ML19011A422
| ML19011A422 | |
| Person / Time | |
|---|---|
| Issue date: | 01/16/2019 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Nathan Siu 415-0744 | |
| Shared Package | |
| ML19011A416 | List:
|
| References | |
| Download: ML19011A422 (25) | |
Text
RIDM in the Nuclear Industry Lecture 1-2 1
Key Topics
- Range of stakeholders and perspectives
- Key policy drivers for risk-informed regulation
- Range and types of risk-informed applications
- General characteristics of NPP probabilistic risk assessment (PRA) and role in RIDM 2
Overview
Resources U.S. Nuclear Regulatory Commission, Use of Probabilistic Risk Assessment Methods in Nuclear Activities; Final Policy Statement, Federal Register, Vol. 60, p. 42622 (60 FR 42622), August 16, 1995.
N. Siu, et al., Probabilistic Risk Assessment and Regulatory Decisionmaking: Some Frequently Asked Questions, NUREG-2201, U.S.
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)
U.S. Nuclear Regulatory Commission, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant-Specific Changes to the Licensing Basis, Regulatory Guide 1.174, Revision 3, January 2018. (ADAMS ML17317A256) 3 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.
U.S. Nuclear Regulatory Commission, Risk-Informed Activities https://www.nrc.gov/about-nrc/regulatory/risk-informed/rpp.html 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 Overview
Stakeholders in NPP RIDM - Organizational
- Stakeholders can:
- have a role (including support) in decision making process
- be affected by decisions
- Stakeholder roles, beliefs, and backgrounds, can affect views on risk assessment as well as views on the appropriate use of risk information in support of decision making 5
Industry Regulators Other Government Agencies Technical Support Organizations Consensus Standards Organizations International Organizations Academia Non-Governmental Organizations General Public Stakeholders
Stakeholders in NPP RIDM - Functional 6
Stakeholders Developers Analysts/
Reviewers Users
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
Stakeholders
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) 11 Applications 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*
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
- Inspection planning
- Determining significance of findings
- Characterize performance deficiency
- Use review panel (if required)
- Obtain licensee perspective
- Finalize
- Performance indicators 13 Applications DCDF < 1E-6 DLERF < 1E-7 1E-6 < DCDF < 1E-5 1E-7 < DLERF < 1E-6 1E-5 < DCDF < 1E-4 1E-6 < DLERF < 1E-5 DCDF > 1E-4 DLERF > 1E-5 CDF = Core damage frequency LERF = Large early release frequency
Accident Sequence Precursor Program Program recommended by WASH-1400 review group (1978)
Provides risk-informed view of nuclear plant operating experience
- Conditional core damage probability (events)
- Increase in core damage probability (conditions)
Supported by plant-specific Standardized Plant Analysis Risk models 14 Applications Licensee Event Reports 1969-2017 (No significant precursors since 2002) significant I. Gifford, C. Hunter, and A. Gilbertson, U.S. Nuclear Regulatory Commission Accident Sequence Precursor Program: 2017 Annual Report, May 2018.
- Risk-informed Licensing Amendment Requests (LARs)
- Severe Accident Mitigation Alternatives (SAMA)
- Outage planning
- Enterprise Risk Management
- Advanced reactor designs 15 Applications OMB Circular A-123, 2016
NPP RIDM - International Examples
- Periodic Safety Reviews
- Plant improvements
- Demonstrating acceptable safety levels 16 Applications
RIDM Process 17 NUREG-2150 NPP RIDM
Licensing Basis Changes - RG 1.174 18 18 Change meets current regulations unless it is specifically related to a requested exemption Change is consistent with defense-in-depth philosophy Maintain sufficient safety margins Proposed changes in risk are small and are consistent with the Commissions Safety Goal Policy Statement Use performance measurement strategies to monitor change Integrated Decision Making NPP RIDM U.S. Nuclear Regulatory Commission, An Approach for Using Probabilistic Risk Assessment in Risk-Informed Decisions on Plant Specific Changes to the Licensing Basis, Regulatory Guide 1.174, Revision 3, 2018.
CDF Acceptance Guidelines - RG 1.174 19 10-5 10-6 10-5 10-4 CDF DCDF NPP RIDM
Before trip After trip 1 hour1.157407e-5 days <br />2.777778e-4 hours <br />1.653439e-6 weeks <br />3.805e-7 months <br /> 1 day 1 week 3300 MWt 260 MWt 50 MWt 15 MWt 7 MWt Nuclear Design 101: How Things Work Nuclear fission heat steam electricity Chain reaction controlled/stopped by control rods Heat generation continues after chain reaction is stopped (decay heat) 20 NPP RIDM Adapted from: https://www.nrc.gov/reactors/pwrs.html
Nuclear Power Plant Design Features General Design Criteria (10 CFR Part 50, Appendix A)
Key safety principles
- Defense-in-depth
- Single failure criterion and redundancy
- Diversity Robust structures, separation 21 NPP RIDM Adapted from: https://www.nrc.gov/reactors/pwrs.html
Core Damage Frequency (CDF) 22 Adapted from: https://www.nrc.gov/reactors/pwrs.html 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.
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.
NPP PRA Distinguishing Characteristics Levels
- Level 1 (core/fuel damage)
- Level 2 (radioactive release)
- Level 3 (offsite consequences)
Hazards
- Internal events (hardware, human, LOOP)
- Internal hazards (flood, fire, heavy load drops, )
- External hazards (seismic, flood, wind, )
Operating Mode
- At power
- Low power/shutdown Sources
- Core
- Spent fuel pool
- Other (e.g., dry cask storage) 25 Hazards Initiating Events Plant Damage States Source Term Groups Release Categories Offsite Consequences Level 1 Level 2 Level 3 PRA and RIDM