DAVIS-BESSE LESSONS LEARNED TASK 

FORCE RECOMMENDATIONS REGARDING 

STRESS CORROSION CRACKING 

(FINAL UPDATE) 

TAC No. Description

MB2916 Non plant-specific activities for Revised: 12/14/09 FINAL

 Bulletin 2001-01 Lead Division: DPR 

MB3567 VHP Action Plan (Coordination Supporting Divisions: DE, DSS, & DIRS 

 and Administration) Supporting Offices: RES & Regions 

MB3954 Development of CRDM NUREGs 

 (Bulletin 2001-01) 

MB4495 Lead PM Activities for Bulletin 2002-01 

MB4603 Non plant-specific activities for 

 Bulletin 2002-01 

MB5465 Lead PM Activities for Bulletin 2002-02 

MB6218 Inspection TI for Bulletin 2002-02 

MB6220 Review of NEI/MRP Crack Growth Rate 

 Report (MRP-55) 

MB6221 Development of Alternate (to ASME Code) RPV 

 Head and VHP Inspection Requirements 

MB6222 Review of NEI/MRP RPV Head and VHP 

 Inspection Plan (MRP-75) 

MB7182 Orders for Interim Inspection Guidelines 

MB9522 Review of Bulletin 2002-01 Responses 

MB8915 Generic Activities for Lower Head Inspection 

MB9891 Develop Bulletin 2003-02 

MC0590 Develop Technical Issues Related to Incorporating 

 RCPB Inspection Requirements into 50.55a 

MC1036 Develop/Revise Inspection Guidance for ISI and BACC 

Milestone 

Date 

(T=Target) 

(C=Complete) 

Lead Support 

Part I - Reactor Pressure Vessel Head Inspection Requirements 

1. Collect and summarize information available 

worldwide on Alloy 600, Alloy 690 and other 

nickel based alloy nozzle cracking for use in 

evaluation of revised inspection requirements. 

[LLTF 3.1.1(1)-High] 

03/04 (C) 

ML040920026 

RES/DET DE 

2. Critically evaluate existing SCC models with 

respect to their continuing use in the 

susceptibility index. 

[LLTF 3.1.4(1)-Medium] 

07/03 (C) 

ML032461221 

RES/DET DE 

3.a Complete initial evaluation of individual plant 

inspections in response to Bulletins and 

Orders. 

05/04 (C) 

ML041560306 

DE DLPM 

Regions 
Milestone 

Date 

(T=Target) 

(C=Complete) 

Lead Support 

3.b Continue to review future inspection results 

until permanent guidelines are issued. 

12/09 (C) 

ML093510192 

DCI DORL 

Regions 

4. Incorporate Order EA-03-009 requirements into 

10 CFR 50.55a 

Note (2) 

 a. Develop technical basis 04/04 (C) 

ML040920628 

ML040920638 

DE DRIP 

 b. Develop rulemaking plan 07/04 (C) 

ML041610180 

DRIP DE 

 c. Commission decision 08/04 (C) 

ML042190072 

 

5. Monitor and provide input to industry efforts to 

develop revised RPV Head inspection 

requirements (ASME Code Section XI). 

[LLTF 3.3.4(8)-High] 

06/05 (C) DE RES/DET 

DSSA 

Regions 

Industry 

6. Participate in meetings and establish 

communications with appropriate stakeholders 

(e.g., MRP, ASME). 

[LLTF 3.3.4(8)-High] 

12/09 (C) 

ML093510192 

DCI RES/DET 

DPR 

DSS 

Industry 

7. Review and evaluate revised ASME Code 

requirements when issued. 

[LLTF 3.3.4(8)-High] 

06/06 (C) 

ML061800439 

DCI RES/DET 

8. If revised ASME Code requirements are 

acceptable, establish schedule to incorporate 

by reference into 10 CFR 50.55a. 

[LLTF 3.3.4(8)-High] 

12/09 (C) 

ML093510192 

DCI DPR 

DIRS 

DSS 

RES/DET 

Industry 

Public 

9. Publish a NUREG report summarizing findings 

from Part I, Items 1 and 2, and Part II, Item 1. 

