ML22040A101
| ML22040A101 | |
| Person / Time | |
|---|---|
| Site: | Surry  |
| Issue date: | 02/09/2021 |
| From: | Mladen F Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 22-015A | |
| Download: ML22040A101 (11) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 23261 f EB O 9 2022 United States Nuclear Regulatory Commission Attention: Document Control Desk Washington, DC 20555-0001 VIRGINIA ELECTRIC AND POWER COMPANY SURRY POWER STATION UNIT 1 Serial No.:
SPS LIC/MMT Docket No.:
License No.:
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION 2021 STEAM GENERATOR INSERVICE INSPECTION REPORT 22-015A RO 50-280 DPR-32 By letter dated August 27, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21243A313), Virginia Electric and Power Company (Dominion Energy Virginia) submitted information summarizing the results of steam generator (SG) tube inspections performed at Surry Power Station Unit 1 during the spring 2021 refueling outage.
On January 11, 2022, the NRC requested additional information related to the SG inspections. The NRC's questions and Dominion Energy Virginia's responses are provided in the attachment to this letter.
If you have any questions or require additional information, please contact Mr. Michael True at (757) 365-2446.
Respectfully, Fred Mladen Site Vice President Surry Power Station Attachment -
Response to NRC Request for Additional Information Regarding Spring 2021 Steam Generator Tube Inspection Report - Surry Power Station Unit 1 Commitments made in this letter: None
cc:
U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Ave., NE Suite 1200 Atlanta, Georgia 30303 Mr. John J. Klos - Surry NRG Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, Maryland 20852 Mr. G. Edward Miller - North Anna NRG Sr. Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 09 E-3 11555 Rockville Pike Rockville, Maryland 20852 NRG Senior Resident Inspector Surry Power Station Mr. R. R. Richardson Authorized Nuclear Inspector Surry Power Station Serial No.: 22-015A Docket No.: 50-280 Page 2 of 2
ATTACHMENT Serial No.: 22-015A Docket No.: 50-280 Response to NRC Request for Additional Information Regarding Spring 2021 Steam Generator Tube Inspection Report Surry Power Station Unit 1 Virginia Electric and Power Company (Dominion Energy Virginia)
Serial No.: 22-01 SA Docket No.: 50-280 Attachment RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING SURRY UNIT 1 SPRING 2021 STEAM GENERATOR TUBE INSPECTIONS NRC Comment By letter dated August 27, 2021 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML21243A313), Virginia Electric and Power Company (the licensee) submitted information summarizing the results of the spring 2021 steam generator (SG) tube inspections performed at Surry Power Station (Surry), Unit 1. These inspections were performed during refueling outage (RFO) 30.
Title 10 of the Code of Federal Regulations Part 50.36 establishes the requirements for pressurized water reactors to have technical specifications (TS) which include a SG program with specific criteria for the structural and leakage integrity, repair, and inspection of SG tubes.
Specifically, Surry's Technical Specification (TS) 6. 6.A. 3 requires that a report be submitted within 180 days after Tavg exceeds 200°F following completion of an inspection of the SGs performed in accordance with TS 6.4.Q, "Steam Generator (SG) Program."
Additionally, these requests for additional information (RAls) were discussed with your staff and it was determined that a clarification call was not required for these RAls.
To complete its review of the inspection report, the U.S. Nuclear Regulatory Commission staff requests the following additional information. This request is now released formally with a 30 day calendar response period,* thereby, these RAls are due on February 10, 2022.
- 1) Please identify any differences compared to the RFO 29 (Fall 2019) inspections in the sampling strategy for eddy current examination of locations such as tube support plate (TSP) intersections, freespan dings, and bulges. The RFO 29 sampling strategy was described in the request for additional information response dated June 23, 2020 (ADAMS Accession No. ML20181A308). As part of the response, please provide the definitions for dents and dings applied to Surry Unit 1 SG inspections.
Response
Previous steam generator tube inspections at Surry Power Station employed a sampling approach, whereas 100% of the tubes were inspected in one or two steam generators each outage, alternating the steam generator(s) selected such that each steam generator was inspected every other refuel. During the Spring 2021 refueling outage, 100% of the tubes in all three steam generators were inspected.
Page 1 of 8
Serial No.: 22-015A Docket No.: 50-280 Attachment Identical to the 1 R29 inspection, the in-service tube base scope included a 100% bobbin probe exam, 100% array probe exam of the top-of-tubesheet on both the hot-leg and cold-leg (including all overexpansions within the tubesheet down to the H* distance),
100% full length array probe of all "Tier 1" tubes identified with potentially high residual stress, and a +Point' exam of all over rolls, bulges, and low row (row 1 and 2) U-bends.
