L-2013-232, Inservice Inspection Plan, RAI Reply to Fourth Ten-Year Interval Unit 1 Relief Request No. 5, Revision 0
| ML13219A254 | |
| Person / Time | |
|---|---|
| Site: | Saint Lucie  |
| Issue date: | 07/30/2013 |
| From: | Katzman E Florida Power & Light Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| L-2013-232, TAC MF0675 | |
| Download: ML13219A254 (26) | |
Text
0July 30, 2013 FPL L-2013-232 10 CFR 50.4 10 CFR 50.55a U. S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555 Re:
St. Lucie Unit 1 Docket No. 50-335 Inservice Inspection Plan RAI Reply to Fourth Ten-Year Interval Unit 1 Relief Request No. 5, Revision 0
References:
- 1. FPL Letter L-2013-044 dated February 4, 2013, "Inservice Inspection Plan Fourth Ten-Year Interval Unit 1 Relief Request No. 5, Revision 0," ML Accession No. ML13046A101.
- 2. NRC email from Siva Lingam to Ken Frehafer dated May 29, 2013, "Request for Additional Information for Relief Request No. 5, "Examination of Cold Leg Dissimilar Metal Welds," at St. Lucie Unit I (TAC NO. MF-0675).
In Reference 1 above, Florida Power & Light (FPL), requested relief from the 10CFR50.55a(g)(6)(ii)(F)(4) exception to ASME Code Case N-770-1 that essentially 100% coverage be achieved for the baseline required volumetric examinations. In Reference 2 above, the NRC submitted a request for additional information (RAI) on the relief request. The reply to the RAI is provided in the attachment to this letter.
Please contact Ken Frehafer at (772) 467-7748 if there are any questions about this submittal.
Sincerely, Eric S. Katzman Licensing Manager St. Lucie Plant Attachment ESK/KWF Florida Power & Light Company 6501 S. Ocean Drive, Jensen Beach, FL 34957
L-2013-232 Attachment Page 1 of 25 Response to NRC Request For Additional Information (RAI) for St. Lucie Unit 1-Fourth Ten-Year Interval, Relief Request No. 5 Revision 0.
Please note that table and figure numbers are applicable to the specific RAI number and part.
NRC RAI-1 On Page 8, first paragraph, the licensee discussed the reactor coolant system (RCS) leakage detection capability at St Lucie Unit 1. Describe the RCS leakage detection systems in detail. Discuss whether the leakage detection systems satisfy the redundancy, sensitivity and reliability specifications of Regulatory Guide 1.45, Revision 1. Discuss leak rates or trends that would cause actions to be taken to determine the location of leaks.
Response to RAI-1 The primary method for quantifying and characterizing RCS identified and unidentified leakage is by means of a reactor coolant water inventory balance.
The inventory balance is performed as required by St. Lucie Unit 1 Technical Specification (TS 3/4.4.6.2.c) at least once every 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> except when operating in the shut down cooling mode (not required to be performed until 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br /> after establishment of steady state operation).
However, the St. Lucie surveillance procedure requires the inventory balance be performed once every 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br />, since it provides the best and earliest trend of an increase in RCS leakage.
The procedure methods use the recommendations and guidance in WCAP-16423-NP (Adams ML070310084) and WCAP-16465-NP (Adams ML070310082). The leak rate calculated using water balance inventory method is the most sensitive of the methods available with the leak rate calculated to the nearest 0.01 gallons-per-minute (gpm).
RCS leak detection at St. Lucie Unit 1 is also provided by 3 separate monitoring systems: 1) reactor cavity (containment) sump inlet flow monitoring system;
- 2) containment atmosphere radiation gas monitoring system; 3) and containment atmosphere radiation particulate monitoring system. These systems have high level and alert status alarms in the control room. These systems also have Technical Specification required monitoring (TS 3/4.4.6.2.a & b) at least once every 12 hours1.388889e-4 days <br />0.00333 hours <br />1.984127e-5 weeks <br />4.566e-6 months <br />.
The sensitivity of the containment atmosphere radiation monitoring system depends on the amount of radioactivity in the primary coolant system which is dependant on the percentage of failed fuel. Calculation results conclude that the containment atmosphere radiation monitors are capable of detecting a change of 1 gpm in the leak rate within one hour using design basis reactor water activity, assuming 0.1% failed fuel.
The containment sump alarm response is also highly variable based on the location of the leak, how much vapor condenses and where it condenses. All
L-2013-232 Attachment Page 2 of 25 drains entering the sump are routed first to a measurement tank. When the water level corresponding to 1 gpm or more into the tank is reached, a sump level alarm is actuated in the control room.
The combination of Technical Specification required inventory balance, reactor cavity sump monitoring, gas and particulate monitoring systems provide diverse measurement means for acceptable monitoring of RCS leakage.
In addition, the St. Lucie Unit 1 Technical Specification was revised to the extent practical to meet the improvements of NRC approved revision 3 to Technical Specification Task Force (TSTF) Standard Technical Specification (STS) Change Traveler-513 to define new time limit for restoring inoperable RCS leakage detection instrumentation to operable status and to establish alternate methods of monitoring RCS leakage when one or more required systems are inoperable (Ref. St. Lucie Letter L-2011-073 dated March 11,2011, ADAMS ML11087128).
