CNRO-2004-00022, Arkansas Unit 1, Proposed Alternative to ASME Weld Examination Requirements for Repairs Performed on Reactor Vessel Head Penetration Nozzles

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Arkansas Unit 1, Proposed Alternative to ASME Weld Examination Requirements for Repairs Performed on Reactor Vessel Head Penetration Nozzles
ML041050668
Person / Time
Site: Arkansas Nuclear Entergy icon.png
Issue date: 04/08/2004
From: Burford F
Entergy Operations
To:
Document Control Desk, Office of Nuclear Reactor Regulation
References
ANO1-R&R-006, CNRO-2004-00022
Download: ML041050668 (22)
v • d • e


Text

-___ Entergy Operations, Inc.

- 1340 Echelon Parkway g

an xJackson, Mississippi 39213-8298 Tel 601-368-5758 F. G. Burford Acting Director Nuclear Safety & Licensing CNRO-2004-00022 April 8, 2004 U. S. Nuclear Regulatory Commission Attn.: Document Control Desk Washington, DC 20555-0001

SUBJECT:

Request for Alternative ANO1 -R&R-006 -

Proposed Alternative to ASME Weld Examination Requirements for Repairs Performed on Reactor Vessel Head Penetration Nozzles Arkansas Nuclear One, Unit 1 Docket No. 50-313 License No. DPR-51

REFERENCES:

1. Entergy Operations, Inc. letter CNRO-2004-00014 to the NRC dated March 4, 2004
2. NRC letter to Entergy Operations, Inc. (TAC No. MB6599) dated November 25, 2003
3. Entergy Operations, Inc. letter CNRO-2002-00054 to the NRC dated November 26, 2002

Dear Sir or Madam:

In Reference 1, Entergy Operations, Inc., (Entergy) submitted a revision to previously proposed Request for Altemative ANOI -R&R-006, Rev. 0 for use at Arkansas Nuclear One, Unit 1 (ANO-1). Specifically, this request proposes an alternative to the requirement to evaluate actual flaw characteristics as defined in ASME Section III NB-5330(b) and ASME Section Xl IWA-3300(b), IWB-3142.4, and IWB-3420. In lieu of fully characterizing any potential flaws, Entergy proposes to utilize worst-case assumptions to conservatively evaluate the acceptance of a postulated flaw.

Since submitting ANO1-R&R-006, Entergy has performed preliminary analysis that indicates the stress intensity factor (SIF) of a crack left in the J-groove weld of a reactor pressure vessel (RPV) head penetration nozzle would not meet the acceptance criterion for normal and upset conditions of ASME Section Xl Paragraph IWB-3613(b). Therefore, Entergy is submitting a second revision to ANO1-R&R-006, which includes the original alternative to the requirements of ASME Section III NB-5330(b) for a newly installed repair weld and revised alternatives to ASME Section XI IWA-3300(b), IWB-3142.4, IWB-3613(b), and IWB-3420 for the J-groove weld remnant. The revised ANO1-R&R-006, which is contained in Enclosure 1,

CNRO-2004-00022 Page 2 of 3 replaces the previously submitted request in its entirety. New information contained in the request is denoted with revision bars in the margins of the affected pages.

AN01 -R&R-006 applies to all 69 RPV head penetration nozzles, including the 6 that were repaired using approved alternative ANO1-R&R-004 during the previous refueling outage.

(The NRC approved ANO1-R&R-004 via Reference 2.)

Entergy previously submitted to the NRC the following documents:

1. Engineering Report M-EP-2004-002, Rev. 0
2. ANO Calculation 86-E-0074-160
3. ANO Calculation 86-E-0074-161
4. ANO Calculation 86-E-0074 -164 Item 1 was transmitted via Reference I while Items 2, 3, and 4 were transmitted via Reference 3. These documents support this latest version of ANO1-R&R-006, Rev. 0.

Entergy requests that the NRC staff authorize use of ANOI-R&R-006 by April 20, 2004 to support inspection and repair activities for refueling outage 1R1 8, which is scheduled to begin during the second quarter of 2004.

Entergy is scheduled to replace the ANO-1 RPV head during the following refueling outage, 1R1 9, which is scheduled for the fourth quarter of 2005.

Should you have any questions regarding this letter, please contact Guy Davant at (601) 368-5756.

This letter contains two commitments as identified in Enclosure 2.

Very truly yours, FGBIGHD/ghd

Enclosures:

1. RequestforAltemativeANO1-R&R-006, Rev. 0
2. Licensee-identified Commitments cc: (see next page)

CNRO-2004-00022 Page 3 of 3 cc: Mr. W. A. Eaton (ECH)

Mr. J. S. Forbes (ANO)

Dr. Bruce. S. Mallett Regional Administrator, Region IV U. S. Nuclear Regulatory Commission 611 Ryan Plaza Drive, Suite 400 Arlington, TX 76011-8064 NRC Senior Resident Inspector Arkansas Nuclear One P. O. Box 310 London, AR 72847 U. S. Nuclear Regulatory Commission Attn: Mr. T. W. Alexion MS 0-7 D1 Washington, DC 20555-0001

ENCLOSURE1 CNRO-2004-00022 REQUEST FOR ALTERNATIVE ANOi-R&R-006, Rev. 0

ENTERGY OPERATIONS, INC.

