ML061010230
| ML061010230 | |
| Person / Time | |
|---|---|
| Site: | San Onofre  |
| Issue date: | 04/07/2006 |
| From: | Scherer A Southern California Edison Co |
| To: | Document Control Desk, Office of Nuclear Reactor Regulation |
| References | |
| Download: ML061010230 (28) | |
Text
SOUTHERN CALIFORNIA A. Edward Sclerer SE R
[tISNC Manager of EDISON l Nuclear Regulatory Affairs An EDISON INVTERNATIOAAL/
Company April 7, 2006 U.',. Nuclear Regulatory Commission Attn: Document Control Desk Washington, DC 20555-0001
Subject:
Docket No. 50-362 Third Ten-Year Inservice Inspection (ISI) Interval Requests for Alternative Repairs (ISI-3-16, ISI-3-17, ISI-3-19, and ISI-3-20)
San Onofre Nuclear Generating Station, Unit 3
Dear Sir or Madam:
Pursuant to 10 CFR 50.55a(a)(3)(i), Southern California Edison (SCE), San Onofre Nuclear Generating Station (SONGS) Unit 3 is submitting Relief Requests ISI-3-19 and ISI-3-20 for review and approval.
SCE is removing a Mechanical Nozzle Seal Assembly (MNSA) and replacing the existing Pressurizer lower shell temperature nozzle. This replacement is being performed because this temperature nozzle was determined to be leaking during the boric acid inspection at the beginning of the current mid-cycle outage. SCE is also planning to remove two MNSAs and replace those two pressurizer lower levl instrument nozzles as a preemptive measure to avoid future leakage at these locations. Consistent with SCE's plans to mitigate primary water stress corrosion cracking of Alloy 600 material, with the completion of these repairs, all pressurizer heater sleeves and pressurizer instrument nozzles will have been modified with the Alloy 690 half-sleeve repair alternative and all MNSAs will have been removed from both Units 2 and 3.
As with the recent repairs on the Unit 2 pressurizer lower level instrument nozzles, implementation of the repairs on the Unit 3 pressurizer lower level instrument nozzles will be performed as described in Relief Requests ISI-3-16 and ISI-3-17. (See the SCE letter to the NRC dated December 23, 2005;
Subject:
Docket Nos. 50-361 and 50-362, Third Ten-Year Inservice Inspection (ISI1) Interval Relief Requests ISI-3-16, and ISI-3-17 to Support Pressurizer Lower Level Instrument Nozzle Repairs, San Onofre Nuclear Generating Station, Units 2 and 3.) The U. S. Nuclear Regulatory Commission (NRC) authorized approval P.O. Box 128 San Clbmente, CA 92672 949-3fE8-7501
- 4)
U Fax 949-368-7575
Document Control April1 7, 2006 of 1',1-3-16 and ISI-3-17 for Unit 2 under 10 CFR 50.55a(a)(3)(i) via a teleconference on March 23, 2006. SCE requests approval of ISI-3-16 and ISI 17 to support the Unit 3 return to service.
Implementation of the repairs on the Unit 3 pressurizer lower shell temperature nozzle will be performed as described in Enclosure 1 and in compliance with the American Society of Mechanical Engineers Boiler and Pressure Vessel Code and the alternatives proposed in the enclosed relief requests (Enclosures 2 and 3).
Also, of the calculations listed in Enclosure 4, Appendix D of M-DSC-260 is still being prepared and is scheduled to be completed by May 1, 2006.
The proposed alternative repair is similar to repairs performed previously at San Onofre Nuclear Generating Station and other facilities.
SCE requests approval of ISI-3-16, ISI-3-17, ISI-3-19, and ISI-3-20 to support the return to service of SONGS Unit 3 from the mid-cycle outage, which is currently scheduled for May 3, 2006.
Should you have any questions, please contact Mr. Jack Rainsberry at (949) 368-7420.
Sincerely,
Enclosures:
1.
Background and Description of the Proposed Repair
- 2.
