ML061360065

Third Ten-Year Inservice Inspection (ISI) Interval Relief Request ISI-3-22 Request for Alternative to ASME Code Rules for the Inside Diameter Structural Weld Overlay Repair Process for Control Element Drive Mechanism (CEDM) # 56

ML061360065
Person / Time
Site:	San Onofre
Issue date:	05/11/2006
From:	Scherer A Southern California Edison Co
To:	Document Control Desk, Office of Nuclear Reactor Regulation
References
ISI-3-22
Download: ML061360065 (24)

Text

SOUTHERN CALIFORNIA A. Edward Scherer FEDI ON Manager of Nuclear Regulatory Affairs An EDISON INTERNATIONALS Company May 11, 2006 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, DC 20555-0001

Subject:

Docket No. 50-362 Third Ten-Year Inservice Inspection (ISI) Interval Relief Request ISI-3-22 Request for Alternative to ASME Code Rules for the Inside Diameter Structural Weld Overlay Repair Process for Control Element Drive Mechanism (CEDM) # 56 San Onofre Nuclear Generating Station Unit 3

Dear Sir or Madam,

Pursuant to 10 CFR 50.55a(a)(3)(i), the Southern Califomia Edison (SCE) Company requests the U. S. Nuclear Regulatory Commission (NRC) approval to allow use of the Inside diameter Weld Inlay repair process as an alternative to the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code Process for Reactor Vessel Head Penetration (RVHP) CEDM # 56.

In accordance with the NRC First Revised Order EA-03-009, "Issuance of Order Establishing Interim Inspection Requirements for Reactor Pressure Vessel Head at Pressurized Water Reactors," SCE will be performing inspection of CEDM # 56 during the San Onofre Nuclear Generating Station Unit 3 Cycle 14 refueling outage in November 2006. This penetration had undergone embedded flaw weld overlay repair during the Cycle 13 refueling outage pursuant to approved SCE relief request ISI-3-13.

SCE does not expect to identify any changes in the indication profile. Nevertheless, in the event growth of the indication is confirmed during the November 2006 inspection, SCE intends to employ an inside diameter structural weld overlay process that is similar to the embedded flaw repair process. The proposed repair process is similar to the process described in the NRC approved WCAP 15987 Revision 2 and SCE Relief Request ISI-3-8 which employ a seal weld to arrest primary water stress corrosion cracking growth. The proposed alternative repair described in this relief request deviates from previously approved repairs in that credit would be taken for overlay weld structural support.

P.O. Box 128 San Clemente, CA 92672 949-368-7501 Fax 949-368-7575

Document Control Desk May 11, 2006 SCE requests NRC approval of ISI-3-22, prior to November, 2006, when the next Unit 3 Reactor Vessel Head Penetration (RVHP) examinations are scheduled to begin.

Should you have any questions, please contact Mr. Jack Rainsberry, Manager, Plant Licensing at (949) 368-7420.

Sincerely, Enclosure cc: B. S. Mallett, 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 & 3

ENCLOSURE 10 CFR 50.55a Request Number ISI-3-22 Proposed Alternative In Accordance with 10 CFR 50.55a(a)(3)(i) the Inside Diameter Structural Weld Overlay Repair Process for Control Element Drive Mechanism (CEDM) # 56 San Onofre Nuclear Generating Station Unit 3

10 CFR 50.55a Request Number ISI-3-22 Proposed Alternative In Accordance with 10 CFR 60.55a(a)(3)(i)

Alternative Provides Acceptable Level of Quality and Safety

1.0 ASME Code Components Affected

San Onofre Nuclear Generating Stations (SONGS) Unit 3 reactor vessel head penetration (RVHP) Control Element Drive Mechanism (CEDM) #

56: All RVHPs are American Society of Mechanical Engineers (ASME)

Boiler and Pressure Vessel Code,Section III, Class I components.

2.0 Applicable Code Edition and Addenda Reactor Vessel Construction Code, ASME Section III, 1971 Edition, through the Summer 1971 Addenda Code of Record for Current (Third) Ten-Year Inservice Inspection (ISI)

Interval, ASME Section Xi, 1995 Edition, through the 1996 Addenda 3.0 ADplicable Code Requirements ASME XI, IWA-4410(a) states the repair/replacement activities, such as metal removal and welding, shall be performed in accordance with the Owner's Requirements and the original Construction Code of the component or system. The applicable Construction Code is ASME IlIl, 1971 Edition, through the Summer 1971 Addenda.