ARKANSAS NUCLEAR ONE, UNIT I 3rd 10-YEAR INTERVAL REQUEST No. ANO1-R&R-006, Rev. 0 REFERENCE CODE:

The original code of construction for Arkansas Nuclear One, Unit 1 (ANO-1) is ASME Section III, 1965 Edition with Addenda through Summer, 1967. The components (including supports) may meet the requirements set forth in subsequent editions and addenda of the ASME Code incorporated by reference in 10 CFR 50.55a(b) subject to the limitations and modifications listed therein and subject to NRC approval. The codes of record for the repairs described within this request are the 1989 Edition of ASME Section III and 1992 Edition of ASME Section Xl codes. ANO-1 is in its third (3r) 10-Year Inservice Inspection interval.

1. Svstem/Component(s) a) Name of Component:

Reactor Pressure Vessel (RPV) head nozzles (There are 69 nozzles welded to the RPV head. This request applies to all 69 RPV head penetration nozzles, including the 6 that were repaired using the approved alternative ANO1-R&R-004 during the previous refueling outage.')

b) Function:

  • The J-groove weld remnant left in place serves no function. It becomes nothing more than a remaining weldment attached to the RPV head.
  • Any new repair welds serve as the pressure boundary weld for the RPV head nozzle and RPV head.

c) ASME Code Class:

The RPV head and RPV head nozzles are ASME Class 1.

d) Category:

Examination Category B-E, Pressure Retaining Partial Penetration Welds in Vessels; Item No. B4.12 II. Code Requirements A. ASME Section Xl (Dertaining to the J-groove weld remnant)

Paragraph IWA-4310 requires in part that uDefects shall be removed or reduced in size in accordance with this Paragraph." Furthermore, IWA-431 0 allows that "...the defect removal and any remaining portion of the flaw may be evaluated and the component accepted in

' Request for Alternative ANO1-R&R-004 (TAC No. MB6599) was approved by the NRC in a letter dated November 25, 2003.

Page 1 of 16

.\

accordance with the appropriate flaw evaluation rules of Section Xl." The ASME Section Xl, IWA-3300 rules require characterization of flaws detected by inservice examination.

Paragraph IWB-3420 requires the characterization of flaws in accordance with the rules of IWA-3300.

Subparagraph IWB-3142.4 allows the use of analytical evaluation to demonstrate that a component is acceptable for continued service. It also requires that components found acceptable for continued service by analytical evaluation be subject to successive examination during the next three inspection periods.

Paragraph IWB-3613 establishes acceptance criteria to be used for evaluating flaws in areas where bolt-up loads play a significant role (i.e., the RPV-to-head interface). IWB-3613(b) requires the use of a safety factor of o10 (3.16) to determine the stress intensity factor (SIF) of a flaw during normal operating conditions.

B. ASME Section III (Dertainina to the new repair weld)

Section III Subsection NB-5330(b) states, "Indications characterized as cracks, lack of fusion, or incomplete penetrations are unacceptable regardless of length.'

Ill. Proposed Alternative Pursuant to 10 CFR 50.55a(a)(3)(i), Entergy proposes the following alternative to IWB-3420/IWA-3300, IWB-3142.4, IWB-3613(b), and NB-5330(b) as they pertain to the examination and evaluation of the repair weld and the remnant J-groove weld of the RPV head penetration nozzle that is not removed. Specifically, this alternative involves:

  • Leaving a remnant of the J-groove weld in place following repair activities and operating with an SIF employing a safety factor of 2 rather than 410 (3.16) until the ANO-1 RPV head is replaced during the next refueling outage (1RI 9)
  • Examining the repair weld Each aspect is discussed below.

A. The Remnant J-Groove Weld The planned repair for the subject RPV head nozzles does not include removing any cracks discovered in the remaining J-groove partial penetration welds. Therefore, per the requirements of IWA-431 0, the cracks must be evaluated using the appropriate flaw evaluation rules of Section Xl. No additional inspections can be performed to characterize the cracks due to the configuration of the nozzle and the weld. Thus, the actual dimensions of the crack cannot be fully determined as required by IWA-3300.

In lieu of fully characterizing any existing cracks, Entergy used worst-case assumptions to conservatively estimate the crack extent and orientation. The postulated crack extent and orientation were evaluated using the rules of IWB-3600. This evaluation, in conjunction with this request, justifies leaving the remnant weld in place without performing successive examinations in accordance with IWB-3142.4.

Page 2 of 16

The evaluation also determined that the SIF of the postulated crack will not meet the acceptance criterion when using a safety factor of q1 0 required by IWB-3613(b). Rather than use this criterion, Entergy proposes to use a safety factor of 2.

B. Examining the Repair Weld The new pressure boundary repair weld that connects the remaining portion of the RPV head nozzles to the low alloy RPV head contains a material "triple point." The triple point is located at the root of the weld where the Alloy 600 nozzle will be welded with Alloy 690 (52) filler material to the SA-533 Grade B, Class 1 Mn-Mo low alloy steel plate (See Figures 1 and 2).

