NL-22-0778, Refueling Outage 2R22 Steam Generator Tube Inspection Report
| ML22273A160 | |
| Person / Time | |
|---|---|
| Site: | Vogtle  |
| Issue date: | 09/30/2022 |
| From: | Gayheart C Southern Nuclear Operating Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| NL-22-0778 | |
| Download: ML22273A160 (14) | |
Text
Regulatory Affairs 3535 Colonnade Parkway Birmingham, AL 35243 205 992 5000 September 30, 2022 Docket Nos.: 50-425 NL-22-0778 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Vogtle Electric Generating Plant, Unit 2 Refueling Outage 2R22 Steam Generator Tube Inspection Report Ladies and Gentlemen:
In accordance with the requirements of Vogtle Electric Generating Plant (VEGP) Technical Specification 5.6.10 as updated by TS Amendment 194 (Adams Accession No. ML21316A055),
Southern Nuclear Operating Company (SNC) submits the enclosed Steam Generator (SG)
Tube Inspection Report for the SG tube inspection performed during the twenty-second refueling outage on Unit 2 (2R22) as an Enclosure to this letter.
This letter contains no regulatory commitments. If you have any questions, please contact Amy Chamberlain at 205.992.6361.
Respectfully submitted, Cheryl A. Gayheart Regulatory Affairs Director CAG/dsp/cbg
Enclosure:
2R22 Steam Generator Tube Inspection Report cc: Regional Administrator NRR Project Manager - Vogtle 1 & 2 Senior Resident Inspector - Vogtle 1 & 2 RType: CVC7000
Vogtle Electric Generating Plant, Unit 2 Refueling Outage 2R22 Steam Generator Tube Inspection Report Enclosure 2R22 Steam Generator Tube Inspection Report E-2
Enclosure to NL-22-0778 2R22 Steam Generator Tube Inspection Report Introduction The Vogtle Electric Generating Plant (VEGP) Unit 2 is a 4-loop Westinghouse plant with Westinghouse Model F steam generators with Inconel 600 thermally treated tubing. VEGP Unit 2 refueling outage 22 (2R22) was conducted after Steam Generator (SG) service equivalent to approximately 2.79 effective full power years (EFPY) from previous SG eddy current inspections. During this operational interval, no tube leakage was reported. Analysis based on conservative assumptions used in the Condition Monitoring (CM) and Operational Assessments (OA) demonstrated that there were no tubes that exceeded the Reg. Guide 1.121 or NEI 97-06 Revision 3 criteria for tube integrity during Cycle 22.
During VEGP 2R22, a total of five (5) tubes were plugged. None of the indications exceeded the condition monitoring limits identified in the Degradation Assessment and therefore did not require in-situ pressure testing. Permanent H* Alternate Repair Criteria (ARC) has been approved for implementation by the NRC. Therefore, SNC and Westinghouse omitted tube end
+Point' inspections below top of tubesheet (TTS) -15.2 inches. TTS inspections ranged from TTS +3 inches to TTS -15.2 inches. The scope and results of inspections on each SG are described below.
A. Technical Specification 5.6.10.a, the scope of inspections performed on each SG; x 100% full-length X-probe (Bobbin and Array) examination of tubes in all SGs, tube end to tube end for Row 6 and higher. Straight leg portion of cold leg (CL) (Rows 1-5) and hot leg (HL) (Rows 1-2).
x 100% low Row U-bend Bobbin and Array probe examination candy cane from HL Rows 3-5, +Point probe examination of Row 1 and Row 2 U-Bends from the top tube support plate (TSP) on the HL to the top TSP on the CL.
x 100% tubesheet +POINT probe examination of HL tubes in all SGs from the TTS to the licensed ARC depth for H* (+3/-15.2 inches). This inspection satisfied the required periodic sample that accompanies regulatory approval of H*.
x 100% +POINT of the HL tube bulge (BLG) and overexpansion (OXP) populations in all four SGs. This scope is captured as part of the HL tubesheet inspection scope. The BLG and OXP indications are defined as follows:
o BLG = differential mix diameter discontinuity signal within the tubesheet of 18 volts or greater as measured by bobbin coil probe.
