ML19253C344
| ML19253C344 | |
| Person / Time | |
|---|---|
| Site: | Point Beach  |
| Issue date: | 11/16/1979 |
| From: | Trammell C Office of Nuclear Reactor Regulation |
| To: | Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 7911300602 | |
| Download: ML19253C344 (14) | |
Text
.g pnMa,o UNITED STATES NUCLEAR REGULATORY COMMISSION y
g WASHINGTON, D. C. 20555 5
- y NOV 161979 Docket No. 50-266 LICENSEE
- Wisconsin Electric Power Company FACILITY : Point Beach Nuclear Plant, Unit No.1
SUMMARY
OF MEETING HELD ON NOVEMBER 5,1979 WITH WISCONSIN ELECTRIC POWER COMPANY AND WESTINGHOUSE ELECTRIC CORPORATION TO DISCUSS RECENT INSPECTION OF STEAM GENERATOR TUBES AT POINT BEACH UNIT N0. 1 On November 5,1979, the NRC staff met with representatives of Wisconsin Electric Power Company and Westinghtne Electric Corporation (W) to discuss the results of a recent steam generator (SG) tube inspection at Point Beach Unit No. 1.
In addition, W presented the results of an examination of 3 SG tubes removed from the "A" SG. A list of attendees
~
is contained in Attachment 1.
Highlights of the meeting are summarized below.
The licensee presented a brief history of steam generator operating experience for Unit 1:
1971 - Initial operation on phosphate chemistry control.
Some tube cracking / wastage experienced.
1974 - Switched chemistry control to AVT.
1977 - First deep crevice cracking experienced.
Three leaking tubes plus other ECT indications.
Eight tubes plugged.
September 1978 - More deep crevice cracking.
Ten tubes plugged.
March 1979 - More deep crevice cracking.
Nine tubes plugged.
August 1979 - Plant shutdown due to tube leaks. 100% ECT, Forty-five tubes plugged in B SG; 52 in A SG, all due to deep crevice cracking.
ECT technique was at single frequency with some multi-frequency samples.
1442 285 rouseo e g g
Meeting Summary for Point Beach 1 NOV 161979 August 29, 1979 - 1.5 gpm leak developed.
Two tubes plugged which were inadvertently not plugged follow 1ng earlier 100% insp'ction.
October 5,1979 - Refueling shutdown plus 100% ECT testing. Three tubes removed for metallurgical examination.
Seventy-fiv a tubes plugged in A SG (3 due to tube removal); 65 tubes plugged in B SG.
ECT technique used multi-frequency testing.
Total number of SG tubes plugged in Unit 1:
A - 326 B - 316 or about 10%
The licensee stated that the Wisconsin PSC has ordered a public hearing to take place November 26 to discuss the economic impact of tube degrada-tion at Point Beach (the Wisconsin PSC attended this meeting).
Three tubes were removed for detailed metallurgical examination - two from the " kidney" area (a good tube and a bad tube), and one from the periphery.
All tubes exhibited intergranular caustic stress corrosion cracking in the " deep crevice" area.
The SG tubes at Point Beach were expanded only 2-1/2" at the bottom of the tube sheet, leavir a crevice between the tube and tube sheet over the balance of the tube sheet thick.
About 35 plants world-wide have this partial expansion design.
ness.
Other plants (San Onofre, H. B. Robinson, Ginna) have experienced deep crevice cracking, but not to the degree seen at Point Beach. Metallurgical results to date:
Tube 1 (R15C45).
"A" SG kidney region (bad tube in bad region).
Indications of intergranular attach over the full length of crevice zone.
Twenty mils general attack.
Deepest crack 40 mils.
(All tubes are 50 mils thick). A pH test of tube surface indicated al kal ini ty.
Na, P, K, Cl, Si, S, Ca detected.
Reason for attack:
Caustic stress corrosion cracking.
Tube 2 (R20C73).
Periphery region - outside kidney zone (good tube, good area).
Results:
similar to tube I but attack less extensive.
Five mils general attack,15 mils deepest crack.
Tube 3 (R22C37).
Good tube from kidney area (good tube, bad area).
Similar results.
5 mils general attack, deepest crack 25 mils.
The worst tube (No. 1) showed 89% tube degradation by ECT.
However, tubes 2 and 3 showed no ECT indications.
