ML042930286
| ML042930286 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 10/15/2004 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| ISI-3-11, ISI-3-12 | |
| Download: ML042930286 (28) | |
Text
d j-EDISON
. .,IA SOUTHERN CALIFORNIA A. Edward Scherer Manager of Nuclear Regulatory Affairs An EDISO\ ITERNATIONAOLS Company October 15, 2004 U.S. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Docket Nos. 50-361 and 50-362 Third Ten-Year Inservice Inspection (ISI) Interval Relief Requests ISI-3-11, Revision I and ISI-3-12 to Support Potential Pressurizer Heater Sleeve Repairs.
San Onofre Nuclear Generating Station, Units 2 and 3
Reference:
Letter from A. E. Scherer (SCE) to the Document Control Desk, (NRC) dated March 22, 2004;
Subject:
Docket Nos. 50-361 and 50-362, Third Ten-Year-lnservice Inspection (ISI) Interval Relief Request ISI-3-11 Regarding American Society of Mechanical Engineers (ASME)
Boiler and Pressure Vessel Code Case N-638 Similar and Dissimilar Metal Welding Using Ambient Temperature Machine Gas Tungsten Arc Welding (GTAW) Temper Bead Technique to Support Potential Pressurizer Nozzle Repairs, San Onofre Nuclear Generating Station, Units 2 and 3
Dear Sir or Madam:
Pursuant to 10 CFR 50.55a(a)(3)(i), Southern California Edison (SCE), San Onofre Nuclear Generating Station (SONGS) Units 2 and 3 is submitting Relief Requests ISI-3-11, Revision I and ISI-3-12 for review and approval, and is hereby withdrawing Relief Request ISI-3-11, submitted on March 22, 2004 (Referenced).
During the Unit 3 Cycle 13 Refueling Outage, SCE is performing examinations of SONGS Unit 3 Pressurizer heater sleeve penetrations. Depending on the results of these examinations, SCE may elect or need to implement repairs as described in Enclosure 1. The approval of the enclosed relief requests (Enclosures 2 and 3) will be needed to complete the sleeve repairs.
1c4 P.O. Box 128 San Clemente, CA 92674-0128 949-368-7501 Fax 949-368-7575
Document Control Desk October 15, 2004 Relief Request ISI-3-11, Revision I (Enclosure 2) is seeking relief from the requirements of Article IWA-4600 of the Boiler and Pressure Vessel Code, Section Xl.
The applicable Construction Code is the 1971 Edition through Summer 1971 Addenda of ASME Section IlIl.
Relief Request ISI-3-12 (Enclosure 3), is seeking relief from the 1995 Edition through 1996 Addenda of ASME Section Xl, IWA-3300, Flaw Characterization and IWB-2420 Successive Inspections. In lieu of fully characterizing any remaining cracks and performing successive examinations to validate flaw stability, SCE proposes, as described in the relief request, to utilize worst-case assumptions to conservatively estimate the crack extent and orientation.
The planned repair is similar to repairs performed previously at Three Mile Island, Crystal River Unit 3, Millstone, St. Lucie, Arkansas Nuclear One, Unit 1, South Texas Project, and other facilities.
SCE is requesting expedited review and approval of these relief requests to support reaching MODE 4 in the Unit 3 Cycle 13 Refueling Outage, which is currently planned for November 12, 2004.
Should you have any questions, please contact Mr. Jack Rainsberry at (949) 368-7420.
Sincerely,
Enclosures:
- 1. Background and Description of the Planned Repair
- 2. Relief Request ISI-3-1 1, Revision 1
- 3. Relief Request ISI-3-12
- 4. Summary of Analyses Performed to Support Welded Sleeve Repair cc: B. S. Mallett, Regional Administrator, NRC Region IV B. M. Pham, NRC Project Manager, San Onofre Units 2 and 3 C. C. Osterholtz, NRC Senior Resident Inspector, San Onofre Units 2 and 3
Southern California Edison San Onofre Nuclear Generating Station, Units 2 and 3 Docket Nos. 50-361 and 50-362 Enclosure 1 BACKGROUND AND DESCRIPTION OF THE PLANNED REPAIR
BACKGROUND AND DESCRIPTION OF THE PLANNED REPAIR The Pressurizer heater sleeves are small bore (1.660" O.D.) penetrations through the lower head of the Pressurizer vessel. The proposed repair process, termed a half sleeve repair, removes a portion of the existing sleeve outside the vessel. A weld buildup (i.e., weld pad) will be formed on the exterior of the vessel wall centered at the sleeve opening. The weld pad will be applied using the machine gas tungsten arc welding (GTAW) ambient temperature temper bead process.
This weld pad will then be machined to accept a new Ni-Cr-Fe Alloy 690 sleeve that is attached using a partial penetration "J" groove weld. A new sleeve-to-shell weld will be installed at the weld pad. The original weld will no longer function as the pressure boundary sleeve-to-vessel weld.
