ML19011A423
| ML19011A423 | |
| Person / Time | |
|---|---|
| Issue date: | 01/16/2019 |
| From: | Office of Nuclear Regulatory Research |
| To: | |
| Nathan Siu 415-0744 | |
| Shared Package | |
| ML19011A416 | List:
|
| References | |
| Download: ML19011A423 (24) | |
Text
Early History Lecture 2-1 1
Overview Key Topics
- Major studies
- Key lessons
- From PRA
- About PRA (technology)
Overview Resources
- T.R. Wellock, A figure of merit: quantifying the probability of a nuclear reactor accident, Technology and Culture, 58, No. 3, 678-721, July 2017.
- W. Keller and M. Modarres, A historical overview of probabilistic risk assessment development and its use in the nuclear power industry: a tribute to the late Professor Norman Carl Rasmussen, Reliability Engineering and System Safety, 89, 271-285, 2005.
- M. R. Hayns, The evolution of probabilistic risk assessment in the nuclear industry, Transactions Institute of Chemical Engineers, 77, Part B, 117-142, May 1999.
- B.J. Garrick, Lessons learned from 21 nuclear plant probabilistic risk assessments, Nuclear Technology, 84, No. 3, 319-339(1989).
- Risk Analysis, Special Issue on Nuclear Probabilistic Risk Analysis, 4, No. 4, December 1984.
3
Overview Other References
- J.S. Walker and T.R. Wellock, A Short History of Nuclear Regulation, 1946-2009, NUREG/BR-0175, October 2010.
- F.E. Haskin, A.L. Camp, S.A. Hodge, and D.A. Powers, Perspectives on Reactor Safety, NUREG/CR-6042, Revision 2, March 2002.
- G.D. Bell, The calculated risk - a safety criterion, in F.R. Farmer (ed.), Nuclear Reactor Safety, Academic Press, London, 1977.
- J.R. Beattie, G.D. Bell, and J.E. Edwards, Methods for the Evaluation of Risk, AHSB (S) R159, UKAEA, 1969.
- M.C. Pugh, "Probability Approach to Safety Analysis," TRG Report 1949, UKAEA, 1969.
- U.S. Nuclear Regulatory Commission, Reactor Safety Study: An Assessment of Accident Risks in U.S.
Commercial Nuclear Power Plants, WASH-1400, (NUREG-75/014), October 1975.
- H.W. Lewis, et al., Risk Assessment Review Group Report to the U.S. Nuclear Regulatory Commission, NUREG/CR-0400, September 1978.
- A. Birkhofer, The German risk study for nuclear power plants, IAEA Bulletin, 22, No. 5/6, October 1980.
- U.S. Nuclear Regulatory Commission, Severe Accident Risks: An Assessment for Five U.S. Nuclear Power Plants, NUREG-1150, December 1990.
- U.S. Nuclear Regulatory Commission, Individual Plant Examination Program: Perspectives on Reactor Safety and Plant Performance, NUREG-1560, December 1997.
- U.S. Nuclear Regulatory Commission, Perspectives Gained from the Individual Plant Examination of External Events (IPEEE) Program, NUREG-1742, April 2002.
4
Why History?
The past might not predict the future but it certainly provides useful lessons Besides providing credit where credits due, past studies and records can provide
- Improved starting points for research and analysis (e.g.,
for new designs and scenarios)
- Examples of mistakes and biases to be protected against
- Previous regulatory precedents
- Decisions
- Supporting Rationale 5
Why History?
Old topic, still valuable?
Paper Title* Modern Topic Probabilistic analysis of rupture in nuclear Credit for Leak Before Break using reactor coolant piping probabilistic fracture mechanics The use of quantitative risk and probabilistic Selection of licensing-basis accidents safety criteria in the conceptual design of a in Licensing Modernization Program large pool-type LMFBR Investigations of the adequacy of the Advanced atmospheric transport meteorological transport model developed for modeling the Reactor Safety Study Tornado missile simulation and risk analysis Risk-informed tornado missile protection Human reliability analysis of dependent Quantitative impact of dependence events between human errors
- Proceedings, ANS Topical Meeting on Probabilistic Analysis of Nuclear Reactor Safety (PSA 78), Newport Beach, CA, May 8-10, 1978.
6
Why History?
Le Blayais 1999 French PWR Le Blayais undergoes serious flooding, leading to mobilization of national resources. (See Lecture 7-2) 2000-2005 French utility (EDF) and regulatory TSO (IPSN) deliver papers on event at various conferences.
2009 ASME/ANS PRA standard includes language indicating flooding is likely to be unimportant.
2010 EDF delivers talk on the Blayais event at NRCs Regulatory Information Conference.
2011 An earthquake-generated tsunami floods Fukushima Dai-ichi NPP, leading to core melt at Units 1-3.
7
Why History?
Caveat Emptor
- Be wary of all oral histories (including this one)
- Speakers need to simplify. (7+/-2)
- Example (WASH-1400):
Main Report (~140 pages) + 11 Appendices (~2260 pages)*
Executive Summary (12 pages)
Oral Version (2 slides of bullets)
- Potential for important gaps and biases
- Potential for lore to perpetuate incorrect characterizations or even myths
- Search tools can find facts; understanding is more difficult.