03/05 (C) 

NUREG-1823 

ML050690012 

RES/DET DE 

10. Propose a course of action and 

implementation schedule to address the 

results of the analysis of Part I, item 1, and 

Part II, item 1. 

[LLTF 3.1.1(1)-High] 

10/04 (C) 

ML043010675 

DE RES/DET 
Part II - Boric Acid Control 

1. Collect and summarize information available 

worldwide on boric acid corrosion of pressure 

boundary materials for use in evaluation of 

revised inspection requirements. 

[LLTF 3.1.1(1)-High] 

10/04 (C) 

ML043000274 

RES/DET DE 

2.a Evaluate individual plant responses to Bulletin 

2002-01 regarding Boric Acid Inspection 

Programs (60-day responses and necessary 

follow-up) 

06/03 (C) 

ML031760568 

DE DLPM 

2.b Issue public document to summarize 

evaluation of plant responses. 

07/03 (C) 

ML032100653 

DE DLPM 

DRIP 

3. Participate in meetings and establish 

communications with appropriate stakeholders 

(e.g., MRP, ASME). 

12/09 (C) 

ML093510192 

DCI RES/DET 

PGCB 

DPR 

DSS 

Industry 

4. Evaluate need to take additional regulatory 

actions and determine appropriate regulatory 

tool(s). 

06/03 (C) 

ML031760568 

DE DLPM 

DRIP 

DIPM 

DSSA 

Regions 

5. Issue Bulletin 2003-02 on Reactor Vessel 

Lower Head inspection. 

08/03 (C) 

ML032320153 

DE DLPM 

6. Develop milestones for additional regulatory 

actions, as necessary. 

07/03 (C) DE DLPM 

DSSA 

DRIP 

7. Complete and evaluate the results of ongoing 

research on materials degradation, engage 

external stakeholders and develop a plan to 

implement a proactive approach to manage 

degradation of the RCPB. 

12/09 (C) 

ML093510192 

DCI RES 

8. Review and evaluate the adequacy of revised 

ASME Code Requirements for Pressure 

Testing/Leakage Evaluation being developed 

by the ASME Code, Section XI, Task Group on 

Boric Acid. 

06/06 (C) 

ML060390427 

DCI RES/DET 
Part III - Inspection Programs 

1. Develop inspection guidance or revise existing 

guidance to ensure that VHP nozzles and the 

RPV head area are periodically reviewed by the 

NRC during licensee ISI activities. 

[LLTF 3.3.4(3)-High] 

06/04 (C) 

ML022940597 

ML041340207 

DIPM DE 

Regions 

2. Develop inspection guidance that provides for 

timely, periodic inspection of PWR plant BACC 

programs. 

[LLTF3.3.2(1)-High] 

06/04 (C) 

ML022940597 

ML041340207 

DIPM DE 

Regions 

3.a Develop inspection guidance for assessing 

the adequacy of PWR plant BACC programs 

(implementation effectiveness, ability to 

identify leakage, adequacy of evaluation of 

leaks). 

[LLTF 3.2.2(1)-High] 

06/04 (C) 

ML022940597 

ML041340207 

DIPM DE 

RES/DET 

Regions 

3.b Perform follow-up evaluation of inspection 

guidance and licensee program acceptability 

after conducting inspections for approximately 

one year. 

05/05 (C) 

ML051360392 

DIPM DE 

RES/DET 

Regions 

Notes: (1) Milestone dates are dependent upon issuance of industry proposals. 

 (2) The subject of this rulemaking will be requirements for inspection of only the upper head. 

Description: The reactor vessel head (RVH) degradation found at Davis-Besse, along with other 

documented incidences of circumferential cracking of vessel head penetration (VHP) nozzles, have 

prompted the NRC staff to question the adequacy of current RVH and VHP inspection programs that rely 

on visual examinations as the primary inspection method. In addition, the failure to adequately address 

indications of boric acid leakage at Davis-Besse raised questions as to the efficacy of industry boric acid 

corrosion control (BACC) programs. Finally, review of the Davis-Besse event identified deficiencies in the 

NRC inspection programs. 

