L-10-099, 10 CFR 50.55a Request for Alternate Repair Methods for Reactor Pressure Vessel Head Penetration Nozzles

10 CFR 50.55a Request for Alternate Repair Methods for Reactor Pressure Vessel Head Penetration Nozzles

ML100960276
Person / Time
Site:	Davis Besse
Issue date:	04/01/2010
From:	Allen B FirstEnergy Nuclear Operating Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
L-10-099
Download: ML100960276 (23)

Text

FENOC  % 5501 North State Route 2 FirstEnergyNuclear Operating Company Oak Harbor, Ohio 43449 Barry S. Allen 419-321-7676 Vice President - Nuclear Fax: 419-321-7582 April 1, 2010 L-10-099 10 CFR 50.55a ATTN: Document Control Desk U. S. Nuclear Regulatory Commission Washington, DC 20555-0001

SUBJECT:

Davis-Besse Nuclear Power Station Docket No. 50-346, License No. NPF-3 10 CFR 50.55a Request for Alternate Repair Methods for Reactor Pressure Vessel Head Penetration Nozzles In accordance with 10 CFR 50.55a, FirstEnergy Nuclear Operating Company (FENOC) is requesting Nuclear Regulatory Commission (NRC) approval of proposed alternatives to certain requirements associated with reactor pressure vessel head penetration nozzle repairs at the Davis-Besse Nuclear Power Station. The enclosure identifies the affected components, applicable American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) requirements, reason for the request, proposed alternative, and basis for the proposed alternative. The alternatives are proposed for use during the remainder of the current Davis-Besse Nuclear Power Station 10-year inservice inspection interval, which ends September 20, 2012.

During the current Davis-Besse Nuclear Power Station sixteenth refueling outage that began on February 28, 2010, reactor pressure vessel head penetration nozzle inspections and bare metal inspections were performed. Examination results at certain reactor pressure vessel head penetration nozzles did not meet the applicable acceptance criteria, and therefore these penetration nozzles require repair. The proposed alternatives are to be implemented during the ongoing maintenance and refueling outage. Therefore, FENOC is requesting expedited NRC review and approval of the proposed alternative.

/QO(!

Davis-Besse Nuclear Power Station L-10-099 Page 2 There are no regulatory commitments contained in this letter. If there are any questions or if additional information is required, please contact Mr. Thomas A. Lentz, Manager -

Fleet Licensing, at 330-761-6071.

Sincerely, Barry S. Allen

Enclosure:

10 CFR 50.55a Request Number RR-A34 cc: NRC Region III Administrator NRC Resident Inspector NRC Project Manager Utility Radiological Safety Board

FOR INTERNAL DISTRIBUTION USE ONLY Internal Distribution of Letter L-10-099 K. A. McMullen B. S. Spiesman P. H. Lashley T. A. Lentz G. H. Halnon G. M. Wolf D. R. Wuokko C. A. Price J. P. Hartigan D. B. Patten C. T. Daft J. D. Kemp A. P. Wise K. W. Byrd V. A. Kaminskas C. I. Custer B. S. Allen D. R,. Wahlers J. H. Lash D. W. Jenkins T. A. StClair W. Mugge Central File

Davis-Besse Nuclear Power Station 10 CFR 50.55a Request Number RR-A34 Page 1 of 20 Proposed Alternative in Accordance With 10 CFR 50.55a(a)(3)(i) 1.0 ASME CODE COMPONENTS AFFECTED Components: Reactor Pressure Vessel (RPV) Head Control Rod Drive Mechanism Penetration Nozzles 1 through 69 Code Class: Class 1 Examination Category: B-P Code Item Number: B4.20 (Code Case N-729-1)

==

Description:==

Control Rod Drive Mechanism Housing Size: 4 Inch Nominal Outside Diameter Material: Inconel SB-167 2.0 APPLICABLE CODE EDITION AND ADDENDA Davis-Besse Nuclear Power Station American Society of Mechanical Engineers In-Service Inspection and Boiler and Pressure Vessel Code Repair/Replacement Programs: (ASME Code) Section Xl, 1995 Edition through 1996 Addenda Davis-Besse Nuclear Power Station ASME Code Section III, 1968 Edition, RPV Head Code of Construction: Summer 1968 Addenda 3.0 APPLICABLE CODE REQUIREMENTS The 1995 Edition/96 Addenda of ASME Code Section Xl, subparagraph IWA-4221(a) states:

An item to be used for repair/replacement activities shall meet the Owner's Requirements and the applicable Construction Code to which the original item was constructed, except as provided in IWA-4221 (b) and (c).

