ML24303A358

Steam Generator Tube Inservice Inspection Discussion-Fall 2024 (Oct. 25, 2024)

ML24303A358
Person / Time
Site:	Beaver Valley
Issue date:	10/25/2024
From:	V Sreenivas Plant Licensing Branch 1
To:	Vistra Operations Company
Sreenivas, V
References
Download: ML24303A358 (6)

Text

Page 1 of 6 STEAM GENERATOR TUBE INSPECTION DISCUSSION POINTS The following discussion points have been prepared to facilitate the conference call arranged with the licensee to discuss the results of the steam generator tube inspections to be conducted during the ongoing fall 2024, Unit 2 refueling outage (2R24). This conference call is scheduled to occur towards the end of the planned SG tube inspections (about 70% complete), but before the unit completes the inspections and repairs.

The NRC staff plans to document a publicly available summary of the conference call, as well as any material that is provided in support of the call.

1.

Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed cycle.

There was no primary to secondary leakage reported during the last operating cycle (Cycle 24).

2.

Discuss whether any secondary side pressure tests were performed during the outage and the associated results.

There were no secondary pressure tests performed during the outage.

3.

Discuss any exceptions taken to the industry guidelines?

There are no exceptions taken to the industry guidelines.

4.

For each steam generator, provide a description of the inspections performed including the areas examined and the probes used (e.g., dents/dings, sleeves, expansion-transition, U-bends with a rotating probe), the scope of the inspection (e.g., 100 percent of dents/dings greater than 5 volts and a 20 percent sample between 2 and 5 volts), and the expansion criteria.

Base Scope Programs:

100% full length 0.720-inch bobbin inspection in Rows 5 and higher (non-sleeved tubes) 0.720-inch bobbin inspection in Row 5 and higher in all sleeved tubes from TEC to STH 100% 0.720-inch bobbin inspection in Rows 1 through 4 HL and CL straight legs (non-sleeved HL tubes) 0.630 inch Wide Groove Bobbin in all sleeved tubes in Rows 2 through 4 from STH to 08H 100% 0.700-inch bobbin inspection in Row 3 and Row 4 U-bend from 08H to 07C 100% hot leg TTS +POINT probe inspection from 6 inches above to 3 inches below TTS in non-sleeved tubes 100% +POINT probe inspection of BLG and EXP bobbin reports in hot leg tubesheet below F*

distance but above tubesheet neutral axis plus 100% +POINT probe inspection of cold leg BLG and EXP bobbin reports above the TTS 100% +POINT probe inspection of cold leg TTS region from +6 to -3 inches in all inservice non-sleeved cold leg tubes and all previously de-plugged tubes (current and historical) in all SGs.

100% gimbaled +POINT probe full length from STH +3 to SBH -4 inches in sleeved tubes (Oct. 25, 2024)

Page 2 of 6 100% Ghent Version 2 probe of sleeve nickel band region in lower tubesheet sleeve joints 100% Row 1 and Row 2 small radius U-bend +POINT probe inspection in each SG using mid-range

+POINT coil 100% +POINT probe inspection at all dented (hot and cold leg) TSP intersections 5 volts 100%+POINT probe inspection at all dented hot leg TSP intersections 2 but < 5V volt (TSPs 01H through 08H) 100% +POINT probe inspection of all TSP DSI/DNI signals 2V 100% +POINT probe inspection of all freespan dings (all reported voltages) 100% +POINT probe inspection of Row 3 through Row 10 U-bends in all SGs (top TSP to top TSP)

+POINT probe inspection of hot leg and cold leg tubes that contain Tubesheet Lower BRT Tubes.

Testing extent to be from 6 inches above the tubesheet to 5 inches below Special Interest +POINT Probe (Mid-Range unless otherwise noted) Inspections:

100% inspection of bobbin special interest I-codes, such as freespan differential signals meeting change criteria 100% inspection at TSP DSI signals >1V (Proactive examination, not required per GL 95-05) 100% inspection of <2V DSI locations previously confirmed by the +POINT probe to contain axial ODSCC (Proactive examination, IQDA recommendation).

25% inspection of all bobbin TSP mix residuals >1.5V but <2V plus 100% of 2V mix residuals (ODSCC concern). TSP mix residuals have bobbin phase angles >55 degrees.

100% inspection of all TSP residuals with bobbin phase angle 55 degrees and 1.25V on the bobbin P1 mix Channel (PWSCC concern - reported as bobbin DNI) 100% of DSI signals regardless of voltage size at TSP 01H/01C and TSP 02C/03C locations.

High frequency +POINT probe testing of Row 1 U-bends with noise values of 0.65 Vvm and greater High frequency +POINT probe confirmatory testing of all U-bend PWSCC indications reported with the mid-range +POINT coil.

100% inspection of all dents at AVB sites (+/- 1 inch of AVB) 100% inspection of all newly reported signals at AVBs plus any atypical growth (>6%TW growth for Cycle 24) AVB wear indications 100% inspection of all freespan signals not resolved as MBH/FSH or without historical review 100% inspection of newly reported PLP signals (includes 2-tube box) plus locations adjacent to tubes plugged in prior outages for PLP interaction (2 tube box), plus one tube box around SG-A 01C PLP signals from 2R23.