Relief Request ISI-3-19
- 3.
Relief Request ISI-3-20
- 4.
Summary of Analyses Performed to Support Welded Repair of Pressurizer Lower Shell Temperature Nozzle cc:
B. S. Malleft, Regional Administrator, NRC Region IV N. Kalyanam, 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, Unit 3 Docket No. 50-362 BACKGROUND AND DESCRIPTION OF THE PROPOSED REPAIR
BACKGROUND AND DESCRIPTION OF THE PROPOSED REPAIR The Pressurizer lower shell temperature nozzle is 1" NPS. The existing temperature nozzle is severed about an inch or so into the bore in the proposed half-nozzle repair. An external weld pad is then applied on the exterior of the lower vessel shell approximately centered on the nozzle opening. The weld pad is applied using the machine gas tungsten arc welding (GTAW) ambient temperature temper bead process.
Next, the weld pad is bored to accept a new Alloy 690 nozzle. The new partial length nozzle is inserted through the pad opening into the vessel nozzle bore and attached to the external weld pad using a partial penetration J-groove weld. The original J-groove weld will no longer function as the pressure boundary nozzle to vessel weld.
A remnant of the original nozzle and its attachment weld located on the vessel's interior surface will remain in place. The original weld and the nozzle remnant have been analyzed for acceptability to remain in place. It is assumed that any flaws present in the original nozzle or attachment weld will remain and not be removed.
Southern California Edison (SCE) will conduct the repairs in accordance with related portions of the American Society of Mechanical Engineers (ASME)
Section Xl, 1995 Edition through 1996 Addenda (as applicable) and Section III, 1971 Edition through Summer 1971 Addenda except as noted and discussed in Relief Request ISI-3-19 (Enclosure 2), and Relief Request ISI-3-20 (Enclosure 3).
Relief Request ISI-3-19 (Enclosure 2), is seeking an alternative to the requirements in ASME Xl, IWA-4600 to perform a portion of the repair with a remotely operated welding machine, utilizing the ambient temperature temper bead method in conjunction with the machine Gas Tungsten Arc Welding (GTAW) process, 501F minimum preheat temperature and no post weld heat treatment, as described in ASME Code Case N-638-1. ASME Code Case N-6313-1 was conditionally approved for use in Regulatory Guide 1.147 "Inservice Inspection Code Case Acceptability, ASME Section Xl, Division 1," Revision 14 (August 2005).
Page 1 of 2
BACKGROUND AND DESCRIPTION OF THE PROPOSED REPAIR Relief Request ISI-3-20 (Enclosure 3) is seeking relief from the 1995 Edition through 1996 Addenda of ASME Code Section Xi, IWA-3300, Flaw Characterization, and IWB-2420, Successive Inspections. With the installation of a rew pressure boundary weld, the function of the original J-groove partial penetration weld is no longer required. Also, SCE believes the alternative described in the proposed relief request 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. Therefore, in lieu of fully characterizing any remaining cracks and performing successive examinations to validate flaw stability, SCE proposes to utilize worst-case assumptions as described in Enclosure 3,Section IV, to conservatively estimate the crack extent and orientation.
The repair technique and ASME Code Relief described above are consistent with the NRC's Safety Evaluation of SONGS Units 2 and 3 Evaluation of Relief for Repair of Pressurizer Sleeves During the Third 10-Year Inservice Inspection (ISI)
Interval (TAC NOS. MC4789 and MC4790) dated March 2, 2005 and 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, Unit 3 Docket No. 50-362 RELIEF REQUEST ISI-3-19
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 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 Vessel Lower Shell Temperature Nozzle: The nozzle is 1" NPS, located on the side of the vessel b) Function:
The Pressurizer Vessel Lower Shell Temperature Nozzle and attachment weld serves as primary pressure boundary.
c) ASME Code Class:
The Pressurizer Vessel Lower Shell Temperature Nozzle is ASME Code Class 1.
d) Category:
Examination Category B-P, All Pressure Retaining Components; Item No. B15.20 applies to the original unmodified and modified Pressurizer Vessel Lower Shell Temperature Nozzle.