The NRC concluded in the safety evaluation that the changes to the St. Lucie Unit 1 Technical Specifications were acceptable and that "The proposed actions for inoperable RCS leakage detection instrumentation maintain sufficient continuity, redundancy, and diversity of leakage detection capability that an extremely low probability of undetected leakage leading to pipe rupture is maintained. This extremely low probability of pipe rupture continues to satisfy the basis for acceptability of LBB in GDC 4."
(NRC Issuance of Amendments regarding TSTF-513 Revision 3, dated 3-30-2012, ML12052A22)
The St. Lucie Unit 1 RCS Inventory Balance procedure ensures that RCS leakage is within Technical specification 3.4.6.2. The procedure also provides early detection of negative trends based on statistical analysis. The inventory balance leak rate calculation is performed more frequently (at a 24 hour2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> rather than 72 hour8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> interval) than required by Technical Specification.
The procedural action levels based on the absolute value of the unidentified RCS inventory balance (from surveillance data) are as follows:
Action Level 1
- An adverse trend over time is observed.
- Seven day rolling average of UNIDENTIFIED Leak Rate is greater than 0.1 gpm.
Nine consecutive RCS UNIDENTIFIED Leak Rates greater than the baseline mean (Ip) value.
Action Level 2 Two consecutive UNIDENTIFIED Leak Rates greater than 0.15 gpm.
Two of three consecutive UNIDENTIFIED Leak Rates greater than the baseline mean plus two times the standard deviation (p + 2a).
L-2013-232 Attachment Page 3 of 25 Action Level 3
° One UNIDENTIFIED Leak Rate greater than 0.30 gpm.
One UNIDENTIFIED Leak Rates greater than the base line mean value plus three times the standard deviation (p + 3u).
NRC RAI-2 A.
Confirm that Performance Demonstration Initiative (PDI) procedure, EPRI-DMW-PA-1, Revision 1 was used for the examination performed in 2010.
Response to RAI-2 A.
Yes, EPRI-DMW-PA-1, Rev. 1 as stated on every sketch was used.
NRC RAI-2 B.
Discuss whether the PDI procedure is qualified for the ASME Code,Section XI, Appendix VIII, Supplement 10, single sided axial examination of 100 percent of the susceptible material (i.e., DMW).
Response to RAI-2 B.
EPRI-DMW-PA-1, rev. 1, procedure is qualified for:
- 1. Detection, length, and through-wall sizing of circumferentially oriented flaw indications where single or dual side access is available.
- 2. Detection and through-wall sizing of axially oriented flaw indications where dual side access is available or if the axial flaw indications are located within an accessible region of a single side access configuration.
NRC RAI-2 C.
Identify any specific limitations associated with the scope of the PDI procedure.
Response to RAI-2 C.
EPRI-DMW-PA-1, rev. 1, procedure is not qualified for:
- 1. Length sizing axially oriented flaws regardless of location. However, the techniques described in this procedure may be used to estimate the length of a detected axial flaw as long as the effect of the component curvature is accounted for.
- 2. Examinations performed from the cast stainless steel side of a component.
- 3. Examination from tapered surfaces.
- 4. The procedure has not been demonstrated to detect, size or characterize embedded flaws, however, guidance is provided.
L-2013-232 Attachment Page 4 of 25 Additionally, the procedure provides specific instructions on the examination requirements for CE RCP dissimilar metal weld configurations that are limited due to geometric or material conditions, such as:
8.9.1 The presence of cast austenitic safe-ends or pump casing, 8.9.2 Sloped or non-uniformed weld crowns that cannot be improved to an acceptable surface condition.
The following techniques shall be used for examination of components limited by the conditions described above:
8.11.1 Examinations for detection and length sizing of circumferential flaws:
a) To the extent possible the examination shall be performed from the non-cast side or accessible side of the weld utilizing the procedurally defined search units. If the weld crown cannot be conditioned to an acceptable level coverage of the non-cast or accessible portion of the examination volume can be claimed from the base material, without scanning on top of the weld provided the procedurally defined angles cover the required examination volume.
8.11.2 Examination for detection of axial flaws:
a) If the weld crown allows scanning on top of the weld the procedurally defined search units and processes shall be used to examine the weld and adjacent non-cast base material.
b) If the weld crown cannot be improved to an acceptable level scanning shall be performed from the adjacent non-cast or accessible base material utilizing a flat non-contoured wedge.
c) In addition to the procedurally defined parallel scans, the search unit shall be skewed into the weld centerline at angles between 0' and 30' in both the clockwise and counterclockwise scan directions.
d) Coverage can be claimed up to the weld centerline from each accessible side provided the center point of the ultrasonic beam is capable of intersecting this area.
NRC RAI-2 D.
Confirm that all aspects of the subject weld examinations have been through blind qualification in accordance with the ASME Code,Section XI, Appendix VIII requirements.
This includes probes and ultrasonic instrumentation, procedure variables, and personnel.
Response to RAI-2 D.
The EPRI-DMW-PA-1 procedure was expanded to the RCP configuration using blind samples and no site specific mock-ups were used.
NRC RAI-2 E.
Describe the manner in which these examinations have been performed, such as by a single examiner or by team scanning.
L-2013-232 Attachment Page 5 of 25 Response to RAI-2 E.
Examinations were performed by a single examiner.
NRC RAI-3 A.
Provide a flaw growth analysis showing the time necessary for the largest potential semicircular (thumbnail) inside diameter-connected axial and circumferential flaw contained in the unexamined region of the susceptible weld material to grow by primary water storage tank (PWSCC) to exceed the allowable size (i.e., 75 percent through wall) in the ASME Code, Section Xl, IWB-3600, and 100 percent through-wall. The flaw growth analysis should model the worst-case weld(s) (e.g., RC-121-6-504 and RC-124-7-504) that has the largest unexamined region.
