ML16298A388
| ML16298A388 | |
| Person / Time | |
|---|---|
| Site: | North Anna  |
| Issue date: | 10/19/2016 |
| From: | Gerald Bichof Virginia Electric & Power Co (VEPCO) |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| 16-248A | |
| Download: ML16298A388 (7) | |
Text
VIRGINIA ELECTRIC AND POWER COMPANY RICHMOND, VIRGINIA 2326I October 19, 2016 U.S. Nuclear Regulatory Commission Attention: Document Control Desk Washington, D.C. 20555 VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
NORTH ANNA POWER STATION UNIT 2 Serial No.
16-248A NAPS/JHL Docket No.
50-339 License No.
NPF-7 RESPONSE TO STEAM GENERATOR TUBE INSPECTION REPORT REQUEST FOR ADDITIONAL INFORMATION Dominion letter dated July 12, 2016 (Serial No.16-248) submitted information summarizing the results of the spring 2016 steam generator tube inspections for North Anna Unit No. 2.
In an email dated September 20, 2016, the Nuclear Regulatory Commission (NRC) transmitted a request for additional information (RAI) related to the North Anna Unit 2 steam generator tube inspections. The Dominion response to the RAI is provided in the Attachment.
If you have any questions or require additional information, please contact Mr. Donald R. Taylor at (540) 894-2100.
Very truly yours, I
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/1dtiJ~
Gerald T. Bischof Site Vice President Attachment Commitments made in this letter: None
cc:
U.S. Nuclear Regulatory Commission Region II Marquis One Tower 245 Peachtree Center Avenue, NE Suite 1200 Atlanta, Georgia 30303-1257 NRC Senior Resident Inspector North Anna Power Station Dr. V. Sreenivas NRC Project Manager U. S. Nuclear Regulatory Commission One White Flint North Mail Stop 08 G9A 11555 Rockville Pike Rockville, Maryland 20852 Serial No. 16-248A Docket No. 50-339 SG Tube Inspection Report RAI Response
ATTACHMENT Serial No. 16-248A Docket No. 50-339 SG Tube Inspection Report RAJ Response NORTH ANNA UNIT 2 RESPONSE TO STEAM GENERATOR TUBE INSPECTION REPORT REQUEST FOR ADDITIONAL INFORMATION VIRGINIA ELECTRIC AND POWER COMPANY (DOMINION)
NORTH ANNA POWER STATION UNIT 2
I
RAI 1
Serial No. 16-248A Docket No. 50-339 SG Tube Inspection Report RAI Response RESPONSE TO STEAM GENERATOR TUBE INSPECTION REPORT REQUEST FOR ADDITIONAL INFORMATION Please discuss the scope and results of the channel head video examinations.
Dominion Response Scope:
Perform video examination of both channel heads (as-found I as-left), specifically inspections identified in Nuclear Safety Advisory Letter (NSAL) 12-1 including the divider plate I tubesheet interface, drain tubes, and previously installed plugs.
Westinghouse issued NSAL-12-1 regarding Steam Generator Channel Head Degradation. The recom~_en~e-9 ~ction i§> tQ_ p_erforn:i_ a _yi§!J?.1 _§ca11_ of_bo~h !JoJ a_nQ ~old _
legs of the inside surface of the channel head during the next scheduled opening of the primary manways for each steam generator (SG). Key areas of inspection shall include the channel head cladding, the divider plate-to-channel head weld and the weld at the top of the channel head bowl drain tube. The inspection shall look for evidence of gross defects such as indications in welds, missing weld filler material, a breach of the weld metal, unusual discoloration of the weld metal, dings or gouges, etc.
Results:
SG "A" had two previously installed plugs (1 tube) and SG "C" had ten previously*
installed plugs (5 tubes).
All twelve of the previously installed plugs were visually examined to confirm that the plugs were still present and that there were no signs of excessive boric acid build up indicative of leaking plugs.
All of the plug visual examination results were satisfactory.
A video camera visual examination in accordance with the requirements of NSAL-12-1 was conducted on SG "A" and "C" which were the only steam generators with open primary manways during End of Cycle (EOC) 24.
The dry-bowl visual examination found no evidence of gross defects such as indications in welds, missing weld filler material, a breach of the weld metal, unusual discoloration of the weld metal, dings or gouges, etc.
I RAl2 Serial No. 16-248A.
