ML023380276
| ML023380276 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 11/21/2002 |
| From: | Gordon Peterson Duke Power Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML023380276 (10) | |
Text
f Duke rPower.
A Duke Energy Company GARY R. PETERSON Vice President Catawba Nuclear Station Duke Power CNOI VP / 4800 Concord Rd York, SC 29745 803 831 4251 803 831 3221 fax grpeters@duke-energy corn November 21, 2002 U.S. Nuclear Regulatory Commission Attention:
Document Control Desk Washington, D.C. 20555
Subject:
Duke Energy Corporation Catawba Nuclear Station, Unit 2 Docket Number 50-414 Steam Generator Outage Summary Report for End of Cycle 11 Refueling Outage Response to NRC Request for Additional Information
Reference:
Letter from Duke Energy Corporation to NRC, dated January 17, 2002 The reference letter transmitted the steam generator tube surveillance program results for the Unit 2 End of Cycle 11 refueling outage.
On October 10, 2002, a telephone conference call was held among representatives of Duke Energy Corporation and the NRC.
The purpose of this letter is to transmit a formal response to the Request for Additional Information discussed in the conference call.
There are no regulatory commitments contained in this letter or its attachment.
If you have any questions concerning this material, please call L.J. Rudy at (803) 831-3084.
LJR/s Attachment www duke-energy corn
)ý C) 0 1
Document Control besk Page 2 November 21, 2002 xc (with attachment):
L.A. Reyes, Regional Administrator U.S. Nuclear Regulatory Commission, Region II Atlanta Federal Center 61 Forsyth St.,
SW, Suite 23T85 Atlanta, GA 30303 E. Guthrie, Senior Resident Inspector U.S. Nuclear Regulatory Commission Catawba Nuclear Station C.P. Patel, Senior Project Manager (addressee only)
U.S. Nuclear Regulatory Commission Mail Stop 08-H12 Washington, D.C. 20555-0001
REQUEST FOR ADDITIONAL INFORMATION CATAWBA UNIT 2 END OF CYCLE 11 STEAM GENERATOR INSPECTION REPORT The technical specifications for Catawba Unit 2 require the complete results of the steam generator tube surveillance program be reported to the NRC.
This report was submitted to the NRC in a letter dated January 17, 2002.
The staff has reviewed the report and has multiple questions necessary for the staff to better understand the indications and imperfections that have been identified and left in service.
The staff requests that the licensee respond to the following questions in order for the staff to complete their review.
- 1.
The licensee's submittal identifies the number of tubes inspected full length and the number of tubes inspected partial length.
These numbers, particularly the partial length inspections, do not appear to match those provided to the NRC staff during a conference call that took place during the outage (ML021780129 -
summary of call).
For example, during the conference call, the licensee stated that 100% of in service tubes in three steam generators were examined at the hot leg top-of-tubesheet (TTS) with a rotating pancake coil (RPC) probe.
This should consist of approximately 4500 partial length inspections per steam generator, which does not match the licensee's documentation of approximately 225 partial length inspections per steam generator.
Clarify the source of the totals for the tubes inspected full length and partial length.
Duke response In our letter dated January 17, 2002 we identified the number of tubes inspected by bobbin.
The partial length inspections were due to running low row U-bends to the top support.
This number of bobbin inspections is a subset of the total inspections discussed during the conference call during the outage.
The reporting
of tubes inspected'by bobbin is consistnt* with previously submitted reports.
Future reports will specify the inspection type for the quantity of tubes inspected.
- 2.
Provide definitions for all codes used in the report under the "IND" and "COMMENTI" columns and explain how they are used at Catawba Unit 2.
For example, VOL might mean
"-volumetric", but it is not clear what imperfection(s) it is used for (i.e.,
manufacturing burnish mark, intergranular attack, wear mark, etc.).
Duke response The three letter codes used are explained in the EPRI PWR SG Examination Guidelines and our site specific guidelines.
Because there are some site specific codes utilized that will not appear in the EPRI guidelines, a copy of the three letter codes used for this examination are being sent to the staff and will be incorporated in future reports.
The example given, "VOL",
would be a signal indicative of all the "imperfections" listed in the RAI, i.e.,
MBM's, IGA, wear, etc.
The characterization, i.e.,
"VOL",
- SAI, SCI, etc., of an indication is determined based on the signal response by coil.
The characterization initially has nothing to do with determining the morphology or "imperfections it is used for".
This is a determination based on resolution analysts and dispositioners reviewing the history and signature of the signal.
