ML18102A323

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Reg Guide 1.121 Assessment of Indications at Salem Unit 2.
ML18102A323
Person / Time
Site: Salem PSEG icon.png
Issue date: 07/01/1996
From: Pleck S, Polstra E
FRAMATOME
To:
Shared Package
ML18102A321 List:
References
RTR-REGGD-01.121, RTR-REGGD-1.121 51-1245628-01, 51-1245628-1, NUDOCS 9608230256
Download: ML18102A323 (38)
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Text

20440-7 (12/95) l-/~

z*~:~RAMATOME rE.CHNOLOGIES ENGINEERING INFORMATION RECORD.

Document Identifier 51--=1=2~4~5~6=2==8_-~0~2'--~~~~~~~~~~~~~~~~-

Title Reg. Guide 1.121 Assessment of Indications at Salem Unit 2 PREPARED BY: REVIEWED BY:

a-t=:-'-~=:o.=.*--=#=a>t=u=~=r-~-~....,_

h.,,____.*-.-_-._D_a_t_e_c_(i_l_ff_b_

Date 1/1/'iG.

Technical Manager Statement: Initials Reviewer is Independent.

Remarks:

The purpose of this document is to evaluate the structural and leakage integrity of the Salem Unit 2 SG tubing. This is done by:

1), assessing the as-found condition of the Salem Unit 2 tubing during the 2R9 ECT inspection, and

2) predicting the number of indications to be reported for the next refueling outage at Salem Unit 2, and
3) assessing the structural integrity of the steam generators with the predicted indication distributions.

Each of the following tube degradation mechanisms are evaluated: axial and circumferential oriented indicati~~ at the top of tubesheet region; distorted signal in_dications, axial, outside diameter and volumetric oriented indications at hot leg tube support plates; circumferential indications at hot leg tube support plates; volumetric indications in the cold leg and wear indications at the U-Bend region.

Based on the evaluations presented in this document, it is concluded that a full cycle of operation (1.3 EFPY) for Salem Unit 2 is justified.

Record of Revisions Revision Description of Change 00 Original Issue 01 Added Section 1. 2, Revised Section 2 .1. 3. 2 02 Revised Introduction, Section 3.2.4 Fri PROPRIETARY This document, including the information contained herein, is the property of Framatome Technologies, Inc. (FTI). It contains proprietary information and may not be reproduced or copied in whole or in part, nor may it be furnished to others without the expressed written pennission of FTI nor may it be used in any way that is or may be injurious to Fri. This document and any copies that may have been made, must be returned upon request.

9608230256 960819 PDR ADOCK 05000311 P PDR Page _1_of 37,A-l

1.0 INTRODUCTION

e The purpose of this document is to evaluate the structural and leakage integrity of the Salem Unit 2 SG tubing. This is done by:

1) assessing the as-found condition of the Salem Unit 2 tubing during the 2R9 ECT inspection, and
2) predicting the number of indications to be reported for the next refueling outage at Salem Unit 2, and
3) assessing the structural integrity of the steam generators with the predicted indication distributions.

The predictions are based on plant experience to date and applicable available data from similar plants. The analysis develops predictions of the cumulative number of indications

. expected as a function of effective full power years. Predictions are developed for each of the following tube degradation mechanisms: axially and circumferentially oriented indications at the top of tubesheet region; distorted support indications, axial, outside diameter and volumetric oriented indications at hot leg tube support plates; circumferential indications at hot leg tube support plates; thinning in the cold leg and wear indications at the AVB region.

Wherever appropriate, references to the Salem documents addressing structural. integrity limits were made in conjunction with Regulatory Guide 1.121 structural criteria and on suggested actions to assess the extent of each damage mechanism addressed in this analysis.

The methodology used in this report is the application of deterministic statistical analysis to project future damage mechanism degradation rates for Salem Unit 2 RlO (9.3 EFPY) from plant experience to date, supplemented by industry experience. Previous plant history was analyzed to determine plant specific growth of each type of damage mechanism when possible. Supplemental industry experience was utilized in projecting the number of indications to be found for each type of damage mechanism when the data for Salem Unit 2 was insufficient. Salem 1 data for each type of damage mechanism was not used for this evaluation since a limited inspection scope was conducted over the last several outages.

During 2R9, Salem Unit 2 conducted a comprehensive As Found Condition Assessment through:

  • eddy current inspection, including 100% bobbin coil inspection for all four steam generators, 100% Top of Tubesheet Plus Point inspection in the hot leg of all four steam generators, 100% Tube Support Plate Plus Point inspection in the hot leg of all four steam generators and 100 % Tube Support Plate Plus Point inspection in the cold leg of steam generator 22.
  • in-situ pressure testing
  • removal of tube samples Salem 2 Reg. Guide Analysis Page 2 of 37 Doc: 51-1245628-02 Date: 7/1/96

Tube pull and in-situ pressure test results are discussed next. A presentation of the operability assessment over the next planned cycle is then given in sections 2.0 through 5.0 for each degradation method identified.

1.1 Tube Pull Results During 2R9 PSE&G elected to remove tube samples from SIG 24 in order to further investigate the cause of certain ECT signals at the tube support plates. The tubes removed and the reason for pulling each tube are given in the Table 1.1.1.

Table 1.1.1 Salem Unit 2 2R9 Pulled Tubes Row-Col Indication Location Reason for Pulling 11-27 SOD 02H + 0.38" Characterize SOD 13-36 SOD 03H + 0.20" Characterize SOD 21-71 SOD 05H + 0.00" Characterize SOD 11-31 SCI 05H + 0.11" Compare SCI with SOD 19-45 SCI 03H + 0.09" Compare SCI with SOD 20-26 MAI 03H + 0.09" Burst Test, Confirm Axial Defects SCI 04H + 0.00" Compare SCI with SOD Definitions: SOD: Shallow Outside Diameter Indication. These anomalous indications had large signal amplitudes, -but the phase angle indicated no penetration.

SCI: Single Circumferential Indication MAI: Multiple Axial Indication All indications listed above were reported with the plus point probe.

The tube samples were inspected with plus point in the laboratory prior to destructive examination to compare the results with the field data. Only the MAI call on tube 20-26 conf'rrmed in the lab. None of the SOD or SCI indications were confirmed in .the lab.

Preliminary results are available at this time from the destructive exam. The results for the areas of interest are listed in Table 1.1.2.

