ML20349A326

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(Vcsns), Unit 1 - Response to NRC Request for Additional Information Regarding RF-24 Steam Generator Tube Inspection Report
ML20349A326
Person / Time
Site: Summer South Carolina Electric & Gas Company icon.png
Issue date: 12/14/2020
From: Lippard G
Dominion Energy South Carolina
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
20-409
Download: ML20349A326 (5)


Text

V.C. Summer Nuclear Station Bradham Blvd & Hwy 215, Jenkinsville, SC 29065

~ Dominion Mailin g Address: ~ Energy P.O. Box 88, Jenki n sville, SC 29065 Dominion Energy. co m December 14, 2020 Document Control Desk Serial No.20-409 U.S. Nuclear Regulatory Commission VCS UC/BAB/Rev 0 Washington, DC 20555 Docket No. 50-395 License No. NPF-12 DOMINION ENERGY SOUTH CAROLINA (DESC)

VIRGIL C. SUMMER NUCLEAR STATION (VCSNS) UNIT 1 RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING RF-24 STEAM GENERATOR TUBE INSPECTION REPORT References : 1. DESC Letter, "Special Report (SPR) 2019-002 - Steam Generator Tube Inspection Report," dated May 14, 2019 (ADAMS Accession No. ML19134A372)

2. E-mail from NRC Senior Project Manager, Vaughn Thomas, "Summer, Unit 1-Final RAls for the SG Tube Inspection Report Review," dated November 16, 2020 (ADAMS Accession No. ML20321A211)

In Reference 1, DESC submitted a Technical Specification required report related to steam generator inspections performed during the Virgil C. Summer Unit 1 Twenty-Fourth Refueling Outage. In Reference 2, the NRC Staff provided a request for additional information (RAI) regarding this report. The enclosure to this letter provides the DESC responses to the RAI.

If you have any questions or require additional information, please contact Mr. Michael Moore at (803) 345-4752.

Sincerely, ~

~~pard Site Vice President V.C . Summer Nuclear Station Commitments contained in this letter: None

Enclosure:

Response to NRC Request for Additional Information cc: G. J. Lindamood - Santee Cooper L. Dudes - NRC Region II V. Thomas - NRC Project Mgr.

NRC Resident Inspector

Serial No.20-409 Docket No.: 50-395 Enclosure Response to NRC Request for Additional Information Virgil C. Summer Nuclear Station (VCSNS) Unit 1 Dominion Energy South Carolina, Inc. (DESC)

Serial No.20-409 Docket No.: 50-395 Enclosure - RAI Response: Page 1 of 3 DESC RESPONSE TO NRC REQUEST FOR ADDITIONAL INFORMATION REGARDING VCSNS Unit 1 RF-24 STEAM GENERATOR TUBE INSPECTION REPORT NRC Request for Additional Information:

1. Please discuss if there were any anomalies noted during the primary side visual inspections performed on each SG.
2. The NRG staff has the following questions regarding the secondary side inspections performed on each SG;
a. Please discuss if there were any anomalies noted during the secondary side inspections performed on each SG.
b. Section 3.4, "Foreign Object Wear," of the fa/12018 SG tube inspection report states that two foreign object wear indications were identified in tubes Row 25, Column 72 (R25C72) and R11 0C77 in SG A, and two foreign object wear indications were identified in tubes R91C88 and R92C87 in SG B. Please discuss whether the foreign objects were still present at the time of the inspection and if they were removed from the SGs.
c. Section 6.0, "Tubes Plugged during the Inspection Outage," of the fa/12018 SG tube inspection report states that a total of 10 tubes were plugged; 3 plugged due to foreign object wear and 7 plugged due to possible loose parts (PLPs). Please confirm whether the PLPs were newly identified during RFO24, how many total PLPs there were in the seven tubes, and describe any additional actions taken to further evaluate these PLPs.

DESC Response to RAI 1:

As noted in the RF-24 Condition Monitoring and Final Operational Assessment, in response to NSAL 12-1, Revision 1, the visual inspection of the SG channel head bowl included inspections of the entire channel head internal surfaces; specifically the entire tubesheet, cladding, divider plate, and associated welds/components. This visual inspection confirmed that the channel head bowl in each SG was in satisfactory condition and identified no signs of degradation, rust, deformation, or abnormal conditions.

DESC Response to RAI 2a:

As noted in Special Report (SPR) 2019-002 - Steam Generator Tube Inspection Report, secondary side inspections were performed during RF-24 for the top of the tubesheet, top support plate, and stream drum in all three steam generators. Inspection results from the RF-24 Condition Monitoring and Final Operational Assessment are discussed below.

Top of the Tubesheet (TTS)

Post sludge lancing TTS visual inspections included inspections performed from the periphery (annulus between the tube bundle and shroud ID) and the no-tube lane.