Response to RAI-3 A.
The PWSCC growth analysis in [1] was re-run using weld residual stress (WRS) in [2], with the additional case of 50% inner surface repair without heat treatment (HT). The MRP-115 PWSCC growth law is used; this was also used in [1]. The end of evaluation period allowable inner diameter (ID) flaw sizes from [1] are listed in Table 1. Figures 1 and 2 illustrate the axial and circumferential flaw PWSCC growth for different postulated cases with inner diameter (ID) repairs.
The dissimilar metal (DM) weld thickness is conservatively assumed to be 3.2 inches based on RCP 11B2 outlet nozzle RC-124-7-504. Table 2 lists the time necessary for the maximum potential undetected flaws to reach 75% and 100%
through-wall at the DM weld. See response to RAI 3b) for the maximum potential undetected flaw depths. The bounding cases are 50% ID repair with no HT for axial flaws, and 25% ID repair with HT for circumferential flaws.
Since outlet DM welds have less coverage than the inlet [3, Table 1], only the limiting outlet DM weld results are presented.
Figure 1 provides a graphic example of how to calculate time necessary for the limiting axial flaw case to reach 75% through-wall; taking the time difference between the initial flaw of 12.47% and final flaw of 75% through-wall yields 64.3 months.
Table 1: End of Evaluation Period Maximum Allowable Inside Surface Flaw Sizes Flaw Aspect Inlet and Outlet (a/t)(1)
Orientation Ratio(2)
Normal/Upset Emergency/Faulted Axial 2
75%
75%
6 75%
75%
Circumferential 6
75%_75%
10 75%
73%
Notes:
(1) a/t = flaw depth/wall thickness (2) aspect ratio = flaw length/flaw depth
L-2013-232 Attachment Page 6 of 25 Table 2: Time for PWSCC Growth to Reach 75% and 100% Through-wall at Outlet DM Weld Postulated Flaw Orientation Axial Flaw Circumferential Flaw ID Repair Case 50% ID Repair 25% ID Repair with No HT with HT Aspect Ratio 2(3) 6 10(3) ao/t = Maximum Potential 12.47%
40.00%
40.0%(l)
Undetected Flaw Months to Reach 75%
64.3 181.6 139.0(2)
Months to Reach 100%
77.2 215.0 168.0 Notes:
(1) Conservatively assume 40%. The actual maximum potential undetected flaw is 25.56%. See the response to RAI 3b.
(2) Months to reach 73% (ASME limit for aspect ratio = 10 is 73%, as listed in Table 1).
(3) The AR = 2 assumption for the axial flaw is due to the constraints of nonsusceptible material on both sides of the DM weld. The circumferential flaw of AR = 10 is the bounding case.
V 0
IT 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0
1 2
3 4
5 6
7 lime (Years) 8 9
10 11 12 13 14 Note: This figure should be viewed in color.
Figure 1: PWSCC Axial Flaw Growth for Reactor Coolant Pump Outlet Nozzle
L-2013-232 Attachment Page 7 of 25
....... 73%Allowable 0.9
---25% Repair w/ HT, AR=6 0.8 25%Repair wI iT. AR=10
- 0.76 10.5 a 0.4 0.3 0.2 0.1 0
2 4
6 8
10 12 14 16 18 20 Time (Years)
Note: This figure should be viewed in color.
Figure 2: PWSCC Circumferential Flaw Growth for Reactor Coolant Pump Outlet Nozzle for 25% ID Repair Based on the analysis above, the time for a postulated safety significant circumferential flaw to grow from an undetectable size of - 40% to the 73-75%
(Table 2) through wall ASME limit is 139 - 181.6 months. Therefore, the ASME Code Case N-770-1 seven (7) year re-exam frequency is supported by the St.
Lucie Unit 1 exam coverage and the postulated crack growth analysis.
For the non-safety significant axial flaw, the time for a postulated flaw to grow from an undetectable size of - 12.47% to the 75% (Table 2) through wall ASME limit is 64.3 months. However, this is overly conservative, since the actual exam coverage due to beam skewing included the entire ID surface of the susceptible material as stated on page 6 of relief request No.5 [Ref. 4]. Therefore, the ASME Code Case N-770-1 seven (7) year re-exam frequency is supported by the St.
Lucie Unit 1 exam coverage.
References for Response to RAI-3 A:
- 1. Westinghouse Report, WCAP-16925-P, Rev. 1, "Flaw Evaluation of CE Design RCP Suction and Discharge, and Safety Injection Nozzle Dissimilar-Metal Welds,"
August 3, 2009 (Though this is a proprietary class 2 document, this report was made
L-2013-232 Attachment Page 8 of 25 available to the NRC via a Form 36 ["WCAP-16925-P Form 36 PWROG PA-MSC-0423 (does not include any international members) and USNRC"] approved on October 2, 2009. (NRC ADAMS ML092740085)
- 2. Westinghouse Report, WCAP-17128-NP, Rev. 1, "Flaw Evaluation of CE Design RCP Suction and Discharge Nozzle Dissimilar Metal Welds, Phase III Study," May 28, 2010.
