ML20210J176
| ML20210J176 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 07/31/1997 |
| From: | TENNESSEE VALLEY AUTHORITY |
| To: | |
| Shared Package | |
| ML20210J166 | List: |
| References | |
| SG-97-07-006, SG-97-7-6, NUDOCS 9708150050 | |
| Download: ML20210J176 (56) | |
Text
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ATTACHMENT 1 r
WESTINGHOUSE PROPRIETARY CLASS 3 SG-97-07 006 SEQUOYAH UNIT - 1 CYCLE 9 ALTERNATE PLUGGING CRITERIA 90 DAY REPORT July 1997 9708150050 970008 7 DR ADOCK 0500
_ _ . - - - - - - J
r TABLE OF CONTENTS Paee No.
1.0 Introduction 1-1 i
2.0 Summary and Conclusions 2 :
1 3.0 EOC-8 Inspection Results and Voltage Growth Rates j
3-1 l 3.1 EOC-8 Inspection Results 3-1
! 3.2 Voltage Growth Rates 3-2 3.3 NDE Uncertainties 3-3 3.4 Probability of Prior Cycle Detection (POPCD) 3-4 4.0 Data Base Applied for ARC Correlations 4 i 5.0 SLB Analysis Methods 5-1 '
6.0 bobbin Voltage Distributions 6-1.
6.1 Probability Of Detection (POD) 6-1 6.2 Calculation of Voltage Distributions 6-2 6.3 Comparison of Predicted and Actual EOC-8 Voltage Distributions 6-2 6.4 Predicted EOC-9 Voltage Distributions 6-3 7.0 SLB Leak Rate and Tube Burst Probability Analyses 7-1 7.1 Calculation of Leak Rate and Tube Burst Probability 7-1 7.2 Predicted and Actual Leak Rate and Tube Burst Probability for EOC 7-1 7.3 Projected Leak Rate and Tube Burst Probability for EOC-9 8.0 References 8-1 c:\ ape \tva97\ulc9.90d.wp5 ii J
SEQUOYAH UNIT - 1 CYCLE 9 ALTERNATE PLUGGING CRITERIA 90 DAY REPORT
1.0 INTRODUCTION
This report provides an evaluation of the Sequoyah Unit-1 steam generator (SG)
. eddy current data at tube support plates (TSPs) at End of Cycle 8 (EOC-8),
including Steam Line Break (SLB) leak rate and tube burst probability results, in support of the implementation of tbs Alternate Plugging Criteria (APC) for Cycle 9 operation as outlined in the NRC Generic Letter GL 95-05, Reference 8.1.
Calculations ofleak rates and probability of tube burst are reported for the EOC-8 condition based on measured bobbin voltage distributions. Also provided are projections of bobbin voltage distributions, leak rates and tube burst probabilities for Cycle 9 operation. The methodology used in these evaluations is in accordance with the methodology described in Reference 8.3.
The application of the TSP APC for the Sequoyah Unit-1 SGs involves a complete, 100% Eddy Current (EC) bobbin coil inspection of all TSP intersections in the tube bundles of all four SGs and plugging of TSP indications greater than 2 volts which are confirmed by a Rotating Pancake Coil (RPC) probe RPC inspections are also performed at certain locations exhibiting dent voltages and mixed residual signals.
The measured bobbin signals are used to predict SG tube leak rate and probability of burst during a postulated SLB and show that they are within the allowable regulatory limits.
o:\ ape \tva97\ulc9_90d wp5 1-1
2.0
SUMMARY
AND CONCLUSIONS SLB leak rate and tube burst probability analyses were performed for the actual EOC-8 bobbin voltage distributions and projected voltage distributions for the EOC-9 condition at Sequoyah Unit-1. As predicted at BOC-8, SG 3 was found to be the limiting SG at EOC-8; however, SG 1 is projected to be the limiting SG for Cycle 9. The calculations demonstrate that APC application at EOC-8 (actual distribution) and EOC-9 (projected distribution) satisfy NRC criteria for allowable leakage and burst probability.
A total of 298 axial outside diameter stress corrosion cracking (ODSCC) indications were found during the inspection in all four steam generators combined, of which 62 indications had a voltage above one volt and 4 indications above two volts.
Steam generator 1 has the largest number ofindications found (88), and SG-4 has the largest indication detected in this inspection (2.52 volts). SG-1 with the largest number of indications returned to service is likely to be the limiting steam generator from the standpoint of SLB leak rate and tube burst probability at the EOC-9 conditions. Eighty-nine indications were inspected with a RPC probe and 85 were confirmed as flaws. The four indications found above 2 volts were all RPC l inspected, confirmed as flaws and repaired. Eight other indications were also l removed from service because of tube repairs for non-ODSCC causes. Accordingly, 286 of the 298 indications were returned to service for Cycle 9 operation. SG 1 with 88 indications had the largest number ofindications reported at EOC-8 and all but one of those indications were returned to service for Cycle 9.
The bounding estimates for SLB leak rate and burst probability calculated using the measured EOC-8 voltage distributions are 0.23 gpm and 3.1 x 10 -5 ,
respectively. These values were calculated for SG 3 which is the limiting SG, and they are much lower than the allowable SLB leakage limit of 3.7 gpm and the NRC reporting guideline of10 8 for the tube burst probability. Leak and burst results based on the actual, measured voltages are slightly higher (leak rate higher by 0.06 gpm and burst probability by 5 x 10-8) than the corresponding projections performed during the last (EOC-7) outage; however, the differences are negligible in comparison to the allowable limits. Significant population ofODSCC indications began to appear only recently in Sequoyah Unit-1 and the population is increasing relatively fast, as observed at other plants when ODSCC indications begin to appear in significant numbers. A relatively significant increase in indication population (from 43 to 298 for all 4 SGs combined) during Cycle 8 resulted in leak rate and burst probability based on actual voltages exceeding the projections.
However, the Unit-1 indication population is still small in comparison to other plants applying APC for ODSCC at TSP intersections.
o:\apc\tva97\ulc9.90d.wp5 2-1
_ _ _ _ _ J
SLB leak rates and tube burst probabilities were also projected to EOC-9 conditions for all four SGs using the Cycle 8 growth rate distribution based on reevaluated voltages from EOC-7 and EOC-8 inspection bobbin data. Projections were made using both the NRC required constant probability of detection (POD) value of 0.6 as well as a voltage-dependent POD termed probability of prior cycle -
detection (POPCD). POPCD is established based on data from past IPC/APC inspections, and it takes into account newly initiated indications which is important for APC application. The POPCD distribution used here is established using data from 16 inspections conducted in 8 plants after 1992.
SG 1 with the largest number ofindications returned to service was found to be the limiting SG for Cycle 9 operation. SLB tube leak rate for SG 1 is projected to be 0.75 gpm at the EOC-9 conditions and the burst probability is projected to be 8.8 x 10 5 These results, which are based cu a conservative POD value of 0.6, are substantially lower than the Sequoyah Unit-1 APC allowable limit for SLB leakage (3.7 gpm) and the NRC guideline of 1.0x10 2 for the burst probability.
l o:\ ape \tva97\ulc9.90d.wp5 2-2 s
3.0 EOC-8 INSPECTION RESULTS AND VOLTAGE GROWTH RATES -
3.1 EOC-8 Inspection Results In accordance with the Generic Letter 95-05, the inspection of the EOC-8 Sequoyah Unit-1 SGs consisted of a complete,100% Eddy Current Test (ECT) bobbin probe full length examination of all hot leg and cold leg tube support plate (TSP) intersections in the tube bundles of the four SGs. A 0.720 inch diameter probe was
- used for all hot leg and cold leg TSP indications where APC was applied. A total of 298 axial TSP ODSCC indications were found in all four steam generators combined in the current inspection, of which 62 indications have a voltage above one volt and 4 indications are above two volts. All 4 indications above 2 volts were RPC confirmed and they were repaired in accordance with a 2 volt APC.
An augmented RPC inspection was performed consistent with the Generic Letter 95-05 requirements. The augmented RPC inspection using the + Point probe included examination of all TSP intersections in all four SGs with a dent voltage over 5.0 volts. As found in the prior inspection, axial PWSCO indications were l found at dented intersections including some that extended outside the-TSP intersection. Circumferential PWSCC and ODSCC were also found at dented -
intersections. As typical of circumferential indications at dented intersections, the crack angles are short with the largest angle being 102 degrees.
Two other TSP indications were found in large dents: one each in SGs 1 and '4.
Per the Generic Letter 95-05 guidance, indications in large dents cannot be adequately sized and APC does not apply to them. Accordingly, those two indications were repaired, and they are not included in the above total bobbin count.
A summary of EC indication statistics for all four SGs is shown on Table 3-1. The table shows the number of field bobbin indications detected during the current '
(EOC-8) inspection, the number of these field bobbin indications that were RPC '
inspected, the number of RPC confirmed indications, the number of repaired ;
indications, and the total number ofindications in tubes returncd to service for Cycle 9 operation.
Overall, the combined data for four SGs of Sequoyah Unit-1 show the following:
-A total of 298 indications were detected at the TSP intersections during the EOC-8 inspection, of which 62 indications have a voltage above one volt and 4 indications above two volts, onape\tva97\ulcy9_90d.wp5 - 3-1
Of the 298 indications detected during the EOC-8 inspection, a total of 89 were RPC inspected.
All but four of the RPC tested indications were confirmed, including all four indications above 2 volts.
Four indications requiring repairs per the 2 volt APC and 8 other indications present in tubes repaired for non-ODSCC causes were removed from service, and the remaining 286 indications were returned to service for Cycle 9.
A review of Table 3 -1 indicates that SG 1 had the largest number ofindications at EOC-8 (a quantity of 88, all but one 2 volts or under), thereby it potentially could be the limiting SG at EOC-9. Among the other three indications above 2 volts, two were found in SG 3 and one in SG 4, the latter being the largest bobbin voltage measured (2.52 volts) in the EOC-8 inspection.
The bobbin voltage distribution for all indications detected during the current inspection is snown in Figure 3-1. Figure 3-2 shows the bobbin voltage i distribution for indications repaired and taken out ofservice, and Figure 3-3 shows the distribution for indications returned to service for Cycle 9.
l The distribution of EOC-7 indications as a function of support plate location is summarized in Table 3 2 and illustrated in Figure 3-4 . Among the 298 indications I
found, 259 were at the hot leg intersections, of which 183 indications (about 73(7c)
I were at the first two TSP intersections. The remaining 39 indications were detected at the cold leg TSP intersections distributed across all 7 cold leg TSPs.
The 73% of indications at the first two hot leg TSPs indicates the predominant temperature dependence of ODSCC at Sequoyah Unit-1 and is consistent with the pattern generally found in other plants, i.e., ODSCCs are found mostly in the first few hot leg TSPs.
3.2 Voltage Growth Rates For projection ofleak rates and tube burst probabilities at the end of Cycle 9 operation, voltage growth rates were developed from EOC-8 inspection data and a reevaluation of the same indications from the EOC-7 inspection EC signals.
Table 3 3 shows the cumulative probability distribution of growth rate per EFPY for each Sequoyah Unit-1 steam generator during Cycle 8. These growth data are also plotted in Figure 3 5. The curve labelled ' cumulative'in Figure 3-5 represents averaged composite growth data from all four SGs. The average growth rate distribution for Cycles 7 and 8 are shown in Figure 3-6, which also includes the Cycle 7 growth distribution for Unit-2. Cycle 8 growth distribution is comparable to Cycle 7 growth distribution for Unit-2 but appears to be significantly higher o:\apc\tva97\uley9.90d.wp5 3-2
e d
4 than its own Cycle 7 growth. However, Cycle 7 growth distribution for Unit-1 was
- obtained using data for only 43 indications, of which only 20 growth values are based on bobbin voltages from consecutive inspections (the remaining 23 growth values are based on bobbin voltages measured two or more inspections apart).
Thus, Cycle 7 growth data is too small to draw any firm conclusions on the growth rate trend for Unit 1. The fact that Cycle 7 growth rates for Unit-2 are so close to the Unit-1 Cycle 8 growth rates suggests that there was no significant change in the growth trends. However, it is noted that chemical cleaning of all four steam generators was performed during the last (EOC-7) outage. Table 3-4 shows average growth rates for the individual SGs, and among the four steam generators, SG 1 has a slightly larger average voltage growth during Cycle 8. Average i-composite growth rate for all SGs for Cycle 8 is compared with the corresponding value for Cycle 7 in Table 3-5. However, since the Cycle 7 average growth value was obtained using data from a total of 20 indications, no meaningful conclusions can be drawn from those data. Table 3-6 shows the top 30 indications from Cycle 8 growth standpoint; the largest growth value was only 0.82 volts.