- Well-researched documents, especially by trained historians (e.g., see Wellock) are extremely useful.
- An NRC NUREG/KM is in the works
- NUREG-1150 main report has ~550 pages, 14 companion NUREG/CR reports
(~10,000 pages) and 15 other supporting reports.
8
PRA/RIDM History Revised Reactor Oversight RG 1.174 A PRA Timeline Safety Atomic Energy Act Goal PRA ASME/ANS No undue risk Policy Policy PRA Standard Price-Anderson Indian IPE/
(non-zero risk) Point IPEEE UKAEA SGHWR Farmer Curve German Risk Study EU Stress Tests WASH-740 WASH-1400 NUREG-1150 Level 3 PRA TMI Chernobyl Fukushima AEC NRC created created 1940 1950 1960 1970 1980 1990 2000 2010 2020 9
PRA/RIDM History Before PRA - Reliability Engineering*
- Post-WW I: qualitative comparisons lead to multi-engine aircraft designs
- 1930s: quantification (average number of failures, mean failure rates)
- WW II: V-1 missile
- Chain cant be stronger than weakest link => strengthen weakest link. Still 100% failures
- Realized a large number of fairly strong links can be more unreliable than a single weak link. Ultimately achieved 60%
reliability.
- A.E. Green and A.J. Bourne, Reliability Technology, Wiley, London, 1972.
10
PRA/RIDM History Post WW II - Safety and Feasibility Concerns
- 1949: Reactor Safeguard Committee expresses concern with possibility and consequences of runaway reactions, desire for information on accident probabilities.
- 1950s: Hanford Site. From T. Wellock, WASH-1400 and the Origins of Probabilistic Risk
- Hanford staff recommend bottom up methodology for calculating Assessment (PRA) in the Nuclear Industry, 2015.
probabilities based on concept of accidents as chains of events (1953).
- WASH-740 includes alarming estimates of consequences for a major reactor accident with no credible estimates of likelihood (1957).
- 1960s:
- Full-scale probabilistic calculations not yet successful. (Too conservative or too optimistic.) USAEC relies on remote siting and ESFs.
- Fault tree analysis (Bell Labs) spreading in reliability engineering.
USAEC funds small-scale nuclear applications (e.g., at Holmes and Narver). F.R. Farmer, Reactor safety and siting: a proposed risk criterion,
- Other countries (Canada, UK, Japan) advocate probabilistic Nuclear Safety, 8, 539-548(1967).
approaches. UKAEA (F.R. Farmer) proposes a risk-based siting criterion (1967), applies to a prototype SGHWR design (1969).
11
Major Studies WASH-1400 - The Study
- Initiated 1972, draft 1974, final 1975
- Director: Prof. Norman C. Rasmussen (MIT)
- Objectives
- Estimate public risks from potential accidents
- Provide a perspective through comparison with non-nuclear risk
- Scope
- Level 3, at power, focus on internal events
- Two plants: Surry (PWR) and Peach Bottom (BWR)
- Key Finding: Risks are comparatively small
- Other Professor Norman C. Rasmussen, MIT (National Academies Press)
- Accident likelihoods higher than previously assumed (around 6x10-5/ry vs. 1x10-8) but consequences are lower
- Risk can be dominated by less severe, more likely scenarios (SLOCA>LLOCA) 12
Major Studies WASH-1400 - The Aftermath
- Criticized by Risk Assessment Review Group Some Technical and (Lewis Committee) and others (e.g., UCS, Regulatory Concerns NRC staff)
- Credit for human
- Executive Summary (advocates brief) adaptability
- Other concerns
- Conservative biases in treating uncertainties
- Criticisms swamped good points
- Common cause failure
- Systematic identification and analysis of accident analysis scenarios
- Meaningfulness of
- Freedom to think creatively beyond Maximum absolute risk estimates
- Need to change existing Credible Accidents licensing process
- Commission withdrew endorsement of
- Training costs Executive Summary and requested staff review of report uses in decisions => chilling effect
- TMI (1979) started change in views.
