Issue Date: 02/21/08 1 2515/172 

 NRC INSPECTION MANUAL CPNB

TEMPORARY INSTRUCTION 2515/172 

REACTOR COOLANT SYSTEM DISSIMILAR METAL BUTT WELDS 

CORNERSTONE: Barrier Integrity 

 Initiating Events 

APPLICABILITY: This temporary instruction (TI) applies to all holders of operating 

 licenses for pressurized-water reactors (PWRs). 

2515/172-01 OBJECTIVES 

The objective of this TI is to: 

a. Support NRC staff oversight of licensees’ dissimilar metal butt weld (DMBW) 

mitigation and inspection activities that are being implemented in accordance 

with the industry guidelines of the Materials Reliability Program (MRP) -139, 

“Primary System Piping Butt Weld Inspection and Evaluation Guidelines,” July 

2005. 

b. Verify that each pressurized water reactor (PWR) plant conforms to its 

commitments to conduct an inspection program consistent with the industry’s 

MPR-139 guidelines. 

c. Verify that mitigation techniques implemented by licensees are consistent with 

MRP-139 as discussed in the inspection requirements section of this TI. 

d. Define and initiate information gathering so that NRC staff can identify and 

develop possible future regulatory positions, generic communications, and 

rulemaking in this area. 

This TI pertains to primary system piping dissimilar metal butt welds 1” NPS or larger, 

including: 

a. pressurizer nozzle dissimilar metal butt welds (DMBWs). 

b. DMBWs less than or equal to 14 inches exposed to temperatures equivalent to 

the hot leg. 

c. DMBWs larger than 14 inches exposed to temperatures equivalent to the hot 

leg. 

d. DMBWs exposed to temperatures equivalent to the cold leg. 
Issue Date: 02/21/08 2 2515/172 

MRP-139 indicates that the initial or baseline volumetric inspections of butt welds in 

these four sets of locations are to be completed in 2007, 2008, 2009, and 2010, 

respectively. 

2515/172-02 BACKGROUND 

Operating experience has demonstrated that Alloy 600/82/182 materials exposed to 

primary coolant water (or steam) at the normal operating conditions of PWR plants have 

cracked due to primary water stress corrosion cracking (PWSCC). The NRC has issued 

several bulletins and an order since 2001 related to the occurrence of PWSCC in 

reactor coolant system components and welds containing Alloy 600/82/182. 

Several methods have been used or are being considered by industry to address 

PWSCC. These methods include increased frequency of inspection, replacement of the 

Alloy 600/82/182 materials with Alloy 690/52/152 materials, structural weld overlays with 

Alloy 52/152 materials, stress improvement processes that place the susceptible 

materials in compression to prevent crack initiation and growth, and application of Alloy 

52 cladding on the inside surface of the susceptible Alloy 82/182 material. 

Section XI of the American Society of Mechanical Engineers Boiler and Pressure Vessel 

Code (ASME Code), which is incorporated into NRC regulations by 10 CFR 50.55a, 

"Codes and Standards," specifies examination requirements for reactor coolant system 

components and piping, including DMBWs. Volumetric, surface, and visual 

examinations are required to ensure the integrity of the reactor coolant pressure 

boundary and safe operation of the plant. 

In September 2005, NEI issued MRP-139, “Material Reliability Program: Primary 

System Piping Butt Weld Inspection and Evaluation Guideline,” with mandatory 

implementation for all PWRs under the industry’s proactive management of materials 

degradation initiative, NEI 03-08. MRP-139 provides industry’s guidance for the 

volumetric and visual inspections of butt welds in PWR primary systems. The MRP-139 

inspections augment examinations of these locations already required by the ASME 

Code, Section XI. MRP-139 Section 1.2 on Implementation, Section 5 on Examination 

Requirements, and Section 6 on Examination Schedules were assigned the mandatory 

implementation category under NEI 03-08. 