Figure 3-7 shows a plot of voltage growth, AV, versus the BOC voltage, V30c, for all Cycle 8 growth data. The data do not show growth rate in terms of AV increasing with V 3oc. The maximum growth in all SGs occurred at a V oc 3 less than one half of the maximum V30c value. The frequency oflarger growth values
~ as fraction of the number of BOC indications appear higher above about 1 volt than below 1 volt.
l The NRC guidelines in Generic Letter 95-05 stipulate P .at a plant-specific growth
- rate distribution used in SLB leak rate and tube preoability analyses to support APC application must contain at least 200 data points that are established using bobbin voltages measured in two consecutive inspections. As the Sequoyah Unit-1 Cycle 8 composite growth data contain 298 data points established using reevaluated voltages from EOC-7 and EOC-8 inspection data, they meet the above
'NRC requirement. Tlms, Cycle 8 growth can be used in the Monte Carlo analyses
- to project SLB leak rates and tube burst probabilities at EOC-9. The analysis methodology described in Reference 8.3 requires the use of the more conservative of composite growth rates and SG-specific growth rates in the Monte Carlo analysis for a specific SG. Since the composite growth distribution envelopes growth
, distribution for all SGs except SG 1, it was applied SGs 2 to 4, while its own growth distribution was applied for SG 1 to project EOC-9 SLB leak rates and tube
] burst probabilities.
3.3 NDE Uncertainties The NDE uncertainties applied for the Cycle 9 voltage projections in this report are documented in References 8.2 and 8.3 and they are consistent with NRC GL 0;\apc\tva97\ulcy9.90d.wp5 3-3
95-05 (Reference 8.1) The probe wear uncertainty has a standard deviation of 7.0% about a mean of zero and has a cutoff at 15% based on implementation of the probe wear standard. The analyst variability uncertainty has a standard deviation of 10.3% about a mean- of zero with no cutoff. These NDE uncertainty >
distributions, presented in Table 3 7 as well as graphically illustrated in Figure 3-7, are included , the Monte Carlo analyses used to predict the EOC-9 voltage distributions.
3.4 Probability of Prior Cycle Detection (POPCD)
The inspection results at EOC-8 permit an evaluation of the probability of detection at the prior EOC-7 inspection. For ARC applications, the important indications are those that could significantly contribute to EOC leakage or burst probability. These significant indications can be expected to be detected by bobbin and confirmed by RPC inspection. Thus, the population ofinterest for ARC POD assessments is the EOC RPC confirmed indications that were detected or not detected at the prior inspection. The probability of prior cycle detection (POPCD) for the EOC-7 inspection can then be defined as follows.
l EOC-7 cycle reported + Indications confirmed indications confirmed by and repaired in EOC-7 RPC in EOC-8 inspection inspection POPCD =
(EOC-7)
{ Numerator) + New indications RPC confirmed in EOC-8 inspection POPCD is expected to be voltage dependent with a relatively low value at low voltages and approaching unity above about 2 volts. To obtain a meaningful distribution for POPCD, data in both inspections must include at least 200 indications. Although the EOC-8 data includes 298 indications, EOC-7 data contains only 49 indications of which only.13 are RPC confirmed. Therefore, there is insufficient data to establish POPCD for EOC-7.
4 o:\apc\tva97\ulcy9_90d.wp5 3-4
Tchte 3-1
- Sequoyah Unit 1 April 97 Outage Summary of Inspection and Repair For Tubes in Service During Cycle 8
- Steam Generator I Steam Generator 2 to-serske During Cycle I Cycle 9 to-Servke During Cycle 8 Cyck 9 vahnge Field end held 8'" RPC RPC Indications RPC RPC Indications end Inspected Confirmed B "
, Repaired Inspected Confirmed Repaired
, gd ,,
0.1 1 0 0 0 1 2 0 0 0 2 0.2 2 0 0 0 2 10 0 0 0 10 03 11 1 0 0 11 13 0 0 1 12 04 10 0 0 0 10 6 0 0 0 6 0.$ 11 0 0 0 11 10 0 0 1 9 0.6 11 0 0 0 9 11 0 0 0 9 0.1 5 0 0 0 5 6 j 1 1 0 6 08 12 1 1 0 12 7 1 1 0 7 09 4 0 0 0 4 8 1 1 0 8 1 4 0 0 0 4 4 1 1 0 4 1.1 4 0 0 0 4 3 0 0 0 3 1.2 1 1 1 0 1 2 0 0 0 2 1.3 3 0 0 0 ~3 2 2 2 0 2 1.4 1 0 0 0 1 1 0 0 0 1 1.5 2 1 1 0 2 1 1 1 0 1 1.6 0 0 0 0 0 1 0 0 0 1 1.7 1 0 0 0 I l 0 0 0 1 1.8 2 0 1.9
~ 0 0 2 0 0 0 0 0 1 1 l 0 1 0 0 0 0 0 2 1 1 1 0 1 0 0 0 0 0 2.1 1 1 0 1 1 0 0 0 0 0 2.6 0 0 0 0 0 0 0 0 0 0 Total 88 7 6 I 87 86 7 7 2 84
>lv 17 5 5 16 11 3 3 0 11 Steam Generator 3 Steam Generator 4 In-Service Dunes Cycle 8 Cycle 9 In-Servke Dartog Cycle a cycle 9 volug, Field Returned Fictd
"' RPC RPC Indications RPC RPC eturned Indications Inspected Confirmed Repaired inspected Id ; , Confirmed Repaired c,
0.1 0 0 0 0 0 0 0 0 0 0 0.2 1 0 0 0- 1 3 0 0 0 3 03 5 0 0 0 5 4 04 1 1 0 4 6
0.5 3 3
I 3 0 6 3 ~6 0 0 3 I O 3 7 I I 2 5 06 12 6 6 0 12 6 2 2 0 6 0.7 9 7 6 0 9 4 0 0 1 3 08 6 4 4 0 6 5 4 3 0 5 0.9 7 7 7 0 7 2 2 2 0 2 1 6 5 5 0 6 I i 1 0 1 1.1 3 2 2 0 3 1 1 1.2 4 1 1 0 4 4 0 4 2 2 2 0 2 1.3 6 5 5 0 6 2 2 l 0 2 14 2 2 2 I I i 1 1 0 I l .5 2 2 2 0 2 0 0 0 0 0 16 I I I O I O
~
O O O 1.7 2 2 2 0 2 2 I I O 0 ~
2 I .8 0 0 0 0 0 0 0 0 0 0 1.9 1 1 1 0 1 I I I O I 2 l 1 1 1 0 0 0 0 0 0 2.1 2 2 2 2 0 0 0 0 0
~26 0 0 0 0 0 1 I i 0
1 0 Total 79 55 54 4 75 45 20 18 5 40
>lv 24 - 22 22 4 20 10 9 8 2 8 Bobarpc.xis Table 317G973 49 PM 3-5 l
Table 3-2 Sequoyah Unit 1 April 1997 TSP ODSCC Indication Distributions for Tubes in Senice During Cycle 8 Steam Generator 1 Steam Generator 2 Tube Humber of Maximum Average Largest Average Number of Maximum Average Support Largest Average Indientions Voltage Voltage Orowth Orowth Indications Voltage Plate Voltage Orowth Orowth 110 1 38 2.01 0.% 0.80 0 34 31 1.57 0.83 0.70 0.23 H02 6 1.87 0.88 0.55 028 6 1.67 0.78 0.45 0.16 H03 7 0.67 0.42 026 0.14 7 0.90 0.47 0.21 0.06 H04 4 0.86 0.42 034 0.10 7 0 96 0.62 0.10 -0.03 1105 5 0.90 0.67 031 0.15 12 0.90 039 0.51 0.07 H06 10 0.79 0.51 029 0.11 5 0.57 0.43 0.25 0.04 H07 2 0.85 0.71 0.16 0.03 2 0.29 0.25 0.08 0.08 C07 2 0.56 0.41 0.00 0.03 0 . . . .
C% 1 0.49 0.49 0.05 0.05 7 0.58 0.44 0.19 0.06 C05 3 0.52 041 0.09 0.07 0 . . . .
C04 2 034 030 0.01 -0.02 5 0.43 031 0.20 0.08 C03 3 0.52 0.44 021 0.14 4 030 0.18 0.08 0.02 l CO2 2 026 0.24 0.08 0.05 0 . . . .
C01 3 036 0.29 0.27 0.11 0 - . . -
Total R8 86 Steam Generator 3 Steam Generator 4 Tube Number of Maximum Average Largest Average Number of Maximum Support Average Largest Average Indications Voltage Voltage Growth Orowth Indications Voltage Plate Voltage Orowth Orowth H01 51 2.05 0.95 0.82 0.18 25 2.52 0.93 0.70 0.19 H02 18 1.40 0.86 0.61 0.23 8 1.05 0.60 0.47 0.19 H01 2 0.60 0.41 0.03 -0.01 5 0.79 0.61 0 44 0.16 H04 1 037 037 0.19 0.19 2 0.50 034 0.08 0.04 1105 1 0.51 0.51 0.06 0.06 1 0.58 0.58 0.04 0.04 H06 1 036 0 36 0.08 0.08 2 0.44 033 0.07 0.06 1I07 0 . . . .
0 . . . .
CG7 1 0.59 0.59 0.07 0.07 0 . . . .
C06 0 . . . .
0 . . - -
C05 0 - - . .
1 0.16 0.16 -0.14 -0.14 i C04 0 - - -
0 . . . -
C03 0 . . . . 0 . . . .
CO2 1 0.23 0.23 0.09 0.09 0 . . . .
C01 3 0.29 0.25 0.00 -0.09 1 0.19 0.19 0.00 0.00 Total 79 45 c swrmwmsem 3-6
s.
Table 3-3 Sequoyah Unit 1 April 97 Signal Growth Statistics For Cycle 8 on an EFPY Basis Delta Steam Generator 1 Steam Generator 2 Steam Generator 3 Steam Generator 4 Camelative Volts Cycle 7 . Cycle 8 Cycle 7 . Cycle 8 Cycle 7 Cycle 8 Cycle 7 Cycle 8 Cycle 7 ' Cycle'8 CPDF CPDF CPDF CPDF CPDF CPDF CPDF CPDF CPDF CPDF
-0.4 0.0 0 0.0 0.0 0 0.0 0.05 0 0.0 0.0 0 0.0 0.023 ' O: 0.0 '
-0.2 0.0 0 0.0 0.0 1 0.012 0.1 1 0.013 0.0 0 0.0 0.047 2 0.007
-0.1 0.2 1 0.011 0.333 0 0912 0.25 0 0.013 0.286 1 0.022 . 0.256 2- 0.013 0 0.7 10 0.125 1.0 22 0.267 0.55 11 0.152 0.57I 5 0.133 0.651 48 0.174 0.1 0.9 24 0.398 30 0.616 0.75 28 0.506 1.0 ~ 18 0.533 0.86 - 100 0.51-0.2 0.9 19 0.614 17 0.814 0.9 20 0.759 12 0.8 0.93 68 0.738 0.3 0.9 12 0.75 6 0.884 1.0 9 0.873 3 0.867 0.977 30 0.839 0.4 0.9 12 ' O.886 7- { 0.965 5 0.937 3 0.933 ' O.977 27 0.93 0.5 0.9 7- 0.966 2 0.988 ' 3 0.975 2 0.978 0.977- 14 0.977 0.6 0.9 1 0.977 .I 1.0 1 0.987 1 1.0 0.977 4 0.99 0.7 0.9 2 1.0 0 1 1.0 -- 0 0.977 3 1.0 0.8 1.0 0 0 0 1.0 0 1.0 0 _j i'otal 88 86 79 45 298 ,
i i
Growth _xis Table 3 3 7/2197 4 S1 PM 3-7
Table 3-4 Sequoyah Unit 1 - April 1997 Outage -
Average Voltage Growth During Cycle 8 Vohage Number of ' Average Voltage Range Indications BOC Entire Cycle Per EFPY
- Entire Cycle Per EFPY
- Composite of All Steam Generator Data Entire Voltage Range 298 0.55 0.167 0.136 30.5 % 24.7 %
V noe < .75 Volts 232 0.41 0.139 0.113 34.2 % 27.8 %
2.75 Volts 66 1.06 0.268 0.218 25.4 % 20.6 %
Steam Generator 1 Entire Voltage Range 88 0.49 0.217 0.176 44.2 % 35.9 %
V eac < .75 Volts 75 039 0.171 0.139 43.6 % 35.4 %
2.75 Volts 13 1.06 0.4h2 0.391 45.5% 36.9%
Steam Generator 2 Entire Voltage Range 86 0.47 0.119 0.097 25.4 % 20.6 %
V noe < .75 Volts 72 038 0.I14 0.092 303 % 74.6 %
2.75 Volts 14 0.95 0.147 0.119 15.4 % 12.5 %
Steam Generator 3 Entire Voltage Range 79 0.68 0.171 0.139 25.0 % 203 %
V noe < .75 Volts 50 0.47 0.141 0.114 30.2 % 24.5 %
2.75 Volts 29 1.06 0.223 0.181 21.0% 17.1%
Steam Generator 4 Entire Voltage Range 45 0.58 0.157 0.128 27.0 % 21.9%
V soc < .75 Volts 35 0.41 0.119 0.096 28.9 % 23.4 %
2.75 Volts 10 1.18 0.292 0.237 24.7 % 20.1%
- Ibsed en Cycle 8 duration of 450 EFFD (1.232 EITY) cnowth xtsfrableM7/2/97A 04 PM 3-8
_ ___ - - - . - -_ __= _ = - - _ _ -_
. . . . . . . . _. _ . . _. _ _ _ .. m _ . .
