ML20206C848
| ML20206C848 | |
| Person / Time | |
|---|---|
| Site: | Hope Creek  |
| Issue date: | 04/22/1999 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20206C846 | List: |
| References | |
| NUDOCS 9905030220 | |
| Download: ML20206C848 (4) | |
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SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION
_ RELIEF REQUESTS ASSOCIATED WITH CORE SPRAY NOZZLE WELD REPAIR PUBLIC SERVICE ELECTRIC & GAS COMPANY HOPE CREEK GENERATING STATION DOCKET NO. 50-354 1
1 1.0 INTRODUQTION Hope Creek Generating Station (HCGS) Technical Specification 4.0.5 states that the inservice inspection of the American Society of Mechanical Engineers (ASME) Code Class 1,2, and 3 components shall be performed in accordance with Section XI of the ASME Boiler and Pressure Vessel Code and applicable addenda as required by Title 10 of the Code of Federal Reaulations (10 CFR), Section 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i). Section 50.55a(a)(3) states that attematives to the requirements of paragraph (g) may be used, when authorized by the Nuclear Regulatory Commission (NRC), if (i) the proposed attematives would provide an acceptable level of quality and safety, or (ii) compliance with the specified requirements would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety.
By letter dated July 28,1998, Public Service Electric and Gas Company (PSE&G or the licensee) submitted relief requests associated with changes made to the repair plan for core spray nozzle weld N5B. The licensee performed the repair during the seventh refueling outage at HCGS.
The original repair plan, submitted by PSE&G in letters dated October 9,1,997, and October 15,1997, proposed an attemative to the ASME Code,Section XI,4 repair requirements under 50.55a(a)(3). The proposed altemative was approved by the NRC in a safety evaluation dated October 17,1997, in a letter to L. Eliason, PSE&G, from J. Stolz, NRC (reference TAC No. M99755). Subsequently, two changes to the repair plan were submitted by PSE&G in letters dated November 12,1997, and November 21,1997. However, the licensee submitted these changes as commitment changes rather than relief requests. The PSE&G submittal dated July 28,1998, re-characterized these changes as relief requests rather than commitment changes and provided additionalinformation. The changas made to the repair plan were: (1) the increase of the maximum interpass temperature during the holding period following post-weld heat treatment (PWHT) from ambient temperature +50*F to ambient i
temperature +100*F and (2) the elimination of the need for the repair of the overlay to meet f
the criteria of ASME Section 111 by using Code Cases N-504-1 and N-416-1 as attematives.
9905030220 990422 PDR ADOCK 05000354-P PDR
. The licensee found the core spray nozzle weld NSB leaking during a routine tour of the drywell in the seventh refueling outage. Weld NSB is a dissimilar metal weld (Alloy 182) connecting the core spray nozzle (SA 508 Class 2 low alloy steel) to the inconel safe-end. The licensee performed a repair by applying a full structural overlay (Alloy 52) to the subject core spray nozzle weld. The design and inspection of the weld overlay followed the guidelines in Code Case N-504-1 and NUREG-0313, Revision 2. Because the overlay design has a portion of the overlay extending onto the core spray nozzle, the licensee used a temper bead welding technique in accordance with Code Case N-432 for fabricating that portion of the weld overlay.
The purpose of using the temper bead welding technique was to avoid excessively hardening the low alloy steel nozzle material.
The licensee stated that the changes to the repair plan were consistent with the intent of the original repair plan and had no detrimental effect on the structuralintegrity of the repair. The staff's evaluation of the licensee's relief requests regarding the two changes made to the repair plan is discussed below.
2.0 EVALUATION Maximum Interpass Temperature The first relief request involved the increase of the maximum interpass temperature during the holding period following PWHT from ambient temperature + 50*F to ambient temperature
+100*F. The licensee stated that this change would allow for continued uninterrupted welding in fabricating the balance of the non-temper bead portion of the weld overlay while still allowing the temper bead portion of the overlay (i.e., the SA-508, Class nozzle material) to be held for 48 hours5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> at ambient temperature prior to the acceptance nondestructive examination (NDE) being performed.
The staff evaluated the potentialimpact of this change to the quality of the overlay repair. The staff determined that the change to the maximum interpass temperature would not detrimentally impact the quality of the overlay repair and, therefore, is acceptable. The staff's determination is based on the following considerations:
4 (a) in the overiay welding of F43 to F43 (Alloy 52) materials, the small increase (50*F) in the interpass temperature is not expected to affect the properties of the non-temper bead portion of the overlay.