13
Major Studies Indian Point PRA
- UCS Petition to close Unit 1, suspend operation of Units 2 and 3 pending resolution of safety issues (1979)
- Indian Point Probabilistic Safety Study (IPPSS): Level 3, full-scope PRA (1980-1982)
- Quantifies risk
- Assesses severe accident management alternatives
- Study plus BNL and SNL reviews provided basis for ASLB finding(1983) and Commission decision to allow continued operation (1985)
- Along with earlier study for Zion, led wave of industry-sponsored PRAs 14
More Studies Some Activities after WASH-1400 Studies Research Programs (c. 1984)
- Biblis B (1978)
- Improved Reactor Safety Program
- Probability of initiating events
- Oyster Creek (1979) - Probability of failure of safety systems to control course of events
- RSSMAP (1981-1982): Sequoyah 1, Oconee 3, - Probability of failure of safety systems to inhibit radioactive releases Grand Gulf 1, Calvert Cliffs 2Big Rock Point (1981)
- PRA Reference Document
- IREP (1981-1983): Crystal River 3, Browns Ferry, - Purpose and content of a PRA ANO-1, Millstone 1 - PRAs performed to date, results, generic insights
- Level of maturity and uncertainties of different
- Zion 1 and 2 (1981) elements
- Limerick 1 and 2 (1981)
- Risk Methods Integration and Evaluation Program (RMIEP)
- Indian Point 2 and 3 (1982) - Integrated treatment of internal, external, and CCF events
- Sizewell B (1982) - Evaluate PRA technological developments, lay basis for improvements
- Millstone 3 (1983) - Identify, evaluate, display uncertainties
- Oconee-3 (1984)
See R. Bernero, Probabilistic Risk Analyses: NRC Programs and Perspectives, Risk Analysis, 4, No. 4, 287-297, See M. R. Hayns, The evolution of probabilistic risk December 1984.
assessment in the nuclear industry, Transactions Institute of Chemical Engineers, 77, Part B, 117-142, May 1999 for sample results. 15
PRA/RIDM History Safety Goal Policy Statement (51 FR 30028; 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 16
Major Studies NUREG-1150 (1990)
- Objectives
- Current snapshot of severe accident risks
- Models and results for prioritizing issues and R&D
- Scope
- Surry, Peach Bottom: internal events, fire, seismic
- Sequoyah, Grand Gulf, Zion: internal events
- Representative results shown elsewhere (e.g., Lecture 2-2)
- Notes
- Initial draft published 1987; criticisms led to major revisions
- No Executive Summary, no short summary of findings
- Hazard results reported separately (not aggregated)
- Intended to be the simple study; companion RMIEP study used as vehicle for advanced methods development and application
- Results widely used in subsequent NRC activities 17
PRA/RIDM History PRA Policy Statement (60 FR 42622; 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 18
Major Studies Individual Plant Examinations
- Generic Letter 88-20 (11/23/1988), 88-20 Supplement 4 (6/28/1991)
- Plants pose no undue risk but systematic examinations are useful to identify severe accident vulnerabilities that can be fixed with low-cost improvements
- Letters request licensee analyses
- Individual Plant Examinations (IPE): internal events and internal flooding
- Individual Plant Examinations of External Events (IPEEE):
seismic, fire, others (high winds, flooding, ) 0.3
- Submittal guidance: NUREG-1335 (IPE), NUREG-1407 Fraction 0.2 (IPEEE)
- Vulnerabilities not defined and PRA not required 0.1
- Most plants use PRA for internal events 0.0
- Many plants use margin analyses for seismic and/or fire 10-6 10-5 10-4 10-3
- No vulnerabilities found but numerous improvements CDF (/ry) identified; studies provide starting point for other applications.
19
PRA/RIDM History Modern History
- Risk-informed applications - Lecture 8-1
- Fukushima Dai-ichi - Lecture 7-2 TEPCO photo from The Yoshida Testimony, Asahi Shinbun, 2014.
20
Key Lessons Some Forgotten Studies and Lessons
- RSSMAP (Reactor Safety Study Methods Application Program) - simplified extensions to Modern Relevance four plants
- Disappointment with
- IREP (Interim Reliability Evaluation Program) - simplified analyses
- Continuing desire to find search for unique features increasing vulnerabilities - barriers?
susceptibility to severe accidents.
- Lack of patience with extended studies; need
- RMIEP (Risk Methods Integration and for near-term applications Evaluation Program) - vehicle for advanced
- Lure of direct statistical estimation methods development and application.
- Polarization from
- ASP (Accident Sequence Precursor) studies - alternative vs.
complementary approach evaluated risk significance of operational events; proposed as possible alternate, statistically-oriented approach to PRA 21
Key Lessons Some Historical Lessons - PRA Results
- Importance of full spectrum of accidents, potential dominance of lesser accidents (e.g., small loss of coolant accidents - SLOCA)
- Importance of station blackout (SBO), loss of ultimate heat sink (LOUHS), human errors, fire, external hazards
- Relatively low likelihood of large-scale health effects, potential for land contamination 22
Key Lessons Some Historical Lessons - PRA Technology
- Feasibility of useful analysis
- Importance of process (not just numbers)
- Key technical challenges
- Human reliability analysis (HRA)
- External hazards analysis
- Common cause failure (CCF) analysis
- No free lunch - limitations of simplified analyses 23
Key Lessons Some Historical Lessons About PRA in RIDM*
- Despite technical challenges, judged sufficiently mature to support practical decisions, major as well as minor
- Long-running (and continuing) challenges in interpretation and use of numerical results
- Appropriateness of adding results of heterogeneous analyses to support comparisons with decision criteria
- Demonstration of acceptable level of safety
- Importance of review (peer and regulatory)
- Identification and correction of problems
- Confidence in decision applications
- See Lectures 2-3, 8-4, and 9-1 for more discussion on challenges 24