubing POPCD Weighted Generalized Linear Model Loglogistic Solution85%86%87%88%

89%90%91%92%93%94%95%96%97%98%99%100%1 10Bobbin Amplitude (Volts)Probability of DetectionSequoyah-2 POPCD RegressionSequoyah-2 POPCD at Lower 95%Add 5 7/8 POPCD RegressionAdd 5 POPCD at Lower 95%

Figure 23-1 E1-35Comparison of 50th, 95th and 99th Percentile Sequoyah 2 POPCD0.900.91 0.92 0.930.940.950.960.970.98 0.99 1.00110100Volts CDF95th Percent LowerBound99th Percent Lower Bound50% confidence Figure 25-1 E1-36Comparison of Sequo yah-2 EOC-12 and EOC-13 POPCD Weighted Generalized Linear Model Loglogistic Solution 0%10%

20%

30%40%50%60%70%

80%

90%100%0.010.1110Bobbin Amplitude (Volts)Probability of DetectionSeq.-2 EOC-12 POPCD RegressionSeq.-2 EOC-12 POPCD at Lower 95%Seq.2 EOC-13 POPCD RegressionSeq.2 EOC-13 POPCD at Lower 95%

Figure 25-2 E1-37Comparison of Sequoyah-2 EOC-12 and EOC-13 POPCD Weighted Generalized Linear Model Loglogistic Solution 85%86%87%88%89%90%91%92%93%94%95%96%97%98%99%100%1 10Bobbin Amplitude (Volts)Probability of Detectio nSeq.-2 EOC-12 POPCD RegressionSeq.-2 EOC-12 POPCD at Lower 95%Seq.2 EOC-13 POPCD RegressionSeq.2 EOC-13 POPCD at Lower 95%

E1-38ColumnHIJKExcluded from POPCDBDD / RDDBDD / RDDBDD w/o RPCBDD w/o RPCBDD / RDDPlugged at EOCnBND w/o RPCBDD / RDDBND w/o RPCBDD w/o RPCBND w/o RPCBND / RDDBDD / RNDBDD w/o RPCAll RND AT EOCn+1Volta g eBDD / RDDBND / RDDBDD / RDDBDD w/o RPCBDD w/o RPCPlugged at EOCnBND / RDDBDD / RDDBND / RDDBDD w/o RPCBND / RDDBND / RDDBDD / RNDBDD / RDDAll BND w/o RPCDetectionNoPOPCD forBinBDD w/o RPCBDD / RDDBND / RNDBDD / RDDBND / RNDBDD w/o RPCBND / RNDBND / RDDBDD / RNDBND / RDDat EOCn+1at EOCnDetectionVoltage BinBDD w/o RPCBND / RDDBND / RDDPlugged at EOCnBDD/RND/Plugged at EOCnat EOCnNote (1)0.01-0.1024380.0950.11-0.20711883410.3550.21-0.301476945340.5650.31-0.4012310415420.6580.41-0.509710643830.7350.51-0.60908792820.7570.61-0.70607392020.7850.71-0.80545531030.8430.81-0.9047410770.8420.91-1.0032267570.8241.01-1.1019176280.8631.11-1.2019131230.8511.21-1.30157670.9161.31-1.40144390.8271.41-1.5083760.8601.51-1.6012630.8971.61-1.7012010.9521.71-1.801801.0001.81-1.905201.0001.91-2.001710.8752.01-2.102401.0002.11-2.200101.0002.21-2.300101.0002.31-2.400101.0002.41-2.500201.0002.51-2.600003.21-3.300003.31-3.400101.0003.41-3.500003.51-3.600101.0003.61-3.700009.61-9.700009.71-9.800101.000000000Total809637726370.707Notes: 0 0 0 66 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 3 0 1 1 9 4

