ML20238D800
| ML20238D800 | |
| Person / Time | |
|---|---|
| Site: | Sequoyah  |
| Issue date: | 12/29/1987 |
| From: | Gridley R TENNESSEE VALLEY AUTHORITY |
| To: | NRC OFFICE OF ADMINISTRATION & RESOURCES MANAGEMENT (ARM) |
| References | |
| NUDOCS 8801040444 | |
| Download: ML20238D800 (3) | |
Text
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TENNESSEE VALLEY AUTHORITY CH ATTANOOGA. TENNESSEE 37401 5N 157B Lookout Place DEiG 291987 U.S. Nuclear Regulatory Commission ATTN: Document Control Desk Hashington, D.C.
20555 Gentlemen:
In the Matter of
)
Docket Nos. 50-327 Tennessee Valley Authority
)
50-328 SEQUOYAH NUCLEAR PLANT (SQN) UNITS 1 AND 2 - CLARIFICATION OF INFORMATION REGARDING FLAS-5 FUSE REPLACEMENT
Reference:
TVA letter to NRC dated November 17. 1987, "Sequoyah Nuclear Plant (SQN) - Units 1 and 2 - Additional Information Requested by NRC on Fuse Replacement" l
The purpose of this letter is to provide NRC with a docketed response by TVA to clarify certain information discussed in a meeting held at SQN on December 16, 1987, with regard to the referenced letter above.
The enclosure contains the supplemental information NRC requested to be docketed in that meeting.
This information should allow NRC to complete their evaluation of the FLAS-5 fuse replacement at SQN and allow them to complete their Safety Evaluation Report in a timely manner.
If any additional information is required concerning this subject, please telephone M. R. Harding at (615) 870-6422.
Very truly yours, TENNESSEE VA EY AUTHORITY j
R.Gridley,Difector Nuclear Licensing and Regulatory Affairs Enclosure cc:
See page 2 l
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8801040444 871229 g\\
ADOCK0500g7 DR An Equal Opportunity Employer
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. U.S. Nuclear Regulatory Commission
[)E6l 291987 cc (Enclosure):
Mr. K. P. Barr, Acting Assistant Director for Inspection Programs TVA Projects Division Office of Special Projects U.S. Nuclear Regulatory Commission Region II 101 Marietta Street, NW, Suite 2900 Atlanta, Georgia 30323 i
l Mr. G. G. Zech, Assistant Director for Projects TVA Projects Division Office of Special Projects U.S. Nuclear Regulatory Commissiori Mail Stop 7E23 7920 Norfolk Avenue Rockville, Maryland 20814 Sequoyah Resident Inspector Sequoyah Nuclear Plant 2600 Igou Ferry Road Soddy Daisy, Tennessee 37379
ENCLOSURE Hith reference to our meeting at Sequoyah Nuclear Plant on December 16, 1987, TVA is making clarification of the following points:
1.
TVA prov?ded NRC with figures 2, 9, and 12 from attachment 2 of the referenced letter at the meeting.
These figures were inadvertently omitted from the referenced letter.
2.
The minimum expected life of these fuses should be 25 months instead of the 23 months as previously reported in enclosure 1 of the referenced letter.
3.
The primary purpose of providing attachments 1, 2, and 3 to NRFC in the referenced letter was:
a.
Attachnient 1 was intended to substantiate the solder junction temperature rise over ambient temperatures for various current loadings.
b.
The purpose of attachment 2 was to relate the solder junction temperature to the predicted life. Also to paraphrase the first sentence in the discussion section at the bottom of page 7, the solder junction variability is of sufficient uniformity to provide consistent data.
- c. is intended to document interim results of long-term elevated current tests on samples from each lot of cadmium fuses.
4.
In reference to the statement contained in the results section of attachment 1, page 4 of 5, "These problems were reviewed as poor quality control...," this was a preliminary conclusion cased on metallography and scanning microscopy of the solder joint before identification of a creek failure mechanism.
The manufacturing process of these fuses did not i
change.
Instead the fuse manufacturer only changed the soldering material from bismuth to cadmium in order to maintain the one N und spring force on the solder joint and to eliminate the creep mechanism.
Subsequent testing in attachment 2 also concluded that geometrical factors identified in attachment 1 were not factors significantly affecting quality control.
Another factor to consider is that the tensile strength of cadmium solder is approximately three times that of bismuth.
It should also be noted that attachment 1 is labeled an " intermediate report" by the cover memorandum that transmitted it, and new information has been obtained since this report was initially written.
The data from the tests documented in attachment 2 establish that the cadmium solder junction is of sufficient uniformity to provide consistent data.
5.
In regard to the concern about the higher melting point of the cadmium l
solder as compared with bismuth, TVA has performed short circuit tests on j
samples of both type fuses at 125 V dc.
The results of these tests showed that bismuth solder fuses indicated (indicator pin extended) in an average of 37.15 seconds, whereas the cadmium indicated in an average of 37.45 seconds.
The time difference between these two fuse types tested is considered to be insignificant.
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