W Table 3-5 Sequoyah Unit 1 April 1997 Average Voltage Growth for Cycle 8 Composite of All Steam Generator Data Bobbin Voltage Number of Average Voltage Average Voltage Growth Average Percentage Growth Range Indications BOC Entire Cycle Per EFPY Entire Cycle . . Per EFPY.
1 Cycle 8 (1995 - 1997) - 450 EFPD Entire Voltage Range 298 0.55 0.167 0.136 30.5 % 24.7 %
V sw < .75 Volts 232 0.41 0.139 0.113 34.2 % 27.8 %
2.75 Volts 66 1.06 0.268 0.218 25.4 % 20.6 %
Cycic 7 (1993 - 1995) - 450 EFPD Entire Voltage Range 20' O.79 0.031 0.025 3.9% 3.2%
V soc < .75 Volts 11 0.45 0.11 0.088 24.2 % 19.6 % !
2.75 Volts 9 1.20 -0.063 _
-0.051 -5.3% -4.3% ,
- Of the 43 indications detected at EOC-7, bobbin data for both EOC-6 and EOC-7 is available only for 20 indications.
Growthrrabk4D/13/97111:27 AM 3-9
Table 3 6 Sequoyah Unit 1 April 1997 Summary of Largest Voltage Growth Rates for BOC 8 to EOC-8 Steam Generator Bobbin Voltage RPC New SG Row Col Elevation EOC BOC Growth Confirmed ? Indication ?
'C 25 66 OlH 1.52 _ 0.7 0.82 _ Y Y A 22 65 OlH 1.62 0.82 0.8 N Y A 6 94 O1H _ l.96 1.2 0.76 Y Y A 2 40 OlH 2.01 1.3 0.71 Y Y B 26 51 OlH 1.21- 0.51 0.7 Y Y C 6 70 , _ OlH _ 2.05 1.35 0.7 Y Y
- D 31 20 OlH 1.69 0.99 0.7 Y Y
, C 10 88 02H 1.27 0.66 0.61 Y Y D 11 62 O1H 1.82 1.21 0.61 Y Y A 10 53 OlH 1.74 1.14 0.6 N Y A 11 32 OlH 0.8 0.21 0.59 _
Y Y C 21 47 02H 1.4 0.82 0.58 Y Y
! A 10 91 OlH 0.97 0.42 N
._ 0.55 Y A 11 91 02H l.32
_ l .87 _ 0.55 Y Y A 21 81 OlH 1.1 0.56 0.54 N Y
_B 11 68 OlH 1.06, _ 0.52 0.54 _ __N Y D 38 28 OlH 2.52 2 0.52 ,_
Y Y A 11 84 OlH 1.29 0.78 0.51 N Y A 24 85 01H 0.93 0.42 0.51 N Y B 32 52 05H 0.9 - 0.39 0.51 N Y C 21 47 OlH 2 1.5 0.5 Y Y A 21 54 01H 1.74 0.47
_l.27 N Y D 14 63 02H l.05 0.58
_ 0.47 _
Y Y C 3 63 OlH 1.25 0.79 0.46 N Y A 18 59 OlH 1.21 0.76 0.45 N Y B 21 76 02H 1.67 1.22 0.45 N Y A 7 94 OlH 0.3
_ _0.74 0.44 _ ____
N Y A 15 84 01H 0.78 0.34 0.44 N Y B 28 19 OlH 0.9 _ 0.46 _0.44 N Y C 31 78 02H 0.93 0.49 0.44 Y Y OrewthTable57/13/9711;37 AM 3-10
Tcble 3-7 Probe Wear and Analyst Variability - Tabulated Values Analyst Variability Probe Wear VariabJllty Std. Dev = 10.3% Mean = 0.0% Std. Dev = 7.0% Mean = 0.0%
No Cutoff Cutoff at +/ 15%
- Value - Cumul. Prob. - Value Cumul. Prob. '
-40.0% 0.00005 < -15.0% 0.00000
-38.0% 0.00011 -15.0% 0.01606
-36.0% 0.00024 -14.0% 0.02275
-34.0% 0.00048 -13.0% 0.03165
-32.0% 0.00095 -12.0% 0.04324
-30.0% 0.00179 -11.0% 0.05804
-28.0% 0.00328 -10.0% 0.07656
-26.0% 0.00580 -9.0% 0.09927 l -24.0% 0.00990 -8.0% 0.12655 l -22.0% 0.01634 -7.0% 0.15866
) -20.0% 0.02608 -6.0% 0.19568 l -18.0% 0.04027 -5.0% 0.23753
-16.0% 0.06016 -4.0% 0.28385
-14.0% 0.08704 -3.0% 0.33412
-12.0% 0.12200 -2.0% 0.38755
-10.0% 0.16581 -1.0% 0.44320
-8.0% 0.21867 0.0% 0.50000
-6.0% -0.28011 1.0% 0.55680
-4.0% 0.34888 2.0% 0.61245
-2.0% 0.42302 0.0%
_ 3.0%- 0.66588 0.50000 4.0% 0.71615 2.0% 0.57698 5.0% 0.76247 4.0% 0.65112 6.0% 0.80432 6.0% _
0.71989 7.0% 0.84134 8.0% 0.78133 8.0% 0.87345 10.0% 0.83419 9.0% 0.90073 12.0% 0.87800 10.0 % 0.92344 14.0 % 0.91296 11.0 % 0.94196 16.0% 0.93984 12.0 % 0.95676 18.0% 0.95973 13.0 % 0.96835 20.0% 0.97392 14.0 % 0.97725 22.0% 0.98366 15.0 % 0.98394 24.0% 0.99010 > 15.0% 1.00000 26.0% 0.99420 28.0 % 0.99672 _
30.0% 0.99821 32.0% 0.99905 34.0 % 0.99952 36.0% 0.99976 38.0% 0.99989 40.0% 0.99995 l
3-11
Figure 3-2 Sequoyah Unit 1 April 97 Outage Bobbin Voltage Distribution for Tubes Plugged After Cycle 8 Service 8 -
7- - - -
i El i 6- - - - --
l
. O2
- E 5 -
3
- 5 03
$ 4- - - - -- -
E
.8 E4 2;
l 3- - - - - -
I 2- r 3
=
5
- g. __ __
g
=
^
' 1 0 ! l I f ! I ! '
m .n r~ ~ -r en - e d 6 d J a ci d Bobbin Voltage Ikenrpe alsfig?
3-13
Figure 3-1 Sequoyah Unit 1 April 97 Outage Bobbin Voltage Distributions at EOC-8 for Tubes in Service During Cycle 8 14 ;
12 -
E1 ;
10 - - - -
g -
02 h g. _ _ _ _ . _ __
g _ _
93 D
,o 6- - - - - - - -
t - -- - - --
z
! B4 4- -- - - - -- -
i - - - ~
i -
2- -- - - - - - -- ---- - - -
0 __.
E.. .
J .
.m N .
a 6 6 6 6 6 6 6 d J J J J J J J J J d d Bobbin Vohnge Boberpe misFig!l l 3-12 u___________ . . -
Bobbin Voltage Dis b ns ube ea e Service for Cycle 9 14 12 - --
El 10 - -- -- -
0
._I i
,! 8 - -- - -- -
l - - --
] ; :
, s3 6- - -- -- -- - - -
e -
f s
! E4 i !
4- - - -- - - -- -- -
l i 2- -- - - - - -
i - -
0 l l l l l l l l l l l l l l l l l l l 0.1 0.2 0.3 0.4 0.5 ' O.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 Bobbin Voltage soi pc wri 3
Figure 3-4 Sequoyah Unit 1 - April 1997 Outage ODSCC Axial Distributions for Tubes in Service During Cycle 8 60 50 - -
Ol l
02
,40 - --
8 -
1
.E B3 i
{30 U E4 o
E 20 -
10 - - -- - -
e > - -
~
E,b . Et = E g _ _; j) l _
i w M, , .
M ;E , . .
1101 IIO2 1103 1104 1105 110 6 1107 C07 C06 C05 C04 C03 CO2 COI Tube Support Plate Growth.xis Figi 7/2/97 4:38 PM 3-15 c- a
l Figure 3-5 Sequoyah Unit 1 Cycle 8 ( Dec.1995 to March 1997 ) j Cumulative Probability Distributions for Voltage Growth on an EFPY Basis l 1.0 ,,, m l s' ' Y-0.9 -
.T;,'I'.--
TS* )
WSU'X
\
l 0.8 - /* , */
' /l a ' '/*.-F '
%*/
-80.7-u C
/ .i i.'s'
/ / .'/
0.6 - ,
-+--- 1
'il
.c
//.-/,.,
- c 0.5 - /r -c-2 2 /
a / }y t- -- x -- 3 f0.4-
.2! /
i C /
' /g* - e- - 4
!0.3-U
/ $ ,']'I 0.2 - y --X- Cumulative f
l /
//'
O.1 - ,'vf '
/?
O.() w - .,
N 9 Q m N O v. 9 9 n-e o o o -o o o e 9 9 Voltage Growth Growth Fig 2 7/14/97 8:44 PM 3-16
Figure 3-6 Sequoyah Unit 1 - April 1997 Outage Bobbin Signal Growth History - Cumulative Probability Distributions on an EFPY Basis Composite of All Steam Generators 1.0 , , ____.....y...... g .a
,o...
0.9- ,-
.cr '
, ~~ '
O.8 -
- g '
a- 1 30.7-a
= -
m '
m0 -
.e .6 > -
- Cycle 7 m .-
.c -
c 0.5 - -- - - - -
D 2
.5 ;
Q .
>0.4 - -- c -- Cycle 8
,./
es -
3 / i
,503 - -
l l U l 0.2 - -
O 0.1- --
O.0 k: ----?-""" l l l l l l l l 5 c. n o -
es n -r e e- s e 9 9 9 o o o o o 0 6 6 .
Vohnge Growth '
i i
Growth.xis Fig 3 7/2/97 4:36 PM ~
3-17
Figure 3-7 Sequoyah Unit -1 April 1997 Outage Voltage Growth During Cycle 8 vs BOC-8 voltage 1
0.8 0 o
D X *A 7 0.6 , , &
? O 00 0 6 do o A
- 0.4 D*-* 9 A h x g, o, Q o
- 8 a a 4'
- A *
- h o xA g A ,
A
"* ^ ^
k~ " [g I*kI*o.fFjIo^i $ .,
x
^
S U
,M D bA 8A A lf A E
- X
-D - A -u ^
O 8 -
- ou ,
a sG-2 x {
-0.2 - a sG-3 -
A CI x s G-4 g
-0.4 -
0 0.4 0.8 1.2 1.6 2 BOC-8 Voltage Cnowthrig3 77/13M712:13 PM 3-18
l 1
i c
Figure 3-8 ;
NDE Uncertainty Distributions l 1 ..
