Key Observations andChallenges
George Apostolakis
Head, Nuclear Risk Research Center, CRIEPINRRC Workshop on

Risk-Informed Decision Making: A Survey of U.S. Experience
Tokyo, Japan, June 1-2, 2017

Nuclear Risk Research Center, CRIEPIThe B. John Garrick Institute for the Risk Sciences

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External Influence
Regulatory agencies are, by their nature, conservative.
Major changes usually require an external intervention.
• Senator Pastore’s letter to the U.S. Atomic Energy Commission (1971) “The members suggested that a comprehensive assessment of the safety aspects ofnuclear reactors be made with the intent of setting down for the industry and public aclear-cut summary of what the facts are in this matter.” Outcome: The Reactor Safety Study (1974)• NRC Chairman Jackson
 Regulatory Guide 1.174, “An Approach for Using Probabilistic Risk Assessment In RiskInformed Decisions on Plant Specific Changes to the Licensing Basis.” (1997)
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The Reactor Safety StudyMajor findings:• Dominant contributors: Small LOCAs and Transients (not large LOCAs)• CDF higher than earlier believed (best estimate: 5x10-5, once every 20,000years; upper bound: 3x10-4 per reactor year, once every 3,333 years)• Consequences significantly smaller

Support systems and operator actions are very important• The auxiliary feedwater system was not a safety-grade system at the time
• Research programs were initiated worldwide

Conclusion: The traditional “deterministic” system is incomplete
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UCLAIndustry: Zion & Indian Point PRAs
Explicit adoption of Bayesian methods
Fires and earthquakes shown to be significant contributors to risk
Rigorous containment response analysis
Atmospheric dispersion methods
PRAs should be plant-specific• Simple plant improvements were identifiedSuccess in hearings avoiding costly plant modifications

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Early Challenges
Cultural issues• Nuclear and mechanical engineers not trained in probability and statistics• “Abandoning” the traditional “deterministic” approaches to regulationsdifficult to accept• There is nothing “deterministic” about traditional approaches• They deal with uncertainties using subjective bounding analyses

Training courses establishedIPE and IPEEE programs established
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Regulatory Activities
Until 1997, the NRC issued regulatory requirements (e.g., SBO andATWS) based on PRA findings
No relief from regulations was granted, even though the PRAs wereshowing that several requirements did not contribute to safety andwere costlyThis changed with the issuance of the 1995 PRA Policy Statementand RG 1.174 in 1997
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UCLAThe 1995 Policy Statement
The use of PRA should be increased to the extent supported by thestate of the art and data and in a manner that complements thedefense-in-depth philosophy.
PRA and associated analyses (e.g., sensitivity studies, uncertainty
analyses, and importance measures) should be used in regulatory
matters, where practical within the bounds of the state-of-the-art, toreduce unnecessary conservatisms associated with current regulatory
requirements, regulatory guides, license commitments, and staffpractices.
PRA evaluations in support of regulatory decisions should be as
realistic as practicable.
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Removing Unnecessary Regulatory BurdenRG 1.174 creates risk-informed decision making (RIDM)• Defense in depth and safety margins are combined with risk insights
subjectively

Risk-Informed (RI) initiatives are voluntary• The utilities decide whether to adopt them using cost-benefit tradeoffs