The original weld, and a portion of the original sleeve within the vessel wall thickness, will remain in place at the junction of the sleeve to vessel inside surface. This weld and sleeve portion has been analyzed for acceptability to remain in place. It is also assumed that any flaws will remain in the original sleeve to shell weld and will not be removed.
Southern California Edison (SCE) will conduct the repairs in accordance with related portions of the 1995 Edition through 1996 Addenda of the American Society of Mechanical Engineers (ASME) Section Xi (as applicable) and the 1971 Edition through Summer 1971 Addenda of Section III (except for nondestructive examination (NDE) methodology and acceptance criteria, as noted above) and the alternative requirements as discussed in Relief Request ISI-3-11, Revision 1 (Enclosure 2), and Relief Request ISI-3-12 (Enclosure 3).
In lieu of a hydrostatic pressure test, SCE intends to perform a system leak test using the provisions in ASME Xl, IWA-4540(a)(2), 1998 Edition through 2000 Addenda. SCE's current code of record, the 1995 Edition through 1996 Addenda, permits the use of specific provisions from a later Edition/Addenda to be used in IWA-4150(b). The NRC has previously approved the use of ASME Xl, 1998 Edition through 2000 Addenda per 10 CFR 50.55a.
Relief Request ISI-3-11, Revision 1 (Enclosure 2), is seeking an alternative to the requirements in IWA-4600 to perform a portion of the repair with a remotely operated welding machine, utilizing the machine Gas Tungsten-Arc Welding (GTAW) process and the ambient temperature temper bead method with 500F minimum preheat temperature and no post weld heat treatment, as described in Code Case N-638.
Relief Request ISI-3-12 (Enclosure 3) is seeking relief from the 1995 Edition through 1996 Addenda of ASME Section Xi, IWA-3300, Flaw Characterization and IWB-2420 Successive Inspections. In lieu of fully characterizing the remaining cracks and performing successive examinations, SCE proposes, as Page 1 of 2
BACKGROUND AND DESCRIPTION OF THE PLANNED REPAIR described in the relief request, to utilize worst-case assumptions to conservatively estimate the crack extent and orientation.
The repair technique and ASME Code Relief described above is consistent with Crystal River submittals dated October 5, 2003 and October 11, 2003, and NRC approval dated January 6, 2004.
Page 2 of 2
Southern California Edison San Onofre Nuclear Generating Station, Units 2 and 3 Docket Nos. 50-361 and 50-362 Enclosure 2 RELIEF REQUEST ISI-3-11, REVISION I
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL REFERENCE CODES: The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code:
Section Xl, 1995 Edition through 1996 Addenda I. System/Component(s) for Which Relief is Requested:
a) Name of component:
Pressurizer Heater Sleeve penetrations. There are 30 heater sleeve penetrations through the lower head of each Pressurizer vessel.
b) Function:
The sleeves and penetration welds serve as primary pressure boundary components.
c) ASME Code Class:
The Pressurizer heater sleeve penetrations are ASME Class 1.
d) Category:
Examination Category B-P, All Pressure Retaining Components; Item No. B1 5.20 applies to the original unmodified and modified locations at the new welds.
II. Current Code Requirement and Relief Request:
a) ASME B&PV Code, Section Xl 1995 Edition through 1996 Addenda, IWA-4410 requires repairs to be made in accordance with the Owner's Requirements and the original Construction Code (ASME l1l) of the component or system. Later Editions and Addenda of the Construction Code, either in their entirety or portions thereof, and Code Cases may be used. If repair welding cannot be performed in accordance with these requirements, the applicable alternative requirements of IWA-4600 may be used.
b) In accordance with 10CFR50.55a(a)(3)(i), Southern California Edison (SCE), San Onofre Nuclear Generating Station (SONGS)
Units 2 and 3 is requesting relief from the following portion of ASME Section Xl, IWA-441 0 and its referenced IWA-4600 to perform Pressurizer heater sleeve penetration repairs:
Page 1 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL "Alternatively, the applicable requirements of IWA4600 may be used for welding . . ."
In lieu of performing the repair using the alternative welding techniques described in IWA-4600, SCE is proposing to perform a portion of the repair with a remotely operated welding machine, utilizing the machine Gas Tungsten-Arc Welding (GTAW) process and the ambient temperature temper bead method with 500F minimum preheat temperature and no post weld heat treatment (PWHT), as described in Code Case N-638. SCE is requesting the use of the Code Case in its entirety, except for deviations as listed in Table 1, below. The description of the proposed alternative is provided in the following section.
c) In lieu of a hydrostatic pressure test, SCE intends to perform a system leak test using the provisions in ASME Xl, IWA-4540(a)(2),
1998 Edition through 2000 Addenda. SCE's current code of record, the 1995 Edition through 1996 Addenda, permits the use of specific provisions from a later Edition/Addenda to be used in IWA-4150(b). The NRC has previously approved the use of ASME Xl, 1998 Edition through 2000 Addenda per 10 CFR 50.55 a.
d) SCE has determined that the proposed alternative will provide an acceptable level of quality and safety, while allowing significant dose reductions.