BASE METAL DEFECT REPAIRS ASME l1l, NB-4131 states that defects in base metals, such as the RVHP tubes, may be eliminated or repaired by welding, provided the defects are removed, repaired and examined in accordance with the requirements of NB-2500.

ASME ll, NB-2538 addresses elimination of base material surface defects and specifies defects are to be removed by grinding or machining. Defect removal must be verified by a magnetic particle or liquid penetrant examination using acceptance criteria of NB-2545 or NB-2546. If the removal process reduces the section thickness below the NB-3000 design thickness, then repair welding per NB-2539 is to be performed.

ASME 1II, NB-2539.1 addresses removal of defects and requires defects 1 of 8

10 CFR 50.55a Request Number ISI-3-22 be removed or reduced to an acceptable size by suitable mechanical or thermal methods.

ASME IlIl, NB-2539.4 provides the rules for examination of the base material repair welds and specifies they shall be examined by the magnetic particle or liquid penetrant methods with acceptance criteria per NB-2545 and NB-2546. Additionally, if the depth of the repair cavity exceeds the lesser of 3/8 inch or 10 percent of the section thickness, the repair weld shall be examined by the radiographic method using the acceptance criteria of NB-5320.

REQUESTED RELIEF Relief is requested from the requirements of ASME Xl, IWA-4410(a), to perform repairs on the RVHP penetrations per the rules of the Construction Code.

Relief is requested from the requirements in ASME Ill, NB-4131, NB-2538 and NB-2539.1 to eliminate base material defects prior to repair welding.

Relief is requested to use substitute examination methods in lieu of those specified in NB-2539.4 for the following cases:

• In the case of embedded flaw welds on the inside diameter (ID) surface of the penetration tubes, eddy current and ultrasonic examinations will be performed on the overlay repair weld which are surface and volumetric examinations but are different methods than specified in NB-2539.4. The proposed inspection methods are consistent with the NRC Order EA-03-009 examinations that originally detected the indication. IWB 3600 acceptance criteria are used for the embedded flaws as described in WCAP 15987-P revision 2.

4.0 Reason for the Request During the previous (Cycle 13) refueling outage, an indication was identified in SONGS Unit 3 CEDM # 56 using ultrasonic examination from the ID surface. Based on the available examination results, it was concluded that the indication might have been an outside diameter (OD) initiated primary water stress corrosion cracking (PWSCC) flaw. The resulting depth of approximately 78 percent through wall exceeded the approved limit of 75 percent for embedded flaw repairs (References 3 and 5). As a result, SCE submitted Relief Request ISI-3-13 (Reference 6) to perform repairs that address this condition. Repairs performed on CEDM 2 of 8

10 CFR 50.55a Request Number ISI-3-22

1. 56 consisted of a non-structural weld overlay encapsulating the entire J-weld and OD penetration surfaces consistent with the description provided in Section 2.2.3 of Reference 2. Those repairs have been shown to effectively arrest any further PW$CC degradation associated with this indication. Relief Request ISI-3-13 was approved for operation during Cycle 13 only. SCE has generated a new relief request, ISI-3-21, which if approved, will allow continued operation during Cycle 14 with the existing repairs provided that no measurable growth of the indication has occurred.

Southern California Edison (SCE) Company will be performing RVHP inspections during the SONGS 3 Cycle 14 refueling outages to meet the requirements of the February 20, 2004, NRC First Revised Order EA 009 (Reference 1). This inspection will include examination of the previously repaired CEDM # 56 for detection of measurable growth.

In the event that any growth is confirmed in the CEDM # 56 indication during the Cycle 14 refueling outage inspections, SCE intends to perform a penetration base metal weld repair pursuant to this relief request. This proposed repair would reduce the flaw depth to an acceptable size.

Reduction of flaw depth to less than 75 percent through wall resolves the deviation of the embedded flaw in CEDM # 56 relative to the approved generic Westinghouse topical report on embedded flaw repairs (WCAP 15987-P Revision 2) and the SONGS specific application of that repair methodology approved in Reference 5. Therefore, implementation of repairs described in this relief request will eliminate the need for further relief from the 75 percent maximum through wall depth limitation.