Historical Background: In March 2002, while conducting inspections in response to Bulletin 2001-01, the 

Davis-Besse Nuclear Power Station identified three CRDM nozzles with indications of axial cracking, 

which were through-wall, and resulted in reactor coolant pressure boundary leakage. During the nozzle 

repair activities, a 7 inch by 4-to-5 inch cavity on the downhill side of nozzle 3, down to the stainless steel 

cladding was identified. The extent of the damage indicated that it occurred over an extended period and 

that the licensee’s programs to inspect the RPV head and to identify and correct boric acid leakage were 

ineffective. 

One of the NRC follow-up actions to the Davis-Besse event was formation of a Lessons Learned Task 

Force (LLTF). The LLTF conducted an independent evaluation of the NRC’s regulatory processes related 

to assuring reactor vessel head integrity in order to identify and recommend areas of improvement 

applicable to the NRC and the industry. A report summarizing their findings and recommendations was 

published on September 30, 2002. The report contains several consolidated lists of recommendations. 

The LLTF report was reviewed by a Review Team (RT), consisting of several senior management 
personnel appointed by the Executive Director for Operations (EDO). The RT issued a report on 

November 26, 2002, endorsing all but two of the LLTF recommendations, and placing them into four 

overarching groups. On January 3, 2003, the EDO issued a memo to the Director, NRR, and the 

Director, RES, tasking them with developing a plan for accomplishing the recommendations. This action 

plan addresses the recommendations in the “Assessment of Stress Cracking” grouping of the RT report. 

The LLTF recommendations are listed in the attached Table 1, and have been identified under the 

appropriate milestone(s). 

Proposed Actions: The NRC staff is interacting with all PWR licensees, the American Society of 

Mechanical Engineers (ASME), the Electric Power Research Institute (EPRI) Materials Reliability 

Program (MRP), and other external stakeholders in addressing the issues discussed above. This action 

plan includes milestones aimed at guiding the NRC and industry to effectively manage RVH degradation 

and BACC. Throughout the implementation of this action plan, the NRC will establish the necessary 

communications mechanisms to ensure that the NRC, the industry, and all stakeholders are informed and 

sharing the same information. This will be accomplished through public meetings, technical working 

groups, ACRS briefings, and web site postings, as appropriate. 

The Part I milestones deal with development of improved inspection requirements for the RPV head and 

VHP nozzles. Interim inspection guidelines for the RPV upper head have been issued via 

Order EA-03-009 and associated temporary inspection guidelines (TI-150) have been issued for use by 

NRC inspectors. These will be updated as needed based on inspection results. The ASME Boiler and 

Pressure Vessel Code (ASME Code) published ASME Code Case N–729–1 in May 2005. ASME Code 

Case N–729–1 provides alternative inspection requirements for reactor pressure vessel closure heads. 

NRC staff performed a technical evaluation of N–729–1 and found the code case, with certain conditions, 

is acceptable for implementation in lieu of the requirements of Order EA-03-009. Therefore, the NRC 

staff initiated an action to incorporate ASME Code Case N–729–1, with conditions, in a revision to 

10 CFR 50.55a. This action was included in the 10 CFR 50.55a update rulemaking package to 

incorporate the 2004 Edition of the ASME Code. For those licensees which choose to implement ASME 

Code Case N–729–1, with conditions, in lieu of current Order EA-03-009 requirements prior to the 

completion of the rulemaking, they may do so through a relaxation request from the requirements of the 

Order EA-03-009 as explained in a letter dated August 9, 2006, from J. Grobe, NRC, to J. Riley, NEI 

(ADAMS Accession No. ML062220594). 

The Part II milestones evaluate whether industry BACC programs are meeting NRC expectations and 

whether additional inspection guidance should be issued. First, the NRC staff will establish a technical 

basis for BACC program requirements through ongoing and planned research programs. This will include 

evaluation of boric acid events in past reports and in responses to Bulletin 2002-01, and studies of rates 

of reactor pressure boundary materials in boric acid solutions. The NRC staff is also monitoring 

development of revised ASME Code requirements by the Section XI Task Group on Boric Acid. If the 

NRC staff determines that additional interim guidelines are needed prior to issuance of the revised Code 

requirements, they will be issued by an appropriate regulatory tool. When the ASME Code requirements 

are revised, the NRC will initiate action to endorse them, if acceptable. If the revised ASME Code 

requirements cannot be made acceptable to the NRC, then alternate requirements would have to be 

developed and implemented by an appropriate regulatory tool. Based on the leaks discovered in lower 

vessel head penetrations at South Texas Project, the NRC staff issued Bulletin 2003-02 regarding RPV 

lower head inspections. Associated temporary inspection guidelines (TI-152) were issued for use by 

NRC inspectors. The NRC staff will complete and evaluate the results of ongoing research on materials 

degradation, engage external stakeholders and develop a plan to implement a proactive approach to 

manage degradation of the RCPB. 

