ML20024C293
| ML20024C293 | |
| Person / Time | |
|---|---|
| Site: | Fort Calhoun  |
| Issue date: | 07/01/1983 |
| From: | OMAHA PUBLIC POWER DISTRICT |
| To: | |
| Shared Package | |
| ML20024C283 | List: |
| References | |
| NUDOCS 8307120489 | |
| Download: ML20024C293 (8) | |
Text
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Straa gin:ratsr Tube Eddy Curr:.nt Inspection'Repcrt Steam Generators 'A' and 'B' 1983 Refueling Outage ,
, Introduction The Fort Calhoun Station Unit No.1 utilizes two inverted U-tube steam gen-
- erators, i.e., Steam Generator ' A' and Steam Generator 'B' . The in-service
-inspection is ordinarily performed on each steam generator on a rotating schedule in accordance with Section 3.3(2) of the Technical Specifications.
The surveillance requirements for inspection of the steam generator tubes ensure that the structural integrity of this portion of the reactor coolant
-system will be maintained and also provide a means of characterizing the nature and cause of any tube degradation so that corrective measures can be taken.
l The most recent previous in-service eddy current test (ECT) of tubes in Steam Generator ' A' was performed during the 1978 refueling outage. At that time approximately 10% of the tubes were examined with the results classified as " Category C-1" per Table 3-8 of the Technical Specifications.
I The most recent previcus in-service ECT of tubes in Steam Generator 'B' was performed during the 1981 refueling outage. At that time approximately 7%
of the tubes were examined with the results classified as " Category C-1" per Table 3-8 of the Technical Specifications.
Discussion The inspection covered by this report was perfonned during the period Decem-ber 27, 1982 through January 2,1983 on approximately 6% of the tubes in each steam generator, by a qualified ECT vendor. The multi-frequency in-spection technique was used because of the better resoluti_on provided over the single frequency technique. The inspection was conducted from the cold leg side, completely over the U-bend and down to the tube sheet on the hot
- leg.
' The steam generator tube bundle is supported at several elevations by a com-bination of ' egg crate supports, drilled hole supports and bat wings. The partial drilled hole supports at the various elevations are shown in Fig-ures 1, 2, and 3. The upper tube supports are shown in Figure 4.
The location of the majority of tubes inspected in each steam generator l
11es in that portion of the tube bundle that passes through the drilled hole partial support plates. The ' A' Steam Generator program consisted of 308 tubes for discontinuity indications. A profilometry examination was perfonned on 52 tubes, and 88 tubes were examined at lower gains so dent
- amplitude could be measured. The 'B' Steam Generator program for discon-tinuity indications consisted of 302 tubes and 114 tubes were examined at lower gains so dent amplitude could be measured. A total of 40 tubes in i, each steam generator were inspected at 25 KHz for sludge height measure-i ments. The inspection patterns for Steam Generator ' A' and Steam Generator
'B' are shown in Figures 5 and 6, respectively.
The data from the inspection was recorded on magnetic tape and strip charts. These recordings were evaluated for any tube wall anomalies and the results were tabulated. The tabulated results were compared to the previous inspections to detennine if any changes might have occurred.
8307120409 830701 gDRADDCM05000g5
- Resul ts '
The Technical Specifications define a tube containing ~ imperfections greater than or equal to 20% of the nominal wall thickness as degraded and one with greater than 40% wall thinning as defective. The results of the 1983 inspection for Steam Generator ' A' show one tube to be degraded with wall thinning of 20% on the hot leg side. Steam Generator 'B' ECT located one degraded tube with measured wall thinning of 25% on the cold leg side. The examination also located two (2) other tubes that exhibited wall thinning of less than 20%.
As noted in the 1981 ECT report for Steam Generator 'B', denting or dent-like indications were. observed on several tubes in the region of the #8
. tube support plate. These same dent-like indications were again observed during this examination. A small amount of dent growth was noted by com-parison to the 1981 examination. Approximately fifty percent (505) of the tubes examined showed denting. The dent size ranged from approxiately
.001" to .030" . A circumferential dent standard was used to quantify dent size, in addition to an ECT technique that shows the profile of the dents examined. - The profiles of dents in those tubes examined with this tech-nique showed denting from either one or two sides, but not the full cir-cumference of the tube.
The sludge-height measurements indicated an increase in the depth of the sludge pile. However, the deposition was as expected based upon the trend established by previous inspections.
Conclusions The low extent of degradation, i.e., one tube in ' A' with 20% wall thinning l and one tube in 'B' with 25% wall thinning, indicates that no substantial
! mechanisms are in progress. The evidence of denting was reviewed by the i steam generator manufacturer and an evaluation provided. The manufacturer concluded that the amount of denting is of no major consequence with res-pect to continued safe plant operation during the next operating cycle. In addition, it is noted that the steam generator manufacturer conducted a visual inspection of the secondary side of both units during this outage.
l The results indicate the condition of the steam generators has not degraded i significantly since the 1981 inspection.
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