The proposed repair weld will be similar to ID penetration weld overlay described in Section 2.2.1 and Section C.2 of the approved Westinghouse Topical Report WCAP 15987-P Revision 2 (Reference 3). That approved repair is designed to seal off PWSCC flaws that had originated on the ID surface of the penetration. As described in Reference 3, that repair would consist of an excavation from the ID surface to a depth of at least 3/16 inch. Subsequently, the excavation is restored to the original ID surface contour by application of an equivalent depth seal weld using Alloy 52 weld metal.

The proposed application of this previously approved repair technique is to reduce the depth of an OD initiated flaw by excavation of approximately 1/4" (approximately 35 percent wall thickness) from the ID surface. This excavation would remove the intact ligament of CEDM # 56 penetration wall as well as approximately 10 percent of the wall bearing the indication.

This excavation will be restored to the original ID surface contour by application of an equivalent depth structural weld. As a result, the intact penetration ligament will be restored to approximately 35 percent wall thickness and the embedded flaw will be reduced to approximately 65 3 of 8

10 CFR 50.55a Request Number IS1-3-22 percent through wall.

The differences associated with the proposed repair relative to the repair process described in Reference 2 and approved in reference 3 are:

1. Application of an ID weld inlay to mitigate a previously repaired OD initiated PWSCC flaw

2. Crediting the inlay weld as a structural weld repair instead of a seal weld

3. A potential change in residual surface stresses, and future PWSCC susceptibility associated with a repair weld approximately 4/16 inch deep compared to an approved weld depth of "at least 3/16 inch deep"

4. A potential decrease in the ability to accurately monitor the residual indication using ultrasonic techniques deployed from the ID surface.

As described in the Attachment to this enclosure, the approved embedded flaw repair is designed to arrest PWSCC and to ensure that the residual structure meets appropriate design margins. The addition of weld material to reduce the size of flaw is an acceptable repair method. Application of an ID weld inlay for the purpose of reducing the embedded flaw to a size that is acceptable by criteria provided in reference 2 combines approved repair methods to achieve an acceptable alternative to Code requirements. The weld materials, design, and techniques employed for ID weld inlay repairs described in Reference 2 incorporate the required quality to achieve a structural weld repair. The residual stresses associated with the proposed 1/4 inch repair weld are consistent with the inlay repair method already approved in Reference 3.

The ability to accurately monitor the residual indication using the ultrasonic techniques deployed from the ID surface for this type of repair has been addressed and has undergone third party review with satisfactory results.

These inspections employ the same Westinghouse tooling and techniques that are in use at SONGS for Reactor Vessel Head Penetration (RVHP) inspections required by NRC Order 03-009 (Reference 1). The inspection consists of a penetration volumetric exam using time of flight tip diffraction ultrasonic examination, and a surface examination using eddy current methods. These examinations are deployed from the penetration ID and cover 360 degrees of penetration surface and volume from greater than two inch above the top of the J-weld, to approximately 1 inch below the J-weld.

For inspection of CEDM # 56, a new mockup with site-specific parameters will be used to demonstrate the NDE capability. For the ID surface examination, equivalent electron machine discharge (EDM) notches of two 4 of 8

10 CFR 50.55a Request Number ISI-3-22 depths (0.020 inch and 0.040 inch) will be made in the weld metal and base metal material in both the circumferential and axial orientation to demonstrate that the background noise associated with the IDweld repair does not degrade the flaw detection capability.

For OD initiated and/or embedded flaws, EDM notches (axial and circumferential) will be made in the base material and beneath the weld inlay repair region. The notches will address an embedded flaw that penetrates to the repair weld interface, as well as a flaw that potentially grows into the repair weld region. The test will employ the existing inspection tooling, procedures, and training. The test will demonstrate both the flaw detection capability and the ability to detect flaw growth into a weld repair. As in the above case, notches in both the base material and weld repair region will be used to demonstrate equivalent inspection capability.

Only EDM notches will be used for the purpose of this demonstration of equivalency between base material and weld repair regions. It has been shown that the weld repair has negligible effects on the inspection; therefore, cold isostatically pressed notches will not be used. A comparison of results between base metal and weld repair regions will be used to assess the efficacy of the NDE in the repaired region.

SCE is planning to have an UT qualified NDE Level Ill, that is not an employee of either SCE or the inspection vendor, review the results of this study.