In addition to the base scope, a preplanned special interest scope was developed for both the 1 R29 inspection and the 1 R30 inspection, which includes a sample of previously identified dents, dings, manufacturing burnish marks, volumetric indications, and wear (excluding AVB wear).
The only departure from the 1 R29 preplanned special interest strategy and the preplanned 1 R30 special interest scope was the sample plan for the inspection of dents/dings.
As a result of concerns for possible degradation at dent/ding locations, the special interest scope of dents/dings with a +Point' probe was increased significantly.
The specific dent/ding scope performed during the 1 R29 inspection included fifty percent of previously identified dents/dings >2 Volts located in hot-leg straight sections (TSH+0.00 to 07H+1.00"), plus any additional indications required to ensure that the five largest voltage dents/dings in hot-leg straight sections are included in the sample. Also, the five largest voltage dents/dings located between the cold-leg tubesheet and the straight section of the hot-leg, (between TSC+0.00 and 07H+1.01 ") were included in the preplanned scope.
The specific dent/ding scope performed during the 1 R30 inspection included 100% of all dents/dings;:: 2 Volts located in the hot leg straight section and 100% of all dents/dings 2::
5 Volts in the U-bend and cold-leg sections of the tubes.
It should be noted that both terms Dent and Ding refer to a plastic deformation of the tube that results in a reduction in the tube diameter.
The two different terms were used to differentiate between the location of the signal.
Historically (early generation designs) the term dent referred to local tube diameter reductions due to corrosion products from carbon steel (typically, drilled carbon steel tube support plates). The term ding referred to local tube diameter reductions due to mechanical means (manufacturing, vibration, incidents during maintenance activities, or impact from foreign objects). Since the eddy current signals from both dents and dings are similar, the location of the indication was used to differentiate which term was used (dent for indications at supports and ding for all free span indications).
At Surry Power Station, the referenced dent signals do not represent the same phenomena as classical denting on older generation units caused by drilled carbon steel support plate corrosion damage.
Since the Surry units are not similar in design (i.e.,
quatrefoil stainless steel tube support plate design vs. drilled hole carbon steel tube support plate design) these same "denting" issues do not directly apply to the Surry units.
Tube support plate areas are not susceptible to denting caused by corrosion of the tube support plates.
However, the historical nomenclature assigned to these signals has existed in the database since the steam generators were installed and has remained unchanged since that time.
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Serial No.: 22-015A Docket No.: 50-280 Attachment In addition to the preplanned scope, if indications are detected during the examination such as deposits, possible loose parts signals, and ambiguous or anomalous indications, which require additional categorization with diagnostic techniques, these indications are examined with a +Point' probe.
The total special interest scope examined with a
+Point' probe in 1 R30 was 1,694 locations.
- 2) With respect to the stress corrosion crack indication in SG C, a) Was the indication located in an anomaly, such as an over-expansion?
b) Discuss the relative performance of the array probe and the +Point probe at the crack location, including the results of any lookbacks from previous inspections for the location with the crack indication.
Response
The indication of circumferential Primary Water Stress Corrosion Cracking (PWSCC) within the Hot-Leg Tubesheet (TSH -0.34 inches) was located adjacent to a historical Single Circumferential Anomaly (SCA). The eddy current signal from the SCA extends upwards from the Top-of-Tubesheet (TTS) and the PWSCC indication is slightly below the TTS. The +Point' examination on this location of the tube was performed as part of the preplanned special interest scope because of the historical SCA.
The PWSCC indication was not detected by the 100% TTS array probe examination which includes both auto-analysis and manual analysis in a dual analysis process.
A reevaluation of previous eddy current data (i.e., historical or look-back evaluation) using the benefit of hindsight was performed. The array probe signal is very small and in the extreme OD plane (172 degrees) beyond the threshold of reportability for either the manual or auto-analysis processes. The depth measurements obtained from the look-back evaluation of the +Point' data concluded that depth of the indication remained relatively unchanged from the 1 R26 (Spring 2015) and 1 R28 (Spring 2018) inspections. A diminished discontinuity response can be traced back as far as the 1 R23 (Fall 2010) inspection.
- 3) With respect to the secondary-side inspections, please clarify for each SG whether foreign objects or loose parts were removed, and the number and type of objects removed. In addition, please describe any foreign objects or loose parts known to remain in the SGs.
Response
During the 1 R29 outage an enhanced tubesheet cleaning process was performed in all three steam generators to remove as much debris and as many legacy foreign objects as possible and to gain an accurate accounting of all un-retrievable foreign objects Page 3 of 8
Serial No.: 22-01 SA Docket No.: 50-280 Attachment remaining. The as-left condition also provided a known baseline to positively identify any new foreign object intrusion during future operational cycles.
