ML19301B758
| ML19301B758 | |
| Person / Time | |
|---|---|
| Site: | Turkey Point  |
| Issue date: | 11/24/1976 |
| From: | Robert E. Uhrig Florida Power & Light Co |
| To: | Lear G Office of Nuclear Reactor Regulation |
| References | |
| Download: ML19301B758 (7) | |
Text
t P. O. BOX 013100, MIAMI, FL 33101 y~klllgy
+/ErruAO FLORIDAPOWER & LIGHTCOMPANY November 24, 1976 L-76-403 Office of Nuclear Reactor Regulation Attention:
Mr. George Lear, Chief Operating Reactors Branch 03 Division of Operating Reactors U. S. Nuclear Regulatory Commission Washington, D. C.
20555
Dear Mr. Lear:
ILGWU>~ECIt4i~h iJ Li a<,g~3 Re:
Turkey Point Unit 4 Docket No. 50-251 Steam Generator Ins ection Results In Florida Power 6 Light Company (FPL) letter L-76-369 of October 26,
- 1976, we described our participation in a joint inspection program that. was designed to investigate the cracking of small bend radius steam generator tubes at VEPCO's Surry Unit 2.
We are now providing you with significant results obtained from the Turkey Point Unit 4 portion of the program, including the corrective action that FPL is taking in preparation for returning Turkey Point Unit 4 to service.
Attachment 1 contains the most significant results obtained to date from metallurgical examinations of the tube samples removed from the "B" steam generator at Turkey Point Unit 4.
A more complete description of the steam generator 4B inspection results will be included in a report now being prepared by the Westinghouse Electric Corporation.
The Westinghouse report will contain the results of all inspections performed as a part of the joint inspection program.
Attachment 2 describes the corrective action planned in preparation for returning Turkey Point Unit 4 to service, and includes the basis for the proposed corrective action.
The unit is presently scheduled to return to power operation on December 1,
1976.
- However, as stated in FPL letter L-76-369, we will not return the unit to power operation until we receive NRC concurrence with our corrective action.
Therefore, in
$.4 ~)~>~
PEOPLE... SERVING PEOPLE
Office of Nuclear Reactor Regulation Attention:
Mr. George Lear, Chief Page Twg November 24, 1976 accordance with our letter L-76-369 and your letter of October 29,
- 1976, we request written NRC concurrence with our corrective action as soon as possible in order that we may startup Turkey Point Unit 4 on schedule.
Very truly yours, Robert E. Uhrig Vice President REU/HNP/MAS/cpc Attachments (2) cc:
Mr. Norman C. Moseley Robert Lowenstein, Esquire
ATTACHMENT 1 L-76-403 November 24, 1976 ASSESSMENT OF TURKEY POINT U-BEND EXAMINATIONS The intensive examination of the 31 U-bend samples removed from steam generator 4B revealed that 3 bends, all in Row 1, contained short (1/16" long) longitudinal intergranular cracks, all at the apex of the bends and initiating from the ID surface.
The attached chart identifies the U-bends which were examined, the inspection technique, and the results.
The cracks were not detected by the non-destructive X-ray and eddy current examination because of their short length.
They were detected by exposing the ID of the U-bends at the apex and bending the tube such that the ID surface was put in tension.
This opens up any tight fissures which may be present and permits their detection by either visual examination under low power microscopy or by 'metallographic examination.
These. results are consistant.with the previous findings from Surry 1, where only the Row 1 tubes were affected.
The difference between the two plants appears to be a matter of degree only, with the Turkey Point situation less severe in terms of crack frequency and magnitude.
ATTACHMENT l
- Q5KV POKE '4B FLOW SLOT a
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Xray examination EC:
Eddy Current examination Met:
Metallographic examination BEND: Bend Test ovality:
[diameter (max) diameter (min) ] in inches
ATTACHMENT 2 L 403 November. 24, 1976 Pa e
1 Florida Power
& Light Company CORRECTIVE ACTION PLAN TO RETURN TURKEY POINT UNIT 4 TO OPERATION As a result of investigations conducted at Surry Units 1
a 2
and Turkey Point Unit 4, a hypothesis has been developed to explain the cracking of small bend radius steam generator tubes at the apex of the U-bend.
The hypothesis requires that three primary phenomena be present simultaneously, and in sufficient magnitude, to permit the initiation of a defect.
The phenomena are:
l.
significant plastic prestraining of the metal',
2.
tensile stress, and 3.
dynamic straining in service.
The details of"the hypothesis are 'contained in VEPCO letter 260B/092276 to'he'NRC dated November 15,'976.
" (Dockets 50-280
& 281)
J Analysis of the tube samples removed from Surry. Units 1 6
2 has indicated that the three phenomena listed'ab'ove exist only in Tube Row 1.
There were no cracks in the Surry tube samples removed from Rows 2 and 3.
Similar results were obtained from analysis of Turkey Point steam generator 4B tube samples.
Table 1 summarizes the results of Surry and Turkey Point tube examinations as of November 17, 1976.
'The first two conditions of the tube cracking hypothesis, plastic prestraining and tensile stress, are expected to be essentially the same at Surry and Turkey Point because both plants have similar steam generator operating conditions and a similar small bend radius tube geometry.
Therefore, comparison of the inservice dynamic straining calculated for 'Turkey Point tubes with the minimum dynamic straining calculated for a cracked Surry tube results in the prediction that cracking of Turkey Point Row 1 tubes should occur.
Metallurgical analysis has confirmed that Turkey Point tube samples taken from Row 1 of steam generator 4B are cracked.
4 ATTACHMENT 2 L 403 November,. 24, 1976 Pae2 Florida Power
& Li'ght Company, acting to provide the greatest assurance for maintaining the public health and safety, has decided to take the corrective action of plugging all Row 1 tubes for all three Unit.
By doing so, all Unit 4 tubes hypothesized as susceptible to cracking will be removed from service.
An additional 32 tubes will be plugged in steam generator 4B as a result of the sample removal opera-tions.
The corrective action is in accordance with recommendations from Westinghouse Electric Corporation, which is the steam generator manufacturer and which has been a major participant in the overall investigative effort.
By plugging steam generator tubes as described above, Florida Power 6 Light Company has concluded that Turkey Point Unit 4 can be safely returned to power operation.
ATTACHMENT 2 TABLE 1 Row 1 Row 2
Row 3
PLANT Turkey Point 4
Surry 1
- Surry 2
- Tube Samples 15 Cracked Samples Tube Samples 15 Cracked Samples 0
0 Tube Samples Cracked Samples.
0 0
- Taken from UEPCO Letter 260B/092276 to the NRC dated November 15, 1976