o OXP = a tube diameter deviation within the tubesheet of 1.5 mils or greater as measured by bobbin coil profile analysis.
x 100% +Point probe examination of dents and dings 2 volts in HL straight lengths and U-bends of all SGs x 50% +Point dents/dings >5.0 volts in CL straight lengths x 25% +Point dents/dings 2.0-5.0 volts in CL straight lengths. Scope expanded to 100%
+Point of dents >2.0 volts at support plate seven on cold leg side (7C)
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report x 100% +Point probe examination of all HL and CL TSP intersections, HL and CL TTS expansion transitions and all dents/dings 2 volts in 2-sigma high stress tubes in all SGs.
x Any existing possible loose part (PLP) indications from the most recent inspection were boxed-in with the +Point probe by at least one tube. Any newly reported PLPs or foreign object wear indications were boxed-in with the +Point probe by at least two tubes with a +Point probe.
x 100% visual inspection of all installed tube plugs from the primary side in all SGs.
x Visual inspection in all SGs of channel head primary side HL and CL inclusive of the entire divider plate to channel head weld and all visible clad surfaces.
x Secondary side activities included:
o Foreign object search and retrieval (FOSAR) o Sludge lancing As a measure of conservatism after detecting axial outer diameter stress corrosion cracking (ODSCC) at a dent at 7H in SG4, the +Point special interest scope in SG4 was expanded to include 100% of dents >2.0 volts at 7C. No scope expansion was required for the X-Probe since 100% full-length inspection was already performed.
B. Technical Specification 5.6.10.b, the nondestructive examination techniques utilized for tubes with increased degradation susceptibility.
+Point probe inspections were performed for HL tubes in all SGs from the TTS to the licensed ARC depth for H*, Row 1 and Row 2 U-bends from the top TSP on the HL side to the top TSP on the CL side, HL tube BLG and OXP, dents and dings at specific volts in HL straight lengths and U-bends, and all potential stress risers in the high stress tube population. These regions have increased degradation susceptibility to stress corrosion cracking.
X-probe inspections were performed for 100% of the SG tubes. This includes HL and CL periphery and tubelane to identify foreign objects or foreign object wear. These regions are considered to have increased susceptibility to foreign object wear. The 100% X-probe inspection included all potential high stress tubes and dents/dings.
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report C. Technical Specification 5.6.10.c, for each degradation mechanism found:
- 1. The nondestructive examination techniques utilized, Table 1: Degradation Found and Techniques Degradation Mechanism Found Technique Used (Probe Type)
Mechanical wear due to foreign objects Bobbin and Array - detection
+Point - detection and sizing Mechanical wear at AVB supports Bobbin - detection and sizing Tube wear and wall loss from secondary side Bobbin - detection cleaning process +Point - detection and sizing Mechanical wear at TSP Bobbin - detection
+Point - sizing ODSCC at the Hot Leg Expansion Transitions +Point - detection and sizing ODSCC at Dents and Dings Bobbin and Array - detection
+Point - detection and sizing
- 2. The location, orientation (if linear), measured size (if available), and voltage response for each indication. For tube wear at support structures less than 20 percent through-wall, only the total number of indications needs to be reported, Mechanical wear due to foreign objects Table 2: Vogtle 2R22 Foreign Object Wear Indications
%TW Length SG Row Column Location Depth (in) Voltage 1 47 84 TSH+0.18 11 0.08 0.12 1 47 85 TSH+0.16 8 0.08 0.09 4 12 57 TSH+0.37 22 0.17 0.27 4 42 93 TSC+0.92 25 0.22 0.31 4 46 87 TSC+0.59 28 0.46 0.37 4 46 87 TSC+6.56 14 0.52 0.15 4 46 87 TSC+7.18 21 0.22 0.25 4 57 68 BPC+0.35 30 0.24 0.4 BPC - Baffle Plate on CL side TSH - Tubesheet region on HL side TSC - Tubesheet region on CL side No loose parts were found to remain at any of the foreign object wear locations in Table 2.
