ML090430507
| ML090430507 | |
| Person / Time | |
|---|---|
| Site: | Wolf Creek  |
| Issue date: | 01/29/2009 |
| From: | Garrett T Wolf Creek |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ET 09-004 | |
| Download: ML090430507 (5) | |
Text
WF CREEK NUCLEAR OPERATING CORPORATION Terry J. Garrett Ja 29, 2009 Vice President Engineering nuary ET 09-0004 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555
Reference:
Subject:
Docket No. 50-482: Response to Request for Additional Information Concerning the Results of the Fifteenth Steam Generator Tube Inservice Inspection Gentlemen:
Reference 1 submitted the Steam Generator Tube Inspection Report in accordance with Wolf Creek Generating Station (WCGS) Technical Specification 5.6.10, "Steam Generator Tube Inspection Report." This report provided the results of the WCGS fifteenth steam generator tube inservice inspection. Reference 2 provided a request for additional information (RAI) based on the Nuclear Regulatory Commission (NRC) staff review of Reference 1'. The Attachment provides Wolf Creek Nuclear Operating Corporation's responses to the questions in the RAI.
This letter contains no commitments. If you have any questions concerning this matter,, please contact me at (620) 364-4084, or Mr. Richard D. Flannigan at (620) 364-4117.
- Sincere rry J. Garrett TJG/rlt Attachment cc
- E. E. Collins (NRC), w/a V. G. Gaddy (NRC), w/a B. K. Singal (NRC), w/a Senior Resident Inspector (NRC), w/a P.O. Box 411 / Burlington, KS 66839 / Phone: (620) 364-8831 An Equal Opportunity Employer M/F/HCNET
Attachment to ET 09-0004 Page 1 of 4 RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING THE RESULTS OF THE FIFTEENTH STEAM GENERATOR TUBE INSERVICE INSPECTION Reference 1 submitted the Steam Generator Tube Inspection Report in accordance with Wolf Creek Generating Station (WCGS) Technical Specification 5.6.10, "Steam Generator Tube Inspection Report." This report provided the results of the WCGS fifteenth steam generator tube inservice inspection. Reference 2 provided a request for additional information (RAI) based on the Nuclear Regulatory Commission (NRC) staff review of Reference 1. Provided below are the NRC's requests followed by Wolf Creek Nuclear Operating Corporation's (WCNOC's) responses to those requests.
- 1. Please provide a high-level summary of the results of the scale profiling analysis.
WCNOC Response:
Scale profiling analysis was performed using the low frequency eddy current data collected during Refueling Outage 16 eddy current inspection of Steam Generator B and Steam Generator C. This is part of WCNOC's proactive position for Steam Generator Management.
Scale profiling assesses the status of the deposit levels in terms of both spatial distribution and inventory estimate. This information in conjunction with visual inspection data is used to plan future maintenance and cleaning activities. The scale profiling analysis consisted of three parts:
- An analysis of the low frequency eddy current bobbin data
- Review of the available Rotating Pancake Coil (RPC) inspection data of tube-tube support plate intersections
- Review of the available RPC inspection data collected at the top of the tubesheet Some general observations from the analysis are:
- 1. The scale distribution patterns in Steam Generator B and Steam Generator C are similar.
- 2. The heaviest concentration of tube scale deposit was observed on the hot leg side between tube support plate (TSP) 7 extending upwards through the U-Bend region for both steam generators.
- 3. A concentration of tube scale deposit was also observed between the tubesheet and flow distribution baffle region on the hot leg side within the region where the cutout of the flow distribution baffle exists.
- 4. As expected from previous trending of scale profiling results, the tube scale distribution pattern between Refueling Outage 14 and Refueling Outage 16 for Steam Generator B remained consistent. However, a decrease in scale buildup was observed, primarily in the upper bundle and U-Bend region on the hot leg side. This was attributed to the Advanced Scale Conditioning Agent/Pressure Pulse Cleaning (ASCA/PPC) that was performed during Refueling Outage 14. Comparison data from Refueling Outage 14 for Steam Generator C was not available.
- 5. The lower TSP regions have tube scale occurring mainly within the periphery of both steam generators (B and C) on the hot leg side.
Attachment to ET 09-0004 Page 2 of 4
- 6. The cold leg side of both steam generators is relatively clean. The largest region of deposits on the cold leg side occurs at the top tube support plate (TSP 7) towards the tube lane region.
- 7. A review of the TSP intersection RPC data was made in Steam Generators B and C.
The majority of the intersections examined. were clean. Very light deposits were identified at a small number of intersections (approximately 10 out of 569).
- 8. The RPC data of approximately 1000 tube sheet intersections were reviewed. The majority of tube sheet intersections were clean. Deposits were identified in a few of the tube sheet intersections.
- 9. Deposit inventory was estimated to be 1746 lbs for Steam Generator B and 1661 lbs for Steam Generator C. The majority of the scale deposits are located in the U-Bend region and the upper TSP bundle on the hot leg side. This quantity has been trended along with the corrosion product mass balance.
The current deposit inventory is acceptable and well below the threshold that would require additional action.
2., In the submittal, there is discussionr of the results of the J-tube secondary inspections (presumablyfrom SG B). Please describe the results of the other secondary side inspections (e.g., upper bundle in-bundle in SG C, and upper steam drum in SG B).
