ML050940259
| ML050940259 | |
| Person / Time | |
|---|---|
| Issue date: | 04/04/2005 |
| From: | Norris W Materials Engineering Branch |
| To: | |
| References | |
| DG-1124, DG-1125, DG-1126, RG-1.084, RG-1.147, RG-1.193 | |
| Download: ML050940259 (15) | |
Text
EVALUATION OF CODE CASES IN SUPPLEMENT 12 to the 1998 EDITION and SUPPLEMENT 1 THROUGH SUPPLEMENT 6 to the 2001 EDITION 1
Purpose:
For Proposed Revision 33 to Regulatory Guide 1.84 (DG-1124), Design, Fabrication, and Materials Code Case Acceptability, ASME Section III, Proposed Revision 14 to Regulatory Guide 1.147 (DG-1125), Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1, and Proposed Revision 1 to Regulatory Guide 1.193 (DG-1126), ASME Code Cases Not Approved for Use, the NRC staff reviewed the Code Cases in Supplement 12 to the 1998 Edition and Supplement 1 through Supplement 6 to the 2001 Edition (except for those Code Cases pertaining to high-temperature gas-cooled reactors; certain requirements in Section III, Division 2, not endorsed by the NRC; liquid metal; and submerged spent fuel waste casks). Lists are provided indicating the proposed disposition of new, revised, and reaffirmed Code Cases. For Code Cases determined to be conditionally acceptable, a summary of the basis for the determination is provided to afford users of the ASME Code an opportunity to comment on the proposed disposition and basis.
2 Discussion of ASME Process:
Code Cases provide alternatives developed and approved by ASME to the applicable provisions of the ASME Boiler and Pressure Vessel Code. Code Cases are approved by the ASME with three-year terms. Code Cases can be categorized as one of three types: new, revised, or reaffirmed. A new Code Case addresses a specific need for the first time. Existing Code Cases may be revised or modified to address, for example, enhancements in examination techniques. Code Cases still in use and not requiring revision may be reaffirmed or approved without change by the ASME for another three years.
3 Discussion of Regulatory Process:
The NRC considers each Code Case in a supplement. New Code Cases that are determined to be acceptable by the NRC are approved as published by the ASME and may be used in the design, construction, and ISI of components and their supports for water-cooled nuclear power plants. When a determination is made that the provisions of a new Code Case need to be augmented, that Code Case is conditionally approved. These Code Cases are acceptable to the NRC within the limitations recommended by the NRC staff. Unless otherwise stated, limitations recommended by the NRC staff are in addition to the conditions specified in the Code Case. A discussion of the basis for the limitation or modification is provided, and the NRC invites public comment on these conditions. A determination may be made that a new Code Case is unacceptable for use by licensees. Code Cases determined to be unacceptable are listed in proposed Revision 1 to Regulatory Guide 1.193. A summary of the basis for the determination is provided, and the NRC invites public comment on the basis for the disapproval.
Revised Code Cases were modified in some manner by the ASME, and the NRC compares the revised Code Case to the original Code Case (that has become part of the regulations through the incorporation by reference process), and a determination is made whether the revised Code Case is acceptable, conditionally acceptable, or unacceptable. Reaffirmed in the context of the regulatory guides means that a Code Case was approved in a previous version of a regulatory
8 - 2 guide. The status of these Code Cases remains unchanged in the regulatory guide unless additional information becomes available (e.g., emerging degradation issues) indicating that a change in position is warranted.
4 List of Code Cases and Summary of Bases:
4.1 Acceptable Code Cases: The Code Cases in Supplement 12 to the 1998 Edition and Supplement 1 through Supplement 6 to the 2001 Edition listed below are acceptable to the NRC.