SCE anticipates a potential need to use the modified embedded flaw repair process if the indication previously identified in CEDM # 56 is determined to have grown since the Cycle 13 refueling outage. As described in the approved Westinghouse embedded flaw Topical Report (Reference 3), and supplemented by the evaluations provided in the attachment, SCE has concluded that the proposed repair process provides an acceptable alternative to repair RVHP.

5.0 Proposed Altemative and Basis for Use PROPOSED ALTERNATIVE The axial indication subject to this repair is located on the downhill side of CEDM # 56 near the zero degree reference. This indication extends from approximately 0.7 inch below the bottom of the adjoining portion of the J-weld, to approximately 0.4 inch below the top of the adjoining portion of the J-weld. This indication exceeds 75 percent depth from the OD surface over an axial length extending from approximately -0.1 inch to +0.4 inch above the bottom of the J-weld.

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10 CFR 50.55a Request Number ISI-3-22 The proposed ID inlay repair will consist of an excavation of penetration base metal from the ID surface adjacent to the indication in CEDM # 56.

The excavation will be designed to minimize residual stresses on the penetration ID surface as described in the approved embedded flaw Topical Report WCAP 15987-P Revision 2 and Attachment 1. The maximum excavation depth will be limited to an area directly adjacent to the indication and will be tapered in depth toward the weld periphery. The maximum excavation depth will be between approximately 3/16 inch and 1/4 inch. This depth will ensure that the residual embedded flaw will be less than 72 percent through the 0.661 penetration wall. The excavation will extend circumferentially towards the 90 degrees and 270 degrees orientations where tensile stresses are minimal as described in the attachment. The repair weld will extend approximately 1 inch (from 0.3 inch below the lowest point of the indication), upward to an area of minimal stress, at least 0.75 inch above the top of the weld.

The repair design, implementation, and inspection is equivalent to the ID inlay repairs described in WCAP 15987-P Revision 2. SCE has performed a Code reconciliation to verify that the bases contained in WCAP 15987-P Revision 2 are applicable to SONGS Unit 3.

The embedded flaw repair overlay welds on the inside diameter (ID) of the penetration tube material will consist of a minimum of 3/16 inch deposited layers of weld embedding the indication, consistent with Reference 3. To minimize welding induced residual stresses and material distortion while ensuring continued service life, a weld deposit of approximately 1/4 inch will be applied. The weld materials, design and techniques employed for the approved seal weld repair are equivalent to the process required for a structural base metal repair weld.

BASIS FOR USE In the NRC Safety Evaluation Report (SER) (Reference 3) the NRC staff concluded that, subject to the conditions of the SER, the embedded flaw process provides an acceptable level of quality and safety. It also concluded that licensees may reference the SER and technical report.

The proposed modification to the approved repair process reflects a new application of that repair. However, the efficacy of the repair to achieve an appropriate level of safety and quality is not adversely affected by this new application.

The proposed modification to examination methods for the ID inlay repair weld has been demonstrated to be adequate for flaw detection and sizing for similar repair geometries.

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10 CFR 50.55a Request Number ISI-3-22 The embedded flaw repair process is considered a permanent repair that will last through the useful life of the RVHP. As long as a PWSCC flaw remains isolated from the primary water environment the only known mechanism for any further potential propagation is fatigue. The calculated fatigue usage in this region is very low because the reactor vessel head region is isolated from the transients that affect the hot leg or cold leg piping.

Calculations performed in support of SCE Relief Requests ISI-3-13 and ISI-3-21 have shown that the existing flaw will remain within Code margins for at least 10 years. As described inAttachment I to this enclosure, the proposed repair will reduce the indication dimensions and will extend the assured repair life. The methodology used in Attachment "Structural Evaluation of the Proposed Embedded Flaw Repair of the Indication in Reactor Vessel Head Penetration No. 56 at SONGS Unit 3," for determining flaw acceptance is consistent with the methodology approved in the Westinghouse Topical Report WCAP 15987-P Revision 2.

The thickness of the weld used to embed the flaw has been set to provide a permanent embedment of the flaw. As shown in Attachment 1, the embedded flaw process imparts less residual stresses than weld repair following the complete removal of the flaw.

Therefore, the embedded flaw repair process is considered to be an alternative to Code requirements that provides an acceptable level of quality and safety, as required by 10 CFR 50.55a(a)(3)(i).