Based on recent experience with industry that arose from multiple flaws found in 

pressurizer nozzle welds at Wolf Creek, the staff concluded that it is essential that NRC 

staff monitor more closely the MRP-139 inspection programs and, in particular, the 

deviations utilities may be planning to take from the guidelines stated in MRP-139. This 

TI contains inspection and reporting requirements pertaining to deviations taken from 

MRP-139. 

The NRC staff is relying on the industry MRP-139 program as a short term approach for 

addressing PWSCC, but the NRC staff needs to verify that each licensee has 

developed an inspection program and is implementing its commitments to conduct the 

inspections in accordance with MRP-139. As a long term approach for addressing 
Issue Date: 02/21/08 3 2515/172 

PWSCC, the NRC staff is working with the ASME Code to develop inspection 

requirements for dissimilar metal butt welds. These Code inspection requirements will 

be contained in an ASME code case that the NRC will endorse in its regulations if the 

code case is found acceptable. 

2515/172-03 INSPECTION REQUIREMENTS 

03.01 Licensee’s Implementation of the MRP-139 Baseline Inspections.

Verify the following: 

 a. The licensee’s inspection program includes inspections of the pressurizer, hot 

leg and cold leg temperature DMBWs and that the schedules for these baseline 

inspections are consistent with the requirements stated in MRP-139. If any 

baseline inspection schedules deviate from MRP-139 guidelines, determine 

what deviations are planned and what is the general basis for the deviation. 

 b. The licensees (except for the nine plants specified below) have completed their 

MRP-139 baseline inspections of all pressurizer DMBWs by 

December 31, 2007. For nine PWR plants (Braidwood Unit 2, Comanche Peak 

Unit 2, Diablo Canyon Unit 2, Palo Verde Unit 2, Seabrook, South Texas Station 

Unit 1, V.C. Summer, Vogtle Unit 1 and Waterford Unit 3), verify that the 

baseline pressurizer DMBWs are completed during the spring 2008 outages. 

 

03.02 Volumetric Examinations.

Licensees perform volumetric examinations as part of the inspection/mitigation activities 

as described in MRP-139. Inspectors should use Inspection Procedure (IP) 57080, 

“Ultrasonic Testing Examination” and ASME Code Section XI, Appendix VIII, 

“Performance Demonstrations for Ultrasonic Examination Systems” as guidance when 

observing or reviewing the volumetric examinations performed by the licensee. Perform 

the following inspections through either direct observation (preferred method) or records 

review. If no examinations are being performed during the current outage, perform a 

records review of an examination during the previous outage. 

 a. Observe or review at least one examination of a weld (for example, an 

examination of a weld that is categorized as not being mitigated, an examination 

of a weld prior to mitigation by either weld overlay or mechanical stress 

improvement, or an examination of a weld after mitigation by mechanical stress 

improvement). Verify that the inspection is performed in accordance with the 

guidelines in MRP-139, Section 5.1. 

 b. Observe or review at least one weld overlay volumetric examination. Verify that 

the inspection performed is consistent with the NRC staff relief request 

authorization for the weld overlay. If the inspection coverage warrants further 

evaluation, review the licensee’s documentation of the basis for achieving the 

required inspection coverage. 
Issue Date: 02/21/08 4 2515/172 

c. Verify that the examinations were performed by qualified personnel. 

d. Verify that any deficiencies identified were appropriately dispositioned and 

resolved. 

03.03 Weld Overlays. 

MRP-139 addresses inspection of dissimilar metal welds mitigated by weld overlays as 

part of the strategy to address the DMBW issue. Inspectors should use guidance 

contained in IP 55050, “Nuclear Welding General Inspection Procedure,” when 

performing their review of licensee’s weld overlay techniques. Perform the following 

inspections to verify that the proper weld overlay techniques were used. If no 

examinations are being performed during the current outage, perform a records review 

of an examination during the previous outage. 

 a. For at least one weld overlay verify that the welding activities were performed 

consistent with ASME Code requirements as modified by NRC staff relief 

request authorizations. 

 

b. Verify that the licensee has submitted a relief request and obtained NRR staff 

authorization to install the weld overlays, whether full structural or optimized 

weld overlays. 