Salem 2 Reg. Guide Analysis Page 3 of 37 Doc: 51-1245628-02 Date: 7/1196

Table 1.1.2 Salem Unit 2 2R9 Pulled Tubes - Destructive Exam Results Field ECT Row-Col Indication Location Laboratory Observations 11-27 SOD 02H + 0.38" IGA 3 .4 % TW at Deepest Point 13-36 SOD 03H + 0.20" IGA < 6 % TW at Deepest Point 21-71 SOD 05H + 0.00" IGA 2.2 % TW at Deepest Point 11-31 SCI 05H + 0.11" IGA 4.9% TW at Deepest Point 19-45 SCI 03H + 0.09" IGA < 10% TW at Deepest Point 20-26 MAI 03H + 0.09" IGA 30% TW at Deepest Point SCI 04H + 0.00" IGA 8.2% TW at Deepest Point

, As Table 1.1-2 shows, all the SOD and SCI indications in the pulled tubes were associated with very shallow surface IGA. The IGA is so shallow that it is very unlikely that it is the source of the ECT signal. This is supported by the laboratory ECT inspection, which resulted in no indications being reported at any location where a SOD or SCI was reported in the field. It is expected that the signals observed in the field were associated with deposits on the tube OD, which is a possible explanation for the indication of no depth penetration.

Based on the above results, it is concluded that the SOD indications observed in the field are not associated with significant tube degradation, therefore no significant degradation in structural integrity is expected in these .areas. The results further indicate that the SCI indications at support plates are most likely indicative of deposits, or of very shallow bands of IGA.

1.2 In-Situ Pressure Testing As discussed in section 2.1.1, three tubes were in-situ pressure tested to Regulatory Guide 1.121 structural limits. The tubes tested contained the most limiting indications found during the 2R9 inspection. The tested tubes not only met the structural requirements, but also exhibited no measurable leakage during the course of the test.

Based on this result, probability of leakage for any of the other indications found during the 2R9 inspection is negligible, and therefore will not be addressed in this analysis.

Salem 2 Reg. Guide Analysis Page 4 of 37 Doc: 51-1245628-02 Date: 7/1/96

2.0 TOP OF TUBESHEET During the 2/96 outage at Salem Unit 2, 100% of the Hot Leg WEXTEX expansion regions were examined using the +Point RPC probe. As a result of this examination, a small number of tubes were found to have indications. Table 2.0 presents the number of indications found in the four steam generators during the 2R9 inspection.

Table 2.0 2R9 Hot Leg Top of Tubesheet Indications Number of Tubes Inspected 13,066 Number of Axial Indications ID 167 OD 10 Number of Circumferential Indications ID 3 OD 9 Number of Volumetric Indications ID 2 OD 6 2.1 Axial Indications - Hot Leg Top of Tubesheet The axial indications found are made up of two types, ID initiated (PWSCC) and OD initiated (ODSCC). As shown above, the vast majority (94%) of the axial indications were ID initiated. To more accurately describe the size distribution and population, only those ID indications that were within 1.5" of the top of the tubesheet are addressed in the 2Rl 0 predictions. This approach focuses the predictions on TIS PWSCC near or in the roll transition. However, all hot leg axial indications found in the tubesheet are checked against Reg Guide 1.121 structural limits.

2.1.1 Size Distribution The axial indications found were predominately below the top of the tubesheet. In fact, all but 9 of the indications were located below the top of the tubesheet. Figure 2.1.1 presents the length distribution of the axial indications found during the 2R9 inspection.

Salem 2 Reg. Guide Analysis Page 5 of 37 Doc: 51-1245628-02

  • Date: 7/1/96

Figure 2.1.1 SALEM 2 HOT LEG TIS AXIAL INDICATIONS 2R9 ALL STEAM GENERATORS 2.1.2 NRC Regulatory Guide 1.121 Structural Limit Structural integrity limits for indications near the WEXTEX transition region for Salem Unit 2 were provided to FTI by PSE&G. The limit for axial indications is 0.41" and assumes the indication is 100% TW. This structural limit satisfies

  • 3*(normal operating delta P) burst pressure for axial cracks that extend above the highest tubesheet contact point a distance of 0.41" or less. If the indication is located completely below the top of the tubesheet, it is precluded from burst due to the presence of the tubesheet.

All axial indications, both ID and OD are addressed as one group because the Reg Guide length limit assumes a 100 %TW indication. Of the 177 axial indications found, 11 were found to be in excess of 0.41". These locations are presented in Table 2.1. l.

Salem 2 Reg. Guide Analysis Page 6 of 37 Doc: 51-1245628-02 Date: 7 /1/96

Table 2.1.1 Axial Indications With Lengths Greater Than 0.41" Of these 11 indications, 6 are completely contained within the tubesheet and therefore are precluded from burst. The other 5 indications have extents above the top of the

  • tubesheet. These indications have been in-situ pressure tested and the results are presented in Table 2.1.2. The indications tested conservatively bound the lengths and -

voltages of all indications above the top of the tubesheet. It is noted that all 167 ID axial indications were below the top of the tubesheet.

Table 2.1.2 Results of In-Situ Pressure Testing SG ROW COL. MAXIMUM TIME AT LEAKAGE PRESSURE MAXIMUM (gpm)

(psi) PRESSURE (min) 22 14 56 5100 10 None 22 19 61 5100 - 10 None 22 14 53 5100 10 None The maximum test pressure corresponds to Regulatory Guide 1.121 structural limits, as corrected for temperature and tooling effects. The tested tubes met the structural requirements and exhibited no measurable leakage. Therefore, all indications that challenged the Regulatory Guide 1.121 length limit are shown to meet the Reg Guide structural requirements.

Salem 2 Reg. Guide Analysis Page7 of 37 Doc: 51-1245628-02 Date: 7/1196

2.1.3 Salem Unit 2 Predicted 2R10 As stated in the previous section, those indications that are below the ITS meet NRC structural limits because the tubesheet prevents tube burst. For this reason, those axial indications that are located more than 1.5" below the top of the tubesheet are excluded from the number predicted for 2R10. The 1.5" distance was conservatively chosen such that the longest expected axial ID indication found during 2R9 (0. 73 ")

would be contained totally within the tubesheet if any part of the indication was located 1.5" below the ITS. Also, based on the 2R10 predictions, no axial ID indications are expected to exceed 1.5" in length (the probability that an ID axial indication exceed 1.5" is 0.0008), so an indication located 1.5" below the ITS would not challenge Reg Guide structural requirements.