Ill. Alternate Criteria for Acceptability:
SCE may elect or need to perform Pressurizer heater sleeve repairs as follows:
- 1. Mechanical removal of a portion of the existing sleeve.
- 2. Application of a weld pad (or weld buildup) using F-No. 43 to the Pressurizer shell (P-No. 3, Group 3) base material.
- 4. Installing the replacement sleeve by using conventional manual gas tungsten arc welding (GTAW) and a "J" groove partial penetration weld.
The proposed alternative to the applicable portion of ASME, Section Xi involves the use of the ambient temperature temper bead repair described in Code Case N-638. This methodology is proposed to be used only for the weld pad Page 2 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL application, Step 2 of the repair process. Code Case N-638 was approved for use in Regulatory Guide 1.147, Revision 13 (June 2003).
Table 1 was prepared as a means to readily describe those areas where the proposed methodology deviates from the requirements of the original construction code, ASME Xi, or the code case.
Table 1 Reference Requirement Alternative, Including Reference I I for Justification ASME Section III Relief NB-3357 "All vessels and vessel parts 500 F minimum preheat shall be given the appropriate temperature and no post-weld postweld heat treatment heat treatment (PWHT) prescribed in NB-4620" performed as described in Code Case N-638. {See IV.2.b & c below}
NB-4622.1 Except as otherwise stated in 500 F minimum preheat the Notes to Table NB-4622.1- temperature and no PWHT 1, all welded components or performed as described in Code pieces of components shall be Case N-638. {See IV.2.b & c given a final postweld heat below}
treatment at a temperature not less than specified in Table NB-4622.1-1.
Note 11.B to . . . postweld heat treatment is 500F minimum preheat Table NB- mandatory for ... and SA-533 temperature and no PWHT 4622.1-1 material for all thicknesses performed as described in Code Case N-638. {See IV.2.b & c below}
NB-61 11.1 All components and System leak test will be appurtenances constructed performed in lieu of a hydrotest and/or installed under the rules per IWA-4540 (a)(2),1998 of this Section of the Code shall Edition, 2000 Addenda.
be hydrostatically tested, in the presence of the Inspector.
Page 3 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL Table 1 Reference Requirement Alternative, Including Reference I I for Justification ASME Section Xl RELIEF IWA-4600(b)(1) When postweld heat treatment Code Case N-638 will be used in is not to be performed, the lieu of IWA-4600. {See IV.2.b & c welding methods of IWA-4630 below}
(for dissimilar materials) may be used in lieu of welding and NDE requirements of ASME IlIl, provided requirements of IWA-4610 are met.
IWA-4610(a) For GTAW process, weld area Qualification test and field and 5" band shall be preheated welding process per Code Case to 300OF minimum; Maximum N-638; 501F minimum preheat; 0
interpass temperature of 450 F 150OF maximum interpass to be used temperature to be used for the procedure qualification and 3500 F maximum for field welding.
{See IV.2.b and c below}
IWA-4610(a) Thermocouples and recording A contact pyrometer will be used instruments shall be used for for monitoring preheat and monitoring process interpass temperatures in lieu of temperatures thermocouples and recording instruments. Interpass temperatures to be monitored on first three layers of each repair location. In first repair location, interpass temperatures to be measured every three to five passes. Subsequent repair locations will be measured every six to ten passes.
{See IV.2.d below}
IWA-4633.2(c) Six temper bead layers are Code Case N-638 requires three required. temper bead layers. {See IV.2.c below}
IWA-4633.2(d) After at least 3/16" deposit, the Post Weld Heat Soak not used weld area shall be maintained per Code Case N-638. {See at 300°F for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> minimum IV.2.c below}
(P-No. 3 materials)
Page 4 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL Table 1 Reference Requirement Alternative, Including Reference
_I I for Justification CODE CASE N-638 RELIEF N-638 Code Case provides relief to This methodology is applied due allow use of machine GTAW to dose considerations, even with ambient temperature though the vessel can be preheat and no PWHT when drained. This philosophy is in draining vessel is impractical accordance with the SONGS ALARA program. {See IV.2.a below}
N-638 The Code Case requires Only a surface examination of surface examination and the 5 inch band surrounding the volumetric examination (UT) of weld (PT or MT) will be a 5 inch band of base metal performed.
surrounding the weld repair {See IV.2.e below}
area after the 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time.
IV. Basis for Relief:
The basis for the relief request is that the use of an ambient temperature temper bead welding process provides an equivalent acceptable level of quality and safety when compared to the welding process in ASME, Sections Xl and Ill, while offering substantial savings in accumulated radiation dose. In support of this conclusion, the process is described below, followed by technical justification for the technique, as well as the expected dose savings.
