Engineering Challenges in U'S' Nuclear Reactor Safety

1
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

2
Agenda

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

3
NRC Mission

• License and regulate the Nations 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.

4
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

5
NRC Organization

• Two Major Programs
• Nuclear Reactor Safety Program
• Accounted for 74 of NRCs costs in FY 2007
• Nuclear Materials and Waste Safety Program
• Accounted for 26 of NRCs costs in FY 2007

6
NRC Budgetary Authority FY 2002-2008
(In millions)
7
NRC Personnel Ceiling FY 2002-2008
(Staff)
8
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.

9
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
• www.nrc.gov/about-nrc/grants.html

10
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 Grants.gov during
  the week of February 11, 2008.

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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

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Operating Power Reactors
13
Research Test Reactors
14
Potential New Reactor Applicants
15
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)

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7 Cornerstones of ROP
17
2006 Average Industry Performance(Secy-07-0063 /
4-3-07 / ML070660099)
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2006 Average Industry Performance(Secy-07-0063 /
4-3-07 / ML070660099)
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2006 Average Industry Performance(Secy-07-0063 /
4-3-07 / ML070660099)
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Action Matrix Trends
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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

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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.
• http//www-pub.iaea.org/MTCD/publications/PDF/Pub1
  137_scr.pdf
• INSAG-4, Safety Culture.
• http//www-pub.iaea.org/MTCD/publications/PDF/Pub8
  82_web.pdf
• INSAG-13, Management of Operational Safety in
  Nuclear Power Plants.
• http//www-pub.iaea.org/MTCD/publications/PDF/P083
  _scr.pdf
• 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
• http//www.nrc.gov/reading-rm/doc-collections/gen-
  comm/reg-issues/2006/ri200613.pdf

23
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.

24
Boiling Water Reactor Pressure Vessel
25
QC1 Steam Dryer FailureNovember 2003(close-up)
Missing portion of outer bank vertical plate,
approx. 6 in. x 9 in.
26
QC2 Steam Dryer FailureMarch 2004
Tie bar to attachment welds
Plate attachment stitch weld
Tip of gusset plate
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Singing Safety-Relief Valve
28
Quad Cities Unit 2 Spring 2006 MSL B Strain Gage
Data Compared to Pre-ASB Data
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ASB Modification
Relief valve
ASB
30
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
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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

32
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.

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Advanced Finite Element Analyses

• Industrys 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

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Typical ASME Pipe Flaw Evaluation Procedure
35
Advanced FE Analysis Crack Growth Progression
36
Advanced FE Analysis Crack Growth
36
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Technical Issues Operating Reactors

• Fire Protection
• Proactive materials degradation assessment
• Integrated digital IC and human- machine
  interface

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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

39
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

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• Digital IC Issues

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Current Technology
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Future Technology
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Digital IC 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

44
Digital IC Project

• Steering Committee established January 2007
• Seven Task Working Groups (TWGs) have been
  formed
• Cyber Security
• Diversity and Defense-In-Depth
• Risk-Informed Digital IC
• 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 IC Website
• http//www.nrc.gov/about-nrc/regulatory/research/
  digital.html

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Cyber Security ISG

• Clarifies the NRC staffs 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 IC Website on
  December 31, 2007

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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 IC Website on
  9/26/2007

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Risk Informing Digital IC 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

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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 IC Webpage

49
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 IC Webpage

50
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

51
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

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Path Forward for Digital IC

• 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

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• Questions ?