0.9 -
0.8 - /l -
x 5 0.7 [ -
q 0.6 -
g -M-- Analyst Variability 0.5 -
,$ Probe Wear ' , 1 5c 0.4 -
E o 0.3 --
U 0.2 0.1 - -f
/
0
/
-40% -30% -20% -10% 0% 10 % 20 % 30 % 40%
Percent Variation in Signal Voltage (%)
Bobarpe fig 317/13871123 PM 3-19 l
4.0 DATA BASE APPLIED FOR APC CORRELATIONS The database used for the APC correlations applied in the analyses of this report are consistent with those used in the initial APC submittal for Sequoyah Units 1&2 (Reference 8.2) and described in Reference 8.4 as approved by the NRC in GL 95-05.
Per NRC r<' quests, this database has been updated to include more recent pulled tube '
data from plants P-1 and A-2. The database also includes leak and burst test data -
obtained from tube segments pulled during the last outages at both sequoyah Units 1 and 2. The updated database is same as that presented in Reference 8.5.
For the SLB leak rate correlation, the NRC recommends that Model Boiler specimen 542-4 and Plant J-1 pulled tube RSC74, TSP 1 be included in the database. This database is referred to as the NRC database and is applied for the leak rate analyses of this report. As noted in Section 6, the leak rate data does not satisfy statistical requirements for a voltage dependent leak rate correlation.
( .-
4 0;\apc\tva97\ulcy9.90d.wp5 41 l
__ _ _ __j
)
- 5.0 SLB ANALYSIS METHODS
- i I Monte Carlo analyses are used to predict the EOC-8 voltage distributions and to cal
- ulate the SLB leak rates and tube burst probabilities for both the actual EOC 8 voltage distribution and the predicted EOC 9 voltage distribution. These methods are
] consistent with those described in the generic methods report of WCAP-14277, j Revision 1 (Refereneo 8.8).
i Based on the NRC recommended leak rate database, the leak rate data do not satisfy
- the requirement for applying the SLB leak rate versus bobbin voltage correlation.
The NRC requirement is that the p value_obtained from the regression for the slope <
- parameter be less than or equal to 5% For the NRC recommended data, the p v
- .lue is about 6.5% and the leak rate versus voltage correlation is not applied. The SLB '
- leak rate correlation applied is based on an average of allleak rate data independent
of voltage. The analysis methods for applying this leak rate model are given in j
Section 4.6 of WCAP-14277 (Reference 8.3). A Monte " 's analysis is applied to
- account for parameter uncertainties even though th, eak rate is independent of i voltage.
I i
I i
l 4
i a
E
. i 4
j-1 d
0;\ ape \tva97\uley9.90d.wp5 51
. _ . _ __., _ _ _ ._- - . _ , . . . _ . . _ , . . . _ . . ._.-2_.__._ . _ . , _ _ . , , _ _ _ _ . . .
< 1 6.0 BOBBIN VOLTAGE DISTRIBUTIONS 6.1 Probability of Detection (POD)
The number ofindications assumed in the analysis to predict tube leak rate and burst probability is obtained by adjusting the number of indications reported, to account for measurement uncertainty and birth of new indications over the projection i period. This is accomplished by using a Probability of Detection (POD) factor. The calculation of projected bobbin voltage frequency distribution is based on a net total number ofindications returned to service, defined as follows.
N ~
Nr* an
- POD "*""d d'" "d
- where:
Nu 33 = Number of bobbin indications being returned to service for the next cycle.
N, = Number of bobbin indications (in tubes in service) reported in the
- current inspection.
- POD = Probability of Detection.
N,,,,,,a = Number of N i which are repaired (plugged) after the last cycle,
, . No,,3,,,,a = Nurnber ofpreviously-plugged indications which are deplugged after t the last cycle and are returned to service in accordance with APC '
applicability.
There are no deplugged tubes returned to service at Sequoyah Unit-1 BOC-9.
Tne NRC generic letter (Reference 8.1) requires the_ application or'a constant POD i . value of 0.6 to define the beginning of cycle (BOC) distribution for the EOC voltage projections, unless an alternate POD is approved by the NRC Sufficient data exist now to uefine an alternate POD based on the past inspection data. A voltage- '
dependent POD known as POPCD has been established using data from 16 post-1992 inspections at 8 different plants, It takes into account newly initiated indications which are important for APC. application. The development of POPCD and supporting data are presented in Reference 8.6. Table 6-1 shows POPCD data as a function of bobbin voltage and, in Figure 6-1,- POPCD is compared with EPRI POD (EPRI POD is based on expert opinion and multiple analysts' evaluations for plants with 8/4" diameter tubes). It is evident from Figure 6-1 that below about 0.4 volt the NRC recommended POD of 0.6 is non-conservative while it is too conservative above about 0.5 volt. It is ofinterest to apply POPCD for sensitivity analysis and compare the results for the case with a POD value of 0.6.
f o:\ pe\tv 97\uicyst90d.wps . 6-1
- . + - - ~ ,- e- ,e
, w .-- , a + s - - . - .,-: - v
6.2 Calculation of Voltage Distributions Bobbin voltage projections start with a cycle initial voltage distribution which is projected to the corresponding cycle final voltage distribution, based on the growth rate adjusted for the anticipated cycle operating time period. The overall growth rates for each of the Sequoyah Unit-1 steam generators during Cycle 8, as represented by their cumulative probability distribution functions, are shown in Table 3 3 and on Figure 3 5. The composite growth data with 298 data points meet the Generic Letter 95-05 requirements. Further conservatism for the EOC 9 bobbin voltage prediction is provided by using the more conservative of the plant specific and composite growth rates. The methodology used in the calculatione of EOC bobbin
- voltage distributions is described in Reference 8.3.
For each SG, the initial bobbin voltage distribution ofindications being returned to service for the next cycle (BOC 9)is derived from the actual EOC-8 inspection results adjusted for tubes that are taken out of service by plugging. The Cycle 9 bobbin voltage population, summarized on Table 6 2, shows EOC-8 bobbin voltage indications, indications removed from service because of tube repairs and the BOC-9 indications corresponding to two values of POD.
The estimated Cycle 9 operating period used in the EOC-8 voltage projection calculations is 503 EFPD.
6.3 Comparison of Predicted and Actual EOC-8 Voltage Distributions The actual EOC-8 bobbin voltage distributions and the corresponding predictions illustrated on Figure 7-2 provide a comparison of the EOC-8 voltage distributions.
SG 3 was predicted to be limiting for EOC-8 which is consistent with the actual measurement since this SG yielded the highest leak rate and burst probability values based on the measured voltages. The total number ofindications detected in SG 3 as well as the other SGs we higher than the predicted for both POD of 0.6 as well as POPCD which c.an be attributed to the fact that ODSCC indications began to i
appear only meestly in Sequoyah Unit-1 and in this early stage the indication population can be expected to inetease relatively fast, as observed at other plants with ODSCC indications. However, the Unit 1 indication population is still small in comparison to other piants applying APC fer ODSCC at TSP intersections. It is evident from Figures 6-2 and 6 3 that most of the new indications are under one volt.
The largest predicted witage, same value predicted for SGs 1 and 3, is higher than the measurement (for es,2,G volts vs. 5.2 volts for SG 3).
0;\ ape \tva97\uleyD_90dxp5 6-2
- 6.4 Predicted EOC 9 Voltage Distributions
- Using the Monte Carlo analysis methodology described in Section 5.0, analyses were performed to predict the performance of the Sequoyah Unit.1 steam generators at i
EOC-9, based on the BOC 9 conditions summarized in Table 6 2 and the limiting of J
the plant specific and the composite growth rate distributions shown in Table 3 3.
Calculations were carried out with a constant POD of 0.6, in accordance with the i
NRC direction of Reference 8.1 as well as with POPCD. The results based on a POD of 0.6 are the reference values and those based on- POPCD are intended for i comparison with the reference results.
i' As shown in Figure 6-1, below about 0.4 volt the NRC recommended POD of 0.6 is >
non conservative relative to POPCD while it is too conservative above about 0.5 volt.
For SG 2, since a large fraction of the indications at EOC-8 are below 0.5 volt, the number ofindications at BOC-8 predicted with POPCD is higher than that with a POD of 0.6, as seen in Table 6 2.
! The EOC 9 predicted APC voltage distributions are summarized on Table 6 3. As q anticipated, the limiting steam generator is SG 1 with about 145 indications predicted at EOC 9 for a POD value of 0.6. The assumed BOC 9 and predicted EOC-9 bobbin
' frequency distributions for each steam generator are shown on Figures 6 3 through 6-6 for constant POD value cf 0.6 as well as the voltage dependent POPCD. The maximum bobbin voltage predicted for EOC-9 is 3.1 volts for POD value of 0.6 and 2.9 volts for POPCD.
4 W
i 0;\apc\tva97\ulcy9.90dxp5 6-3
l l
l Table 61 Comparison of POPCD with EPRI POD POPCD Based on Data from 16 Post '92 inspections in 8 Plants j
Voltage EPRI I POPCD, Bin POD 0.1 0.30 0.24 0.2 0.38 0.34 l 0.3 0.49 0.44 0.4 0.57 0.53 0.5 0.62 0.62
- 0.6 0.66 0.07 0.7 0.71 0.73 0.8 0.76 0.77 0.9 0.80 0.61 1 0.83 0.83 '
1.2 0.90 0.88 1.4 0.93 0.91 1.6 0.96 0.92 1.8 0.98 0.93 2 0.984 0.04 3 1.00 0.98 3 3.5 1.00 1.00
' Data Taken from Reference 9.6.
I a
l 4
4 4
I i
i
, PREDCOhr.zis Tatseret 7/2/9? 7;11 PM 6-4
=
Tebic 6 2 Sequoyah U:lt i April 1997 EOC-8 Field Bobbin and Assumed 80C 9 Bobbim Distribullons in SLB lask Rate and Tube Burst Analyses Steam Generator i Steam Generator 2 roc.8 .oc., roc.. soc.,
y la laduimme = ; - la = ; ,mo indssuuns 01 I O ! 67 4.20 2 0 3.33 ~
8 40 0.2 2 0 3.33 5 89 10 0
~ 16 67 29 44 03 11 0 18.33 24 93 13 1 2067 28 46 04 10 0 16 67 6 0 10 00 18 92_ 11.35 0$ 11 0 18 33 17.86 10 1 15 67 15.24 06 ll 0 18.33 16.35 9 0 15 00 13.37 07 5 0 8 33 6 85 6 0 10 00 8 22 08 12 0 20.00 15.5 t 7 0 11.67 9 09 09 4 0 6 67 8 94 8 0 13.33 9 87 1 4 0 6 67 4 79 4 0 6 67 4 79 1.1 4 0 6 67 4 71 3 0 5 00 3 53 1.2 1 0 1 67 1.15 2 0 3.33 2.30 1.3 3 0 5 00 3.39 2 0 3.33 226 14 1 0 1.67 1. l l 1 0 1.67 1.11 1.5 2 0 3.33 2.20 0 1 1.67 1 10 16 0 0 0 0 1 0 1.67 1 09 1.7 1 0 1.67 1 08 1 0 1.67 1.08 18 2 0 3.33 2.16 0 0 0 0 19 1 0 1 67 1.07 0 0 0 0 2 1 0 1 67 1.07 0 0 0 0 2.1 1 1 0 67 0 06 0 0 0 0 26 ,
0 0 0 0 0 0 0 0 Total 88 1 145 67 138 29 86 2 141.33 150 70
> IV 17 1 27.33 0 1833 liO9 11 12.47
>2V i 1 0 67 0 06 0 0 0 0 Steam Generator 3 Steam Generator 4 ROC.8 DOC.9 EOC.8 aOC.9 W held bobem 0.1 0
inecarnens
.d 0
. P.O.D "=
0 00 0 00
= 0 tedmsonna 0
P.O.D 0 00
=
0 00 02 1 0 1.67 2.94 3 0 5 00 8 83
~
0.3 5 0 8 33 11.33 4 0 6 67 9 07 04 6 0 10 00 I I .35 3 0 5 00 5 68 0.5 3 0 5.00 4 87 7 2 9 67 9.37 06 12 0 20 00 17 83 6 0 10 00 8 92
_07 0 0 15 00 12.33_ 4 1 5 67 4 48 08 6 0 10 00 7.79 5 0 8 33 6 49 09 7 0 11.67 8 64 2 0 3.33 2 47 1 6 0 10.00 7.19 1 0 1.67 1.20 1.1 3 0 5 00 3 53 I I 0 67 0.18 1.2 4 0 6 67 4 60 2 0 3.33 2.30 1.3 6 0 10.00 - 6 78 2 0 3.33 2.26 14 2 1 2 33 1.22 1 0 1.67 1.11 1.5 2 0 3.33 2.20 0 0 0.00 - 0.00 1.6 1 0 1.67 1 09 0 0 0 00 0.00 1.7 2 0 3.33 2 16 2 0 3.33 2.16 1.8 0 0 0 00 0 00 0 0 0 0 1.9 1 0 1.67 1 07 1 0 1.67 1 07 2 I I 0 67 0.07 0 0 0 0 2.1 2 2 1.33 0.12 0 0 0 0 26 0 0 0 0 1 1 1 67 0 03 Total 78 4 126 104 17 42 5 66 56 77 ~
>lV 24 4 36 00 22 84 10 2 15 67 9 11
>2V 2 2 1.33 0 12 I i 1 67 0 03
- -. a ~
6-5
I Table 6 3 4 Sequoyah Unit.1 April 1997 Voltage Distribution Projection for EOC 9 l i
Steam Generator 1 Stoem Generator 2 Steam Generator 3 Steam Generator 4 Vohage Projected Number ofinWostions at EOC5 9 ,