- 3. Materials Reliability Program Crack Growth Rates for Evaluating Primary Water Stress Corrosion Cracking (PWSCC) of Alloy 82, 182, and 132 Welds (MRP-1 15),
EPRI, Palo Alto, CA: 2004. (NRC ADAMS ML051450555)
- 4. Florida Power and Light Letter, L-2013-044, Rev. 0, "Fourth Ten-Year Interval Unit 1 Relief Request No. 5, Revision 0," February 4, 2013. (NRC ADAMS ML13046A101)
NRC RAI-3 B.
Provide the criteria for determining how far the PWSCC flaw must extend into the examined region before it can first be detected using the ultrasonic test (UT) technique employed.
Response to RAI-3 B.
As described in the Florida Power and Light relief request [1], ultrasonic testing (UT) could not examine 100% of the dissimilar metal (DM) weld due to obstructions (e.g.,
spray nozzles) in the vicinity of the DM weld.
Table 1 lists the maximum potential undetected flaw depths. These are calculated based on the unexamined length [1] and the assumed minimum inspectable inner diameter (ID) flaw of 10% wall thickness. The 10% wall thickness assumption is conservative based upon the flaw depths that are used in the equipment, procedure, and personnel qualification process of ASME Section XI, Supplement 10 [2].
The requirement in Supplement 10, subparagraph 1.2(c)(1) states that "all flaw depths shall be greater than 10% of the nominal pipe wall thickness".
The procedure, EPRI-DMW-PA-1, used for St. Lucie Unit 1 examinations [1] requires "all indications produced by reflectors within the volume to be examined, regardless of amplitude, that cannot be clearly attributed to the geometry of the weld configuration shall be considered as flaw indications". That is not to say that flaws less than 10%
nominal wall thickness cannot be detected and would not be identified. However, the qualification test only includes flaws greater than 10% nominal wall thickness.
Therefore, the 10% minimum inspectable ID flaw is conservative.
Circumferential Flaws Figure 1 illustrates the axial UT examination coverage (hatched area) for positions B and H. The hatched area is missing a small part of the buttering, which is also Alloy 600 material.
Therefore, the unexamined length measured position, B to H, at the outer diameter (OD) is 8.85 inches, as illustrated in Figure 2. The position B to H dimension in Figure 2 is the OD circumferential distance. The unexamined length at the ID is scaled by the ID and OD as:
L-2013-232 Attachment Page 9 of 25 Designed ID = 30 inches Pipe Thickness = 2.9 inches (DM Weld Checklist, RC-121-6-504 and RC-124 504)
OD = 30 + (2 x 2.9) = 35.8 inches Unexamined Length at ID = 8.85 x (30 / 35.8) = 7.416 inches As illustrated in Figures 3 and 4, semi-elliptical flaws with aspect ratios (ARs) of 6 and 10 are plotted with an unexamined (missed) length from -3.708 to +3.708. Assuming that a minimum UT detectable flaw depth is 10% wall thickness (0.32 inches), the inspectable area is greater than 3.708 inches on the positive x-axis, and greater than 0.32 inches on the y-axis.
Keeping the AR and the center of the flaw at x = 0, the flaw depth is increased iteratively until it reaches into the inspectable area shaded in the blue in Figures 3 and 4.
The AR of 6:1 (AR = 6) for a circumferential flaw orientation was chosen because it is the traditional flaw shape for fracture mechanics calculations, suggested by the ASME Code in Appendix G of Section III and in Appendix G of Section Xl [2]. The AR of 2:1 was chosen due to the constraint of unsusceptible material on both sides of the DM weld. This is also supported by the field measurements of the V.C. Summer safe end region [3]. Additionally, the 10:1 AR for circumferential flaws was also conservatively included for information.
Table 1: Maximum Potential Undetected Flaw Depths Maximum Potential Flaw Geometry Undetected Flaws
(% Wall Thickness)
Axial, AR = 2 12.47%
Circumferential, AR = 6 40.00%
Circumferential, AR =2556%
10
L-2013-232 Attachment Page 10 of 25 DM Weld Buttering MRP-13g inspection Examination Volume Coverage (per EPRI.DUMW.PA,1 Rev. I; examn volume can be onlyceite= d
,,/.
/
for beam angles between 40. 50 dcege)
(1.25 sq. in.)
t I
I,.
Axial Scan Lne (Circumferential Flaws) Cross-Sectlon 0 Position B & Position H 82,2% Coveage. MRP-39 Exam Volume ((125 sq. InAl.52 sq. In.)
- 100) 55.8% Coverage - ASME Section Xl Exam Volume ((1.25 sq. InJ2.24 sq. In.)* 100)
Figure 1: RCP 11B1 Outlet DM Weld Obstruction due to Spray Nozzle [1, Figure 6i]
L-2013-232 Attachment Page 11 of 25
. IM -
9utt.
$4,1n U". 0 o~lf Carbon 6"0 P" Wold Int..1c MD0)
Ifltw41M, (00)
Eto 9so0Faoto IIf Li.nena Positon C Uno
.00 411 Sft"*0C~~1 "Sol P4w WeldIn~etbos (00) 3 Z
spray *01rio Obou'uisa"o V4soft e nd If*t*C* (OD)
S~ceton A-A Figure 2: RCP IBI Outlet DM Weld Obstruction due to Spray Nozzle [I, Figure 6g]
L-2013-232 Attachment Page 12 of 25 25 15 0
-UnsgeNOdIUW WC%w10 2
~-dtteCh&&ftw.
7 7
/
0.5 N
(Y
+
-5.0
-4.0
-30
-20
-1.0 O0 10 2.0 3.0 4,0 50 Flew Lulgil "4I Inch Note: This figure should be viewed in color.