4.2 Section III Code Cases CODE CASE NUMBER TYPE TITLE N-4-11 Reaffirmed Special Type 403 Modified Forgings or Bars,Section III, Division 1, Class 1 and CS N-60-5 Reaffirmed Material for Core Support Structures,Section III, Division 1 N-192-3 Revised Use of Braided Flexible Connectors,Section III, Division 1, Class 2 and 3 N-205 Reaffirmed Use of Ductile Iron SA-395,Section III, Division 1, Class 3 N-213 Reaffirmed SA-203, Grade E (Plate) and SA-350, Grade LF3 (Forging),
3.5% Ni Nominal Composition Used in Class 1 Construction N-329 Reaffirmed Examination of Bar Material,Section III, Division 1, Class 1 N-373-2 Revised Alternative PWHT Time at Temperature for P-No. 5 Material,Section III, Division 1, Classes 1, 2, and 3 N-391-2 Reaffirmed Procedure for Evaluation of the Design of Hollow Circular Cross Section Welded Attachments on Class 1 Piping,Section III, Division 1 N-392-3 Reaffirmed Procedure for Evaluation of the Design of Hollow Circular Cross Section Welded Attachments on Classes 2 and 3 Piping,Section III, Division 1 N-405-1 Reaffirmed Socket Welds,Section III, Division 1 N-453-3 Reaffirmed Nickel-Chromium-Molybdenum-Copper Stainless Steel (UNS N08925) for Class 2 and 3 Construction,Section III, Division 1
8 - 3 N-493 Reaffirmed Alternative Radiographic Acceptance Criteria for Vessels Used as Shipping Casks,Section III, Division 1, Class 1 N-505 Reaffirmed Alternative Rules for the Examination of Butt Welds Used as Closure Welds for Electrical Penetration Assemblies in Containment Structures,Section III, Division 1 N-511 Reaffirmed Design Temperature for Atmospheric and 0-15 psi Storage Tanks,Section III, Division 1 N-525 Reaffirmed Design Stress Intensities and Yield Strength Values for UNS N06690 With a Minimum Specified Yield Strength of 30 ksi, Class 1 Components,Section III, Division 1 N-539 Reaffirmed UNS N08367 in Class 2 and 3 Valves,Section III, Division 1 N-548 Reaffirmed Air Cooling of SA-182 Grades F304, F304L, F316, F316L Forgings Instead of Liquid Quenching After Solution Heat Treatment, Class 1, 2, and 3,Section III, Division 1 N-558 Reaffirmed Stamping of Class 2 Vessels Fabricated to Subsection NB,Section III, Division 1 N-570 Reaffirmed Alternative Rules for Linear Piping and Linear Standard Supports for Class 1, 2, 3, and MC,Section III, Division 1 N-572 Reaffirmed Use of SB-425 (UNS N08825) Bar and Rod for Class 1 Construction,Section III, Division 1 N-594 Reaffirmed Repairs to P-4 and P-5A Materials for Pumps and Valves Without Postweld Heat Treatment,Section III, Division 1 N-607 Reaffirmed Guidance on Implementation of NS Certificate of Accreditation,Section III, Division 1 N-625-1 Revised Ni-Cr-Mo Alloy (UNS N06059) Welded Construction to 800EF,Section III, Division 1 N-631 Reaffirmed Use of Fracture Toughness Test Data to Establish Reference Temperature for Pressure Retaining Materials Other Than Bolting for Class 1 Vessels,Section III, Division 1 N-635 Reaffirmed Use of 22Cr-5Ni-3Mo-N (Alloy UNS S31803) Forgings, Plate, Bar, Welded and Seamless Pipe, and/or Tube, Fittings, and Fusion Welded Pipe With Addition of Filler Metal, Classes 2 and 3,Section III, Division 1
8 - 4 N-637 Reaffirmed Use of 44Fe-25Ni-21Cr-Mo (Alloy UNS N08904) Plate, Bar, Fittings, Welded Pipe, and Welded Tube, Classes 2 and 3,Section III, Division 1 N-650 New Use of SA-537, Class 2 Plate Material in Non-pressure Boundary Application Service 700EF to 850EF, Class 1 or CS,Section III, Division 1 N-657 New Use of the N-1A Data Report for Spent Fuel Canisters,Section III, Division 1 4.3 Section XI Code Cases CODE CASE NUMBER TYPE TITLE N-307-3 Revised Revised Ultrasonic Examination Volume for Class 1 Bolting, Table IWB-2500-1, Examination Category B-G-1, When the Examinations Are Conducted from the End of the Bolt or Stud or from the Center-Drilled Hole,Section XI, Division 1 N-323-1 Reaffirmed Alternative Examination for Welded Attachments to Pressure Vessels,Section XI, Division 1 N-416-3 Revised Alternative Pressure Test Requirement for Welded Repairs or Installation of Replacement Items by Welding, Class 1, 2, and 3,Section XI, Division 1 N-432-1 Revised Repair Welding Using Automatic or Machine Gas Tungsten-Arc Welding (GTAW) Temper Bead Technique,Section