ML072740510

Lltf Action Plan Feb 2008 Update - Public

ML072740510
Person / Time
Site:	Davis Besse
Issue date:	02/11/2008
From:	NRC/NRR/ADRO/DPR
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Download: ML072740510 (3)

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DAVIS-BESSE LESSONS LEARNED TASK FORCE RECOMMENDATIONS REGARDING STRESS CORROSION CRACKING TAC No.DescriptionMB2916Non plant-specific activities for Last Update: 02/01/08 Bulletin 2001-01Lead Division: DPRMB3567VHP Action Plan (CoordinationSupporting Divisions: DE, DSS, & DIRSand Administration) Supporting Offices: RES & RegionsMB3954Development of CRDM NUREGs (Bulletin 2001-01)MB4495Lead PM Activities for Bulletin 2002-01 MB4603Non plant-specific activities for Bulletin 2002-01MB5465Lead PM Activities for Bulletin 2002-02 MB6218Inspection TI for Bulletin 2002-02 MB6220Review of NEI/MRP Crack Growth Rate Report (MRP-55)MB6221Development of Alternate (to ASME Code) RPV Head and VHP Inspection RequirementsMB6222Review of NEI/MRP RPV Head and VHP Inspection Plan (MRP-75)MB7182Orders for Interim Inspection Guidelines MB9522Review of Bulletin 2002-01 Responses MB8915Generic Activities for Lower Head Inspection MB9891Develop Bulletin 2003-02 MC0590Develop Technical Issues Related to Incorporating RCPB Inspection Requirements into 50.55aMC1036Develop/Revise Inspection Guidance for ISI and BACCMilestoneDate (T=Target)(C=Complete)LeadSupport Part I - Reactor Pressure Vessel Head Inspection Requirements1.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)ML040920026RES/DETDE2.Critically evaluate existing SCC models with respect to their continuing use in the susceptibility index.

[LLTF 3.1.4(1)-Medium]

07/03 (C)ML032461221RES/DETDE3.aComplete initial evaluation of individual plant inspections in response to Bulletins and

Orders.05/04 (C)ML041560306DEDLPM Regions3.bContinue to review future inspection results until permanent guidelines are issued.OngoingDCIDORL Regions MilestoneDate (T=Target)(C=Complete)LeadSupport4.Incorporate Order EA-03-009 requirements into 10 CFR 50.55a a.Develop technical basis b.Develop rulemaking planc.Commission decision Note (2)04/04 (C)ML040920628

ML040920638 07/04 (C)ML041610180 08/04 (C)ML042190072 DE DRIP DRIP DE5.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)Note (1)DERES/DET DSSA Regions Industry6.Participate in meetings and establish communications with appropriate

stakeholders (e.g., MRP, ASME).

[LLTF 3.3.4(8)-High]OngoingDCIRES/DET PGCB DPR DSS Industry7.Review and evaluate revised ASME Code requirements when issued.

[LLTF 3.3.4(8)-High]

06/06 (C)ML061800439DCIRES/DET8.If revised ASME Code requirements are acceptable, establish schedule to incorporate

by reference into 10 CFR 50.55a.

[LLTF 3.3.4(8)-High]06/08 (T)DCIDPR DIRS DSS RES/DET Industry Public9.Publish a NUREG report summarizing findings from Part I, Items 1 and 2, and Part

II, Item 1.

03/05 (C)NUREG-1823 ML050690012RES/DETDE10.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)ML043010675DERES/DET MilestoneDate (T=Target)(C=Complete)LeadSupport Part II - Boric Acid Control1.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)ML043000274RES/DETDE2.aEvaluate individual plant responses to Bulletin 2002-01 regarding Boric Acid

Inspection Programs (60-day responses and

necessary follow-up)2.bIssue public document to summarize evaluation of plant responses.

06/03 (C)ML031760568 07/03 (C)ML032100653 DE DE DLPM DLPM DRIP3.Participate in meetings and establish communications with appropriate

stakeholders (e.g.,MRP, ASME).OngoingDCIRES/DET PGCB DPR DSS Industry4.Evaluate need to take additional regulatory actions and determine appropriate regulatory

tool(s).06/03 (C)ML031760568DEDLPM DRIP DIPM DSSA Regions5.Issue Bulletin 2003-02 on Reactor Vessel Lower Head inspection.