Figure 3: Maximum Potential Undetected Circumferential Flaw with AR = 6 2.5 23 ARIO, VCir FIWW I1*n-,
W msse e
-t O%wIJI 2-dotectwo~l:*
0-5 0
-5.0 4-0
-3.0
-20
-.0 00 1.0 2-0 3-0 4.0 5.0 Flaw Lengh (L), hich Note: This figure should be viewed in color.
Figure 4: Maximum Potential Undetected Circumferential Flaw with AR = 10 The axial flaw length is bounded by the width of the DM weld, including the buttering, since neither the carbon steel pipe nor the stainless steel safe end are susceptible to PWSCC. The unexamined length is assumed to be half of the DM weld width and buttering since the circumferential scan (for axial flaws) was only performed from one side. The width of the DM weld and buttering is 15/16 inches, as shown in the sketch in Figure 5. Therefore, the unexamined length is 15/32 (or 0.469) inches. Similar to the circumferential flaw illustrations, Figure 6 shows the maximum undetected axial flaws
L-2013-232 Attachment Page 13 of 25 with an AR = 2 (i.e., semi-circular flaw). An axial flaw with an AR = 2 can be detected when it reaches the inspectable area shaded in blue in Figure 6. Table 1 summarizes the maximum potential undetected flaws using this method. The maximum undetected axial flaw with an AR = 2 and the circumferential flaws with AR = 6 and AR = 10 are 12.47%, 40.00%, and 25.56%, respectively.
4 A4r SOLW4~4-Assume OM Weld width Is 5/8 + 5116 z 15116 Inch Figure 5: DM Weld Width Sketch 0.5 0.45 0.4 0.35 0.3 1025 02 0.15 0.1 0.05 0
I I
0.45 Missed Lnt~h
-0.5
-0.4
-0.3
-0.2
-0.1 0
01 02 0.3 0.4 0.5 ma LtenMi (i* kch Note: This figure should be viewed in color.
Figure 6: Maximum Potential Undetected Axial Flaw with AR = 2
L-2013-232 Attachment Page 14 of 25 References for the Response to RAI-3 B:
- 1. Florida Power and Light Letter, L-2013-044, Rev. 0, "Fourth Ten-Year Interval Unit 1 Relief Request No. 5, Revision 0," February 4, 2013.
- 2. ASME Boiler and Pressure Vessel Code, Section Xl, 2001 Edition Including 2003 Addenda.
- 3. Moffat, G. et al., "Development of the Technical Basis for Plant Startup for the V.
C Summer Nuclear Plant," Proceedings of ASME 2001 Pressure Vessels and Piping Conference, Atlanta, GA, 2001.
RAI-4
In order for the NRC staff to verify the above flaw analysis, provide the following items.
NRC RAI-4 A.
A scaled drawing coverage map of the axial cross section of the weld showing the unexamined region of the susceptible material and the dimensions of the largest potential undetected circumferential and axial PWSCC flaw (idealized/elliptical in shape) that can exist, along with its position when it can be detected.
Response to RAI-4 A.
The drawings provided in the relief request are scaled drawings that show coverage of the axial cross section of the weld showing the unexamined region of the susceptible material.
The largest potential undetected circumferential and axial flaws are described in the response to RAI-3 B.
NRC RAI-4 B.
The weld residual stress profile used and whether the effect of the safe end stainless steel weld is included in the stress profile.
Response to RAI-4 B.
The total applied hoop stresses due to normal operating pressure and fabrication weld residual stress are listed in Table 1. The hoop stress profiles are for axial flaws, and are applicable to both inlet and outlet dissimilar metal (DM) welds.
The total applied axial stress profiles for circumferential flaws for outlet DM welds are listed in Table 2. The finite element analysis that produced the weld residual stress (WRS) profiles included the effect of the safe end stainless steel weld.
L-2013-232 Attachment Page 15 of 25 Table 1: Total Normal Operating Hoop Stress for Axial Flaws Including WRS x/tf')
No Repair 10% Repair 10%
25%
50%
50%
(ksi) with HT(2)
Repair Repair Repair Repair (ksi)
No HT with HT with HT No HT (ksi)
(ksi)
(ksi)
(ksi) 0.000 43.402 42.245 45.333 39.076 34.013 44.412 0.050 47.230 47.542 52.805 45.946 40.411 50.812 0.100 47.456 46.357 52.377 48.439 40.377 51.767 0.150 46.665 49.007 55.164 48.739 41.444 52.736 0.200 48.529 48.296 54.661 50.045 44.066 55.692 0.250 45.157 39.758 45.569 47.752 44.751 55.944 0.300 43.927 36.423 41.613 48.462 43.922 54.978 0.350 44.222 34.628 39.502 48.197 44.426 55.715 0.400 42.824 35.118 40.479 24.212 44.479 56.500 0.450 43.414 34.001 39.892 27.489 43.578 56.692 0.500 46.352 37.299 44.170 29.808 42.493 56.858 0.550 49.176 39.937 47.821 32.648 42.035 57.562 0.600 50.649 40.954 49.504 35.030 38.223 53.519 0.650 50.612 42.734 51.186 33.667 25.677 38.562 0.700 50.982 43.792 51.701 38.291 19.082 31.282 0.750 55.124 45.993 54.141 45.401 28.341 40.510 0.800 55.635 48.580 54.758 49.013 35.244 47.697 0.850 56.326 50.928 54.520 52.491 43.811 53.700 0.900 53.244 52.961 54.892 53.641 45.325 51.958 0.950 53.771 53.788 56.987 50.155 46.296 53.535 1.000 54.368 53.150 53.679 52.737 52.695 54.466 Notes:
(1) x/t = normalized through-wall locations.