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 1II) 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-4410 and IWA-4600 to perform the Pressurizer Vessel Lower Shell Temperature Nozzle repair:
Page 1 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL "Alternatively, the applicable requirements of IWA-4600 may be used for welding..."
In lieu of performing the repair using the alternative welding requirements described in IWA-4600, SCE is proposing to perform a portion of the repair with a remotely operated Gas Tungsten Arc Welding (GTAW) welding machine, utilizing the ambient temperature temper bead method with 500F minimum preheat temperature and no post weld heat treatment (PWHT), as described in ASME Code Case N-638-1. 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) 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 intends to perform the Pressurizer vessel lower shell temperature nozzle repair as follows:
- 1. Mechanical removal of a portion of the existing nozzle.
- 2. Application of a weld pad (or weld buildup) using F-No. 43 filler metal to the lower vessel shell.
- 3. Machining the weld pad to accept the new alloy 690 nozzle (P-No. 43).
- 4. Installing the replacement nozzle 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 ASME Code Case N-638-1. This methodology is proposed only for the weld pad application, Step 2 of the repair process listed above. ASME Code Case N-638-1 was conditionally approved for use in Regulatory Guide 1.147 "Inservice Inspection Code Case Acceptability, ASME Section Xl, Division 1," Revision 14 (August 2005).
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 Xl, or ASME Code Case N-638-1.
Page 2 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL Table 1 Reference Requirement Alternative, Including Reference I
I for Justification ASME Section III Relief NB-3357 All vessels and vessel parts 501F 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 AS)ME Code Case N-638-1. {See IV.2.b
& c below}
NB-4622.1 Except as otherwise stated in 500F minimum preheat the Notes to Table NB-4622.1-temperature and no PWHT 1, all welded components or performed as described in AS'ME pieces of components shall be Code Case N-638-1. {See IV.2.b given a final postweld heat
& c below}
treatment at a temperature not less than specified in Table NB-4622.1-1.
Nole 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 A'SME Code Case N-638-1. {See IV.2.b
& c below)
ASIME Section Xl Relief IWA-4600(b)(1)
When postweld heat treatment ASME Code Case N-638-1 will is not to be performed, the be used in lieu of IWA-4600 for welding methods of IWA-4630 welding. {See IV.2.b & c below}
(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 Preheat and interpass and 5" band shall be preheated temperatures per ASME Code to 300OF minimum; Maximum Case N-638-1; 50°F minimurn interpass temperature of 450°F preheat for procedure shall be used.
qualification and field welding; 150OF maximum interpass temperature to be used for the procedure qualification and 350°F maximum for field welding.
{See IV.2.b and c below}
Page 3 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL Table 1 Reference Requirement Alternative, Including Reference for Justification IWA-4610(a)
Thermocouples and recording A contact pyrometer will be used instruments shall be used for for monitoring preheat and monitoring the welding 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 ASME Code Case N-638-1 required.
requires three temper bead layers. {See IV.2.c below}
IWA-4633.2(d)
After at least 3/16" deposit, the Postheating not used per ASME weld area shall be maintained Code Case N-638-1. {See IV.2.c at 300OF for 4 hours4.62963e-5 days <br />0.00111 hours <br />6.613757e-6 weeks <br />1.522e-6 months <br /> minimum below)
(P-No. 3 materials)
ASME Code Case N-638-1 Relief N-6 38-1 The Code Case requires a Both surface and UT preweld surface examination of examinations will be performed area to be welded.
of the area to be welded and the 5" band surrounding the areai to be welded. {See IV.2.e belovw}
N-638-1 The Code Case requires Surface and UT examinations will postweld surface and be performed on the weld final volumetric (UT) examinations surface. Only a surface of the final weld surface and examination of the 5 inch band the 5 inch band of base metal surrounding the weld will be surrounding the weld repair performed.
area after 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> at ambient
{See IV.2.e below}
temperature.