Experience has shown that during solidification of the Alloy 52 weld filler material, a lack of fusion (otherwise known as a welding solidification anomaly) area may occur at the root of the partial penetration welds.

Entergy is requesting relief from the requirement of NB-5330(b) regarding the potential lack of fusion at the root of the repair weld. If a weld triple point anomaly occurs in any of the repair welds, it will be evaluated in accordance with the appropriate flaw evaluation rules of ASME Section Xl. Calculations have been completed to justify this welding solidification anomaly. 2 IV. Basis and Justification for Proposed Alternative Inspections of the RPV head will be performed in accordance with revised NRC Order EA-03-009, Issuance of Order Establishing Interim Inspection Requirements for Reactor Pressure Vessel Heads at Pressurized Water Reactors, dated February 20, 2004 and/or approved relaxation requests. These inspections may identify conditions that indicate a need to repair flaws discovered in the RPV head penetrations. The use of any of the alternatives permitted by the applicable ASME Codes for repairs will result in increased radiation dose with no compensating increase in quality or safety. The post-weld heat treatment (PWHT) parameters required by NB-4622 would be difficult to achieve on a RPV head in containment and would pose significant risk of distortion to the geometry of the RPV head and vessel head penetrations. In addition, the existing J-groove welds would be exposed to PWHT for which they were not qualified. This request applies to repair of any or all of the 69 RPV head penetrations.

A. The Remnant J-Groove Weld The requirements of IWA-431 0 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 specifies the inside comer of the J-groove weld be progressively chamfered from the center to outermost penetrations to maintain an acceptable flaw size.Section III paragraph NB-3352.4(d)(3) requires that the comers of the end of each nozzle to be rounded to a radius of % t, or % inch whichever is smaller. A 1/8-inch minimum chamfer considered equivalent to the radius specified in NB-3352.4(d)(3) will be incorporated on the bottom corner of the repaired RPV head nozzle penetrations in lieu of the radius. The radius is specified to reduce the stress concentration that might occur at a sharp comer; however, since the original partial penetration weld that remains in this area is analyzed assuming through-weld cracks exist therein the presence or absence of a radius or chamfer at this location is not significant with respect to stress 2

See ANO Calculation E-6-0074-161 submitted to the NRC via Entergy letter CNO-2002-00054 dated November 26,2002.

Page 3 of 16

concentration. The primary purpose of the chamfer is to assure that any remaining cracks are no larger than those assumed for the analysis.

The assumptions of IWB-3600 are that the cracks are fully characterized to be able to compare the calculated crack parameters to the acceptable parameters addressed 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. In these welds, operating and residual stresses are obtained using finite element analysis of the RPV head. Since hoop stresses will be the dominant stress as determined by calculations, it is expected that radial type cracks (with respect to the penetration) will occur. Using worst case (maximum) assumptions with the geometry of the as-left weld, the postulated crack will be assumed to begin at the intersection of the RPV head inner diameter surface and the RPV head nozzle bore and propagate slightly into the RPV head-to-butter interface. The depth and orientation are worst-case assumptions for cracks that may occur in the remaining J-groove partial penetration weld configuration.

The original nozzle-to-RPV head weld configuration is extremely difficult to UT due to the compound curvature and fillet radius as can be seen in Figures 1 and 2. These conditions preclude ultrasonic coupling and control of the sound beam in order to perform flaw sizing with reasonable confidence in the measured flaw dimension. Therefore it is impractical, and presently, the technology does not exist, to characterize flaw geometries that may exist therein. Not only is the configuration not conducive to UT but the dissimilar metal interface between the Ni-Cr-Fe weld and the low alloy steel RPV head increases the UT difficulty.

Furthermore, due to limited accessibility from the RPV head outer surface and the proximity of adjacent nozzle penetrations, it is impractical to scan from this surface on the RPV head base material to detect flaws in the vicinity of the original weld. Entergy proposes to accept these flaws by analysis of the worst case that might exist in the J-groove. Since the worst case condition is to be analyzed as described below, no future examinations of these flaws is planned.

As previously discussed, after boring and removing the nozzle end, the remaining J-groove weld material will be chamfered to reduce the SIF.

Since the hoop stresses in the J-groove weld are generally about two times the axial stress at the same location, the preferential direction for cracking is axial, or radial relative to the nozzle. A radial crack in the Alloy 182 weld metal is postulated to propagate by primary water stress corrosion cracking (PWSCC) through the weld and butter, to the interface with the low alloy steel RPV head.

Detailed analyses, including residual stress evaluation and fracture mechanics, have been performed to establish the chamfer design that will result in an applied SIF, at the interface between Inconel alloy 600 butter weld and the low alloy steel reactor vessel head. This SIF exceeds the ASME Code Section Xl allowable limit for normal-upset conditions using a safety factor of 41i0 per IWB-3613(b). The analyses were performed for an outermost nozzle penetration location (38.50), which provides a bounding analysis for the other nozzles in the RPV head.