XI, Division 1 N-435-1 Reaffirmed Alternative Examination Requirements for Vessels With Wall Thickness 2 in. Or Less,Section XI, Division 1 N-471 Reaffirmed Acoustic Emission for Successive Inspections,Section XI, Division 1 N-494-3 Reaffirmed Pipe Specific Evaluation Procedures and Acceptance Criteria for Flaws in Class 1 Ferritic Piping that Exceed the Acceptance Standards of IWB-3514.2 and in Class 1 Austenitic Piping that Exceed the Acceptance Standards of IWB-3514.3,Section XI, Division 1 N-496-2 Revised Helical-Coil Threaded Inserts,Section XI, Division 1 N-508-2 Revised Rotation of Serviced Snubbers and Pressure Relief Valves for the Purpose of Testing,Section XI, Division 1
8 - 5 N-522 Reaffirmed Pressure Testing of Containment Penetration Piping,Section XI, Division 1 N-523-2 Reaffirmed Mechanical Clamping Devices for Class 2 and 3 Piping,Section XI, Division 1 N-526 Reaffirmed Alternative Requirements for Successive Inspections of Class 1 and 2 Vessels,Section XI, Division 1 N-553-1 Revised Inservice Eddy Current Surface Examination of Pressure Retaining Pipe Welds and Nozzle-to-Safe End Welds N-566-2 Revised Corrective Action for Leakage Identified at Bolted Connections,Section XI N-588 Reaffirmed Attenuation to Reference Flow Orientation of Appendix G for Circumferential Welds in Reactor Vessels,Section XI N-592 Reaffirmed ASNT Central Certification Program N-598 Reaffirmed Alternative Requirements to Required Percentages of Examinations N-600 New Transfer of Welder, Welding Operator, Brazer, and Brazing Operator Qualifications Between Owners,Section XI, Division 1 N-601 Reaffirmed Extent and Frequency of VT-3 Visual Examination for Inservice Inspection of Metal Containments N-603 Reaffirmed Alternative to the Requirements of IWL-2421, Sites with Two Plants N-605 Reaffirmed Alternative to the Requirements of IWE-2500(c) for Augmented Examination of Surface Areas N-613-1 New Ultrasonic Examination of Penetration Nozzles in Vessels, Examination Category B-D, Item Nos. B3.10 and B3.90, Reactor Nozzle-to-Vessel Welds, Figs. IWB-2500-7(a), (b),
and (c),Section XI, Division 1 N-617 Reaffirmed Alternative Examination Distribution Requirements for Table IWE-2500-1, Examination Category C-G, Pressure Retaining Welds in Pumps and Valves N-623 Reaffirmed Deferral of Inspections of Shell-to-Flange and Head-to-Flange Welds of a Reactor Vessel N-624 Reaffirmed Successive Inspections
8 - 6 N-629 Reaffirmed Use of Fracture Toughness Data to Establish Reference Temperature for Pressure Retaining Materials N-640 Reaffirmed Alternative Reference Fracture Toughness for Development of P-T Limit Curves N-649 New Alternative Requirements for IWE-5240 Visual Examination,Section XI, Division 1 N-651 New Ferritic and Dissimilar Metal Welding Using SMAW Temper Bead Technique Without Removing the Weld Bead Crown for the First Layer,Section XI, Division 1 N-652 New Alternative Requirements to Categorize B-G-1, B-G-2, and C-D Bolting Examination Methods and Selection Criteria,Section XI, Division 1 N-658 New Qualification Requirements for Ultrasonic Examination of Wrought Austenitic Piping Welds,Section XI, Division 1 N-663 New Alternative Requirements for Classes 1 and 2 Surface Examinations,Section XI, Division 1 N-664 New Performance Demonstration Requirements for Examination of Unclad Reactor Pressure Vessel Welds, Excluding Flange Welds,Section XI, Division 1 N-695 New Qualification Requirements for Dissimilar Metal Piping Welds,Section XI, Division 1 4.4 Conditionally Acceptable Code Cases: The Code Cases listed below are acceptable to the NRC subject to the limitations and modifications listed. Notations have been made to indicate those conditions carried over from previous versions of the regulatory guides.
4.4.1 Section III Code Case N-71-18 Type:
Revised
Title:
Additional Materials for Subsection NF, Class 1, 2, 3, and MC Component Supports Fabricated by Welding,Section III, Division 1 This revision updates references to material specifications, and the NRC has determined that these changes are acceptable. Code Case N-71-17 was conditionally approved in RG 1.84, Revision 32. The conditions on the use of N-71-18 in Revision 33 to RG 1.184 are the same as those for N-71-17.
