ML20217K047
| ML20217K047 | |
| Person / Time | |
|---|---|
| Site: | Duane Arnold  |
| Issue date: | 04/01/1998 |
| From: | NRC (Affiliation Not Assigned) |
| To: | |
| Shared Package | |
| ML20217K010 | List: |
| References | |
| NUDOCS 9804070108 | |
| Download: ML20217K047 (5) | |
Text
c urg gM k UNITED STATES g j
't NUCLEAR RE2ULATORY COMMISSION
. WASHINGTON, D.C. 20066 0001 o
- ** , SAFETY EVALUATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION OF RELIEF REQUEST NDE-R004 FOR THE THIRD INSERVICE INSPECTION INTERVAL EQB IES UTILITIES INC.
DUANE ARNOLD ENERGY CENTER DOCKET NUMBER: 50-331
1.0 INTRODUCTION
The Technical Specifications for the Duane Amold Energy Center (DAEC), state that the i inservice inspection of the American Society of Mechanical Engineers (ASME) Code Class 1,2, i 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 10 CFR 50.55a(g), except where specific written relief has been granted by the Commission pursuant to 10 CFR 50.55a(g)(6)(i).
10 CFR 50.55a(a)(3) states that attematives to the requirements of paragraph (g) may be used, when authorized by the 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. i Pursuant to 10 CFR 50.55a(g)(4), ASME Code Class 1,2, and 3 components (including supports) shall meet the requirements, except the design and access provisions and the pre-service examination requirements, set forth in the ASME Code,Section XI, " Rules for Inservice Inspection of Nuclear Power Plant Components," to the extent practical within the limitations of design, geometry, and materials of construction of the components. The regulations require that ,
inservice examination of components and system pressure tests conducted during the first 1 10-year interval and subsequent intervals comply with the requirements in the latest edition and addenda of Section XI of the ASME Code incorporated by reference in 10 CFR 50.55a(b) 12 months prior to the start of the 120-month interval, subject to the limitations and modifications listed therein. The applicable ASME Code,Section XI, for the third inspection interval of the Duane Amold Energy Center, is the 1989 Edition. 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 Commission approval. Pursuant to 10 CFR 50.55a(g)(5), if the licensee determines that conformance with an examination requirement of Section XI of the ASME Code is not practical for its facility, information shall be submitted to the Commission in support of that determination and a request made for relief from the ASME Code requirement. After evaluation of the determination, pursuant to 10 CFR 50.55a(g)(6)(i), the Commission may grant relief and may impose attemative requirements that are determined to be authorized by law, will not endanger life, property, or the common defense and security, and are otherwise in the public interest, giving due consideration to the burden upon the licensee that could result if the requirements were imposed.
9s040701os 9s04o1 PDR ADOCK 05000331 P PDR
~ In a letter dated October 15,1997 as supplemented on December 5,1997, IES Utilities (the licensee) submitted a request for relief to perform one more radiographic inspection of the non-code repair area on the "D" MSIV when the valve is disassembled for other reasons. The licensee stated that a conservative estimate of growth of a postulated flaw indicated that for the remaining life of the plant, the flaw was bounded by an evaluation in accordance with paragraph IWB-3600 of the applicable ASME Code,Section XI and the disassembly of the MSIV solely for the purpose of performing a radiographic inspection during the past refueling outage 13 or 14, would have resulted in undue hardship or unusual difficulty without a compensating increase in the level of quality and safety.
. 2.0 DISCUSSION.
System / Component (s)
Code Class: 1
References:
IWA-4000, IWB-4000, IWB-4120 Examination Category: B-M-2 item Number: B12.50
Description:
Valve bodies exceeding NPS 4" casting repair Component Number: Main steam isolation valve "D" outboard, CV-4421 Code Requirement ASME Section XI IWA-4000, requires repairs to be performed in accordance with owner's design specification and construction code. lWB-4120, requires a complete removal of the defect or flaw. lWB-4230 states that after final grinding, cavities prepared for welding, shall be examined by magnetic particle or liquid penetrant to ensure indications have been reduced to an acceptable limit in accordance with IWA-3000. The repair weld shall be post-weld heat treated.
Licensee's Basis for Relief A subsurface casting shrinkage was uncovered during a routine maintenance machining operation to correct unacceptable seat leakage of the "D" main steam isolation valve CV-4421 and a weld overlay in the affected area was deposited. A code repair to the MSIV would require I a post-weld heat treatment (PWHT) of the valve body casting. Prior experience with PWHT has demonstrated that unacceptable distortion of the valve body may occur and correction of the distortion may not be feasible. Hence, a non-code repair was performed without post-weld heat treatment. A prior relief request approved by the NRC for the second inspection interval, stipulated performance of two radiographic inspections (RT) during refueling outages 13,14,15, or 16. However, disassembly of the "D" outboard MSIV solely for the purpose of performing a radiograph is undesirable for the following reasons;
- a. As discussed in the NRC safety evaluation transmitted by letter dated December 27, 1994, "Per the findings of NUREG-1169, excessive valve disassembly should be avoided if the leak tightness of valves such as MSIVs is to be optimum. Disassembly for no other reason than to perform a radiograph (necessary in this case due to overall valve size and thickness) is contrary to the guidance of the NUREG."
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< b. The DAEC has lemmed from extensive experience that an MSIV can not just be taken ;
apart and put back together. It requires extensive inspection, machining, grinding, and !
possible weld repair prior to reassembly to ensure the lowest practical leakage levels. !
This effort requires engineering personnel, mechanics, and machinists, unnecessarily diverting these resources from other outage projects.