 

c. Verify that welding was performed by qualified personnel. 

d. Verify that any deficiencies identified were appropriately dispositioned, and 

resolved. 

03.04 Mechanical Stress Improvement. 

MRP-139 addresses inspection of dissimilar metal welds mitigated by stress 

improvement (SI) as part of the strategy to address the DMBW issue. For each 

application of SI used, inspectors should review the SI qualification report that describes 

the essential parameters of the SI process (e.g., the location radial loading is applied 

and the applied load, as well as the inspection requirements). Inspectors should verify 

the following for each location where SI was applied: 

 a. The nozzle, weld, safe end, and pipe configurations, as applicable, are 

consistent with the configuration addressed in the SI qualification report. 

b. The SI qualification report addresses the location radial loading is applied, the 

applied load, and the effect that plastic deformation of the pipe configuration 

may have on the ability to conduct volumetric examinations. 

 c. The licensee’s inspection procedure records document that a volumetric 

examination per the ASME Code, Section XI, Appendix VIII was performed prior 

to and after the application of the SI. 
Issue Date: 02/21/08 5 2515/172 

 d. The SI qualification report addresses limiting flaw sizes that may be found during 

pre-SI and post-SI inspections and that any flaws identified during the volumetric 

examination are to be within the limiting flaw sizes established by the SI 

qualification report. 

 e. Verify that any deficiencies identified were appropriately dispositioned, and 

resolved. 

03.05 Inservice Inspection Program.

MRP-139 contains industry mandatory requirements for baseline and inservice 

inspection. In accordance with MRP-139, inservice inspections are performed based on 

the categorization of the weld configuration, which are classified as Categories A–I for 

volumetric examinations and Categories J and K for visual examinations. The 

inspectors will perform an inspection to verify that the licensee has prepared an MRP139 inservice inspection program applicable welds are included in a category consistent 

with MRP-139 guidelines. The inspectors will verify that the licensee’s inspection 

program and procedures specify inspection frequencies consistent with Tables 6-1 and 

6-2 of MRP-139. The inspectors will determine if any welds are categorized as H or I 

and review the licensee’s basis for the categorization and the licensee’s plans for 

addressing potential PWSCC. The inspector will determine if any deviations are 

planned from the inspection guidelines in MRP-139, i.e., frequencies, examination 

volumes, methods. 

2515/172-04 GUIDANCE 

Certain inspection requirements will have to take place during plant outages when the 

activities occur. For inspection activities related to programs and reports, it may be 

necessary to perform inspection onsite during a non-outage period to obtain adequate 

support from the licensee’s staff. Additionally, if nondestructive testing performed at a 

licensee’s facility by an inspection vendor is not directly observed (preferred method), a 

records review may require that portion of the inspection be performed at the vendor’s 

facility since the data may not available at the plant. 

04.01 Licensee’s Implementation of the MRP-139 Baseline Inspections.

MRP-139 establishes an industry mandatory requirement for licensees to complete 

baseline inspections of DMBWs in the reactor coolant system. The licensee’s baseline 

inspections may be performed on a number of different weld configurations based on 

their MRP-139 categorization. Regardless of licensee’s plans to mitigate a particular 

weld, the MRP-139 baseline inspections must be performed using ASME, Section XI, 

Appendix VIII, qualified methods. 

MRP-139 Table 2-1 contains a listing of locations involving Alloy 82/182 piping butt 

welds in Westinghouse, Combustion Engineering and Babcox & Wilcox design plants. 

This listing can be used to determine if the licensee appropriately placed these DMBWs 

into the MRP-139 inspection program. A complete listing of Alloy 82/182 welds should 

also be contained in licensee documentation prepared in response to MRP-126. 
Issue Date: 02/21/08 6 2515/172 

It is the NRC staff’s view that if the licensee plans to mitigate a weld by a mechanical 

stress improvement, the licensee has to conduct a pre-stress improvement inspection, 

and this pre-stress improvement inspection is the MRP-139 baseline inspection. This 

view is generally consistent with the code case being prepared by ASME Section XI on 

inspection of dissimilar metal butt welds. 

