ML20080U132
| ML20080U132 | |
| Person / Time | |
|---|---|
| Site: | Braidwood  |
| Issue date: | 03/08/1995 |
| From: | Kofron K COMMONWEALTH EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| BW-95-0033, BW-95-33, NUDOCS 9503140239 | |
| Download: ML20080U132 (6) | |
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" f'r:Idwood Nuclear Pow:r St: tion -
ll f. Route #1, Box 64
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v Braceville, Illinois 60407 TI.
Telephone a15(45s-2a011
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[N March 8,1995' BW/95-0033 !
U. S. Nuclear Regulatory Commission Document Control Desk
- Washington, D.C. 20555 4
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Subject:
Braidwood Station Unit I h
Cycle 5 Mid-Cycle Outage Steam Generator Inservice Inspection Report j
4 Docket No. STN 50-456 i
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References:
(1)
NUREG-1276, Tec..nical Specifications, Braidwood Station, Unit Nos. I and 2 1
1
. Specification 4.4.5.5.c of Reference (1) requires that results of steam generator (SG) tube -
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inspections which fall into Category C-3 shall be reported in a Special Report to the l-Commission pursuant to Specification 6.9.2 within thirty days and prior to resumption off plant operation. This report shall provide a description ofinvestigations conducted to
_i determine the cause of tube degradation and corrective measures taken to prevent j
L recurrence.
The results of the initial sample inspection resulted in the following SGs being classified into Category C-3 based on the number of defective tubes found this outage:
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on March 3,1995 at 09:15 hours IC on March 2,1995 at 12:30 hours ID on March 3,1995 at 19:45 hours Notification per Technical Speci3 cation Table 4.4-2 pursuant to 10 CFR 50.72(b)(2)(i) for steam generators being classified in Category C-3 was initiated.
The enclosure summarizes the inspection results. Included are the C-3 Classification totals for each SG with the current Interim Plugging Criteria (IPC) applied. Also included is a description of the investigations being performed to determine the cause of degradation and corrective actions'to prevent recurrence.
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4 e es a A 9503140239 950308
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PDR ADOCK 05000456
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BW/95-0033 March 8,1995
. Page 2 -
Please direct any questions regarding this submittal to Doug Huston, Braidwood Licensing
- Supervisor, (815) 458-2801, extension 2511.
Yours truly, f
K. L. Kofron
- Station Manager Braidwood Nuclear Station KLK/DH/dia
.:ww Enclosures Attachments cc:
S. G. DuPont, Senior Resident Inspector, Braidwood R. R. Assa, Braidwood Project Manager, NRR J. B. Martin, Regional Administrator, Region III.
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j Braidwood Station Unit 1
. Cycle 5 Mid-Cycle Ontage
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Staass Generator C-3 Report j
LOn February 23,1995, a Steam Generator (SG) Tube Inservice Inspection was initiated on i
Braidwood Unit 1 in accordance with Technical Specincstion Surveillance requirement '
(TSSR) 4.4.5.0.
-i An initial sample size of 100% of all available tubes was selected.
_ TSSR 44.5.2.c requires that the results of each sample inspection be classified into one of l
three categories. A SG will be classified in Category C-3 ifmore than 10% of the total tubes inspected are degraded or more than 1% of the inspected tubes are defective. A SG tube is considered degraded ifit has an imperfection ofgreater than or equal to 20%
l nominal tube wall thickness A SG tube is considered defective ifit has an imperfection of
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. greater than or equal to 40% nominal tube wall thickness in non-Tube Support Plate regions In the tube suppon plate regions, a tube is considered to be defective ifit q
contains an indication greater than 2.7 volts or ifit contains an indication greater than 1 volt but less than or equal to 2.7 volts and it is confirmed by rotating pancake coil (RPC) q inspection i
The results of the initial sample inspection resulted in the following SGs being classified into Category C-3 based on the following number ofdefective tubes found this outage l
1A On March 3,1995 at 09:15 hours,256 tubes out of 4335 (5.9%)
IC On March 2,1995 at 12:30 hours,319 tubes out of 4212 (7.6%)
q ID On March 3,1995 at 19:45 hours,190 tubes out of 4407 (4.3%)
7 All support plate indications greater than 1.0 volt were examined using 3-coil RPC probes.
Of these indications, 834 were confirmed by use of RPC. Since some tubes had indications at muhiple hot leg support plates, the total number of tubes effected was 815.
i Attachment A provides, by SG, the number of tubes plugged this outage as well as those plugged in prdous outages. This attachment also includes the reason why each tube was j
plugged dunni;this outage.