- 1. Description of the process Figure 1 provides a general overview of the configuration.
a) Volumetric examinations or visual inspections for leakage/boric acid deposits of the Pressurizer heater sleeve penetrations may identify a need to repair a pressurizer heater sleeve. SCE plans to use remote machine processes similar to those used previously at other facilities, including Crystal River Unit 3, South Texas Project, Arkansas Nuclear 1, Unit I (ANO), and Millstone.
b) The sleeve will be cut close to the Pressurizer shell. A portion of the sleeve inside the vessel bore will then be removed by machining and the area around the sleeve will be prepared for the application of the weld pad by grinding smooth and performing a surface examination Page 5 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL (PT or MT) and ultrasonic examination of the area to be welded and the 5 inch wide band surrounding the weld area.
c) A weld pad will be applied to the surface of the Pressurizer shell using the ambient temperature temper bead weld process and GTAW method as described in Code Case N-638. The weld pad is to be applied as a weld buildup centered on the existing sleeve opening.
d) The weld pad will be prepared suitable for nondestructive examination (NDE). The pad and its heat affected zone (HAZ) below the pad will be volumetrically examined (UT) to the extent practical. The weld pad and a 5-inch wide band surrounding the weld pad will also be surface examined (PT or MT). The examinations and acceptance criteria will be in accordance with ASME III, 1995 Edition through 1996 Addenda, NB-5000.
Ultrasonic examinations, before and after welding, of the full parent material thickness beneath the weld pad, to the extent practical, are performed to discern laminar type indications therein. Laminar type indications observed will be recorded and evaluated to assure the structural integrity of the modification configuration is not adversely affected.
e) The center of the weld pad will be ground or machined to re-establish a free path into the Pressurizer penetration. The weld pad will be prepared to accept the new sleeve using a "J" groove partial penetration weld.
f) The new sleeve will be inserted and welded using conventional welding and NDE techniques (manual GTAW and progressive PT).
Note that this weld is in full ASME construction code compliance and relief from code requirements is not required.
- 2. Justification a) As low as reasonably achievable (ALARA)
Experience gained from the performance of similar repairs/
modifications at other plants indicate that remote automated repair methods reduce the radiation dose to repair personnel and still provide acceptable levels of quality and safety. SCE is aware that ASME has revised Code Case N-638 to reflect the acceptability of this method for ALARA considerations as well as the inability to drain the vessel. SCE recognizes the importance of ALARA principles and this remote repair Page 6 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL method is being proposed for the possibility of repairing pressurizer heater sleeves at SONGS.
This approach for the repair of Pressurizer sleeves will significantly reduce radiation dose to repair personnel while still maintaining acceptable levels of quality and safety. SCE estimates the dose accumulated providing access, installing heating pads and performing the preheat and post weld heat treatment required by the construction code would be approximately 1.8 REM per sleeve repair. Assuming that only one sleeve requires repair, use of the ambient temperature temper bead process results in a reduction of approximately 1.8 REM for the repair.
b) Procedure Qualification Results of procedure qualification work undertaken to date on low alloy steel base material indicate that the ambient temperature temper bead process produces sound and tough welds. Industry experience also indicates that the machine GTAW ambient temper bead process has the capability of producing acceptable welds on P-No.3 Group No. 3 ferric steel base materials. Westinghouse-PCI (PCI), Welding Services (WSI), and Framatome ANP (FANP) have all qualified the welding process and procedures for this specific application in accordance with code and code case requirements prior to its use at SONGS.
These Code Case N-638 qualifications were performed at room temperature on P-No. 3 Group No. 3 base materials with ERNiCrFe-7 weld filler and similar low heat input controls that will be used for this repair application. These qualifications did not include a post weld heat soak. The successful qualification of the ambient temperature temper bead welding process demonstrates that the proposed alternative provides an acceptable level of quality and safety.
To ensure the acceptability of the welding process procedures for the SONGS application, SCE will review the chosen contractor's welding procedure specification and qualification records and verify the qualifications meet all Code and Owner's Requirements and Code Case N-638. Additionally, SCE will require either a mock-up demonstration or documentation that a representative mock-up demonstration has been previously performed.
Page 7 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL c) Weld Quality The proposed alternative repair technique has been demonstrated as an acceptable method for performing Pressurizer sleeve repairs. The ambient temperature temper bead technique has been approved by the ASME committee per Code Case N-638. The ambient temperature temper bead technique has also been previously approved by the NRC as having an acceptable level of quality and safety and used successfully at several utilities (Three Mile Island, Crystal River Unit 3, Millstone, St. Lucie, ANO, South Texas Project, and others). This Code Case has been approved in Regulatory Guide 1.147, Revision
- 13. This approval indicates that the methodology is capable of producing quality in-situ repairs.
As documented in EPRI Report GC-1 11050, research shows that carefully controlled heat input and bead placement allow subsequent welding passes to relieve stress and temper the HAZ of the base material. The use of the machine GTAW temper bead process will allow precise control of heat input, bead placement, bead size, and contour as compared to the SMAW process. The very precise control over these factors afforded by the machine GTAW process provides effective tempering of the HAZ. The research in the EPRI Report and numerous procedure qualification tests performed on P-No. 3, Group No. 3 by the industry have shown that acceptable weld quality and HAZ impact toughness can be obtained using machine GTAW, ambient preheat, three controlled temper bead layers, and no post weld heat treatment.