Page 4 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL 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 Code, Sections Xl and IlIl, while offering substantial savings in accumulated radiation dose. In support of this conclusion, the process is described below, followed by technical justification for the proposed repair process, as well as the expected dose savings.
- 1. Description of the process Figure 1 provides a general overview of the configuration.
a) 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 1 (ANO), and Millstone.
b) The nozzle will be cut close to the vessel exterior surface. A portion of the nozzle inside the vessel bore will then be removed by machining and the area around the nozzle will be prepared for the application of the weld pad by an abrasive disc or flapper wheel and performing a surface examination (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 lower shell using the ambient temperature temper bead weld technique and the machine GTAW process as described in ASME Code Case N-638-1.
The weld pad will be applied as a weld buildup approximately centered on the existing nozzle opening.
d) The weld pad surface will be suitably prepared 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).
Ultrasonic examinations, before and after welding, of the full parent material thickness beneath the weld pad, to the extent practical, are performed to detect laminar type indications in the examination boundary. Laminar type indications observed will be recorded and evaluated to assure the structural integrity of the modification configuration is not adversely affected.
Page 5 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL SCE will follow the NRC's condition of approval of ASME Code Case N-638-1 as described in Regulatory Guide 1.147.
UUT examinations shall be demonstrated for the repaired volume using representative samples which contain construction type flaws. The acceptance criteria of NB-5330 of Section III edition and addenda approved in 10 CFR 50.55a apply to all flaws identified within the repaired volume."
e) The approximate center of the weld pad will be machined to re-establish a free path into the nozzle bore of the vessel. A J-groove partial penetration weld preparation will be machined into the weld pad for the attachment weld of the new nozzle.
f) The new nozzle will be inserted and welded in using conventional welding and NDE techniques (manual GTAW and progressive PT).
Note that this weld is in full compliance with the construction code (ASME l1l) and therefore requires no relief from the existing code requirements.
- 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 recognizes the importance of ALARA principles and this remote repair method is being proposed for the repair of the Pressurizer vessel lower shell temperature nozzle at SONGS.
This approach for the repair of Pressurizer lower shell temperature nozzle will reduce radiation dose to repair personnel while still maintaining acceptable levels of quality and safety. SCE estimates the dose accumulated in Unit 3 for installing heating pads, performing the preheating and postheating, removing heating pads, and performing NDE of the heating pad locations required by the existing code rules would be approximately 1 REM.
Page 6 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL 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) all have qualified welding procedures for this specific application that comply with the ASME Code Case N-638-1 requirements.
These ASME Code Case N-638-1 qualifications were performed at room temperature on P-No. 3 Group No. 3 base materials with UNS N06052 and/or UNS N06054 weld filler materials and similar low heat input controls that will be used for the proposed repair application.
These qualifications did not include postheating after welding. 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, Owner's Requirements and ASME Code Case N-638-1 requirements. Additionally, SCE will require either a mock-up demonstration or documentation that a representative mock-up demonstration has been previously performed.
c) Weld Quality The proposed alternative repair technique has been demonstrated as an acceptable method for performing small bore vessel nozzle repairs.
The ASME Code Committee per ASME Code Case N-638-1 has approved the ambient temperature temper bead technique. 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 (SONGS Unit 3, Three Mile Island, Crystal River Unit 3, Millstone, St. Lucie, ANO, South Texas Project, and others). ASME Code Case N-638-1 was conditionally approved by the NRC (Regulatory Guide 1.147, Revision 14). This approval indicates that the methodology is capable of producing quality field welded repairs.
Page 7 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL Research documented in EPRI Report GC-1 11050 shows that carefully controlled heat input and bead placement allows subsequent welding passes to relieve stress and temper the base metal heat affected zone (HAZ). 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. Precision control over these variables is an inherent feature of the machine GTAW process and 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 treatments are used to mitigate the effects of atomic hydrogen absorption 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 a nonconsumable tungsten electrode and bare wire filler metal with no flux to trap moisture. An inert gas blanket provides shielding for the weld and surrounding metal. During welding, this shielding protects the region from the atmosphere and any moisture it may contain and typically produces porosity free welds.