Additionally, inner bundle passes were performed across both the hot leg and cold legs to pass through the kidney region of each steam generator. Other than the foreign object

Serial No.20-409 Docket No.: 50-395 Enclosure - RAI Response: Page 2 of 3 related findings discussed below, no abnormal conditions were identified during the TTS inspections.

Top (9th ) Tube Support Plate (TSP)

Visual inspections of the top (9 th ) TSP along the no-tube lane region were performed in each SG. The inspections focused on the general condition of the TSP including the general condition of sludge/fouling of the no-tube lane, TSP ligaments, and low row U-bends. The inspection also covered webbing or bridging between the tubes/broaches, tube-to-tube bridging and blocked/partially blocked flow/broached holes. Inner bundle passes (hot leg and cold leg), at right angles to the 9th support no-tube lane, were also performed to the extent possible. These visual inspections identified no conditions adverse to quality, with the exception of heavy deposit formations. Tube denting was identified in SG Cat the 09H Top Support Plate which could be related to the heavy deposit formation.

The deposit accumulation identified in RF-24 (Fall 2018) was one of the drivers for the SG chemical cleaning performed in RF-25 (Spring 2020).

Steam Drum All steam drum components including the feedring and associated spray-nozzles (spray cans), various manways/access hatches, primary and secondary separators, sludge collectors, level tap nozzles, ladders, and attachments were inspected in each SG during RF-24. Additionally, the outlet nozzle flow limiting venturi was also inspected in SG A.

The purpose of these inspections was to identify evidence of corrosion, erosion, chemical deposition, foreign material, or other degradation, and conditions not commensurate with design. No conditions adverse to quality were identified. However, foreign material was found inside the feedring spray-nozzles (spray cans) in each steam generator. Foreign material determined to be a threat to tube integrity was removed from the feedrings and spray-nozzles.

DESC Response to RAI 2b:

The RF-24 (Fall 2018) steam generator inspections found no foreign objects present at the foreign object wear locations in SG A at tube R25-C72, SG Bat tube R91-C88, and SG Bat tube R92-C87. Gasket material and a round sludge ball were identified at the wear location in SG A at tube R 11 0-C77. The gasket material was identified to be stuck in the tube broach on one end at tube R110-C77 with the other end elevated between (and touching) tubes R109-C78 and R108-C77. As such, tubes R110-C77, R108-C77, and R109-C78 were preventively plugged. During RF-25 (Spring 2020), the gasket material was visually confirmed at the same as-left location from RF-24. The sludge ball could not be removed in RF-24 but was considered loose or free to move and not a threat to tube integrity.

DESC Response to RAI 2c:

From the RF-24 Condition Monitoring and Final Operational Assessment, there were seven (7) tubes plugged due to PLPs. Five (5) of these tubes had new PLP single indications whose locations were not accessible by secondary side inspection/foreign object search and retrieval (SSI/FOSAR). These indications were at locations on the

Serial No.20-409 Docket No.: 50-395 Enclosure - RAI Response: Page 3 of 3 01 C or 01 H Tube Support Plate that do not have inspection ports. Although these five locations could not be visually inspected, based on the locations, it is surmised that the single PLP indications in SG A at tube R111-C62 and tube R113-C62 are for the same foreign object. This is also the case for the PLP indications in SG C at tube R11 0-C91 and tube R 111-C92. The final tube plugged due to inaccessible PLPs at the 01 C or 01 H Tube Support Plate was in SG A at tube R95-C34. The remaining two (2) PLPs were associated with confirmed foreign objects that could not be removed (a piece of flexitallic gasket and a sludge ball located on the hot leg side of the baffle plate). Tubes R 108-C77 and R109-C78 (along with tube R110-C77 which was plugged due to loose part wear) were plugged to bound the piece of flexitallic gasket.

The RF-24 Condition Monitoring and Final Operational Assessment determined that with the exception of the flexitallic gasket and sludge ball in SG A at tube R11 0-C77, no known loose foreign objects were returned to service in RF-24. The Condition Monitoring and Final Operational Assessment concluded the following with regard to foreign objects:

- The foreign object wear indications observed during RF-24 did not exceed the condition monitoring limits.

- Reasonable assurance is provided that the foreign objects being returned to service at RF-24 should not experience foreign object wear to the point of violating structural and/or leakage integrity.

- Reasonable assurance is provided that any potential foreign objects that could enter the steam generators over cycles 25, 26, and 27, should not experience foreign object wear to the point of violating structural and/or leakage integrity.

It should be noted that no new foreign object wear indications were identified in RF-25.

Foreign object wear was detected in SG B; however, this was a repeat wear indication with no increase in depth, which was expected since no part was found at the affected tube location during RF-24.