Typically, preheat and post weld heat treatment are used to mitigate the effects of the solution of atomic hydrogen in ferritic materials prone to hydrogen embrittlement cracking. The machine GTAW temper bead process uses a welding process that is inherently free of hydrogen.
The GTAW process relies on bare welding electrodes and bare wire filler metal with no flux to trap moisture. An inert gas blanket provides shielding for the weld and surrounding metal, which protects the region during welding from the atmosphere and the moisture it may contain and typically produces porosity free welds. Inaccordance with the weld procedure qualification, welding grade argon is used for the inert gas blanket. To further reduce the likelihood of any hydrogen evolution or absorption, specific controls will be used to ensure the welding electrodes, filler metal, and weld region are free of all sources of hydrogen. Argon flow rates are adjusted to assure adequate shielding of the weld without creating a venturi affect that might draw oxygen or water vapor from the ambient atmosphere into the weld.
Page 8 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-1 1, REVISION I THIRD TEN YEAR INTERVAL d) Preheat and Interpass Temperature Measurement Due to the location of the repair and area radiation dose rate, the placement of thermocouples for monitoring weld interpass temperature is determined to be not beneficial based on dose savings. Therefore, thermocouples are not planned for use to monitor interpass temperature during welding. Preheat and interpass temperatures for the weld pad will be measured using a contact pyrometer. Interpass temperature will be monitored for the first three layers of each repair location. On the first repair location, the interpass temperature measurements will be taken every three to five passes. At subsequent repair locations, interpass temperature measurements will be taken every six to ten passes. Heat input beyond the third layer will not have a metallurgical affect on the low alloy steel HAZ.
e) Examination The pressure test provisions being used from ASME Xl, IWA-4540(a)(2), 1998 Edition, through 2000 Addenda mandate that NDE methodology and acceptance criteria from ASME 1II, 1992 Edition or later be used. All examinations will be performed in accordance with ASME III, 1995 Edition through 1996 Addenda, NB-5000, using personnel qualified in accordance with IWA-2300 and/or NB-5500.
The area to be welded, plus a 5 inch surrounding band, will be surface examined (PT or MT) both prior to and following welding. All post weld exams will be performed after the required 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> hold time. The entire volume of the weld pad, to the extent practical, will be scanned from the face of the pad, using examination angles of 00, 450 RL, 600 RL and an OD creeping wave. The examination volume shall include the weld-deposited material and the ferritic vessel HAZ.
Ultrasonic examination, before and after welding, of the full parent material thickness beneath the weld pad, to the extent practical, will be performed to discern laminar type indications therein. Laminar type indications observed will be recorded and evaluated to assure the structural integrity of the modification configuration is not adversely affected.
Because this is a surface application of the temper bead process, there will be minimal impact to the volume of metal of the Pressurizer vessel in the area surrounding the weld. Since this weld is applied to the exterior surface of the Pressurizer, there is no additional useful information that can be gained by a volumetric examination of the area Page 9 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL surrounding the weld. The weld and HAZ below will be post weld volumetrically examined to the extent possible. This reduction in the post welding inspection will provide additional dose reduction for this repair while still ensuring sound weld metal is deposited and that the process has not introduced flaws in the base material.
f) Corrosion The automated repair method described above leaves an area of ferritic low alloy steel at the outside diameter (OD) of the sleeve [inside diameter (ID) of the sleeve bore] exposed to the primary coolant. The effect of corrosion on the exposed area, including reduction in vessel wall thickness, has been evaluated by Aptech Engineering Services and concurred with by SCE (SONGS Document M-DSC-402). The analysis shows that the total corrosion is insignificant when compared to the thickness of the vessel shell. SCE has determined that the expected extremely low rate of material loss will provide an acceptable level of safety.
g) Stresses Design stress analysis of the modified heater sleeve weld attachments was performed (see Enclosure 4). The stress analysis demonstrates that the modified heater sleeve configuration complies with the criteria of NB-3000, ASME Section III, 1971 through Summer 1971 Addenda, as described in the calculations referenced in Enclosure 4, using design and service conditions applicable to the Pressurizer.
Therefore, based on the discussion above, SCE has determined that the proposed alternative provides an acceptable level of quality and safety while reducing radiation exposure to as low as reasonably achievable.
V. Documentation:
The use of the Code Cases and this Relief Request shall be documented on the NIS-2 Form for each repair.
VI. Implementation Schedule:
This relief request is being implemented during the Third Inservice Inspection Interval and it is only applicable to the repairs to the Pressurizer heater sleeves. SONGS third ten-year Inservice Inspection Interval began on August 18, 2003 and is scheduled to end on August 17, 2013.