T. Esselman presented a preliminary structural evaluation of the degraded tubes.
See Attachment 2 for viewgraphs presented.
44}
} g/g Tube degradation appears to be accelerating.
Although a different ECT technique was used in the October 1979 inspection (multi-frequency testing), the licensee stated that the same results were achieved with single frequency testing at 400 KHz and the multi-frequency response at:400 KHz.
Therefore, the additional
Meeting Summary for NOV 161979 Point Beach 1 number of tubes plugged this time (which is beyond previous experience) does not appear to be attributable to the new inspection method. There are indications that defects have grown in size.
The licensee did a comparison of 75 tubes between August and October.
Two-thirds of these have new indications or indicate some growth over this relatively short operating period.
Penetration depth was about the same, but the defect size had increased. Therefore, there is strong evidence that degradation is accelerating, although the number of tubes plugged this time does include some which should have been plugged earlier as a precautionary measure.
Tube degradation is restricted entirely to the deep crevice zone.
The licensee stated that the deep crevice cracking problem and present SG tube conditions do not present a safety concern with respect to continued operations, but that economic concerns remain, since plant availability is being affected due to shutdowns to plug and inspect tubes. The licensee is pursuing solutions up to and including SG replacemer.c.
Before resuming power operations, the licen ee will flush both SGs with demineralized water in an attempt to remove chemicals believed to be trapped in the deep crevice zone.
Thermal cycling between 2500F and 2000F is planned to boil out the crevice zone, and draw water back into the' crevice (4-5 days of flushing).
The SGs will be pressure tested at 800 psig (0 psig primary pressure) to inspect for leakage prior to reinstallation of the manway covers.
A primary leak test will be conducted at 2335 psig (250 psig secondary side pressure) prior to resuming operation.
The licensee has submitted a Technical Specification change request which would lower the normal primary pressure to 2000 psia to reduce SG tube stress.
The licensee is studying reductions in primary average temperature (or reduced power) since no cracking has been observed in the cold leg side of the SGs.
The licensee is conducting a revised ECCS analysis assuming 18% of SG tubes plugged in anticipation of the need for further tube plugging.
[
M
. M. Trammell, Project Manager Operating Reactors Branch #1 Division of Operating Reactors Attachments 1.
List of Attendees 2.
Viewgraphs 1442 287
ATTACHMENT 1 LIST OF ATTENDEES POINT BEACH STEAM GENERATOR MEETING NOVEMBER 5,1979 NRC Staff Westinghouse E. Murphy R. Kelly J. Smith H. Von Hollin C. Trammell C. Hirst B. D. Liaw F. Pement E. Jordan E. Morgan D. Malinowski T. Esselman R. Begley W. White Wisconsin Electric Power G. Frieling C. W. Fay D. Porter Other J. Silberg, Shaw, Pittman, Potts & Trowbridge L. Smith, Wisconsin Public Service Commission i
i442 288
