ML19320C592
| ML19320C592 | |
| Person / Time | |
|---|---|
| Site: | Trojan File:Portland General Electric icon.png |
| Issue date: | 07/11/1980 |
| From: | Goodwin C PORTLAND GENERAL ELECTRIC CO. |
| To: | Clark R Office of Nuclear Reactor Regulation |
| References | |
| NUDOCS 8007170424 | |
| Download: ML19320C592 (8) | |
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'~ + July 11, 1980 Trojan Nuclear Plant Docket 50-344 License NPF-1 Director of Nuclear Reactor Regulation ATTN: Mr. Robert A. Clark, Chief Operating Reactors Branch No. 3 Division of Licensing U. S. Nuclear Regulatory Commission Washington, D. C. 20555
Dear Sir:
In accordance with your letter of May 22, 1980, please find attached an interim report describing the results of the nondestructive examina-tion of U-bends removed from the Trojan steam generator D. We will attempt to adhere to the schedule for reporting additional interim and final results as requested in your letter although this schedule is more stringent than that originally contemplated in our letter of March 27, 1980. We will inform you of any scheduling problems regarding report submittal as they become evident. Should you have any questions regarding this report, please contact us as appropriate. Sincerely, 1- - - %,/4 C. Goodwin, Jr. Assistant Vice President Thermal Plant Operation and Maintenance CC/DRS/4sa9A11 Attachment c: Mr. Lynn Frank, Director 00/ State of Oregon Department of Energy .S Mr. R. H. Engelken, Director / U. S. Nuclear Regulatory Commission Region V 80'07170f2.f
STATUS REPORT NONDESTRUCTIVE EXAMINATION RESULTS OF U-BENDS REMOVED FROM TROJAN STEAM CENERATOR D JULY 1980 INTRODUCTION A total of 29 U-bendo have been removed from steam generator D for nondestructive and destructive examination with the objective of deter-mining the cause and resolution of Row 1 U-bend leakage. The selected U-bends were Row 1-Column i through 26 and Row 2-Column 1 through 3. These include one leaking tute (RIC6), and one tube (RIC26) which was identified by previous Plant eddy current (ET) examination during the Fall 1979 outage as containing On indication. The other 27 U-bend sections removed did not display ET indications during the Fall 1979 inspection. This report presents the preliminary findings of the various nondes~ruc-t tive tests performed to date by Westinghouse. (Upon completion of this phase, selected bends will be retained by Westinghouse for destruc-tive examination and a number will be sent to Battelle Northwest for additional nondestructive and destructive examination.) The nondestructive examination (NDE) reported herein consists of the followings 1. Measurement of leg spacing of each bend takoa in situ below the tangent points before the bends were cut. The measurement of the cut bend at the same location was made in the laboratory. 2. Ovality measurements taken on each removed bend at the apex and at the cold and hot leg tangent points and more detailed ovalities measured on selected tubes. 3. Visual examination of each bend. 4. Double wall radiography of each bend. 5. Eddy current examination of each bend. In addition, Silastic molds were taken of the inner diameters of three tubes (RIC6, RIC10 and RIC22) at the hot-and cold-leg tangent points and will be retained for detailed measurements, if required, since these bends will be destructively evaluated. Finally, wall thickness traverses are currently being made by ultrasonic gaging on selected bends; these results will be reported subsequently. NONDESTRUCTIVE EXAMINATION RESULTS 1. Dimensional Measarements Table 1 presents the leg spacing, before and after cutting of each Row I bend and the maximum ovality measured, after removal, at the apex of the bends and at the hot-and cold-leg tangent points. Also included are the NDE findings.