The 1995 Edition/96 Addenda of ASME Code Section XI, subparagraph IWA-4221(b) states, in part:

The item may meet all or portions of the requirements of different Editions and Addenda of the Construction Code, or Section III when the Construction Code was not Section III, provided the requirements of IWA-4222 through IWA-4226, as applicable, are met.

10 CFR 50.55a Request Number RR-A34 Page 2 of 20 The 1995 Edition/96 Addenda of ASME Code Section Xl, subarticle IWA-4400 provides welding, brazing, metal removal, and installation requirements related to repair and replacement activities.

The 1995 Edition/96 Addenda of ASME Code Section Xl, subparagraph IWA-4410(a) states:

Repair/replacement activities shall be performed in accordance with the Owner's Requirements and the original Construction Code of the component or system, except as provided in IWA-4410(b), (c), and (d).

The 1995 Edition/96 Addenda of ASME Code Section Xl, subparagraph IWA-4410(b) states, in part:

Later Editions and Addenda of the Construction Code or a later different Construction Code, either in its entirety or portions thereof, and Code Cases may be used, provided the substitution is as listed in IWA-4221(b).

The 1995 Edition/96 Addenda of ASME Code Section Xl, subparagraph IWA-4610(a) states, in part:

Thermocouples and recording instruments shall be used to monitor the process temperatures.

Code Case N-638-1, Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique, provides requirements for automatic or machine Gas Tungsten Arc Welding (GTAW) of Class 1 components without the use of preheat or postweld heat treatment.

Code Case N-638-1, paragraph 3.0(d) states:

The maximum interpass temperature for field applications shall be 350OF regardless of the interpass temperature during qualification.

Code Case N-638-1, paragraph 4.0(b) states, in part:

The final weld surface and the band around the area defined in para. 1.0(d) shall be examined using a surface and ultrasonic methods when the completed weld has been at ambient temperature for at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />. The ultrasonic examination shall be in accordance with Appendix I.

Code Case N-729-1, Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds, Figure 2 provides the examination volume for nozzle base metal and examination area for weld and nozzle base metal.

10 CFR 50.55a Request Number RR-A34 Page 3 of 20 The 1995 Edition/1996 Addenda of ASME Code Section Xl, subparagraph IWA-4611.1(a) states, in part:

Defects shall be removed or reduced in size in accordance with this Paragraph.

... the defect removal area and any remaining portion of the flaw may be evaluated and the component accepted in accordance with the appropriate flaw evaluation provisions of Section Xl or the design provisions of the Owner's Requirements and either the Construction Code or Section I11.

The 1995 Edition/1996 Addenda of ASME Code Section Xl, subarticle IWA-3300 requires characterization of flaws detected by inservice examination.

The 1995 Edition/1996 Addenda of ASME Code Section Xl, subarticle IWB-3420 states:

Each detected flaw or group of flaws shall be characterized by the rules of IWA-3300 to establish the dimensions of the flaws. These dimensions shall be used in conjunction with the acceptance standards of IWB-3500.

The 1995 Edition/1996 Addenda of ASME Code Section Xl, subparagraph IWB-3142.4 states:

A component containing relevant conditions is acceptable for continued service if an analytical evaluation demonstrates the component's acceptability. The evaluation analysis and evaluation acceptance criteria shall be specified by the Owner. A component accepted for continued service based on analytical evaluation shall be subsequently examined in accordance with IWB-2420(b) and (c).

The 1992 Edition of ASME Code Section III subparagraph NB-5330(b) states:

Indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.

4.0 REASON FOR REQUEST Flaw indications requiring repair have been detected in the Davis-Besse RPV head penetration nozzle base material.