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report Mechanical wear at Anti-vibration bar (AVB) supports In SG1, there are a total of 99 indications for AVB wear with 88 less than 20% through-wall (TW). In SG2, there are a total of 168 indications for AVB wear with 151 less than 20% TW. In SG3, there are a total of 71 indications with 63 less than 20% TW. In SG4, there are a total of 216 indications for AVB wear with 179 less than 20% TW. Table 3 - 6 includes V2R22 AVB wear indications greater than or equal to 20%TW.
Table 3: Vogtle 2R22 SG1 AVB Wear Indications 20%TW SG Row Column Location %TW Depth Voltage 1 41 20 AV2 20 0.71 1 42 20 AV2 20 0.7 1 46 43 AV2 20 0.64 1 46 58 AV5 20 0.68 1 43 100 AV4 21 0.84 1 49 36 AV2 22 0.91 1 44 23 AV3 24 0.89 1 47 27 AV2 24 1.08 1 49 36 AV5 29 1.54 1 44 23 AV5 30 1.35 1 50 29 AV5 36 2.5 Table 4: Vogtle 2R22 SG2 AVB Wear Indications 20%TW SG Row Column Location %TW Depth Voltage 2 28 115 AV6 20 0.73 2 44 72 AV5 20 0.8 2 43 73 AV4 21 0.68 2 49 74 AV3 21 0.84 2 40 52 AV3 23 1.01 2 42 74 AV3 27 1.26 2 49 91 AV2 27 1.19 2 53 88 AV5 27 1.36 2 51 87 AV4 28 1.38 2 42 74 AV2 29 1.43 2 51 74 AV3 29 1.42 2 51 91 AV5 30 1.49 2 51 89 AV5 34 1.93 2 51 89 AV4 35 2.01 2 51 87 AV2 36 2.2 2 51 87 AV3 36 2.2 2 51 87 AV5 42 3.13 E-4
Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report Table 5: Vogtle 2R22 SG3 AVB Wear Indications 20%TW SG Row Column Location %TW Depth Voltage 3 32 12 AV5 20 0.66 3 39 72 AV2 20 0.69 3 41 77 AV5 22 0.8 3 41 77 AV4 23 0.87 3 46 36 AV4 26 1.01 3 39 72 AV3 30 1.35 3 43 82 AV5 30 1.41 3 39 72 AV4 34 1.71 Table 6: Vogtle 2R22 SG4 AVB Wear Indications 20%TW SG Row Column Location %TW Depth Voltage 4 31 10 AV5 20 0.66 4 43 68 AV3 20 0.81 4 51 55 AV3 20 0.78 4 51 65 AV6 20 0.79 4 52 66 AV2 20 0.8 4 53 74 AV4 20 0.77 4 43 95 AV3 21 0.76 4 45 32 AV3 21 0.8 4 49 93 AV4 21 0.75 4 51 76 AV2 21 0.87 4 52 71 AV2 21 0.68 4 56 45 AV4 21 0.56 4 58 47 AV5 21 0.57 4 39 64 AV2 22 0.72 4 43 68 AV5 22 0.96 4 44 54 AV2 22 0.81 4 45 66 AV5 22 0.89 4 50 70 AV3 22 0.89 4 56 47 AV3 22 0.64 4 55 41 AV5 23 0.82 4 43 68 AV4 24 1.12 4 52 71 AV3 24 0.84 4 44 42 AV5 25 1.07 4 51 54 AV4 25 1.04 4 49 93 AV5 26 1.07 4 52 72 AV2 26 1.27 4 30 9 AV5 27 0.9 4 52 45 AV3 27 0.93 4 52 45 AV4 27 0.9 4 39 64 AV6 28 1.18 4 46 31 AV3 28 1.28 4 39 64 AV3 29 1.2 4 45 58 AV3 31 1.76 4 51 76 AV5 31 1.73 E-5
Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report SG Row Column Location %TW Depth Voltage 4 44 54 AV5 32 1.61 4 51 65 AV4 33 2.05 4 51 65 AV5 44 4.04 AV# - Location of AVB intersection with the tube (there are up to 6)
Mechanical wear and wall loss from secondary side cleaning process Table 7 lists tube locations and volumetric indications associated with the ultrasonic energy cleaning (UEC) and pressure pulse cleaning (PPC) secondary side cleaning processes. Based on these nondestructive examination (NDE) uncertainty levels and the results, it is apparent that there has been no measurable progression in the wall loss associated with these historical indications. Further, the mechanisms that caused this form of degradation are no longer applied and therefore no wear progression can occur.