Page 10 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL VII. Precedents:
Letter from James H.Terry (Progress Energy) to the Document Control Desk (NRC) dated October 5, 2003;
Subject:
Crystal River Unit 3 - Relief Requests 03-0001-RR, Revision 0, and 03 - 0002-RR, Revision 0 Letter from James H.Terry (Progress Energy) to the Document Control Desk (NRC) dated October 11, 2003;
Subject:
Crystal River Unit 3 - Supplemental Information to Relief Request 03-0001-RR, Revision 0 Letter from Allen G. Howe (NRC) to Dale E. Young (Crystal River Nuclear Plant) dated January 6, 2004;
Subject:
Crystal River Unit 3 - Safety Evaluation of Relief Requests 03-001[sic]-RR and 03-0002-RR Concerning Alternative Repair Method and Flaw Characterization for Pressurizer Instrument Nozzle Penetrations (TAC NOS. MC0947 and MC0963)
Page 11 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-11, REVISION 1 THIRD TEN YEAR INTERVAL Figure 1 ORIGINAL J GROVE WELD CLAD ALLOY 600 HEATER SLEEVE SA-533 GR.B CL.1 WELD PAD ;
ALLOY 52 (UNS N06052);
PARTIAL SLEEVE ALLOY 690 Typical Half Sleeve Repair For Pressurizer Heater Sleeve Page 12 of 12
Southern California Edison San Onofre Nuclear Generating Station, Units 2 and 3 Docket Nos. 50-361 and 50-362 Enclosure 3 RELIEF REQUEST ISI-3-12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-12 THIRD TEN YEAR INTERVAL REFERENCE CODE: The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel (B&PV) Code, Section Xl, 1995 Edition through 1996 Addenda
- 1. System/Component(s) for Which Relief is Requested:
a) Name of component:
Pressurizer Heater Sleeve penetrations. There are 30 heater sleeve penetrations through the lower head of each Pressurizer vessel.
b) Function:
The sleeves and penetration welds serve as primary pressure boundary components.
c) ASME Code Class:
The Pressurizer heater sleeve penetrations are ASME Class 1.
d) Category:
Examination Category B-P, All Pressure Retaining Components; Item No. B15.20 applies to the original unmodified and modified locations at the new welds.
- 2. Current Code Requirement and Relief Request:
In lieu of a hydrostatic pressure test, SCE intends to perform a system leak test using the provisions in ASME Xl, IWA-4540(a)(2), 1998 Edition through 2000 Addenda. SCE's current code of record, the 1995 Edition through 1996 Addenda, permits the use of specific provisions from a later Edition/Addenda to be used in IWA-4150(b). The NRC has previously approved the use of ASME Xl, 1998 Edition through 2000 Addenda per 10 CFR 50.55 a.
IWA-461 1.1 requires in part that, "Defects shall be removed or reduced in size in accordance with this Paragraph." Furthermore, IWA-461 1.1 allows that "...the defect removal and any remaining portion of the flaw may be evaluated and the component accepted in accordance with the appropriate flaw evaluation rules of Section Xl." ASME Section Xl, IWA-3300 requires characterization of flaws detected by inservice examination.
SCE is requesting relief from ASME Section Xl, IWA-3300. It is assumed that flaws in the original Pressurizer heater sleeve to Pressurizer J-groove weld will Page 1 of 6
INSERVICE INSPECTION RELIEF REQUEST ISI-3-12 THIRD TEN YEAR INTERVAL not be removed. In lieu of fully characterizing the existing cracks, SCE proposes to utilize worst-case assumptions to conservatively estimate the crack extent and orientation. SCE has determined that the proposed alternative will provide an acceptable level of quality and safety, while allowing significant dose reductions.
IWB-2420 requires successive examinations of flaws evaluated in accordance with IWB 3132.3 or IWB 3142.4.
SCE is requesting that no additional inspections be performed to observe flaw stability because initial flaw characterization is not being performed. Thus, the actual dimensions of the flaw will not be fully determined. In lieu of fully characterizing any cracks that exist, and performing successive examinations SCE proposes to utilize worst-case assumptions to conservatively estimate the crack extent and orientation. Then, the postulated crack extent and orientation will be evaluated using the appropriate rules of ASME Xl. SCE has determined that the proposed alternative will provide an acceptable level of quality and safety, while allowing significant dose reductions.
- 3. Alternate Criteria for Acceptability:
In lieu of the requirements of IWA-3300 and IWB-2420, per 10 CFR 50.55a(a)(3)(i), the following alternative is proposed:
The planned repair for the subject Pressurizer heater sleeves does not include removal of any flaws assumed to be present in the remaining J-groove partial penetration welds. Therefore, per the requirements of IWA-461 1.1, the cracks must be evaluated using the appropriate flaw evaluation rules of Section Xl. In addition, no additional examinations are planned to characterize the cracks.
Thus, the actual dimensions of the flaw will not be fully determined. If a flaw is not fully characterized, the requirements for successive inspections of IWB-2420 become futile in that there is no reference point from which to evaluate changes in the flaw characteristics. In lieu of fully characterizing the existing cracks, SCE will utilize worst-case assumptions to conservatively estimate the crack extent and orientation. Then the postulated crack extent and orientation will be evaluated using the rules of IWB-3600.