The foreign objects identified in Table 1 below include all foreign objects removed during the 1 R30 FOSAR and water lancing activities and the foreign objects known to be remaining at the conclusion of 1 R30.
Page 4 of 8
Table 1: 1 R30 Foreign Objects SG-ECT Estimated Item#
Description Location Configuration Results Size R6-C69 R7-C68 Legacy metal disk lodged between Historical (1 R20)
R7-C69 tubes R6-C69 and R7-C69. The 1.1" diameter A-1 Metal disk disk is sitting on its edge and is NOD 0.2"thick fused to the top of the C/L TSC +0.24" to tubesheet.
+1.24" Historical (1R21) mass of fine wire R30-C47 Legacy mass of fine wire and Not A-2 and sludge at R30-C48 sludge located at TSH located NOD Determined TSH behind the center stay rod A-3 (1R29) Irregular R36-C73 Irregular shaped object discovered NOD
~0.4" diameter object at TSH R37-C73 at TSH during 1 R29 post lance SSI (1R30) Disk shaped object R25-C82 Disked shaped object discovered A-4 discovered and R24--C82 at TSH during 1 R30 post lance SSI NOD 0.35" Diameter removed (1R30) Flat R44-C44 A-5 shaped object R44--C45 Flat shaped object discovered at NOD 0.30 X 0.30" X discovered and TSH during 1 R30 post lance SSI 0.10" removed
( 1 R30) Lancing Parts captured in the lancing Various parts A-6 strainer parts TTS strainers during 1 R30 TTS lancing NIA ranging from
~118" to ~112" Page 5 of 8 Fixity Fixed Fixed Fixed Retrieved during 1R30 Retrieved during R30 Retrieved during 1 R30 Serial No.: 22-015A Docket No.: 50-280 Attachment 2021 Disposition Initially identified 1R20. Evaluated in 2009 (1 R22) with Framatome CR 2009-2529.
Object has remained fixed since that time.
Position and fixity again confirmed during 1 R30. Object has not caused tube degradation. Leave as is and monitor during future visual and eddy current inspections.
During 1 R29. a small pile of legacy fine wires embedded in fixed sludge was aggressively raked and water lanced. During 1 R30, configuration confirmed by SSI. Wires pose no threat to tube integrity (since 2007).
Leave as is and monitor by ECT and SSI at next ISi.
Irregular object identified during 1 R29 Post Lance. Object is tightly lodged in place between two tubes. ECT history shows object present back to 2006. 1 R30 ECT was NOD. Leave as is and continue to monitor by ECT and SSI at next ISi.
During 1 R30. a disk-shaped object was discovered and subsequently removed. ECT PLPs changed to LPR after performing post removal ECT. Item is considered closed out and no future actions required.
During 1 R30, the flat-shaped object was discovered and subsequently removed. ECT was NOD. Item is considered closed out and no future actions required.
During 1R30, many objects were captured in the SG-A lancing strainers. Most are sludge related. There were also fragments of small diameter wire, flex gasket material. and other metallic obiects.
SG-ECT Item#
Description Location Configuration Results Historical (1R23)
Foreign object wear at 02H that Plugged tubes:
During 1R30, No signs of wear or 8-1 resulted in two R37-C22 PLPs on bounding tubes at 02H NDD tubes being R38-C21 plugged at 1R23.
(1 R29) Lodged 8-2 round object at R40-C39 1 R29 Foreign object lodged NDD TSH. Likely hard R40-C40 between two tubes at TSH sludge.
Object appears to be part of a hex (1R30) Metallic R45-C47 8-3 Object R44-C47 nut. Discovered 1 R30 post lance NDD inspection and removed 8-4 (1 R30) Lancing TTS Parts captured in the lancing N/A strainer parts strainers during 1 R30 TTS lancing (1 R20) Historic 1 R26 Legacy FO wear at 02H.
C-1 R29-C77 @ 02H NDD FO wear at 02H Tube plugged.
(1 R20) Historic 1 R20 Legacy FO wear at 03H.
C-2 R15-C62@ 03H NDD FO wear at 03H Tube plugged.
(1 R20) Historic 1 R20 Legacy FO wear at 01 H.
C-3 R38-C62@ 01H NDD FO wear at 01 H Tube plugged.