(2) HT = heat treatment x/t = 0 is at ID. x/t = 1.0 is at outer diameter.
L-2013-232 Attachment Page 16 of 25 Table 2: Total Normal Operating Axial Stress for Circumferential Flaws Including WRS and Outlet Nozzle Stress 10% Repair 10% Repair 25% Repair 50% Repair 50% Repair with HT (ksi)
No HT (ksi) with HT (ksi) with HT (ksi)
No HT (ksi) 0.000 8.284
-4.152 6.636 0.773
-5.368 0.050 9.866 9.113 10.593 5.943 6.289 0.100 9.333 12.833 16.372 8.678 13.690 0.150 12.670 16.880 14.617 8.175 14.145 0.200 9.742 13.088 12.146 9.419 14.466 0.250
-9.099
-7.343 4.794 6.854 9.518 0.300
-14.012
-13.925 5.263 4.130 5.654 0.350
-13.071
-14.236 4.702 4.642 5.511 0.400
-11.102
-12.603
-19.007 4.676 5.321 0.450
-10.817
-12.589
-14.091 3.450 4.025 0.500
-4.480
-5.796
-10.517 2.078 3.914 0.550
-0.643
-1.686
-6.260 4.771 6.362 0.600 1.626 0.904
-2.053 2.260 1.528 0.650 5.633 5.176
-3.269
-7.693
-14.357 0.700 8.897 8.806 3.581
-12.800
-22.249 0.750 13.589 14.358 14.686
-0.470
-5.595 0.800 19.443 20.335 22.055 9.492 8.125 0.850 25.785 26.176 30.251 21.497 22.706 0.900 31.681 31.579 35.096 28.253 29.740 0.950 31.488 30.438 28.830 29.615 30.114 1.000 40.083 39.118 41.466 41.161 41.104 NRC RAI-4 C.
Data on the weld operating temperature and internal pressure.
Response to RAI-4 C.
The nominal cold leg operating temperature was 548.50F prior to the 2011 uprate. The current nominal cold leg operating temperature is 5510 F. The RCS nominal system internal pressure is 2235 psig.
NRC RAI-4 D.
Data on the pipe diameter and wall thickness, and safe end length.
Response to RAI-4 D.
As stated in the relief, FPL's, St. Lucie unit 1 contains a thirty (30) inch I.D. inlet and a thirty (30) inch I.D. outlet weld connected to each of the four (4) reactor coolant pumps (RCPs). Each weld joins mill-clad SA-516, Grade 70 carbon steel
L-2013-232 Attachment Page 17 of 25 (CS) pipe with SA-240-304L stainless steel cladding to a SA-351, Grade CF8M cast stainless steel safe end.
Additional thickness information is provided in the attached sketches for each weld. Cast stainless steel (SS) safe-end lengths from an original walkdown are provide in the below table.
CS PipelElbow SS Safe End Component ID Location Length Min Design Min Design Thickness Thickness RC-112-5-503 RCP 1A1 Inlet 2.375" 3.00" 3.094" Elbow(CS) to Safe-end (Cast SS)
RC-1 12-5-504 RCP 1A1 Outlet Safe-end (Cast 2.75" 2.50" 3.094" SS) to Pipe(CS)
RC-115-6-503 RCP 1A2 Inlet 0.5" 3.00" 3.094" Elbow(CS) to Safe-end (Cast SS)
RC-115-8-504 RCP 1A2 Outlet 2.3" 2.50" 3.094" Safe-end (Cast SS) to Pipe (CS)
RC-121-5-503 RCP 11B1 Inlet 2.0" 3.00" 3.094" Elbow (CS) to Safe-end (Cast SS)
RC-121-6-504 RCP 11B1 Outlet
RC-124-5-503 RCP 1B2 Inlet 2.0" 3.00" 3.094" Elbow (CS) to Safe-end (Cast SS)
RC-1 24-7-504 RCP2.8" 2.50" 3.094" Safe-end (Cast SS) to Pipe (CS) 2 2
NRC RAI-4 E.
A description of the weld process, including any post-weld machining (e.g.,
back chipping and re-welding on the inside diameter), and information on any known weld repairs Response to RAI-4 E.
The typical fabrication process is for the component fabricator to perform an alloy 82/182 weld build up on the end of the carbon steel pipe end prep with a target minimum depth of 1/4" after machining. The end prep, referred to as "weld butter,"
receives a post weld heat treatment as required by the fabrication code for the carbon steel piping.
The stainless steel safe end is then welded to the weld butter prep from the OD in a single "J" groove joint design. To complete the butt weld joint, the ID root is back grooved to sound metal and welded flush from the ID.
The stainless steel safe end weld is welded to the stainless steel reactor coolant pump in the field at the construction site. A review of weld radiographic reader sheets did not give an indication of any repairs. However, the ID is back grooved to remove the unfused weld joint land, typically 1/4 inch, to sound metal, followed by welding flush, which would be similar to a 3600 ID repair of - 10%
thickness.
L-2013-232 Attachment Page 18 of 25
RAI-5
The NRC staff requests the following information for a computer modeling, which is used by the NRC staff, to evaluate the examination coverage achieved at St. Lucie Unit 1:
NRC RAI-5 A.