It should be noted that there is an uncertainty associ-ated with the pre-and post-leg spacing values due both to the difficulties inherent in making the measurements in the steam generator prior to catting and in duplicating the location for the laboratory measurements afterward. With regard to ovality, there does not appear at this time to be a correlation between the maximum ovality measured and the incidence of cracking. More detailed ovality measurements, taken at 1/4-in. axial increments above and below the hot-and cold-leg tangent points, have been developed on the three bends with indi-cations of crackir.g (RIC6, RIC7 and RIC26) and have been compared with similar measurements taken on three tubes with no obvious cracking (RIC4, RIC13 and RIC18). Again, there does not appear to be any correlation between the maximum value of ovality and cracking. In fact, as shown in Table 1, the ovalities at the particular tangent points which are cracked, the cold leg in each of these three cases, are essentially equal or less than the ovalities at the corresponding hot-leg tangent points which are not believed to be cracked, and are well below the ovalities observed in many of the other tubes which are apparently uncracked. There does appear to be a characteristic shape to the ovality plots, however, as shown in Figure 1, which compares one of the tangent locations in two bends, arbi*-'rily called the " smooth" transitien (because of the even c ntour of the bend in the transition from the straight portion) with the " opposite" transition (which does not have quite as smooth a transition). All of the cracks reported in Table 1 are believed to be located in the " opposite" transition, but as shown in Figure 1, there does not appear to be an obvious distinction in this region between cracked and uncracked bends. t.dditional effort is underway, to be supplemented with the destructive examination results, to evaluate these characteristics. 2. Visual Examination All U-bend tubes were examined visually upon arrival. Several were further examined at magnifications up to 30X in an attempt to correlate crack locations and patterns with those indicated by radiography. All U-beads were covered with a tenacious black scale. This scale is typical for tube samples removed from steam generators at other plants. The scale was judged to be intact before sample removal; but due to removal opetations and subsequent handling, some scale flaked off at several locations. Tube RIC6 revealed a crack-like indication on the OD la the vicinity of the radiographic indication. The area was covered by a thin oxide layer which made exact visual exami-nation questionable. Looking at the tube ID, however, two or possibly three distinct longitudinal " crack-like" indications were visible. Similar examinations were carried out on RIC7 and RIC26. Neither bend exhibited any indication on the tube OD. Exami-nations on the ID of the tube RIC7 revealed one possible indication. It was difficult to assess positively if this was the indicati m seen on the radiograph due to oxide deposits on the ID and the short length of the indication. No obvious indications were found on the inside of RIC26. The ids of these U-bends will be further examined and documented later. 3. Radiography double-wall techniqueta]phed after removal, using the Each U-bend was radiogra with shots taken at 0 degrees and 90 degrees at the apex of each bend and at 0 degrees, 45 degrees, 90 degrees and 135 degrees at both hot-and cold-leg transitions. A total of 303 radiographs were taken. Axial cracks were observed in three U-bends (RIC6, RIC7, and RIC26) as described in Table 2. 4. Laboratory Eddy Current Testing Each U-bend was examined after removal utilizing the inservice inspection probe, Zetec 0.650" BF. Test fre-quencies were 400 kHz and 100 kHz differential and also 100 kHz absolute. The ET results are presented in Table 2.