I i
Bin POD EPRI POD EPRI POD EPRI POD EPRI l
0.6 POD 0.6 POD 0.8 POD 0.8 POD !
0.1 0.10 _026 0.28 0.71 0 0 .,__0 ,. , ,o _
0.2 _ 0.31 0.63 1.72 3.26 0.14 025 0 43 0.76 0.3 1.83 3.10 4.54 8.17 0.89 1.27 1.07 1.66 -
04 4.00 6 94 9.67 16.81 2.46 3 35 2 90 4.47 0.6 7.78 9 98 16.70 11.83_ _ 4.66 6.91 _411_ _._,_617_,_
06 10.31 12.22 11.60 14.53 6.72 7.46 6.22 6.96 0.7 11.78 12.95 12.34 14.16 8.66 8.67 6.34 6.69 0.8 12.86 13.33 13.06 14.03 10.50 9.79 7 141 6 93 0.9 13.70 13.65 12.68 12.42 11.63 1028 6.18 6.30 1.0._ 13.19 12.32 _ 11.68 10.57 _ 11.31 9.62 6.96 _ _ 6.26_ , _
1.1 12.11 - 10.77 10.64 9.14 10 68 8.60 6.08 4.31 1.2 10.43 8.81 9.17 _ 7.52 9.86 7.73 . _ 4.2L _ _ _3_44 1.3 8.92 7.31 7.48 6.89 8.98 6.80 3.S? 2.73 1.4 7.35 6.76 6.98 4.62 7.96 6.83 3/>0 2.21 1.6 _ 6.99_ 4.61 _ _4.77 3.50 6.06 4.86 1.6 2 56 _ _ 1.81 ,
4.77 3 49 3.76_ 2.68 6.76 3.99 s
1.7 3 80
- 2. '0_ ,,_. 1.4 5_,_
2.69 2.89 2.02 4_72 3.20 1.8 1.11 _ .,,, _ 317 _
3.13 2.16 2.20 1.61 3.80 2.62 _1.48 0.98 4 1.9 2.62 1.76 1.63 1.11 3.03 1.95 1.27 0.83 2.0 2.22 1.40 1.18 0.79 2.39 1.49 1.07 0.70 2.1 1.87 1.21 0.82 0.54 1.86 1.10 0.88 4 0.67 1 2.2 1.67 1.00 0.49 0.00 1.43 0.80 0.70 0 45 1 2.3 1.30 0.80 0 0.70 1.08 0.67 0.54 0.10
- _ _ 2.4 1.04 0.63 0.70 0 0.81 0.09 0.41 ,0,, _ _
a 2.5 0.81 0.48 0 0.30 0.58 0.70 0.31 0.70
, i i-3.6 0.0 _1 0.05 0.30 0 0 0 0
_,,_._0 2.7 0 0.70 0 0 0 0.30 0 0.30 [
2.8 0 0 0 0 0.70 0 0.70 0
]. 2.9 0.70 0.30 0 0 0 0 0 0 3.0 0 0 0 0 0 0 0 0 3.1 0.30 0 0 0 0.30 '0 6.30 ~"O'~
TOTAL 145 66 138.16 141.31 150.58 127.66 107.03 70 02 65.52 4
>1V 69.80 53.88 62.01 40.22 70 90 50 53 29 90 21.75 3 2V 8 46 5.17 2.31 1.54 6.96 3.56 3 88 2.12 1
4
)
1 i
mm.m=w . 6-6
Figure 61 Sequoyah Unit 1 Cornparison of Actual and Predicted Ilobbin Voltage Distribution for Cycle 3 SG.1 12 10 - --- -
OActual 8 ~~ ~ ~
E Predicted (POD *0.6) 6- - - -
a4 - - - - -
0 E E E o E $ $ E $ E ! U U ! O I I I I E E $ $
, A Bobbin Voltage SG 2 14
,, DActual to E Prodicted (POD =0.6) g __ _.
6 - --- -
. pkg =.ie'erem - ew- =**** h '**888'" N~ N N 0
- B- ^ ~~ "
01 0.2 03 04 06 06 07 04 09 1.0 1.1 12 1.3 14 1.6 16 1.7 Bobbin Voltage mancaw.e.tt rw s ie av 6-7
Figure 6 2 Sequoyah Unit 1 Cornparison of Actual and Predicted Ilobbin Voltage Distribution for Cycle 8 SG 3 12 to DActual e -
5 Predicted (POD =0.6) a - - - .-
g - - ._ - . -
- ; = ========,==,=====;===
--Illiin<.....
Bobbin Vottage
==
SG-4 7
e OActual 8 -
u Predicted (POD =0.6) j .
3 ___ ._ _ _ . .
E g .- - - _ .. -
[T
~
EE $ $ $E $ $$ 3 lill U U Bobbin Voltage I lit u i.
U I U I I E 5 NU$%
mrocrw ewscann G-8
i 1
l
} Figarc G.3 i Sequoyah Unit.1 SG 1 i
Predicted llobbin Voltage Distribution for Cycle D
.i POD . 0.6 j u l
to i
i l DDOC.p 4
[ gg < - - ~. .-.
{ [ E Predicted EOC 9 to -. -- - - _ _ _ _
i i
i
}
{ g . . _ _ _ _ _ _ _
l 6
l o
- : : : : : : : : : :::::::::;==;====m DotMn Voltage Illiam.....
POPCD es i
i j 8
- ODOC 9 1
1 4
1
- gg _ _ ._
M Predicted EOC
- 9 e
i I I 1
jg .- . . . _ . .
1
)
s - -- . . - - -
I I _ .I . I_I_3 I I n a s..
f
- a..E. : : : : : e <= me : . Bobbin Voltage
- ====;
- ~ . . .
6-9 A
. . . . . _ _ . , . _ . . . _ . _ _ _ _ _ . . . ~ . . . _ _ _ . _ _ . . _ _ _ _ . . . _ . . . . . . . . . _ . _ _ .
1 1
1 l'agure G 4 i Sequoyah Unit.1 SG 2 j
l'redicted Ilobbin Voltage Ulstribution for Cycle 9 1
4
.m.,
M f .
i 26 i
}
!' 0D00 9 l e
(
i E Predicted EOC . 9 l
l -
i -
S -
1 -
1 i
1 io - - . .
1 j e -. -- . _ _ _ _ . _ _
l .
L
. a -
o e o o o o o o . - . . . . . . . . a a Dobbintortage -' *---a 1 l}lr11
........a 1 ...
a a a a a
, unun l M ~
l i
I I =
i as -
DBOC.9 l
r l
i l to -
E Predicted EOC .9 f -
- i io - _ _ _ _ _ __ __. !
i l
i .-
J o r rrl.Is... . .
o EEo o E o E E E ! obbinTottke B I
PredDNSF igm I'lM7 $ $1 PW 6-10 i
. . . , _ _ . ~
- _ _ _ . _ . _ . . . _ _ _ _ . . _ _ _ - _ . . _ .m___ -__
i a
i
- Figure 6 5 Sequoyah Unit 1 SG 3 l'redicted Ilobbin Voltage Distribution for Cycle 9 l .
j POD = 0.0 1
l so l
l i
i 14 000C.9 I
g 14 .. -
4 s Predictsd EOC . 9 l
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7.0 SLB LEAK HATE AND TUBE BURST PROBABILITY ANALYSES 7.1 Calculation of Leak Rate and Tube Burst Probability This section discusses tube leak and burst probability analyses using voltage distributions projected for the end of the operating period. The calculation utilizes correlations relating bobbin voltage amplitudes (either measured or calculated) to free span burst pressure, probability ofleakage and associated leak rates for ODSCC indications at TSP locations. The methodology used is documented in Reference 8.3, and is consistent with NRC criteria and guidelines of Reference 8.1.
7.2 Predicted and Actual Leak Rate and Tube Burst Probability for EOC 8 Analyses were performed to calculate EOC-8 SLB tube leak rate and probability of burst for the actual bobbin voltage distribution at EOC-8 (with no growth projection applied) previously presented in this report. The results of Monte Carlo calculations performed for the actual voltage distributions including NDE uncertainties are compared to the predictions based on the EOC 7 data, as shown on Table 7-1.
A comparison of the EOC-8 af,uals with the corresponding projections based on a POD value of 0.6 indicates the SLB leak rates are slightly underpredicted (by 0.06 gpm for the limiting SG 3) for all SGs and burst probabilities are slightly underpredicted (by 5x10 ' for the limiting SG 3) for all SGs except SG 4; however, the differences between the predictions and actuals are very small in comparison to their respective acceptance limits. As noted in Section 6.2, underprediction of EOC-8 SLB leak rates and burst probabilities is due to the fact the projections are based on a small indication population which inc cased relatively fast during Cycle 8.
7.3 Projected Leak Rate and Tube Burst Probability for EOC 9 Using the methodology previously described, calculations were also performed to predict the EOC-9 performance of all four steam generators in Sequoyah Unit-1, and the results are summarized in Table 7-2. EOC-9 bobbin voltage distributions as well as leak rates and tube burst probabilities based on those distributions are predicted.
Two sets of results are shown in Table 7-2: one set of results based on a constant POD of 0.6, and a second set based on voltage-dependent POPCD.
The EOC-8 predictions shown in Table 7-2 for all SGs meet the ARC acceptance for Sequoyah Unit-1. As expected, SG 1 with largest number of BOC-9 indications and 4
highest Cycle 8 growth rate is predicted to be the limiting SG. The predicted EOC-9 SLB leak rate for SG 1 based on the present licensing basis database and method o;\ ape \tva97\uley9_90d.wp5 7-1
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(constant POD of 0.6 and a leak rate independent of voltage)is 0.75 gpm which is substantially less than the Sequoyah Unit-1 allowable SLB limit of 3.7 gpm. The EOC-9 SLB tube burst probabilities for all four SGs are at least two orders of l magnitude below the NRC reporting guideline for tube burst probability ofl.0 x 10-8 In summary, the EOC 9 SLB leak rates and tube burst probabilities calculated for all four SGs using the present NRC approved database and method meet and exceed the SER limits for Sequoyah Unit 1 with a substantial margin.
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Table 7 1 Sequoyah Unit 1 1995 Outage Summary of SLB Tube Leak Rate and Burst Probability !
No,of Burst Probability !
Steam Indica- Max. SLB Generator POD tions"' Volts (8' Single Leak Rate One or Tube More KP:n Tubes
- EOC 8 Predicted 0.6 15 3.2 1.7 x 10 8 1.7 x 10 8 0.034 1
EPRI 14 1.9 5.3 x 10.s 5.3 x 10~5 0.006 0.6 10 1.5 < 1 x 104 < 1 x 10 4 < 0.001 2
EPRI 9 1.5 < 1 x 10 ' 8 < 1 x 10 8 < 0.001 0.6 38 3.2 2.6 x 10 4 2.6 x 10'5 0.173-EPRI 30 2.5 1.3 x 104 1.3 x 10 5 0.083 0.6 15 2.8 1.9 x 104 1.9 x 104 0.077 EPRI 12 2.7 9.3 x 10 8 9.3 x 10 ' 8 0.037 EOC 8 Actuals 1 1 88 2.5 1.9 x 10
- 8 1,9 x 10 5 0.17 2 1 86 2.0 1.9 x 10 5 1,9 x 10 ' 8 0.09 3 1 79 2.6 3.1 x 10 ' 8 3.1 x 10 ' 5 0.23 4 1 45 2.9 < 4 x 10 8 < 4 x 10 5 0.09 Adjusted for POD.
