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NRC Section XI Report - August 2008

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Presented By:  Mr. Wally Norris, United States Nuclear Regulatory Commission


NRC Report
August 2008

1.    Amendments to 10 CFR 50.55a – ASME Code Edition/Addenda

 

A proposed amendment to Part10 of the Code of Federal Regulations, Section 50.55a (10 CFR 50.55a) to incorporate by reference the 2004 Edition of the ASME Boiler and Pressure Vessel Code (ASME Code) and Code for Operation and Maintenance of Nuclear Power Plant Components (OM Code) was published on April 5, 2007 (72 FR 16731).  The public comment period closed on June 19, 2007.  Responses to the comments have been developed.  The final rule should be published in September 2008.

 

The Executive Director for Operations approved a Lean Six Sigma Project for the purpose of reducing the rulemaking process cycle time to incorporate edition and addenda of the ASME Code and OM Code into 10 CFR 50.55a.  The project started on May 27, 2008, and includes staff from the Office of the General Counsel, Office of Nuclear Reactor Regulation, Office of Regulatory Research, and Office of New Reactors.  The project team has been reviewing the current process to determine how a more efficient process can be developed to improve NRC resource utilization.  All other rulemaking activities are excluded from the scope of this project.  However, lessons learned and identified process enhancements from this project will be evaluated for making improvements to other rulemakings (e.g., ASME Code Case regulatory guide rulemaking process).

 

2.    ASME Code Case Rulemaking/Regulatory Guides

 

Proposed Revision 35 to RG 1.84, “Design, Fabrication, and Materials Code Case Acceptability, ASME Section III,” proposed Revision 16 to RG 1.147, “Inservice Inspection Code Case Acceptability, ASME Section XI, Division 1,”and proposed Revision 3 to RG 1.193 “ASME Code Cases Not Approved for Use” are currently in review.  The guides address Code Cases from Supplement 2 to the 2004 Edition through Supplement 0 to the 2007 Edition (Supplement 0, 2007 Edition also serves as Supplement 12 to the 2004 Edition).  The draft guides are expected to be published for public comment in the September/October 2008 time frame.

 

The NRC staff has completed its review of Supplements 1, 2, and 4 to the 2007 Edition (there were no nuclear Code Cases in Supplement 3).

 

3.    Risk–Informed Activities

 

Alternative Risk-Informed Inservice Inspection (RI-ISI) Program – Code Case N-716

 

On September 21, 2007, the NRC conditionally approved an alternative risk-informed inservice inspection program based on Code Case N-716 for Grand Gulf Nuclear Station Unit 1 (the safety evaluation is available in the NRC’s Agencywide Documents Access and Management System (ADAMS) as Accession No. ML072430005).  On September 28, 2007, the NRC conditionally approved a similar alternative RI-ISI program for Donald C. Cook Nuclear Plants 1 and 2 that is based on Code Case N-716 but deviates and expands upon the Code Case (the safety evaluation is available in ADAMS [ML072620553]).  Finally, a similar alternative RI-ISI program was approved on April 28, 2008 [ML080980120] for Waterford Steam Electric Station.  The approvals were specific to these units and relied on several changes to the methodology described in Code Case N-716.  The Working Group Implementation of Risk-Based Examination is considering the alternative RI-ISI programs as described in the safety evaluations.

 

10 CFR 50.46a - Option 3 Rulemaking (Risk-Informed Emergency Core Cooling System - ECCS)

 

The NRC staff prepared a proposed rule containing emergency core cooling system evaluation requirements, that could be used as an alternative to the current requirements in 10 CFR 50.46, “Acceptance Criteria for Emergency Core Cooling Systems (ECCS) for Light-Water Nuclear Power Reactors.”  The proposed rulemaking was designed to redefine the large-break LOCA requirements to provide a risk-informed alternative maximum break size.  In October 2006, the staff produced a draft final rule (ML062760146) and briefed the ACRS.

 

The Advisory Committee on Reactor Safeguards (ACRS) issued a letter on November 16, 2006, (ML063190465) with three general recommendations: (1) the Rule to risk-inform 10 CFR 50.46 should not be issued in its current form.  It should be revised to strengthen the assurance of defense in depth for breaks beyond the transition break size (TBS); (2) the revision of draft NUREG-1829, "Estimating Loss-of-Coolant Accident (LOCA) Frequencies Through the Elicitation Process," to include changes resulting from the resolution of public comments, should be completed before the revised Rule is issued; (3) the interpretation that the Rule limits the total increase in core damage frequency (CDF) resulting from all changes in a plant to be "small" (i.e., <10-5/yr) represents a significant departure from the current guidance for risk-informed regulation and should be reviewed for its implications.