Because of the risk of damage to the RPV head material properties or dimensions, it is not feasible to apply the post welding heat treatment requirements of the original Construction Code. As an alternative to the requirements of the RPV head Code of Construction, FirstEnergy Nuclear Operating Company (FENOC) proposes to perform the repair of the RPV head penetration nozzle utilizing the inside diameter temper bead (IDTB) welding method to restore the pressure boundary of the degraded nozzle. The IDTB welding method is performed with a remotely operated weld tool, utilizing the machine Gas Tungsten-Arc Welding (GTAW) process and the ambient temperature bead method with 50 degrees Fahrenheit minimum preheat and no post weld heat treatment. The repairs will be conducted in accordance with the 1995 Edition through the 1996 Addenda of ASME Code Section Xl, Code Case N-638-1, Code Case N-729-1, and the alternative requirements discussed below.

10 CFR 50.55a Request Number RR-A34 Page 4 of 20 Basic steps for the IDTB repair are:

1. Roll expansion above the area of repair. This stabilizes the nozzle to prevent any movement when the nozzle is separated from the RPV head J-groove weld.

2. Machining to remove portions of the nozzle above the J-groove weld containing unacceptable indications. This machining operation also establishes the weld preparation area. (As shown in Figure 1.)

3. Liquid penetrant (PT) examination of the machined area. (As shown in Figure 3.)

4. Weld the remaining portion of the nozzle to the RPV head using primary water stress corrosion cracking (PWSCC) resistant Alloy 52M weld material. (As shown in Figure 2.)

5. Machining the weld/nozzle to provide a surface suitable for nondestructive examination (NDE).

6. PT and ultrasonic (UT) examination of the weld and adjacent area. (As shown in Figure 3.)

7. Abrasive water jet machining remediation on the portion of the remaining nozzle most susceptible to PWSCC. The abrasive water jet machining process removes a small amount of material thickness while imposing compressive residual stress on the nozzle surface.

FENOC has determined that repair of the RPV head penetration nozzle utilizing the requirements specified in this request will provide an acceptable level of quality and safety. The proposed alternative is requested in accordance with 10 CFR 50.55a (a)(3)(i).

5.0 PROPOSED ALTERNATIVE AND BASIS FOR USE Monitoring of Interpass Temperature Code Case N-638-1, paragraph 3.0(d) states:

The maximum interpass temperature for field applications shall be 350°F regardless of the interpass temperature during qualification, Code Case N-638-1 states that all other requirements of IWA-4000 must be met. IWA-4610(a) requires that thermocouples and recording instruments be used to monitor process temperatures. Direct interpass temperature measurement inside the nozzle bore is impractical during welding operations due to the physical configuration of the nozzle. As an alternative, the maximum interpass temperature will be determined by one of the following methods:

(1) heat-flow calculations, using at least the variables listed below (a) welding heat input (b) initial base material temperature (c) configuration, thickness, and mass of the item being welded

10 CFR 50.55a Request Number RR-A34 Page 5 of 20 (d) thermal conductivity and diffusivity of the materials being welded (e) arc time per weld pass and delay time between each pass (f) arc time to complete the weld (2) measurement of the maximum interpass temperature on a test coupon that is no thicker than the item to be welded. The maximum heat input of the welding procedure shall be used in welding the test coupon.

This alternative method of determining the maximum interpass temperature is consistent with the associated requirements specified in Code Case N-638-2 and subsequent versions. The use of these criteria for interpass temperature monitoring was previously approved in Davis-Besse 10 CFR 50.55a Request RR-A33 (Accession No. MIL100080573).

Acceptance Examination Area Code Case N-638-1 paragraph 4.0(b) states, in part:

The final weld surface and the band around the area defined in para. 1.0(d) shall be examined using a surface and ultrasonic methods...

Code Case N-638-1 paragraph 1.0(d) defines the area requiring examination as the area to be welded and the band around the area of at least 1.5 times the component thickness or 5 inches, whichever is less.

The band includes an annular area extending five inches around the penetration bore on the inside surface of the RPV head. The purpose for the examination of the band is to ensure all flaws associated with the weld repair area have been removed or addressed since these flaws may be associated with the original flaw and may have been overlooked. In this case, the repair welding is performed remote from the known flaw(s).

The band around the area defined in paragraph 1.0(d) cannot be examined due to the physical configuration of the partial penetration weld. The alternative final examination of the new weld and immediate surrounding area within the bore will be sufficient to verify that defects have not been induced in the low alloy steel RPV head material due to the welding process and will assure integrity of the nozzle and the new weld. Figure 3 identifies the alternative areas for PT and UT examination of the modified RPV head penetration. The UT examination is qualified to detect construction type flaws in the new weld and base metal interface beneath the new weld. Acceptance criteria for the UT examination will be in accordance with ASME Section III, NB-5330. The extent of the examination is consistent with Construction Code requirements.