WCNOC Response:
A summary of the Refueling Outage 16 secondary side inspection results is included below.
These inspections are part of the overall program to assess the condition of the steam generators and to help plan future maintenance activities in order to ensure tube integrity and reliability over the licensed life.
Upper Bundle In-Bundle visual inspection was performed in Steam Generator C. This inspection is performed to capture the general condition of support plates, quatrefoils of the support plates, 7th support plate flow holes, th patch th plate plug weld regions, and the tubes.
Locations inspected were between the 4 and 7 support plates.. Due to a failure of the inspection tooling, the inspection in Steam Generator C was suspended and the planned inspections in Steam Generator B were cancelled. Because of long term trending of visual inspection results, mass balance, and the scale profiling results, ample information is available to assess the deposit inventory and spatial distribution of deposits in lieu of the visual inspection results.
Top of Tubesheet visual inspections were performed within the bundles of Steam Generators B and C to monitor areas of deposits in order to plan future maintenance and cleaning activities.
The inspection results were consistent with previous inspection history and trends that show a small area of deposits located in the center of the tubesheet on the hot leg side.
Visual inspections were completed throughout the mid deck, intermediate deck, and lower deck of the steam drum in Steam Generator B. These locations included demister banks, swirl vanes, tangential nozzles, the central drain, elongated steam vents, drain lines, feed ring and associated components. There were no visible anomalies and a mild coating of magnetite was observed 'on all surfaces. During the upper.. steam drum work, detailed inspections of.'the'..
Attachment to ET 09-0004 Page 3 of 4 feedring J-nozzles were also performed. Minor erosion was identified in two J-nozzle locations.
The erosion was evaluated and did not require additional action. Also, during the upper drum inspections, top down inspections were performed thru several swirl vanes to access the top of the tube bundle. The following areas of interest were inspected: Anti-Vibration Bars (AVB),
AVB to tube interface, tube and support plate integrity, and general scale buildup. These locations appeared normal and there was no visible tube wear. Scale buildup was present on the tubes and it was evident that some scale had recently fallen off.
All visual inspection results were acceptable and no additional action is required.
- 3. In the submittal on page 6 of 7, it is stated, "One new indication was identified in SG B at the top of the tubesheet on the cold leg side." It is not clear from the remaining discussion in that paragraph whether this indication was attributed to a "transient" foreign object and whether it was presentin previous inspection data. Please clarify.
WCNOC Response:
The indication referred to was in Steam Generator B, row 45, column 24. A 9% indication was reported 0.31 inches above the top of the cold leg tubesheet. The indication was not present in previous inspection data. The tube is located in the periphery of the tube bundle. This volumetric indication is attributed to wear from a transient foreign object. No possible loose parts were identified in this area, indicating that no foreign object currently resides at this location.
- 4. Please discuss the results of your inspections of the plugs. Forexample, were all the plugs confirmed to be present?
WCNOC Response:
The plugs installed in the steam generators were found to be in acceptable condition based on visual inspection. Installed plugs were confirmed to be present and none were determined to be leaking.
- 5. In the submittal, it was indicated that there were no new indications of wear at the flow distributionbaffle. These indicatorshad been attributedto pressurepulse cleaning.
Please confirm that these indications have not changed in size (other than would be attributedto normal variabilityin sizing techniques).
WCNOC Response:
Existing indications at the flow distribution baffle have not changed in size (within reasonable bounds of technique and analyst error) since their last inspection.
- 6. In your submittal, there is a paragraphthat indicates that no operationalleakage was observed during Cycle 16 and that no other potential sources of accident-induced leakage were identified.above the tubesheet during refueling outage 16. The remaining part of the paragraphappearsto relate to a limit that would'be imposed on the amount of
Attachment to ET 09-0004 Page 4 of 4 operationalleakage (as determined from your accident-inducedleakage limit). In other words, it appears to the staff that the first part of the paragraphis focused on condition monitoring and the second part of the paragraph is focused on the operational assessment. Please clarify the purpose of the second part of the paragraph. For example, is the purpose of the second part of the paragraphto simply indicate that no administrative limit is needed on the amount of operational leakage for the next operating cycle (i.e., Cycle 17)? If so, please confirm that your analysis of your refueling outage 16 inspection results indicates that there are no other potential sources of accident-inducedleakage from above the tubesheet for Cycle 17.
WCNOC Response:
The second part of the referenced paragraph describes that no adjustment to the administrative limit for normal operating leakage is required. There were no sources of potential leakage identified in the Refueling Outage 16 inspection. There are no other potential sources of accident-induced leakage from above the tubesheet for Cycle 17.
References:
- 1. WCNOC letter ET 08-0047, "Results of the Fifteenth Steam Generator Tube Inservice Inspection," October 27, 2008
- 2. NRC letter, "Wolf Creek Generating Station - Request for Additional Information RE:
Review of Results of the 1 6 th Steam Generator Tube Inservice Inspection (TAC NO.
ME01 24)," December 22, 2008 Note: This was actually the 1 5 th Steam Generator Tube Inservice Inspection performed during the 1 6 th Refueling Outage at Wolf Creek Generating Station.