ML19011A421
| ML19011A421 | |
| Person / Time | |
|---|---|
| Issue date: | 01/16/2019 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Nathan Siu 415-0744 | |
| Shared Package | |
| ML19011A416 | List:
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| References | |
| Download: ML19011A421 (22) | |
Text
What is RIDM?
Lecture 1-1 1
Key Topics
- Practical purpose of risk assessment
- Triplet definition of risk
- Difference between risk-informed and risk-based decision making 2
Overview
Resources G. Apostolakis, et al., A Proposed Risk Management Regulatory Framework, NUREG-2150, U.S. Nuclear Regulatory Commission, April 2012.
International Nuclear Safety Group, A Framework for an Integrated Risk Informed Decision Making Process, INSAG-25, International Atomic Energy Agency, 2011.
National Research Council, Understanding Risk: Informing Decisions in a Democratic Society, P.C. Stern and H.V. Fineberg (eds), National Academies Press, 1996.
U.S. Nuclear Regulatory Commission, White paper on risk-informed and performance-based regulation, SECY-98-144, June 22, 1998.
S. Kaplan and B.J. Garrick, On the quantitative definition of risk, Risk Analysis, 1, 11-37(1981).
N. Siu, et al., Probabilistic Risk Assessment and Regulatory Decisionmaking: Some Frequently Asked Questions, NUREG-2201, U.S. Nuclear Regulatory Commission, September 2016.
M. Drouin, et al., Glossary of Risk-Related Terms in Support of Risk-Informed Decisionmaking, NUREG-2122, U.S. Nuclear Regulatory Commission, November 2013.
3 Overview
An Unexpected Research Result As part of an international research program, NRC-supported experimentalists intentionally create electrical faults in medium voltage switchgear to determine the potential consequences. The resulting explosions appear to be reasonably consistent with (or even bounded by) current models. Then one day 4
Risk assessment purpose
OECD/NEA High Energy Arcing Fault (HEAF) Program Phase 1 Project information: http://www.oecd-nea.org/jointproj/heaf.html 5
Risk assessment purpose HEAF Video
Sample Decision Options A. Stop the experiments until the relevance to field conditions is confirmed and the regulatory applications are clarified B. Continue the current experiments while alerting the industry and other stakeholders of preliminary findings C. Shut down all plants with similar switchgear 6
Risk assessment purpose
FC1 FC2 S
FB1 FB2 FA1 FA2 Potential Outcomes 7
HEAF Accident?
Power Generation Loss Probability N
None pA1 Y
Major pA2 N
Minor pB1 Y
Major pB2 N
Major pC1 Y
Major pC2 Notes:
Outcomes are simplified for illustration Probabilities and consequences for Option B depend on industry response to alert Probabilities and consequences for Option C recognize possibility of accidents while shutdown Risk assessment purpose
Observations Worst case (a HEAF-induced accident and major losses of power) is possible (albeit unlikely) for all three options Selection of the best alternative requires consideration of likelihood and consequence, i.e., risk Risk assessment is a useful tool for decision support The scope, approach, level of detail, etc. of the risk assessment depend on the needs of the decision problem 8
Risk assessment purpose Risk assessment is a set of tools, not an end in itself.
The limited resources available should be spent to generate information that helps risk managers to choose the best possible course of action among the available options.
- National Research Council, 1994
Dictionary Definitions of Risk 9
- 1. The chance of injury, damage, or loss; a dangerous chance; a hazard.
- 2. In insurance, (a) the chance of loss; (b) the degree of probability of loss; (c) the amount of possible loss to the insuring company; (d) a person or thing with reference to the risk involved in insuring him or it; (e) the type of loss that a policy offers (e.g., fire risk).
=> Consideration of likelihood OR consequences Risk definition
Common Scalar Definition Risk x
- Includes effects of likelihood and consequences
- Purely quantitative
- Enables simple scalar comparisons
- Average value, equates
- Low-probability/high-consequence
- High-probability/low-consequence 10 Risk definition
Low-Probability/High Consequence vs. High-Probability/Low Consequence 11 National Transportation Safety Board, 2016.