6.0 Duration of Proposed Alternative Relief is requested for the third ten-year in-service inspection interval at SONGS Unit 3, which began on August 18, 2003 and is scheduled to end on August 17, 2013.

7.0 References

1. U. S. Nuclear Regulatory Commission (NRC) First Revised NRC Order EA-03-009, "Issuance of Order Establishing Interim Inspection Requirements for Reactor Pressure Vessel Heads at Pressurized Water Reactors," issued February 20, 2004 7 of 8

10 CFR 50.55a Request Number ISI-3-22

2. Letter from H.A. Sepp (Westinghouse) to the Document Control Desk (NRC) dated May 16, 2003;

Subject:

Request for Review and Approval Westinghouse Topical Report WCAP 15987-P,"Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations" (Proprietary) and WCAP-1 5987-NP (Non-proprietary)

3. Letter from H. N. Berkow, (NRC) to H. A. Sepp, (Westinghouse) dated July 3, 2003;

Subject:

"Acceptance for Referencing - Topical Report WCAP 15987-P, Revision 2, "Technical Basis of the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations, (TAC No.

MB8997)"

4. Letter from A. E. Scherer (SCE) to the U.S. Nuclear Regulatory Commission (NRC) Document Control Desk dated December 3, 2003;

Subject:

Docket Nos. 50-361 and 50-362, Third Ten-Year Inservice Inspection (ISI) Interval Relief Request ISI-3-8 Request to Use Alternative To ASME Code Rules For The Embedded Flaw Repair Process, San Onofre Nuclear Generating Station Units 2 and 3

5. Letter from Stephen Dembeck (NRC) to A. E. Scherer (SCE) dated May 5, 2004;

Subject:

San Onofre Nuclear Generating Station, Units 2 and 3, Inservice Inspection Program Relief Request ISI-3-8, Embedded Flaw Repair Process (TAC Nos. MC1470 and MC 1471)

6. Letter from A. E. Scherer (SCE) to the U.S. Nuclear Regulatory Commission (NRC) Document Control Desk dated October 26, 2004;

Subject:

Docket No. 50-362, Third Ten-Year Inservice Inspection (ISI)

Interval Relief Request ISI-3-13 Request to Use Alternative To ASME Code Rules For The Embedded Flaw Repair Process for Reactor Vessel Head Penetration 56, San Onofre Nuclear Generating Station Unit 3

7. Letter from Robert A. Gramm (NRC) to A. E. Scherer (SCE) dated December 23, 2004;

Subject:

San Onofre Nuclear Generating Station (SONGS) Unit 3- Re: Request for Relief from Requirements of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code (CODE) Concerning Reactor Pressure Vessel Head Penetration (RVHP) Repairs (TAC No. MC4969) 8 of 8

ATTACHMENT 10 CFR 50.55a Request Number ISI-3-22 Structural Evaluation of the Proposed Embedded Flaw Repair of the Indication in Reactor Vessel Head Penetration No. 56 at SONGS Unit 3

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment Structural Evaluation of the Proposed Embedded Flaw Repair of the Indication in Reactor Vessel Head Penetration No. 56 at SONGS Unit 3

1. Introduction The embedded flaw repair technique is considered a permanent repair because as long as a Primary Water Stress Corrosion Cracking (PWSCC) flaw remains isolated from the primary water (PW) environment it cannot propagate. Since Alloy 52 (690) weldment is considered highly resistant to PWSCC, a new PWSCC crack should not initiate and grow through the Alloy 52 overlay to reconnect the PW environment with the embedded flaw. The resistance of the alloy 690 material has been demonstrated by laboratory testing for which no cracking of the material has been observed in simulated PWR environments, and in approximately 10 years of operational service in steam generator tubes, where likewise no PWSCC has been found. This experience has been documented in EPRI Report TR-109136, "Crack Growth and Microstructural Characterization of Alloy 600 PWR Vessel Head Penetration Materials," [1] and other papers.

In WCAP-1 3565, Revision 1 [2] the critical flaw length for an axial flaw was discussed and it was stated that the critical size for such a flaw would be through the wall in thickness and over 20 inch in length. The basis for this determination is found on page 12 of WCAP-1 3565, Revision 1 [2], where critical length is identified as equal to 13 inch plus the head thickness. The critical length for a circumferential through-wall flaw was shown to be over 90 percent of the circumference. Similar conclusions were reached in the CEOG report CEN-607

[3] for axial flaws, and CEN 614 [4] for circumferential flaws.

