ML051250065
| ML051250065 | |
| Person / Time | |
|---|---|
| Site: | Calvert Cliffs  |
| Issue date: | 04/28/2005 |
| From: | Vanderheyden G Constellation Energy Group |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| TAC MC6320 | |
| Download: ML051250065 (12) | |
Text
George Vanderheyden 1650 Calvert Cliffs Parkway Vice President Lusby, Maryland 20657 Calvert Cliffs Nuclear Power Plant 410.495.4455 Constellation Generation Group, LLC 410.495.3500 Fax I Constellation Energy April 28, 2005 U. S. Nuclear Regulatory Commission Washington, DC 20555 ATTENTION: Document Control Desk
SUBJECT:
Calvert Cliffs Nuclear Power Plant Unit No. 1 Docket No. 50-317 Response to Request for Additional Information Regarding Steam Generator Inservice Inspection Summary Report (TAC No. MC6320)
REFERENCE:
(a) Letter from Mr. R. V. Guzman (NRC) to Mr. G. Vanderheyden (CCNPP),
dated March 30, 2005, Calvert Cliffs Nuclear Power Plant, Unit No. I -
Request for Additional Information (RAI) Re: Steam Generator Inservice Inspection Summary Report (TAC No. MC6320)
By letter dated March 30, 2005 (Reference a), you requested additional information regarding the results of the first in-service inspection conducted on Calvert Cliffs Unit 1 replacement steam generators during the spring 2004 refueling outage. Attachment (1) to this letter provides the requested information.
Should you have questions regarding this matter, please contact Mr. L. S. Larragoite at (410) 495-4922.
Very t ors, GV/GT/bjd
Attachment:
(1) Response to Request for Additional Information Regarding Calvert Cliffs Unit 1, 2004 Steam Generator Inservice Inspection Results cc: R. V. Guzman, NRC Resident Inspector, NRC S. J. Collins, NRC R. I. McLean, DNR LOWS
ATTACHMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING CALVERT CLIFFS UNIT 1, 2004 STEAM GENERATOR INSERVICE INSPECTION RESULTS Calvert Cliffs Nuclear Power Plant, Inc.
April 28, 2005
ATTACHMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING CALVERT CLIFFS UNIT 1, 2004 STEAM GENERATOR INSERVICE INSPECTION RESULTS Requested Information 1 A number of tubes wvere identified that are experiencing wvear at upper bundle tube support locations.
Please discuss whether the number of locations with wear is consistent with other similarly designed operationalunits. If the number of wear locations is not consistent, discuss any insights as to the reason for the difference. Please discuss whether the extent to which these wear indications are considered "typicalfan bar wear," "atypical U-bend wear," or "localized U-bend wvear. " Typicalfan bar wearrefers to wear caused by the thermal hydraulic conditions and tube-to-support clearances which can vary because of manufacturing tolerances. Atypical U-bend wear refers to pit-like indicationsfound atflat-bar supports and theorized to be the result of asperitieson the flat bars introduced duringfabrication.
Localized U-bend wear refers to wear "localized" to specific columns of tubes and possibly the adjacent column as a result of arch-bardistortion insteadof a more random manufacturingtolerance issue ('which causes typicalfan bar wvear).
Calvert Cliffs Response The overall number of fan bar wear indications experienced at Calvert Cliffs Units 1 and 2 is more than other similarly designed Babcock & Wilcox (B&W) operational units. The locations and size of the wear is consistent with other similarly designed operational units. The type of wear at the upper bundle tube support locations is consistent with other similarly designed operational units.
The Units 1 and 2 Calvert Cliffs steam generators are similar in design to other B&W replacement re-circulating steam generators. There are no major design changes between the various re-circulating steam generators that would account for the differences in the upper bundle support wear. The upper bundle tube support wear at Calvert Cliffs is typical fan bar wear. As you characterized it in your request, this type of wear is caused by the thermal hydraulic conditions and tube-to-support clearances which can vary because of manufacturing tolerances. Calvert Cliffs performed rotating probe examinations on each area of wear in both the Units I and 2 steam generators. All were confirmed as typical fan bar wear, no anomalies were detected.