The characterization entered into our eddy current database is by analysts as directed by the Duke guidelines.
Once reported to the database, further evaluation of these indications is part of the dispositioning process that considers the previous history of the tube and the signature of the eddy current signal.
All the information required to disposition the indications is not contained in the database or the report.
Inclusion of those factors of the dispositioning process into the eddy current database or the reports is not feasible.
Previous experience has demonstrated that it is more conservative to leave these coded as VOL in the historical database, therefore ensuring they will get evaluated in the next inspection for any potential changes.
This evaluation each
inspection interval of the VOL indication~s generates a more independent dispositioning than might be obtained should the indications be characterized as MBM in the database.
The following is a general description of the process used to perform historical comparison or disposition indications detected and reported at Catawba Unit 2.
Historical comparison In general, the historical comparison is performed as part of the overall process.
" Initially, the reportinglis-the responsibility of the primary and secondary analysts where they would report-all indications according to the analysis guidelines.
Part of this analysis process is to ensure historical indications have been addressed, i.e.,
reporting again, "INR",
etc.
This is accomplished by use of what is called a "report validator".
"* The next step of the process occurs during resolution of any discrepancies between the primary and secondary'analysts.
The resolution analysts are responsible for reviewing indications to determine whether they are indications indicative of degradation.
It is the responsibility of the resolution analysts to perform a historical comparison of indications which have been reported in the past as well as the current outage.
This historical comparison is accomplished by using objective criteria established as part of the analysis guidelines.
The criteria include changes in voltage and phase as well as the requirement for an indication to have previously been inspected with a rotating coil technology.
No historical comparison is to be performed on any indication which did not exist in a
previous outage or was not previously inspected with a rotating coil technology.
In addition to the historical comparison, the resolution analysts also review signal signatures to aid in determining the morphology of indications.
- The last step of the process is final dispositioning which is performed by Steam
Generator Maintenance Engineering engineers and an ECT Level III.
This dispositioning process is veryi1similar to the resolution process with some minor differences.
The dispositioners do not determine the reportability of indications.
Indication queries, generated by the data management database, are reviewed to further determine whether they should be left in service or removed.
The disposition process includes reviewing historical results for signal changes, all information related to indications, i.e.,
location in the tube, location of the tube, signal signature, industry experience, etc., to the final disposition of indications/tubes.
Each analyst (primary, secondary, resolution) has the option of reporting a volumetric indication as a Single or Multiple Volumetric Indication, SVI/MVI, if they determine the indication should be considered for removal from service.
- 3.
Identify all types of imperfections that are being left in service (e.g., wear, loose parts, manufacturing burnish marks, etc.),
the number of each type of imperfection, and the basis for leaving them in service.
Ensure that this information, in combination with the information requested in RAI #2 enables the staff to read the January 17, 2002, report and identify the imperfection listed for each tube and the basis for leaving it in service.
Duke response The only active flaw at Catawba 2 is AVB wear.
We also see wear from foreign objects and indications of PLP's which are thought to be sludge or deposits.
MBM's are routinely observed and IGA has not been identified.
To summarize, the indications that are left in service are mechanical wear and small volumetrics that are (to date) all MBM's.
Wear is most typically found in the u-bend regions at the AVB supports, while the small volumetric indications can be found over the length of the tube (free span and supports).
According to our guidelines VOL calls are below the plugging limit.
As described in response to item 2, the dispositioning process
completes an independent review of these indications each inspection to determine if they may remain in service.
- 4.
Denting at tube supports and in the free span was reported.
Are these dents manufacturing related or corrosion related?
Duke response Yes, there are manufacturing dents at both the tube support plates and in the freespan.
There are no corrosion induced dents.
The voltage threshold for dent calling was changed in 2001 from 5 volts to 2 volts to be more consistent with industry practices.
Because of the shift to a lower threshold for reporting dents, the report for End of Cycle 11 contains DNT indications that are not reported in prior outages.
- 5.
Ensure that the following questions are addressed in response to questions above, or separately.
- a.
In the January 17, 2002, report, a tube was identified (steam generator-A, Row 2 Column 8) with an NQI based on a bobbin probe examination and a VOL at the same location based on a rotating probe examination.
This tube was left in service.
In a letter to the NRC dated October 23, 2001, the licensee discussed a tube (steam generator B, Row 16 Column 29) with the same coding (NQI/VOL) and was removed from service during the end of cycle (EOC) 10 steam generator inspection.
