ML20023A406
| ML20023A406 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Point Beach |
| Issue date: | 12/12/1978 |
| From: | Noonan V Office of Nuclear Reactor Regulation |
| To: | Grimes B Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19302F297 | List:
|
| References | |
| FOIA-82-309 NUDOCS 7812200285 | |
| Download: ML20023A406 (2) | |
Text
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WASHINGTON, D. C. 20555 Y',bIQ,j'f s.~....y DEC 1 2 1978 MEMORANDUM FOR:
B. K. Grimes, Assistant Director for Engineering & Projects Division of Operating Reactors i
FROM:
V. S. Noonan, Chief, Engineering Branch Division of Operating Reactors i
SUBJECT:
STEAM GENERATOR TUBE LEAK AND INSPECTION AT f
POINT BEACH UNIT 1 Point Beach Unit 1 was shutdown on the morning of September 20, 1978, i
when a primary to secondary leak in the A steam generator exceeded l
the plants Technical Specification limit of 500 gallons per day (gpd).
On September 20, the leak increased from 116 gpd at 3:15 a.m. to 560 gpd at 5:00 a.m.
The tube leak incident and the subsequent plant
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shutdown occurred only nine days prior to a scheduled refueling outage.
With the shutdown due to the steam generator leakage the licensee
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immediately began the refueling outage.
In a conference call on October 4,1978, the Engineering Branch dis-cussed with Wisconsin Electric Power Company (the licensee) the results of the steam generator inspections conducted at Point Beach Unit 1.
The leak in steam generator A was determined to be a result of two tubes with cracks located within the thickness of the tube sheet and one tube with a leaky plug.
Cracking within the thickness of the tubesheet is a phenomenon affect-ing early generation steam generators in which the steam generator tubes were not fully expanded in the tubesheet. This " deep crevice cracking" is a form of caustic stress corrosion cracking which can affect steam generators which have seen conversion from phosphate to AVT or have operated exclusively on AVT water chemistries.
Point Beach Unit I converted from phosphate to AVT water chemistry approximately three years ago.
In addition to the two leaking tubes, eddy current testing revealed four tubes in steam generator A and five tubes in stean generator C with deep crevice cracking in excess of 50%.
All of these tubes wera plugged. All of these cracks were located approxi-y mately 17 inches from the top of the 23 inch thick tube sheet.
Because j
of the constraint provided by the tubesheet, the deep crevice cracks are not considered a significant safety concern during normal operation I
or postulated accident conditions.
However, this form of degradation does have a significant impact on plant availability.
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Contact:
J. Strosnider 1
49-28060 L
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.DEC 121978
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B. K. Grimes '
Point Beach Unit 1 has experienced a nuaber of leaky tube plugs in the past few years. The leaks are generally categorized as " weepers" resulting in very small, stable leak rates and are not considered a significant safety issue. Ho plug is knm.n to have cone loose from a plugged tube at N. int Coach Unit 1.
A loose plug recovercd f, ca the botten of the reactor vessel on Hovenber 10, 1975 was determined to be unexploded and believed to have been dropped by a technician.
The licensee has reported that inspection results indicate no signifi-cant increase in tube denting.
Several actions havc been taken by the licensee to retard the denting pheno:aenon. These include:
a.
modifications cade to increase the steara generator circulation
- ratio, b.
putting new resins in the water treatment filters, c.
increasing the sensitivity of determining condensate inleakage, and 3
d.
naintaining air inleakage to less than 3 Ft 7ajn, An on-site safety review connittee report sumarizing the results of this inservice inspection and an evaluation of these results will ba submitted by the licensee through the Office of Inspection cnd Enforcement.