As-built weld geometry (1) Provide scaled and dimensional drawings of the subject welds including the immediate region around the weld location so that the NRC staff can create accurate computer models of the weld and surrounding geometry.
(2) Provide depth of geometrical anomalies (e.g., concavity or waviness) on the outside diameter (OD) surface of the welds that impact volumetric inspection.
Response to RAI-5 A.
(1) Sketches provided in the relief request are scaled. Additional dimensional information is provided in response to question 4.d.
(2)
During the 2010 outage, the surface condition was improved through extensive grinding and contouring of the carbon steel side of the welds to meet the ASME Section Xl, Appendix VIII, Supplement 10 qualified procedure scanning requirements for the search units.
The surface conditioning effort was monitored by qualified examination personnel to ensure that no more than 1/32" gap between the search unit and the examination surface for the entire length of the search unit was present upon completion. The general examination surface condition was ground to an RMS finish approximately 250 RMS and free of irregularities, loose material, or coatings, that could interfere with the ultrasonic wave transmission.
NRC RAI-5 B.
Phased array probe used (1)
Discuss center frequency, bandwidth, pulse excitation type and duration.
(2)
Operating mode; (a) Transmit-receive (TR), pulse/echo, etc.,
and (b) Longitudinal (L) and/or shear(S) wave.
(3)
Array configuration (matrix): (a) Whether identical or different transmit-receive arrays, if used, (b) Physical separation between arrays (if TRL/TRS configuration). Identify distance between first element of one array and first element of second array (array separation - see Error! Reference source not found.below), and (c) If TRL or TRS mode is used, identify transmit and receive arrays (relative to weld geometry).
L-2013-232 Attachment Page 19 of 25 Figure 1 Top View of 2D Matrix Array Depicting Separation Dimension (4)
Total number of elements per array: (a) Number of elements along the primary axis, and (b) Number of elements along the secondary axis.
(5)
Element dimensions along primary and secondary axes, spacing between elements, and center-to-center distance (pitch - see below), and element shape if not rectangular.
I "W I
I U
W
-- o W
W rW I a I Figure 2 Top View of 2D Matrix Array Depicting Primary and Secondary Axis Pitch Dimensions
L-2013-232 Attachment Page 20 of 25 (6)
Element wiring configuration and element firing/receiving ordering sequence for each array.
(7)
Probe manufacturer and/or part number.
Response to RAI-5 B.
(1) Center frequency, bandwidth, pulse excitation type and duration were compliant with ASTM E-1065 guidelines.
The probe (SIN 01VR5K) consisted of a two identical units labeled as 01VR5K-1 and 01VR5K-2.
Each unit contained a 2 x 16 element matrix and was evaluated separately using ASTM E-1065 guidelines.
For three elements on each unit, the center frequency, bandwidth and pulse duration was obtained.
The location of each unit on the wedge is not recorded.
Probe Unit 01VR5K-1: (the three elements tested include #3, #15 and
- 30) Center Frequency - 1.65 MHz Bandwidth (@-6dB) - 66%
Pulse Excitation Type - shock excitation per ASTM E-1 065 Pulse Duration (@-20dB) - ranges from 1.98 x 10-6 sec to 2.06 x 10-6 sec Probe Unit 01VR5K-2: (the three elements tested include #2, #16 and
- 30) Center Frequency - 1.59 MHz for two elements, 1.65 MHz for one element.
Bandwidth (@-6dB) - 76% for two elements, 81% for one element.
Pulse Excitation Type - shock excitation per ASTM E-1 065.
Pulse Duration (@-20dB) - ranges from 1.98 x 10-6 sec to 2.06 x 10-6 sec.
(2) Operational Mode:
- a. Transmit-receive (TR)
- b. Both longitudinal and shear wave modes were used.
(3) Array configuration (matrix).
- a. Identical transmit-receive arrays were used.
- b. Array separation per Figure 1: 0.724-inch
- c. Transmit and receive arrays are side-by-side (left and right on the wedge). For axial scans (beams perpendicular to weld centerline) the primary axis of each array is perpendicular to the weld centerline.
For circumferential scans (beams parallel to weld centerline), the primary axis of each array is parallel to the weld centerline.
(4) Total number of elements per array.
- a. Each probe array/unit consists of 16 elements along the primary axis.
- b. Each probe array/unit consists of 2 elements along the secondary axis.
L-2013-232 Attachment Page 21 of 25 (5) Element dimension along primary axis - 0.0767-inch.
Element dimension along secondary axis - 0.1948-inch.
Spacing between elements (kerf) - 0.002-inch (both primary and secondary elements).
Center-to-center distance (pitch) - 0.0787-inch (primary), 0.1 968-inch (secondary).
Element shape - rectangular.
(6) 16 32 15 31 14 30 13 29 12 28 11 27 10 26 9
25 8
24 7
23 6
22 5
21 4
20 3
19 2
18 1
17 Left Array 64 48 63 47 62 46 61 45 60 44 59 43 58 42 57 41 56 40 55 39 54 38 53 37 52 36 51 35 50 34 49 33 Right Array Firing elements 1/17, 2/18, 3/19... (row elements are tied together with the cable wiring).
Receiving elements 33/49, 34/50, 35/51... (row elements are tied together with the cable wiring).
(7) GE Inspection Technologies, Part Number 115-000-545 NRC RAI-5 C.