Review and approval of these reports by the NRC staff was documented in a November 19, 1993 Safety Evaluation Report [5] transmitted to Mr. W. Rasin, Director of NUMARC at that time. These conclusions remain valid today. Based upon these approvals, no additional flaw evaluation is needed as part of an embedded flaw repair.

The "embedded flaw" repair methodology has been approved on a generic basis by the NRC in July 200317]. It was also approved on a plant specific basis by the NRC in at least two separate SERs, the first for North Anna 2, dated Feb. 5, 1996[8], and the second for DC Cook 2, dated April 9, 1996[9].

The embedded flaw repair to be discussed herein is a structural repair designed to seal cracks from exposure to the PWR environment, as well as to add structural thickness to the head penetration. The process has already been approved as a non structural overlay, in reference 7, but the post overlay inspection requirements imposed by NRC are the same as those for a structural 1 of 12

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment overlay of a pipe. Likewise, the weld material is identical to that used for structural overlays, so there is no longer any need to limit the application to being non-structural.

Westinghouse has developed the basis for this embedded flaw repair with three complementary approaches:

• Stress and Fracture Analysis

• Laboratory testing

• Field Experience Each of these areas will be reviewed in detail in the paragraphs to follow.

Stress and Fracture Mechanics Analysis. To investigate the effect of a patch repair on the stresses in a typical head penetration, a finite element model was constructed, as shown in Figure I. The OD of the tube modeled was 4.0 inch, and the thickness was 0.625 inch. The patch was applied to the ID of the tube, centered on the uphill side of the tube, and directly opposite the J-grove attachment weld. The patch was two inch wide, and extended up to approximately 0.75 inch above the top of the weld, and then downward to well below the weld, away from the highest stressed region near the weld. Stresses were determined at several locations, under steady state conditions, at 600F.

The weld overlay causes compressive stresses in the base metal under the weld itself, because of the shrinkage of the weld during the solidification process. The areas of concern are near the boundaries of the patch, where the stresses are generally tensile. On the vertical edges of the patch, this problem has been solved by positioning the patch such that the vertical edges are located in the compressive stress field in the head penetration tube.

The stresses in the un-repaired penetration caused by the J-groove welding process are very high at a plane through the penetration, at the location nearest to the center of the head [called the uphill side, or 180 degree location here], and also at a location directly opposite to that spot [defined as 0 degrees]. These two locations are typically where the service induced cracks have been found. At positions of 90 degrees and 270 degrees, the stresses are actually compressive, as shown for example in Figure 2. It is this fact that allows the patch to be effective, since the stresses along the edges of the patch after the patch installation are still low.

The top of the patch is another area of concern, because the stresses in the base metal along the top of the patch can be rather high. Figures 3 and 4 show this for both hoop and axial stresses, but also reveal another important finding, and that is that the tensile stresses do not penetrate much beyond the thickness of the patch, and beyond that point they drop precipitously, becoming compressive at a depth equal to about twice the thickness of the patch. Therefore, the positioning of the top of the patch sufficiently far above the high stress region is important.

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10 CFR 50.55a Relief Request Number ISI-3-22 Attachment The recommendation is that the top of the patch be positioned at least 0.75 inch above the top of the J-groove weld.

Laboratory Testing. Measurements have been made of weld inlay repairs, and reveal additional key findings that support the technical basis for the embedded flaw repair. The most extensive measurements were reported in reference 6. In this project, patch repairs on the IDwere made, and residual stress measurements were made, in the locations shown in Figures 5 and 6.

Measurements were made in both the as-received condition and after the application of the embedded flaw repair. The results are listed in Table 1, both on the top of the weld, and along the side boundary of the patch.

Along the top boundary of the patch, the hoop stresses ranged from 40-50 ksi at the surface, slightly lower than the finite element determined stresses. The axial stresses are also high, about 65 ksi, similar to the finite element stresses discussed above. These stresses are local to the top boundary of the patch, and drop quickly with distance from the edge of the patch. Along the vertical boundaries of the patch, the stresses before the repair ranged from low to strongly compressive, and remained low after the application of the weld, as shown in Table 1.

