ML20134L314
| ML20134L314 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 02/06/1997 |
| From: | Gibson G SOUTHERN CALIFORNIA EDISON CO. |
| To: | NRC OFFICE OF INFORMATION RESOURCES MANAGEMENT (IRM) |
| References | |
| NUDOCS 9702190014 | |
| Download: ML20134L314 (9) | |
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. EDISON-An f l#SOV 14TI RN4TIOMI Cunepony February 6,1997 U. S. Nuclear Regulatory Comndssion Document Control Desk Washington, D.C. 20555 l
l Gentlemen:
l
Subject:
Docket No.' 50-361 l
Special Report: Inservice Inspection of Steam Generator Tubes l
San Onofre Nuclear Generating Station, Unit 2 l
On January 24,1997, Edison completed an inservice inspection of steam generator tubes at i
San Onofre Nuclear Generating Station, Unit 2. Reporting Requirement 5.7.2.c of Appendix A, Technical Specifications to Facility Operating License NPF-10, requires the results of steam generator tube inspections be reported to the Nuclear Regulatory Commission.
i The enclosed report provides the number of tubes plugged or sleeved, and the results of tube inspections which fall into Category C-3 (as defined in Section 5.5.2.11.c).
The initial inspection results indicate that an additional inspection should be performed after about 12 months of operation. Edison will submit a final assessment of the enclosed i
L inspection results within 180 days of the end of the Unit 2 Cycle 9 refueling outage. Because Unit 2 Cycle 9 is scheduled for about 24 months of operation, Edison is planning a mid-cycle outage to complete this inspection.
l If you require any additional information, please so advise.
Sincerely, O
1
- M 9702190014 970206 PDR ADOCK 05000361 Manager, Compliance 0
PDR j
Enclosure:
cc:
L. J. Callan, Regional Administrator, NRC Region IV J. E. Dyer, Director, Division of Reactor Projects, NRC Region IV K. E. Perkins, Jr., Director, Walnut Creek Field Office, NRC Region IV 1
J. A. Sloan, NRC Senior Resident, San Onofre Units 1,2 & 3 M. B. Fields, NRC Project Manager, San Onofre Units 2 and 3 a
Institute of Nuclear Power Operations (INPO) 1 P. O. Box 128 San Clemente. CA 92b74-0128 I -.
SPECIAL REPORT - INSERVICE INSPECTION OF STEAM GENERATOR TUBES Inspection Program Planned Inspection Scope j
l Table I summarizes the planned inspection program. In addition, the inspection program meluded:
a) eddy current profilometry at the top of the tubesheet of a small number of tubes adjacent to " tie rods" where denting has been experienced, and a sampling of hot leg dented tube support intersections.
b) inspection with the Plus-Point Probe ofindications by the bobbin probe that were non-quantifiable or distorted.
Inspection Scope Expansion Table 2 summarizes significant inspection program scope expansion in response to inspection results. In addition:
a) all hot leg eggerate intersections that were identified by bobbin probe to have a quantifiable indication, were examined with the Plus-Point Probe to verify that the degradation mechanism was volumetric mechanical wear.
b) tubes that were selected for plugging due to tube-to-support wear were examined with the Plus-Point Probe to verify that the degradation mechanism was volumetric mechanical wear.
c) significant numbers of dented tube support intersections were examined with an eddy current profilometry probe to confirm and improve Edison's understanding of the size and shape profile of these intersections.
Results The most salient point in the inspection of tubing falling into Category C-3 is the continuing progression of circumferential and axial cracking in the vicinity of the explosively formed expansion transition at the top of the inlet (hot leg) tubesheet.
j Other tubing degradation was also identified.
a)
Most notable was axial cracking at the intersections of tubing and eggerate supports on the inlet (hot leg) side of the steam generator. This cracking was observed at intersections experiencing denting, and at intersections with no conclusive indications of denting. (Denting is the plastic deformation of tubes resulting from the growth / buildup of corrosion products (magnetite)in the tube-to-tube support structure annuli.)
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b)
Axial cracking was identified in areas between supports (commonly called "freespan") on the hot leg side of the steam generators.
l c)
A five-fold increase in denting was identified in the region composed of L
intersections of supports with tubing on the hot leg side of the steam generators. These suppon intersections are labeled 04H, 05H, 06H, 07H, and 08H on Figure 1, the steam generator internal location reference guide.
d)
Previously identified tubing mechanical wear at tube supports is progressing typically for this steam generator design.
