ML20004E791
| ML20004E791 | |
| Person / Time | |
|---|---|
| Site: | Summer  |
| Issue date: | 06/08/1981 |
| From: | Nichols T SOUTH CAROLINA ELECTRIC & GAS CO. |
| To: | Harold Denton Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8106150263 | |
| Download: ML20004E791 (3) | |
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/a, g, j,Q h Mr. Harold R. Denton, Director
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Office of Nuclear Reactor Regulation U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Subject:
Virgil C. Summer Nuclear Station Docket No 50/395 Steam Generator Row 1 Tubes / Inspection Ports.
SER Licensing Conditions 1.8.9, 1.8.7.
Dear Mr. Denton,
The NRC issued a letter dated 4 80 to the Virgil C. Summer Nuclear Station requiring the plugging of all row one steam generator tubes prior to the start of operation. This requirement was reaffirmed by the NRC in the Virgil C. Summer Safety Evaluation Report (Licensing condition 1.8.9).
This concern by the NRC was prompted by the occurrence of tight cracks in the row one tube "U" bend transition region of row one tubes for some operating plants. All of the operating plants that have experienced this cracking have Westinghouse Model 51 series steam generators. The Virgil C.
Summer Nuclear Station is supplied with Westinghouse Model D-3 steam gene-rators. There is evidence indicating that the tubing in the Model D-3
-steam generator represents a different population than the tding in the Model 51 steam generators and should not be included in any generic assess-ment of the row one "U" bends until additional data is developed. The tube size parameters for the two model steam generators are itsted below:
Steam Generator Series 51 Model D-3 Tube Diameter.(D), in.
0.875 0.750 Minimum Bend Radius (R), in.
2.188 2.250 R/D 2.5 3.0 Wall Thickness, in.
0.050 0.043 Maximum Ovality %
10 6
As can be seen, the tube diameter, wall thickness, and maximum ovality are less in the case of the Model D-3 tubing than for the Model 51.
The ratio of the tube diameter to bend radius is greater for the Model D-3.
All of these factors are in the direction of minimizing difficulties in the tube bending process and support the contention that the 3/4" diameter Model D-3 tubing represents a different population.
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.i Mr. liarold R. Denton May 28, 1981 Page 2 Referenced in the Summer SER was the program conducted at.the Trojan plant, a plant with Series 51 steam generators. The results of that program were sent to the NRC Staff in January,1981, where review of this program is still
.in progress.
For these reasons, combined with the results of the Trojan program, it is believed highly inappropriate to remove approximately 3% of the tubes from operation by plugging the row one tubes in the Model D-3 steam generators.
Also included in the 4-21-80 letter to the Virgil C. Summer Nuclear Station, was a requirement to install steam generator inspection ports. The inspec-tion ports are to be located 3ust above the top tube support plate, and between the tubesheet and the lower tube support plate, with both ports in line with the tube lane. The purpose for these inspection ports is to monitor tube and support plate degradation due to denting. This requirement was reaffirmed by the NRC in the Virgil C. Summer Safety Evaluation Report.
(Licensing condition 1.8.7) The need to install an inspection port just above the top tube support plate is unnecessary. The denting phenomena is detectable by eddy current inspection in all areas of the tube bundle. The denting phenomena occurs on the hot leg side of the tube bundle and progresses from the first and second tube support plates upward to the top tube support plate. The progression of denting to the point where visual indications would be apparent through an inspection port above the ton -ube support plate would occur long af ter denting would be detectable by eddy current inspection and visually apparent through the lower inspection port.
For these reasons, it is believed to be unnecessary to install an inspection port just above the top tube support plate in any stuan generaters to monitor denting.
It should also be noted that for Model D-3 steam generators, mechanical modifications are required beyond the simple installation of the inspection part.
SCE&G requests that the NRC act on this information now since one of the issues requires resolution prior to the issuance of a full power license for Summer Station.
If you have any questions, please let us know.
Yours very truly, a
T. C. Nichols, Jr.
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4 Mr. Harold R. Denton' May'28, 1981
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