- 4. Basis for Relief:
Volumetric examinations or visual inspections of the Pressurizer heater sleeve penetrations may identify a need to repair the pressurizer heater sleeve as follows:
- 1. Mechanical removal of a portion of the existing sleeve.
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INSERVICE INSPECTION RELIEF REQUEST ISI-3-12 THIRD TEN YEAR INTERVAL
- 2. Application of a weld pad (or weld buildup) using F-No. 43 to the Pressurizer shell (P-No. 3, Group 3) base material.
43).
- 4. Installing the replacement sleeve by using conventional manual gas tungsten arc welding (GTAW) and a "J" groove partial penetration weld.
The existing sleeve(s) and weld(s) will no longer function as the pressure boundary. However, the possible existence of cracks in these welds mandates that the potential for flaw growth be evaluated. The requirements of IWA-461 1.1 allow two options for determining the disposition of discovered cracks. The subject cracks are either removed as part of the repair process or left as-is and evaluated per the rules of IWB-3600. The repair design dictates that the inside weld and sleeve portion be left intact inside the vessel.
The assumptions of IWB-3500 are that the cracks are fully characterized to be able to compare the calculated crack parameters to the acceptable parameters provided in IWB-3500. In the alternative being proposed, the acceptance of the postulated crack is calculated based on the two inputs of expected crack orientation and the geometry of the weld.
Typically, an expected crack orientation is evaluated based on prevalent stresses at the location of interest. Using worst case (maximum) assumptions with the geometry of the as-left weld, the postulated crack is assumed to begin at the inside surface of the heater sleeve and penetrates the heater sleeve wall, and through to the intersection of the vessel inner diameter surface and the vessel sleeve penetration bore and propagate into the vessel wall low alloy steel. The depth and orientation are worst-case assumptions for cracks that may occur in the remaining J-groove partial penetration weld configuration. It is assumed that the "as-left" condition of the remaining J-groove weld includes degraded or cracked weld material.
A fracture mechanics evaluation has been performed (Calculation M-DSC-402) in accordance with ASME Section Xl evaluation procedures of IWB-3600. The analysis determines if a degraded J-groove weld material could remain in the vessel, with no examination to size any flaws that might remain following the repair. Since the hoop stresses in the J-groove weld are higher than the axial stresses, the preferential direction for cracking is axial, or radial relative to the sleeve. It is postulated that a radial crack in the Alloy 182 weld metal would propagate by Primary Water Stress Corrosion Cracking (PWSCC) through the Page 3 of 6
INSERVICE INSPECTION RELIEF REQUEST ISI-3-12 THIRD TEN YEAR INTERVAL weld to the interface with the low alloy steel shell. It is fully expected that such a crack would then arrest at the weld-to shell interface.
Crack growth through the Alloy 182 material would tend to relieve the residual stresses in the weld as the crack grows to its final size. Although residual stresses in the shell material are low, it is assumed that a weld flaw formed by PWSCC could grow into the low alloy steel material by fatigue. This flaw will form a continuous radial corner flaw that would propagate into the low alloy steel shell by fatigue crack growth under cyclic loading conditions.
Flaw evaluations are performed for a postulated radial corner crack. Hoop stresses are used since they are perpendicular to the plane of the crack. The life of the repair is determined based on fatigue crack growth and crack growth per year of operation. It has been calculated as 40 years of additional service. The final flaw size meets the fracture toughness requirements of the ASME Code using an upper shelf value of 200 ksi in"2 for unirradiated ferritic materials. The results of the analyses indicate that it is acceptable to leave the alloy 600 heater sleeve and original attachment J-groove weld in the vessel, even with the possibility that cracks exist in the weld for 40 years of service.
As noted above, radial cracks are postulated to occur in the weld due to the dominance of the hoop stress at this location. The occurrence of transverse cracks that could intersect the radial cracks is considered remote. There are no identified forces that would drive a transverse crack. Only thermal and welding residual stresses could cause a transverse crack to grow. However, the presence of radial cracks limits the growth potential of the transverse cracks.
The radial cracks would relieve the potential transverse crack driving forces.
Hence, it is unlikely that a series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged. Therefore the release of debris generated by a cracked weld is highly unlikely.
Additionally, SCE has previously evaluated the consequences of loose parts of similar or larger dimensions and mass being carried into the reactor vessel and concluded that the probability of damage to any RCS component is not significant (reference Action Request (AR) 960901028, assignment 8). For the heater sleeves in the pressurizer, the sleeve remnant is prevented from becoming a loose part by the pressurizer heater penetrating through the center of the remnant. Inthe unlikely event that a small part of the heater sleeve remnant breaks away, the density of the loose part material is significantly greater than that of the water, and the loose part would tend to settle to the bottom of the pressurizer. Flow velocities in the pressurizer are relatively low and are not likely to transport loose pieces of metal to the surge line. Additionally, the surge line nozzle is equipped with a surge screen, with half-inch holes. The evaluation in Action Request (AR) 960901028, assignment 8 concluded that no damage is Page 4 of 6
INSERVICE INSPECTION RELIEF REQUEST ISI-3-12 THIRD TEN YEAR INTERVAL expected in the event that the loose part does not remain in the bottom of the reactor.
