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Engineering Challenges in U.S. Nuclear Reactor Safety Jack Grobe, Associate Director for Engineering and Safety Systems Office of Nuclear Reactor Regulation Massachusetts Institute of Technology February 11, 2008 Agenda NRC Overview NRC Educational Support Activities NRR Overview

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engineering challenges in u s nuclear reactor safety

Engineering Challenges in U.S. Nuclear Reactor Safety

Jack Grobe, Associate Director for Engineering and Safety Systems

Office of Nuclear Reactor Regulation

Massachusetts Institute of Technology

February 11, 2008

  • NRC Overview
  • NRC Educational Support Activities
  • NRR Overview
  • Operating and New Reactors
  • Operating Reactor Trends and Technical Issues
  • Digital Instrumentation & Control Issues
nrc mission
NRC Mission

License and regulate the Nation’s civilian use of byproduct, source, and special nuclear materials to ensure adequate protection of public health and safety, promote the common defense and security, and protect the environment.

nrc regulatory functions
NRC Regulatory Functions
  • Establish standards, regulations and requirements
  • Issue licenses for nuclear facilities and users of nuclear materials
  • Inspect facilities and users of nuclear materials to ensure compliance with requirements
nrc organization
NRC Organization
  • Two Major Programs
    • Nuclear Reactor Safety Program
      • Accounted for 74% of NRC’s costs in FY 2007
    • Nuclear Materials and Waste Safety Program
      • Accounted for 26% of NRC’s costs in FY 2007
nrc grant opportunities
NRC Grant Opportunities
  • NRC FY 2008 Budget includes $ 19.7 million in educational support to colleges, universities, and trade schools.
  • NRC Grant Programs:
    • Nuclear Education Grant Program
      • $4.7 million towards curriculum development.
    • Scholarships and Fellowship Grant Program
      • $15 million towards scholarships and fellowships at colleges, universities, and trade schools.
nuclear education grant program
Nuclear Education Grant Program
  • Description
    • Provides funding support to institutions of higher education to support courses, studies, training, curricula, and disciplines pertaining to the NRC mission.
  • Process (FY08)
    • Applicants submit letter of intent – Jan. 22
    • NRC issues invitation for full proposal – Feb. 15
    • Full proposal submissions – March 21
  • Additional Information
scholarship and fellowship grant program
Scholarship and Fellowship Grant Program
  • Description
    • Allows students to pursue an education in science, engineering, or other fields or study related to the NRC mission.
  • Requirements
    • Recipients agree to 1 year employment for each full or partial year of academic support.
    • Eligible applicants attend regionally accredited 4-year U.S. public and private institutions of higher education.
    • Strong interest in areas of probabilistic risk, thermodynamics, mechanics, fuels, and digital instrumentation and controls.
  • Additional Information
    • Solicitation will be posted on during the week of February 11, 2008.
office of nuclear reactor regulation
Office of Nuclear Reactor Regulation
  • What does NRR do?
    • Contributes to the NRC mission to protect public health, safety, and the environment for reactors regulated under 10 CFR Part 50
  • How does NRR do this?
    • By developing and implementing the following major reactor programs:

- Rulemaking

- Licensing

- Oversight, and

- Incident Response

potential new reactor applicants


Amarillo Power

Ameren UE

PPL Generation





Progress Energy

S.C. Electric & Gas

Southern Co.


TXU Power


NRG Energy





Potential New Reactor Applicants
recent nrr activities
Recent NRR Activities
  • Safety of Operating Reactors
    • Recent Trends
  • Operating Experience
    • Safety Culture
    • Extended Power Uprates (EPU) – Steam Dryer Analysis
    • Alloy 82/182 Dissimilar Metal Butt Weld (DMBW)
safety culture
Safety Culture
  • Human performance and organization effectiveness are the keys to sustain safe operations
  • Many complex factors influence successful performance
  • Several facilities exhibited weak performance
    • Peach Bottom
    • Millstone
    • D.C. Cook
    • Clinton
    • Davis-Besse
    • Palo Verde
  • INPO and NRC engaging in organizational effectiveness assessment
safety culture22
Safety Culture
  • Fall 2002 – INPO SOER
    • Immediate requirement
    • All facilities perform assessment
    • Report results to INPO
  • IAEA Documents
    • INSAG-15, “Key Practical Issues in Strengthening Safety Culture.”