C-4 (1 R30) Lancing TTS Parts captured in the lancing N/A strainer parts strainers during 1 R30 TTS lancing Page 6 of 8 Estimated Size Fixity Inaccessible to SSI Unknown 0.4" diameter Fixed 1.25" X 0.6" X Retrieved 0.5" during 1R30 Various parts ranging from Retrieved
-1/8" to -1/2" during 1R30 Inaccessible to Unknown SSI Inaccessible to Unknown SSI Inaccessible to Unknown SSI Various parts ranging from Retrieved
~1/8" to -1/2" during 1R30 Serial No.: 22-015A Docket No.: 50-280 Attachment 2021 Disposition Two tubes were plugged and stabilized at EOC23 for PLP and WAR indications. During subsequent outages and at 1 R30 bounding tubes showed no signs of PLPs or wear.
Continue to monitor with ECT.
Review of 1 R23, R25, and R27 ECT data confirmed object present. No wear identified.
Object is tightly lodged. During 1 R30 ECT was PLP with no wear. Continue to monitor with ECT and SSL During 1 R30, item identified during post lance ISi and removed. ECT results NDD.
Item closed out at 1 R30. Going forward no further actions required.
During 1 R30, many objects were captured in the SG-8 lancing strainers. Most are sludge related. There were also fragments of small diameter wire and flex gasket material.
During 1 R30, bounding tubes inspected by ECT. All tubes NDD. Going forward continue to monitor with ECT.
During 1 R30, bounding tubes inspected by ECT. All tubes NDD. Going forward continue to monitor with ECT.
During 1R30, bounding tubes inspected by ECT. All tubes NDD. Going forward continue to monitor with ECT.
During 1R30, many objects were captured in the SG-C lancing strainers. Most are sludge related. There were also fragments of small flex gasket material.
Serial No.: 22-015A Docket No.: 50-280 Attachment
- 4) The spring 2021 inspection revealed perforations of moisture separator riser barrels in SG C attributed to erosion. Please provide the following additional information:
a) Considering no such degradation was described in the previous inspection reports for SG B (fall 2019, fa/12016), SG C (spring 2018), or SG A (spring 2015), is this considered a new form of degradation or change in trend for previously detected degradation?
b) How is the potential for loose parts from this degradation being managed?
c) Please describe plans for future inspection of the moisture separators and other steam drum components and structures.
Response
The localized erosion of some primary moisture separator riser barrels was detected and repaired during the mid 1990's at both Surry units. Repairs were also performed on the riser barrels of Unit 2 in the Spring of 2011.
The erosion appears to be due to impingement of feedwater discharge through an adjacent J-nozzle, which would not have generated foreign objects. Riser barrel erosion is on the outer surface of the barrel, i.e.,
the internal diameter of the barrel is essentially the same as originally designed.
The riser barrel repair consists of installing impingement plates over the degraded areas on the riser barrels. The impingement plates were approximately 16x16 inches and rolled such that the plate inside diameter (ID) surface matched the outer diameter (OD) surface of the riser barrels and provide protection for all degraded areas.
Based on the site ultrasonic thickness measurements of the degraded regions, the installed impingement plates extend well beyond the scouring pattern and onto undamaged base material.
Although the riser barrels are not pressure boundary components, the addition of the impingement plates represents a change to the original design of the moisture separator riser barrels. Structural analyses have been performed to demonstrate the adequacy of the attachment welds.
The welds attaching the impingement plates are structurally adequate such that the presence of the impingement plates will not increase the potential for operation with a loose part/foreign object in the steam generator. Moisture separator and impingement plate weld integrity following replacement will be maintained during all plant conditions.
Since the degraded areas have been repaired, future inspections are described and performed in accordance with the Surry Steam Generator program.
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BPC BPH C/L ECT EFPM EOC ETSS FO GPD H/L ID ISi LPR MRPC NDD NSAL NTE OD ODSCC OVR OXP PARC PLP PWSCC SSI TEC TEH TSC TSH TSP TTS TW WAR Acronyms Baffle Plate Cold Baffle Plate Hot Cold Leq Eddy Current Testinq Effective Full Power Month End of Cycle Examination Technique Specification Sheet ForeiQn Object Gallons Per Day Hot Lei::i Inside Diameter In-Service Inspection Loose Part Removed Motorized Rotatinq Pancake Coil No Degradation Detected Nuclear Safety Advisory Letter No tube Expansion Outer Diameter Outside Diameter Stress Corrosion CrackinQ Over Roll Over Expansion Permanent alternate repair criteria Possible Loose Part Primary Water Stress Corrosion Crackinq Secondary Side Inspection Tube End Cold-leg Tube End Hot-leg Top of Tube Sheet Cold-leg Top of Tube Sheet Hot-leg Tube Support Plate Top of Tubesheet Throuqh Wall Wear Page 8 of 8 Serial No.: 22-015A Docket No.: 50-280 Attachment