The activities after 1997 create the wrong impression among somepeople that risk-informing the regulations is a means for weakening
the regulations
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Safety Goals (1986)
PRAs raised the question “How Safe is Safe enough?”
The NRC believed that establishing the safety goals would enhance
public understanding of regulatory criteria and public confidence innuclear power safety.
They are goals, not criteria.
• Safety goals are to be used as a reference point in ascertaining the need forsafety enhancements (Backfit Rule).
• Safety goals (CDF and LERF) are used as the basis for risk-informed changes tothe licensing basis (RG 1.174).
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UCLAPRA Quality
PRAs quantify judgments explicitly. Traditional methods do not.
The quality of PRAs is often questioned while that of “deterministic”
judgments is not.
Many traditional “deterministic” judgments have been shown to beincomplete.
• Not appreciating the significance of human errors and support systems• Underestimating the significance of external events• Not appreciating the significance of station blackout• Underestimating the risk significance of low-power operations
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UCLAPRA Standards
ASME and ANS have formed a Joint Committee on Nuclear Risk
Management (JCNRM) to develop and maintain PRA standards.
“ASME/ANS RA-S–2008,” Revised in 2013, is currently maintained by
the JCNRM.
It includes a Level 1 CDF and LERF PRA standard for internal events
at-power and standards for external hazards and internal fires atpower for LWRs.
The standard defines “what” must be done, not “how”.
To reduce the need for regulatory PRA technical review, NEI
developed a peer review process.
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Risk-Informed Initiatives
Regulatory Guide 1.174 defines basic principles.
It establishes the “Integrated Decision-Making Process.”A subjective integration of the defense-in-depth and safety-margins
philosophy with risk changes.
The risk-informed approach permitted small risk increases, which
was a significant cultural challenge.
The RI initiatives are voluntary; the utilities weigh costs and benefits
in their decisions.
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UCLAA Detailed Picture (INSAG 25)

13

A Broader View of Decision Making
Options

TechnicalAnalysis
one or more
techniques

Decision
Criteria

Assumptions,
Uncertainties
andSensitivities

ResourceandSchedule
Constraints

Deliberation
Other
Factors

Stakeholder
Input

Decision &Implementation

From NUREG-2150

Figure 3-2 Deliberations

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UCLAObjective Assessment of Plant Performance:
The ROP Action Matrix
Regulatory Response
ColumnDegraded Cornerstone
ColumnMultiple Repetitive
Degraded Cornerstone
ColumnUnacceptable
Performance
ColumnAll assessment inputs(performance
Indicators (PI) andinspection findings)
Green; cornerstone
objectives fully met

One or two White inputs (indifferent cornerstones) in astrategic performance area;
Cornerstone objectives fullymet

One degraded cornerstone(2 White inputs or 1 Yellowinput) or any 3 White inputs
in a strategic performancearea;
cornerstone objectives met
with minimal reduction insafety margin

Repetitive degraded
cornerstone, multiple
degraded cornerstones,multiple Yellow inputs, or 1
Red input1 ;cornerstone objectives met
with longstanding issues
or significant reduction insafety margin

Overall unacceptableperformance; plants not
permitted to operate within
this band, unacceptable
margin to safety

Regulatory
Conference

Routine Senior
Resident Inspector(SRI) interaction

Branch Chief (BC) or
Division Director (DD) meetwith Licensee

DD or Regional
Administrator (RA) meetwith Licensee

EDO (or Commission)
meet with Senior Licensee
Management

Commission meeting withSenior Licensee
ManagementLicensee
ActionLicensee Corrective
ActionLicensee corrective action
with NRC oversight

Licensee self assessmentwith NRC oversight

Licensee performance
improvement plan with
NRC oversight

NRC
Inspection

Risk-informed
baseline inspection
programBaseline and supplemental
inspection
95001

Baseline and supplemental
inspection
95002

Baseline andsupplemental inspection
95003

Regulatory
Actions

None

Document response todegrading area inassessment letter

Document response todegrading condition inassessment letter

10 CFR 2.204 DFI
10 CFR 50.54(f) letter
CAL/Order

Licensee Response
ColumnCommunications

ResponseResults

リレーションシップ ID rId3 のイメージ パーツがファイルにありませんでした。

Assessment
ReportPublicAssessment
Meeting

BC or DD review /sign assessment
report(w/ inspection plan)

DD review / signassessment report(w/ inspection plan)

SRI or BC meet withLicensee

BC or DD meet with
Licensee

Order to modify, suspend,or revoke licensed
activities

RA review / signassessment report(w/ inspection plan)

RA review / signassessment report(w/ inspection plan)

Commission informedRA discuss performancewith Licensee

EDO (or Commission)
discuss performance with
Senior Licensee
Management

Commission meeting withSenior Licensee
Management

Increasing Safety Significance
1It is expected in a few limited situations that an inspection finding of this significance will be identified that is not indicative of overall licensee performance.
The staff will consider treating these inspection findings as exceptions for the purpose of determining appropriate actions.