'8' Voltages include NDE uncertainties from Monte Carlo analyses and exceed measured voltages.
- Inciudes probability of a single burst.
O:\ ape \tva97\uley9_90d.wp5 7-3
0 Table 7 - 2 Sequoyah Unit-1 1996 Outage Summary of SLB Tube Leah Rate and Burst Probability Burst Probability No. of i Steam POD Indic- SLB Leak Max. Rate Generator ations'" Volt s"'
Single One or Tube More Epm i
Tubes) i8 EOC - 9 Projection (Assumed duration = 503 EFPD)
O.0 145.7 3.1 8.8 x 10 8.8 x 10 ' 8 0.75 POPCD 138.1 2.9 4.9 x 10 ' 8 4.9 x 10 O.55
, 0.0 141.3 2.0 4.4 x 10 ' 8 4.4 x 10 O.47
, POPCD 150.0 2.5 1.0 x 10 8 1.6 x 10 O 30 0.6 127.7 3.0 5.4 x 10
- 8 5.4 x 10 ' 5 0.71 j- POPCD 107.0 2.7 3.9 x 10 ' 8 3.9 x 10 ' 5 0.40 i 0.G 70.0 3.1 3.7 x 10 8 3.7 x 10 8 0.31 POPCD G5.5 2.7 2.5 x 10 ' 8 2.5 x 10 O.20 i
Adjusted for POD.
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- Voltages include NDE uncertainties from Monte Carlo analyses and exceed measured voltages.
(3) Includes probability of a single burst.
0:\ ape \tra97\ulcy9.90d.wp3 74
8.0 REFERENCES
8.1 NRC Generic Letter 95 05, " Voltage Based Repair Criteria for the Repair of Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking", USNRC Office of Nuclear Reactor Regulation, August 3, 1995.
8.2 WCAP-13990, "Sequoyah Units 1 and 2 - Steam Generator Plugging Criteria for -
Indications at the Tube Support Plate", Westinghouse Nuclear Services Division, May 1994.
8.3 WCAP 14277, "SLB Leak Rate and Tube Burst Probability Analysis Methods for ODSCO at TSP Intersections", Revision 1, Westinghouse Nuclear Services Division, December 1996.
8.4 EPRI Report NP-7480 L, " Steam Generator Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternate Repair Criteria, Volume 1: - 7/8 Inch Diameter Tubing," Revision 1, December 1993.
8.5 Letter from S. C. Jain, Duquesne Light Company to U. S. Nuclear Regulatory _
Commission, " Beaver valley Power Station Unit No.1, Docket No. 50 334, License No. DPR-66, Steam Generator Pulled Tube Data (Supplemental) Supporting Alternate Tube Plugging Criteria Implementation," dated March 27,1996.
8.6 Addendum to EPRI Report NP-7480 L, " Steam Generator Outside Diameter Stress Corrosion Cracking at Tube Support Plates Database for Alternate Repair Criteria, Addendum-1,1996 Database Update" August 1996.
O.\ ape \tva97\uley9_90d.wp5 8-1
Y ATTACHMEN? 3 Tennessee Valley Authority Sequoyah Nuclear Plant Unit 1 Westinghouse Electric Corporation Steam Generator Tube Integrity Assessment for Cycles 8 and 9 x
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l SECL-97145 Page 1 of 12 WESTINGHOUSE '
SAFETY EVALUATION CHECK LIST t
- 1) NUCLEAR PLANT (S) Seouovah Unit l_
The written safety evaluation of the rnised proccJure, design change or modificadon required by 10 CFR $0.59 has been prepared to the extent required and is attached. If a safety nalestion is not required or is incomplete for any reason, explain on Page 2. Parts A and B of this Safety Evaluation Check List are to be completed only on the basis of the safety evaluation performed.
- 3) CHECK LIST.PART A *
(3.1) Yes_ NoX A change to the plant as described in the FSAR?
(3.2) Yes_ No2. A change to procedures as described in the FS AR7 (3.3) Yes_ NoX A test or experiment not described in the FSAR?
(3.4) Yes_ No2. A change to the plant technical specifications (Appendix A to the ;
Operating License)?
CHECK LIST . PART B (Justification for Part B answers must be included on page 2.)
(4.1) Yes_ No2. Will the probability of an accident prniously evaluated in the FSAR be increased?
(4.2) Yes_ No1 Will the consequences of an accident previously evaluated in the FSAR be increased?
(4.3) Yes_ No2 May the possibility of an accident which is different than any already evaluated in the FSAR be created?
(4.4) Yes_ NoX. Will the probability of a malfunction of equipment important to safety <
prniously evaluated in the FS AR be increased?
! (4.5) Yes_ No2. Will the consequences of a malfunction of equipment important to safety previously evaluated in the FSAR be increased?
! (4.6) Yes_ NoX May the possibility of a malfunction of equipment important to safety different than any already evaluated in the FSAR be created?
(4.7) Yes_ No1 Will the margin of safety as defined in the bases to any technical specification be reduced?
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SECL 97145 l Page 2 of 12 .
Lf the answers to any of the above questions are unknown, indicate under 5) REMARKS and explain below. -
)
If the answer to any of the above questions in Part (3.4) or Past B cannot be answered in the
..*6adve, the change review requires an applicadon for license amendment in accordance with 10 C, A 30 59 (c) and submitted to the NRC pursuant to 10 CFR 50.90. i REMARKS: !
The answers given in Section 3. Part A, and Section 4. Part B, of the Safety Evaluadon Checklist, are based on the attached Safety Evaluadon.
Reference document (s):
See Section 7.0 FOR FSAR UPDATE Seedon: Pages: Tables: Figures:
Rearon for / Descripdon of Change:
N/A SIGNATURES Prepared by: A'# Date: 7
/5h2 Independently Resiewed by Date bNf 9 Licensing Review by: Date
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SECL 97145 Page 3 of 12 SEQUOYAH UNIT 1 STEAM GENERATOR TURE INTEGRITY ASSESSMENTt CYCLES 8 AND 9 '
i
1.0 INTRODUCTION
Inservice inspection of the steam generators at the Sequoyah Unit 1 Nuclear Plant during IR8 has revealed the presence -
of several tnodes oflocalized tube wall degradationc Axial crack indications were found at the tube support plate (TSP) intersections, in Row 1 U-bends (PWSCC)and in the WEXTEX expansion region (PWSCC and ODSCC). De ,
indice:lons at the TSP intersections include PWSCC at dented intersections and ODSCC, primarily at non-dented l inteisections. Circumferential PWSCC and ODSCC indications were also found at dented TSP intersections and PWSCC was found in the WEXTEX transition. De more signincant indications found in the inspection were axial PWSCC at dented intersections and in a Row I U-bend. Other axial and ell circumferential indications found were small compared to sizes that would challenge tube integrity. De evaluation for axial ODSCC at the TSPs is evaluated in a separate report as part of the analysis required by NRC Generic Letter 95-05, and is not included in this safety evaluation.
His safety evaluation addresses plant operation with various types oflocalized tuSe wall degradation ongoing in the Sequoyah Unit i steam generators, ne purpose of this evaluation is to show that RG 1.121 criteria," Bases for Plugging Degraded PWR Steam Generator Tubes", and the supplemental performance cri teria identined in the newly proposed regulatory guide, were met for Cycle 8 operation and are expected to continue to be met during Cycle 9 operation. Inservice inspection and in situ burst testing are used to complete a condition rnonitoring assessment of Cycle 8 operation. Inservice inspection, in situ burst testing, no significant change in expected plant operating parameters during Cycle 9 operation (i.e., cycle length, temperatures, primary to-secondary pressure differential, ,
primary / secondary water chemistry) and primary to-secondary leakage monitoring capability are key elements used in ,
supporting the determination that all applicable performance criteria will centinue to be met during Cycle 9 operation of Sequoyah Unit I, i 2.0 REGULATORY HASES i . .
i . It is the NRC stafl's position that utilitien should develop a program that provides reasonable assurance that :he steam j_ generator tubes are capable of performing their intended safety function, nis includes establishing performance ,
a criteria commensurate w ith adequate tube integrity, programmatic considerations for providing reasonable assurance l that the performance criteria will be met during plant operation, and guidelines for monitoring the condition of the tubing to conGrm that the performance criteria are in fact being met, in addition, the program framework should
- provide that measures be maintained to mitigate the consequences of occurrences involving gross rupture of the tubing
. and'or abnormalIcakage.
ne program strategy begins with an NDE tube inspection following plant shutdown. ne inspection is intended to J provide information concerning the active degradation mechanisms present in the steam generators, the identity of
- tubes containing flaws and the size of these flaws for each active degradation mechanism, and the rate of flaw evolution for each active degradation mechanism. This information is to be used as part of other program elements to assess tubc
^
integrity performance, to determine the appropriate time interval to the next inspection, to determine the tube repair limits, and to determine which tubes fail to satisfy these repair criteria (and must be repaired or removed from service).
i ne tube inspections are followed by assessments of tube integrity performance relative to NRC accepted performance
- criteria and are currently provided in a draft regulatory guide. NRC Regulatory Guide 1.121, " Bases for Plugging Degraded PWR Steam Generator Tubes", issued for comment in August of 1976, provides guidelines for determining the current depth-based tube repair criteria (sleeve and tube plugging limits) and the operational leakage limits which are specified in the Sequoyah Unit 1 plant technical specifications. De new draft regulatory guide supplements the l
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Page 4 of 12 guidance of RG 1.121 to address ahernate types of repair criteria (e.g. length-based and voltage-based repair criteria) and it addresses the treatment of uncenainties in tube Feometry, material properties, NDE flaw measurements, and flaw growth rates.
Tube integrity performance is subject to two different types of assessments in the proposed regulatory guide; a condition monitoring assessment and an operational assessment. De condition monitoring assessment is "backwcrd i looking" and its purpose is to confirm that adequate tube integrity has been maintained since the previous inspection.
Condition monitoring involves an assessment of the "as found" condition of the tubing relative to the tube integrity performance criteria. De operational assessment difTers from the condition monitoring assessment in that it is " forward looking". Its purpose is to demonstrate rea.< enable assurance that the tube integrity performance criteria will be met throughout the period prior to the next scheduled tube inspection. His projection is based on the inservice inspection results, the tube repair criteria to be implemented for each degradation mechanism, and the time interval to the next scheduled inspection.
Tennessee Valley Authority has implemented such a program at Sequoyah Unit I and both a condition monitoring and operational assessment have been completed utilizing the current inservice inspection results. De cod of cycle EOC 8 and projected EOC 9 condition of the Sequoyah Unit I steam generator tubes have been compared to the performance criteria identified in the draft regulatory guide and are discussed in detail below.
3.0 EVAL,UATION l Based on the results ofin situ testing and supporting analyses (Reference 1), it is concluded that all indications found in the EOC 8 inspection satisfied 1.121 burst margin guidelines and all structural and leakage integrity requirements for condition monitoring. Similarly, it is shown that all operational assessment structural and leakage requirements uould be satisfied at the EOC 9. His safety evaluation provides a steam generator tube integrity assessment following the EOC 8 inspection.
3.1 Aslal PWSCC at Dented TSP Intersections The initial inspection of TSP intersections included 100% bobbin coil inspection for initial screening and detection ofindications, in SGs 1,2, and 4,100% of the hot leg dent signals > $ volts by bobbin were + Poir t inspected. In SG 3,100% of the hot leg dent signals > 5 volts by bobbin at the first, second, and third TSPs, and 20% of fourth TSPs dent signals > 5 volts were + Point inspected. The following 4 Point inspections were performed in hot leg dent signals > 2 volts but < 5 volts: SG I and 2,100% at the first and second TSPs,20% at the third TSP; SG 3, 100% at the first, second, and third TSP,20% at the fourth TSP; SG 4,100% at the first, second, third, and fourth TSPs,20% at the fifth TSP. This inspection of small dents was performed to envelope the highest TSP with identined PWSCC indications since the PWSCC degradation mechanism is strongly temperature dependent. In SG 3, one indication was found at the 4th TSP in a dent < $ volts, and the inspection was increased to include 100% of the < $ volt dents at the 4th hot leg TSP and 20% of the < $ volt dents at the 5th hot leg TSP. No further PWSCC indications were found in this program.