Welding grade argon is typically the gas used for the inert gas shielding. To further reduce the likelihood of any hydrogen evolution or absorption, specific controls will be used to ensure the welding electrode, filler metal, and weld region are free of all sources of hydrogen. Shielding gas flow rates are adjusted to assure adequate shielding of the weld without creating a venturi affect that could draw oxygen or water vapor from the ambient atmosphere into the weld.
d) Preheat and Interpass Temperature Measurement Due to the location of the repair and area radiation dose rate, the placement of welded thermocouples for monitoring weld interpass temperature is determined to be not beneficial based on dose savings.
Therefore, welded 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 at each repair location. On the first repair location, the interpass temperature measurements will be taken every three to five passes.
Page 8 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL At subsequent repair locations, interpass temperature measurements will be taken every six to ten passes. The heat input from layers beyond the third layer will not have a metallurgical affect on the low alloy steel HAZ.
e) Examination All NDE will be performed in accordance with ASME Code Section 1II, 1995 Edition through 1996 Addenda, NB-2500 (for base materials) and NB-5000 (for welds).
The area to be welded, plus a 5-inch surrounding band, will be surface examined (PT or MT) and volumetrically examined (UT) prior to welding. All post weld NDE 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 finished surface of the welded pad and a 5" band surrounding the pad will be surface examined (MT or PT) and the weld pad will be examined volumetrically (UT). 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 detect laminar type indications in the examination boundary. 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 vessel base metal in the area surrounding the weld. Since this weld is applied to the exterior surface of the vessel, there is no useful additional information that can be gained by a volumetric examination of the base metal 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.
Page 9 of 12
INSERVICE INSPECTION RELIEF REQUEST ISI-3-19 THIRD TEN YEAR INTERVAL f) Corrosion The 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 nozzle bore] exposed to the primary coolant. The effect of corrosion on the exposed area, including reduction in vessel wall thickness, has been evaluated (see Enclosure 4). 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.
h) Stresses Design stress analysis of the modified Pressurizer lower shell temperature nozzle weld attachment was performed (see Enclosure 4).
The stress analysis demonstrates that the modified instrument nozzle 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 Vessel.
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 ASME Code Case N-638-1 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 for the repairs to the Pressurizer lower shell temperature nozzle. 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-3-19 THIRD TEN YEAR INTERVAL VII.
Precedents:
Letter from Robert A Gramm (NRC) to Harold B. Ray (SCE) dated March 2, 2005;
Subject:
SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 AND 3 - EVALUATION OF RELIEF FOR REPAIR OF PRESSURIZER SLEEVES DURING THE THIRD 10-YEAR INSERVICE INSPECTION (ISI)
INTERVAL (TAC NOS. MC4789 AND MC4790)
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-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-3-19 THIRD TEN YEAR INTERVAL Figure 1 I'-ORIGINAL J-GROOVE WELD CLAD
/
EXISTING REINFORCItNG PAD (ORIGINAL FOUIPMtENT VANUFACTURE)
PRESSURIZER WALL SA-533 GR.E CL.1 EXISTING ALLOY 600 NOZZLE Typical Half Nozzle Repair Page 12 of 12
Southern California Edison San Onofre Nuclear Generating Station, Unit 3 Docket No. 50-362 RELIEF REQUEST ISI-3-20
INSERVICE INSPECTION RELIEF REQUEST ISI-3-20 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 I.
System/Component(s) for Which Relief is Requested:
- a. Name of component:
Pressurizer Vessel Lower Shell Temperature Nozzle: The nozzle is 1" NPS, located on the side of the vessel.
- b. Function:
The Pressurizer Vessel Lower Shell Temperature Nozzle and attachment weld serves as primary pressure boundary.