6 8 6 10 6 0 0 5

6New EOCn+1 Bobbin NotRPC InspectedInd.Found Only by RP C at E OCn+1 or at EOC n & Plu gged at EOC n(3)EOC nRPC NDD Bobbin Indications (2)Totals for POPCD EvaluationEOC n Bobbin Ind. RPC Confirmed at EOCn+1EOC n Bobbin Ind. Not RPC Inspected at EOCn+1 EOC n Bobbin Ind. Repaired at EOC nNew EOCn+1 Bobbin RPC Confirmed GSequoyah-2 Specific POPCD Data TableDetection at EOC nNo Detection at EOCn (New Indications)BCDE3) Includes indications at EOCn plugged at EOCn and new indications at EOCn+1, not reported in the bobbin inspection, and found only by RPC inspection of dents, mixed residuals or other reasons for the RPC inspection. 4) BDD = Bobbin detected indication; BND = Bobbin NDD intersection; RDD = RPC detected indication; RND = RPC NDD intersection2236141) POPCD for each voltage bin calculated as (Detection at EOCn)/(Detection at EOCn + No Detection at EOCn). By column, POPCD = (A+B+C)/(A+B+C+D+E+F+G).2) EOCn RPC NDD bobbin indications are treated as new indications per NRC request836545388321 00 00 00 00 00 00 10 00 00 00 00 00Table 10: Sequoyah-2 Composite POPCD Summary Evaluation for Results for EOC-7 (1996) thru EOC-14 (2006) for POPCD at EOC-6 thru EOC-13 A0403350 F6181111498020667728330050103320251007341018124393844824114971362672541226115104929445410729852552399163522 6210570113251101 118544552014 29301125 1127826 01 00 0118515410 304130 002000 00 00 00 420040 110010 000010 00 00 00 000020 10 000000 0000000010 000000 00 00 00 000000 10 E1-39 Table 11 Sequoyah Unit 2 EOC-13 POPCD Log-Logistic Distribution Parameters Parameter Sequoyah Unit 2 POPCD at EOC-13 Number of Data Points 9014 b 0(intercept)1.8865 b 1(Slope)2.7789 V 11 2.308E-03 V 12 4.489E-03 V 22 1.169E-02 E2-1 ENCLOSURE 2 TENNESSEE VALLEY AUTHORITY (TVA)

SEQUOYAH NUCLEAR PLANT (SQN)

UNIT 2 REFORMATTED TECHNICAL SPECIFICATION (TS) AND BASES PAGE MARKUPS FOR SQN TS CHANGE 06-06, PROBABILITY OF PRIOR CYCLE DETECTION E2-2 ADMINISTRATIVE CONTROLS STEAM GENERATOR (SG) TUBE INSPECTION REPORT (continued)a. The scope of inspections performed on each SG, b. Active degradation mechanisms found, c. Nondestructive examination techniques utilized for each degradation mechanism, d. Location, orientation (if linear), and measured sizes (if available) of service induced indications, e. Number of tubes plugged during the inspection outage for each active degradation mechanism, f. Total number and percentage of tubes plugged to date, g. The results of condition monitoring, including the results of tube pulls and in-situ testing, and h. The effective plugging percentage for all plugging in each SG. 6.9.1.16.2 A report shall be submitted within 90 days after the initial entry into MODE 4 following completion of an inspection performed in accordance with the steam generator program (6.8.4.k) when voltage based alternate repair criteria have been applied. The report shall include information described in Section 6.b of Attachment 1 to NRC Generic Letter 95-05, Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking. 6.9.1.16.3 For implementation of the voltage-based repair criteria for tube support plate (TSP) intersections, notify the staff prior to initial entry into MODE 4 following completion of an inspection performed in accordance with Specification 6.8.4.k, Steam Generator (SG) Program, should any of the following conditions arise: 1) If circumferential crack-like indications are detected at the TSP intersections. 2) If indications are identified that extend beyond the confines of the TSP. 3) If indications are identified at the TSP elevations that are attributable to primary water stress corrosion cracking. 6.9.1.16.4 For implementation of W*, the calculated steam line break leakage from the application of TSP alternate repair criteria and W* inspection methodology shall be submitted within 90 days after the initial entry into MODE 4 following completion of an inspection performed in accordance with Specification 6.8.4.k, Steam Generator (SG) Program. The report will include the number of indications within the tubesheet region, the location of the indications (relative to the bottom of the WEXTEX transition [BWT] and TTS), the orientation (axial, circumferential, skewed, volumetric), the severity of each indication (e.g., near through-wall or not through-wall), the side of the tube from which the indication initiated (inside or outside diameter), and an assessment of whether the results were consistent with expectations with respect to the number of flaws and flaw severity (and if not consistent, a description of the proposed corrective action).

May 22, 2007 SEQUOYAH - UNIT 2 6-14a Amendment No. 305 IN S ERT 1 E2-3 INSERT 16.9.1.16.5 For implementation of the probability of prior cycle detection (POPCD) method, for the voltage-based repair criteria at tube support plate intersections, if the end-of-cycle conditional tube rupture probability for a postulated main steam line break, the projected

primary to secondary leak rate during a postulated main steam line break, or the number of

indications are under predicted by the previous cycle operational assessment, the following

shall be reported to the Commission within 90 days after initial entry into MODE 4 following

completion of inspection performed in accordance with specification 6.8.4.k, Steam

Generator Program. 1. The assessment of the probable causes for the under prediction, proposed corrective actions, and any recommended changes to probability of detection or growth

methodology indicated by potential methods assessments. 2. An assessment of the potential need to revise the alternate repair criteria analysis methods if: the burst probability is under predicted by more than 0.001 (i.e.,

10 percent of the performance criteria) or an order of magnitude; or the leak rate is

under predicted by more than 0.5 gallon per minute (gpm) or an order of magnitude. 3. An assessment of the potential need to increase the number of predicted low voltage indications at the beginning of cycle if the total number of as-found indications in any

SG are underestimated by greater than 15 percent or by greater than 150 indications.