The inspection at EOC 8, as well as for EOC 7, for dents < 2 volts was based on bobbin coil inspection. During the course of the inspection, a PWSCC axial indication was found at a TSP intersection with a < 2 volt dent that had not been identified in the bobbin inspection. As a result, the bobbin calling guidelines were arvised to tighten the calling criteria. Since detection of Daws in dents < 2 volts is based on boboin coil inspection calls and detection of flaws in dents > 2 volts is based on + Point detection, these two groups are evaluated separately below for the tube integrity operational assessment. The condition monitoring assessment is combined for both types of degradation since this assessment of as-measured indications is based on + Point sizing and in situ test results and is essentially independent of detection by bobbin or + Point coils.
) -
)
SECL 97-145 Page 5 of 12 For tube integrity considerations, it is important to note that the extent ofinspection and calling criteria at the EOC.
8 inspection were enhanced relative to the EOC 7 inspection. As a minimum, the tightened bobbin calling criteria were applied and supplemented by the historical industry trend toward progressively more conservative Daw calls.
Establishing that tube integrity was satis 0ed at EOC 8 then implies that integrity would be satisfied at EOC 9 since operating cycles are comparable (Cycle 9 is slightly longer with a pro.iected duration of 460 El'PD versus 450 actual EFPD for Cycle 8) and the degradation mechanisms represent progression of previously identined degradation modes, it is shown in WCAF-14707 (Reference 2) that TSPs will not displace in a SLD event for sos having experienced tube support plate corrosion even if the corrosion has not progressed to denting deformation of the tube. The conclusion applies even following chemical cleaning which is applicable to Sequoyah 1 $1nce the SGs were chemically cleaned at EOC 7. As a result of negligible TSP displacement, the crack lengths within the TSP do not contribute to burst and only the length outside the TSP must be evaluated for burst potential as a free span indication. The packed crevices also limit leakage for crack leng6s within the TSP compared to free span indications. Since the TSPs do not displace in a SLB avent, in situ leak and pressure testing can be applied to assess leakage and burst margins for indications at TSP intersections and these test results are used to support the tub
- Integrity assessment given below, llowever, to conservatively demonstrate the large margins for the PWSCC l
I Indications, a tube integrity assessment for the limiting indications at SLB conditions is also performed assuming that the indications are free span.
3.1.1 Indications at Dented TSPs with >2 Volt Dent Signals The Geld indications were reviewed to identify the indications with the longest lengths for burst considerations and the largest voltages for primary-to-secondary leakage considerations. He deepest fiaws based on + Point data were used to further evaluate the longest and highest voltage indications. Rese indications were then evaluated for tube integrity to bound both leak and burst considerations. The largest voltage indications were found at tubes R14C73 in SG 3 of 3.ll volts, R37C28 in 50 4 of 2.7 volts, R21C47 in SG 3 of 3.21 volts and R6C10 in SO 2 of 2.92 vo%.
The longest indications were R37C28 in 50 4 of 0.89", Rl7C44 in SO 4 of 0.86", R13C57 in SO I of 0.70", and R7C7 of SG 3 of 0.68".
For tube burst considerations, the free span crack length must be greater than 9.47" which corresponds to satisfying the 3AP b.irst margin guideline of RO 1.121 for a uniformly throughwall crack. Only the crack length outside the TSP contributes to burst since the TSP contrains burst for the length inside the TSP. The longest crack length indications outside the tube support plate were at R36C42, SO 4,111 and R14C73, SG 3, lit, with lengths outside the TSP of 0.31" and 0.43", respectively. The average depths for these indications were 71.1% and 56.5%, which are well less thet the 100% depth at 0.47" that satisfies RG l.121 criteria, and adequate burst margins would be expected ror these indications. Rese indications were in situ burst tested to 4750 pq (4318 psi equivalent pressure at operating conditions) and did not leak or burst w hich confirms tM conclusion based on NDE analyses.
Therefore, all axial PWSCC indications at TSP intersections satisfied the RO 1.121 burst margin guidelines.
As a very conservative measure, the burst capability of the indications can be assessed assuming that the TSPs are displaced in a SLB evem to expose the entire length of the crack. Since the TSP prevents burst at normal operating conditions, a burst capability of 1.43APst, = 3661 psi satisfies the RO l.121 burst margin guideline. The crack length and average depth together with the depth profile provide the basis for estimating the free span burst pressure. The limiting crack is clearly R37C28 w hich has the longest length of 0.89" with an average depth of 54.8% which is also the largest average depth for any indication exceeding the throughwall crack length limit satisfying the burst -argin guideline. The calculated burst pressure of this indication assuming the entire Haw profile is free span is $238 psi using LTL material properties. The depth pronic is fairly uniform and the indication burst pressure would not be expected to be below that corresponding to the average depth For a 0.90" long 1 indication, an average depth of 80% satisfies the 1.43aP st , buin margin using LTL material properties. The difference of approximately 25% between the acceptable average depth and the NDE average depth of 54.8%
l
SECL 97145 Page 6 of 12 provides an allowance for NDE uncertainties. It is concluded that all axial PWSCC indications at dented TSP intersections satisfied RG 1.121 burst margin requirements at EOC 8 even under the unrealistic assumption that the TSPs displace in a SLB cvent to expose the entire crack length.
For SLD leakage considerations, maximum voltage and maximum depth provide the best estimate ofleakage potential. For dented TSP intersections, the length of crack outside the TSP would leak approximately as a free span indication and the length inside the TSP wculd not contribute significantly to leakage. Tubes Rl4C73 and R36C42 extend outside the TSP and have two of the largest voltage indications at 3.11 and 1.84 volts at locations outside the TSP and thus represent limiting leak tests even if the plates were conservatively assumed to displace in a SLB event. Only tube R36C42 with a maximum depth of 91% is considered to represent a leakage potential. Both of these indications were in situ leak tested with no leakage up to 4750 psi. The only other indication having a moderately high voltage (> 1.5 volts) and maximum depth > 80% was R37C28 (crack extension outside TSP of only 0.19") and this indication was also tested to 4750 psi with no leakage, his indication has only two local data points over 80% depth with one of the indications at the edge of the TSP and the other within the TSP. This indication would not be expected to !c*k even under free span conditions. Consequently, primary to-secondary leakage would not be expected at SLB conditions even under the conservative assumption of TSP displacement in a SLB event, Several indications, including the maximum lengths outside the TSP, were leak tested and none leaked even up to the maximu n pressure differential tested which ranged from 4750 to 4900 psi (4318 to 4455 psi equivalent pressure at operating temperature). The in situ test results support none or negligible leak,.ge at SLB conditions, ne + Point inspection at EOC 8 of dented TSP intersections was slightly more extensive than that performed at EOC 7. Allindications at dented TSP intersections satisfied burst and leakage requirements at EOC 8 and can thus be expected to satisfy requirements at EOC 9. Cycle 9 is projected to have a slightly longer operating cycle than Cycle 8 (460 vs 450 EFPD). Additional growth over a 503 day maximum licensed operating cycle length would not significantly reduce burst margins over that found at EOC 8 due in part to the large percentage of negative growths observed for PWSCC at dented intersections from EOC 7 to EOC 8. It is concluded that tube integrity requirements for axial PWSCC at dented intersections > 2 volts will also be satisfied at EPC 9.
A first order demonstration of acceptable tube integrity at EOC 9 can also be obtained from considerations of +
Point detection thresholds. An estimate of the + Point detection threshold for PWSCC at dented TSP intersections can be obtained from the smallest pulled tube indication that was detected in the field inspection. This detected indication can be reasonably expected to bound undetected indications. From Reference 2, the smallest pulled tube indication had a crack length of 0.12", a maximum depth of 38% and an average depth of 23%. A 0.9 inch long free span crack would satisfy RG 1.121 requirements with an average depth of 80%. It is very unlikely that an indication near the detection threshold of about 23% average depth would grow to challenge tube integrity at EOC-9.
3.1.2 ludications at TSPs with Dents < 2 Volts ne inspection at EOC-8 for dents < 2 volts was based on bobbin coil inspection. Bobbin calling criteria were made more conservative for the current inspection and it can be expected that undetected indications len in service for Cycle 9 would be as small or smaller than len in service for Cycle 8. Since operating conditions are essentially the same between cycles and the cycle lengths are expected to differ by only 10 EFPD, it is judged that the limiting indications at EOC-9 will be bounded by those found at EOC 8, which satisfied tube integrity requirements. It can therefore be concluded that tube integrity requirements will be satisfied at EOC 9 for indications at TSPs with dents
< 2 volts.
Two indications found by + Point and not detected by the bobbin inspection were RIC21, TSP 2 and R33C21, TSP I in SO 4 with dent voltages of 3.53 and < 2 volts, respectively. TSP intersections with > 2 volt dents were inspected by + Point and the detection threshold is that for the + Point coil as described above. The R33C21 w
i SECL 97145 Page 7 of 12 indication is the on'y indication found by + Point that was bobbin NDD at a TSP intersection with a < 2 volt dent.
His would indicate that the bobbin detection threshold would be slightly greater than 30% average depth for an indication of about 0.25" length. Although the data is limited, a bobbin detection threshold of about 35% average depth appears reasonable. It is unlikely that indications in this depth range would grow to exceed the structural limit such as an average depth of 80% which satisues the RG l.121 burst margin guideline of 3APm for a 0.9 inch long Daw, This further supports satisfaction of tube integrity requirements at EOC 9. Both of the bobbin NDD's were in situ testei with no leakage or tube burst.
3.2 Atlal PWSCC at U bend Locations The U-bend inspection included 100% + Point inspection of the Row I tubes. Two indications were found by the 100% + Point inspection; the limiting indication was in tube RIC84 in steam generator 1. The indication in RIC36 in steam generator 3 may be a signal from an diametral irregularity at the tangent point of the tube. Both of these indications were in situ tested burst and leak tested. The predicted burst pressure for RIC84 based on the depth using lower bound Row 10cw stress for U-bends for tubes heat treated in the field is 4870 psi. Tube RIC84 did not rupture ut the 4750 psi pressure test representing 3AP., thus supporting the NDE based estimate, although resulting in a SLB leak rate of 113.9 gpd (< 0.1 gpm) based on the room temperature test at 2800 psi. No leakage was cbserved at a 6P of 1600 psi. Thus, the indications satisfy RG 1,121 burst margin requirements. The SLB leak rate is negligible compared to the 3.7 gpm allowable SLB leak rate at Sequoyah l. The only other potential SLB contribution to SLB leakage results from the ARC for ODSCC at TSP intersections for which a SLB leak rate of 0.28 gpm was predicted from the EOC-8 measured distribution ofindications. Consequently, the total SLB leak rate at EOC 8 is negligible compared to the allowable limit and the U-bend PWSCC indications satisned all tube integrity requirements for condition monitoring.
The U bend inspection at EOC-8 was more extensive in scope than the EOC 7 inspection uhich did not incitste 100% of Row I U-bends. Tube RIC84 was last inspected at EOC-6 and review of data from this inspection shows that an indication was likely present at this time. The RIC84 indication, therefore, represents at least two cycles of growth. Given the 100% RPC inspection at EOC-8, the potential undetected indications left in service for Cycle 9 can be expected to be smaller than that for Cycle 8. Since operating conditions are essentially the same between Cycler 1 and 9, cycle lengths are within 10% and all EOC 8 indications sa'isned tube integrity requirements, it can be expected that all U-bend indications found at EOC 9 will also satisfy RG l.121 guidelines.
3.3 Asial Indications at WEXTEX Espansions 3.3.1 Conditional Assessment Both axial PWSCC and ODSCC indications were found in the WEXTEX transition. The maximum crack length from these indications was 0.36" found in R41C32 as an axial OD indication. This length is well below the 0.47" free span through-wall length satisfying burst margins. Thus, the WEXTEX indications do not challenge burst integrity for condition monitoring at EOC-8.
Except for R13C54, the voltages (<l.75) for the indications are such that leakage would not be expected based on comparable results for pulled tubes and in situ testing of hard roll expansions. The indication for R13C54 was reported in the Geld as a 6.38 volt indication. The indication is located entirely within the tubesheet extending from about 0.06" to 0.40" below the TTS with part of the crack below the bottom of the WEXTEX transition.
