ML19011A422

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Lecture 1-2 RIDM in Nuclear Industry 2019-01-16
ML19011A422
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Issue date: 01/16/2019
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Office of Nuclear Regulatory Research
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Nathan Siu 415-0744
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RIDM in the Nuclear Industry Lecture 1-2 1

Overview Key Topics

  • Range of stakeholders and perspectives
  • Key policy drivers for risk-informed regulation
  • Range and types of risk-informed applications
  • General characteristics of nuclear power plant (NPP) risk-informed decision making (RIDM)

Overview Resources

Nuclear Regulatory Commission, September 2016.

  • Organisation for Economic Co-operation and Development, Use and Development of Probabilistic Safety Assessment: An Overview of the Situation at the End of 2010, NEA/CSNI/R (2012)11, Nuclear Energy Agency, Paris, France, 2012, (Available from: http://www.oecd-nea.org/nsd/docs/indexcsni.html)

Overview Other References

  • U.S. Nuclear Regulatory Commission, Safety Goals for the Operation of Nuclear Power Plants; Policy Statement; Correction and Republication, Federal Register, Vol. 51, p. 30028 (51 FR 30028), August 21, 1986.
  • K. A. Coyne, Risk-Informed Regulation at the U.S. Nuclear Regulatory Commission, April 14, 2016. (ADAMS ML16105A427)
  • U.S. Nuclear Regulatory Commission, Integrated Risk-Informed Decision-Making Process for Emergent Issues, Office of Nuclear Reactor Regulation Office Instruction LIC-504, Revision 4, June 2, 2014. (ADAMS ML14035A143)
  • F.E. Haskin, A.L. Camp, S.A. Hodge, and D.A. Powers, Perspectives on Reactor Safety, NUREG/CR-6042, Revision 2, March 2002.

4

Stakeholders Stakeholders in NPP RIDM - Organizational

  • Stakeholders can:
  • Industry
  • Regulators

- have a role (including support)

  • Other Government Agencies in decision making process
  • Technical Support

- be affected by decisions Organizations

  • Stakeholder roles, beliefs,
  • Consensus Standards Organizations and backgrounds, can
  • International Organizations affect views on risk
  • Academia assessment as well as
  • Non-Governmental Organizations views on the appropriate
  • General Public use of risk information in support of decision making 5

Stakeholders Stakeholders in NPP RIDM - Functional Analysts/

Users Reviewers Developers 6

Stakeholders External Flooding : A Really Big Picture

  • Sparse data and concerns with extrapolation => mechanistic analysis
  • Daunting scale

- Regional analysis

- Human actions

- Besides flooding level: duration, debris, dynamic forces, warning time

- Multi-site impacts

  • Good enough can vary across organizations 7

Applications Policy Driver: Safety Goal Policy Statement (1986)

  • How safe is safe enough?
  • Qualitative health objectives

- Individuals should bear no significant additional risk

- Societal risks should be risks from other generating technologies, should not be a significant addition to other societal risks

  • Quantitative health objectives (QHOs)

- Prompt fatality risk for an average, nearby individual < 0.1% risks from all other accidents

- Cancer fatality risk for population in area) < 0.1% cancer fatality risks from all other causes

  • Surrogate risk measures

- Prompt fatality: LERF < 10-5/ry

- Latent cancer: CDF < 10-4/ry 8

Applications Policy Driver: PRA Policy Statement (1995)

  • Policies:

- Increase use of PRA technology to the extent supported by the state of the art and data.

- Complement deterministic approach, support defense-in-depth philosophy

- Reduce unnecessary conservatism, support additional requirements as appropriate

- Analyses should be as realistic as practicable; data should be publicly available for review

- Consider uncertainties when using the Commissions Safety Goals and subsidiary objectives

  • Expected Benefits:

(1) Considers broader set of potential challenges (2) Helps prioritize challenges (3) Considers broader set of defenses 9

Applications RIDM - NRC Examples 10

Applications 10 CFR 50.65, Maintenance Rule (1991)

  • Rule

- Requires monitoring of in-scope SSC performance to identify and address maintenance related issues

- Paragraph (a)(4) requires licensees to assess and manage the increase in risk that may result from the proposed maintenance activities

  • Risk-informed and performance-based
  • Outcome: widely viewed as a success

- NEI: Improved equipment reliability and plat performance

- UCS: focus necessary resources on todays problems so as to prevent them from becoming tomorrows disaster*

Applications Changes in Plant Licensing Basis (RG 1.174)

  • Voluntary changes:

licensee requests, NRC reviews

  • Small risk increases may be acceptable
  • Change requests may be combined
  • Decisions are risk-informed 12

