ML13330A065
| ML13330A065 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 06/24/1980 |
| From: | Baskin K Southern California Edison Co |
| To: | Crutchfield D Office of Nuclear Reactor Regulation |
| Shared Package | |
| ML13329A103 | List: |
| References | |
| TAC-47835 NUDOCS 8006270194 | |
| Download: ML13330A065 (4) | |
Text
Southern California Edison Company P.
- 0. BOX 800 2244 WALNUT GROVE AVENUE ROSEMEAD. CALIFORNIA 91770 K. P. BASKIN June 24, 1980 TELEPHONE MANAGER, NUCLEAR ENGINEERING (213) 572.1401 AND LICENSING Director, Office of Nuclear Reactor Regulation Attention:
D. M. Crutchfield, Chief Operating Reactors Branch No. 5 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D.C.
20555 Gentlemen:
Subject:
Docket No. 50-206 Steam Generator Inspections San Onofre Nuclear Generating Station Unit 1 During a meeting with the Regulatory staff held on June 18, 1980 in Pittsburgh, Pennsylvania, we reviewed the results of the (1) general surveil lance inspections made in order to evaluate steam generator tube integrity due to wastage type imperfections, (2) antivibration bar-area inspections made in order to reassess the overall growth of steam generator tube wear indications at antivibration bar locations, (3) denting inspections made in order to reassess the magnitude of steam generator tube support plate inplane expansion or hourglassing and the potential for continued steam generator tube denting, (4) tube sample metallographic examinations made to determine the mechanism/cause of the significant number of steam generator tube indications at the top of the tubesheet, and (5) steam generator chemistry survey made in order to assess the phosphate chemistry control operations. The following conclusions were made during the meeting:
- 1. Based on the general surveillance inspections, significant or excessive degradation of tube integrity due to wastage type thinning imperfections is not occuring in the steam generators.
- 2.
Based on the antivibration bar-area inspections, significant or excessive overall growth of tube wear indications at antivibrati n bar locations is not occurring in the steam generators.
- 3.
Based on the denting inspections, significant or excessive progression in the magnitude of steam generator tube support plate inplane expansion or hourglassing and in steam generator tube denting is not occurring in the steam generators.
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- 1)(1 Mr. D. M. Crutchfield, Chief
-2
- 4.
Based on the tube sample metallographic examinations, significant caustic induced intergranular attack has occurred at the top of the tubesheet in the hot legs (inlet side) of the steam generators. The circumferential nature of the.intergranular attack is such that within the eddy current inspection data base gathered to date, there are complex eddy current signals for which interpretation at this time is inconclusive in detect ing steam generator tube degradation in excess of the plugging limit.
(In addition to the significant caustic induced intergranular attack at the top of the tubesheet, one tube exhibited significant caustic induced intergranular attack below the top of the tubesheet within the tubesheet crevice; that tube was removed for metallographic examination.)
In order to better characterize the complex eddy current signals at the top of the tubesheet, near term plans have been initiated to acquire additional data as follows:.
- a. reinspect representative sample of tubes in Steam Generator C with multifrequency, surface coil type probe, if available,
- b. remove additional tube samples from Steam Generator C representing different complex eddy current signals observed at the top of the
'tubesheet,
- c. investigate and apply means, if necessary, to test individual tubes in Steam Generator C in order to confirm leak before break mechanism of tube corrosion at the top of the tubesheet, and
- d. continue metallographic examination of present tube samples.
- 5.
Based on the steam generator chemistry survey, the phosphate chemistry control utilized has allowed somevariation in the desired chemistry at intermittent periods. The survey has shown evidence of free caustic presence in the steam generator bulk water and in the crevices as indi cated by the return of high sodium to phosphate molar ratios during transient conditions.
In order to improve.the steam generator phosphate chemistry control, near term plans will be initiated as follows:
- a. perform cold and hot water flushing of Steam Generators A, B and C prior to startup,
- b. adjust operational chemistry to slightly lower the sodium to phos phate molar ratio and increase the phosphate concentrations, and
- c. check treatment chemical purity and recheck and closely monitor makeup evaporation purity.