8 - 7 Code Case N-249-14 Type:
Revised
Title:
Additional Materials for Subsection NF, Class 1, 2, 3, and MC Component Supports Fabricated Without Welding,Section III, Division 1 This revision updates references to material specifications, and the NRC has determined that these changes are acceptable. Code Case N-249-13 was conditionally approved in RG 1.84, Revision 32. The conditions on the use of N-249-14 in Revision 33 to RG 1.184 are the same as those for N-249-13.
Code Case N-292 Type:
Reaffirmed
Title:
Depositing Weld Metal Prior to Preparing Ends for Welding,Section III, Division 1, Class 1, 2, and 3 Code Case N-292 was conditionally approved in Revision 32 to RG 1.84. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 33 to the guide.
Code Case N-626 Type:
Reaffirmed
Title:
Use of Plastic Analysis for the Design of Type B Containment Components for Nuclear Material Transportation Casks,Section III, Division 3 Code Case N-626 was conditionally approved in Revision 32 to RG 1.84. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 33 to the guide.
Code Case N-655 Type:
New
Title:
Use of SA-738, Grade B, for Metal Containment Vessels, Class MC,Section III, Division 1 The guide would require for metal containment vessels up to 1.75 inch thick that Supplementary Requirements S17 and S20 of Material Specification SA-738 be applied to the use of SA-738, Grade B. These two conditions are needed to ensure adequate material properties and weldability of the containment vessel material. The ASME Code,Section III, exempts SA-738, Grade B, material up to 1.75 inch of thickness from post-weld stress relief heat treatment. Because the welds in containment vessel material thickness up to 1.75 inch thick will not be stress relieved, higher residual stresses will be present in the welds. Also, the material will likely be procured in the quenched and tempered condition. Welding will reduce the impact properties of the material in the heat affected zone. Requiring Supplementary Requirement S17 and the use of vacuum-degassed steel will ensure adequate material properties because non-metallic inclusions such as oxides and silicates will be minimized as a result of the vacuum-degassing of the steel. Requiring Supplementary Requirement S20 and a carbon equivalent weldability check will ensure that the steel is readily weldable.
8 - 8 Code Case N-656 Type:
New
Title:
Rules for the Construction of Inner Transportation Containments,Section III, Division 3 The Code Case does not address the condition of the material being shipped. Because the presence of water introduces a criticality issue, the inner transportation containment must contain only solid and dry material.
4.4.2 Section XI Code Case N-498-4 Type: Revised
Title:
Alternative Requirements for 10-Year System Hydrostatic Testing for Class 1, 2, and 3 Systems,Section XI, Division 1 Code Case N-498-3 was conditionally approved in Revision 13 to RG 1.147. This Code Case has been revised to clarify what portions of systems must be pressurized and at what pressures. The revision is acceptable, and no changes to the conditions have been made in Revision 14 to the guide.
Code Case N-504-2 Type:
Revised
Title:
Alternative Rules for Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping,Section XI, Division 1 Code Case N-504-2 was unconditionally approved in Revision 13 of Regulatory Guide 1.147. The ASME recently recognized certain shortcomings relative to the repair and examination of austenitic stainless steel piping that has experienced stress corrosion cracking. The ASME approved publication of Appendix Q, Weld Overlay Repair of Class 1, 2, and 3 Austenitic Stainless Steel Piping Weldments. In the Evaluation of Code Cases for Proposed Revision 14 to the guide, the NRC expressed its intent to condition Code Case N-504-2 in the final guide pending public comment. One public comment was received. The commenter had no objections to the planned condition, but noted that the ASME had approved the appendix as Q and not P as had been originally thought.
Thus, Code Case N-504-2 has been conditioned in the final guide to require that the provisions of Appendix Q also be applied when using this Code Case.
Code Case N-513-1 Type: Revised
Title:
Evaluation Criteria for Temporary Acceptance of Flaws in Moderate Energy Class 2 or 3 Piping,Section XI, Division 1 Code Case N-513 was endorsed in Revision 13 to RG 1.147. Code Case N-513 addressed the timing of the repair of Class 3 moderate energy (200 EF, 275 psig) piping systems. A Section XI Code repair may be impractical for a flaw detected during plant operation (i.e., a plant shutdown would be required to effect the Code repair). Under
8 - 9 certain conditions, temporary acceptance of flaws, including through-wall leaking, of low and moderate energy Class 3 piping has been deemed acceptable provided that the conditions are met, and the repair is effected during the next outage. The Code Case has been revised (N-513-1) to address Class 2 moderate energy piping. The NRC has found this to be acceptable subject to the same conditions contained in Revision 13 to RG 1.147.