Table 7: Vogtle 2R22 Tube Wall Loss from Secondary Cleaning Process
%TW Volts SG Row Col Location Indication Depth 1 1 42 TSH+10.01 PCT 10 0.11 1 1 45 TSH+9.98 PCT 12 0.13 1 1 46 TSH+10.52 PCT 21 0.24 1 1 78 TSH+9.75 PCT 17 0.19 1 1 78 TSH+11.57 PCT 9 0.1 1 1 78 TSC+11.94 PCT 19 0.22 1 1 78 TSC+12.12 PCT 28 0.36 2 1 46 TSC+11.34 PCT 22 0.26 3 1 112 TSC+18.31 PCT 21 0.26 PCT - Volumetric Indication Mechanical Wear at TSP There is one indication of mechanical wear at TSP that is less than 20% TW.
ODSCC at the Hot Leg Expansion Transitions During the 2R22 SG inspections, two circumferential ODSCC indications were reported at HL TTS expansion transitions. Both were detected and sized with the +Point probe.
Table 8 includes the ODSCC indications.
Table 8: Vogtle 2R22 ODSCC at Tubesheet Expansion Transitions Max PDA SG Row Column Volts Deg Location Depth%
(%)
TW 1 15 57 0.24 114 TSH+0.17 35 9.4 4 12 56 0.12 102 TSH+0.2 22 4.5 PDA - Percent Degraded Area ODSCC at Dents and Dings E-6
Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report During 2R22, there was one indication of axial ODSCC detected at a dent by the +Point probe. Table 9 includes the ODSCC indication. The dent itself was measured at 2.81 volts with the bobbin probe and the axial length of the dent was determined to be 0.28-inch. The sizing technique for this mechanism is ETSS I28432, which calls for a voltage-based sizing approach. The flaw maximum depth with ETSS I28432, using a voltage amplitude correlation, is 28.6% TW. The flaw was also sized with a phase angle-based calibration curve, which resulted in a maximum depth of 58% TW. For comparison to CM limits, the more conservative phase-based depth is considered.
Table 9: Vogtle 2R22 Axial ODSCC at TSP Dent
+Point Max Length SG Row Column Voltage Deg Location Depth%
(in)
(Vpp) TW 4 40 105 0.09 65 7H-0.67 58 0.11
- 3. A description of the condition monitoring assessment and results, including the margin to the tube integrity performance criteria and comparison with the margin predicted to exist at the inspection by the previous forward-looking tube integrity assessment Table 10: Vogtle 2R22 Condition Monitoring Summary for Limiting Flaws 2R22 Limiting Flaw CM Limit Mechanism Loc Depth Length Mechanical wear due SG4-R57-C68 54% TW 30% TW 0.24-inch to foreign objects BPC+0.35 0.55-inch flaw Mechanical wear at SG4-R51-C65 67% TW 44% TW 0.30-inch AVB supports AV5 0.4-inch Mechanical wear SG1-R1-C78 48% TW from secondary side 28% TW 0.25-inch TSH+12.12 1.5-inch flaw cleaning process Mechanical wear at SG3-R54-C79 53% TW 18% TW 0.22-inch TSP 5H+0.39 1.12-inch flaw ODSCC at the Hot SG1-R15-C57 54 PDA Leg Expansion 9.4 PDA 134° circ TSH+0.17 194° Transitions SG4-R40-ODSCC at Dents and 82% TW C105 58% TW 0.11-inch Dings 0.11-inch flaw 7H-0.67 For volumetric wear flaws with pressure-only loading condition, tube burst and ligament tearing (i.e., pop-through) are coincident, therefore, satisfaction of the tube burst criteria at 3¨PNO also satisfies the accident induced leakage performance criteria (AILPC) at steam line break (SLB) differential pressure.