The information provided at the June 18, 1980 meeting as handout material in support of the Conclusions discussed above is contained in Enclosures 1 through 7 of this letter. With respect to the near term plans discussed in Conclusions 4 and 5 above, Enclosure 8 of this letter contains
Mr. D. M. Crutchfield, Chief
-3 the details of our plans to acquire additional data to better characterize the complex eddy current signals at the top of the tubesheet while the details of our plans to improve the phosphate chemistry control are contained in of this letter.
To facilitate your review and understanding of the information provided at the June 18, 1980 meeting as contained in the Enclosures 1 through 7 of this letter, the following summary descriptions are provided, with additional clarification where appropriate: outlines the events which occurred prior to conducting the eddy current inspections and the general conclusions made based on the inspection results. provides the inspection programs conducted in each steam generator, the location of eddy current indications in each steam generator, the location of tubesheet denting in each steam generator, the number of plugged tubes prior to the current inspections, and the number of tubes to be plugged, including location, based on the current inspections. With respect to the summary of tubes to be plugged, two separate tables are provided:
the first table includes only those tubes having discretely quantified eddy current indications exceeding the plugging limit and the second table includes those tubes having discretely quantified eddy current indications exceeding the plugging limit and those tubes having the complex eddy current signals which could not be discretely quantified.. provides the results of the steam generator tube gauging/denting inspections conducted in Steam Generators A and C. Based on the results, a number of tubes (i.e., 19 in Steam Generator A and five in Steam Generator C) exhibited an apparent increase in the amount of restriction when compared to previous inspections. Four other tubes (two in Steam Generator A outlet side and two in Steam Generator C outlet side) were restricted to less than a.460" probe and will be plugged; however, these tubes had not previously been gauged. The apparent increase in restrictions is most likely an artifact of the gauging technique (i.e., due to pushing speed, pushing force, etc.) and does not represent a significant progression of denting. This conclusion has.
been substantiated by a preliminary evaluation of the photographic and videotape inspections and measurements made to reassess the extent of flow slot hourglassing and support plate cracking in each steam generator. Based on the preliminary evaluation, there has been no perceptible change in the overall conditions of the secondary side of each of the steam generators when compared to previous inspections. The evaluation of the photographic and videotape inspections and measurements is currently being completed and will be submitted as part of the final report documenting the results of the additional inspections and examinations being conducted to better characterize the complex eddy current signals at the top of the tubesheet.
Mr. D. M. Crutchfield, Chief
-4 provides the statistically calculated wear rates at antivibration bar intersections in each steam generator, the statistically calculated growth rates of eddy current indications above the tubesheet in Steam Generators A and C and the distribution of all eddy current indications at and above the top of the tubesheet. provides the results of the nondestructive (visual and radiography) and destructive (metallography) examinations of the three tube samples removed from Steam Generator A. provides the results of the steam generator chemistry survey and the details of the near term plans to improve the phosphate chemistry control. outlines the near term plans relative to additional data acquisition and chemistry control.
It is our understanding, based on discussion with representatives of the Regulatory staff present at the June 18, 1980 meeting, that our near term plans discussed at the meeting and outlined in Enclosure 7 constitute appro priate actions in light of the conclusions drawn to date. As discussed above, the details of our plans to acquire additional data to better characterize the, complex eddy current signals at the top of the tubesheet are contained in of this letter. The reinspections with the surface coil type probe and the removal of additional tube samples are scheduled to commence during the week of June 23, 1980, while the pressure tests, if necessary, are scheduled to commence approximately July 1, 1980. It is currently estimated that sufficient information will be available from the reinspection, tube removal and metallographic examinations and pressure tests, if necessary, during the week of July 6, 1980 to determine the overall condition of the steam generators. Accordingly, we expect to be prepared to meet with you at that time in order to facilitate your review of the available information and will keep you advised of our progress to assist you in scheduling such a meeting.
If you have any questions or desire further information concerning our plans, please contact me,.,
Very truly yours, Enclosures (8) cc:
R. H. Engelken (Director, OIE, Region V)