Technical Specification 4.4.5.5.c requires results of SG tube inspections which fall into Category C-3 to be reported in a Special Report to the Commission parsuant to Specification 6.9.2 within 30 days and prior to resumption of plant operation. This report shall provide a description ofinvestigations conducted to determine the cause of the tube degradation and corrective measures to prevent recurrence.
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INVESTIGATION OF DEGRADATION ROOT CAUSE The Interim Plugging Criteria (IPC) calls for RPC inspection of all support plate i
indications greater than I voit and less than or equal to 2.7 volts. In addition, all indications greater than 2.7 volts were inspected by RPC. Inspection results were typical of other plants having axially oriented cracks due to Outer Diameter Stress Corrosion Cracking (ODSCC) confined within the tube support plate intersections.
CORRECTIVE MEASURES TO REDUCE DEGRADATION Braidwood Station implemented the following programs to mitigate the corrosive environment in the tube support plate region which leads to ODSCC:
Industry Guidelines Compliance with the EPRI Secondary Chemistry Guidelines, Revision 3.
l SG Tube Crevice Fouling Maintain hotwell dissolved oxygen concentrations <3 ppb Use of advances amines, such as ethanolamine (ETA), for secondary pH control SG Crevice pH Braidwood implemented secondary SG Boric Acid program at the start of Cycle 5 for mitigation of SG Tube Support Plate ODSCC per EPRI Boric Acid Application Guidelines. Both low power boric acid soaks during startup and full power operation on i
boric acid chemistry was implemented.
Evaluation of SG hideout return during shutdown to assess the impact of operating chemist:y on SG crevice chemistry, and potential formation of caustic crevices which can cause Tube Support Plate ODSCC.
The molar ratio control program begun at the start of Cycle 4 will be maintained.
This program adjusts the sodium to chloride ratio in the SG by adding ammonium chloride to the condensate system.
Installed a reverse osmosis unit in the makeup water system to reduce sodium input to the secondary side.
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Performed 100% eddy current laWum on 3 out of the 4 condenser water boxes L
over the last two refuel outages. The founh condenser water box is scheduled for the refuel outage in the Fall of1995.
. SG Electrachical Fotential (ECF) Reduction Continue use of high hydrazine concentrations for maintaining reducing conditions in the SGs and passivation ofpiping systems and components.-
Braidwood does not have any copper c=panents in its feedwater or condensate systems.
Currently, Braidwood Station, in conjunction with our Corporate Chemistry Support Organization, is pursuing additional methods to funher enhance our SG corrosion control.
program They are as follows:
The addition of other amines either with ETA or in place of ETA will be evaluated to optimize the pH control and minimize iron transport.
Chemistries are being evaluated to improve iron transpon out of the SG The goal
' is to increase the efficiency ofiron removal via the_SG blowdown system.
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Attachment A A1M05 Plugging.Results l
e SG 1 A t
- SG.181
- 'SG 1 C -
,:SG 1D-eTOTALS.
TotalTubes.
4578 4578 4578 4578 18312
..;.frr?/.Plue0ed.
Tubes'
-243 58 366 171 838 T.otal Tubes 3..
Inspected This?
Outaos 4335 4520 4212 4407 17474 A1M06 Tubes.
1 Support Plesel Pluonable C 235 41 315 180
'771 NENI Vitr$tioh Bar!
.l Wear ?
2 0
1 0
3 i
t CcNirmed hedde) location l'ndisM 17 2
12 13 44
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i Top of T0besheet Circamtwencial Cracks' 4
4 0
11 0
15 MisciTop of-;
Tubeeheet Indications 1 4
1 1
1 7
l A1M06 TotalTubes
- 194 t.
840 J-Plucced
!:-282 e i44s 2:340'1 Restart. Total Tubes' Available 1 4073 4476 3872 4213 16634 Total Tubes Plugged
(%)3 11.0 2.2 15.4 8.0 9.2 1
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