+POINT probe inspection of tubes with newly identified FOs that have the potential to cause tube wear that are identified from secondary side visual inspections at the applicable elevation (includes 1 tube box)

Page 3 of 6 Additional special interest examinations in accordance with the Vistra controlled BVPS 2R24 SG decision tree logic charts.

Expansion Criteria:

Scope expansion will be in accordance with the EPRI SG Integrity Assessment Guidelines. Most eddy current inspections are already at 100% for each critical area so no expansion would be required for those programs.

Visual Inspections:

Tube plugs video inspection, including PIP repaired plugs and PIP tack welds Primary channel head visual inspections per Nuclear Safety Advisory Letter NSAL-12-1, Revision 1, which includes:

o Divider plate-to-channel head weld o Divider plate-to-stub runner weld o Tubesheet-to-channel head Z-seam area o Entire inside surface of the channel head bowl cladding o Targeted visual inspection of the potential cladding anomaly identified in 2R20 o Tubesheet (primary side)

SG secondary side FOSAR of annulus, tube lane, and selected in-bundle locations with FOSAR of in-bundle PLP reports from eddy current testing.

Secondary side visual inspections of internal steam drum and feedwater header components in SG-A.

1. 5.

For each area examined (e.g., tube supports, dent/dings, sleeves, etc), provide the following:

a. A summary of the number of indications identified to date for each degradation mode (e.g.,

number of circumferential primary water stress corrosion cracking indications at the expansion transition).

b. For the most significant indications in each area, provide an estimate of the severity of the indication (e.g., voltage, depth, and length of the indication), including whether tube integrity (structural and accident induced leakage integrity) was maintained during the previous operating cycle. In addition, discuss any analyses performed specifically for the most significant indications to demonstrate tube integrity, if any indications were close to the condition monitoring limit.

c. Discuss whether any location exhibited a degradation mode that had not previously been observed at this location at this unit (e.g., observed circumferential primary water stress corrosion cracking at the expansion transition for the first time at this unit).

Data as of 13:00 10/24/2024.

Page 4 of 6 AVB wear:

A total of 141 indications of AVB wear have been reported in 83 tubes in all three SGs, with the majority in SG A and SG B. Only 11 indications in 7 tubes have been reported in SG C.

Two (2) indications in 2 tubes exceeded the Tech Spec 40% TW repair limit. Both tubes were in SG B and were 40% TW and 42% TW. The largest indications measured in SG 2A and SGC were 35%TW and 34%TW, respectively. All AVB wear indications satisfy the condition monitoring limit of 62% TW.

TSP/FDB Wear:

Two indications of FDB/TSP wear were reported in SG C and were historical in nature. One indication has been depth sized. The historical wear indication that was measured is 18%TW with and was 17%

TW at the prior inspection. The wear indication that has not be size was 26%TW at the prior inspection.

The TSP wear condition monitoring limit is 57% TW.

Volumetric/Foreign Object Indications:

There are 9 indications in 8 tubes that were reported with volumetric indications in the freespan. Seven (7) indications were historical in nature and have been monitored each inspection. Depth sizing has not been completed, of the wear that was sized the depths ranged from 10%TW to 31%TW and were consistent with the sizes at the prior outage. There are no foreign objects remaining for these historical indications. There were 2 newly reported volumetric indications in SG C above the cold leg tubesheet, the indications were 10% TW and 17%TW. Both indications were reported from the 100% cold leg top of tubesheet inspection. One of the indications had precursor indications traced to at least 2002 by historical data reviews from the bobbin coil. This indication was located ~1.4 above the tubesheet.

History data reviews from the bobbin coil on the other indication could not detect precursor indications in prior indications, however this indication was located only 0.13 above the tubesheet making bobbin detection challenging. This was the first MRPC inspection of this tube at the cold leg tubesheet.

Axial ODSCC Indications at TSPs (GL 95-05):

A total of 1307 axial ODSCC indications (DSIs) are currently reported from all SGs. 1390 DSIs were reported in the prior 2R23. The NRC GL 95-05 voltage-based repair criteria is applicable to these indications. The largest bobbin coil voltage measured in all SGs is 1.69 volts (the largest DSI observed in the last outage was 1.44v). The GL 95-05 voltage repair limit is 2.0-volts. All indications are below the repair limits.

Axial and Circumferential ODSCC/PWSCC at Expansion Transitions:

A total of 191 tubes contained indications of circumferential ODSCC at the hot leg expansion transition region: 116 in SG A, 50 in SG B, and 34 in SG C. The +POINT probe 300 kHz voltages range from 0.01 volts to 0.24 volts. All indications are below the in situ pressure test initial voltage screening criteria of 0.5v for burst testing and 1.0v for leak testing. Line by line depth profiling is in-progress for selected sample of indications based on voltage, depth, PDA, and length to bound the largest sized flaws for all parameters. No indications met the initial voltage screening criteria for proof and leakage in situ testing.