In accordance with " DRAFT" Regulatory Guide 1.121 (Bases for Plugging Degraded PWR Steam Generator Tubes) an assessment of the significance of these various indications will be conducted using-(a) The " DRAFT" Proposed Steam Generator Rule (50.XX), " Steam Generator Tube Integrity" (b) The associated " DRAFT" Regulatory Guide X.XX, " Steam Generator Tube Integrity" (c) Nuclear Regulatory Commission Generic Letter 95-05, " Voltage-Based Repair Criteria for Westinghouse Steam Generator Tubes Affected by Outside Diameter Stress Corrosion Cracking" Removal of Tubes from Service (by Plugging)
Table 3 illustrates the number of tubes removed from service in each steam generator. Each l
tube is only accounted for once in this listing, although it may also have an eddy current indication of a type below the point in the listing where it appears.
In-Situ Hydrostatic Testing of Tubing Table 4 provides a summary ofin-situ hydrostatic testing of tubing.
Removal of Tubing Samples from the Steam Generators l
Ponions of tubes (Row-Column) 94-32,61-111, and 16-164 were removed from Steam Generator E-089 for destructive examination. Edison will update the Commission on the results of these examinations in the follow-up report discussed in the cover letter.
Supplemental Performance Demonstration: Eddy Current Bobbin Technique f
This demonstration will use portions of" DRAFT" Regulatory Guide X.XX, " Steam j
Generator Tube Integrity" The main purpose of this demonstration is to validate Probability of Detection (POD) performance. These POD data will serve as input to the Edison 2
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l-submittal on the assessment of the significance of eddy current indications that has been previously discussed in the cover letter.
Input data for this demonstration will include both nondestructive examination and destmetive examination results from the tubes removed from Steam Generator E-089 during this present outage. These data will be the " flawed grading units" that have been evaluated against actual flaw geometry. Tube identity will be protected in Data Sets for this demonstration. Data sets will be constructed from these input data and a " pool" of more than 300 tubes removed from service during this current outage. The " pool" will provide the "unflawed grading units" to permit evaluation of POD performance.
' A protocol for the supplemental demonstration will address analyst teams, analyst training and testing, and data evaluation. Edison will update the Commission on the results of this demonstration in the follow-up report discussed in the cover letter.
Investientions into Cm====d Corrective Measum An accumulation of corrosion products on the secondary-side of the tubing surfaces had been previously identified.' Data from various sources indicated that such deposits might contribute to tubing corrosion. Consequently, Edison convened a panel of expert industry L
personnel with extensive knowledge in steam generator corrosion and water chemistry l
control. The panel reviewed the pertinent information and recommended that Edison chemically clean the deposits from the steam generator tubes. The deposits were removed during this refueling outage.
Chemical cleaning of the Unit 3 steam generators is planned for the April 1997 refueling l
outage. Existing inspection results from both units indicate that Unit 3 may lag Unit 2 by two
,or more fuel cycles in the onset of some of the tubing-related problems discussed above (i.e.,
denting and intergranular attack / stress corrosion cracking in the vicinity of the expansion of the tubing at the top-of-tubesheet).
A review of steam generator secondary-side water chemistry control strategy is ongoing for 1
San Onofre Units 2 and 3. Edison has re-convened the expert panel ofindustry personnel to l
review new information. This thorough and balanced review will be a significant part of investigation into the cause and further corrective measures for steam generator tubing degradation. Edison will update the Commission on the progress of this review in the follow-up report discussed in the cover letter.
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FIGURE 1 -Steam Generator Internal Location Reference Guide
+
CE bODEL 3410 TUBE SUPPORT DRAWING VH2 VSM VC2 l VH3 VH1 VC3 VC1 l
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OSH OSC s
ION 100 30.75*
OSH 0
000 t
n r.-
nrn-l OTH GrC gg.
OSH OSC 4
N' OSH OSC 85*
04H 04C gg.