Code Case N-516-3 Type: Revised
Title:
Underwater Welding,Section XI, Division 1 Code Case N-516-2 was endorsed in Revision 13 to RG 1.147. The Code Case has been revised to add laser beam welding as one of the methods that may be used for under water welding. Laser beam welding has been demonstrated to be an acceptable welding method provided certain guidelines are followed. Specialized welding methods are proprietary. The Code Case addresses the welding of critical Class 1 in-vessel components, and there are a variety of methods and techniques which may be used in the weld repair. Because the Code Case is not specific relative to the techniques to be followed (i.e., proprietary information), Code Case N-516-2 was conditioned to require NRC approval regarding the technique to be used in the weld repair or replacement of irradiated material underwater. The NRC has determined that N-516-3 is acceptable subject to the same conditions contained in Revision 13 to RG 1.147.
Code Case N-517-1 Type: Reaffirmed
Title:
Quality Assurance Program Requirements for Owners,Section XI, Division 1 Code Case N-517-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-528-1 Type:
Reaffirmed
Title:
Purchase, Exchange, or Transfer of Material Between Nuclear Plant Sites,Section XI, Division 1 Code Case N-528-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-533-1 Type: Reaffirmed
Title:
Alternative Requirements for VT-2 Visual Examination of Class 1, 2, and 3 Insulated Pressure-Retaining Bolted Connections,Section XI, Division 1 Code Case N-533-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
8 - 10 Code Case N-546 Type:
Reaffirmed
Title:
Alternative Requirements for Qualification of VT-2 Examination Personnel Code Case N-546 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. The second condition in regarding the requalification of examination personnel every three years has been deleted to be consistent with the recent amendment to 10 CFR 50.55a.
Code Case N-552 Type: Reaffirmed
Title:
Alternative Methods - Qualification for Nozzle Inside Radius Section from the Outside Surface Code Case N-552 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-557-1 Type: Revised
Title:
In-Place Dry Annealing of a PWR Nuclear Reactor Vessel Code Case N-557-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-567-1 Type: Revised
Title:
Alternative Requirements for Class 1, 2, and 3 Replacement Components Code Case N-567-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-569-1 Type: Revised
Title:
Alternative Rules for repair by Electrochemical Deposition of Class 1 and 2 Steam Generator Tubing Code Case N-569-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
8 - 11 Code Case N-576-1 Type: Revised
Title:
Repair of Class 1 and 2 SB-163, UNS N06600 Steam Generator Tubing Code Case N-576-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-586 Type:
Reaffirmed
Title:
Alternative Additional Examination Requirements for Class 1, 2, and 3 Piping, Components, and Supports,Section XI, Division 1 Code Case N-586 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-597-1 Type:
Reaffirmed
Title:
Requirements for Analytical Evaluation of Pipe Wall Thinning Code Case N-597-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-599 Type: Reaffirmed
Title:
Alternatives to Qualification of Nondestructive Examination Personnel for Inservice Inspection of Metal (Class MC) and Concrete (Class CC) Containments Code Case N-599 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-606-1 Type: Reaffirmed
Title:
Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique Code Case N-606-1 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-616 Type: Reaffirmed
Title:
Alternative Requirements to Stress-Based Selection Criteria for Category B-J Welds
8 - 12 Code Case N-616 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-619 Type:
Reaffirmed Code Case N-619 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes to the conditions have been made in Revision 14 to the guide.
Code Case N-638-1 Type:
Reaffirmed
Title:
Similar and Dissimilar Metal Welding Using Ambient Temperature Machine GTAW Temper Bead Technique Code Case N-638 was listed in Table 1, Acceptable Section XI Code Cases, in Revision 13 to RG 1.147. After further consideration however, the NRC has determined that Section III acceptance criteria for nondestructive examination must be used. The Code Case specifically states that repair of Class 1 components for certain materials may be made without the nondestructive examination requirements of the Construction Code, provided certain requirements are met. Thus, the Code Case permits the use of Section XI acceptance criteria for nondestructive examination. The NRC believes that this is not appropriate. The Section XI nondestructive examination requirements are directed at detecting operationally induced flaws, not fabrication flaws. In addition,Section XI examinations typically examine the inner one-third of the component and not the entire weld. Hence, the NRC has determined that the Code Case is acceptable provided that the Section III acceptance criteria for nondestructive examination are used, and that UT examinations be demonstrated using samples with construction type flaws.