The projections for 2R10 assume a 1.3 EFPY cycle time.

2.1.3.1 Predicted Hot Leg ITS ID Indications Since only limited examinations of the Hot Leg TS region have been conducted at Salem 2 previous to the 2R9 inspection, industry data better serves to predict the population growth of the axial ID indications. To achieve this, a representative Series 51 plant with WEXTEX tubesheet expansions was chosen. Based on plant data spanning three comprehensive inspections, a regression line was fitted and used to predict the cumulative number of ID axial indications projected for 2Rl0 at Salem 2 (see Figure 2.1.2).

Salem 2 Reg. Guide Analysis Page 8 of 37 Doc: 51-1245628-02 Date: 7/1/96

(.

Figure 2.1.2 The figure above shows that based on the predicted population growth rate, Salem Unit 2 could have as many as 180 new axial ID indications after operating 1.3 EFPY. To predict what the population length distribution will be, it is assumed that the length distribution found during 2R9 will be found again during 2R10. This is conservative for two reasons:

1. The 2R9 inspection was the most comprehensive done on these SG's. It is reasonable to assume that the largest of the indications found this outage would have been found previously, had a 100 3 inspection been conducted.
2. All axial ID indications found will be plugged, so current indications will not be in the 2Rl 0 length distribution.

Salem 2 Reg. Guide Analysis Doc: 51-1245628-02 Page 9 of 37 Date: 7/1/96

This population length distribution, when combined with the predicted number of indications, forecasts the potential number of axial ID indications that could challenge Reg Guide structural limits. Figure 2.1.3 presents the size distribution of the axial ID indications found during the 2R9 inspection.

Figure 2.1.3 SALEM 2 HOT LEG TTS ID AXIAL INDICATIONS 2R9 ALL STEAM GENERATORS 80 70

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0 u

fl 50  ::c

~

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0 40 z Ul i;...

0 ...J 30 Ul

~ -

0

~

20 0 0

10 t.IJ et::

0 0.0-0.10 0.21-0.30 0.41-0.50 0.61-0.70 0.81-0.90 LENGTH (IN)

Note: The above figure includes all indications L_TSH -1.5" (See discussion in section 2.1).

  • It was determined that a probability distribution based on the inverse of the observed lengths best represented the data in Figure 2.1.3 (hypothesis of normality not rejected at the 5 3 level). This distribution was then used to predict the number of indications that might exceed the 0.41" structural limit for 100%TW indications. The best estimate of the number of indications exceeding 0.41 ", based on the projected 180 new indications is 6. These indications are expected to be below the ITS, and therefore not a structural concern (1003 of the ID axial indications found in 2R9 are below the ITS).

However, for conservatism, the probability of getting an indication that approaches the length bounded by in-situ pressure testing (1.39") conducted during 2R9 was calculated. The results show that based in the distribution above, none of the projected 180 new indications for 2Rl0 are expected to exceed 1.39" in length (the probability of exceeding 1.39" is 0.0009).

Salem 2 Reg. Guide Analysis Doc: 51-1245628-02 Page 10 of 37 Date: 7/1196

Table 2.1.3 Predicted Hot Leg TTS ID Axial Indication for 2R10 Number of Predicted New Indications 180 Less than 0.41" 174 Greater than 0 .41" 6 Greater then 1.39" 0 Conclusions Based on the number and length of ID axial indications at found at Salem Unit 2 during 2R9, it is predicted that 180 new indications could be found during 2R10. These predictions indicate that only a very small number (6) may challenge the structural length limit of 0 .41", and none are expected to challenge the 1.39" MAI indication that was in-situ pressure tested during 2R9 and exhibited no leakage. Therefore, operation for the next planned fuel cycle based on this damage mechanism is justified.

Salem 2 Reg. Guide Analysis Page 11of37 Doc: 51-1245628-02 Date: 7/1196

'2.1.3.2 Predicted Hot Leg ITS OD Indications As stated previously, limited previous history data is available to trend tlie cumulative number of ITS indications. However, during the 2R7 inspection, comprehensive hot leg RPC examinations (nearly 1003) were conducted in SG's 22 and 24 (All but 3 of the ITS ODSCC calls are in these two steam generators.). Based on this inspection, a total of nine ODSCC indications had been called for the life of the SG's. As a result of the 2R9 1003 inspection, 10 new TIS ODSCC indications were found. By not including the 2R8 inspection (which wasn't comprehensive), a conservative projection is achieved by using the 2R7 and 2R9 cumulative data. While this method is quite conservative, it still demonstrates that few new indications are predicted.

Figure 2.1.4 shows that based on the predicted population growth* rate, Salem Unit 2 could have as many as 19 new axial OD indications after operating 1.3 EFPY.

Figure 2.1.4 SALEM 2 HOT LEG TTS OD AxlAL INDICATIONS ALL STEAM GENERATORS 100

~

~ 38 -2R10 u< (Predicted)

~

~

0

~

f;:;:l 10 f;:;:l 9-2R7

  • 9-2R8 (Not Used)

~

iu 1

1 10 EFPY Salem 2 Reg. Guide Analysis Doc: 51-1245628-02 Page 12 of 37 Date: 7/1/96

\

Based on the limited number of indications found during 2R9 (10), performing a regression analysis based on the frequency distribution was not statistically meaningful. Industry experience has shown that the shape of the length distr~bution is based mainly on the threshold of detect ability of the inspection technique. Data from another plant that has a large population of TIS OD axial indications is therefore utilized to determine the shape of the distribution for OD axial indications (Figure 2.1.5).

Figure 2.1.5 HOT LEG TTS OD AXIAL INDICATIONS -

ALL STEAM GENERATORS 90 Cl) 80 z *u:l Cl ::i:: -

0 70 ...... E-< ;:....

E:= g 0 '<!;

u< 60

@5 Zo JI

~

~

50 40 lZ 0

30 i 20 10 0

.... C': "<t V'l \0 r-- 00 °' ....

0 0 0 0 0 0 0 0 LENGTH (IN)

I* SALEM 2R9 a PLANT WITH DEVELOPED ITS ODSCC POPULATION I Salem 2 Reg. Guide Analysis Page 13 of 37 Doc: 51-1245628-02 Date: 7/1196

This distribution was used to predict the number indications that might exceed the 0.41" structural limit for 1003TW indications.