(b) In Code Case N-432 for temper bead welding, there is a requirement for a 48-hour holding period at ambient temperature prior to the performance of a nondestructive examination of the repair area. The licensee stated that, depending on plant conditions, the ambient temperatures of primary components could vary from 80*F to 150*F. For repairing the core spray nozzle, the repair plan defines the ambient temperature as 150*F (50*F + ambient temperature of the component). The purpose of the holding period is to ensure that there is adequate time for the hydrogen to leave the repair area to avoid the potential for delayed hydrogen cracking. Therefore, the 50*F increase of the maximum
. interpass temperature during the holding time is expected to have a potentially beneficial effect of removing the residue hydrogen more efficiently.
(c) The staff notes that the allowed maximum interpass temperature in fabricating the first three temper bead layers is 400*F. Therefore, the staff does not expect the use of a maximum interpass temperature of 200*F for the non-temper bead portion of the overlay to have any undesirable effect to the material properties of the temper bead portion of the overlay and the heat-affected zone of the low alloy steel nozzle. Furthermore, the licensee did not credit the first three layers of the temper bead portion of the overlay structurally in the design of the oveday.
Acceotance Criteria for Post-Reoair Examinations The second relief request involved the elimination of the need for the repair to meet the acceptance criteria of ASME Section 111 by using Code Cases N-504-1 and N-416-1 as an attemative. The licensee reported that a laminar flaw was identified in the weld overlay by using 0* straight beam in the GE's automated Smart 2000 UT system. However, this flaw could not be confirmed by inspecting with manual UT. For disposition purposes the licensee conservatively assumed this flaw to be lack of fusion. The circumferentially oriented laminar flaw has a length of about 8.75 inches and a width of 0.32 inches. The depth of the flaw is not discemable.
In accordance with Code Case N-504-1 for weld overlay repair, it is necessary to perform a hydrostatic test after completion of the weld overiay repair because there is a through-wall flaw in the repaired component. The licensee referenced Code Case N-416-1, which allows the performance of a system leakage test at nominal operating pressure and temperature in lieu of the hydrostatic test, provided that volumetric and surface examinations are performed in accordance with ASME Code, Section Ill,1992 Edition with no Addenda. However, the lamination in the overlay did not meet the UT acceptance criteria in the ASME Code, Section lil, NB-5330. Therefore, a Code repair of the lamination in the overiay would be required in i
order to meet Section 111 requirements. The licensee requested the use of the acceptance criteria of ASME,Section XI, IWB 3500,1989 Edition with no Addenda, in beu of tne referenced ASME Code, Section 111 requirements. No specific requirements exist for pre-service examinations versus inservice examinations for laminar flaws, i
i The staff reviewed the licensee's relief request and determined that a repair of the overlay is not necessary. Therefore, the licensee's use of the acceptance criteria of ASME,Section XI, IWB-3500,1989 Edition with no Addenda as originally specified in Code Case N-504-1 is acceptable. Although the results of NDE do not satisfy the provisions in Code Case N-416-1, I.e., a lamination is present, the staff agrees that the use of a leakage test in lieu of a hydrostatic test is acceptable. The staff's detemiination is based on the following considerations.
(a) The subject overlay repair was approved by the NRC pursuant to Code Case N-504-1 as an altemative to the ASME Code,Section XI requirements. The Code Case allows the use of the preservice requirements of IWB-3514-2 for planar i
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4 repairs but does not specifically address faminations. However, the staff feels it is appropriate to use the flaw acceptance criteria in ASME Code,Section XI, to evaluate the lamination. The reported laminar flaw has an area of 2.5 inches which is much smaller than the Code allowable (7.5 inches ) in Section XI, 2
Table IWB 3514-3. Based on the result of this evaluation we conclude that the reported flaw would not impact the structural integrity of the repair overlay.
Therefore, the subject weld overlay can be used "as-is" without repair.
(b) If repa!rs were performed on the overlay, the repairs could create an adverse residual stress distribution in the overlay repaired component which might promote the initiation and growth of the cracks. Industrial experience has shown that, the probacle cause in a number of cases, resulted from the repair welding.
(c) Further, the subject overlay repaired weld will be inspected in accordance with GL 88-01 for overlayed components.
3.0 CONCLUSION
Based on the above evaluation, the staff concludes that the proposed and implemented altematives provided an acceptable level of quality and safety. Therefore, PSE&G's proposed relief requests associated with changes made to the repair plan for core spray nozzle weld NSB are authorized pursuant to 10 CFR 50.55a(a)(3)(i).
PrincipalContributor: W Koo Date: April 22, 1999 4
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