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~ f 7f CD:'ill110:!5 EVAlI!AIfli h { l / N /AIA $ f o UNIFORM WASTAGE WITHIN OR OUTSIDE THE TUBESHEET o CRACKING OF THINNED TUBE WITHIN OR OUTSIDE THE TUBESHEET o EXAMINATIONS PERFORMED DO NOT INDICATE THAT WASTAGE OR CRACKING EXTENDS AB0VE THE TUBESHEET - THIS CONDITION IS EVALUATED FOR COMPLETE COVERAGE OF POSSIBLE CONDITIONS N hkhk[,. 1442 291
~ l LIMITING CONDITIONS FOR UNIFORM WASTAGE OUTSIDE THE TUBESilEET ggg jgfggy REQUIRED CONDITION THICKF!Ffi SAFETY REQUIREMENTS e DOUBLE-ENDED FAILURE DURING SLB .005 INCH e TUBE RUPTURE DURING NORMAL OPERATION .008 INCH e TUBE RUPTURE DURING SLB .013 INCH e NO COLLAPSE DURING LOCA .020 INCH (6% OVALITY) llENCE, LIMITING CONDITIONS ARE T = 0.020 OUTSIDE THE TUBESHEET 1442 292
Itl,ffyy LIMITING CONDITIONS FOR UNIFORM WASTAGE WITHIN THE TUBES!iEET P R E U M M A R y' REQUIRED CONDITION THICKNESS e DOUBLE-ENDED FAILURE DURING SLB .005 INCH e TUBE RUPTURE DURING NORMAL OPERATION e TUBE RUPTURE DURING SLB
- DUCTILITY OF REMAINING MATERIAL MUST ALLOW THE TUBE TO EXPAND TO CONTACT TUBESHEET 1442 293 9
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!lli/19 PRft'M !"A"Y RESULTS OF LEAD PLUG TESTS ON PULLED TUBE TEST NUMBER DIAMETRAL INCREASE 5A6
- .045 INCH 5A7
.045 INCH 5B2 .030 INCH NOMINAL TUBE-TO-TUBESHEET HOLE DIAMETRAL CLEARANCE =.016 INCH EXPECTED TUBE-TO-TUBESHEET HOLE DIAMETRAL CLEARANCE ZERO THEREFORE, TUBE WILL BACK-UP AGAINST THE TUBESHEET 1442 294
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SUMMARY
FOR THE UNIFORM WASTAGE CONDITION PREc/Hmyy REQUIREMENTS e MINIMUM TUBE THICKNESS OUTSIDE TUBESHEET MUST BE GREATER THAN.020 INCH (140% OF WALL) e EQUIVALENT TUBE THICKNESS INSIDE TUBESHEET MUST BE GREATER THAN.005 INCH (10% OF WALL) e THE DUCTILITY OF THE TUBE INSIDE THE TUBESHEET MUST ALLOW EXPANSION TO THE TUBESHEET WALL CONDITION OF THE TUBES EXAMINED AND TESTS PERFORMED INDICATE THAT THESE REQUIREMENTS ARE MET 1442 295
4llChy N$l/H/AMAf TU!T lifil GRl'lY Vf RIfI(STin:1-Cl(ACKilui Wi~llllN 'lubLSI'.LLI o LEAK RATE F0,R CRACKING WITHIN Tf!E TUBESHEET IS GOVERNED BY ANNULAR E.oP o CIRCUMFERENTIAL CRACK e LIMITING CASE - FULL CIRCUMFERENTIAL CRACK O LEAKAGE - 7 GPM (LOWER BOUND ESTIMATE) -WILL ALLOW DETECTION DURING NORMAL OPERATION 0 EITHER 1) LEAKAGE WILL SHOW THAT THE BREAK HAS OCCURRED LEADING TO PLANT SHUTDOWN OR 2) BREAK WILL BE DEEP ENOUGH IN THE TUBESHEET THAT IT CANNOT CAUSE PROBLEMS 0 TUBE WILL NOT PULL OUT DURING SLB BECAUSE OF TOTAL BUNDLE RESTRAINT o AXI AL C-O RI. Slit.'I S OF LEAL) I'I UG TI:STS INI)lCATE TUBE ilA!; Stil l'IC ll N I 11 tic'l l t. Il Y 10 l'. AC K-UI' AGAIf'. 'l 1 11: 1 Ul:ESillLT }kk2
ap/>r 1011. lifil:GRITY VERIFICAT10N - ggfgfggy Cl:ACKING Al!0VE TUl!ESilEET e FOR UNSUPPORTED TUBES, GOVERNING CRACK ORIENTATION IS AXIAL o FOR AXIAL THRU-WALL CRACKS SUPERIMPOSED ON THINNED TUBES, TEST RESULTS INDICATE THE LEAK-BEFORE-BREAK CRITERION IS VALID o THEREFORE, LEAK RATES WILL REQUIRE PLANT SHUTDOWN PRIOR TO CRACK REACHING CRITICAL LENGTH LEADING TO TUBE BURST 1442 297
P .i 4 Meeting Summary for ocke Files NRCPD(R-M ORbl Reading NRR Reading H. Denton E. Case D. Eisenhut R. Tedesco G. Zech B. Grimes W. Gammill L. Shao J. Miller R. Vollmer T. J. Carter A. Schwencer D. Ziemann P. Check G. Lainas D. Crutchfield
- 8. Grimes T. Ippolito R. Reid V. Noonan G. Knighton D. Brinkman Project Manager OELD OI&E (3)
C. Parrish/P. Kreutzer ACRS (16) NRC Participants NSIC TERA Licensee Short Service List 1442 298 .}}