ML20345A368

Review of the Fall 2017 and Spring 2019 Steam Generator Tube Inspection Reports

ML20345A368
Person / Time
Site:	Millstone
Issue date:	12/16/2020
From:	Richard Guzman NRC/NRR/DORL/LPL1
To:	Stoddard D Dominion Energy Nuclear Connecticut
Guzman R
References
EPID L-2019-LRO-0106, EPID L-2020-LRO-0050
Download: ML20345A368 (4)

Text

December 16, 2020 Mr. Daniel G. Stoddard Senior Vice President and Chief Nuclear Officer Dominion Nuclear Innsbrook Technical Center 5000 Dominion Blvd.

Glen Allen, VA 23060-6711

SUBJECT:

MILLSTONE POWER STATION, UNIT NO. 3 - REVIEW OF THE FALL 2018 AND SPRING 2019 STEAM GENERATOR TUBE INSPECTION REPORTS (EPID L-2020-LRO-0050 AND EPID L-2019-LRO-0106)

Dear Mr. Stoddard:

By letters dated April 19, 2018 and September 19, 2019 (Agencywide Documents Access and Management System Accession Nos. ML18114A105 and ML19275D254, respectively),

Dominion Energy Nuclear Connecticut, Inc. (the licensee) submitted information to the U.S. Nuclear Regulatory Commission (NRC) summarizing the results of the fall 2017 and spring 2019 steam generator tube inspections that were performed at Millstone Power Station, Unit No. 3 (Millstone 3). These inspections were performed during the Millstone 3 Refueling Outages 18 and 19, respectively.

The NRC staff has completed its review of these reports and concludes that the licensee provided the information required by the Millstone 3 Technical Specifications. No additional follow-up is required at this time. The NRC staffs review is enclosed.

If you have any questions concerning this matter, please contact me at (301) 415-1030 or by e-mail to Richard.Guzman@nrc.gov.

Sincerely,

/RA/

Richard V. Guzman, Senior Project Manager Plant Licensing Branch I Division of Operating Reactor Licensing Office of Nuclear Reactor Regulation Docket No. 50-423

Enclosures:

1. Review of the Fall 2017 Steam Generator Tube Inspection Report

2. Review of the Spring 2019 Steam Generator Tube Inspection Report cc: Listserv

STAFF ASSESSMENT BY THE OFFICE OF NUCLEAR REACTOR REGULATION REVIEW OF THE FALL 2017 STEAM GENERATOR TUBE INSPECTION REPORT DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION, UNIT NO. 3 DOCKET NO. 50-423 By letter dated April 19, 2018 (Agencywide Documents Access and Management System Accession No. ML18114A105), Dominion Energy Nuclear Connecticut, Inc. (the licensee) submitted information summarizing the results of the fall 2017 steam generator (SG) tube inspections that were performed at Millstone Power Station, Unit No. 3 (Millstone 3), during Refueling Outage 18.

Millstone 3 has four Westinghouse Model F steam generators, each of which contains 5,626 thermally treated Alloy 600 tubes. Each tube has a nominal outside diameter of 0.688 inches and a nominal wall thickness of 0.040 inches. During SG fabrication, the tubes were hydraulically expanded at both ends over the full depth of the 21.23-inch thick tubesheet.

The tubesheet was drilled on a square pitch with 0.98-inch spacing. There are 59 rows and 122 columns in each SG. The radius of the row 1 U-bends is 2.20 inches. The U-bends in rows 1 through 10 were stress-relieved after being formed. Eight Type 405 stainless steel tube support plates, which have broached quatrefoil holes, support the vertical section of the tubes, and six anti-vibration bars (AVBs) support the U-bend section of the tubes.

The licensee provided the scope, extent, methods, and results of the SG tube inspections in its April 19, 2018, letter. In addition, the licensee described corrective actions (e.g., tube plugging) if any were taken in response to the inspection findings.