The residual stress analyses were performed using finite element methods that have been developed by Dominion Engineering Inc. for evaluating RPV head penetration J-groove weld residual stresses. The analyses are similar to those that supported various relaxation Page 4 of 16

I requests to NRC Order EA-03-009 that have been approved by the NRC staff.3 The analyses simulate the original installation of the RPV head penetration nozzle. The process includes the installation of the butter layer followed by a post-weld heat treatment, J-groove welding of the nozzle followed by a Code hydro-test and subsequent steady state operation. Upon achieving ambient conditions the nozzle was removed. At this point, variations in chamfering depths were modeled, each model subjected to a normal heat-up followed by a steady state condition and then a cooldown to ambient. Two additional transient conditions, starting from an initial steady state condition, representing a reactor trip (normal and upset condition) and rod withdrawal (accident condition) were analyzed. This completes the full spectrum of the required analysis for performing finite element based fracture mechanics evaluations.

The fracture mechanics analysis uses a finite element model similar to that used in the residual stress analysis. The finite element model has a refined mesh that includes crack tip elements along the interface between the Inconel Alloy 600 butter weld and the low alloy carbon steel RPV head. This model simulates a fully cracked J-groove weld including the butter layer. The fracture mechanics analysis was performed using a linear elastic superposition method. Relaxing the residual stresses due to cracking was not utilized since the analysis used a linear elastic formulation. The SIFs were obtained at several locations along the postulated crack front. The stresses obtained from the residual and operating stress analysis were entered as crack face pressure. Reactor vessel internal pressure on the crack face was added to the distribution obtained from the stress analysis.

The stress plots at selected locations in the finite element stress analysis for non-steady state operation (i.e., heat-up, cool-down, reactor trip, and rod withdrawal) were reviewed to capture the maximum stress during the specific condition. In this manner, the SIF was maximized for use in fatigue evaluations.

The fracture mechanics analysis produced SIFs along the crack front for the conditions evaluated. The conditions evaluated were:

1) Normal steady state operation;
2) Normal heat-up from ambient condition;
3) Normal cool-down from steady state condition;
4) Reactor trip from steady state condition; and,
5) Rod withdrawal accident from steady state condition.

The obtained SlFs were compared to the applicable ASME Code Section Xl IWB-3613(b) value for the specified condition of operation.

3 See letters to Entergy from the NRC dated October 9,2003, November 7, 2003, and November 12, 2003.

Page 5 of 16

The NRC has documented its position for fracture mechanics analysis as follows:

So far, the NRC accepted only an approach of applying residual stresses directly on crack faces (i.e., as primary stresses) for various applications related to reactor pressure vessels, control rod drive mechanism (CRDM) penetrations, and in-core instrument (ICI) nozzles.4 A summary of the results from fracture mechanics analysis, which were performed in accordance with this guidance, for the various assumed J-groove weld configurations is presented in Table 1. In this analysis, the fracture mechanics analysis was performed to evaluate the remnant J-groove weld by applying the stresses due to operating pressure, temperature gradients and residual stress effects on the crack face as primary stresses.

Table 1 below shows that 14 of 16 values for maximum SIF obtained from these analyses exceed the currently allowable fracture toughness of 63.2 kshlin in accordance with the 41 0 criterion of ASME Section Xl, IWB-3613(b).

Table 1: Maximum SIF from Fracture Mechanics Analysis Maximum Applied Stress Intensity Factor' (ksi4ln)

J-groove Weld Remnant Steady State Residual Stresses Operating Condition Configuration Operation Only Only' No Chamfer 77.4 - Downhill 75.3- Downhill 2.1-Downhill 103.4 - Uphill 105.0 - Uphill Note 5 - Uphill Design Minimum 80.0 -Downhill 78.6 - Downhill 1.4 - Downhill Chamfer 94.4 - Uphill 99.3 - Uphill Note 5 - Uphill Design Maximum 79.4 - Downhill 57.8 - Downhill 21.6 - Downhill Chamfer 84.8 - Uphill 68.7- Uphill 16.1 Uphill Theoretical Maximum 65.2 - Downhill 67.9 - Downhill Note 5-Downhill Chamfer 62.5 - Uphill 69.1 - Uphill Note 5 - Uphill Notes:

1) The applied SIF is based on considering the three conditions discussed in Z 3, and 4, below.
2) The steady state condition is the combined SIF based on residual stress plus the steady state operating stresses (pressure and temperature).
3) The residual stress condition is based on the residual stress state after completion of the specific operation on the J-groove weld as indicated by the configuration column.
4) The operating condition is the difference between the steady state condition and the residual stress state. This column provides the SIF estimate due to the operating condition alone.
5) The SIF due to the residual stress is higher than at steady state operating condition.

4See NRC letter, Request forAdditional Information Concerning WCAP-16180NP, Revision 0, "Operability Assessment for Combustion engineering Plants with Hypothetical Flaw Indications in Pressurizer heater Sleeves" (TAC No. MC1751) from Mr. D. Holland, Project Manager, Office of NRR, to Mr. G. Bischoff, Manager, Owners Group Program Management Office, Westinghouse Electric Company.

Page 6 of 16

The allowable SIF based on IWB-3613(b) is 63.2 ksi'Iin for an upper shelf fracture toughness of 200 ksinin. As shown in the Table 1,the applied SIFs are above the allowed minimum.

