ML20023A413
| ML20023A413 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Point Beach |
| Issue date: | 08/17/1979 |
| From: | Noonan V Office of Nuclear Reactor Regulation |
| To: | Eisenhut D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML19302F297 | List:
|
| References | |
| FOIA-82-309 NUDOCS 7909280105 | |
| Download: ML20023A413 (3) | |
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UNITED STATES 8
NUCLEAR REGULATORY COMMISSION o
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WASHINGTON, D. C. 205S5 k*****/.
AUG 171979 MEMORANDUM FOR:
D. G. Eisenhut, Acting Director-Division of Operating Reactors FROM:
V. S. Noonan, Chief. Engineering Branch
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Division of Operating Reactors THRU: )
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L. C. Shao, Acting Assistant Director
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for Engineering Programs Division of Operating Reactors SUBJECO STEAM GENERATOR TUBE LEAK AND INSPECTION AT POINT BEACH UNIT 1 Occurrence and ISI Results Point Beach Unit 1 was shutdown on the morning of August 5,1979, when a primary to secondary leak (1.45 gpm) in steam generator A exceeded the plant's Technical Specification limit of 500 gallons per day (.35 gpm).
A slight leak at a constant rate of 15 gpd had existed in the A generator since May,1979.
Following return to power on August 5,1979, aft.er being down for approximately one day to repair a high pressure turbine steam leak
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and to make a temporary repair to the Auxiliary Feedwater Line, a 1.45 gallon per minute (gpm) leak developed i'n steam generator A.
Subsequent to the shutdown due to the tube leakage, the licensee began a complete i
(100%) in-service inspection of both steam generators A and B.
In a conference call on August 13, 1979, we discussed with Wisconsin Electric Power Company (the licensee) the type and extent of the inspections being l'
performed and the results obtained to date.
The leak in steam generator A was determined to be a result of " deep crevice cracking" of three tubes within the thickness of the tube sheet.
The three leakers were characterized as one 'tjusher" and two %eepers".
In addition, 100% eddy current testing (ECT) of the hot leg tubes in steam generator A indicated 52 tubes with deep crevice cracking in excess of the 50% plugging limit.
A_11 af +hes= cracks were located one inch below the upper surface 9f the tube sheet.
These cracks generally occurred in the " kidney" shaped zone of relatively 1cw flow velocity.
No cold leg ECT indications were found.
Six percent of the hot leg tubes were probed around the U be to the top of the cold leg side.
The remaining tubes were probed thre _
the first support plate.
No progressive denting since previous in-servh ?
inspection in September,1978, was indicated in the 6% tube sample.
A 100% ECT inspection of the hot leg B generator tubes is in progress.
Of the 2500 tubes (of total of 6000) inspected to date, 52 tubes with deep l
crevice cracking in excess of the 50% plugging limit have been found.
The 100% inspection of the B generator is avnected tn _b completed before the end of the week (8/17/79
Contact:
E. L. M phy hM x27041
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i of-6 AUG 171979 D. G. Eisenhut
-3 Recent Experienc'es Point Beach Unit 1 was previously shutdown on February 2. May 25, and September 20, 1978, and March 12, 1979 due to steam generator tube leak-ace.
Inservice inspection during the September,1978 outage revealed
deep cre vice cracking" as the source of the leaks and resulted in the plugging of six (6) tubes in steam oenerator A and five (S) tubes in c
Stean generator leakage prior to the March,197?
outage (225 god) did not exceed the Technical Specification limit of 500 gpd.
Nine tubes in the A generator ar.d one tube in the B generator were plugged during the repair outage in March, but a general ECT inspec2 tion was not perforted.
l Preliminary Evaluation Cracking within the thickness of the tube sheet is a phenomenon affecting early generation steam generators in which the stean generator tubes were not fully expanded in the tube sheet. This ' deep crevice cracking is a form of caustic stress corrosion cracFing that has been observed in steam generators which have been converted from phosphate to AVT or can affect plants that have been operated on exclusively AVT secondary water chemistry.
Point Beacn was converted from phosphate to AVT water chemistry approximately five years ago.
Because of the contraint provided by the tube sheet. the deep crevice cracks are not considered a significant safety concern durine nonnal operation or postulated accident conditions.
In view of the apparent increasing rate of this type of degradation at Point Ccach Unit 1 and its potential impact on plant availability, we feel that the licensee has acted responsilly in carrying out a 10% in-service inspection of both steam generators A l
and B.
All tubes with indications exceeding the plugaing limits will be plugged and water lantino of sludge deposits will be performed prior to returning the unit to power. ~ Additional ceasures being considered by the licensee to improve steam generator reliability include use of chemical c1 caning to clean out the tube to tube sheet crctices and the use of mechanical plugs for defective tubes, which can be removed to permit future inspection for monitoring the rate of degradation.
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A repart summarizing the results of this in-service inspection and an eval ar tion of tne results will be submitted by the licensee by August 20.197
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d.G.Eisenhut AUG 171979 cc:
L. C. Shao W. Gammill J. P. Knight A. Schwencer B. D. Liaw W. Hazelton,[
C. Trammell M. Grotenhuis J. Weeks, BNL J. Strosnider F. A! meter E. L. Murphy 1
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