Code Case N-639 Type:
Reaffirmed
Title:
Alternative Calibration Block Material Code Case N-639 was conditionally approved in Revision 13 to RG 1.147. This Code Case was reaffirmed by the ASME. No changes have been made to the conditions in Revision 14 to the guide.
Code Case N-660 Type:
New
Title:
Risk-Informed Safety Classification for Use in Risk-Informed Repair/Replacement Activities,Section XI, Division 1 This Code Case provides a process for determining the risk-informed safety classification (RISC) for use in risk-informed repair/replacement activities. Code Case N-662, Alternative Repair/Replacement Requirements for Items Classified in Accordance with Risk-Informed Processes,Section XI, Division 1, a companion Code Case, contains the repair/replacement requirements to be used for components classified under the RISC process. The NRC staff has determined that the Code Case may only be applied to
8 - 13 ASME Code Class 2 and 3, and non-class pressure retaining items and their associated supports, except core supports.
Per the scope, the Code Case would be applicable to ASME Code Classes 1, 2, and 3.
The South Texas Project (STP) exemption from repair/replacement requirements is only applicable to ASME Code Class 2 and 3 items, however. Similarly, proposed 10 CFR 50.69 would only exempt ASME Code Class 2 and 3 structures, systems, and components that are categorized as RISC-3 or RISC-4 from the repair and replacement requirements of 10 CFR 50.55a(g). The categorization process used to support the STP exemption was based on the EPRI RI-ISI methodology and included the pipe failure potential. In practice, this means that segments with a conditional core damage probability less than 1E-4 and exposed to no degradation mechanism would be placed in the low safety significance (LSS) category. The result could be that much of the Class 1 piping would be categorized as LSS. For example, if licensees account for leak-before-break, as is permitted by the Code Case, relatively large piping might be categorized as LSS. In addition, there are other piping segments that could be placed in the LSS category that would result in a LOCA if a break occurs. The NRC staff will review on a case-by-case basis application of the method to ASME Code Class 1 piping.
Code Case N-661 Type:
New
Title:
Alternative Requirements for Wall Thickness Restoration of Classes 2 and 3 Carbon Steel Piping for Raw Water Service,Section XI, Division 1 The NRC has determined that several conditions on the use of the Code Case are necessary. The first condition is If the root cause of the degradation has not been determined, the repair is only acceptable for one cycle. An adequate root cause determination requires establishing a reinspection frequency. A suitable reinspection frequency cannot be established without confirmation of the cause of the degradation.
The second condition is Weld overlay repair of an area can only be performed once in the same location. This will ensure that ineffective repairs are not being repeatedly implemented in the same location. The third condition is When through-wall repairs are made by welding on surfaces that are wet or exposed to water, the weld overlay repair is only acceptable until the next refueling outage. Problems with performing through-wall weld repairs on surfaces that are wet or exposed to water include porosity, lack of fusion, and cracking. Performing a surface exam on the seal weld, first pass, and final pass can provide a measure of assurance that the root of the joint has been successfully sealed and defects do not extend though-wall. A 48 hour5.555556e-4 days <br />0.0133 hours <br />7.936508e-5 weeks <br />1.8264e-5 months <br /> PT/MT on the final weld inspects for through-wall or surface delayed hydrogen cracking. Hydrogen cracking can still be present below the surface of the weld. It is highly unlikely that a weld can be made on an open root joint with water present on the backside of the weld without having several weld defects. These types of weld defects can, and many times do, lead to premature failure of a weld joint. These types of defects would render the weld unacceptable based on a construction radiograph. Also, this type of weld is outside the conditions for which the procedure is qualified. Thus, these types of repairs should only be considered temporary.
8 - 14 Code Case N-662 Type:
New
Title:
Alternative Repair/Replacement Requirements for Items Classified in Accordance with Risk-Informed Processes,Section XI, Division 1 This Code Case has been conditioned in the same manner as Code Case N-660, i.e., the Code Case may only be applied to ASME Code Class 2 and 3, and non-class pressure retaining items and their associated supports, except core supports. As discussed above in Code Case N-660, this makes use of the Code Case consistent with the staff positions taken in the NRC safety evaluation in support of South Texas Project (STP) multiple exemption request (SE dated August 3, 2001, ADAMS Accession No.: ML012040370, Sections 10.3.1 and 10.4.1, pp 73 to 76) and proposed 10 CFR 50.69. As with Code Case N-660, application of Code Case N-662 to ASME Code Class 1 items will be reviewed and approved by the NRC staff on a case-by-case basis.