The basis for the safety factor of "410" in IWB-3613(b) can be found in Chapter 29 of the ASME Companion Guide to the ASME Boiler and Pressure Vessel Code, Volume 2, 'Section Xl Flaw Acceptance Criteria and Evaluation Using Code Procedures". The Guide states:

The acceptance criteria of IWB-3611 on flaw size were developed with the original purpose of maintaining the design margins of Section III. It is well known that the nominal factor of safety for normal and upset conditions is 3. Consider the general relationship between the stress intensity factor and the stress and flaw size at failure based on linear-elastic fracture mechanics, as noted in the following equation:

Kic = as where Kin = the fracture toughness.

It may therefore be deduced that a factor of safety of 3 on stress at failure is consistent with a factor of safety of 9 on flaw size. Code committees tend to prefer round numbers, so the value of 9 is rounded up to 10 to provide a safety factor slightly higher than the design safety factor.

Therefore, the safety factor on the SIF, based on the above equation, results in a value of 41 0. The design safety factor value of 3 was based on the ultimate tensile strength of the ferritic material thereby limiting the applied general primary membrane stress (Pm) to be less than or equal to one-third of the material ultimate strength. 5 In addition the design rules for Section Ill of the ASME Boiler and Pressure Vessel Code are defined for primary bending stress (Pb) and local primary membrane stress (PL) to be lower than 1.5Sm, which is approximately equal to the material yield strength. Further, the stress range when considering secondary stresses is increased by an additional factor of two to 3Sm.

This increase for local primary stresses then results in a nominal safety factor of two with consideration of bending and local stress effects. The limit on secondary stresses was included to prevent gross distortion of Code components.

The aspect of using different safety factors based on loading type was recognized in Appendix G to ASME Section Xl. Although this appendix is for "hypothetical flaw analysis" to ensure safety against non-ductile fracture, its applicability to the evaluation of flaws potentially left in the CRDM J-groove welds is appropriate. The current evaluation assumes that the entire J-groove weld (including the buffer) is cracked, which is analogous to postulating a maximum worse-case hypothetical flaw. In particular the guidance provided in paragraph G-2222 (Consideration of Membrane and Bending Stresses) notes that; "Equation (1) of G-2215 requires modification to include the bending stresses which may be important contributors to the calculated Ki value at a point near a flange or nozzle." Therefore, the controlling SIF equation, based on material toughness, was defined as:

K,. 2 2(KIm + Klb)puymay +(Kim + Klb)Seconday 5See Chapter 6 of the Companion Guide to the ASME Boiler and Pressure Vessel Code, Volume 1, "Subsection NB - Class I Components".

Page 7 of 16

where:

K,0 = the available fracture toughness based on crack arrest for the corresponding crack tip temperature; Kim = the applied SIF due to membrane stress; and, Kib = the applied SIF due to bending stress In Appendix G, the distinction between primary and secondary stresses are recognized by using a safety factor of 2 on primary stresses and not requiring a safety factor on secondary stresses.

The safety factor considerations in the Code (Section III and Appendix G of Section Xl) are based on the through-wall stress distribution, which is also the consideration for IWB-3600 of ASME Section Xl. However, the safety factor presented in IWB-3613(b) considers the same safety factor for all stresses. This results in an overly conservative allowable SIF when the predominant loading mechanism is highly localized and due to residual stresses.

A more reasonable approach would be to utilize the philosophy of Appendix G to ASME Section Xi and the safety factors utilized in Section IlIl. This approach would result in the governing equation for SIF as:

K1, 2 3.O(KIm + Kib)pfmary + 1.5 (Kim + Kjb)Secondary(orResiduav In the above equation the primary stresses would be those from operating pressure, which are the only non-displacement limited load on the top head. The secondary stresses would be those due to local structural discontinuity effects and thermal gradients. The safety factors applied are determined by multiplying those in Appendix G by a factor of 1.5. In this manner, the appropriate safety margin against non-ductile fracture would be maintained in a manner similar to that prescribed by Appendix G but with a higher safety factor. However, as shown in Table 1, this approach would provide a safety factor of 1.5, since the stresses are shown to be predominantly those due to residual stresses.

As an alternative, a safety factor applied to the residual stresses can be deduced from the structure of the safety factor for primary bending and primary local membrane stresses defined in ASME Section IlIl. It was observed that the safety factor for these stresses was two-thirds of that for the general primary membrane stress. In addition, the fracture mechanics analysis for the current evaluation demonstrates that the predominant loading is due to the localized residual stress distribution, thereby, reducing the safety factor in IWB-3613(b) to a value of 2. Thus, the allowable SIF would be as follows:

Krrotes KV/2 Using the results from the fracture mechanics analysis, for the maximum design chamfer case, the two approaches lead to the following result:

Criteria 1: K,8 k 3.O(Khm + KitJpdimay 4 1.5(Kim + Kib)Secondary or Residual 3(16. IJoperating CoKMion + 1.5(68. 7)Resldua = 151.4 s 200 Uphill Flaw 3 (2 1 .6 )o witic,+ 1.5(57. 8)Re.Wdu.i = 151.5 s 200 Downhill Flaw Page 8 of 16

Altemate Criteria: KTot.I S Kw/2 2(84.8) = 169.6 5 200 Uphill Flaw 2(79.4) = 158.85 200 Downhill Flaw.

