ML20023A519
| ML20023A519 | |
| Person / Time | |
|---|---|
| Site: | 05000000, Ginna |
| Issue date: | 04/08/1982 |
| From: | NRC |
| To: | |
| Shared Package | |
| ML19302F297 | List:
|
| References | |
| FOIA-82-309 NUDOCS 8210070165 | |
| Download: ML20023A519 (2) | |
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i As reported previously, Rochester Gas and Electric Corporation (RG&E) proposed the removal of selected tube samples through two access ports i
drilled in the side of the steam generator, to obtain metallurgical data needed for evaluation of the "B" steam generator tube failure mechanism.
Following a meeting with the licensee and Westinghouse, l
l NRR approved this proposal on March 1,1982.
Seven tube samples, l
including the ruptured tube, have been removed and sent to Westinghouse for metallurgical examination.
Results of the examinations indicate that the two tubes immediately i
outboard of the ruptured tube, which were severed just above the tube sheet, and the ruptured tube all show signs of metal to metal wear.
The rupture occurred at one of the wear areas. The licensee indicated that photomicrography of the rupture showed that the failure was a i
ductile tear occurring after the loss of approximately 90% of the tube wall thickness. The staff is obtaining a number of samples of the tubes for independent laboratory examination.
On March 23, 1982, members of the NRC staff met with representatives of RG&E and Westinghouse to discuss the status of repair activities proposed for the Ginna Plant. RG&E recieved NRC permission to remove from the "B" steam generator another 17 tubes that showed signs of external damage.
This would brin (to 24 the total number of tubes removed from the "B" generator since Janugy 25, 1982. This number includes the tubes already 7,
removed for metallurgical samples and the three tubes that were severed just above the tube sheet and just below the first support plate.
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, 4 the sections of the tubes between the tube sheet and the first support l
j plate will be removed. Westinghouse evaluation shows that there will be no adverse effects on the steam generator or remaining tubes caused by the removal of this number of tubes.
Investigations as to the failure meche nism are continuing. Originally, i
the cause investigation centered around possible mechanical loading i
mechanisms on tubes between the first support plate and the tube sheet with flow induced vibration as a contributing factor. The current cause investigation, since discovery of foreign objects in the steam generators, is focusing on mechanical failure of plugged tubes as the i
result of impact by foreign objects and the progression of damage on structurally degraded plugged tubes with possible resultant damage to the ruptured tube.
The licensee's schedule calls for completion of work in the steam generator related to the rupture in early April, the submittal of a report on the event by April 16, 1982, and projected restart in early to mid-May. The staff will provide a comprehensive Safety Evaluation prior to restart.
The NRC Task Force discussed in last month's report has completed its review of the Ginna event.
The report is scheduled = to be presented to theCommissiongrsonApril 14, 1982.
The staff is also continuing its generic review of recent steam generator problems with meetings involving the various steam generator vendors and owners groups.
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