SUMMARY
Nondestructive examination by radiography and eddy current testing detected axial cracks in the cold-leg transition, at or near the extra-dos surface in three of the 29 Row I and Row 2 U-bends removed from steam generator D of the Trojan plant; these were RIC6, RIC7 and RIC26. The crack discovered in RIC7 during this inspection is not discernible in tapes from the Fall 1979 inspection. Maximum ovality measurements do not coincide with the reported crack locations, but he relationship, if any, between the crack locations and the smoothness of the transition from the straight legs will be investigated. [a] Voltage: 200 kV initially; 150 kV for verification Amperage: SmA Time: 129 sec. Film: Type M Double Film Source to film 60 in. distance: DRS/4sa66.17B12 TABLE 1 STEAM GENERATOR TUBE DIMENSIONAL MEASUREMENTS AND NDE RESULTS Percent Ovality Tube Leg Spacing (Inches) (Maximum) Number Pre Post a CL Apex HL NDE Results R1-C1 3.505 3.457 .048 4.8 2.06 1.71 OK RI-C2 3.481 3.480 .001 4.23 1.37 2.40 OK R1-C3 3.483 3.566 +.083 1.71 3.54 4.57 OK R1-C4 3.483 3.479 .004 1.26 2.06 0.57 OK R1-C5 3.476 3.489 +.013 2.17 2.74 4.11 OK R1-C6 3.447 3.495 +.048 3.66 1.60 4.80 Crack in cold-leg transition per RT and ET R1-C7 .3.452 3.474 +.022 2.17 2.40 2.06 Crack in cold-leg transition per RT and ET R1-C8 3.465 3.435 .030 2.06 2.97 2.40 OK RI-C9 3.473 3.466 .007 1.23 2.29 3.20 OK R1-C10 3.501 3.450 .015 2.06 1.71 4.57 OK RI-C11 3.493 3.478 .051 4.80 2.97 2.17 OK R1-C12 3.479 3.466 .013 2.51 1.37 2.97 OK R1-C13 3.481 3.463 .018 2.06 1.71 5.14 OK R1-C14 3.497 3.480 .017 4.91 2.74 1.37 OK R1-C15 3.481 3.420 .061 4.11 2.17 2.40 OK i R1-C16 3.478 3.470 .008 3.31 2.17 3.09 OK R1-C17 3.471 3.417 .054 2.74 2.06 3.54 OK R1-C18 3.513 3.535 +.022 4.34 3.26 1.66 OK R1-C19 3.483 3.450 .033 3.09 2.06 1.14 OK R1-C20 3.503 3.556 +.053 4.91 2.97 2.51 OK R1+C21 3.506 3.534 +.028 4.69 3.20 1.26 OK R1-C22 3.507 3.510 +.003
- .69 3.77 1.26 OK R1-C23 3.502 3.535
+.033 2.86 3.31 0.97 OK R1-C24 3.503 3.542 +.059 4.23 3.09 1.03 OK R1-C25 3.495 3.466 .029 -2.17 2.51 5.37 OK R1-C26 3.503 3.509 +.006 2.63 2.40 2.57 Crack in cold-leg transition per RT and ET DRS/4sa66.17B16
TABLE 2 Page 1 of 2 NONDESTRUCIIVE EVALUATION OF STEAM GENERATOR D TUBE U-BEND SECTIONS Tube , Number Visual Examination Radiography [a] Eddy Current Examination [b] RICI No indications (NI) No discontinuity (ND) No indications (NI) RIC2 NI ND NI RIC3 NI ND NI RIC4 NI ND NI RICS NI ND Indication - hot leg RIC6 1 indication - OD One axial crack Large indication - 3 indications - ID (3 segments) at cold-cold leg leg transition on extrados, total length 0.75-in. RIC7 No indication - OD One axial crack at Indication - cold leg 1 indication - ID cold-leg traasition near extrados, total length 0.5 to 0.625-in. RIC8 NI ND NI RIC9 NI ND NI i RIC10 NI ND NI RIC11 NI ND NI RICl2 NI ND NI RICl3 NI ND NI RICl4 NI ND NI RIC15 NI ND NI .RIC16 NI ND NI RIC17 NI ND NI [a] W RT analysis at 150 kV (6-26-80) .[b] W ET analysis with Zetec probe (6-12-80)
TABLE 2 Page 2 of 2 Tube Number Visual Examination Radiographyt3] Eddy Current Examination {DI RIC18 NI ND NI R ! 19 NI ND NI RIC20 NI ND NI 1 RIC21 NI ND NI RIC22 NI ND NI RIC23 NI ND NI RIC24 N1 ND NI RIC25 NI ND . NI RIC26 NI Two axial cracks at Indication - cold leg cold-leg transition on extrados, total length 0.625-in. R2Cl NI ND NI R2C2 NI ND NI R2C3 NI ND NI t i DRS/sa/4gah66.17B18 j
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