After reviewing the information provided by the licensee, the staff has the following comments and observations:

The licensee performed secondary side inspections in all four SGs, including sludge lancing and foreign object search and retrieval inspections. In SG D only, inspections of the upper internals included the steam drum, moisture separators, drain systems, upper bundle and AVB inspections, internal inspections of the feedring for flow-accelerated corrosion, and visual inspections of the upper tube support plates to assess cleanliness.

The licensee reported that all secondary side inspections performed were satisfactory and no degradation was detected.

Two tubes were reported plugged - one for foreign object wear and one for AVB wear.

No stress corrosion cracking was reported.

Based on a review of the information provided, the staff concludes that the licensee provided the information required by its technical specifications. In addition, the staff concludes that there are no technical issues that warrant follow-up action currently, since the inspections appear to be consistent with the objective of detecting potential tube degradation, and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.

STAFF ASSESSMENT BY THE OFFICE OF NUCLEAR REACTOR REGULATION REVIEW OF THE SPRING 2019 STEAM GENERATOR TUBE INSPECTION REPORT DOMINION ENERGY NUCLEAR CONNECTICUT, INC.

MILLSTONE POWER STATION, UNIT NO. 3 DOCKET NO. 50-423 By letter dated September 19, 2019 (Agencywide Documents Access and Management System Accession No. ML19275D254), Dominion Energy Nuclear Connecticut, Inc. (the licensee) submitted information summarizing the results of the spring 2019 steam generator (SG) tube inspections that were performed at Millstone Power Station, Unit No. 3 (Millstone 3), during Refueling Outage 19.

Millstone 3 has four Westinghouse Model F steam generators, each of which contains 5,626 thermally treated Alloy 600 tubes. Each tube has a nominal outside diameter of 0.688 inches and a nominal wall thickness of 0.040 inches. During SG fabrication, the tubes were hydraulically expanded at both ends over the full depth of the 21.23-inch thick tubesheet.

The tubesheet was drilled on a square pitch with 0.98-inch spacing. There are 59 rows and 122 columns in each SG. The radius of the row 1 U-bends is 2.20 inches. The U-bends in rows 1 through 10 were stress-relieved after being formed. Eight Type 405 stainless steel tube support plates (TSPs), which have broached quatrefoil holes, support the vertical section of the tubes, and six anti-vibration bars (AVBs) support the U-bend section of the tubes.

The licensee provided the scope, extent, methods, and results of the SG tube inspections in its September 19, 2019, letter. In addition, the licensee described corrective actions (e.g., tube plugging) if any were taken in response to the inspection findings.

After reviewing the information provided by the licensee, the staff has the following comments/observations:

The licensee performed secondary side inspections in all four SGs, including sludge lancing and foreign object search and retrieval inspections. In SG C only, inspections of the upper internals included the steam drum, moisture separators, drain systems, upper bundle and AVB inspections, internal inspections of the feedring for flow-accelerated corrosion, and visual inspections of the upper TSPs to assess cleanliness. The licensee reported that all secondary side inspections performed were satisfactory and no degradation was detected.

No tubes were reported plugged, and no stress corrosion cracking was reported.

Based on a review of the information provided, the staff concludes that the licensee provided the information required by its technical specifications. In addition, the staff concludes that there are no technical issues that warrant follow-up action currently, since the inspections appear to be consistent with the objective of detecting potential tube degradation, and the inspection results appear to be consistent with industry operating experience at similarly designed and operated units.

ML20345A368 OFFICE NRR/DORL/LPL1/PM NRR/DORL/LPL1/LA NRR/DNRL/NCSG/BC NAME RGuzman LRonewicz SBloom DATE 12/14/2020 12/14/2020 12/10/2020 OFFICE NRR/DORL/LPL1/BC NRR/DORL/LPL1/LA NAME JDanna RGuzman DATE 12/16/2020 12/16/2020