In engaging external stakeholders to develop a plan to implement a proactive approach to manage 

degradation of the RCPB, the industry has developed a staggered approach to addressing all areas 

susceptible to PWSCC and boric acid corrosion in pressurized water reactors. This industry approach is 
partially complete with activities concerning susceptible butt welds as identified in MRP-139. NRC staff 

review of this action is underway and has provided industry with questions and comments concerning 

MRP-139. Further industry actions for the lower reactor pressure vessel head and other components are 

expected by the March 2007. However, this estimate is tied to industry activities which have experienced 

some delay. 

The ASME published Code Case N–722, “Additional Examinations for PWR Pressure Retaining Welds in 

Class 1 Components Fabricated with Alloy 600/82/182 Materials,” in Supplement 6 to the 2004 Code 

Cases. ASME Code Case N–722 provides recommended additions to the requirements of Table IWB2500-1 for inspection of partial and full penetration welds in Class 1 components fabricated with Alloy 

600/82/182 material. This material is susceptible to cracking, which can lead to leakage that could cause 

boric acid corrosion. NRC staff performed a technical evaluation of Code Case N–722 and found the 

code case, with certain conditions, provides an acceptable approach for addressing safety issues 

associated with boric acid corrosion due to cracking in Alloy 600/82/182 material. Therefore, the NRC 

staff initiated an action to incorporate ASME Code Case N–722, with conditions, in a revision to 

10 CFR 50.55a. 

The Part III milestones address the LLTF findings that the NRC inspection guidelines did not provide 

effective oversight of licensee RPV head inspection and BACC programs. Revised guidelines for these 

activities will be developed. Throughout the process of establishing new requirements, existing NRC 

inspection procedures would be evaluated to verify whether they adequately address the revised 

requirements, and would be updated as needed. 

Originating Documents: 

Memorandum from Travers, W.D. to Collins, S. and Thadani, A.C., dated January 3, 2003, “Actions 

Resulting From The Davis-Besse Lessons Learned Task Force Report Recommendations.” (ADAMS 

Accession No. ML023640431) 

Memorandum from Paperiello, C.J. to Travers, W.D., dated November 26, 2002, “Senior Management 

Review of the Lessons-Learned Report of the Davis-Besse Nuclear Power Station Reactor Pressure 

Vessel Head.” (ADAMS Accession No. ML023260433) 

Memorandum from Howell, A.T. to Kane, W.F., dated September 30, 2002, “Degradation of the DavisBesse Nuclear Power Station Reactor Pressure Vessel Head Lessons-Learned Report.” 

(ADAMS Accession No. ML022740211) 

Regulatory Assessment: The current method for managing PWSCC in the VHP nozzles of U.S. PWRs is 

dependent on the implementation of inspection methods intended to provide early detection of 

degradation of the reactor coolant pressure boundary. Title 10, Section 50.55a(g)(4) of the Code of 

Federal Regulations requires, in part, that ASME Code Class 1, 2, and 3 components must meet the 

inservice inspection requirements of Section XI of the ASME Boiler and Pressure Vessel Code throughout 

the service life of a boiling or pressurized water reactor. Pursuant to Inspection Category B-P of 

Table IWB-2500-1 to Section XI of the ASME Boiler and Pressure Vessel Code, licensees are required 

to perform VT-2 visual examinations of their vessel head penetration nozzles and reactor vessel heads 

once every refueling outage for the system leak tests, and once an inspection interval for the hydrostatic 

pressure test. 

