ML20031F243
| ML20031F243 | |
| Person / Time | |
|---|---|
| Site: | San Onofre, Farley  |
| Issue date: | 08/27/1981 |
| From: | Murphy E Office of Nuclear Reactor Regulation |
| To: | |
| Shared Package | |
| ML13319A640 | List:
|
| References | |
| FOIA-81-313 NUDOCS 8110190412 | |
| Download: ML20031F243 (2) | |
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SAN ON0FRE STEAM GENERATOR TUBE DEGRADATION Prepared by Emmett L. Murphy Materials Engineering Branch Division of Engineering The unit was shut down with a 270 gpd primary to secondary steam generator leak cn April 9, 1980.
Five (5) confirmed, and three (3) probable, leakers have been identified. Multifrequency eddy current test (ECT) inspection and labora-l tory examination of tubes specimens removed from the plant indicated these leakers to be among several hundred, or possibly several thousand, tubes with extensive caustic intergranulsi utack and circumferential cracking at the top of the tubesheet elevation.
The extensive intergranular corrosion at the top of the tubesheet elevation had not been previously identified in earlier inspections as a significant d: gradation mode at San Onofre. A data review covering the last two years of operation indicates that free caustics have been present in the secondary bulk water throughout this period due to difficulties in controlling the sodium to phosphate ratios. Thus, we believe that this intergranular corrosion problem has developed over at least this period of time. The recent application of multifrequency techniques for eddy current testing in the field has resulted in greatly enhanced capability to detect intergranular corrosion at locations such as the top of the tubesheet, where previous single frequency techniques had 8
only very limited capability. Nonetheless, even with the multifrequency tech-nique, there remains a concern regarding how reliably such intergranular corrosion may be detected.
o In view of the extensive number of tubes known to be affected by this phenomenon, and concerns regarding the reliability by which the affected tubes can be identified, the licensee has initiated a program to develop, qualify by test, and install sleeves in all steam generator tubes within the zone (consisting of several thousand tubes) where this phenomenon is occurring.
It is the licensee's intention that the sleeving repair be considered a long ten.. corrective action in lieu of other repair options such as retubing or replacement of the steam g nerators.
The following issues are anong those which will be addressed by the staff before i
approval to install sleeves into the steam generators or to resume power opera-tion is granted:
1)
Inspectability of the. repaired tubes including the sleeves themselves.
- 2) Leak-tightness; potential relaxation due to heat Ep and cool-down cycles.
- 3) Mechanical strength considerations.
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- 4) Stagnation of the secondary water in crevice between sleeve and repaired tube.
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- 5) Man-rem exposure during installation of sleeves.
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0190412 810827 IA
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The staff has met with the licensee on several occasions 'ec discuss the inspection results, additional inspections and analyses to be perfonmed, and possible corrective actions. Additional meetings are planned for August 15 and September 1,1980 to discuss the results of the sleeving development program. The licensee plans to request NRC approval by September 10, 1980 to install sleeves in the steam generator, and by-November 1,1980 to resume power operation.
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