Wedge Used (1)
Material type - Rexolite, other, etc. (a) Longitudinal and shear wave velocity. (b) Attenuation (if known) and (c) Density (if known).
(2)
Wedge Geometry: (a) Wedge angle, (b) Roof angle (if used), (c)
All physical dimensions necessary to create a 3-Dimensional solid model, such as height at front of wedge, height at back of wedge, width of wedge, and length of wedge. (d) Placement of each probe on each wedge (i.e., what is the height of the middle of the first element?), and (e) Is wedge contact geometry contoured to the specimen? If not, what contour does it have, if any?
L-2013-232 Attachment Page 22 of 25 Figure 3 Definition of Wedge Angle Response to RAI-5 C.
(1) Material type - Rexolite
- a. Longitudinal wave velocity in wedge - 0.092 in/ps. Shear wave velocity in wedge - N/A.
- b. Wedge attenuation - not known.
- c. Wedge density - 1,056 kg/M 3 (2) Wedge Geometry
- a. Wedge cut angle - 22 degrees.
- b. Wedge roof angle - 2.5 degrees
- c. Wedge Front Height- 0.774 inch, Wedge Back Height - 0.178 inch, Wedge Width - 1.607 inches, Wedge Length - 1.812 inches.
- d. Height at the middle of the first element - 0.2469 inch.
- e. Wedge contour is flat. Same wedge used for both axial and circumferential scans.
NRC RAI-5 D.
Beam focusing (See Figure 4 below)
(1) Discuss the type of focusing used, including associated details.
The four types of focusing techniques are listed below and shown graphically in Figure 4 below. (a) Projection - focusing in a specific vertical plane. Parameters: distance from probe reference point, sweep angles (start, stop, interval), skew angle(s), (b) True depth -
L-2013-232 Attachment Page 23 of 25 interval), skew angle(s), (b) True depth - focusing at specific constant depth with all angles focused at this depth. Parameters:
focusing depth, sweep angles (start, stop, interval), skew angle(s),
(c) Half-path - sound path held constant as beam is swept.
Parameters: sound path length, sweep angles (start, stop, interval),
skew angle(s), (d) Focal plane - arbitrary user-defined plane of focus. Low angle path length, high angle path length, sweep angles (start, stop, interval), skew angle(s).
(2) Number and configuration of elements used in data acquisition (active aperture), if different than total number of elements within each probe (e.g., if a linear array probe physically contains 64 elements but only the first 32 were active - this needs to be defined).
(3) Provide a set of transmit and receive delay law values for each element at a particular angle and focus to validate model Pfcctjon. (z)
True deplh (x)
Half path Focal plane (je+zi" z-ax+b Figure 4 Beam Focusing Options for Phased Array Probes Response to RAII-5 D.
(1)
Half path focusing used for both longitudinal and shear wave modes.
Longitudinal Waves:
Sound Path Length - 3.0 inches Sweep Angles - 25 to 70 degrees, 1 degree interval Skew Angle - none Shear Waves:
Sound Path Length - 3.0 inches Sweep Angles - 35 to 65 degrees, 1 degree interval Skew Angle - none
L-2013-232 Attachment Page 24 of 25 (2)
Each array (left and right) contains a matrix of 16 rows and 2 columns.
The cable wiring arrangement ties the two elements in each row together thus is functions as a 1 x 16 array.
(3)
Not available. These examinations were performed using the WesDyne IntraPhase instrument. The IntraPhase has an internal proprietary focal law generator based on the essential input parameters defined in the qualified EPRI-DMW-PA-1 procedure.
NRC RAI-6 On page 5 of 62 of the February 4, 2013 submittal, the licensee stated that "...For circumferential beam directions (axial flaws), coverage of the examination volume is based upon ID [inside diameter] impingement angles between 45 and 60 degrees..." According to generic dissimilar metal weld (DMW) ultrasonic examination procedure 10 (PDI-UT-1O) of the industry's Performance Demonstration Initiative (PDI) program, the optimum ID impingement angles for detecting axially-oriented primary water stress corrosion cracking in the subject welds is in the range of 55 to 60 degrees. Please clarify whether the inspection beam angles stated by the licensee are for initially transmitted (refracted), or ID surface-impinged, values. The following equation provides a basis for determining axial flaw ID impingement angle calculations:
sin(ao)
= D sin (8)
ID where:
a is the ID impingement angle,
,8 is the initial refracted angle from the probe on the OD surface, and OD/ID is the ratio of the outside-to-inside pipe diameters.
Response to RAI-6.
The inspection beam angles stated by the licensee are initially transmitted (refracted). The ultrasonic examination method used for these examinations was phased array UT using the EPRI procedure, EPRI-DMW-PA-1.
For the circumferential beam scans, the initially transmitted longitudinal wave beam angles used ranged from 25-degrees to 70-degrees with a resolution of 1-degree. For the RCP Inlet and Outlet welds, the initially transmitted longitudinal wave beams that will provide the optimum ID impingement angles of 55 to 60 degrees for the detection of axially oriented primary stress corrosion cracking (as stated in PDI-UT-10) are calculated to be in the approximate range of 42 to 46 degrees. This range of 42 to 46 degrees is well within the sector scan range of 25 to 70 degrees. These calculations are based on the measured circumference of the welds (then converted to an OD dimension) and the averaged measured UT thickness readings in the examination volume (then converted to an ID
L-2013-232 Attachment Page 25 of 25 dimension using the measured OD) combined with the equation for determining axial flaw ID impingement angle calculations.