ML20215H517
| ML20215H517 | |
| Person / Time | |
|---|---|
| Site: | Yankee Rowe |
| Issue date: | 06/15/1987 |
| From: | Heider L YANKEE ATOMIC ELECTRIC CO. |
| To: | Russell W NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| FYR-87-65, NUDOCS 8706240133 | |
| Download: ML20215H517 (3) | |
Text
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Telephone (617) 8778100 TWX 710 380-7619 YANKEE ATOMIC ELECTRIC COMPANY
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June 15, 1987 FYR 87-65 United States Nuclear Regulatory Commission Document Control Desk Washington, DC 20555 Attention:
William T. Russell Regional Administrator
References:
(a) License No. DPR-3 (Docket No. 50-29)
(b)
I&E Inspection No. 50-29/87-07
Dear Sir:
An inspection was conducted by your Ms. Audrey Lodewyk during the period May 11-14, 1987 at the Yankee Atomic Electric Company (YAEC), Yankee Nuclear Power Station (YNPS) in Rowe, Massachusetts (Reference (b)). The subject of the inspection was our recent steam generator eddy current testing program conducted in accordance with Technical Specification surveillance requirements.
Subsequently, through a series of telephone discussions, additional information has been requested to help clarify certain aspects of eddy current signal analysis, to characterize the operating experience of the Rowe steam generators, and to document a specific administrative commitment.
This letter partially fulfills the requests and delineates a schedule for transmitting the remaining information. The status of each topic is as follows:
1.
Our reasons for concluding that the predominant steam generator tube defect is secondary side pitting are provided in Attachment A.
2.
Samples of typical calibration and defect traces from the 1984 and 1985 Zetec reports on Yankee steam generators were provided to the site senior resident inspector on June 15, 1987.
The 1987 report will be available, on request, after it is received.
3.
Yankee will submit additional information via supplementary special report to update the results of the 1984 baseline cold leg inspections for three steam generators.
In addition, an LER will be written and will include an evaluation of root causes and corrective actions.
50
United States Nuclear Regulatory Commission June 15, 1987 Attention:
Mr. William T. Russell Page 2 4.
Yankee has adopted an administrative limit for primary-to-secondary leakage during Cycle 19, which is consistent with the current standard Westinghouse Technical Specifications. The Main Coolant System primary-to-secondary leakage shall not exceed 1 gpm.through all steam generators not isolated from the Main Coolant System and'.
500 gallons per day through any one steam generator not isolated from the Main Coolant System.
Please contact us if you have any questions.
Very truly yours, L uis H. Heider Vice President Manager of Operations LHH/dib cc: USNRC, Region I USNRC Resident Inspector, YNPS l
ATTACHMENT A TO FYR-87-65 The predominant steam generator tube defect mechanism for the steam generators at Yankee Nuclear Power Station is interpreted to be pitting.
This conclusion is drawn from three sources of information and experience:
1.
Yankee's operating experience significantly predates eddy current technology as we know it today. Our experience with actual leaking steam generator tubes demonstrates a consistent character and rate of progression. We have observed some 38 actual penetrations and all followed the same pattern of gradual increase in leak rate over periods of many months. Their slow rate of progression suggests that they are initially pinhole in size and increase in diameter with time. They do not catastrophically fail or fail rapidly over a short (days) period.
i 2.
The potential that the failure mechanism is stress corrosion cracking is low. Our historically good secondary side chemistry, the locations of the defects above the tube sheet, the low oxygen level, low air inleakage, and the presence of copper in the secondary system all fit the environmental conditions for pitting and not stress corrosion cracking.
3.
The signal analyses suggest a pitting mechanism for the following reasons:
a.
Virtually all signals originate from the OD and are in the free span of the tubes in an area immediately above the tube sheet. Cracks are most likely to appear at high stress locations, i.e.,
at the role transition.
b.
The signals are short duration. They have no length when viewed on the strip chart format of the DDA-4 analysis.
c.
During the past 15 years (nine inspection programs), Zetec readers, based on their professional experience, have consistently indicated to Yankee that the defects appear to be pitting.
i J