Rcuested Information 2 Tube-to-tube contact is an area of concernfor the replacement steam generators at several operational units. Have any tubes at Calvert Cliffs Nuclear Powver Plant, Unit Nos. I and 2 (CCNPP I and 2) been identified as being in close proximity to other tubes and/or coming in contact with adjacent tubes? If so, please discuss how many tubes are currently considered to be in close proximity and whether any tube wear has been observed at the location of "close proximity." In addition, please discuss whether the number of tubes affected by tube-to-tube contact has increased,decreased,or remained the same since the steam generators were installed If the number of tubes in close proximity is increasing with time, please discuss the cause (the staff understandsthat the tube proximity issue is a result ofmanufacture and that it was expected that the "condition"may correct itself with time).
Calvert Cliffs Response No tubes at Calvert Cliffs in either Units 1 or 2 have been identified as being in close proximity to other tubes or have come in contact with adjacent tubes as a result of the first cycle of operation. There were two tubes in Unit 2 No. 21 Steam Generator that were identified as potentially having tube-to-tube contact during the pre-service examination. These tubes were preventatively plugged by the manufacturer.
I
ATTACHMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING CALVERT CLIFFS UNIT 1, 2004 STEAM GENERATOR INSERVICE INSPECTION RESULTS Requested Information 3 Please discuss whether your steam generatortubes have any dents/dings. If your steam generatortubes contain dents/dings, please discuss whether any rotationalprobe inspections were performed at these locations and the potential for a through-wall or near through-wallflaw to exist at these locations (e.g., are there any anomalous dents/ding signals). Please discuss your primary-to-secondary leakage history since installationof the steam generators.
Calvert Cliffs Response Calvert Cliffs steam generators contain a few dings that were identified during the pre-service inspections. The numbers of dings are 14 indications affecting 14 tubes in Unit I No. 11 Steam Generator, 16 indications affecting 15 tubes in Unit I No. 12 Steam Generator, 18 indications affecting 7 tubes in Unit 2 No. 21 Steam Generator, and 2 indications affecting 2 tubes in Unit 2 No. 22 Steam Generator. Most of the dings were spun with the rotating probe during the pre-service examination for characterization. No anomalous signals were noted. A 100% bobbin examination was performed as a baseline exam at the first refueling outage on both Calvert Cliffs units. No new dents were identified during the baseline examination in any of the steam generators. Based on the bobbin signals during the first refueling outage, the ding signals did not exhibit any change such that they warranted a rotating probe examination. Therefore, no rotating probe examinations were performed on any of the dings.
There are no anomalous ding signals in any of the Calvert Cliffs steam generators. Based on the inspection results, the potential for a through-wall or near through-wall flaw is extremely low.
There was no primary-to-secondary leakage attributed to the steam generators on either unit during the first operating cycle. There are currently no indications of primary-to-secondary leakage during the second cycle of operation on either unit.
Requested Information 4 General information concerning the design of your replacement steam generators was provided in previous submittals. Each replacement steam generator at CCNPP I and 2 contains 8471 tubes composed of thermally treated alloy 690 material. The tube supports are lattice grids composed of type 410 stainless steel. In orderfor the NRC staff to better understandtre design ofyour replacement steam generators,please provide the following information for both units: (a) model number for the replacement steam generators, (b) tube manufacturer, (c) tube support thickness, (d) tube pitch and pattern, (e) anti-vibration bar (fan bar) design, 69 number of tubes plugged (if any) in each steam generatorprior to installation, (g) tube expansion method in tubesheet, (h) tubesheet thickness (with and wvithout clad), (i) tubesheet map, and a) a sketch of the steam generatordepictingyour tube supportplate naming convention. In addition, please clarify the smallest U-bend radius in your steam generator (e.g., row 3 has a radius of 3.6 inches). Are there any major differences between the Unit I and Unit 2 replacement steam generators?
Calvert Cliffs Response a) The replacement steam generators were not assigned a model number by the steam generator manufacturer. The numbers used to identify the steam generators are an order number and the number of the steam generators. For example, the order number is 7811 and there were four steam generators made for Calvert Cliffs. Therefore, the numbers are 7811-01 (11), 7811-02 (12),
7811-03 (21), and 7811-04 (22). These numbers cannot be tied to specific model numbers for comparison purposes. This is the method B&W utilizes for replacement steam generators.