A range of weld overlay thicknesses has been investigated. It was found that the thickest overlays produced measurable deformation of the tubes, as shown in Chapter 6 [6]. Smaller deformations occur with a smaller amount of weld metal thickness. One of the benefits of the embedded flaw overlay is that with a smaller amount of weld deposit the deformation and residual stresses are minimized. Distortions were measured in [6] and reported in Table 2. Additional distortion measurements were reported for CEDM tubes and the thinner ICI penetrations, and are reproduced in Tables 3 and 4. Ineach of these tables the thickness of the patch is shown, as well as the thickness of the penetration tube.

In each of these tables, the ratio of patch depth to tube thickness was also reported. It can be seen that the distortions measured are proportional to this ratio. The ratio of interest for the SONGS repair is 0.30. The distortions measured for the patch weld thickness to tube thickness ratios of interest are very small, all less than 0.033 inch. This means that the proposed repair will not cause any meaningful distortion of the tube.

Field Experience. An example of an embedded flaw repair applied to the ID of head penetration is found at the DC Cook Unit 2. That IDembedded flaw was installed in penetration 75, in 1996. The patch was two inch wide, and has been inspected with eddy current in 2002, 2003, and recently in 2006, with no evidence of any deterioration during service. The field experience demonstrates that the embedded flaw repair is a reliable technique.

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10 CFR 50.55a Relief Request Number ISI-3-22 Attachment The residual stresses produced by the embedded flaw technique have been measured and found to be relatively low, as discussed above [6]. This implies that no new cracks will initiate and grow in the area adjacent to the repair weld.

This information, and the D.C. Cook patch experience, were used to size the proposed repair at SONGS. There are no other known mechanisms for significant crack propagation in this region because the cyclic fatigue loading is considered negligible. Cumulative Usage Factor (CUF) in the upper head region was calculated in the reactor vessel design report, as well as in various aging management review reports as less than 0.2.

The thermal expansion properties of Alloy 52 weld metal are not specified in the ASME code, as is the case for other weld metals. In this case, the properties of the equivalent base metal (Alloy 690) should be used. For that material, the thermal expansion coefficient at 6000 F is 8.2 E-6 in/in/degree F as found in Section II Part D. The Alloy 600 base metal has a coefficient of thermal expansion of 7.8 E-6 inin/ degree F.

The effect of this small difference in thermal expansion is that the weld metal will contract more than the base metal when it cools, thus producing an additional compressive stress on the Alloy 600 tube or the attachment weld, where the crack may be located. This effect has already been accounted for in the residual stress measurements reported in the technical basis for the embedded flaw repair [2].

The small residual stress produced by the embedded flaw weld will act constantly, and therefore, should have no impact on the fatigue effects in the CRDM region. Since the stress would be additive to the maximum as well as the minimum stress, the stress range would not change, and the already negligible usage factor, noted above, for the region would not change at all.

2. References

1. TR-109136, "Crack Growth and Microstructural Characterization of Alloy 600 PWR Vessel Head Penetration Materials," EPRI, December 1997.

2. WCAP-1 3565, Revision 1,"Alloy 600 Reactor Vessel Head Adapter Head Cracking Safety Evaluation."

3. CEN-907 'Alloy 600 Reactor Vessel Head Adapter Head Cracking Safety Evaluation, Axial Flaws."

4. CEN-914 "Alloy 600 Reactor Vessel Head Adapter Head Cracking Safety Evaluation, Circumferential Flaws."

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10 CFR 50.55a Relief Request Number ISI-3-22 Attachment

5. NRC SER for WCAP-14024 and WCAP-1 3565 NRC letter from W. T.

Russell to W. Raisin, NUMARC, dated November 19,1993.

6. WCAP-1 3998, "RV Closure Head Penetration Tube IDWeld Overlay Repair," March 1994. (Westinghouse Proprietary).

7. WCAP-1 5987, Rev. 2-P-A, Technical Basis for the Embedded Flaw Process for Repair of Reactor Vessel Head Penetrations", December 2003. (Westinghouse Proprietary)

8. NRC SER for Use of an alternate Repair Technique for Reactor Vessel Head Penetrations for North Anna Unit 1, NRC letter from D.B. Mathews to J.P. O'Hanlon, Virginia Electric and Power Co., Feb. 5,1996.

9. NRC SER for Use of an alternate Repair Technique for Reactor Vessel Head Penetrations for D.C. Cook Units I and 2, NRC letter from D.B.

Mathews to Indiana Michigan Power Co., April 9, 1996.