 

As a result, the staff provided SECY-07-0082, “Rulemaking To Make Risk-Informed Changes to Loss-of-Coolant Accident Technical Requirements,” to the Commission recommending how to proceed with the rulemaking (ML070180466).  The Commission’s August 10, 2007, Staff Requirements Memorandum directed the staff to continue with the rule making but to change the priority from high to medium and provided additional direction (ML072220595).

 

In March 2008, the staff provided the Executive Director for Operations its proposed schedule for completing the final rule (ML080370354).  It is projected that the staff will meet with the ACRS to discuss the revised draft final rule in May 2009.

 

Pressurized Thermal Shock – 10 CFR 50.61

 

On October 3, 2007, the NRC published a proposed amendment to 10 CFR 50.61, “Alternate Fracture Toughness Requirements for Protection Against Pressurized Thermal Shock Events,” to provide updated requirements for pressurized thermal shock (PTS) events for PWR reactor vessels (72 FRN 56275).  The proposed rule is commonly referred to as 10 CFR 50.61a.  The updated technical basis uses many different models and parameters to estimate the yearly probability that a PWR will develop a through-wall crack as a consequence of PTS loading.  These new requirements would be voluntarily utilized by any PWR licensee as an alternative to complying with the existing requirements.  The public comment period closed on December 17, 2007.  The NRC received over 40 comments.  The staff is currently developing responses to the comments.  It is anticipated that the final rule will be published in mid-2009.

 

Reactor Vessel Weld Inspection

 

By letter dated January 26, 2006, the Westinghouse Owners Group, later the Pressurized-Water Reactor Owners Group (PWROG), submitted topical report WCAP‑16168-NP, Revision 1, “Risk-Informed Extension of the Reactor Vessel In-Service Inspection Interval.”  The PWROG topical report provides the technical and regulatory basis for decreasing the frequency of inspections by extending the American Society of Mechanical Engineers Boiler and Pressure Vessel Code (ASME Code) Section XI inservice inspection interval for reactor vessel welds from the current 10 years to 20 years (ASME Code Section XI, Categories B-A and B-D, reactor vessel welds).

 

The Final Safety Evaluation for Pressurized Water Reactor Owners Group (PWROG) Topical Report (TR) WCAP-16168-NP, Revision 2, “Risk-Informed Extension of the Reactor Vessel In-service Inspection Interval,” was issued on May 8, 2008 (ML081060051).  The topical report relies extensively on work described in NUREG-1874, "Recommended Screening Limits for Pressurized Thermal Shock (PTS)."  The NRC staff has accepted TR WCAP-16168-NP, Revision 2, based on the imposition of a condition related to the augmented evaluation of in-service inspection (ISI) results taken from Section (e) of the proposed rule 10 CFR 50.61a, published in the Federal Register on October 3, 2007 (72 FR 56275).  The NRC staff is in the process of reviewing public comments on the proposed rule and preparing the final rule.  If the final 10 CFR 50.61a differs from the proposed 10 CFR 50.61a with regard to the augmented ISI evaluation requirements, it is expected that the PWROG will review the requirements in the final 10 CFR 50.61a and determine whether a revision to the accepted TR WCAP-16168-NP, Revision 2, is required.  Furthermore, licensees that choose to implement 10 CFR 50.61a must perform the ISI required in Section (e) of the rule, and must submit the required information for review and approval to the Director, Office of Nuclear Reactor Regulation, at least three years before the limiting RTPTS value calculated under 10 CFR 50.61 is projected to exceed the PTS screening criteria in 10 CFR 50.61.  Licensees implementing Section (c) of 10 CFR 50.61a must perform the inspections and analyses required by Section (e) of 10 CFR 50.61a prior to implementing the extended interval.

 

Phased Approach to Probabilistic Risk Assessment Quality

 

The increased use of probabilistic risk assessments (PRAs) in the NRC’s regulatory decisionmaking process requires consistency in the quality, scope, methodology, and data used in such analyses.  A key aspect of implementing a phased approach to PRA quality is the development of PRA standards and related guidance documents.  To achieve that objective, professional societies, the nuclear industry, and the staff have undertaken initiatives to develop national consensus standards and guidance on the use of PRA in regulatory decisionmaking.  ASME and ANS recently published a joint PRA standard, “Level 1 and Large Early Release Frequency (LERF) PRA Standard” (ASME/ANS RA-S-2008), which applies to at-power internal events, internal fire events, and external events for operating reactors.