Based on the experience with the VHP nozzle cracking phenomenon, the VT-2 visual examination 

methods required by the ASME Code for inspections of VHP nozzles do not provide reasonable 

assurance that leakage from a through-wall flaw in a nozzle will be detected. The VT-2 visual 

examination methods specified by the ASME Code are not directed at detecting the very small amounts 

of boric acid deposits, e.g., on the order of a few grams, that have been associated with VHP nozzle 
leaks in operating plants. In addition, the location of thermal insulating materials and physical 

obstructions may prevent the VT-2 visual examination methods from identifying minute amounts of boric 

acid deposits on the outer surface of the vessel head. Specifically, Paragraph IWA-5242 of Section XI of 

the ASME Boiler and Pressure Vessel Code does not require licensees to remove thermal insulation 

materials when performing ASME VT-2 visual examinations of reactor vessel heads. Cleanliness of 

reactor vessel heads during the examinations, which is critical for visual examination methods to be 

capable of distinguishing between boric acid residues that result from VHP nozzle leaks and those 

residues that result from leaks in other reactor coolant system components, is not addressed by the 

ASME Code. 

Based on knowledge obtained from evaluation of the Davis-Besse event, and information provided from 

PWR licensees in response to Bulletins 2001-01, 2002-01, and 2002-02, the NRC issued an Order to all 

PWR plants establishing enhanced inspection requirements on an interim basis, which will provide 

adequate assurance of safe plant operation until permanent requirements are established and 

promulgated. 

Current Status: 

As described in detail below, all items are complete and this action plan is closed. 

Part I Status - Part I activities included continued monitoring of outage inspection results, follow-up with 

plants discovering defects, and evaluation of requests for relaxation from First Revised Order EA-03-009. 

The NRC staff evaluated the existing SCC models and determined that they are acceptable for use in 

prioritizing RPV head inspections. The report is publicly available in ADAMS (ML032461221). 

The NRC staff collected information on Alloy 600, Alloy 690 and other nickel-based alloy nozzle cracking 

and issued a summary report for internal use. The report is publicly available in ADAMS (ML040910354). 

The NRC staff developed a rulemaking plan to incorporate the inspection requirements for the RPV upper 

head into 10 CFR 50.55a. This was submitted for Commission approval in July 2004. The Commission 

decided not to proceed with this rulemaking and directed the NRC staff to continue to work with the 

industry to incorporate revised inspection requirements into the ASME code (SRM-SECY-04-0115, 

August 6, 2004). The NRC staff participated in ASME Code Committee development of revised 

inspection requirements. In June 2005, the ASME Board on Nuclear Codes and Standards approved 

Code Case N–729, which provides additional inspection requirements for RPV upper heads. Therefore, 

Part I, item 5 is considered complete. However, NRC staff review of the code case identified significant 

publishing errors that necessitated a reissuance of the code case as N–729–1. The revision was 

published in May 2006. The NRC staff has evaluated the revised code case and found it, with certain 

conditions, to be an acceptable long term reactor vessel closure head inspection plan. NRC staff has 

documented its review and acceptance in a memorandum from the Division of Component Integrity to the 

Division of Policy and Rulemaking (Accession No. ML061800439) to initiate rulemaking to endorse Code 

Case N–729–1, with conditions, in a revision to 10 CFR 50.55a. Therefore, Part I, item 7 is considered 

complete. 

On September 10, 2008, the NRC issued the final rule (73 FR 52730) to amend its regulations including 

the addition new paragraph 10 CFR 50.55a(g)(6)(ii)(D) to incorporate by reference ASME Code 

Case N–729–1 with conditions, effective October 10, 2008. This establishes permanent guidelines for 

reactor vessel closure head inspections. The NRC staff issued a memorandum (Accession No. 

ML093510192) on December 19, 2009, that closed all remaining items under Part I. 

Part II Status - For Part II activities, the review and evaluation of licensee responses to Bulletin 2002-01 

regarding BACC have been completed. A summary of the evaluation was published in RIS 2003-13 
(Accession No. ML032100653). The evaluation of responses to Bulletin 2002-01, which included audits 

of BACC programs at five plants, determined that the plants complied with requirements at the 

programmatic level. In general, the results indicated weaknesses in the licensees’ BACC and ASME 

Section XI programs. The weaknesses identified in the RIS included identifying pressure boundary 

leakage and potential leakage paths, looking for boric acid crystals, walking down systems when the plant 

is entering or leaving the hot shutdown mode, and detecting small leaks during normal power operation. 