2
ATTACHMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING CALVERT CLIFFS UNIT 1, 2004 STEAM GENERATOR INSERVICE INSPECTION RESULTS b) The tubing manufacturer was Sumitomo of Japan.
c) The Calvert Cliffs Steam Generators contain type 410 stainless steel lattice grid tube supports. The lattice grid is made up of a series of high bars (approximately 3" in width) oriented 300 and 150° to the tube freelane and located every forth pitch to accommodate steam generator loading conditions.
Low bars (approximately 1" in width) are located at every pitch location between the high bars. All low bars flush to the top plane of the high bars are oriented at 30° to the tube freelane. All low bars flush to the bottom plane of the high bars are oriented 1500 to the tube freelane. All of the lattice bars are 0.100" nominal thickness. The bar ends are fitted into precise slots of the specially designed peripheral support ring (see Figures in Enclosure 1). The lattice grids are positioned within the steam generator shroud at elevations selected to prevent flow-induced vibration while not creating excessive flow resistance. There are a total of seven lattice grid supports in the Calvert Cliffs replacement steam generators. The tubes are held in position within the diamond shaped bar opening, which provide line support contact. This minimizes the area of crevices between the tubes and bars, which could trap corrosion products.
d) The Calvert Cliffs steam generators have a 600 triangular pitch tube arrangement. The tube pitch is on 1" centers (see Figures in Enclosure 1).
e) The flat bar U-bend restraint system incorporates a series of flat bar fan assemblies on each side of the tube bundle. The fans are positioned so that all U-bends are supported at close intervals. The supports are made of type 410 stainless steel that provides high resistance to fretting wear, excellent strength, and high resistance to corrosion and related tube denting (see Figures in Enclosure 1).
f) The number of tubes plugged in Unit 1,No. 11 Steam Generator prior to installation was zero. The number of tubes plugged in Unit 1, No. 12 Steam Generator prior to installation was zero. The number of tubes plugged in Unit 2, No. 21 Steam Generator prior to installation was three. The number of tubes plugged in Unit 2, No. 22 Steam Generator prior to installation was zero.
g) The replacement steam generator tubes were hydraulically expanded through the entire thickness of the tubesheet to a point 0.125" nominally below the secondary face of the tubesheet. The expansion process is controlled to ensure that expansion of the tube is as close as possible to the secondary face of the tube sheet without going past the face. For peripheral tubes, where access is limited by the curvature of the primary bowl, expansion is performed in two overlapping zones with a shorter mandrel. The expansion zones overlap near the center of the tubesheet to ensure full depth expansion. Following expansion, the profile of each tube is measured through the entire expanded area of the tubesheet, including the transition zone, using eddy current profilometry. There are no over expansions in any of the four replacement steam generators for Calvert Cliffs.
h) The tubesheet for the Calvert Cliffs replacement steam generators is approximately 21.875" thick.
The austenitic stainless steel tubesheet cladding has a minimum thickness of 0.375". The total tubesheet thickness including cladding is approximately 22.25".
i) A figure showing a typical tubesheet map is contained in Enclosure (1).
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ATTACHMENT (1)
RESPONSE TO REQUEST FOR ADDITIONAL INFORMATION REGARDING CALVERT CLIFFS UNIT 1, 2004 STEAM GENERATOR INSERVICE INSPECTION RESULTS j) Enclosure (1) contains five figures depicting the tube support configuration and naming convention.
The actual measurement of the smallest radius U-bend, Row 1, as measured during manufacturing, is 3.5". The U-bend radius increases for all subsequent rows. The first 18 rows of the U-bends were all stress relieved. There are no major differences between any of the Calvert Cliffs replacement steam generators.
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Enclosure (1)
Replacement Steam Generator (RSG) Figures CCNPP RSG Typical Lattice Grid CCNPP RSG Tube Spacing CCNPP RSG Fan Bar Support Layout CCNPP RSG Typical Tubesheet Map CCNPP RSG Tube Support Layout Calvert Cliffs Nuclear Power Plant, Inc.
April 28, 2005
CCNPP RSG Typical Lattice Grid HIGH ISOMETRIC VIEW
CCNPP RSG Tube Spacing DETAIL OF HOLE SPACING
CCNPP RSG Fan Bar Support Layout lF0 E08 I Latfce Grid Hot LegO7l I I [lLseoGrid ColdLeg07C
CCNPP RSG Typical Tubeshoet Map LN in in Ia I" If U0.
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