 

The staff has initiated work on Revision 2 of Regulatory Guide 1.200, “An Approach for Determining the Technical Adequacy of Probabilistic Risk Assessment Results for Risk-Informed Activities.”  This revision will endorse the joint ASME/ANS Level 1/LERF PRA standard.  The staff recently held public meetings on this topic and plans to issue Revision 2 for public comment in mid-2008.

 

In November 2007, the staff issued draft NUREG-1855, “Treatment of Uncertainties from PRAs in Risk-Informed Decision-Making,” for public review and comment.  It is being developed in collaboration with the Electric Power Research Institute (EPRI) who has issued a draft report on uncertainties, as part of the NRC/EPRI Memorandum of Understanding.  These two documents are meant to be complimentary.  The NRC report along with the EPRI report provides information and guidance on uncertainties associated with PRA.  They are meant to provide guidance on meeting the requirements in the ASME/ANS PRA standard on uncertainties, and provide guidance on how to treat the results from the uncertainty analyses in decision making for risk-informed activities.  The staff held two public meetings and plans to issue a final version in late 2008.

 

The regulatory guide and NUREG report (including the EPRI report) will assist the staff in establishing the technical acceptability of the PRA results to be used in regulatory decision making.  When used in support of an application, these documents will obviate the need for an in-depth review of the base PRA by NRC reviewers, and provide for a more focused and consistent review process.

 

Repair and Replacement

 

In September 2006, the Pressurized Water Reactor Owners Group (PWROG) submitted WCAP-16308-NP, Revision 0, “Pressurized Water Reactors Owners Group 10 CFR 50.69 Pilot Program - Categorization Process - Wolf Creek Generating Station” [ML062770345].  The Topical includes, in part, an alternative methodology to the NRC endorsed Code Case N-660, “Risk-Informed Safety Classification for Use in Risk-Informed Repair/Replacement Activities,” for categorization of passive components.

 

On April 9, 2008, a public meeting was held with industry to discuss the topical report (TR).  Specifically, industry representatives met with the NRC staff to discuss responses (ML080780403) to the NRC staff’s request for additional information (RAI) dated August 27, 2007 (ML072220129).  Several key technical issues in the TR were identified with which the staff had disagreement.  Regarding the final document method, the NRC staff stated that it plans to write its safety evaluation based on a review of TR WCAP-16308-NP, Revision 0, as supplemented by the RAI responses.  The NRC staff identified several concerns with regards to the contents of Table A-2a and A-2b of TR-WCAP-16308-NP.  During the meeting, Westinghouse representatives discussed proposed changes to these tables, to make it easier for the NRC staff to compare/track changes between the approved Code Case N-660 and the TR.

 

The handouts that Westinghouse representatives presented to facilitate the discussion are available in ADAMS as Accession Nos. ML081020419, ML081020431, and ML081020439.  Based upon discussions that occurred during the public meeting, Westinghouse plans to submit a revised Table A-2a and A-2b, prior to the NRC staff’s development of the draft safety evaluation.

 

4.    Generic Activities on Material Degradation/PWR Alloy 600/182/82 PWSCC

 

Prior to 2005, inspection of dissimilar metal (DM) butt welds was performed in accordance with ASME Code, Section XI, requirements.  In late 2005, the industry implemented an initiative for more aggressive inspection schedules than required by Code.  This initiative is documented in MRP-139, “Materials Reliability Program: Primary System Piping Butt Weld Inspection and Evaluation Guideline.”  The base line inspection schedules in MRP-139 are based on temperature and size; for example, pressurizer inspections were required to be completed first.  The on-going inspection frequency is based on the mitigation method applied to a weld (for example, the most frequent inspections would occur in unmitigated pressurizer welds).  The staff is monitoring the implementation of the MRP-139 program for managing PWSCC in DM butt welds.  NRC recently issued Temporary Instruction (TI-172) for regional staff to verify that all PWRs with DM butt welds are implementing MRP-139.

 

For the longer term, the NRC staff requested that ASME develop a Code Case for inspection of Alloy 82/182 butt welds.  ASME has been actively working on the Code Case and has been responsive to NRC input on the Code Case.  The Code Case is nearing completion.  Based on progress to date, the staff expects that the Code Case will be acceptable for referencing with minimal comments/conditions and that the Code Case will be incorporated by reference into 10 CFR 50.55a.

 

In Oct 2006 inspections were performed at Wolf Creek prior to the pressurizer DM welds being mitigated by application of weld overlays.  Large circumferential flaw indications were found in the Wolf Creek pressurizer safety, relief, and surge nozzle welds.  Based on industry and NRC advanced finite element (AFE) fracture mechanics analyses, NRC staff agreed to industry’s original planned inspection schedules, i.e., some plants inspected their welds a few months later than called for in MRP‑139.