Consequently, the tubesheet prevents signi0 cant crack opening and the leak rate under the conservative assumption of a through wall indication can be calculated using the W' methods of Reference 4. The SLB leak rate for an assumed through-wall indication would be about 0.06 gpm which is negligible compared to the allowable limit.
SECL-97145 Page 8 of 12 Since the operating cond;tions are essentially the same between cycles 8 and 9, the cycle lengths are within 10% and all EOC 8 indications satisGed tube integrity requirements,it can be expected that all axial indications at the WEXTEX expansions found at the EOC 9 would be mmparable to Cycle 8 and will also satisfy RO 1.121 criteria.
3.4 Circumferential Indications 3.4.1 Circumferential Indications at Dented TSPs Circumferential PWSCC and ODSCC indications were found at dented TSP intersections. All indications are 102' or less and are too small to chahenge RO 1.121 burst margin guidelines w hich would be satisned by a uniformly
' throughwall indication of about 263*, or about 73% percent degraded area (PDA) for a 3AP value of 4250 psi.
Accounting for NDE uncertainty, a practical PDA structural limit of 50% is defined for the Sequoph Unit I steam
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generator tubes. The small crack angles are typical of circumferential indications found at dented TSP intersections !
which, to date, have consistently been < 180' in azimuthal extent.
The + Point depth sizing for the circumferential indications at dented TSP intersections shows local depths up to I 62% with no significant circumferential extent throughwall. Within NDE uncertainties, the possibility exists for l
short throughwall penetration. De modest peak voltages also indicate a low likelihood of signliicant throughwall t
penetration. It is expected that the indications are not throughwall and, even if throughwall, SLB leakage would he negligible. Due to the small indications found, it was not considered necessary to in situ test circumferential indications at the TSP intersections other than the mixed mode indication at R16C83 in S0 3 which is further discussed below.
Adequate detection of circumferential indications at dented TSP intersections is supported by the prior tube pulls from Sequoyah 1 and Diablo Canyon l. The Sequoyah l pulled tube was an ODSCC indication of 65' extent with a maximum depth of $4% and a PDA of 7.3%. The Diablo Canyon pulled tube was a PWSCC indication of $1' extent (total of 2 cracks) with a maximum depth of 50 % and a percent degraded area (PDA) of about 3 %. Rus, it is expected that no significantly large indications are left in service for the DOC-9. Since the + Point inspection at EOC-8 was somewhat more extensive than at EOC 7, indications anticipated at EOC 9 would be comparable or smaller than found acceptable at EOC 8. Therefore, tube integrity requirements would also be satisfied at EOC 9.
The abilit/ to identify low PDAs is shown by the pulled tube results, w hich are substantially less than the structural limit of 73% PDA based on a single uniform throt.gh wall flaw and also well below a practical PDA structural limit of 50% based on NDE.
3.4.2 Circumferentiat indications at WEXTEX Espansions PWSCC indications were found in the WEXTEX expansion transition. Tube R12C27 (2.86 volts + Point,92%
maximum depth) was in situ tested to 4900 psi with no leakage and no burst, nis indication was one of the largest voltage indications and represents the most likely WEXTEX region leakage candidate. Tube R24C70 had the largest field reported indication of 217', but was only 1.20 volts. Reanalysis based on depth profiling found only about 93' with detectable depth and any larger extent w ould be very shallow if degraded. It can be concluded that all circumferential indications found in the WEXTEX expansions satisfy burst and leakage integrity at EOC S.
Similar or smaller indications would be expected at the end of the next operating cycle and operational assessment tube lategrity requirements would be satisfied at EOC 9.
SECL 97145 Page 9 of 12 3.$ Potential Mised Mode Indications A mixed mode indication (MMI) that could burst at less than that associated with the individual indications requires intersection of the axial and circumferential cracks to form T, L or U shaped flaws. In addition, the indications must be through-wall or near through-wall for a reduction in burst pressure. Both axial and circumferential indications were found at the dented TSP intersections and these indications u ere renewed for potential mixed mode indications.
Tube R16C83 was in situ tested with no leakage since this intersection includes three short PWSCC axial indications and a short PWSCC circumferential indications. Both axial and circumferential depths are shallow and there does not appear to be any intersection between them. Thus, the NDE assessment supports the successful in situ test results. Plus Point data reviews for Rl7C44 and R6C31411 in SG 4 also show no apparent interaction between the axial and circumferential indications. R6C31 lli appears to have some interaction but the depths are too shallow for concerns with mixed mode burst or leakage. R6C31 lli was also in situ leak and burst tested to 4900 psi with no leakage and no indication of burst.
It is concluded that there are few mixed mode indications due to separation of the axial and circumferential indications. Where potential interaction is present, the depths are shallow and the indications would not challenge leak or burst integrity at EOC-8 and similar results would be expected at EOC 9.
4.0 REMEDIAL MEASURES ne primary to-secondary leakage limit of 150 gpd established at Sequoyah Unit i enhances the potential for leak-before-break for both circumferentially and axially orientc< racking occurring at the different locations within the tube bundle. Additionally, leakage trending capability consistent with EPRI Report TR 104788,"PWR Primary to-Secondary Leak Guidelines", has been implemented at Sequoyah Unit 1.
5.0 POTENTIAL FOR ADJACENT TURE AMAGE FROM PLUGGED TURES WITil CIRCUMFERENTI AL INDICATIONS An analysis has been perfomied defining the criteria for determining which tubes with indications of circumferential cracking require stabilization (Reference 5). The analysis considered the elTects of mechanically induced crack propagation resulting from thermal mismatch leadings (load follow type loadings) and flow induced vibration loadings.
The analysis addressed the potential for single circumferential indications to occur at specific locations (zones) within the steam generators. He zones considered in the analysis are zones 3 and 4 as identified in the WEXTEX inspection program. Based on these criteria, nine (9) tubes have been determined to reqt .x stabilization by Tennessee Valley Authority. His includes 2 tubes in SG 1,2 tubes in SO 2,3 tubes in SG 3, and 2 tubes in SG 4 (Reference 6).
6.0 UNREVIEWED SAFETY QUESTION ASSESSMENT He subsequent operation of Sequoyah Unit I with the identified localized tube wall degradation has been evaluated and determined that an unreviewed safety question is not involved, per the criteria of 10 CFR 50.59, on the basis of the followingjustification
- 1. [] YES [X] NO May the proposed activity increase the probability of occurrence of an accident previously evaluated in the FSAR7 Of the criteria considered in RG 1.121, " Bases for Plugging Degraded PWR Steam Generator Tubes", the limiting condition for localized tube wall degradation is a 263* circumferentially oriented crack. His 263' are length limit coincides with the single,100% through wall, circumferential crack extent that is expected to provide a factor of safety of 3 against tube burst during normal operating pressure ditTerential. De corresponding limiting axial crack length
SECL 97145 Page 10 of 12 that meets RO 1.121 criteria is 0.47 inches. Based upon the results of the eddy current inspection e acribed above and repair / plugging efforts following Cycle 8 operation, none of the tubes in the Sequoyah Unit I steam generators are expected to experience cracking to the extent that we tube structural limit would be exceeded during Cycle 9 operation.
De available safety margin upon completion of Cycle 9 operation of Sequoyah Unit I is expected to be maintained for both axial, circumferentially, and mixed mode cracking that may be occurring in the Sequoyah Unit I steam generators.
Therefnre, the probability of the o:currence of a steam generator tube rupture event is not increased.
- 2. [] YES [X] NO May the proposed activity increase the consequences of an accident previously evaluated in the FSAR7 in the unlikely event that a crack may initiate and propagate towards the limiting 263* arc or the axial crack length of 0.47 inch, the 150 gpd technical specification allowable leakage limit and leakage trending capability consistent with EPRI Report TR 104788 implemented by Tennessee Valley Authority should minimize the possibly that crack growth will exceed these limits. Therefore, a single tube rupture event is not expected to occur. Ilowever, should a tube rupture event occur, the accident analysis considers a double ended break of the steam generator tube. He consequences of this event remain bounding for the current circumstance.
i As demonstrated by in-situ test results, any primary to secondary leakage that may occur during postulated accident conditions as the result of the development of any through-wall crack (s) would be expected to remain consistent with FSAR analyses assumptions. With the exception of one tube with U-bend PWSCC, no leakage was experienced during the in situ leakage testing. He SLB leak rate for an assumed through-wall, axial crack at the WEXTEX expansion l' transition was determined to be well within thc allowable SLB limit of 3.7 gpm.
- 3. [ ] YES [X] NO May the proposed activity create the possibility of an accident of a ditTerent type than any previously evaluated in the FSAR7 Steam generate: tut bregrity is expected to be maintained during Cycle 9 operation during all plant conditions, in the event that a through wall, circumferentially or axially oriented crack may develop, the technical specification primary to secondary leak rate limit WM ~1 and leakage trending capability should minimize the potential for an unanalyzed accident such as a multipl in c w . e or a coupled Steam Line Break and Tube Rupture Event.
No interaction with adjacent actis e tubes is expected during all plant conditions for plugged and/or stabilized tubes due to the presence of a circumferential indication.
- 4. [ ] YES [X1 NO May the proposed activity increase the probability of occurrence of a malfunction of equipms.it important to safety previously evaluated in the FSAR7 The overall safety and functional requirements of the steam generator tube bundles are not adversely alTected. The steam generator tube bundles (r' .gged and unplugged tubes) are expected to maintain, within recommended margins, loads during normal operation ud postulated accident conditions without loss of safety function.
- 5. [ ] YES [X] NO May the proposed activity increase the consequences of a malfunction of equipment important to safety previously evaluated in the FSAR7 he worst case consequences that could occur during subsequent plant operation is primary-to-secondary leakage during normal operating and plant transient conditions. Based on the conditional and operational monitoring assessments completed for the type oflocalized tube wall degradation occurring in the Sequoyah Unit I steam generators, it is expected that tube burst capability and leak tightness will remain within acceptable limits during all plant conditions during Cycle 9 operation of Sequoyah Unit 1.
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E I 6, [ ] YES [X] NO May the proposed activity create the possibility of a malfunction of equipment important
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to safety of a difTerent type than any previously evaluated in the FSAR7 :
r j Based on v, operational assessment completed for Cycle 9, the Sequoyah Unit I steam generators are expected to .
l; continue to meet individual tube integrity and tube bundle leaktightness requirements.- .
- 7. [ ] YES [X] NO Does the proposed activity reduce the margin of safety as defined in the basis for any Technica: Specification?
!, Plant operation of Sequoyah Unit i is determined to have been in compliance with RG 1.121 during Cycle 8 operation
- and it is expected to remain in compliance during Cycle 9 operation. De use of eddy current surveillance requirements . i consistent with EPRI Report NP-6201, Rev. 4 " ISI Guidelines for the laservice Inspection of Steam Generator Tubes" -
along with the continued implementation of a primary to secondary leak rate limit of 150 gpd support the maintenance of steam generator tube integrity during Cycle 9 operation.
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j ( 6.0 ' Conclusion L
' Based on the above, it is concluded that the operation of Sequoyah Unit I for the next operating cycle is not expected to adversely affect steam generator tube integrity, and does not represent an unreviewed safety question in accordance
, with 10 CFR 50.59 L ,
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7.0 References '
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- 1. .NSD-E-TAP _-055,Sequoyah Unit i 1997 SO Tube Integrity Assessment,7/28/97 -1
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- 2. ': WCAP 14707,"Model 51 SO Limited Tube Support Plate Displacement Analysis for Dented and Packed Tube to Tube Support Plate Crevice" August 1996 i
~ 3. Westinghouse Report SO 97 002-007," Qualification of Rotating Coll Depth Sizing for Axial PWSCC at -
3 Dented TSP Intersections", February 1997 --
- ~ 4, WCAP 14797, Rev.1," Generic W' Tube Plugging Criteria for 51 Series SG Tubesheet Region WEXTEX
. . Expansions", February,1997 .
- 5. NSD-JLli.5371, Rev.1. " Recommended Stabilization Zones for Tubes With Single Circumferential Indications at Sequoyah Unit 1", 10/16/95
_. 6. Goetcheus, D.F. to Ralph Shell, Tennessee Valley Authority,"NRC 15-Day Steam Generator Tube Plugging Report", Rev.1,4f28/97 i-l >
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