    • INSAG-4, “Safety Culture.”

    • INSAG-13, “Management of Operational Safety in Nuclear Power Plants.”

  • NRC Regulatory Information Summary 2006-13, “Information on the Changes Made to the Reactor Oversight Process to More Fully Address Safety Culture”
    • Evaluate safety culture weaknesses
    • Structured process for assessing results
    • Cross cutting attributes

extended power uprates steam dryers
Extended Power Uprates- Steam Dryers
  • Many licensees have been implementing power uprates to increase nuclear power electric output.
  • Some boiling water reactors have experienced adverse flow effects on safety related and non-safety related equipment during power uprate operation.
  • Most significant problems occurred at Quad Cities Units 1 and 2, which experienced failures of steam dryers and electromatic relief valves during Extended Power Uprate (EPU) operation.
  • Licensees need to consider potential adverse flow effects when planning to implement a proposed power uprate.
qc1 steam dryer failure november 2003 close up
QC1 Steam Dryer FailureNovember 2003(close-up)

Missing portion of outer bank vertical plate, approx. 6 in. x 9 in.

qc2 steam dryer failure march 2004
QC2 Steam Dryer FailureMarch 2004

Tie bar to attachment welds

Plate attachment stitch weld

Tip of gusset plate

asb modification
ASB Modification




pwr alloy 82 182 dissimilar metal butt welds
PWR Alloy 82/182 Dissimilar Metal Butt Welds

Surge Nozzle-to-Safe End

Dissimilar Metal Weld

Safety/Relief Nozzle-to-Safe End Dissimilar Metal Weld

alloy 82 182 dissimilar metal butt welds
Alloy 82/182 Dissimilar Metal Butt Welds
  • Stress corrosion cracking
    • Residual stress
    • Challenging environment
    • Susceptible material
  • NDE identified flaws in Alloy 82/182 welds due to PWSCC beginning in 2000.
  • Circumferential involvement was limited until 2006.
  • 5 circumferential indications discovered in Wolf Creek pressurizer nozzle welds in October 2006:
    • Up to 50 percent circumferentially; 40 percent through-wall
    • One weld contained three circumferential cracks

NRC concerns:

    • First case of multiple, long, circumferential flaws
nrc wolf creek flaw evaluation scoping study
NRC Wolf Creek Flaw Evaluation Scoping Study
  • NRC staff evaluated integrity of pressurizer nozzles using ASME Section XI flaw evaluation methodologies
    • Result of study showed little margin between leak and rupture for nozzle with the largest flaw
  • NRC staff obtained agreements from all licensees to resolve issue in 2007.
  • Industry concern with nine units that did not have scheduled outages in 2007.
  • NRC staff agreed that industry advanced finite element analyses could be conducted to address staff concern.
advanced finite element analyses
Advanced Finite Element Analyses
  • Industry’s advanced finite element analyses were completed in August 2007 (ML072410240)
  • NRC staff completed confirmatory analyses (ML072470394)
  • NRC staff issued safety assessment (ML072400199) concluding reasonable assurance that PWSCC in pressurizer nozzles of the nine plants would not lead to rupture without adequate time to shutdown the facility
    • allowed operation to the spring 2008 outages to complete pressurizer nozzle inspections
technical issues operating reactors
Technical Issues: Operating Reactors
  • Fire Protection
  • Proactive materials degradation assessment
  • Integrated digital I&C and human- machine interface
fire protection
Fire Protection
  • Fire barrier performance
    • Potential issues with performance of Thermo-Lag and other barrier systems
    • Confirmatory studies
      • HEMYC performance
  • Cable performance
    • Potential for multi-conductor cable failures in fires
    • Confirmatory studies
      • CAROLFIRE tests
technical issue materials degradation
Technical Issue: Materials Degradation
  • Materials degradation has been experienced worldwide since the inception of nuclear power plant operation
  • Degradation is expected to continue as plants age
  • Develop technical basis for proactive materials degradation management
    • Identify components where