Table 2.1.4 Projected Hot Leg TTS OD Axial Indication for 2R10 Number of Projected New Indications 19 Less than 0 .41"

  • 10 Greater than 0 .41 " 9 Greater then 1.39" 0 Conclusions Based on the number of OD axial indications found at Salem Unit 2 during 2R9, and industry length distribution data, it is predicted that 19 new
  • indications could be found during 2R10. These predictions indicate that 9 indications may challenge the structural length limit of 0.41", and none are expected to challenge the 1.39" MAI indication (probability of finding an indication 1.39" or greater is 0.0055) that was in-situ pressure tested during 2R9 and exhibited no leakage. These* predictions are conservative for two reasons:
1) The use of the Salem 2 population growth includes the inspection transient associated with utilizing the RPC +Point pr:obe. Using this approach conservatively biases the slope to a larger value. Also, industry experience has shown that plants with ODSCC problems see a large increase in number of indications when inspecting with +Point versus RPC. Salem 2 experienced no such increase.
2) The use of industry data for the distribution of axial indication lengths conservatively assumes that Salem 2 will have a large population of ITS ODSCC. Based on the as-found condition and the future*

projections, there is no evidence that ODSCC will affect a large population of tubes.

Therefore, operation for the next planned fuel cycle based on this damage mechanism is justified.

Salem 2 Reg. Guide Analysis Page 14 of 37 Doc: 51-1245628-02 Date: 7/1196

2.2 Circumferential Indications - Top of Tubesheet 2.2. l Indications Reported .

During 2R9 a total of 12 circumferential indications were detected near the top of the hot leg tubesheet in the vicinity of the WEXTEX transition. Three of these were reported to be ID initiated based on the plus point inspection, while the remaining nine were OD initiated. Prior inspections at Salem Unit 2 have reported one (1) ID initiated circumferential indication during the 2R7 examination. No OD initiated circumferential indications have been previously reported.

2.2.2 Predicted Propagation Rate In order to predict the propagation rate of these indications at Salem Unit 2 the experience of a similar plant with Westinghouse Series 51 steam generators was used. Based on inspection data from 3 eddy current examinations the following indications were reported.

TABLE 2.2.1 PROPAGATION OF CIRCUMFERENTIAL ITS INDICATIONS AT W-51 PLANT INDICATION Reported Indications Each Inspection TYPE 9.62 EFPY 10.8 EFPY 11.8 EFPY CIRC ID 0 1 0 CIRC OD 0 0 4 Based on this data and the small nllinber of indications reported at Salem Unit 2 during a 100 3 examination it is concluded that the number of new indications expected at the end of the next cycle of operation of Salem Unit 2 will not increase significantly relative to the present outage results.

2.2.3 Structural Integrity The criteria for evaluating circumferential indications relative to the Reg.

Guide 1.121 criteria is documented in Ref. 3. From this reference, the limit is 216 degrees based on the burst pressure of a tube with a 100 %TW flaw. The maximum extent of the circumferential indications reported *at Salem Unit 2 during the 2R9 inspection is approximately 115 degrees. Therefore none of the existing flaws exceed the Reg. Guide 1.121 limits.

Salem 2 Reg. Guide Analysis Page 15 of 37 Doc: 51-1245628-02 Date: 711196

2.2.4 Conclusions - ITS Circumferential Indications Based on the small expected propagation rate over the next fuel cycle and the large margin that exists for structural integrity of the present population it is concluded that no ITS circumferential indications are expected to exceed the Reg. Guide limits prior to the next scheduled inspection. Full cycle operation for this damage mechanism is therefore justified.

2.3 Volumetric Indications - Top of Tubesheet

2. 3 .1 Indications Reported During 2R9 a total of 8 indications were detected near the top of the hot leg tubesheet that were characterized as single volumetric indications (SVI) based on the plus point examination. Two of these were reported to be ID initiated and the remaining six were OD initiated. Prior inspections at Salem Unit 2 have reported no other volumetric indications at this location.
2. 3. 2 Predicted Propagation Rate In order to predict the propagation rate of these indications at Salem Unit 2 the experience of a similar plant with Westinghouse Series 51 steam generators was used. Based on inspection data from 3 eddy current examinations the following indications were reported.

TABLE 2.3.l PROPAGATION OF VOLUMETRIC ITS.INDICATIONS AT W-51 PLANT INDICATION Reported Indications Each Inspection TYPE 9.62 EFPY 10.8 EFPY 11.8 EFPY SVI ID 2 1 1 SVI OD 7 12 14 Salem 2 Reg. Guide Analysis Page 16 of 37 Doc: 51-1245628-02 Date: 7 /1/96

Based on this data and the small number of indications reported at Salem Unit 2 during a 100% examination it is concluded that the number of new indications expected at the end of the next cycle of operation of Salem Unit 2 will not increase significantly relative to the present outage results.

2.3.3 Conclusions - ITS Volumetric Indications Based upon their location in the steam generator it is expected that the OD volumetric indications are associated with wastage type degradation under a sludge layer. This type of degradation may have been present in the S/G's for some time but has just now been detected as a result of the extensive plus point exam performed during the 2R9 outage. Based on the slow propagation rate predicted from the previous section and the extensive inspection performed during the current outage, no flaws are expected that would challenge the Reg. Guide 1.121 limits during the next operating cycle.

Salem 2 Reg. Guide Analysis Page 17 of 37 Doc: 51-1245628-02 Date: 7/1196

  • 4 3.0 TUBE SUPPORT PLATE 3 .1 Axial Indications - Tube Support Plates During the 2/96 outage at Salem Unit 2, 1003 of the hot leg Tube Support Plates (TSPs) of all four steam generators were inspected with Bobbin Coil and MRPC. As a result of this comprehensive examination, a small percentage of tubes were found to have Distorted Support Plate Indications (DSI) at the Tube Support Plates. Table 3 .1.1 presents the results of the number of indications found in the four steam generators during the 2R9 inspection.

Table 3.1.1 2R9 Tube Support Plate DSI Indications Number of Indications Number of Tubes Inspected 112 13066 3 .1.1 Size Distribution The DSis found during 2R9 were all located within the TSP region and none of the DSis found during 2R9 were confirmed with MRPC inspection. Figure 3 .1.1 presents the voltage distribution of the DSis found during 2R9 inspection.