The cited evaluations provide an acceptable level of safety and quality in insuring that the Pressurizer shell remains capable of performing its design function with flaws existing in the original J-groove weld. See Enclosure 4 for a summary of the supporting analyses.
Justification for Granting Relief Removal of the cracks in the existing J-groove partial penetration welds would incur excessive radiation dose for repair personnel. With the installation of the new pressure boundary welds previously described, the original function of the J-groove partial penetration welds is no longer required. It is well understood that the cause of the cracks in the subject J-groove welds is Primary Water Stress Corrosion Cracking (PWSCC). As shown by industry experience, the low alloy steel wall of the Pressurizer impedes crack growth by PWSCC. SCE believes the alternative described will provide an acceptable level of quality and safety when compared to the code requirements in IWB-3500 to characterize the cracks left in service. Using flaw tolerance techniques, it has been demonstrated that the assumed worst case crack size will not grow to an unacceptable depth into the Pressurizer shell low alloy steel base material over the life of the repair.
Thus, the Pressurizer shell can be accepted per the requirements of IWA-461 1.1.
- 5. Implementation Schedule:
This relief request is being implemented during the Third Inservice Inspection Interval and it is applicable to repairs to the Pressurizer heater sleeve penetrations. SONGS third ten-year Inservice Inspection Interval began on August 18, 2003 and is scheduled to end on August 17, 2013.
- 6. Precedents:
Letter from James H. Terry (Progress Energy) to the Document Control Desk (NRC) dated October 5, 2003;
Subject:
Crystal River Unit 3 - Relief Requests 03-0001-RR, Revision 0, and 03- 0002-RR, Revision 0 Letter from James H.Terry (Progress Energy) to the Document Control Desk (NRC) dated October 11, 2003;
Subject:
Crystal River Unit 3 - Supplemental Information to Relief Request 03-0001-RR, Revision 0 Letter from Allen G. Howe (NRC) to Dale E. Young (Crystal River Nuclear Plant) dated January 6, 2004;
Subject:
Crystal River Unit 3 - Safety Evaluation of Relief Page 5 of 6
INSERVICE INSPECTION RELIEF REQUEST ISI-3-12 THIRD TEN YEAR INTERVAL Requests 03-001-RR and 03-002-RR Concerning Alternative Repair Method and Flaw Characterization for Pressurizer Instrument Nozzle Penetrations (TAC NOS. MC0947 and MC0963)
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Southern California Edison San Onofre Nuclear Generating Station, Units 2 and 3 Docket Nos. 50-361 and 50-362 Enclosure 4
SUMMARY
OF ANALYSES PERFORMED TO SUPPORT WELDED SLEEVE REPAIR RELIEF REQUEST ISI-3-11, REVISION 1 and RELIEF REQUEST ISI-3-12
SUMMARY
OF ANALYSES PERFORMED TO SUPPORT WELDED SLEEVE REPAIR Calculation IDescription ISummary Half-sleeve repair fatigue 1) This analysis evaluated M-DSC-402 Rev. 0 Pressurizer Heater Sleeve crack growth and borated the long-term impact of the J-Groove Weld Flaw water corrosion evaluation newly exposed low alloy Evaluation for Pressurizer Heater steel base metal (resulting Sleeves. from the repair) to reactor coolant. This analysis concluded that the corrosion rate is negligible and the corrosion depths after 40 years are less than the allowable corrosion depths.
- 2) This analysis also determined the impact of an assumed flaw in the existing J groove weld on low alloy steel base material. The analysis concluded that a postulated axial crack through the entire existing J groove weld would be acceptable for forty years following installation. This is based on an evaluation of fatigue crack growth into base metal.
- 3) The effect of the residual stresses in the existing pressurizer heater sleeve J-weld due to fabrication processes was included in the weld flaw evaluation.
M-DSC-356 Rev. 1 Half-sleeve repair for Analyzed the repairs to the Evaluation of Modified Pressurizer Heater Sleeves requirements of ASME Section Pressurizer Heater Sleeves - ASME Section III Code 111. This analysis concluded that evaluation the stresses and fatigue meet the requirements of the Code and that repair life is forty years from time of installation.
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SUMMARY
OF ANALYSES PERFORMED TO SUPPORT WELDED SLEEVE REPAIR Calculation Description Summary Action Request (AR) Non Conformance Report. Determined the probability of 960901028 Assignment 8 Evaluation of a potential damage to any RCS loose part of similar size component, as a result of a and mass. loose part is negligible.
Action Requests (AR) Inspections of an The Alloy 690 half nozzle was 970601575 and AR instrument nozzle repaired removed and the remnant was 030400092 using the proposed half- examined. Negligible to no nozzle method at 5 and 10 wastage was observed.
years following the initial Therefore, Pressurizer shell repair. wastage and release of iron will be negligible.
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