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UCLAA Success: RI-Inservice Inspection (RI-ISI)

V. Dimitrijevic, Short Course: Risk-Informed Operational Risk Management, Massachusetts Instituteof Technology, 2008.
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Limited Success: Risk-Informed Graded Quality
Assurance (RI-GQA) or Rule 10 CFR 50.69
Licensees have only slowly embraced risk significance categorization due
to the substantial initial investment.
A categorization in and of itself does not provide benefits.
The benefits are realized when a procedure or program is changed torecognize the categorization.
The RI-GQA process could be applied to the many thousands of pieces ofequipment in a plant.
All of the associated special treatment requirements for each component
would be identified, including the basis for their requirement.
This required extensive resources.
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RI-GQA or Rule 10 CFR 50.69
The IDP (Integrated Decision-Making Panel ) is a representative,
multi-disciplinary committee of experienced experts that approves
the final categorization.
NRC personnel raised concerns about relaxing special treatment
requirements.
These concerns were in part technical, relating to potential decreases
in equipment performance.
They were also part philosophical, as the resources saved by thelicensee may not necessarily be re-invested in safety.
Estimates of the potential cost savings were rather uncertain.
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Licensee Decision on RI-GQA
Licensees have been reluctant to pursue RI-GQA (with the exceptionof South Texas Project).
The additional analysis of equipment and related record keeping
appeared substantial with uncertain cost savings.
These challenges are now being revisited as part of the new industry
effort on “Delivering the Nuclear Promise.”There are non-regulatory applications for the risk significancecategorization such as prioritization of station activities, and selection
criteria for audits and inspections.
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UCLAA Failure: Risk-Informed In-Service TestingIn the early days, consensus standards committees that included
ASME developed conservative standards to define testing
requirements, frequencies, and scope.
PRAs provide a more realistic assessment of the safety importance ofplant equipment, important equipment failure modes, and the safety
implications of operational decisions such as testing frequency andsystem testing configurations.
Licensees had to develop new testing procedures with alternate
testing approaches based on component risk significance levels.
They also had to develop extensive information collection systems tocatalog equipment potentially involved in the RI-IST program.
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Risk-Informed In-Service TestingSome NRC individuals involved with the existing IST programs raised
concerns that the RI-IST programs could lead to safety-related
equipment degradation, even though the risk-informed approachindicated more optimal approaches could be available.
Although both the NRC and ASME have implemented programs that
could be used by licensees to implement RI-IST, neither has attracted
much attention.
It appears that the initial costs of regulatory approval andimplementation outweigh the perceived long-term benefits,
especially, in consideration of the more limited reductions inequipment testing
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UCLAAn Industry InitiativeOn December 9, 2003, STP’s Unit 2, Diesel Generator (DG) #22 had acatastrophic failure that resulted in significant damage. Repair time wasinitially estimated to be 120 days.
On December 30, STP was granted a one-time extension of the Allowed
Outage Time (AOT) to 113 days in order to make repairs. As part of theapproval, STP would develop a planned risk profile showing the changes inrisk levels (both CDF and LERF) over the extended AOT.
The risk management approaches taken were successful: STP units
continued to provide power, and the regulator gained new insights on theDG failure. Importantly, the use of PRA provided robust means to manage
allowed outage times.
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Concluding Remarks
Significant changes to the regulations are usually the result ofexternal pressure.
PRA and traditional methods are complementary.
The major obstacles to RIDM are cultural.
• Discomfort with probabilities• Familiarity with traditional methods creates reluctance to change.

Risk-informed initiatives are voluntary• The utilities weigh costs and benefits• Great successes: ROP and RI-ISI• Failure: RI-IST

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