Regulating Nuclear Power Plants

George Apostolakis
Head, Nuclear Risk Research Center
Former Commissioner, USNRC
apostola@mit.edu
Presented to theJapan Atomic Energy Commission
June 3, 2015
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The U.S. Nuclear Regulatory Commission• Mission: Ensure adequate protection of publichealth and safety, promote the common defense andsecurity, and protect the environment.
• Five Commissioners appointed by the President andconfirmed by the U.S. Senate.
• Oversight: Senate Committee on Environment andPublic Works and the House of Representatives.
• The Commission formulates policies, develops
regulations governing nuclear reactor and nuclear
material safety, issues orders to licensees, andadjudicates legal matters.
• All Commissioners vote on these issues.
 Commissioners have an open-door policy
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Principles of Good Regulation• Independence
 Independence does not imply isolation. All available
facts and opinions must be sought openly from licensees
and other interested members of the public.

• Openness• Efficiency• Clarity
 Regulations should be coherent, logical, and practical.
 Agency positions should be readily understood andeasily applied.

• Reliability
 Regulations should be based on the best available
knowledge from research and operational experience.
 Once established, regulation should be perceived to bereliable and not unjustifiably in a state of transition.
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Advisory Committee on Reactor Safeguards• Fifteen part-time experts from academia, nationallaboratories, and former industry managers• Reviews and advises the Commission with regard to
the licensing and operation of production andutilization facilities and related safety issues, theadequacy of proposed reactor safety standards, andother matters referred to it by the Commission.
• On its own initiative, may conduct reviews ofspecific safety-related items. Submits a report to theCommission commenting on the NRC Safety
Research Program.
• Open meetings (exceptions: security, proprietaryinformation)• Formal letters and NRC staff responses
20154New Rules• The Adequate Protection Standard
 “…under the adequate-protection standard of section 182(a), the NRC
need ensure only an acceptable or adequate level of protection topublic health and safety…..”• Safety Enhancement Measures
 “If it so desires, however, the Commission may impose safetymeasures on licensees or applicants over and above those required bysection 182(a)’s adequate-protection standard…. If the Commission
wishes to do so, it may order power plants already satisfying thestandard of adequate protection to take additional safety precautions.
When the Commission determines whether and to what extent toexercise this power, it may consider economic costs or any otherfactors.”

Court of Appeals for the D.C. Circuit, 1987.
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Rule 10 CFR 50.109 Backfitting Backfitting is defined as the modification of or addition tosystems, structures, components, or design of a facility; or thedesign approval or manufacturing license for a facility; or theprocedures or organization required to design, construct oroperate a facility; any of which may result from a new oramended provision in the Commission's regulations or theimposition of a regulatory staff position interpreting theCommission's regulations that is either new or different from apreviously applicable staff position
 The Commission shall require the backfitting of a facility only
when it determines that there is a substantial increase in theoverall protection of the public health and safety or the common
defense and security to be derived from the backfit and that thedirect and indirect costs of implementation for that facility are
justified in view of this increased protection.

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The Traditional Approach to Regulation
Prior to Risk Assessment (1975)• Management of (unquantified at the time)
uncertainty was always a concern.
• Defense-in-depth and safety margins became
embedded in the regulations.
• “Defense-in-Depth is an element of the NRC’s safetyphilosophy that employs successive compensatory
measures to prevent accidents or mitigate damage if
a malfunction, accident, or naturally caused event
occurs at a nuclear facility.” [USNRC White Paper,February, 1999]

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Major Elements of Defense in Depth

Accident Prevention

Safety Systems

Containment
Accident Management

Siting & Emergency Plans

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Design Basis Accidents(Adequate Protection)• A DBA is a postulated accident that a facility isdesigned and built to withstand without exceeding
the offsite exposure guidelines of the NRC’s sitingregulation.
• They are stylized and very unlikely events.
• They protect against “unknown unknowns”.