For all SCC flaws, the burst and ligament tearing pressures are greater than the minimum burst and leakage integrity limits of 4044 psi and 2560 psi, respectively. This includes material property, burst relation, and NDE uncertainties at 0.95 probability and 50%
confidence.
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report For existing degradation mechanisms, a comparison of the previous OA projection was compared to the 2R22 inspection results. The following provides a discussion of each comparison.
For potential wear caused by known (legacy) foreign objects remaining in the SGs, the previous 2R20 OA stated that the legacy foreign objects remaining in the SGs will not adversely affect SG tube integrity for at least two full operating cycles. During the 2R22 eddy current inspections no tube wear was reported that was associated with legacy foreign objects. Therefore, the foreign object wear projection methodology remains valid and conservative. During the 2R22 eddy current inspections, three new indications that are believed to be foreign object wear in one tube (SG4 R46C87 at TSC) were detected.
This wear is not associated with legacy foreign objects. The depths of the three indications were measured at 28% TW, 14% TW, and 21% TW. These measurements are well below the 68% TW condition monitoring limit.
For wear and wall loss from secondary cleaning no wear or wall loss progression is expected outside of eddy current depth measurement uncertainty. The maximum increase in legacy wear from secondary side cleaning from 2R15 to 2R22 is 6% TW, well within the measurement uncertainty. Therefore, the OA assumptions, inputs and methodology for these projections remain valid and conservative.
For AVB wear, the OA projection from this assessment predicted existing AVB wear at a maximum depth of 54% TW. The largest existing AVB wear depth reported during 2R22 was 44% TW. The previous OA predicted new AVB wear at a maximum depth of 39.6%
TW. The largest new AVB wear depth reported during 2R22 was 20% TW. Therefore, the OA assumptions, inputs, and methodology for AVB wear projections remain valid and conservative.
The previous OA used a fully probabilistic full bundle analysis for projection of the existing degradation mechanism of circumferential ODSCC at expansion transition. The OA projected probability of burst (POB) and probability of leakage (POL) of 0.0012% and 0.369%, for 2 undetected flaws. Review of the analysis inputs shows conservative populations were used for undetected flaws and growth rates, relative to the flaws detected at 2R22. The 95th percentile beginning of Cycle 21 parameters used were 28 PDA and a growth rate of 5.9 PDA/EFPY. The simulations use these undetected flaw distributions to predict the POB and POL over two cycles. The largest of the two end-of-cycle circumferential ODSCC indications detected at expansion transitions during 2R22 (SG1 R15C57) was 9.4 PDA. The burst and ligament tearing pressure of this flaw (with material, burst relation, and NDE uncertainties included at 95/50) are 7627 psi and 9353 psi, respectively. This most limiting flaw detected during 2R22 was bound by the 2-cycle fully probabilistic projections in the previous OA with a predicted burst pressure of 6867 psi for 5 undetected flaws.
Based on this review, the OA assumptions, inputs, and methodology for circumferential ODSCC projections remain valid and generally conservative.
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report
- 4. The number of tubes plugged during the inspection outage.
Table 11 presents a summary list of all SG tubes plugged in 2R22.
Table 11: Vogtle 2R22 Plugging List Plugging Stabilizer SG Row Column Indication Location Basis 1 15 57 SCI TSH+0.03 Circ. ODSCC Yes - HL TTS No-no AVB Wear >
2 51 87 PCT AV5 accelerated 40% TW wear 4 12 56 SCI TSH+0.06 Circ. ODSCC Yes- HL TTS Axial dent No - Axial 4 40 105 SAI 7H-0.75 ODSCC indication No - no AVB Wear >
4 51 65 PCT AV5 accelerated 40% TW wear SCI - Single Circumferential Indications, SAI - Single Axial Indication, PCT - Percent Through-Wall D. Technical Specification 5.6.10.d, analysis summary of the tube integrity conditions predicted to exist at the next scheduled inspection (the forward-looking tube integrity assessment) relative to the applicable performance criteria, including the analysis methodology, inputs, and results.
The 2R22 eddy current inspections detected three newly identified indications of foreign object wear in one tube (SG4 R46C87), with the deepest measured as 28% TW using ETSS 21998.1.