Scanning is performed from the inner diameter surface of the new weld and the adjacent portion of the nozzle bore, excluding the transition taper portion at the bottom of the weld. The volume of interest for the UT examination extends from at least one-inch above the new weld and into the RPV head low alloy steel base material beneath

10 CFR 50.55a Request Number RR-A34 Page 6 of 20 the weld, to at least one-quarter inch depth. The PT examination area includes the weld surface and extends upward on the nozzle inside surface to include the area required for inservice inspection and at least one-half inch below the new weld. Figure 3 identifies the alternative area for PT examination of the modified RPV head penetration nozzle after machining and before welding.

Code Case N-638-1, Paragraph 4.0(b) requires that the specified volumetric examination be in accordance with Section Xl, Appendix I. Paragraph 4.0(e) specifies volumetric examination acceptance criteria in accordance with Paragraph IWB-3000.

Paragraph IWB-3000 does not have any acceptance criteria that directly apply to the partial penetration weld configuration. Regulatory Guide 1.147, Revision 15 has conditionally approved Case N-638-1 with the condition that UT volumetric examinations be performed with personnel and procedures qualified for the repaired volume and qualified by demonstration using representative samples containing construction type flaws. As an alternative, the acceptance criteria, of NB-5330 in the 1998 Edition through 2000 Addenda,Section III, will apply to all flaws identified within the repaired volume. Code Case N-416-3 will be used to satisfy pressure testing requirements subsequent to the repair. This Code Case specifies that the NDE and acceptance criteria shall be in accordance with the 1992 Edition of ASME Code Section II1. Code Case N-416-3 is identified as acceptable to the NRC for application in licensees' Section Xl inservice inspection programs, in NRC Regulatory Guide 1.147, Revision 15.

Both versions of Section III, Paragraph NB-5245 require incremental and final surface examination of partial penetration welds. Due to the welding layer disposition sequence (each layer is deposited parallel to the penetration centerline), the specific requirements of Paragraph NB-5245 cannot be met. The Construction Code requirement for progressive surface examination in lieu of volumetric examination is because volumetric examination is not practical for conventional partial penetration weld configurations.

As an alternative to progressive surface examination, post-weld PT and UT examination coverage will be as shown in Figure 3. In this case the repair weld is suitable, except for the taper transition, for ultrasonic examination and a final surface examination can be performed. Final examination of the repair weld and the immediate surrounding area will be sufficient to verify that defects have not been induced in the ferritic low alloy reactor vessel head material due to the welding process. The UT is qualified to detect flaws in the new weld and base metal interface in the repair region, to the maximum practical extent.

The UT examination transducers and delivery tooling are capable of scanning from cylindrical surfaces with inside diameters near 2.75 inches. The UT equipment is not capable of scanning from the face of the transition taper portion at the bottom of the weld. Scanning of the area of interest is performed using 00 L-wave, 450 L-wave, and 700 L-wave transducers. Approximately 70 percent of the weld surface will be scanned by UT examination. Approximately 83 percent of the RPV head ferritic steel heat

10 CFR 50.55a Request Number RR-A34 Page 7 of 20 affected zone will be covered by UT examination. The UT examination coverage volumes for the various scans are shown in Figures 4 through 8.

As an alternative, examination of the area depicted in Figure 3 will ensure that all unacceptable flaws associated with the weld repair area have been removed.

48-Hour Hold Code Case N-638-1 paragraph 4.0(b) states, in part:

The final weld surface and the band around the area defined in para. 1.0(d) shall be examined using a surface and ultrasonic methods when the completed weld has been at ambient temperature for at least 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br />.

Hydrogen cracking is a form of cold cracking. It is produced by the action of internal tensile stresses acting on low toughness heat affected zones. The internal stresses are produced from localized build-ups of monatomic hydrogen. Monatomic hydrogen forms when moisture or hydrocarbons interact with the welding arc and molten weld pool. The monatomic hydrogen can be entrapped during weld solidification and tends to migrate to transformation boundaries or other microstructure defect locations. As concentrations build, the monatomic hydrogen recombines to form molecular hydrogen

- thus generating localized internal stresses at these internal defect locations. If these stresses exceed the fracture toughness of the material, hydrogen induced cracking occurs. This form of cracking requires the presence of hydrogen and low toughness materials. It is manifested by intergranular cracking of susceptible materials and typically occurs within 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> of welding.