03H 03C SS*
I 02H 02C 35' 01H 01C l
TSH }L M S.2 5' ML J
TSC 23.00' TEH
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TEC
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INLET OUTLET i
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TABII 1 - Summary of Planned Inspection Program Steam Generator E-088 Steam Generator E-089 Number of Tubes / Percentage of Tubes Full length of tube with the bobbin probe 9051 / 100 %
8958 / 100 %
Tight radius U-bend regions with the 24 / 20 %
24 / 20 %
Plus-Point Probe Upper. bundle freespan region (based on i
thermal-hydraulic 609/20% of Region 609/20% of Region condition predictions) with the Plus-Point Probe Hot leg expansion transition at the top-of-tubesheet with the 9051 / 100 %
8958 / 100 %
Plus-Point Probe j
Cold leg expansion transition at the top-of-tubesheet 655 / 7 %
656 / 7 %
with the Plus-Point Probe Hot leg dents with the Plus-Point Probe 50/20 %
39 /20 %
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TABLE 2 - Summary of Significant Scope Expansion Steam Generator E-088 E-089 Number of Tubes / Percentage of Tubes Plus-Point Probe examination of upper bundle freespan (bounding of indications None 800/Not in 3 tubes)
Applicable Plus-Point Probe examination of all hot leg dented eggerate supports 1094 / 100 %
733 /100 %
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TABLE 3 - Number of Tubes Removed From Service Indication Orientation / Location Steam Generator E-088 E-089 Mixed mode (circumferential and axial oriented indications) that intersect in the tube and are near the expansion transition at the hot leg i
top-of-tubesheet 0
1 Both circumferential and axial oriented indications that do not intersect and are near the expansion transition at the hot leg top-of-tubesheet 5
3 Circumferentiaily oriented indications near the expansion transition at the hot leg top-of-tubesheet 88 49 Axially oriented indications in the upper bundle (typically above elevation 07H), and not associated with a tube suppon (freespan) 0 3
]
1 As above, but located at a tube suppon 0
1 Axially oriented indications in the lower bundle (typically below elevation 07H), and not associated with a tube support (freespan) 5 21 Axially oriented indications at a hot leg eggerate tube support location 2
6 Axially oriented indications at a dented hot leg eggerate tube support location 4
4 Axially oriented indications near the expansion transition at the hot leg top-of-tubesheet 58 50 Preventive plugging of tubes adjacent to a tie rod 6
0 Indication of wear at a tube support location 2
7 Volumetric indication at a miscellaneous location in a tube 3
4 Preventive plugging based on presence of a foreign object 0
3 Highest growth rate dent 1
0 Miscellaneous preventive plugging 4
2 Total 178 154 7
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TABLE 4 - Summary ofIn-Situ Hydrostatic Testing of Tubing STEAM GENERATOR E-088 REGION TURE NUMBER GPM LEAKAGE AT MAX TEST ROW-COLUMN LOC.
NOPD MSLB POST-MSL PRESS Eggerate 44-56 07H 0
0 N/A 4746 Iwwer bundle 11-169 Full Tube 0
0 N/A 4746 Tubesheet 52-70 TSH 0
0 N/A 5292 53-111 TSH 0
0 N/A 4746 STEAM GENERATOR E-089 REGION TUBE NUMBER GPM LEAKAGE AT MAX TEST ROW-COLUMN LOC.
NOPD MRB POST-MSL PRESS Eggerate 13-117 06H 0
0.31 0.051 3200 92-128 02H 0
0 N/A 4746
]
94-110 08H 0
0 N/A 4746 Lower bundle 16-166 Full Tube 0
0 N/A 4746 15-15 Full Tube 0
0 N/A 4746 23-15 Full Tube 0
0 N/A 4746 31-17 Full Tube 0
0 N/A 4746 82-24 Full Tube 0
0 N/A 4746 92-34 Full Tube 0
0 N/A 4746 106-38 Full Tube 0
0 N/A 4746 110-42 Full Tube 0
0 N/A 4746 112-36 Full Tube 0
0 N/A 4746 Upper bundle 122-112 Full Tube 0
0 N/A 4746 122-120 Full Tube 0
0 N/A 4746 Tubesheet 40-56 TSH 0
0 N/A 4746 59-79 TSH 0
0 N/A 5292 94-86 TSH 0
0 N/A 4746 Notes:
GPM = Gallons per Minute NOPD = Normal Operation Pressure Differential MSLB = Main Steam Line Break Pressure Differential N/A = Not Applicable l
The Test pressure that correlates to 3 times NOPD is 4746 psi for axial flaws and 5292 psi l
for circumferential flaws.
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