Original SI ned byr E
Vincent 5. Hoonan, Chief Engineering Branch Division of,0perating Reactors cc:
V. Stello, Jr.
D. Eiser. hut B. D. Liaw C. Trasel R. LaGrange F. Alm.eter J. Strasnider I
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\\ ~ 8;;, f DEC 1 5 1978 MEMORANDUM FOR:
D. Eisenhut, Deputy Director Division of Operating Reac' ors FROM:
V. Noonan, Chief, Engineering Branch l
Division of Operating Reactors THRU:
B. Grimes, Assistant Director for Engineering and Projects n, Division of Operating Reactors SUBJEC'T:
SUMMARY
OF RECENT ADVERSE STEAM i
GENERATOR OPERATING EXPERIENCE i
i In accordance with your request, the Engineering Branch, Division of Operating Reactors, has made a summary of recent adverse j
steam generator operating experience at Point Beach Unit 1, Yankee Rowe, and Oconee Unit 1.
Also included in the summary is our assessment of each event and its safety significance.
C. 4 Vincent S. Noonan, Chief Q
Engineering Branch Division of Operating Reactors i
Contact:
J. Strosnider 49-28060
Attachment:
As state'd cc:
V. Stello, Jr.
B. Grimes G. Knighton P. Check A. Schwencer D. Ziemann R. Reid B. D. Lica F. Almeter R. LaGrange C. Tramme M. Fairtile F. Burger J. Strosnider J. P. Knight R. Bosnak S. Pawlicki k.
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POINT BEACH UNIT 1 A.l. May 24, 1978, Tube Leak s
Indication of a primary to secondary leak was noted on May 24, 1978 in the Unit 1, A steam generator. The initial leak rate of 8 gpd increased to almost 90 gpd by May 25 and the plant p
was shut down to perform steam generator repairs in conjunction 6
with a maintenance outage originally scheduled for the Memorial Day weekend. The leak test revealed one leaking tube originally reported as tube R44C58. 'An October 23, 1978 licensee event i
update report indicated that the leaking tube had been mis-identified and was actually located at R44C35. The mode of tube degradation was not conclusively determined.
Because of the originally indicated tube location, the Engineering Branch re-l quested information regarding the possible relation of the leak to denting and requested the licensee to submit their S.G. ISI I
program planned for the September 29, 1978 refueling outage.
l The licensee's response established that the leak was not dent-ing related since the tube defect was located just above the tubesheet.
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A.2.
September,1978 Tube Leak f
The Unit was shut down again on September 20, 1978 when a primary to secondary leak increased from 116 gpd to 560 gpd, exceeding
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the unit's 500 gpd technical specification leakage rate limit.
The plant was shut down and the licensee began a refueling outage i
originally scheduled for September 29, 1978. Steam generator inspections and repairs were conducted during the shutdown.
On October 5, members of the Engineering Branch along with Mr. C.
Trammell, the Project Manager, had a conference call with Point Beach to learn the specifics of the S.G. leak.
The source of i
the leak was determined to be two tubes with cracks located -
within the thickness of the tubesheet..In addition to the two l
leaking tubes, eddy current testing revealed four tubes in steam generator B with " deep crevice cracking" in excess of 50%.
All of these tubes were plugged.
All of the cracks were located approximately 17 inches from the top of the 23 inch tubesheet.
Early generation steam generators in which the tubes were not full depth expanded in the tubesheet may be susceptible to this type of cracking, tentatively attributed to caustic stress corrosion cracking.
Because of the constraint provided by the tubesheet, the deep crevice cracks are not considered a signif-icant safety concern during normal operation or postulated accident conditions.
Table I outlines the sequence of the above events at Point Beach Unit 1.
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i".2 3, I 4
TABLE I POIflT BEACH UNIT fi0. 1 E
3 A.
6/10/78 LER nn 1.
Plant shutdown on 5/25/78 due to leak in S.G. A.
E 2.
Leaking tube incorrectly reported as R44C58.
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B.
7/13/78 EB requested information regarding leak:
P 1.
Was the leak denting related?
fI 2.
Submit 9/29/78 refueling outage S.G. ISI program for NRC f
comment.
p C.
8/18/73 Point Beach response to EB request 1.
Leak not denting related.
7 2.
Proposed ISI program submitted.
D.
9/20/78 LER 3
1.
Plant shutdown 9/20/78 because of leak in S.G. A.
2.
Plant started refueling previously scheduled for 9/29/78 3.
S.G. ISI performed
" Deep crevice" cracks detected.
E.