Based on this review and the discovery of leakage on vessel bottom penetrations at South Texas Project, 

Bulletin 2003-02 was issued. 

The NRC staff collected information on available worldwide operating experience on boric acid corrosion 

of pressure boundary materials. The NRC staff also contracted Argonne National Lab to conduct a test 

program on boric acid corrosion of light-water reactor pressure vessel materials. The results were 

published in NUREG/CR-6875. This information and the information previously collected on nozzle 

cracking along with the NRC staff evaluation of the SCC models have been incorporated into NUREG1823, “U.S. Plant Experience with Alloy 600 Cracking and Boric Acid Corrosion of Light-Water Reactor 

Pressure Vessel Materials” (ML050690012). 

The NRC staff used the information collected regarding boric acid corrosion and the information 

previously collected regarding Alloy 600, Alloy 690 and other nickel-based alloy nozzle cracking to 

develop a course of action and an implementation schedule to address LLTF 3.1.1(1). The NRC staff met 

with industry representatives on March 24, 2005, to discuss their activities for addressing PWSCC in 

nickel based alloy butt welds and in other locations in the reactor coolant system. Industry presentations 

were high level and lacked the technical details and scheduler commitments the NRC staff was 

expecting. On September 29, 2005, the NRC staff again met with the industry, during which 

representatives of the Materials Reliability Program (MRP) indicated that their inspection guidelines for 

this issue would not be available until the end of 2006. At a meeting with NRC senior management on 

February 22, 2006, MRP representatives indicated that these inspection guidelines would not be available 

until 2007. Based on the result of these meetings, the NRC staff has concluded that an effective course 

of action for completing milestone II.7 is to incorporate ASME Code Case N–722 into 10 CFR 50.55a. It 

contains inspection rules for boric acid corrosion and cracking of nickel-based alloy nozzles and 

addresses the course of actions associated with the closure of LLTF 3.1.1(1). The NRC staff has 

completed its evaluation of ASME Code Case N–722 and has provided proposed rule language and input 

to the regulatory analysis in a memorandum from the Division of Component Integrity to the Division of 

Policy and Rulemaking (Accession No. ML060390427) to initiate rulemaking to endorse Code 

Case N–722, with conditions, in a revision to 10 CFR 50.55a. Therefore, Part II, item 8 is considered 

complete. On September 10, 2008, the NRC issued the final rule (73 FR 52730) to amend its regulations 

including the addition new paragraph 10 CFR 50.55a(g)(6)(ii)(E) to incorporate by reference ASME Code 

Case N–722 with conditions, effective October 10, 2008. The NRC staff issued a memorandum 

(Accession No. ML093510192) on December 19, 2009, that closed all remaining items under Part II. 

Part III Status - For Part III activities, inspection procedure revisions addressing RPV head inspection and 

boric acid corrosion control programs were issued. Temporary Instruction (TI) 2515/150, issued on 

October 18, 2002, provides guidance for assessing the licensees’ RPV head inspections pursuant to 

Order EA-03-009. The TI also includes instructions for follow-up on findings of boric acid accumulation. 

Inspection Procedure (IP) 71111.08, “Inservice Inspection Activities,” dated May 11, 2004, provides 

periodic inspection requirements and guidance for boric acid corrosion control. The Regions provided 

feedback regarding the implementation of TI 2515/150 and IP 71111.08 since October 2002. In addition, 

the Inspection Program Branch (IIPB) reviewed inspection results from TI 2515/150 and IP 71111.08. As 

a result of the licensees’ visual and non-visual inspections and NRC direct observations and oversight of 

licensees’ activities, a number of facilities have made repairs to their vessel heads and some have 

replaced the vessel heads. In some cases, repairs were required; in others, the licensee took actions 

voluntarily. Feedback from each Region and IIPB staff review indicates that the licensees’ programs are 

generally adequate for locating and evaluating and/or correcting boric acid leaks. Although several 
inspection findings were identified, none were of greater than very low significance. The NRC staff will 

continue to evaluate the effectiveness of this IP as part of annual ROP self-assessment and make 

appropriate improvements as needed. 

Contacts: 

NRR Lead PM: David Beaulieu, PGCB, 301-415-3243 

NRR Lead Contact: Edmund Sullivan, DCI, 301-415-2796