This wear was not associated with a legacy foreign object. Lookback of the bobbin data shows the indications were first detectable in 2019 (2R20), but no sign of wear in 2016 (2R18). These indications were not reported in the previous steam generator tube inspection report from 2R20 (ADAMS accession no. ML19255170). There was no change in the signals between 2019 and 2022; additionally, there is no evidence in the 2R22 +Point data of a loose part remaining at this location. Based on review of the eddy current signals, no loose part remains in this area and the wear indications have not changed over the past two operating cycles. Therefore, no continued wear over the next two cycles is expected to occur. There was no apparent growth in legacy foreign object wear. The existing foreign object wear indications do not pose a threat to the SG structural integrity over the next inspection interval.
Based on application of conservative AVB wear growth rates, the condition of the Vogtle Unit 2 SG tubes has been analyzed with respect to continued operability of the SGs until the end of Cycle 25 without exceeding the limits for structural and leakage integrity. A 2- and 3-cycle OA was performed for AVB wear indications existing at 2R22 and assumed undetected flaws. The growth rates were determined by comparative analysis of AVB wear sites for all SGs. The maximum growth rate observed between 2R20 and 2R22 was 2.51% TW/effective full power years (EFPY). It is expected that the growth rates from 2R20 to 2R22 will continue to 2R25 because there are no planned changes to operational conditions. However, in order to provide a level of conservatism, the growth rate from the previous operating interval of 5.21% TW/EFPY was used for 2R22 OA. The condition monitoring limit for AVB wear is 67% TW while the largest AVB wear indication left in service at 2R22 was 36% TW. The maximum AVB wear indication E-9
Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report existing at 2R22 is projected to be 51% TW at the next planned inspection (2R24), which does not include NDE uncertainties. The maximum AVB wear indication assumed to be undetected at 2R22 is projected to be 32% TW at 2R24. All AVB wear projections for 2 and 3 cycles satisfy the condition monitoring limit of 67% TW.
Mechanical wear at TSP locations was detected in one tube during 2R22. 2R22 was the first inspection at which TSP wear was reported. Review of the previous 2R20 bobbin signal showed that the indication has precursor wear and only small changes in depth over the past two cycles were observed. Despite this evidence, a conservative assumption was made that the indication grew from 0% TW to 18% TW since the last inspection, resulting in a growth rate of 6.45%
TW/EFPY. Based on this application of conservative TSP wear growth rates, the condition of the Vogtle Unit 2 SG tubes has been analyzed with respect to continued operability of the SGs until the end of Cycle 25 for existing and assumed undetected flaws, without exceeding the performance criteria. The TSP wear indication existing at 2R22 is projected to be 36.7% TW at the next planned inspection (2R24), which does not include NDE uncertainties. The maximum AVB wear indication assumed to be undetected at 2R22 is projected to be 36.7% TW at 2R24.
All AVB wear projections for 2 and 3 cycles satisfy the condition monitoring limit of 53% TW.
There has been a recurrence of circumferential ODSCC in the hot leg expansion transitions, with two indications detected at 2R22. Axial ODSCC at a HL dent was also detected at 2R22 in one tube. A fully probabilistic OA analysis was performed for all of existing degradation mechanisms for an inspection interval of 2 cycles.
The operational assessment of SCC degradation mechanisms is performed using fully probabilistic methods. The basic methodology for the fully probabilistic analysis is the same for each SCC mechanism, however, the specific inputs for each mechanism may differ. The basic fully probabilistic analysis method includes:
x Determination of beginning of cycle (BOC) flaw distributions o max depth o total length o PDA (for circumferential flaws) x Flaw characteristic growth rates o based on the EPRI typical default growth rates for SCC o corrected for Vogtle Unit 2 hot leg temperature x Length of cycles x The remainder of critical inputs to the fully probabilistic model, including number of undetected flaws, tube geometry, material properties, normal operating, accident pressures, and leakage limits.
