ML083380263
| ML083380263 | |
| Person / Time | |
|---|---|
| Site: | Arkansas Nuclear  |
| Issue date: | 11/03/2008 |
| From: | Clark R Entergy Operations |
| To: | Wang A Plant Licensing Branch IV |
| Shared Package | |
| ML083380255 | List: |
| References | |
| Download: ML083380263 (5) | |
Text
1 OFFICE OF NUCLEAR REACTOR REGULATION STEAM GENERATOR TUBE INSPECTION DISCUSSION POINTS REFUELING OUTAGE 1R21 RENEWED FACILITY OPERATING LICENSE NO. DPR-51 ENTERGY OPERATIONS, INC.
ARKANSAS NUCLEAR ONE, UNIT NO. 1 (ANO-1)
DOCKET NO. 50-313 The following discussion points have been prepared to facilitate the telephone conference call arranged with the Entergy Operations, Inc. (Entergy, the licensee), to discuss the results of the steam generator tube inspections to be conducted during the upcoming fall 2008, Arkansas Nuclear One, Unit 1 (ANO-1) refueling outage (1 R21). This conference call is scheduled to occur towards the end of the planned SG tube inspections, but before the Entergy completes the inspections and repairs.
The U.S. Nuclear Regulatory Commission staff plans to document a summary of the conference call as well as any material that is provided in support of the call.
- 1.
Discuss any trends in the amount of primary-to-secondary leakage observed during the recently completed cycle.
No indication of primary-to-secondary leakage present prior to the current refueling outage (1R21). (Ar-41 < MDA, H3 ~1.0 gpd)
- 2.
Discuss whether any secondary side pressure tests were performed during the outage and the associated results.
No secondary side pressure tests have been performed or scheduled for 1R21.
- 3.
Discuss any exceptions taken to the industry guidelines.
No exceptions were taken to NEI 97-06 and EPRI Steam Generator Guidelines.
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- 4.
For each steam generator, provide a description of the inspections performed including the areas examined and the probes used (e.g., dents/dings, sleeves, expansion transition, U-bends with a rotating probe), the scope of the inspection (e.g., 100% of dents/dings greater than 5 volts and a 20% sample between 2 and 5 volts), and the expansion criteria.
Area Inspected Exam Type Probe Used OTSG
- of Inspection s
Expansion Full Length Tubing 100% Full Length 0.510 Bobbin A
15595 None Full Length Tubing 100% Full Length 0.510 Bobbin B
15596 None Special Interest Wear X-Probe at wear location X-Probe A
689 None Special Interest Wear X-Probe at wear location X-Probe B
541 None 5.a For each area examined (e.g., tube supports, dent/dings, sleeves, etc), provide a summary of the number of indications identified to-date for each degradation mode (e.g., number of circumferential primary water stress corrosion cracking indications at the expansion transition). For the most significant indications in each area, provide an estimate of the severity of the indication (e.g., provide the voltage, depth, and length of the indication). In particular, address whether tube integrity (structural and accident induced leakage integrity) was maintained during the previous operating cycle. In addition, discuss whether any location exhibited a degradation mode that had not previously been observed at this location at this unit (e.g., observed circumferential primary water stress corrosion cracking at the expansion transition for the first time at this unit).
Mechanical wear is currently the only degradation mechanism in both steam generators and is limited to the tube support plates in both steam generators.
Condition report CR-ANO1-2008-01700 has been initiated due to the significant number of new wear locations in Steam Generator Eddy Current Examination of E24A (SG A)and E24B (SG B) during 1R21. Many of the wear indications are occurring near the eighth tube support. This is true for both Steam Generators.
The 10 largest wear indications for each steam generator are provided in an attached table with location, voltage, depth and length of indication. The total number of wear indications in both steam generators identified to date is listed below:
Wear was previously identified during the last steam generator inspection. The structural integrity limit for mechanical wear is 75% through-wall (TW) based on 1.5 long tapered wear. No wear indication has exceeded the structural wear limit for the last operating cycle or challenged accident induced leakage integrity. Steam generator tube integrity has been maintained during the last operating cycle.
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- b.
Describe in-situ pressure test plans and results (as applicable and if available).
No indications exceeded screening criteria have been identified to date.
- 6.
Discuss the following regarding loose parts:
What inspections are performed to detect loose parts.