The examples provided above show that there is a significant margin of safety against brittle fracture with either of the proposed acceptance criteria. In addition, the overall approach is conservative in that:

1. The fracture mechanics evaluation has been based on a hypothetical flaw that is assumed to exist in the entire J-groove.
2. The evaluation is based on linear elastic fracture mechanics principles with an assumed fracture toughness of 200 ksisin. At elevated temperatures, the value of allowable fracture toughness is assumed, and the principles of elastic-plastic fracture mechanics, if used, could certainly demonstrate that significantly more margin would exist.

Entergy will submit a preliminary analysis report to the NRC staff to support their review of this request by April 13, 2004, and a final, completed analysis report by June 1, 2004.

An additional evaluation was performed to determine the potential for debris from a cracking J-groove partial penetration weld. 6 As noted above, radial cracks were postulated to occur in the weld due to the dominance of the hoop stress at this location. The possibility of occurrence of transverse cracks that could intersect the radial cracks was considered remote since 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 series of transverse cracks could intersect a series of radial cracks resulting in any fragments becoming dislodged. 7 The cited evaluations provide an acceptable level of safety and quality in insuring that the RPV head remains capable of performing its design function for a sufficient number of heat-uplcool-down cycles to support one (1) operating cycle, with flaws existing in the original J-groove weld.

For the reasons described above, areas of J-groove welds containing flaws accepted by analytical evaluation will not be reexamined as required by IWB-3142.4. Although solidification anomalies may occur in the new repair weld, volumetric examination of these welds during a subsequent refueling outage is not required since Entergy plans to replace the ANO-1 RPV head during refueling outage 1R1 9, which is scheduled to begin during the fall of 2005.

Removing 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 PWSCC. As shown by industry experience, the low alloy steel of the RPV head impedes crack growth by PWSCC. Using an assumed worst-case crack size, the analysis e See ANO Calculation E-86-0074-164 submitted to the NRC via Entergy letter CNRO-2002-00054 dated November 26, 2002.

7 ANO Calculation E-86-0074-164, page 4 Page 9 of 16

ensures that unacceptable crack growth into the RPV head does not occur within the next operating cycle. Thus, the RPV head can be accepted per the requirements of IWA-431 0.

Based on extensive industry experience and Framatome-ANP direct experience, there are no known cases where flaws initiating in an Alloy 82/182 weld have propagated into the ferritic base material. The surface examinations performed associated with flaw removal during recent repairs at Oconee I and 3 on RPV head penetrations, Catawba 2 steam generator channel head drain connection penetration, ANO-1 hot leg level tap penetrations and the V. C. Summer hot leg pipe to primary outlet nozzle repair (reference MRP-44: Part l: Alloy 82/182 Pipe Butt Welds, EPRI, 2001 TP-1001491) all support the assumption that the flaws would blunt at the interface of the Ni-Cr-Fe weld to ferritic base material. Additionally, the Small Diameter Alloy 600/690 Nozzle Repair Replacement Program (CE NPSD-1 198-P) provides data that shows PWSCC does not occur in ferritic pressure vessel steel. Based on industry experience and operation stress levels, there is no reason for service related cracks to propagate into the ferritic material from the Alloy 82/182 weld.

B. Examining the ReDair Weld Industry experience gained from earlier repairs of RPV head nozzles indicates that removal and repair of the defective portions of the original J-groove partial penetration welds were time consuming and radiation dose intensive. The prior repairs indicated that more automated repair methods were needed to reduce radiation dose to repair personnel. For the present ANO-1 repairs, a remote semi-automated repair method will be used for each of the subject nozzles. Using a remote tool from above the RPV head, each of the nozzles subject to this repair will first receive a roll expansion into the RPV head base material to insure that the nozzle will not move during subsequent repair operations. Second, a semi-automated machining tool from underneath the RPV head will remove the lower portion of the nozzle to a depth above the existing J-groove partial penetration weld. This operation will sever the existing J-groove partial penetration weld from the subject RPV head nozzles. Third, a semi-automated weld tool, utilizing the machine GTAW process, will then be used to install a new Alloy 690 pressure boundary weld between the shortened nozzle and the inside bore of the RPV head base material (see Figures 1 and 2). It was intended, as a part of the new repair methodology and to reduce radiation dose to repair personnel that the original J-groove partial penetration welds would be left in place. These welds will no longer function as pressure boundary RPV head nozzle to RPV head welds. However, the possible existence of cracks in these welds mandates that the flaw growth potential be evaluated.

In the case of the RPV head nozzle inside diameter (ID) temper bead repair, the term "anomaif is applied to the unusual solidification patterns that result along the low alloy steel /

Alloy 600/Filler Metal 52 interface of the repair weld. The anomalies originate along the low alloy steel (RPV head) to Alloy 600 (original nozzle) interface where melting occurs and generally extend back towards the center of the weld bead. These anomalies are typical for welds that involve a "lap joint" type interface, such as typical partial penetration weld geometries, in the weld joint design. Cross sections of nickel alloy welds made utilizing similar joint designs with Alloy 600 base materials and Alloy 82 filler metals have exhibited these phenomena consistently.