Figure 3 .1.1 SALEM 2 DSI VOLTAGE DISTRIBUTION FOR 2R9 AT TSPs 20 18 e::: ,.,

0;::;

~ 16 u.. 5

....l er.

E- ~

E::: 14 ....l c=:

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N \0 00 ~ ..Q ~ c:: 0 ci ci 0 ci ..... (") V)

VOLTAGE Salem 2 Reg. Guide Analysis Page 18 of 37 Doc: 51-1245628-02 Date: 7/1/96

3.1.2 *NRC Regulatory Guide 1.121 Structural Limit Stress corrosion cracking initiating at the outer diameter (ODSCC) of Alloy 600 steam generator tubes has been diagnosed in the tube support region of many Westinghouse steam generators. ODSCC refers to a range of stress corrosion cracking morphologies which have been observed to occur along the outside diameter of Alloy 600 steam generator tubes within the TSP intersection. Limited local patches of intergranular attack (IGA) have also been observed as well. Experience shows that TSP ODSCC cracks are generally short, axially orientated and sometimes through wall. The cracks generally are found in tubes in the steam generator hot leg. With few exceptions, ODSCC has been conf'med to the region within the TSP.[Ref.l]

Generic Letter 95..:05 "Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking" sets criteria for plants to implement an alternate repair criteria for these type of indications based on leak and burst testing results.

The structural integrity limits for DSis recorded at the TSPs for Salem Unit 2 were evaluated based on the 7/8" APC criteria established by Generic Letter 95-05. Salem Unit 2 does not have an APC criteria currently in place, however, the structural limits established by the APC can be applied to Salem Unit 2 to establish structural integrity of the DSis recorded during 2R9. The current APC structural burst limit satisfies 3~P buri;t pressure for DSis located at the TSPs of 7/8" Westinghouse steam generators. Assuming a lower tolerance limit (LTL) of 95% for the APC burst pressure, a voltage amplitude of 4.15 V is determined to be the vqltage limit for structural integrity of a 7/8" Westinghouse plant. This value was determined using EPRI equations for the 7/8" APC burst pressure evaluation. Of the 112 DSI indications found, none exceeded the 4.15 V structural limit.

Salem 2 Reg. Guide Analysis Page 19 of 37 Doc: 51-1245628-02 Date: 7/1/96

' 3 .1. 3

  • Predicted DSis at the Tube Support Plate The predictions for the hot leg TSP indications were made by projecting from the current level of degradation using the slope of ODSCC TSP degradation from a similar Westinghouse Model 51 series plant. As shown in Figure 3.1.2, the predicted cumulative number of hot leg TSP indications for 2R10 is 174.

Figure 3.1.2 SALEM 2 PREDICTED DSls AT TSPs 2R9 SALEM2 DSls ALL STEAM GENERATORS 10000-r----------------------------------------------.

~

0 1000

~

~Cf.)

~~

~-< 100 174 - 2R10 Predicted

>u E== ,_,

112 - 2R9

~~

§ IO u

IO 100 EFPY i-7/8" Model 51 Predicted Growth -+-Salem 2; Salem 2 Reg. Guide Analysis Page 20 of 37 Doc: 51-1245628-02 Date: 7/1/96

In order to predict* the number of DSis to challenge the APC Lower Tolerance Limit of 4.15 Volts for 2R10, a log-normal distribution of the DSI voltages was performed.

Assuming the same distribution of indications is present for the predicted number of indications to be found during 2Rl0 (174 cumulative DSls), no indications are projected to challenge the LTL of 4.15 volts.

3.1.4 Conclusions Based on the 7/8" APC for DSis found at other Westinghouse Plants, the DSis found during 2R9 at Salem Unit 2 are relatively small in number and voltage. ODSCC is a common degradation mechanism at Westinghouse plants and has been widely researched with pulled tube data and model boiler samples. Assuming a 4.15 volt at the 95% LTL at 3.c.P for Salem Unit 2 is a conservative approach. Also, from the log-normal distribution of the distribution of the DSI voltages; the probability that one DSI would exceed the LTL is very small. Operation for the next planned fuel cycle based on this damage mechanism is justified.

3. 2 Circumferential Indications - Hot Leg Tube Support Plat~

During the 2/96 outage at Salem Unit 2, a comprehensive hot leg Eddy Current Inspection was conducted on all four steam generators. As a result of this comprehensive examination, a very small percentage of tubes. were found to have circumferential indications at the TSPs. Table 3.2.1 presents the r~sults of the number of indications found in the four steam generators during the 2R9 outage.

Table 3.2.1 2R9 Tube Support Plate Circumferential Indications Number of Indications Number of Tubes Inspected 24 13066

3. 2 .1 Size Distribution From this inspection, twenty-four circumferential indications were reported at the hot leg tube support plates. The distribution of the lengths of these circumferential indications are shown in Figure 3.2. l.

Salem 2 Reg. Guide Analysis Page 21of37 Doc: 51-1245628-02 Date: 7/1196

  • Figure 3.2.1 SALEM 2 CIRCUMFERENTIAL INDICATION LENGTH DISTRIBUTION FOR 2R9, HOT LEG TSPs 8

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d 0 d 0 0 N N C'i INDICATION LENGTH (inches) 3.2.2 NRC Regulatory Guide 1.121 Structural Limit Circumferential limits for TSP indications have not been specifically established. It will be assumed for the purposes of this assessment that the limits developed for the WEXTEX expansion which are controlled by tube burst pressure can be applied here.

For the WEXTEX expansion, the structural limit for circumferential indications is 216° [Ref. 3] . As seen from length distribution in Figure 3. 2 .1, none of the circumferential indications found during 2R9 challenge the Reg. Guide structural limit.

Salem 2 Reg. Guide Analysis Page 22 of 37 Doc: 51-1245628-02 Date: 7/1/96

,3.2.3 . Projections for 2Rl0 Circumferential Indications at Hot Leg Tube Support Plates Few plants have developed circumferential indications at the TSPs. As stated in Section 1.1 of this report, none of the SCI indications recorded in the field conf'mned in a comprehensive laboratory examination. Based on the number of indications reported at Salem Unit 2 during a 100% examination and the pulled tube results, it is concluded that the number of new indications expected at the end of the next cycle of operation of Salem Unit 2 will not increase significantly relative to the present outage results. To predict the number of circumfer~ntial indications for 2Rl 0 that could challenge the Reg. Guide structural limit of 1.65" (216°), a log-normal distribution of the lengths of the 2R9 SCI indications reported was determined. The probability that one circumferential indication would challenge the structural limit of 216° is 3.8 xl0-3

  • 3.2.4 Tube Pull Results for Circumferential Indications at Hot Leg Support Plates Three of the tubes with circumferential indications found during 2R9 were pulled for laboratory inspection during this outage. The following tubes listed in Table 3.2.2 with circumferential indications were evaluated in the laboratory.