There are nine plants scheduled to perform the pressurizer DMBW inspections in the 

spring 2008 time frame. This schedule for inspection of the pressurizer weld 

connections was the subject of extensive NRC staff review and evaluation as 

documented in the NRC staff’s safety assessment on this issue which can be obtained 

in Agency Documents Access and Management System (ADAMS) using accession 

number ML072400199. 

04.02 Volumetric Examinations.

Examination of a weld prior to application of a full structural weld overlay (FSWO) is not 

required by either MRP-139 or the ASME code cases pertaining to weld overlays. 

While such an examination is not required to be performed prior to application of a 

FSWO, some licensees may choose to perform this type of examination. 

04.03 Weld Overlays. 

ASME Section XI does not presently contain inspection requirements for weld overlays. 

Section XI has issued Code Cases N-504-3, “Alternative Rules for Repair of Classes 1, 

2, and 3 Austenitic Stainless Steel Piping” and N-638-1, “Similar and Dissimilar Metal 

Welding Using Ambient Temperature Machine GTAW Temper Bead Technique.” These 

two code cases are listed in Regulatory Guide (RG) 1.147, Revision 15, “Inservice 

Inspection Code Case Acceptability, ASME Section XI, Division 1,” with limitations. 

Although these code cases are approved with limitations in RG 1.147, their use for a 

weld overlay on an Alloy 82/182 weld requires a relief request, since they were not 

written for this application. ASME Section XI has issued N-740 and N-740-1, “Dissimilar 

Metal Weld Overlay for Repair of Class 1, 2, and 3 Items,” and is working on the second 

revision to this code case. When the NRC staff approves code case N-740-X in 

RG 1.147 and endorses this regulatory guide in an update to 10 CFR 50.55a, 

application of weld overlays will no longer require NRR approval through authorization 

of a relief request. 

04.04 Mechanical Stress Improvement. 

Mechanical stress improvement is generally applied through a proprietary process 

referred to as the Mechanical Stress Improvement Process or MSIPTM. This process 

was originally employed in the nuclear power industry to boiling water reactor piping 

susceptible to intergranular stress corrosion cracking. Each application of the process is 

expected to be accompanied by a qualification report that documents the specific stress 

improvement parameters to be applied to the weld, the basis for the parameters, and 

the inspection requirements. While SI has been through MSIPTM in the past, industry 

intends to also use what is referred to as optimized weld overlays. Optimized weld 

overlays are not as thick as full structural weld overlays, but are designed to obtain 
Issue Date: 02/21/08 7 2515/172 

essentially the same stress improvement benefits as an MSIPTM. ASME Code, 

Section XI, Appendix VIII volumetric examination must be performed prior to and after 

the application of stress improvement whether by an MSIPTM or an optimized weld 

overlay. 

04.05 Inservice Inspection Program.

MRP-139 categorizes welds according to their mitigation status. Mitigation techniques 

noted in MRP-139 are full structural weld overlays and stress improvement. MRP-139 

requires less frequent inspection of welds that have been mitigated. These categories 

also relate to the condition of the weld as cracked or uncracked. Categories H and I 

pertain to welds for which a qualified ASME examination can not be performed. NRR is 

aware of some welds for which a qualified examination may not be possible without 

taking additional measures. Category H and I welds may include welds joined to cast 

austenitic stainless steel piping. 

2515/172-05 REPORTING REQUIREMENTS 

Each refueling cycle for each unit document inspection results in section 4OA5 of the 

routine resident inspectors’ integrated inspection report and send a copy of the 

inspection report to NRR/DCI, Attention: Edmund Sullivan or e-mail the electronic file of 

the inspection report to EJS@NRC.gov. In addition, forward the electronic file(s) that 

documents the results of this TI to Mr. Edmund Sullivan when the TI is completed. Mr. 

Sullivan can also be reached by telephone at (301) 415-2796. 