- c. ASME Code Class:
The Pressurizer Vessel Lower Shell Temperature Nozzle is ASME Code Class 1.
- d. Category:
Examination Category B-P, All Pressure Retaining Components; Item No. B15.20 applies to the original unmodified and modified Pressurizer Vessel Lower Shell Temperature Nozzle.
- 11.
Current Code Requirement and Relief Request:
IWA-461 1.1 requires in part that, "Defects shall be removed or reduced in size in accordance with this Paragraph." Furthermore, IWA-4611.1 allows that "...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 that flaws detected by inservice examination have their dimensions determined and be characterized.
SCE is requesting relief from ASME Section Xi, IWA-3300. It is assumed that any flaws present in the original Pressurizer lower shell temperature nozzle or J-groove attachment weld will not be removed.
In lieu of sizing or 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.
Page 1 of 6
INSERVICE INSPECTION RELIEF REQUEST ISI-3-20 THIRD TEN YEAR INTERVAL IWB-2420 requires existing flaws be reexamined and reevaluated in accordance with IWB-3132.3 or IWB-3142.4 in successive inspection intervals.
SCE is requesting that no additional inspections be performed to monitor the flaw stability because initial flaw sizing and characterization is not being performed so the actual dimensions of the flaw will not be determined. In lieu of 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.
Ill.
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 proposed repair of the Pressurizer lower shell temperature nozzle does not include removal of any flaws assumed to be present in the remaining remnant of the original nozzle or its J-groove partial penetration attachment weld. Therefore, per the requirements of IWA-4611.1, the cracks must be evaluated using the appropriate flaw evaluation rules of Section Xl. Also, no additional examinations are planned to characterize the cracks so the actual dimensions of a flaw will not be determined. If a flaw is not 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 characterizing the existing cracks, SCE will utilize worst-case assumptions to conservatively estimate the crack extent and orientation. The postulated crack extent and orientation will then be evaluated using the rules of IWB-3600.
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INSERVICE INSPECTION RELIEF REQUEST ISI-3-20 THIRD TEN YEAR INTERVAL IV.
Basis for Relief:
SCE proposes to perform the Pressurizer lower shell temperature nozzle repairs as follows:
- 1. Mechanical removal of a portion of the existing nozzle.
- 2. Application of a weld pad (or weld buildup) using F-No. 43 filler metal to the vessel lower shell.
- 3. Machining the weld pad to accept the new alloy 690 nozzle (P-No. 43).
- 4. Installing the replacement nozzle using conventional manual gas tungsten arc welding (GTAW) and a J-groove partial penetration weld.
The existing nozzle and its weld will no longer function as the pressure boundary. However, the possible existence of cracks in the nozzle or weld 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 proposed repair design dictates that the original nozzle remnant and its attachment weld be left intact inside the vessel.
The assumptions of IWB-3500 are that the cracks are fully characterized in order 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 instrument nozzle, penetrate the nozzle wall, continue through to the intersection of the vessel inner diameter surface and the vessel nozzle bore by primary water stress corrosion cracking (PWSCC). Further crack propagation into the vessel wall low alloy steel could then occur by fatigue. 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 and nozzle material.
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INSERVICE INSPECTION RELIEF REQUEST ISI-3-20 THIRD TEN YEAR INTERVAL A fracture mechanics evaluation has been performed (see Enclosure 4) in accordance with ASME Section XI evaluation procedures of IWB-3600 and 3700. The evaluation concludes that 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 nozzle. It is postulated that a radial crack in the Alloy 182 weld metal would propagate by Primary Water Stress Corrosion Cracking (PWSCC) through the 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 continue to extend into the low alloy steel material due to cyclic loading. 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 into for unirradiated ferritic materials. The results of the analyses indicate that it is acceptable to leave the original Alloy 600 instrument nozzle remnant 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 Page 4 of 6
INSERVICE INSPECTION RELIEF REQUEST ISI-3-20 THIRD TEN YEAR INTERVAL reactor vessel and concluded that the probability of damage to any RCS component is not significant (reference Action Request (AR) 960901028, assignment 8). In the unlikely event that a small part of the lower shell temperature nozzle 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 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 pressure boundary remains capable of performing is design function with flaws existing in the original J-groove weld. See Enclosure 4 for a summary of the supporting analyses.