10/23/78 Updated LER - leaking tube plugged in 5/78 was actually tube R44C35.
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YAf;KEE R0WE I
During their I;ovember,1978 refueling outage Yankee Rowe perfocmed 100% ECT inspections of steam generators I;o.1 and fio.
4.
On flovember 7 members of the Engineering Branch along with fir. F. Burger h
had a conference call with Yankee Rowe to discuss their proposed M
c technical specifications governing steam generator inspection and
'Is l;
results of the inspections of steam generators 1 and 4.
The unit was operating with a 125 gpd primary to secondary leak in steam j
generator fio. I prior to the shutdown.
Results of the inspection revealed two tubes (f!41 and I44) with through wall defects originating from the outside tube diameter (OD) approximately one half inch above the tubesheet.
An additional 13 tubes in steam generator fio.1 had OD defects greater than 40% through wall. All of these defects were located 0.5 to 3.0 inches above the tubesheet.
Two tubes in steam generator 1 had OD degradation greater than 20% but less than 40%
through wall.
Twelve tubes with defects greater than 40% and 8 tubes with degradation greater than 20% but less than 40% were reported in steam generator tio. 4.
All defects were located within 0.5 inch to 4.0 inches of the tubesheet except one tube with a 67% through wall i
defect 27.0 inches above the tubesheet and one tube with an inside i
surface ECT indication less than 20% through wall and 25.0 inches above the first support plate.
The 67% through wall defect was believed to be a manufacturing defect. The inside surface degradation was un-i explained but represents an isolated case. A 100% inspection of steam generators fio. 2 and fio, 3 was performed in July 1977 and resulted in the plugging of approximately 5 or 6 tubes in each steam generator.
t;o denting was observed in any of the steam generators. These inspec-tion results represent excellent baseline data for the plant and provide useful insight to the conditions existing in steam generators which have had relatively good operating experience.
Results of these inspections were disc 6ssed in the Engineering Branch safety evaluation I
regarding Yankee Rowe technical specifications governing steam gener-ator inservice inspections dated December 5,1978.
Table II and Table III summarize the results of the inspections in steam generators fio.1 and tso. 4.
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By letter dated October 19, 1978 Duke Power Company informed the fiRC that two steam generator tube plugs had been lost at the Oconee h-,
EN Unit 1 I;uclear Power Plant and were possibly loose in the primary
$8 coolant system.
Details of the lost tube plugs incident are dis-cussed in a fiovember 1.1978 safety evaluation.
In addition to the lost plugs incident licensee event report number R0-269/78-24 from Duke Power Company, dated flovember 15, 1978, informed the liRC of the discovery of a large number of misplugged tubes at Oconee Unit 1.
The errors in tube plugging were discovered as a result of leakage from a supposedly plugged tube during hydro-testing on October 3,1978, following the inservice inspection conducted during the refueling outage.
The report indicated a total of 7 misplugged tubes.
The Engineering Branch has learned the following information by conference calls placed through Mr. M. Fairtile the Oconee Unit 1 Project Manager.
As a result of the loose tube and mis-plugging incidents Duke Power Company implemented the following QA improvements:
1.
All procedures improved in program.
2.
Use of standard techniques in tooling fixtures for tube identi-fication - this will eliminate tube plugging errors.
3.
Use of ECT template for identification of tubes to be plugged.
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4.
Installation of ECT template on lower head tubesheet when necessary (not complete).
5.
Establish better communication between upper and lower head crews and with outside of S.G. personnel.
6.
Build and 0TSG mockup to facilitate training (not complete).
7.
Expand personnel training.
8.
Clearly define role of first line supervisors in S.G. work.
i 9.
Improve management of vendor related activities.
10.
Improve health physics activities to keep down occupational exposure and reduce dose per man by better planning of work.
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, The NRC Office of Inspection and Enforcement (I&E) reviewed the QA. -
l changes and was dissatisfied with items 1 and 4.
Duke modified these items to incorporate I&E's comments.
The Office of I&E plans to audit the modified QA program at Oconee Unit 1 on December 7,1978.
j The results of this audit are to be forwarded to 00R in an ISE report as soon as they are available, y
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