The purpose of this TI is to support NRR/DCI by inspecting and reporting on the 

licensees’ performance on implementing MRP-139. Specifically, the inspectors should 

provide a qualitative description of the effectiveness of the licensees’ DMBW inspection 

and mitigation program. As a minimum, the inspectors shall document the following 

aspects in an inspection report: 

 a. For MRP-139 baseline inspections: 

1. Have the baseline inspections been performed or are they scheduled to be 

performed in accordance with MRP-139 guidance? Were the baseline 

inspections of the pressurizer temperature DMBWs of the nine plants listed 

in 03.01.b completed during the spring 2008 outages. 

2. Is the licensee planning to take any deviations from the MRP-139 baseline 

inspection requirements of MRP-139? If so, what deviations are planned 

and what is the general basis for the deviation? If inspectors determine 

that a licensee is planning to deviate from any MRP-139 baseline 

inspection requirements, NRR should be informed by email as soon as 

possible. 

 b. For each examination inspected, was the activity: 
Issue Date: 02/21/08 8 2515/172 

1. Performed in accordance with the examination guidelines in MRP-139 

Section 5.1 for unmitigated welds or mechanical stress improved welds and 

consistent with NRC staff relief request authorization for weld overlaid 

welds? 

2. Performed by qualified personnel? (Briefly describe the personnel 

training/qualification process used by the licensee for this activity.) 

3. Performed such that deficiencies were identified, dispositioned, and 

resolved? 

 c. For each weld overlay inspected, was the activity: 

1. Performed in accordance with ASME Code welding requirements and 

consistent with NRC staff relief requests authorizations? Has the licensee 

submitted a relief request and obtained NRR staff authorization to install 

the weld overlays? 

2. Performed by qualified personnel? (Briefly describe the personnel 

training/qualification process used by the licensee for this activity.) 

3. Performed such that deficiencies were identified, dispositioned, and 

resolved? 

d. For each mechanical stress improvement used by the licensee during the 

outage, was the activity performed in accordance with a documented 

qualification report for stress improvement processes and in accordance with 

demonstrated procedures? Specifically, 

1. Are the nozzle, weld, safe end, and pipe configurations, as applicable, 

consistent with the configuration addressed in the SI qualification report? 

2. Does the SI qualification report address the location radial loading is 

applied, the applied load, and the effect that plastic deformation of the pipe 

configuration may have on the ability to conduct volumetric examinations? 

3. Do the licensee’s inspection procedure records document that a volumetric 

examination per the ASME Code, Section XI, Appendix VIII was performed 

prior to and after the application of the SI? 

4. Does the SI qualification report address limiting flaw sizes that may be 

found during pre-SI and post-SI inspections and that any flaws identified 

during the volumetric examination are to be within the limiting flaw sizes 

established by the SI qualification report. 

5. Performed such that deficiencies were identified, dispositioned, and 

resolved? 

 

 e. For the inservice inspection program: 
Issue Date: 02/21/08 9 2515/172 

1. Has the licensee prepared an MRP-139 inservice inspection program? If 

not, briefly summarize the licensee’s basis for not having a documented 

program and when the licensee plans to complete preparation of the 

program. 

 

2. In the MRP-139 inservice inspection program, are the welds appropriately 

categorized in accordance with MRP-139? If any welds are not 

appropriately categorized, briefly explain the discrepancies. 

3. In the MRP-139 inservice inspection program, are the inservice inspection 

frequencies, which may differ between the first and second 10-year 

intervals after the MRP-139 baseline inspection, consistent with the 

inservice inspection frequencies called for by MRP-139? 

4. If any welds are categorized as H or I, briefly explain the licensee’s basis 

for the categorization and the licensee’s plans for addressing potential 

PWSCC. 

5. If the licensee is planning to take deviations from the inservice inspection 

“requirements” of MRP-139, what are the deviations and what are the 

general bases for the deviations? Was the NEI 03-08 process for filing 

deviations followed? 