V.
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 function of the original 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.
VI.
Implementation Schedule:
This relief request is being implemented during the Third Inservice Inspection Interval and it is only applicable to the repairs of the Pressurizer lower shell temperature nozzle. SONGS third ten-year Inservice Inspection Interval began on August 18, 2003 and is scheduled to end on August 17, 2013.
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INSERVICE INSPECTION RELIEF REQUEST ISI-3-20 THIRD TEN YEAR INTERVAL VII.
Precedents:
Letter from Robert A Gramm (NRC) to Harold B. Ray (SCE) dated March 2,2005;
Subject:
SAN ONOFRE NUCLEAR GENERATING STATION, UNITS 2 AND 3-EVALUATION OF RELIEF FOR REPAIR OF PRESSURIZER SLEEVES DURING THE THIRD 10-YEAR INSERVICE INSPECTION (ISI) INTERVAL (TAC NOS. MC4789 AND MC4790)
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 2 -
SAFETY EVALUATION OF RELIEF REQUESTS 03-001-RR AND 03-0002-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, Unit 3 Docket No. 50-362
SUMMARY
OF ANALYSES PERFORMED TO SUPPORT WELDED REPAIR OF PRESSURIZER LOWER SHELL TEMPERATURE NOZZLE RELIEF REQUEST ISI-3-19 and RELIEF REQUEST ISI-3-20
SUMMARY
OF ANALYSES PERFORMED TO SLEEVE REPAIR SUPPORT WELDED Calculation Description Summary M-DSC-260 Rev. I Half-Nozzle repair for Analyzed the repairs to the Pressurizer lower shell requirements of ASME Section 1I1.
Appendix D - Pressurizer temperature nozzle. ASME This analysis concluded that the Instrumentation nozzle Section III Code evaluation.
stresses and fatigue meet the Evaluation requirements of the Code and that repair life is forty years from time of installation.
M-DSC-414 Rev. 0 Half-Nozzle repair fracture This analysis determined the impact mechanics and fatigue of an assumed flaw in the existing J Pressurizer Lower Level crack growth evaluation for groove weld on low alloy steel base and Thermowell Nozzles J-Pressurizer lower shell material. The analysis concluded Weld Fracture Mechanics temperature nozzle.
that a postulated axial crack Evaluation 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.The original weld residual stresses were included in the analysis.
M-D)SC-412 Rev. 0 Calculation of the residual The effect of residual stresses due welding and transient to welding in the existing Pressurizer Thermowell stresses in the original J-pressurizer lower shell temperature Nozzle Welding and weld.
nozzle J-weld were calculated.
Transient Analysis.
M-E)SC-360 Rev. 0 Half-Nozzle repair borated This analysis evaluated the long-water corrosion evaluation term impact of the newly exposed Evaluation of Half-Nozzle for Pressurizer lower shell low alloy steel base metal (resulting Repair for PZR and SG Inst.
temperature nozzle.
from the repair) to reactor coolant.
Nozzles Under Long-Term This analysis concluded that the Senrice Conditions - SONGS 2 corrosion rate is negligible and the and 3 corrosion depths after 40 years are less than the allowable corrosion depths.
Action Request (AR)
Non Conformance Report.
Determined the probability of 960901028 Assignment 8 Evaluation of a potential damage to any RCS-compcnent as loose part of similar size a result of a loose part is negligible.
and mass.
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SUMMARY
OF ANALYSES PERFORMED TO SUPPORT WELDED SLEEVE REPAIR Calculation Description Summary Adcion 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. Therefore, years following the initial Pressurizer shell wastage 2ind repair.
release of iron will be negligible.
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