Table 1: Results of Residual Stress Measurements for Internal Embedded Flaw Repair (Locations shown in Figures 5 and 6)

Location l Hoop l Axial (numberlangle) l (Before/After) l (Before/After) l Top Boundary of Patch 5 (360) 1 21.0140.2 6.8 164.3 11,11b(180) 1 -26.4/51.0 -37.6168.2 l One Inch Above Top Boundary 16 (180) NAI-33.5 NAI-14.0 l Side Boundary of Patch 12b (315) 13.4/38.6 -4.7/ -16.9 14b (260) NA /2.1 NA / -12.2 15b (270) -78.8 / NA -67.0 / NA 5 of 12

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment Table 2: Measured Distortions on CRDM Tubes CRDM Tubes: WCAP 13998 [6]

OD = 4.0 in.

Tube Thickness = 0.625 in.

Weld Depth (in) Average OD Shrinkage Maximum OD Shrinkage

[weld depthAtube thkness) (in) (in) 0.09 [0.1441 0.0085 0.022 0.25 [0.401 0.012 0.022 0.47 ((0.75] 0.085 0.099 Table 3: Measured Distortions on CEDM Tubes CRDM Tubes: PCI OD = 4.0 in.

Tube Thickness = 0.625 in.

Weld Depth (in) Repair Size Maximum OD Shrinkage

[weld depth/tube thkness] (in) (in) 0.150 [0.24] 2" wide x 3" long 0.033 0.150 [0.24) 2" wide by 5" long 0.020 Table 4: Measured Distortions on ICI Tubes ICI Tubes: PCI OD = 5.563 in.

Tube Thickness = 0.469 in.

Weld Depth (in) Repair Size Maximum OD Shrinkage

[weld depth/tube thkness] (in) (in) 0.100 [0.21] 2" wide x 2" long 0.006 in. @ 135 degrees 0.100 [0.21] 2" wide by 2" long 0.016 in. @ 180 degrees 6 of 12

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment Figure 1: Finite element model c)f patch Repair on CRDM penetration. The patch is shown in purple, and eictends into the penetration ID for a distance of 0.125 inch 7 of 12CO

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment

_ ANIJ2YS5.7 JAN I.S 2002 26:31z44 PLOT ND. 2 TIwx=4004 RSY9=SCW iAeX =.427110 XV zV =

XE' =-.69385

-_ =63640i2 PREI}SE HIDOM NOIDAL SOLUTION Tuc!=4004 RSYS=BOLU rM~ = 4265~2 SMN =-52505 Oac ='?2723

- 5sa I20000

-10000

__300 40000 50a000 100000 Wat3clm(49.7dcYC SBH4.05,f2.720.2.§N-03.~A - qrating Figure 2: Axial Stress Distribution at Steady State for the Outermost CEDM (49.7 Degrees) Penetration, Along a Plane Oriented Parallel to, and Just Above, the Attachment Weld 8 of 12

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment

-.- Base Case . Lon(oi (Opeating) -- 1.6"lnlay(Operating) I

_ 40000 I

$ 20000

-40000- 4l4 l i 4 0 1t6 1I8 3/16 1/4 5/16 3/8 7/16 12 9/16 SI8 1W OIstace *om ID fi Nft: BaseCae OAtLU b gtthe Bornofthe WAhBl~d Figure 3: Hoop Stress distribution through the tube thickness, at the top of the Weld Patch 9 of 12 CC0 3

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment 1-- Base Case Ihbx Locason (Opisning) 1l' Inlay(OpersUng) I i

1/16 1 3/16 1/ 5/lB 34S 7/16 1/2 9/t1B 54 TW Ustance ftm ID ) Note Be CeOutL is attesBtmofthe phl Weld Figure 4: Axial stress through the tube thickness, at the top of the Weld Patch 10 of 12

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment 12

.2 E

I I

I-S I

Does Figure 5: Locations for Residual Stress Measurements reported in [6],

before patch Installation. Sinusoidal curves represent the boundaries of the J-groove attachment weld, and the figure represents the patch unrolled.

11 of 12

10 CFR 50.55a Relief Request Number ISI-3-22 Attachment 12 E

I

.1.

U, 0

0 Figure 6: Locations for Residual Stress Measurements reported in [6], after patch Installation. Sinusoidal curves represent the boundaries of the J-groove attachment weld, and the figure represents the patch unrolled.

12 of 12