(http://www.ntsb.gov/investigations/)
From Traffic Safety Facts: Research Note, U.S. Dept. of Transportation, 2016.
Risk definition
The Farmer Curve 12 Adapted from Farmer, F.R., Reactor safety and siting: a proposed risk criterion, Nuclear Safety, 8, 539-548(1967).
Risk definition
The Triplet Definition of Risk (Kaplan and Garrick, 1981) 13 Risk {si, Ci, pi }
Features
- Vector, not scalar
- Qualitative and quantitative
- Differences across accident spectrum
- What can go wrong?
- What are the consequences?
- How likely is it?
Risk definition
Other Organizational Definitions International Atomic Energy Agency (referring to radiation risks):
detrimental health effects of radiation exposure (including the likelihood of such effects occurring) (IAEA SF-1, 2006)
Department of Homeland Security: the potential for an adverse outcome assessed as a function of threats, vulnerabilities, and consequences associated with an incident, event, or occurrence (DHS Risk Lexicon, 2010)
National Aeronautics and Space Administration: the potential for performance shortfalls, which may be realized in the future, with respect to achieving explicitly established and stated performance requirements (NASA/SP-2010-576, 2010)
Office of Management and Budget: the effect of uncertainty on objectives (OMB Circular A-123, 2016)*
14
- Text generally refers to risks as sources of risk Risk definition
Deliberative Decision Making 15 NUREG-2150 Risk-informed decision making
Naturalistic Decision Making
- Recognition-Primed Decision model
- Pattern recognition
- Mental simulation
- Go with first match
- Continue until change is required
- Risk consideration: Will it work?
- Not limited to field applications 16 G.A. Klein, A recognition-primed decision (RPD) model of rapid decision making, in Decision Making in Action: Models and Methods, G.A. Klein, et al., eds. 1993.
Risk-informed decision making
Risk-Based vs Risk-Informed Accidents are rare events Empirical data are sparse Models play central role SECY-98-144: A risk-informed approach to regulatory decision-making represents a philosophy whereby risk insights are considered together with other factors to establish requirements that better focus licensee and regulatory attention on design and operational issues commensurate with their importance to public health and safety.
17 OK OK Not OK Not OK Risk-Based Risk-Informed other factors limit line Risk-informed decision making
Allocating Resources: Risk-Based?
18 23%
22%
6%
5%
5%
4%
3%
2%
2%
2%
26%
U.S. Mortalities (2016)
S.L. Murphy, et al., "Mortality in the United States, 2017,"
NCHS Data Brief, Number 328, November 2018.
Or Risk-Informed?
19 23%
22%
6%
5%
5%
4%
3%
2%
2%
2%
26%
U.S. Mortalities (2016)
Heart Disease Other Cancer Accidents Suicide Kidney Disease Influenza & Pneumonia Diabetes Alzheimer Disease Stroke Chronic Lower Respiratory Diseases S.L. Murphy, et al., "Mortality in the United States, 2017,"
NCHS Data Brief, Number 328, November 2018.
Other Factors for NPP RIDM 20 20 Current regulations Defense-in-depth Safety margins Risk Monitoring Integrated Decision Making Adapted from RG 1.174 Risk-informed decision making
RIDM Implications for Risk Assessment
- Decision support
- Use science, but aim is not science
- Subject to economic and time constraints
=> needs to be good enough
- Decisions can be insensitive to some aspects
- Bounding analyses can be sufficient
- Risk is one of a number of inputs to RIDM
- Need to characterize uncertainties
- Risk considerations
- Despite best efforts by designers, operators, etc., risk is never zero => need to search for scenarios that can challenge assumptions
- Recognize weaknesses and implicit assumptions in possibilistic/worst case approaches 21 Risk-informed decision making
Risk Assessment vs. Risk Management 22 National Research Council, Understanding Risk: Informing Decisions in a Democratic Society, National Academy Press, 1996.
Risk-informed decision making