ML19317H019
| ML19317H019 | |
| Person / Time | |
|---|---|
| Site: | Rancho Seco |
| Issue date: | 10/08/1977 |
| From: | Mattimoe J SACRAMENTO MUNICIPAL UTILITY DISTRICT |
| To: | Reid R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8004020696 | |
| Download: ML19317H019 (3) | |
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[ssCatPT1oM Consists of conclusions rqarding
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95813; (916) 452-3211 October 8,1977 s
Director of Nuclear Reactor Regulation
((;5 ATTN:
Mr. Robert W. Reid, Chief Operating Reactors, Branch 4
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U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Re:
Docket No. 50-312 Rancho Seco Nuclear Generating Station, Unit One
Dear Mr. Reid:
In compliance with the September 26, 1977, telephonc conversation with L. Olshan, J. Strosnider, L. Shao and R. Steward of your office, the District is forwarding the conclusions regarding the ding-like OTSG tube eddy current indications observed during the current refueling outage.
A 9% eddy current inspection of OTSG A and a 3% inspection of OTSG B revealed four tubes with ding-like indications, all in the "A" generator.
Diese tubes are numbered 75-2, 70-2, 74-2 and 66-130 and all indications are at the 15th support plate. Tubes 75-2, 70-2 and 74-2 were stabilized using the segmented nail technique.
The sole basis for stabilizing tubes is to improve the reliability of the steam generator in an effort to reduce the likelihood of a shutdown and subsequent.
costly power outage due to tube failure.
Specifically, tube stabilization is not based on safety considerations.
The criteria for stabilizing dinged tubes is based on experience with other OTSG's where two tubes in the outer peripheral region of the open tube lane, with ding-like indications at the 15th support plate and upper tube sheet locations, failed and several tubes away from the open lane with similar indications did not fail.
That is, tubes having ding-like indications at the 15th SP and/or UTS are to be stabilized if they are outer peripheral tubes along or near the open tube lane.
This is true for tubes 75-2, 70-2 and 74-2.
Tubes with ding-like indications that do not fall within this category were not stabilized, as is the case for tube 66-130, which is located on the opposite side of the generator from the open tube lane.
The term " ding-like indication" is used to describe an eddy current signature similar to that obtained in the lab from a crimped tube where the wall has been displaced.001 in.
.002 in., but no loss of wall has occurred.
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Robert W.' Reid
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'Although no causative relationship has been established between the ding-like, eddy current indications and the tube failures, it seems prudent from a plant reliability point of view to remove from service by means of stabilization any tubes in the peripheral region near the open tube lane that have ding-like indications.
It is noted that ding-like signals are not indicative of any tube-wall thinning nor degradation-of structural integrity and thus the. recommendation to stabilize tubes is not made because of safety considerations.
In an_ effort to firmly establish that a ding-like eddy current signal is not related to tube failure, a detailed metallurgical examina-tion of a ding-like indication of one of the Oconee tubes will be conducted.
We expect the results of the examination will be forwarded to the NRC by the first of December.
Tube 66-130 in OTSG A will be selected for eddy current testing during the next scheduled refueling shutdown.
This should close out all items of discussion pertaining to our September 26, 1977 conversation.
If you have any questions or require additional information, please advise.
Respectfully submitted, A
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'J.
J. Mattimoe Assistant General Manager and Chief Engineer 1
JJM:RWC: sal cs:
J. Mattimoe R. Rodriguez D. Raasch P. Oubre' J. McColligan Fourth Floor Files R.S. File
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