- c. The disassembly and reassembly would result in unnecessary expenditure of both resources and exposure. Simple disassembly and reassembly costs about $20,000 and results in approximately 0.5 rem exposure. Refurt>ishment, including parts and labor, could increase the cost by approximately $60,000,
- d. The MSIV is located in the Steam Tunnel, a contaminated and congested work area l containing extensive safety-related equipment. During the performance of the RT all l other work in the Steam Tunnel is deferred, delaying work activities on other equipment.
The radiography performed during RFO 12 indicated resolution of the 1T hole in a #40 )
penetrameter which represents a sensitivity of 1.26%. Since no indication is visible, a i conservative estimate of the remaining flaw size may be obtained by assuming the flaw to be the size of the smallest hole in the penetrameter which was resolved. The size of the remaining flaw can therefore be conservatively estimated as 1.26% of wall thickness. Since the wallis about !
3.175 inches thick, the flaw size is bounded by approximately 0.04 inch.
A flaw evaluation was performed in accordance with Appendix A of ASME Section XI 1980 with the Winter 81 Addenda. The evaluation was performed for several aspect ratios (1/6,1/4,1/3,
%). The size (0.4 inch), length (2 inch) and aspect ratio (1/100) of a postulated flaw detectable by the radiography technique was estimated to be bounded by the flaw evaluation for the remaining life of the plant. Since the predicted flaw size was determined to be bounded by the evaluation, there was reasonable assurance of operational readiness and the disassembly of 4 the outboard "D" MSIV during the outage 13 or 14 solely to perform a radiographic examination would have resulted in undue hardship or unusual difficulty without a compensating increase in l the level of quality and safety. Therefore, relief is requested in accordance with 10 CFR 50.55a(a)(3)(ii).
Licensee's Alternate Examination The flaw was excavated to a depth not exceeding 20% of the wall thickness (0.6 inch in this case). A magnetic particle examination (MT) was performed to document the remaining flaw ;
dimensions. Using a 200 degree F preheat, a low heat input multipass weld was performed to i fill the excavated cavity. The integrity of weld was ensured by performing a visual examination and hot MT of each layer of weld metal. Shielded metal arc welding (SMAW) using small diameter electrodes was employed. The fluxing action of the SMAW electrodes (E7018 in this case) would aid in removal of any casting impurities that may have been present in the fluxing area.
After machining of the weld was completed, an MT of the machined surface was performed. ,
The repaired area was radiographed to ensure that there was no defect in the weld deposit and that the casting around the repaired area met the original construction code. Structuralintegrity i
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i for the remaining embedded flaw was demonstrated by performing bounding analyses using the appropriate Section XI embedded flew evaluation methods. The radiography used for the repair was capable of resolving a flaw size of 1.26% of the wall thickness. This size of flaw is bounded by flaw evaluation per the requirements of IWB-3600 of the ASME Section XI 1980 Edition with the Winter 81 Addenda, which determined that the flaw size was acceptable for 40 years of plant operation.
One more radiographic inspection of the non-code repair area on the *D" outboard MSIV will be performed when the valve is disassembled for other reasons. The inspection results will be compared with the previous results per IWB-3121.
3.0 EVALUATION.
The staff has determined that the weld repair of a subsurface casting shrinkage in "D" MSIV followed sound engineering practice but it did not meet the requirements of the applicable construction code due to no post-weld heat treatment (PWHT). - Nevertheless, compliance with the Code by performing a localized PWHT could render the component unserviceable due to unacceptable distortion. Due to application of preheat to the weld area, multi-pass welding of the groove using small diameter electrodes and machining of the final pass weld, as performed on the repair weld, it is believed that the resulting residual stresses in the weld and the heat -
affected zone are of low order of magnitude and hence, there will be no adverse effect on the integrity of the repair weld. Furthermore, the structuralintegrity of the repair weld has been ensured by magnetic-particle testing of each layer of the weld and a radiographic inspection of the completed weld. However, the staff had previously imposed two additional radiographic j inspections of the repair weld during subsequent outages 13,14,15, and 16. The radiographic i inspection could not be performed during the outage 13 or 14 since the valve was not disassembled for maintenance or repair. The licensee has now proposed to perform one more radiographic inspection of the repair weld when the valve is disassembled for other reasons, as an attemative to the previous requirement of the staff. In support of licensee's proposed attemative, an analysis using the methodology of the ASME code,Section XI, of a postulated ;
flaw based on the results of radiographic inspection performed during refueling outage 12, !
indicates that the predicted size of the flaw is bounded by the evaluation for the remaining l operating life of the plant. 1 The staff has reviewed the licensee's evaluation and concluded that the proposed alternative provides a reasonable assurance of structural integrity and that the disassembly of the *D' MSIV during the outage 13 or 14 for the sole purpose of performing a radiographic inspection would have resulted in hardship or unusual difficulty without a compensating increase in the level of i quality and safety.
4.0 CONCLUSION
The staff concludes that the non-code repair of a casting shrinkage in the "D" MSIV performed during the refueling outage 12, without a post-weld heat treatment followed sound engineering practice. On the basis of licensee's evaluation of a postulated flaw in accordance with the flaw l evaluation criteria of the applicable ASME Code,Section XI, the staff has determined that it is acceptable to perform one more radiographic inspection of the repair when the valve is disassembled for other reasons. The proposed attemative in relief request (NDE-R004) is hereby authorized pursuant to 10 CFR 50.55a(a)(3)(ii) for the Duane Amold Energy Center's third 10-year inservice inspection interval based on a finding that compliance with the code
I-5- 4 would result in hardship or unusual difficulty without a compensating increase in the level of quality and safety, j 1
Principal Contributor: P. Patnaik '
Date: April 1, 1998 i
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