E2-4 REACTOR COOLANT SYSTEM BASES where V GR represents the allowance for flaw growth between inspections and V NDE represents the allowance for potential sources of error in the measurement of the bobbin coil voltage. Further discussion of the assumptions

necessary to determine the voltage repair limit are discussed in GL 95-05. The mid-cycle equation of SR 4.4.5.4.a.10.e should only be used during unplanned inspection in which eddy current data is acquired for indications at the tube support plates. SR 4.4.5.5 implements several reporting requirements recommended by GL 95-05 for situations which NRC wants to be notified prior to returning the S/Gs to service. For SR 4.4.5.5.d., Items 3 and 4, indications are applicable only where alternate plugging criteria are being applied.For the purposes of this reporting requirement, leakage and conditional burst probability can be calculated based on the as-found voltage distribution rather than the projected

end-of-cycle voltage distribution (refer to GL 95-05 for more information) when it is not practical to complete these

calculations using the projected EOC voltage distributions prior to returning the S/Gs to service. Note that if leakage

and conditional burst probability were calculated using the measured EOC voltage distribution for the purposes of

addressing GL Sections 6.a.1 and 6.a.3 reporting criteria, then the results of the projected EOC voltage distribution

should be provided per GL Section 6.b(c) criteria. Wastage-type defects are unlikely with proper chemistry treatment of the secondary coolant. However, even if a defect should develop in service, it will be found during scheduled inservice steam generator tube

examinations. Plugging will be required for all tubes with imperfections exceeding the repair limit defined in

Surveillance Requirement 4.4.5.4.a. The portion of the tube that the plugging limit does not apply to is the portion

of the tube that is not within the RCS pressure boundary (tube end up to the start of the tube-to-tubesheet weld).

The tube end to tube-to-tubesheet weld portion of the tube does not affect structural integrity of the steam generator

tubes and therefore indications found in this portion of the tube will be excluded from the Result and Action

Required for tube inspections. It is expected that any indications that extend from this region will be detected during

the scheduled tube inspections. Steam generator tube inspections of operating plants have demonstrated the

capability to reliably detect degradation that has penetrated 20% of the original tube wall thickness. Tubes experiencing outside diameter stress corrosion cracking within the thickness of the tube support plate are plugged or repaired by the criteria of 4.4.5.4.a.10.

The W* criteria incorporate the guidance provided in WCAP-14797, Revision 2, Generic W* Tube Plugging Criteria for 51 Series Steam Generator Tubesheet Region WEXTEX Expansions. W* length is the length of tubing into the tubesheet below the bottom of the WEXTEX transition (BWT) that precludes tube pullout in the event of a complete circumferential separation of the tube below the W* length. W* distance is the distance from the top of the tubesheet to the bottom of the W* length including the distance from the top of the tubesheet to the BWT and measurement uncertainties. Indications detected within the W* distance below the top-of-tube sheet (TTS), will be plugged upondetection. Tubes to which WCAP-14797 is applied can experience through-wall degradation up to the limits defined in Revision 2 without increasing the probability of a tube rupture or large leakage event. Tube degradation of any type or extent below W* distance, including a complete circumferential separation of the tube, is acceptable. As applied at Sequoyah Nuclear Plant Unit 2, the W* methodology is used to define the required tube inspection depthinto the hot-leg tubesheet, and is not used to permit degradation in the W* distance to remain in service. Thus while primary to secondary leakage in the W* distance need not be postulated, primary to secondary leakage from potential degradation below the W* distance will be assumed for every inservice tube in the bounding steam generator.

May 3, 2005 SEQUOYAH - UNIT 2 B 3/4 4-3a Amendment No. 181, 211, 213, 243, 291 INSERT 2 E2-5 INSERT 2 For the operational assessment, the Probability of Prior Cycle Detection (POPCD) voltage based probability of detection (POD) method, as described in a September 15, 2006 letter from Westinghouse Electric Company to TVA (LTR

-CDME-06-121, Technical Support for Application of Probability of Prior Cycle Detection for Sequoyah Unit 2 Voltage Based Alternate Repair Criteria), is used to determine the beginning of cycle voltage distributions. The POPCD method is an exception to the GL 95-05 guidance that requires the application of a POD of 0.6 to all

previous bobbin indications.

Approved by NRC letter dated _________________.

E3-1 ENCLOSURE 3 TENNESSEE VALLEY AUTHORITY (TVA)

SEQUOYAH NUCLEAR PLANT (SQN)

UNIT 2 TVA COMMITMENT TVA will revise SQNs steam generator program to incorporate the methodology for implementation of Probability of Prior Cycle

Detection (POPCD) as described in Enclosure 1 of this submittal.

The program revision will be completed within 45 days following

NRC approval of the SQN Unit 2 POPCD TS Change 06-06.