The machine gas tungsten arc welding process is inherently free of hydrogen. Unlike the shielded metal arc welding process, gas tungsten arc welding filler metals do not rely on flux coverings that may be susceptible to moisture absorption from the environment. Conversely, the gas tungsten arc welding process utilizes dry inert shielding gases that cover the molten weld pool from oxidizing atmospheres. Any moisture on the surface of the component being welded is vaporized ahead of the welding torch. The vapor is prevented from being mixed with the molten weld pool by the inert shielding gas that blows the vapor away before it can be mixed. Furthermore, modern filler metal manufacturers produce weld wires having very low residual hydrogen. This is important because filler metals and base materials are the most realistic sources of hydrogen for the automatic or machine gas tungsten arc welding temper bead process. Therefore, the potential for hydrogen-induced cracking is greatly reduced by using the machine gas tungsten arc welding process. Extensive research has been performed by the Electric Power Research Institute (EPRI). EPRI Report 1013558, "48-Hour Hold Requirements for Ambient Temperature Temperbead Welding" (Accession No. ML070670060) provides justification for starting the 48-hour hold after completing the third temper bead weld layer rather than waiting for the weld overlay to cool to ambient temperature.

10 CFR 50.55a Request Number RR-A34 Page 8 of 20 As an alternative to commencing the 48-hour hold period when the weld reaches ambient temperature, FENOC will commence the 48-hour hold period upon completion of the third weld layer. This approach has been previously reviewed and approved by the NRC for dissimilar metalweld overlays in Davis-Besse 10 CFR 50.55a Request RR-A33 (Accession No. ML100080573).

Triple Point Anomaly The 1992 Edition of ASME Code Section III subparagraph NB-5330(b) states:

Indications characterized as cracks, lack of fusion, or incomplete penetration are unacceptable regardless of length.

An artifact of the ambient temperature temper bead repair weld is an anomaly in the weld at the triple point. The triple point is the point in the repair weld where the low alloy steel RPV head, the Alloy 600 nozzle and the first Alloy 52M weld bead intersect. The location of the triple point anomaly is shown in Figure 2. This anomaly consists of an irregularly shaped very small void. Mock-up testing has verified that the anomalies are common and do not exceed 0.10 inch in length and are assumed to exist around the entire bore (360 degrees), at the triple point elevation, for purposes of analysis. The proposed alternative permits anomalies at the triple point area to remain in service.

A fracture mechanics analysis is performed to provide justification, in accordance with Section Xl, for operating with the postulated triple point anomaly. The anomaly is modeled as a 0.10 inch, circular, crack-like defect, extending 360 degrees around the circumference at the triple point location. Postulated flaws could be oriented within the anomaly such that there are two possible flaw propagation paths, as discussed below.

Path 1:

Flaw propagation path 1 that traverses the nozzle wall thickness from the nozzle outside diameter (OD) to inside diameter (ID). This is the shortest path through the component wall; passing through the new Alloy 52M weld material. However, Alloy 600 nozzle material properties or equivalent are used to ensure that another potential path through the heat affected zone between the new repair weld and the Alloy 600 nozzle material is bounded.

For completeness, two types of flaws are postulated at the outside surface of the nozzle. A 360 degree continuous circumferential flaw, lying in a horizontal plane, is considered to be a conservative representation of crack-like defects that may exist in the weld anomaly. This flaw is subjected to axial stresses in the nozzle. An axially oriented semi-circular outside surface flaw is also considered, since it would lie in a plane normal to the higher circumferential stresses. Both of these flaws would propagate toward the inside surface of the nozzle.

10 CFR 50.55a Request Number RR-A34 Page 9 of 20 Path 2:

Flaw propagation path 2 extends down the outside surface of the repair weld between the weld and the RPV head. A cylindrically oriented flaw is postulated to lie along this interface, subjected to radial stresses with respect to the nozzle. This flaw may propagate through either the new Alloy 52M weld material or the low alloy steel RPV head material.