Periphery exam at the top of tubesheet (TTS) based on visual inspection and 100% full length (FL) Bobbin Exam.
a description of any loose parts detected and their location within the steam generator (SG), including the source or nature of the loose part, if known, None to date; however, bobbin and visual exams are still in progress.
if the loose parts were removed from the SG None to date.
indications of tube damage associated with the loose parts, None to date.
- 7.
Discuss the scope and results of any secondary side inspection and maintenance activities (e.g., in-bundle visual inspections, feed ring inspections, sludge lancing, assessing deposit loading, etc).
SG A Secondary Visual:
First Span - Annulus for loose parts, Inner Bundle for tie rod bowing, and Orifice Plate 15th Span - Use of cart via secondary manway - top side of 15th 14th Span - via 14th inspection port - top side of 14th and underside of 15th SG B - First span only - annulus for loose parts and orifice plate
- 8.
Discuss any unexpected or unusual results.
None (tie-rod bowing discussed below).
- 9.
Provide the schedule for steam generator-related activities during the remainder of the current outage.
Eddy current inspections should complete 11/6/08 and repairs and visual inspections are in progress and expected to complete by 11/10/08.
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- 10.
Discuss the results of the tie-rod bowing identified during the outage. Include the following in the discussion:
Was bowing identified in one or both SGs Was bowing consistent with what was expected -if not explain What areas of the SG has bowing What is the maximum lateral bow identified Is the current operability still bounding What repairs if any will be required for startup Tie rod bowing was detected in SG A and not detected in SG B at 1R21. This is consistent with the 1R20 inspection results. As at 1R20, bowing was detected only on one side of SG A. The locations of bowing are consistent with previous root cause finite element analysis (FEA) calculations. From preliminary observations the maximum lateral bow has increased from 0.9 to 1.2 inches. Preliminary information regarding locations of wear scars relative to the tube support plate (TSP) surfaces in the cold condition suggests that locking on the side of the steam generator without bowing has increased leading to increased bowing on the other side of the steam generator. This possibility was considered in the root cause analysis. To date inspection results are consistent with expectations prior to the outage. Root cause FEA calculations show some degree of bowing of tie rods in the outermost ring at all elevations. Previously bowing was detected at the 1st, 14th and 15th spans. At 1R21 bowing was detected at these locations in addition to one tie rod in the 2nd span and one tie rod in the 13th span. An increase in the number of tubes with proximity signals is consistent with the apparent increase in lateral bowing. A review of 1R20 proximity signals and gap measurements is needed to ensure that the differences in 1R21 results are not simply the result of increased detectability and gap measurement accuracy. A review of the 1R20 data indicates that bowing in the 2nd and 13th spans was at the threshold of detection at 1R20. Approximately 17 proximity signals are new indicating that the increase in bowing magnitude is correct. The inspection also revealed 12 proximity signals that were at the threshold value of detectability in 1R20 and not reported as proximity signals at that time. The operability evaluation remains bounding and no repairs are required prior to start up as of the data available through November 2, 2008.
Condition report CR-ANO-1-2008-01685 was initiated to document the proximity indications in numerous tubes around several tie rods. Eddy current testing of the "A" steam generator (E24A) is being performed during 1R21 as part of the assessment of bowed tie rods found in 1R20 (CR-ANO-1-2007-959). These proximity indications show that some of the tie rods are now bowed in a similar manner as 1R20, and preliminary evaluations suggest that amount of tie rod bow has increased somewhat. These preliminary assessments indicate that the amount of bow is close to that predicted in the root cause analyses, and is bounded by the current operability evaluations. Accordingly, based on the preliminary results, the current operability remains valid.
5 Below are the preliminary results for the four worst tie rod locations as determined during 1R20, for only the first span. The comparisons show that the amount of bow has increased. These numbers will be verified.
Tie Rod Row (Z-axis)
Bow at 1R20 (per Root Cause Rpt)
Bow at 1R21 Root Cause Acceptance Criteria Operability Acceptance Criteria Row 88 0.69 < Bow < 0.75 1.12 < Bow < 1.17 Row 64 0.83 < Bow < 0.89 1.17 < Bow < 1.19 Row 66 0.30 < Bow < 0.37
~0.5 Row 86 0.25 < Bow < 0.32
~0.5
< 1.2
< 1.5 15th Span
< 0.14 0.17 14th Span
< 0.14 0.17