degradation can reasonably

be expected in the future

    • Coordinate research for

effective implementation

of proactive materials

degradation management

digital i c challenges
Digital I&C Challenges
  • Increased complexity
    • Consolidation of discrete analog functions into single digital system
    • Potential consolidation of independent safety systems into a single digital system
    • Potential new failure modes
  • Limited operational history in nuclear applications
  • Specialized staff skills
digital i c project
Digital I&C Project
  • Steering Committee established January 2007
  • Seven Task Working Groups (TWGs) have been formed:
    • Cyber Security
    • Diversity and Defense-In-Depth
    • Risk-Informed Digital I&C
    • Highly Integrated Control Room – Communications
    • Highly Integrated Control Room – Human Factors Issues
    • Licensing Process Issues
    • Fuel Cycle Facilities
  • Goal is to develop Interim Staff Guidance (ISG) licensing guidance for digital issues
  • Developed Digital I&C Website:

cyber security isg
Cyber Security ISG
  • Clarifies the NRC staff’s guidance on cyber security requirements
  • Addresses entire plant including safety and nonsafety systems programmatically
  • Reg. Guide 1.152 positions 2.1 through 2.9 address cyber security licensing criteria for safety systems
  • ISG issued and placed on Digital I&C Website on December 31, 2007
diversity and defense in depth d3 isg
Diversity and Defense-in-Depth (D3) ISG
  • Clarifies what is adequate diversity
  • Clarifies applicability of Common Cause Failure (CCF) in digital systems
  • CCF even though beyond design basis requires diverse RPS (RTS and ESFAS) for digital systems
  • Clarifies time required (30 minutes) for taking credit for manual actions
  • Clarifies position on system level vs. component level actuation
  • ISG issued and placed on Digital I&C Website on 9/26/2007
risk informing digital i c isg
Risk Informing Digital I&C ISG
  • Guidance for use of PRA evaluations
  • Addresses the appropriateness of risk-insights to resolve issues
  • Establishes an acceptable state-of-the-are model methodology
  • ISG scheduled to be issued on 3/28/08
highly integrated control room communications isg
Highly Integrated Control Room - Communications ISG
  • Addresses communication between different safety divisions and between safety division and non-safety equipment
  • Provides guidance for command prioritization
  • Provides guidance for Multidivisional Control and Display Stations
  • ISG was issued on 9/28/2007 and placed on the Digital I&C Webpage
highly integrated control room human factors issues isg
Highly Integrated Control Room – Human Factors Issues ISG
  • Clarifies approach the NRC staff would use to evaluate acceptable human factors aspects of highly-integrated control rooms
  • Guidance on minimum inventory for the Main Control Room and the Remote Shutdown Facility
  • Guidance on development, use, update (including software controls), and automation of Computer-Based Procedures System
  • ISG was issued on 9/28/2007 and placed on the Digital I&C Webpage
licensing process issues isg
Licensing Process Issues ISG
  • Clarifies the level of detail necessary for licensing reviews
  • Guidance on applicability of SRP, Ch. 7
  • Clarifies protocols for licensing action application development
  • Guidance on cyber security
  • ISG (w/o cyber security) scheduled to be issued on 7/31/08
fuel cycle facility isg
Fuel Cycle Facility ISG
  • Guidance for reviewing adequacy of cyber security protective measures
  • Clarifies adequate diversity and defense-in-depth design features
  • Guidance on channel independence for criticality and non-criticality related safety actions
  • Guidance on separation of safety-related functions from non-safety related functions in common operator interface devices
  • Clarifies acceptable use of software for safety functions to minimize common cause failures
  • ISG scheduled to be issued on 10/31/08
path forward for digital i c
Path Forward for Digital I&C
  • After issuance of ISGs, industry standards will be updated to include the applicable portions of the ISGs as part of the standards
  • NRC staff will issue Regulatory Guidance to endorse the applicable industry standards
  • NRC staff will issues updated/new Standard Review Plans to address the updated Regulatory Guides
  • The ISGs will be cancelled on the completion of the above items