 

Recently, two B&W plants experienced PWSCC in decay heat removal to hot leg welds.  The staff evaluated the experience from these plants and concluded that these experiences are within the assumptions upon which the current inspection schedules are based.

 

Recently a potential safety issue was identified related to inspections of nozzles from a retired pressurizer.  These inspections caused the staff to question whether the initial flaw characterization was inconsistent with the advanced finite element analysis basis for pressurizer inspections scheduled in spring 2008.  Based on quick turn around but more advanced inspection techniques used by industry and witnessed by the NRC staff, the staff concluded that the flaws were fabrication-induced and there was no structurally significant PWSCC in the welds.  This was confirmed via destructive analysis.  The NRC staff continues to monitor and evaluate operating experience to ensure the current inspection schedules are adequate.

 

5.    New Reactor Licensing Activities

 

The New Reactor Licensing public web-site [http://www.nrc.gov/reactors/new-reactors.html has a list of expected new nuclear power plant applications, and an estimated schedule by fiscal year for new reactor licensing applications.

 

New Reactor License Application Reviews

 

On June 11, 2008, the Office of New Reactors published a Notice of Availability of the Final Interim Staff Guidance DC/COL-ISG-03 on Probabilistic Risk Assessment Information to Support Design Certification and Combined License Applications.  The Final Interim Staff Guidance (ISG) DC/COL-ISG-03 (ML081430087) supplements the guidance provided to the staff in Section 19.0, “Probabilistic Risk Assessment and Severe Accident Evaluation for New Reactors,” of NUREG-0800, “Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants,” concerning the review of probabilistic risk assessment (PRA) information and severe accident assessment submitted to support design certification (DC) and combined license (COL) applications.

 

Advanced Reactor Regulatory Structure: NUREG-1860

 

The staff issued NUREG-1860, “Feasibility Study for a Risk-Informed and Performance-Based Regulatory Structure for Future Plant Licensing,” Volumes 1 and 2, in December 2007.  This NUREG establishes the feasibility of developing a risk-informed and performance-based regulatory structure for the licensing of future nuclear power plants.  It documents a framework that provides an approach, scope, and criteria that could be used to develop an alternative set of requirements to 10 CFR Part 50, “Domestic Licensing of Production and Utilization Facilities,” for future nuclear power plants.  The staff will, as resources permit, continue its pre-application discussions supporting a proposed risk-informed licensing approach for the pebble-bed modular reactor (PBMR).  The licensing strategy for the next generation nuclear plant (NGNP) that is currently being prepared in cooperation with the Department of Energy will also include recommendations for the use of risk insights in the licensing of the NGNP prototype facility.  These experiences will inform the staff's recommendation to the Commission in 2009 on the possible use of risk-informed and performance-based approaches within rulemakings to support the licensing of Generation IV reactors.

 

6.    Periodic Meeting to Discuss Development of Nuclear-related Codes and Standards at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland

 

On July 9, 2008, staff of the NRC, National Institute of Standards and Technology, and Department of Energy held a public meeting with representatives of standards developing organizations (SDOs) and nuclear industry representatives to discuss priorities for developing nuclear-related codes and standards that may be endorsed in lieu of developing Government-unique standards.  The discussion focused on identifying and addressing gaps and overlapping efforts among SDOs.  The Government agencies recommended that SDOs increase their cooperative efforts, while the SDOs suggested that Government increase the attention given to international standards.

 

7.    Preliminary Assessment of NDE Methods for the Inspection of HDPE

 

The NRC has been conducting research at Pacific Northwest National Laboratory to assess issues related to the NDE of high density polyethylene (HDPE) piping.  A Technical Letter Report, PNNL-17584, “Preliminary Assessment of NDE Methods on Inspection of HDPE Butt Fusion Piping Joints for Lack of Fusion,” is available in ADAMS (ML081780765).

 

Issues currently under consideration are PE pipe joining methods, NDE effectiveness in detecting fabrication flaws, the degradation process to which PE pipe might be susceptible, and the effectiveness of NDE to detect this degradation and structural integrity.

 

Some high-speed tensile impact tests of HDPE butt joints have been completed.  The butt joints were fused under conditions expected to produce lack of fusion (LOF) in the joint.  Time-of-flight diffraction and phased-array (PA) methods were used to evaluate the joints to select both “good” and “bad” areas (i.e., areas expected to contain LOF).  The results are being evaluated, and additional testing will be performed.


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