08/03 (C)ML032320153DEDLPM6.Develop milestones for additional regulatory actions, as necessary.07/03 (C)DEDLPM DSSA DRIP7.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.06/08 (T)DCIRES8.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)ML060390427DCIRES/DET MilestoneDate (T=Target)(C=Complete)LeadSupport Part III - Inspection Programs1.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

ML041340207DIPMDE Regions2.Develop inspection guidance that provides for timely, periodic inspection of PWR plant

BACC programs.

[LLTF3.3.2(1)-High]

06/04 (C)ML022940597

ML041340207DIPMDE Regions3.aDevelop 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]3.bPerform follow-up evaluation of inspection guidance and licensee program acceptability

after conducting inspections for

approximately one year.

06/04 (C)ML022940597

ML041340207 05/05 (C)ML051360392 DIPM DIPM DE RES/DET Regions DE RES/DET RegionsNotes:(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 cra cking of vessel head penetration (VHP) nozzles, haveprompted the NRC staff to question the adequacy of current RVH and VHP inspection programs that rely

on visual examinations as the primary inspecti on method. Also, the failure to adequately address indications of boric acid leakage at Davis-Besse rais ed 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 i ndicated 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 TaskForce (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 O perations (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 acco mplishing 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 has performed a technical evaluation of N-729-1 and finds the code case, with certain

conditions, is acceptable for implementation in lieu of the requirements of Order EA-03-009. Therefore, the NRC staff has initiated an action to incorporate ASME Code Case N-729-1, with conditions, in a

revision to 10 CFR 50.55a. This action is 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 ofreactor 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 Coderequirements, 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 inspec tion 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 pl an to implement a proactive approach to manage degradation of the RCPB, the industry has dev eloped 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 prov ided 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 Exami nations 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 IWB-2500-1 for inspection of partial and full penetration welds in Class 1 components fabricated

with Alloy 600/82/182 material. This material is susc eptible to cracking, which can lead to leakage that could cause boric acid corrosion. NRC staff perfo rmed a technical evaluation of Code Case N-722 and found the code case, with certain conditions, prov ides an acceptable approach for addressing safety issues associated with boric acid corrosion due to cr acking in Alloy 600/82/182 material. Therefore, the NRC staff has initiated an action to incorporate ASME Code Case N-722, with conditions, in a revision to

10 CFR 50.55a. This revision is reflected in milestone II.7.

The Part III milestones address the LLTF findings t hat 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 veri fy 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 Davis-Besse 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 cr acking phenomenon, the VT-2 visual examination methods required by the ASME Code for inspecti ons 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 insula ting materials and physical obstructions may prevent the VT-2 visual examination methods from identifyi ng 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 exami nation 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 t he 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

Part I Status - Part I activities included continued monito ring of outage inspection results, follow-up with plants discovering defects, and evaluation of requests fo r 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. T he 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 require ments 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 which 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 ins pection 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.

Once the final rule to incorporate ASME Code Case N-729-1 with conditions into 10 CFR 50.55a is approved, permanent guidelines will have been established for reactor vessel closure head inspections, and all items under Part I will be closed. This rulemaking is scheduled to be completed by June 2008.

Part II Status - For Part II activities, the review and ev aluation 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 respons es to Bulletin 2002-01, which included audits of BACC programs at five plants, determined that the pl ants 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 l eaks 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 worl dwide operating experience on boric acid corrosionof 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 NUREG-1823, "U.S. Plant Experience with Alloy 600 Cr acking 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 nicke l-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 ac tivities 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 t heir inspection guidelines for this issue would not beavailable until the end of 2006. At a meeting with NRC senior management on February 22, 2006, MRP

representatives indicated that these inspection gui delines will 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. The rulemaking to

incorporate ASME Code Case N-722 into 10 CFR 50.55a is scheduled to be completed by June 2008, which will complete all items under Part II.

Part III Status - For Part III activities, inspection proc edure 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 assessi ng 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 Ins pection 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 in spections 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, 415-3243NRR Lead Contact: William Bateman, DCI, 415-2795 NRR Technical Contacts: William Koo, DCI, 415-2706 Edmund Sullivan, DCI, 415-2796