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Problems with the Traditional Approach• There is no guidance as to how much defense indepth is sufficient (unreliable regulations, slide 3)• DBAs use qualitative approaches for ensuringsystem reliability (the single-failure criterion) whenmore modern quantitative approaches exist• DBAs use stylized considerations of humanperformance (e.g., operators are assumed to takeno action within, for example, 30 minutes of an
accident’s initiation)• DBAs do not reflect operating experience andmodern understanding• Industry-sponsored PRAs showed a variability inrisk of plants that were licensed under the same
regulations.
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Probabilistic Risk Assessment•Study the system as an integrated socio-technicalsystem•

Probabilistic Risk Assessment (PRA) supports
Risk Management by answering the questions:

What can go wrong? (thousands of accident sequencesor scenarios)How likely are these scenarios?

What are their consequences?

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Reactor Safety Study Insights(WASH-1400; 1975)
Prior Beliefs:
1.
2.

Protect against large loss-of-coolant accident (LOCA)
Core damage frequency (CDF) is low (about once every
100 million years, 10-8 per reactor year)
Consequences of accidents would be disastrous

3.

Major Findings
1.
2.

Dominant contributors: Small LOCAs and Transients
CDF higher than earlier believed (best estimate: 5x10-5,
once every 20,000 years; upper bound: 3x10-4 per reactor
year, once every 3,333 years)
Consequences significantly smaller
Support systems and operator actions very important

3.
4.

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Regulatory Decision Making• Regulatory decision making (like any decision) should
be based on the current state of knowledge and should
be documented (clear and reliable regulations, slide 3)
 The current state of knowledge regarding design, operation,and regulation is key.
 PRAs do not “predict” the future; they evaluate and assess
future possibilities to inform the decision makers’ current
state of knowledge.
 Ignoring the results and insights from PRAs results indecisions not utilizing the complete state of knowledge.
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Quantitative Health Objectives (QHOs)(August, 1986)• Early and latent cancer mortality risks to anindividual living near the plant should not exceed
0.1 percent of the background accident or cancer
mortality risk, approximately
5x10 -7/year for early death and2 x10 -6/year for death from cancer
The prompt fatality goal applies to an average individual living in
the region between the site boundary and 1 mile beyond thisboundary.
The latent cancer fatality goal applies to an average individual livingin the region between the site boundary and 10 miles beyond thisboundary.
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Evolution of the USNRC’s
Risk-Informed Regulatory System• 1980s:

New or revised regulatory requirements
based on PRA insights introduced• 1990s:

Risk-informed changes to a plant’slicensing basis allowed• 2000s:
 Change to a risk-informed reactor oversight process Risk-informed alternative to comply with fire protection
requirements
 Regulation requiring PRAs for licensing new reactors

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Risk-informed Regulation“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 andregulatory attention on design andoperational issues commensurate with theirimportance to public health and safety.”[Commission’s White Paper, USNRC, 1999]
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The Deliberation (NUREG-2150)
Options

TechnicalAnalysis

Decision
Criteria

one or more
techniques

Assumptions,Uncertainties
andSensitivities

ResourceandSchedule
Constraints

Deliberation
Other
Factors

Stakeholder
Input

Decision &Implementation

Figure 3-2 Deliberations
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Risk-Informed Framework

Traditional“Deterministic”
Approach• Unquantified
probabilities•Design-basis accidents•Defense in depth•Can impose
unnecessary
regulatory burden•Incomplete
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RiskInformedApproach•Combinationof traditionaland riskbasedapproaches
through adeliberative
process
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Risk-BasedApproach• Quantified
probabilities•Thousands ofaccident
sequences•Realistic•Incomplete

Confidence Building• Industry-sponsored PRAs for Zion and Indian PointNPPs
 Reviewed extensively by the USNRC
 Identified the significance of earthquakes and fires Failure modes with easy fixes identified• Early applications of risk-informed decision making
 South Texas Project Experience Allowed Outage Times extended from 3 days to 14 daysfor emergency AC power and 7 days for Essential
Cooling Water and Essential Chilled Water systems.
 Actual experience: Less than 5 days.

• PRA standards
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