Explain how two tubes with the same coding result in different outcomes.
Duke response Row 16 Column 29 in steam generator B was plugged because of its location.
The location is at the upper edge of the flow distribution baffle in the hot leg.
The indication also had no previous history from prior inspections.
The indication was below the repair limit and was conservatively removed from service.
Row 2 Column 8 in steam generator A had an indication 9 inches above a preheater baffle in
the freespan of the tubing.
The indication depth was shallow.
The indication had previous history and was dispositioned as an MBM.
- b.
The code of PID was used for a number of tubes during the EOC 11 steam generator inspection.
The staff typically sees this code associated with an inspection performed for "positive identification" to ensure that the correct tube will be plugged/repaired.
However, at Catawba Unit 2 this code was used and no tubes were plugged/repaired.
(One example is in steam generator A, Row 5, Column 63.)
Explain how PID is used at Catawba Unit 2.
Duke response The "PID" code is simply used to ensure repeatability.
The misnomer historically applied to the "PID" code has been this was to verify tubes to be repaired/removed from service.
Our interpretation of the "PID" code has always been that it was a method of verifying the original tube inspected, thus the repeatability of the exam.
Row 5, Column 63 in steam generator A was an indication from a tubesheet examination.
The guidelines at that time would have PID'ed all tubesheet indications called.
APPENDIX A D5 BOBBIN ANALYSIS GUIDELINES A Bobbin Three Letter Characterization Codes CODE DESCRIPTION I
ADI Absolute Drift Indication 2
AXI Axial Indication 3
BLG Bulge 4
BOR Boron 5
CHG Indication Exhibits Change 6
CHT Chatter 7
DBH Dispositioned By History 8
DNT Dent 9
DWI Dent With Indication 10 FC Final Calibration 11 FCL Final Calibration Late 12 HLC History Location Changed, Resolution code only, Current location different than history location due to landmark table change.
13 HNC Has Not Changed 14 HNI Has Not-changed Indication 15 ICR Incomplete Roll 16 IC Initial Calibration 17 IDOK Tube ID Verified; This code shall be used to identify tubes acquired more than once during the current outage. Use of this code requires tube to tube comparison or fingerprinting of the affected tube(s).
18 s--
INF Indication Not Found 19 INR Indication Not Reportable 20 IRR Irregular Roll 21 L3R Level III Review 22 MSG Analyst Message 23 NEX No Expansion 24 NFC No Final Calibration 25 NQI Non-Quantifiable Indication 26 NSR Needs SGME Review 27 OBS Obstructed 28 OVR Over Roll 29 OXP Over Expansion 30 PID Positive Identification 31 PLG Plugged Tube 32 PLP Possible Loose Parts 33 PVN Permeability Variation 34 RBD Retest - Bad Data 35 RVB Retest - AVB 36 RIC Retest - Incomplete 37 RNC Retest - Tube Number Check 38 ROB Retest - Obstructed 39 RRC Retest - Rotating Coil 40 RPD Retest - Positive Identification 41 SAT Satisfactory 42 SLG Sludge 43 SKR Skip Roll 44 WAR Wear 45 WTG Wetting/Leaking Denotes code to be used in the "UTIL I" field A-10 Revision I
APPENDIX B D5 ROTATING COIL ANALYSIS GUIDELINES B Three Letter Characterization Codes CODE DESCRIPTION ARC Circumferential Extent Measurement AXI*
Axial Indication 1
2 3
4 DNT IDOK*
5 L3R*
6 LEN 7
MAI 8
MCI 9
MMI 10 MVI 11 NDD 12 NDF 13 OBS 14 PID 15 PLP 16 PVN 17 RBD 18 RIC 19 RNC 20 ROB 21 RPD 22 SAI 23 SCI 24 SVI 25 VOL 26 WAR*
27 Denotes code to be Dent Tube ID Verified; This code shall be used to identify tubes acquired more than once during the current outage. Use of this code requires tube to tube comparison or fingerprinting of the affected tube(s).
Level III Review Axial Extent Measurement Multiple Axial Indication Multiple Circumferential Indication Mixed-Mode Indication Multiple Volumetric Indications No Degradation Detected No Degradation Found Obstructed Positive Identification Possible Loose Part Permeability Variation Retest - Bad Data Retest - Incomplete Retest - Tube Number Check Retest - Obstructed Retest - Positive Identification Single Axial Indication Single Circumferential Indication Single Volumetric Indication Volumetric Wear used in the "UTIL 1" field.
Revision I B-7