The range of maximum depth measurements by phase analysis are 40% TW to 91% TW based on the limiting signal entrance or exit phase angles. (flaw depths less than 40% TW are assigned a depth of 40%

Page 5 of 6 TW) It should also be noted that phase-based depth assessment of small voltage signals can be oversized due to the expansion transition geometry and deposit influence. The measured circumferential crack arc lengths range from 20 degrees to 246 degrees, including non-degraded ligaments between multiple indications at the same elevation.

A total of 13 axial ODSCC indications in 12 tubes have been reported at the hot leg expansion transition region. The largest flaw was measured with the +POINT probe 300 kHz voltage was 0.21 volts and 52%TW. The in situ pressure test voltage screening criteria is 0.5v. The measured axial crack lengths range from 0.10 inch to 0.42 inch. Line-by-line depth profiling of all indications are planned and not yet completed.

One indication of circumferential ODSCC at a freespan ding has been detected by the +POINT probe during the 100% ding inspection program. The historical ding was 1.38 volts by the bobbin coil (2R23).

Sizing and disposition of the indication is still in progress.

Cold Leg Thinning:

Cold leg thinning was first reported at BVPS-2 during inspection in 2R21 when one indication was detected. One other cold leg thinning indication was reported in the 2R22 inspection. Both indications have been confirmed in 2R24 and were measured at 11% and 25% TW. These are both less than the 52%TW condition monitoring limit.

6.

Describe repair/plugging plans.

The exact number of tubes to be sleeved and plugged yet to be determined. As of 10/24/2024, there are 195 tubes that are potential repair candidates for plugging or sleeving (111-SGA, 51 in SGB, 33 in SGC).

7.

Describe in-situ pressure test and tube pull plans and results (as applicable and if available).

To-date there are no indications that are required to be in situ pressure tested. There are no tubes planned tube pulls.

8.

Discuss the following regarding loose parts:

a.

The inspections performed to detect loose parts?

Primary side eddy current (100% full-length bobbin, 100% MRPC of Hot Leg and Cold tubesheet);

Secondary side visual inspections of the tubesheet annulus, tube lane, and select in-bundle locations) following sludge lancing. (Foreign Object Search and Retrieval - FOSAR) have been completed in SG B and SG C.

b.

A description of any loose parts detected and their location within the SG (including the source or nature of the loose part, if known).

There were 16 foreign objects found during the FOSAR inspections to-date (11 in SG B and 5 in SG C). In SG B, there was 1 legacy weld slag, 2 small areas where there was multiple bristle wires fixed within hard scale, and 8 sludge rocks/scale. These objects were found in-bundle. In SG C, there were 4 sludge rocks/scale found in-bundle and 1 metallic rod found in the annulus. The rod measured 3.5 long and 0.2 diameter. The rod was retrieved.

Page 6 of 6 All objects remaining in the SGs are smaller than the limiting object size for their type for at least 1-cycle of operation and remain in the SG.

c.

If the loose parts were removed from the SG?

The metallic rod discussed above found in the annulus of SG C was removed from the SG.

d.

Indications of tube damage associated with the loose parts There was no tube damage associated with these objects.

9.

Discuss the scope and results of any secondary side inspection and maintenance activities (e.g., in-bundle visual inspections, feed ring inspections, sludge lancing, assessing deposit loading, etc).

Secondary side visual inspections at the tubesheet elevation included the annulus, blown down lane &

selected in-bundle tube locations. Visual inspections have been completed in SG B and SG C. The inspections in SG A have not yet started.

The SGs are relatively clean without significant deposit. Minor erosion was noted on the first of five tube lane blocking devices in SG B and SG C. This condition has been reported in prior outages and is being monitored each outage.

Sludge lancing is complete in SG B & C, is in-progress in SG A. 35 lbs of deposits were removed from SG B and 15 lbs of sludge have been removed from SG C. These weights do not include the filter that is weighed when all SGs have been sludge lanced.

10.

Discuss any unexpected or unusual results.

There are no unexpected or unusual resulted encountered.

11.

Provide the schedule for steam generator-related activities during the remainder of the current outage.

Complete primary and secondary inspection programs, remediate tubes as required (plug or sleeve), and install manway/inspection port covers.

A de-plugging program is planned for this outage. Tubes that were previously plugged for axial and circumferential cracks at the tubesheet expansion transition will be de-plugged and a tubesheet sleeve will be installed to return the tubes to service. Following plug removal and prior to sleeving, a baseline eddy current inspection of the entire tube will be performed using qualified techniques for the applicable existing and potential degradation mechanisms. The de-plugged tubes will be sleeved, as required, upon acceptable eddy current results of the entire tube. Tubes with TSP degradation may be de-plugged, inspected, or returned to service under GL 95-05.

There were 17 previously plugged tubes in SG A that are being returned to service following successful baseline eddy current inspections.