Page 10 of 16

This phenomenon is compounded by the different solidification rates for the base materials and weld metal used in performing the repair. Other suspected factors in the anomaly occurrence are the size of the interface gap, gap cleanliness and position of the welding arc relative to the edge of the interface. The molten weld puddle simply freezes back to each side of the interface and follows the interface into the weld as solidification of the weld puddle take place. Weld root anomalies have been observed on several mockups with configurations simulating the repair weld. UT methods have been developed based on the characteristics of this anomaly so that verification to the prescribed acceptance criteria can be performed. The defect is treated like a crack, which is worst case. Two types of flaws are common in this area. The first is localized melting away of the feathered end of the beveled nozzle weld prep leaving occasional small voids. The second type flaw is caused due to an inherent problem during solidification of high Ni-Cr alloys in the presence of a notch such as a partial penetration weld. This type of flaw is in fact often called a "solidification anomaly" to differentiate it from what it is not - a crack.

IWA-4170 mandates that the repair design meets the original construction code or the adopted ASME Section III Code. As noted, the 1989 ASME Section III code has been adopted for qualification of the described repairs. Subsection NB-5330(b) stipulates that no lack of fusion area be present in the weld. A fracture mechanics analysis was performed to demonstrate compliance with Section Xl of the ASME Code, for operating with the postulated weld anomaly described above.8 The anomaly was modeled as a 0.1 inch "crack-like" defect, 360 degrees around the circumference at the "triple point" location. Full-size mockups using coupons from the Midland RPV head were metallographically evaluated. Both flaw types were occasionally found as expected and were less than the analyzed maximum allowed of 0.100 inch.9 Based on the fact that this anomaly is predictable as discussed herein, the anomaly can be detected by UT within the prescribed acceptance criteria and evaluated for fatigue and flaw growth using applicable ASME Sections III and Xl methods. Therefore, the intent of the ASME Codes will be met. The ASME Section III analysis conservatively assumes a reduction in weld area (along the new weld-to-ferritic steel penetration fusion line) due to the anomaly and the ASME Section Xl analysis assumes the anomaly is a crack-like defect.

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 traverses the RPV head tube wall thickness from the outside diameter (OD) of the tube to the ID of the tube. This is the shortest path through the component wall, passing through the new Alloy 690 weld material. However, Alloy 600 tube material properties or equivalent are used to ensure that another potential path through the heat affected zone (HAZ) between the new repair weld and the Alloy 600 tube material is bounded.10 8 See ANO Calculations 86-E-0074-160 and 86-E-0074-161 submitted to the NRC via Entergy letter CNRO-2002-00054 dated November 26, 2002.

9ANO Calculation 86-E-0074-160, page 2 and ANO Calculation 86-E-0074-161, page 4 10ANO Calculation 86-E-0074-161, page 7 Page 11 of 16

For completeness, two types of flaws are postulated at the outside surface of the tube. 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 tube. 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 tube."

Path 2:

Flaw propagation path 2 runs down the outside surface of the repair weld between the weld and RPV head. A semi-circular cylindrically oriented flaw is postulated to lie along this interface, subjected to radial stresses with respect to the tube. This flaw may propagate through either the new Alloy 690 weld material or the low alloy steel RPV head material.' 2 The result of the analysis demonstrated that a 0.10-inch weld anomaly is acceptable for 25 years, which is beyond 2005 when the ANO-1 RPV head is scheduled to be replaced.'3 Residual stresses and stresses due to operation were considered. Significant fracture toughness margins were expected for both of the flaw propagation paths considered in the analysis. The minimum calculated fracture toughness margins were required to be greater than the required margin of 41 0 per ASME Section Xl IWB-3612. Based on similar analysis, fatigue crack growth was expected to be minimal. The maximum final flaw size was small considering both flaw propagation paths. A limit load analysis was also performed considering the ductile Alloy 600/Alloy 690 materials along flaw propagation path 1. The analysis was required to show limit load margins for normal/upset conditions and emergency/faulted conditions greater than the required margins of 3.0 and 1.5 for normal/upset conditions and emergency/faulted conditions, respectively, per ASME Section Xl, IWB-3642.' 4 Acceptance of the repair weld is based on this evaluation in accordance with ASME Section Xl and demonstrated that for the intended service life of the repair, the fatigue crack growth is acceptable and the crack-like indications remain stable. These two findings satisfy the Section Xl criteria but do not include considerations of stress corrosion cracking such as PWSCC. However, since the crack-like indications in the weld triple point anomaly 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 from PWSCC is not applicable.

Eliminating the weld triple point anomaly requires use of an entirely different process than that proposed for use on ANO-1. The only qualified method currently available would involve extensive manual welding that would result in radiation doses estimated to be in excess of 30 REM per nozzle as compared to the 5 REM estimated for each nozzle repaired by the proposed process. Compliance with the specified Code requirements would result in excessive radiation exposure.

" Ibid.