Any issues identified during this inspection should be processed and documented in 

accordance with NRC Inspection Manual Chapter (IMC) 0612, “Power Reactor 

Inspection Reports.” The significance of inspection findings should be evaluated in 

accordance with applicable appendices of IMC 0609, “Significance Determination 

Process.” Any noncompliance with NRC requirements resulting from this inspection 

should be evaluated and documented in accordance with NRC Enforcement Policy 

(NUREG -1600) and Section 3.12 of the NRC Enforcement Manual. Also, licensees are 

required to address the findings resulting from the MRP-139 inspections (i.e., perform 

analyses and repairs) in accordance with existing requirements in the ASME code and 

10 CFR 50.55a. 

2515/172-06 COMPLETION SCHEDULE 

Up to three outages may be needed to complete the inspections associated with this 

issue. The inspection activities identified in this TI should be completed within one cycle 

of the last MRP-139 baseline inspections. Inspectors may perform inspection of recordrelated aspects of the TI at any time and, if an inspection opportunity is available, 

perform inspections of mitigation and examination activities in this TI during the 

refueling outages. 
Issue Date: 02/21/08 10 2515/172 

2515/172-07 EXPIRATION 

This TI will expire on June 30, 2011, or upon completion of the MRP-139 baseline 

inspections for all DMBWs in the PWR fleet. This TI will be in effect for more than 24 

months because the mitigation and MRP-139 baseline inspection of DMBWs potentially 

affected by PWSCC will not be fully addressed by all licensees for all affected 

components until at least the end of calendar year 2010. 

2515/172-08 CONTACT 

For questions regarding the performance of this TI and emergent issues, contact Ted 

Sullivan at (301) 415-2796 or e-mail Ted Sullivan at EJS@NRC.GOV. 

2515/172-09 STATISTICAL DATA REPORTING 

All direct inspection effort expended on this TI is to be charged to 2515/172 for reporting 

by the Regulatory Information Tracking System (RITS) reporting with an IPE code of TI. 

2515/172-10 ORIGINATING ORGANIZATION INFORMATION 

10.01 Organizational Responsibility.

This TI was initiated by the Division of Component Integrity (NRR/DCI). 

10.02 Resource Estimate.

The estimated direct inspection effort to perform this TI is estimated to be 40 to 60 

hours per PWR unit per refueling cycle. 

10.03 Training.

No formal training is proposed for the performance of this TI. However, if technical 

support is needed during the inspection of licensees’ weld mitigations, volumetric 

examinations or MRP-139 program, contact DCI through IRIB at least 30 days before 

the anticipated need for technical support. 

2515/172-11 REFERENCES 

Primary System Piping Butt Weld Inspection and Evaluation Guidelines, MRP-139, 

EPRI, Palo Alto, CA, July 2005. [ML052150196] 

Safety Assessment on the Advanced Finite Element Analysis Related to Growth of 

Postulated Primary Water Stress Corrosion Cracking Flaws in Pressurizer Nozzle 

Dissimilar Metal Butt Welds, August 2007. [ML072400199] 
Issue Date: 02/21/08 11 2515/172 

Mayfield, M.E. letter to Marion, A., NRC Staff Comments on MRP-139, 

October 12, 2005 [ML052720290] 

MRP 2006-018 MRP-139 Interim Guidance on Implementation Schedules, August 11, 

2006 [ML080300470 ] 

MRP 2007-039 MRP-139 Interim Guidance on Bare Metal Visual Inspection, November 

1, 2007 [ML080300474] 

MRP 2007-038 MRP-139 Interim Guidance on Small Bore Volumetric Inspection, 

November 1, 2007 [ML080300478] 
Attachment 1 

Revision History for TI 2515/172 

Commitment Tracking Number 

Issue Date Description of Change Training 

Needed 

Training Completion Date 

Comment Resolution Accession Number 

N/A 02/21/08 

CN 08-009 

Support NRC staff oversight of licensees’ dissimilar metal butt weld (DMBW) mitigation and inspection activities that are being implemented in accordance with the industry guidelines of the Materials Reliability Program (MRP) -139. 

N/A N/A 

ML080390335 

Issue Date: 02/21/08 2515/172 Att 1-1