The results of the analysis demonstrate that a 0.10 inch weld anomaly is acceptable for greater than a four year design life for the new configuration. Significant fracture toughness margins are obtained for both of the flaw propagation paths considered in this analysis. The minimum calculated fracture toughness margins are significantly greater than the required margin of '110 per Paragraph IWB-3612 of Section Xl. Fatigue crack growth is minimal. The maximum final flaw size is significantly less than allowed for both flaw propagation paths. A limit load analysis is also performed considering the ductile Alloy 600 and Alloy 52M materials along flaw propagation path 1. The analysis shows limit load margins for normal/upset conditions and emergency/faulted conditions, that are significantly greater than the ASME Code Section Xl, Paragraph IWB-3642 required margins of 3.0 and 1.5, respectively.

This analysis is prepared in accordance with Section Xl and demonstrates that for the intended service life of the repair, the fatigue crack growth is acceptable and the crack-like indications remain stable. This satisfies the Section Xl criteria but does not include consideration of stress corrosion cracking such as primary water stress corrosion cracking (PWSCC). Since the crack-like defects are not exposed to the primary coolant and the air environment is benign for the materials at the triple point, the time-dependent crack growth rates from PWSCC are not applicable.

Inservice Inspections Code Case N-729-1 provides requirements for the inservice inspection of reactor vessel upper heads with nozzles having partial penetration welds. Code Case N-729-1 Table 1, Item B4.20, permits either volumetric or surface examination. Preservice and future inservice examinations of the repaired nozzle will be by the surface examination method.

Item B4.20 examination requirements are specified in Figure 2 of Code Case N-729-1.

The repair proposed by this 10 CFR 50.55a request removes the examination area depicted in this figure. As an alternative, Figure 9 of this 10 CFR 50.55a request will be used to establish the examination area for the preservice inspection following repair and for future inservice inspections. This examination area is equivalent to that required by Figure 2 of Code Case N-729-1 as it includes examination of the nozzle weld and an area above the nozzle weld that is equivalent to the area above the nozzle weld shown in Figure 2 of the Code Case.

10 CFR 50.55a Request Number RR-A34 Page 10 of 20 Conclusions Implementation of an IDTB repair to the RPV head penetration nozzle will produce an effective repair that will restore and maintain the pressure boundary integrity of the Davis-Besse RPV head. Similar repairs have been performed successfully at other plants and have been in service for several years without any identified degradation.

The alternative provides improved structural integrity and reduced likelihood of leakage from the primary system. Accordingly, the use of the alternative provides an acceptable level of quality and safety in accordance with 10 CFR 50.55a(a)(3)(i).

6.0 DURATION OF THE PROPOSED ALTERNATIVE The provisions of this alternative are applicable to the third ten-year in-service inspection interval for the Davis-Besse Nuclear Power Station, which commenced on September 21, 2000 and will end on September 20, 2012.

The repairs installed in accordance with the provisions of this alternative shall remain in place for the design life of the repair.

7.0 RPV HEAD J-GROOVE WELD Examination and evaluation of indications associated with RPV head J-groove welds is addressed by FENOC in accordance with ASME Code requirements as discussed below. This discussion is provided to address an NRC staff concern regarding examination or evaluation of the J-groove weld that was identified during a conference call with FENOC to discuss the planned content of this 10 CFR 50.55a request.

The assumptions of IWB-3600 are that cracks are fully characterized in order to compare the calculated parameters to the acceptable parameters addressed in IWB-3500. The original nozzle to RPV head J-groove weld is difficult to examine with UT due to the compound curvature and fillet radius around the nozzle circumference.

These conditions preclude ultrasonic coupling and control of the sound beam needed to perform flaw sizing with reasonable confidence in the measured flaw dimensions.

Therefore, it is impractical to characterize the flaw geometry that may exist therein. As these J-groove welds have not been examined, they are assumed to have unacceptable flaws.

The assumed J-groove flaws are being evaluated for acceptance in accordance with the analytical evaluation requirements of IWB-3132.3 using worst-case postulated flaw sizes. The results of this evaluation will be submitted to the NRC in accordance with the requirements of IWB-3134.