Table 3.2.2 Laboratory Results of Circumferential Indications Located in Pulled Tubes SG Row Column Field Volt Phase Location Length Lab Lab Result Call Call 24 19 45 SCI 2.48 60 03H-0.09 0.57 NDD < 10.0%

IGA 24 20 26 SCI 1.32 148 04H+0.06 0.73 NDD 8.2% IGA 24 11 31 SCI 2.61 128 05H+0.11 0.54 NDD 4.9% IGA As Table 3 .2.2 shows, the pulled tubes with SCI indications had very shallow surface IGA. However, the IGA is so shallow that it is very unlikely that it is the source of the ECT signal. This is supported by the laboratory ECT inspection, which resulted in no indications being reported at an:y locations where a SCI was reported in the field.

It is expected that the signals observed in the field* were associated with deposits on the tube OD, which is a possible explanation for the indication of no depth penetration. Based on the laboratory results, the SCI indications at the support plates are most likely indicative of deposits, or of shallow bands of IGA.

Salem 2 Reg. Guide Analysis Page 23 of 37 Doc: 51-1245628-02 Date: 7/1/96

3. 2. 5 Other TSP Indications There were four OD axial indications identified at the hot leg TSP's during 2R9. The longest of these indications was reported to be 0.45" in length and is located at the OlH TSP in tube 20-15*I in S/G 21. This indication is completely contained within the TSP. The remaining three OD indications are reported to be much smaller in length (0.25" maximum) and contained within the TSP.

In addition to the four OD indications discussed above, there were a total of three (3)

ID axial indications identified at hot leg TSP's during 2R9. The longest of these indications was reported to be 0.53" long, and is located at the OlH TSP in tube 5-3, SIG 24 . The remaining two indications are reported to be much smaller in length (0.35" and 0.21 ") and contained within the TSP. Since plus point examinations were performed at 100 % of the hot leg and cold leg TSP locations and these are the only axial indications at the TSPs that were reported (out of more than 180, 000 TSP intersections), it is concluded that the total population of these indications is very small and does not contribute significantly to the probability of exceeding the Reg.

Guide 1.121 structural limits. All three axial ID and four axial OD indications reported during 2R9 have been identified for plugging.

3.2.6 Conclusions Therefore, based on the small expected propagation rate over the next fuel cycle and the large margin that exists for structural integrity of the present population, it is concluded that a full cycle of operation for this damage mechanism is justified.

Salem 2 Reg. Guide Analysis Doc: 51-1245628-02 Page 24 of 37 Date: 7/1196

4.0 COLD LEG THINNING 4.1 SVIs in the Cold Leg at the Tube Support Plates - Cold Leg Thinning During the 2/96 outage at Salem Unit 2, 100% MRPC Eddy Current Inspection was conducted in the cold leg of steam generator 22. As a result of this examination, a small percentage of tubes were found to have thinning at the support plates. Table 4 .1.1 presents the results of the number of indications found in the steam generator 22 during 2R9 inspection.

Table 4.1.1 2R9 Cold Leg Thinning Indications (SG 22 only)

Number of SVI Indications without ODI calls Number of Tubes Inspected 75 3229 4.1.1 Size Distribution The cold leg thinning indications were predominately Single Volumetric Indications (SVls) located at the TSPs. ODI indications confirmed with MRPC inspection, were also called at the TSP region and are also considered to be cold leg thinning. These indications are discussed in Section 4.2. Figure 4.1.1 presents the voltage distribution of the SVI indications found during 2R9 inspection in steam gener~tor 22 only.

Salem 2 Reg. Guide Analysis Page 25 of 37 Doc: 51-1245628-02 Date: 7/1/96

  • Figure 4.1.1 SALEM 2 COLD LEG THINNING SVI INDICATION VOLTAGE DISTRIBUTION FOR 2R9, COLD LEG TSPs 30 Cll z

25

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..... ..... ..- ..- ...- N N VOLTAGE 4.1.2 NRC Regulatory Guide 1.121 Structural Limit MRPC inspection data was available for the existing 75 SVI indications when a sample review of the cold leg SVI indications in steam generator 22 was performed.

These indications are attributed to cold leg thinning. Due to all the supports being examined with the +Point probe, a number of SVIs were reported without supporting bobbin calls. Plugging of these indications would generally be based on a depth estimate from bobbin phase angle compared to a plugging limit of 40% TW. For the support indications without bobbin calls, the depth for the SVI calls can be estimated by voltage, similar to wear type indications [Ref.4]. An estimate in depth can therefore by made using voltage from the +Point examinations. The 203 TW yields approximately 4-5 volts and the 60% TW is approximately 22-25 volts. All SVIs were reviewed to verify the +Point voltage calls [Ref.4].

For the structural limit of cold leg thinning, a +Point voltage of 22 volts was utilized for this evaluation. All of the SVIs called at the TSP were less than 7.0 volts, which is less than the 22 volt considered structural limit .

Salem 2 Reg. Guide Analysis Page 26 of 37 Doc: 51-1245628-02 Date: 7/1/96

  • 4.1.3
  • Projections for 2R10 Cold Leg Thinning at the Tube Suwort Plates The prediction for the number of cold leg TSP indications to be found during 2R10 were made utilizing similar cold leg indications at a similar Westinghouse Model 51 plant. Since MRPC inspection on the cold leg was only conducted in steam generator 22 during 2R9, for this evaluation, it was assumed that these volumetric indications would have been found in the other steam generators. Therefore, it was assumed that the same number of indications found in steam generator 22 would have been found in the other three generators. As shown in Figure 4.1.2, the cumulative number of cold leg indications at the TSPs is predicted to be 365 for 2Rl0.