Docket No. 50-339 SG Tube Inspection Report RAI Response Please discuss the results of the secondary side inspections.
Dominion Response The internal feedring I J-nozzle interfaces of all 35 J-nozzles in SG "A" and 6 J-nozzles in "C" were visually examined. All J-nozzles were confirmed to be present and intact.
The video record for each J-nozzle was reviewed and no evidence of flow assisted corrosion (FAC) was identified.
In addition, the internal feedring I J-nozzle interfaces of all 35 J-nozzles in SG "A" were
. ultrasonically examined (UT) with no evidence of degradation. The internal feedwater header pipe was also ultrasonically examined in several areas in both SG "A" and "C".
Eddy current examinations did not identify any possible loose parts (PLP) at the top of the tubesheets in SG "A" and "C". Therefore, top of tubesheet visual examinations were not performed in either of the two (A and C) steam generators inspected during this outage. One foreign object was identified by eddy current at the third tube support plate on the cold leg of SG "C". This location was not accessible by the foreign object search and retrieval (FOSAR). The possible loose part was left in place and two tubes were plugged and stabilized at this tube location.
Ultrasonic Test (UT) inspections performed on the Unit 2 "B" SG feedring during the last outage (2R23) identified localized exterior erosion on the side of the feedring thermal sleeve below the discharge of nozzle #35, with a minimum measured wall thickness of 0.291 ". The localized erosion has been evaluated to justify continued operation until this outage (2R24). The eroded region was successfully repaired during the current outage (2R24) with a weld overlay to build up the wall thickness.
Please provide the location and sizes of the eight new dents reported in steam
- generator (SG) A. Also, please provide any insight you have into the cause of these new service induced indications.
Dominion Response No indications of degradation were detected in SG "A", although 8 new dents were reported in 7 tubes with 5 new dents occurring at anti-vibration bar (AVB) #1. The new
- dents were scattered throughout the bundle rather than clustered near each other. All of the new dents ranged from 2.0 to 2.4 volts, were examined with a rotating probe, and showed no signs of degradation.
1 1
I Serial No. 16-248A Docket No. 50-339 SG Tube Inspection Report RAI Response Additionally, 39 and 31 historical dents were observed again in SG A and SG C respectively. The historical dents range from 1.5 to 12.1 volts with an average of 2.9 volts. We have no insight as to the cause(s) of the new or existing service induced indications.
New Dents SG Row Col Volts Phase Indication Location A
16 25 2.19 189 ONT AV5+7.05" A
25 44 2.00 185 ONT AV1-0.05" A
25 44 2.07 183 ONT AV6-0.05" A
31 51 2.08 178 ONT 04C+0.35" A
36 19 2.00 187 ONT AV1-0.13" A
39 23 2.13 184 ONT AV1-0.08" A
39 50 2.39 186 ONT AV1-0.03" A
43 55 2.11 184 ONT AV1-0.08" RAl4 The circumferential extent (i.e., arc length) of the two wear indications in SG C, created by contact with tube support plates (TSP) were listed as 49 degrees and 42 degrees.
Please provide the arc lengths of the TSP lands. If the tube wear indications have arc lengths larger than the TSP lands, please discuss and insights.
Dominion Response The TSP land dimensions are proprietary to the SG design vendor and are not available. We have reviewed the NOE signals and have concluded that the TSP wear indications are contained within the contact land dimension within the accuracy of the NOE technique.
The NOE techniques systematically oversize the indication and TSP land lengths because the probe sees the indication or TSP land before it actually is on top of it (look ahead) and after (look behind) it has past the indication or TSP land.
RAIS The arc length of the foreign object wear indication in SG C was listed as 56 degrees.
Please provide the arc length of the broached opening in this TSP and discuss how the arc length of the TSP broached opening compares to the size of the foreign object wear indication.
Dominion Response The broached opening dimensions are proprietary to the SG design vendor and are not available.
' 1 1
I ii Serial No. 16-248A Docket No. 50-339 SG Tube Inspection Report RAI Response We have reviewed the NOE signals and have concluded that the foreign object wear indication is contained within the broached opening within the accuracy of the NOE technique.
The NOE techniques systematically oversize the flaw and TSP land lengths and undersize the broached opening dimension because the probe sees the indication or TSP land bef9re it actually is on top of it (look ahead) and after (look behind) it has past the indication 'or TSP land.