Applications Reactor Oversight Program DCDF < 1E-6

  • Inspection planning DLERF < 1E-7
  • Determining significance of findings

- Characterize performance deficiency 1E-6 < DCDF < 1E-5 1E-7 < DLERF < 1E-6

- Use review panel (if required)

- Obtain licensee perspective 1E-5 < DCDF < 1E-4

- Finalize 1E-6 < DLERF < 1E-5

Applications Accident Sequence Precursor Program

  • Program recommended by WASH-1400 review group (1978)
  • Provides risk-informed view of significant nuclear plant operating experience

- Conditional core damage probability (events)

- Increase in core damage probability (conditions)

  • Supported by plant-specific Standardized Plant Analysis Risk Licensee Event Reports 1969-2017 models (No significant precursors since 2002)

I. Gifford, C. Hunter, and A. Gilbertson, U.S. Nuclear Regulatory Commission Accident Sequence Precursor Program: 2017 Annual Report, May 2018.

(ADAMS ML18130A856) 14

Applications NPP RIDM - Industry Examples

  • Risk-informed Licensing Amendment Requests (LARs)
  • Severe Accident Mitigation Alternatives (SAMA)
  • Outage planning
  • Enterprise Risk Management
  • Advanced reactor designs OMB Circular A-123, 2016 15

Applications NPP RIDM - International Examples

  • Periodic Safety Reviews
  • Plant improvements
  • Demonstrating acceptable safety levels 16

NPP RIDM RIDM Process NUREG-2150 17

NPP RIDM Licensing Basis Changes - RG 1.174 Change is consistent Change meets current with defense-in-depth regulations unless it is philosophy Maintain sufficient specifically related to a safety margins requested exemption Integrated U.S. Nuclear Regulatory Commission, An Approach for Using Probabilistic Decision Risk Assessment in Risk-Informed Decisions on Plant Specific Changes to Making the Licensing Basis, Regulatory Guide 1.174, Revision 3, 2018.

Use performance Proposed changes in measurement risk are small and are strategies to monitor consistent with the change Commissions Safety Goal Policy Statement 18

NPP RIDM CDF Acceptance Guidelines - RG 1.174 DCDF 10-5 10-6 10-5 10-4 CDF 19

NPP RIDM Nuclear Design 101: How Things Work

  • Nuclear fission heat steam Before trip 3300 MWt electricity After trip 260 MWt 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 50 MWt
  • Chain reaction 1 day 15 MWt 1 week 7 MWt controlled/stopped by control rods
  • Heat generation continues after chain reaction is stopped (decay heat)

Adapted from: https://www.nrc.gov/reactors/pwrs.html 20

NPP RIDM Nuclear Power Plant Design Features

  • Key safety principles

- Defense-in-depth

- Single failure criterion and redundancy

- Diversity

NPP RIDM Core Damage Frequency (CDF)

From NUREG-2122:

Core Damage: Sufficient damage that could lead to a release of radioactive material from the core that could affect public health.

Frequency: The expected number of occurrences of an event or accident condition expressed per unit of time.*

  • Lecture 3-1 will provide a more precise mathematical definition.

Adapted from: https://www.nrc.gov/reactors/pwrs.html 22

PRA and RIDM Analysis Challenges and Implications

  • Multiple safety systems and barriers (physical and operational) => multiple failures required to cause core damage => need to treat large numbers of possible combinations of events
  • Empirical data are sparse => need to bring in other forms of evidence (e.g., model predictions, expert judgments)
  • Accidents generally involve multiple phenomena => need to integrate multiple technical disciplines Need systematic, scrutable approach to handle these complexities with appropriate treatment of uncertainties 23

PRA and RIDM Probabilistic Risk Assessment (PRA)

  • Process/model(s) to answer the risk triplet questions

- A form of systems analysis

- Expresses uncertainties in terms of probabilities

  • Current practices for NPPs tailored to address

- Rare events

- Sparse data

- Combinations of failures (including dependencies)

- Multiple phenomena

- Difference between aleatory (random, stochastic) uncertainties and epistemic (state of knowledge) uncertainties*

  • The distinction can be arguable on philosophical grounds but has proven useful in practice. See Lecture 3-1 for further discussion.

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PRA and RIDM NPP PRA Distinguishing Characteristics Hazards

  • Levels

- Level 1 (core/fuel damage)

Initiating

- Level 2 (radioactive release) Level 1 Events

- Level 3 (offsite consequences)

  • Hazards Plant Damage

- Internal events (hardware, human, LOOP) States

- Internal hazards (flood, fire, heavy load drops, )

- External hazards (seismic, flood, wind, ) Source Level 2

  • Operating Mode Term Groups

- At power

- Low power/shutdown Release

  • Sources Categories

- Core Level 3

- Spent fuel pool Offsite

- Other (e.g., dry cask storage) Consequences 25

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