Figure 4.1.2 SALEM 2 PREDICTED COLD LEG TBINNING SVIs (ALL GENERATORS) 2R10 0

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-718" Model 51 Predicted Growth -salem2 Salem 2 Reg. Guide Analysis Page 27 of 37 Doc: 51-1245628-02 Date: 7/1/96

  • 4.2.1
  • Outside Diameter Indications in the Cold Leg at the Tube Support Plates - Cold Leg Thinning During the 2R9 outage at Salem 2, a comprehensive bobbin coil inspection was conducted on all four steam generators. As a result of this examination, a small percentage of tubes were found to have thinning at the support plates as detected with bobbin coil. Table 4.2.1 presents the results of the number of indications found in all four steam generators during the 2R9 inspection.

Table 4.2.1 2R9 Cold Leg Thinning Indications (all Generators)

Number of ODI Indications Number of Tubes Inspected 32 13066 4.2.2 Size Distribution From this inspection, thirty-two ODI indications at the cold leg tube support plates were reported. The distribution of the percent TW of these indications are shown in

  • Figure 4.2.1.

Figure 4.2.1 SALEM 2 COLD LEG THINNING % TW DISTRIBUTION ALL GENERATORS FOR2R9, COLD LEG TSPs

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PERCENTTW Salem 2 Reg. Guide Analysis Page 28 of 37 Doc: 51-1245628-02 Date: 7/1/96

.4.2.3 .NRC Regulatory Guide 1.121 Structural Limit Axial flaws that are less than 60% through-wall satisfy Reg. Guide limits for burst pressure regardless of the length of the flaw [Ref.2]. For the cold leg thinning ODI calls, a percent through-wall was reported for each indication. Any indication that exceeds 40% through-wall with bobbin coil is plugged at Salem Unit 2. As seen from Table 4.2.1 none of the ODI indications found during 2R9 exceed the 40% through-wall plugging criteria nor challenge the 60% through-wall structural limit. Cold leg thinning is considered to have a manageable growth rate at Salem Unit 2. The noted indications will be inspected during future outages and plugged when the indications are reported to be 40 % TW.

4.2.4 Projections for 2Rl0 ODI Cold Leg Thinning at the Tube Support Plates.

The prediction for the number of cold leg TSP ODI indications to be found during 2R10 were made with several assumptions. Several cold leg TSP ODI indications were reported during previous outages at Salem Umt 2. However, since the previous outages at Salem Unit 2 were not 100% inspection, the indications found from previous outages were assumed to be only a percentage of the number of indications in the steam generators. Therefore, the number of indications found previously due to cold leg thinning were scaled to represent the number of indications that might have been reported if 100% bobbin coil inspection had been conducted. Therefore, the cumulative nlJIIlber of indications assumed for the 2Rl 0 projections was 78 i.p.dications to date up to and including the 2R9 outage.

The prediction for the number of ODI cold leg TSP indications to be found during 2Rl 0 due to cold leg thinning was made utilizing similar cold leg indications at a similar Westinghouse plant. As shown in Figure 4.2.2, the number of cold leg ODI indications due to cold leg thinning is predicted to be 95 cumulative indications for 2R10.

Salem 2 Reg. Guide Analysis Page 29 of 37 Doc: 51-1245628-02 Date: 7 /1/96

', Figure 4.2.2 SALEM 2 PREDICTED COLD LEG THINNING ODI INDICATIONS, (ALL GENERATORS) 2Rl0 95 - 2RIO (Predicted) 78-2R9 1-i-~~~~~~~~~~~+-~~~~~~~~~~--l 1 10 100 EFPY

-7/8" Model 51 Predicted Growth -Salem2 4.3 Conclusions for All Cold Leg Thinning at the Tube Support Plates Cold leg thinning is a common damage mechanism in several Westinghouse plants.

The indications seem to be slow growing and all cold leg indications found that .

exceed 40% TW will be plugged at Salem Unit 2. Therefore it is concluded that the presence of cold leg thinning in the Salem Unit 2 steam generators does not contribute significantly to probability of tube rupture during MSLB at the end of the next operating cycle.

Salem 2 Reg. Guide Analysis Page 30 of 37 Doc: 51-1245628-02 Date: 7 /1/96

~.O AVB WEAR 5.1. A VB Wear Indications Experience shows that AVB wear is a common occurrence in Model 51 steam generators. Based on industry wide data, wear at the U-bend forms slowly at the OD surfaces of the tubes where they contact the A VB component. Wear at the U-Bend at Salem Unit 2 has been detected during previous Eddy Current inspections.

During the 2/96 outage at Salem Unit 2, 100% of the U-bend region of all four steam generators were examined. As a result of this examination, a small percentage of tubes were found to have AVB wear indications. Table 5 .1.1 presents the results of the number of indications found in the four steam generators during the 2R9 inspection.

Table 5.1.1.

2R9 AVB Indications in the U Bend Region Steam Generator Number of Tubes Inspected Number of Indications SG21 3272 141 SG22 3267 52 SG23 3274 155 SG24 3253 96 5~2. Size Distribution The size distribution of the wear indications by %TW is presented for the 2R9 outage in Figures 5.2.1 and 5.2.2. These Figures present the SG data in pairs due to previous inspections where two of the four SG's were inspected. The alternating outages affect the population growth predictions, so all information is presented on the basis of SG 21 and 23, then SG 22 and 24.

Salem 2 Reg. Guide Analysis Page 31 of 37 Doc: 51-1245628-02 Date: 7/1/96

e Figure 5.2.1 SALEM 2 AVB WEAR INDICATIONS SG 21 & 23 80 70 ~

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  • 2R10 (Predicted) I Figure 5.2.2 SALEM 2 AVB WEAR INDICATIONS SG 22 & 24 50 rn z 40 0 ~ ~

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  • 2R 10 (Predicted) j Salem 2 Reg . Guide Analysis Page 32 of 37 Doc : 51-1245628-02 Date: 7/1196
  • The above figures show that for the 2R9 inspection, only indications in SG21 and 23 actually exceed the plugging limit of 403TW. Fu~ermore, no indications exceeded the estimated structural limit of 60 % TW.
5. 3. AVB Wear Plugging and Structural Limit Measurements made with eddy current (Bobbin Coil) during 2R6, 2R7, 2R8 and 2R9 at Salem Unit 2, show that scars grow very slowly in depth and as long as the susceptible tubes are continuously monitored, there is no concern regarding wear at AVB for any of the SG at the Salem Unit 2. Tubes exceeding the accepted wear limit were taken out of service during 2R9.

There are 6 wear indications exceeding the plugging limit of 403 TW (Table 5.3.1).