BOC flaw distributions account for the differences between destructive analysis results and eddy current measurements. The BOC total length distributions were adjusted for non-destructive examination (NDE) measurement uncertainty through probabilistic simulation, including both the mean regression and standard error. In this way, the BOC lengths are based on site-specific history (when available), but also have been adjusted to account for sizing error to true flaw lengths, as determined by destructive analysis of pulled tubes and laboratory cracks. Similarly, the max depth distributions are derived from the site-specific probability of detection (POD) curves. The Vogtle Unit 2 specific POD distributions account for the correlation of measured voltage amplitudes to true flaw max depth via the ETSS voltage amplitude to true depth distribution correlation (Ahat).
Potential SCC degradation mechanisms were also evaluated for the next 2 cycles.
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report The results of the OA are summarized in Table 12 and conclude that all SG performance criteria for structural and leakage integrity will be satisfied until the next planned inspection at the end of Cycle 24.
Table 12: Vogtle 2R22 OA Results Summary Burst Pressure at Leak Rate at Degradation POB POL Lower 5% Lower 5%
OA Duration Mechanism (%) (%) (psi) (gpm)
Circ. ODSCC 2 Cycle 0.019 0.248 6781 0.00 HL TTS Axial ODSCC 2 Cycle 2.13 0.807 4543 0.00 Dent/Ding Acceptance Criterion 5% 5% 4044 psi 0.35 gpm E. Technical Specification 5.6.10.e, Number and percentage of tubes plugged to date, and the effective plugging percentage in each.
Table 13: Total Plugged Tubes after Vogtle 2R22 2R22 Total SG # Tubes # Plugged # Plugged % Plugging 1 5,626 1 7 0.12%
2 5,626 1 16 0.28%
3 5,626 0 7 0.12%
4 5,626 3 28 0.50%
Total 22,504 5 58 0.26%
F. Technical Specification 5.6.10.f, The results of any SG secondary side inspections.
FOSAR inspections were performed at 2R22. A total of 10 objects were found during FOSAR and none were retrieved. All objects were sludge rocks. Continued steam generator operation with the foreign objects known to be present in the secondary side will not adversely affect the steam generator tube integrity for at least three operating cycles, or until the 2R25 outage.
Sludge lancing was performed and a total of 122.5 lbs of deposits were removed. Tube Support Plate 7 (TSP 7) Inspections in SG 2 were also performed in pre-defined columns. TSP 7 was found to be in acceptable condition, with the support plate and quatrefoils free of deposit. Only a small amount of tube scale was observed at TSP 7.
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Enclosure to NL-22-0779 2R22 Steam Generator Tube Inspection Report G. Technical Specification 5.6.10.g, The primary to secondary LEAKAGE rate observed in each SG (if it is not practical to assign the LEAKAGE to an individual SG, the entire primary to secondary LEAKAGE should be conservatively assumed to be from one SG) during the cycle preceding the inspection which is the subject of the report.
No tube leakage was reported during this operating interval.
H. Technical Specification 5.6.10.h, The calculated accident induced leakage rate from the portion of the tubes below 15.2 inches from the top of the tubesheet for the most limiting accident in the most limiting SG. In addition, if the calculated accident induced leakage rate from the most limiting accident is less than 2.48 times the maximum operational primary to secondary leakage rate, the report should describe how it was determined.
None of the indications reported during the Vogtle 2R22 SG inspections were evaluated to have primary to secondary leakage under accident induced conditions. There was no leakage from the portion of tubing within the H* depth for which to apply the leak rate factor associated with the alternate repair criteria. Since there was no calculated leakage from any other sources none of the Vogtle 2 SGs installed tube plugs require leakage calculations. Therefore, for these indications the accident induced leakage rate would be zero, satisfying the accident induced leakage performance criteria.
I. Technical Specification 5.6.10.i, The results of monitoring for tube axial displacement (slippage). If slippage is discovered, the implications of the discovery and corrective action shall be provided.
During 2R22, as part of the tube inspection program, 100% of the tubes in all SGs were tested with the bobbin and array probe. The bobbin data collected was screened for large amplitude tubesheet indications of greater than 50 volts with a phase angle between 25° and 50° suggestive of tube severance. Both manual and automated data screenings have been performed with SVR as the code to report should a sever-type signal be detected. No SVR call was made for the entirety of the bobbin data collected therefore, no indications of slippage were identified.
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