An additional evaluation was made to determine the potential for debris from a cracking J-groove partial penetration weld. As noted above, radial cracks were postulated to occur in the weld due to the dominance of hoop stresses at this location. The possibility of occurrence for transverse cracks that could intersect the radial cracks is considered remote. There are no forces that would drive a transverse crack. The radial cracks would relieve the potential transverse crack driving forces. Hence it is unlikely that a

10 CFR 50.55a Request Number RR-A34 Page 11 of 20 series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged. An evaluation of the potential consequences of nozzle fragmentation determined that there is a high probability that any fragmentation would enter the top of the column weldments and likely be stopped on one of the casting plates. This might preclude complete insertion of the control rod. Plant safety analyses include consideration of one stuck control rod. The likelihood of weld material debris resulting in the obstruction of more than one control rod to insert was judged to be of such low probability that the proposed repair technique does not pose a safety risk. An evaluation was also performed of a loose part of similar size on the reactor coolant system, including effects on plant equipment. The presence of the small amount of material evaluated was concluded to have no consequence of significance to plant equipment that could adversely affect the health and safety of the public.

8.0 REFERENCES

1. EPRI Report GC-1 11050, November 1998, "Ambient Temperature Preheat for Machine GTAW Temper Bead Applications," EPRI, Palo Alto, CA, and Structural Integrity Associates, Inc., San Jose, CA.

2. ASME Boiler and Pressure Vessel Code, Section Xl, 1995 Edition with Addenda through 1996, Appendix VIII, Supplement 10.

3. EPRI Report 1013558, Temperbead Welding Applications, 48-Hour Hold Requirements for Ambient Temperature Temperbead Welding, EPRI, Palo Alto, CA and Hermann & Associates, Key Largo, FL, December 2006.

4. EPRI Report 1009500, Suitability of Emerging Technologies for Mitigation of PWSCC (MRP-1 18), June 2004.

5. ASME Code Case N-638-1, "Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique,Section XI, Division 1."

6. ASME Code Case N-416-3, "Alternative Pressure Test Requirement for Welded or Brazed Repairs, Fabrication Welds or Brazed Joints for Replacement Parts and Piping Subassemblies, or Installation of Replacement Items by Welding or Brazing, Class 1, 2, and 3, Section Xl, Division 1."

7. NRC Regulatory Guide 1.147, Revision 15, "Inservice Inspection Code Case Acceptability, ASME Section Xl, Division 1."

8. ASME Code Case N-729-1, "Alternative Examination Requirements for PWR Reactor Vessel Upper Heads With Nozzles Having Pressure-Retaining Partial-Penetration Welds, Section Xl, Division 1."

10 CFR 50.55a Request Number RR-A34 Page 12 of 20 Figure 1 Machining

10 CFR 50.55a Request Number RR-A34 Page 13 of 20 TRIPLE POINT Figure 2 Welding

10 CFR 50.55a Request Number RR-A34 Page 14 of 20 Ti1

/

is 1.5 inches for nozzles < 30 degrees, and 1 inch for nozzles > 30 degrees relative to the head surface Figure 3 Examination Areas Pre-Weld PT I-m-n-o-p-q Post-Weld PT m-n-s-p-q-r Post-Weld UT (Weld) a-b-c-d-e-h Post Weld UT (Nozzle e-f-g-h Material)

10 CFR 50.55a Request Number RR-A34 Page 15 of 20 Nozzle Figure 4 UT 0 Degree and 45L Beam Coverage Looking Clockwise and Counter-Clockwise

10 CFR 50.55a Request Number RR-A34 Page 16 of 20 Nozzle 45L Beam Coverage Looking Down Figure 5 45L UT Beam Coverage Looking Down

10 CFR 50.55a Request Number RR-A34 Page 17 of 20 Nozz le 45L Beam Coverage Looking Up Figure 6 45L UT Beam Coverage Looking Up

10 CFR 50.55a Request Number RR-A34 Page 18 of 20 No2 zle 70L Beam Coverage Looking Down Figure 7 70L UT Beam Coverage Looking Down

10 CFR 50.55a Request Number RR-A34 Page 19 of 20 Nozz:le 70L Beam Coverage Looking Up Figure 8 70L UT Beam Coverage Looking Up

10 CFR 50.55a Request Number RR-A34 Page 20 of 20 Ta f"

7/

"a" is 1.5 inches for nozzles <30 degrees, and 1 inch for nozzles > 30 degrees relative to the head surface Figure 9 PSI and ISI Weld and Nozzle Base Metal Surface Examination Area (A-B-C-D)