These wear indications are located in 6 different tubes and will be removed from service prior to the next operating cycle. The percentage of the tubes plugged at 2R9 due to AVB wear after a 1003 inspection is accordingly 0.043 of the total number of tubes in operation (13,066).

Table 5.3.1 A VB Wear Indications with %TW Greater than 40%

SG ROW COL IND %TW@2R9 LOCATION PROBE TEST TYPE 21 27 45 ODI 40 AV2 + 0.00 720UL BOBBIN COIL 21 41 49 ODI 43 AV4 + 0.00 720UL BOBBIN COIL 23 27 60 ODI 44 AV3 + 0.00 720UL BOBBIN COIL 23 30 51 ODI 41 AV2 + 0.00 720UL BOBBIN COIL 23 33 34 ODI 41 AV3 + 0.00 720UL BOBBIN COIL 23 34 48 ODI 44 AV2 + 0.00 720UL BOBBIN COIL As seen in Figures 5.2.1 and 5.2.2, none of the wear indications for 2R9 approach the conservatively selected structural limit of 60 3 TW. The same is true for the predicted in population distribution for the next operating cycle 2R10.

Salem 2 Reg. Guide Analysis Page 33 of 37 Doc: 51-1245628-02 Date: 7I1196

.5.4 , Growth of AVB Wear A calculation of the percent through wall growth rate for the four SGs was conducted for cycles 7 and 8. Indications that had 3TW calls for each inspection were included in the calculation and those indications that had negative growth were set to zero growth. Based on this criteria, 257 data points were used to determine the growth rate distribution presented in Figure 5.4.1. Based on this distribution a one-sided distribution-free tolerance limit (no assumption of normality required) was determined. Using a 953 confidence limit it was determined that 903 of the population will have a growth rate of less than 6 3TW/EFPY.

Figure 5.4.1 SALEM 2 AVB WEAR GROWTH RATE FOR CYCLES 7 AND 8 .

70 60 00 z 50 ,_ ,_

0 E=

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0 30

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

%TW GROWTII RATE PER EFPY

5. 5. Prediction of AVB Wear for Salem 2 2Rl 0 The predictions for AVB wear were made by projecting from the current level of degradation using a plant specific growth rate for each pair steam generators. The value of the plant specific growth was determined to be 6 %TW /EFPY. It has been assumed that the operating cycle for 2Rl0 will span 475 EFPD (1.3 EFPY).

Salem 2 Reg. Guide Analysis Page 34 of 37 Doc: 51-1245628-02 Date: 7/1196

  • From a review of previous data, Eddy Current inspections were only conducted on two of the four steam generators for several outages. 2R9 was the only recent outage inspecting 100% of tubes for all four of its steam generators. Predictions for A VB wear were done on a steam generator pair basis (determined by which pair of SG's were inspected in the same outage) using regression slopes derived from Salem Unit 2 plant specific data.

The prediction for the number of wear indications to be found during 2R10 are as follows: SG 21&23 - 368 indications, SG 22&24 - 239 indications and are shown in Figures 5.5.1 and 5.5.2. Therefore the total number of wear indications to be predicted for 2Rl 0 is 607. It is noted that this predicted number includes both new wear indications and the continuous measurement of existing wear. The predictions have been incorporated in Figures 5.2.1 and 5.2.2 and show none are predicted to be over 60% TW. -

Figure 5.5.1 SALEM 2 PREDICTED AVB WEAR SG21 & 23 1

10 EFPY I- Predicted Indications

  • Actual Indications J Salem 2 Reg. Guide Analysis Page 35 of 37 Doc: 51-1245628-02 Date: 111196
  • \
  • Figure 5.5.2 SALEM 2 PREDICTED AVB WEAR SG22 & 24 1000 Cl.l

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~lir;i 100 0

0 ;N 8 '

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10 I 1 1 IO EFPY I

  • Actwtl Indications - Predicted Indications I 5.5 Conclusions Based on the estimated propagation rate over the next fuel cycle, it is concluded that no AVB wear indications are expected to *exceed the Reg. Guide structural limits prior to the next scheduled inspection. Full cycle operation for this damage mechanism is therefore justified.

Salem 2 Reg. Guide Analysis Page 36 of 37 Doc: 51-1245628-02 Date: 7/1/96

6. O , Overall Conclusions Based on the evaluations presented in this document, it is concluded that a full cycle of 1. 3 EFPY is therefore justified. *
7. 0

References:

1. EPRI TR 100407 PWR Steam Generator Tube Repair Limits - Technical Support Document for Outside Diameter Stress Corrosion Cracking at Tube Support Plates, Revision 2A Draft Report, January 1995.
2. FTI 51-1240202-00 Reg. Guide 1.121 Assessment of WEXTEX 'I:ransition Indications at Salem Unit 2.
3. PSE&G: Document SC.RA-IS.ZZ-0014(Q), Attachment 19.
4. Attachment 1 Salem Station Generating Special Project

Title:

Plugging criteria for Cold Leg SVI Indications.

Salem 2 Reg. Guide Analysis Doc: 51-1245628-02 Page 37 of 37 Date: 7/1196

. ~ ....

    • ATIACHMENT 1 SALEM STATION GENERATING SPECIAL PROJECT TITLE: Plugging criteria for Cold Leg SVI indications CAL NUMBERS:
  • Variety

SUMMARY

On 2-29-96; a sample review of the cold leg SVI indications)n 8022 was perfonned. Typically these indications can be divided into 2 categories; the first are those at a cold leg support, and the second appears to be related to loose part wear and are located at the TSC. Due to all the supports and TSC areas being examined with the +Point probe, a significant number are called without supporting bobbin calls. Plugging of these indications would generally be from a bobbin estimated depth c:all of 40%.
  • RESULTS: AT SUPPORTS: The support indications without bobbin calls can be estimated for depth by voltage, similar to wear type indications. Many~ similar in shape to the 20% ASMB hole but elongated through the middle of the support. An estimate in depth can therefore be Otade using voltage from the +Point examinations. The 20% yields approximately-4 to S volts and the 60% is approximately 22 to 25 volts. It is recommended that all SVI's be reviewed to verify that the +Point voftage calls are correct; and for all >4 volts," the bobbin examination be reviewed for indication depth. PI~gging would not be recommended for any indication < 40% thru wall with bob~in or < l Ovolts +Point. :

AT TSC: Only 2 tubes fall into the loose part wear category and should be plugged only if loose parts are confmned with visual examination. *

  • A-I
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