12 Ibid.

1 3 ANO Calculation 86-E-0074-161, page 38 4 ANO Calculation 86-E-0074-161, pages 22, 23, and 38 Page 12 of 16

V. Duration of the Proposed Alternative Entergy plans to replace the ANO-1 RPV head during Refueling Outage 1R1 9, which is scheduled to begin during the fall of 2005. Therefore, this request applies to:

  • The previous operating cycle for the six (6) nozzles repaired in I RI7 using the Framatome technique, which was approved via alternative ANO1-R&R-004' 5 , and
  • Upcoming Operating Cycle 19 for any of the 69 RPV head penetration nozzles that may be repaired during 1R18.

For the upcoming Operating Cycle 19, Entergy has evaluated the need to employ water jet conditioning and has determined such activities are not required. Entergy has performed an evaluation to determine the time for a postulated crack to grow 75% through-wall in the Alloy 600 nozzle material above the repair weld without employing water jet conditioning, as documented in Engineering Report M-EP-2004-002, Rev. 0.

The evaluation considers RPV head nozzles in the as-repaired condition and encompasses initiation and crack growth due to primary water stress corrosion cracking (PWSCC). This evaluation found that nozzle axial stresses are considerably lower than nozzle hoop stresses.

Because of this, the likelihood of axial cracking is greater than the likelihood of circumferential cracking; therefore, only axial crack conditions were analyzed.

The analysis indicates that a crack will not grow to 75% through-wall in a time period of 4 years. This estimate is based on the following assumptions:

1. After PT and UT examination of the repaired ID surface, an undetected axial crack 0.157 inch long and 0.0679 inch deep (11 % wall thickness) is assumed present."'
2. The crack growth rate under operating conditions was determined using the MRP-55 recommended curve modified for a crack growth amplitude (a) that represents B&W material data.17
3. The minimum wall thickness of the CRDM nozzle repair is 0.6175.18
4. Water jet conditioning is not applied.

Since Entergy plans to replace the ANO-1 RPV head during I R1 9, which is prior to the end of 4 years, water jet conditioning is not necessary.

Given these expected results, the proposed inspection schedules given above, and the planned replacement date for the ANO-1 RPV head, Entergy believes the proposed alternatives to the ASME Code requirements are justified. The proposed alternatives are applicable to the repairs and examinations after repair to any ANO-1 RPV head nozzle.

16 Request for Altemative ANOI-R&R-004 (TAC No. MB6599) was approved by the NRC in a letter dated November 25, 2003.

1 Engineering Report M-EP-2004-002, Rev. 0, Attachment 2 of Appendix C, page 2 of 17 17 Engineering Report M-EP-2004-002, Rev. 0, Appendix B 18 Engineering Report M-EP-2004-002, Rev. 0, Appendix A gives nozzle IDand OD dimensions.

Page 13 of 16

-4 VM Implementation Schedule This request will be implemented during upcoming refueling outage 1R1 8, which is scheduled to begin during the second quarter of 2004. Entergy plans to replace the ANO-1 RPV head during Refueling Outage 1R1 9, which is scheduled to begin during the fall of 2005.

VII. Conclusions 10CFR50.55a(a)(3) states:

Proposed alternatives to the requirements of (c), (d), (e), (f), (g), and (h) of this section or portions thereof may be used when authorized by the Director of the Office of Nuclear Reactor Regulation. The applicant shall demonstrate that:

(i) The proposed alternatives would provide an acceptable level of quality and safety, or (ii) Compliance with the specified requirements of this section would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.

Entergy believes that the proposed alternative provides an acceptable level of quality and safety because, as discussed in Section IV, above:

  • Leaving a remnant of the original J-groove weld in place has been analyzed and shown to pose no adverse effect on plant operations.
  • Although the SIF of a postulated crack in the J-groove weld remnant does not meet ASME Section Xl requirements using a safety factor of 410, an SIF using a safety factor of 2 is commensurate with ASME Section III design requirements.
  • Analysis has been performed demonstrating that a 0.1-inch weld anomaly in a new repair weld is acceptable for 25 years, which is beyond 2005 when the ANO-1 RPV head is to be replaced.

Therefore, Entergy requests that the NRC staff authorize this request pursuant to 10 CFR 50.55a(a)(3)(i).

Page 14 of 16

A.

FIGURE 1l lNew AN 0-1 RPV Head Nozzlel Page 15 of 16

SA-533 Gr. B Cass I EPorc-7 (bS NOW) luIIE FORl I

I AS-WELlED SAFACE

- SmiA E SfinA&E FOR Pr FIGURE 2 ANO-1 New RPV Head Pressure Boundary Welds Page 16 of 16

F ENCLOSURE 2 CNRO-2004-00022 LICENSEE-IDENTIFIED COMMITMENTS to CNRO-2004-00022 Page 1 of 1 LICENSEE-IDENTIFIED COMMITMENTS TYPE (Check one) SCHEDULED ONE-TIME CONTINUING COMPLETION COMMITMENT ACTION COMPLIANCE DATE

1. Entergy will submit preliminary analysis to April 13, 2004 the NRC staff to support their review of this request by April 13, 2004.
2. Entergy will submit a final, completed June 1, 2004 analysis report to the NRC staff by June 1, 2004
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