Risk-Informed

Regulatory

ApplicationsLecture 8-1

1

Key Topics

U.S. applications – general and more examples*

• Regulations and guidance

• Licensing

• Oversight

• Operational experience

2

Overview

*See also Lecture 1-2

Resources

• N. Siu, et al., “Probabilistic Risk Assessment and Regulatory

Decisionmaking: Some Frequently Asked Questions,” NUREG-

2201, U.S. Nuclear Regulatory Commission, September 2016.

• Coyne, K.A., “Risk-Informed Regulation at the U.S. Nuclear

Regulatory Commission,” April 14, 2016. (ADAMS ML16105A427)

• U.S. Nuclear Regulatory Commission, “Risk-Informed Activities”

https://www.nrc.gov/about-nrc/regulatory/risk-informed/rpp.html

3

Overview

Other References

• G. Apostolakis, et al., “A Proposed Risk Management Regulatory Framework,” NUREG-2150, U.S Nuclear Regulatory Commission, April 2012.

• C. Miller, et al., “Recommendations for Enhancing Reactor Safety in the 21st Century: The Near-Term Task Force Review of Insights from the Fukushima Dai-ichi Accident, July 12, 2011. (ADAMS ML111861807)

• U.S. Nuclear Regulatory Commission, “A Review of NRC Staff Uses of Probabilistic Risk Assessment,” NUREG-1489, March 1994.

• Jackson, S.A., “Transitioning to Risk-Informed Regulation: The Role of Research,” NRC Commissioner Speech S-98-26, 26th Annual Water Reactor Safety Meeting, October 26, 1998. (ADAMS ML003711267)

• P.K. Samanta, et al, “Handbook of Methods for Risk-Based Analyses of Technical Specifications” NUREG/CR-6141, December 1994.

• U.S. Nuclear Regulatory Commission, “Generic Environmental Impact Statement for License Renewal of Nuclear Plants—Final Report,” NUREG-1437, Revision 1, June 2013.

4

Overview

Other References (cont.)

• Idaho National Laboratory, “Mitigating System Performance Index (MSPI),” Training Course P111: PRA Technology and Regulatory Perspectives, Module S, U.S. Nuclear Regulatory Commission. (ADAMS M12160A497)

• U.S. Nuclear Regulatory Commission, “Notices of Enforcement Discretion,” Inspection Manual Chapter 0410, October 4, 2012. (ADAMS ML12263A456)

• U.S. Nuclear Regulatory Commission, “Significance Determination Process,” Inspection Manual Chapter 0609, June 2, 2011. (ADAMS ML101400479)

• 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)

• U.S. Nuclear Regulatory Commission, “Generic Issues Program,” Management Directive 6.4, January 15, 2015. (ADAMS ML14245A048)

• U.S. Nuclear Regulatory Commission, “Resolution of Generic Safety Issues: Introduction,” NUREG-0933, Main Report with Supplements 1–34, latest version available from http://nureg.nrc.gov/sr0933/Introduction/Introductions.html, December 2011.

5

Overview

All Functions,

All Arenas

6

Risk-Informed Regulation

Regulatory Approach

Standard*

“Reasonable assurance

of adequate protection”

Principles**

• Independence

• Openness

• Efficiency

• Clarity

• Reliability

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* When granting, suspending, revoking, or amending licenses or construction permits.

(Atomic Energy Act of 1954, as amended – see NUREG-0980, v1, n7, 2005)

**NRC Strategic Plan (NUREG-1614, v6, 2014)

Risk-Informed Regulation

Risk-Informed Regulation

• Risk information used to strengthen requirements, relax requirements, provide flexibility in meeting requirements (as long as adequate protection is ensured).

• Numerous rules:– 10 CFR 50.44 (“Combustible Gas Control”)

– 10 CFR 50.48 (“NFPA 805”)

– 10 CFR 50.61a (“PTS Rule”)

– 10 CFR 50.63 (“Station Blackout Rule”)

– 10 CFR 50.65 (“Maintenance Rule”)

– 10 CFR 50.69 (“Special Treatment”)

– 10 CFR 50.109 (“Backfit Rule”)

– 10 CFR 52.47 (New Reactor Certification and Licensing)

• Guidance documents support each application. (See Lecture 8-2)

8

“For each rulemaking,

regulatory guide, or generic

letter we issue, the

Commission conducts a

regulatory analysis to

weigh the costs associated

with the action against the

risk reduction and safety

enhancement to be

achieved.”

– S.A. Jackson (1998)

Regulations and Guidance

In the Future?

• Post-Fukushima Near-Term Task Force: recommended restructuring “patchwork of regulatory requirements and other safety initiatives”

• NUREG-2150 (initiated pre-Fukushima): proposal to increase use of risk information

• Concerns with resources, disruption during agency response

9

Regulations and Guidance

Changes in Plant Licensing Basis (RG 1.174)

• Voluntary changes:

licensee requests,

NRC reviews

• Small risk increases

might be acceptable

• Change requests may

be combined

• Decisions are risk-

informed

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Licensing

Risk-Informed Technical Specifications

• An early application of PRA technology [See Bickel

(1983), Samanta et al. (1994)]

• Completion times (aka “Allowed Outage Times”)

• Surveillance frequencies (aka “Surveillance Test

Intervals”)

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Unavailability (and

risk) increases

with AOT and with

STI. Why might

the proposed

changes be

acceptable?

Currently allowed completion time

Proposed completion time

Currently allowed STI

Proposed STI

Licensing

Plant License Renewal

• Environmental reviews consider potentially cost-

beneficial severe accident mitigation alternatives

(SAMA)

• Plant-specific PRAs not required but typically used to

support evaluations

• NRC reviews (supplements to NUREG-1437) often

have information on risk contributors, sometimes have

history of PRA model

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Licensing

Oversight Activities

• Reactor Oversight Program*

– Inspections

– Performance indicators (including

Mitigating Systems Performance Index)

– Significance Determination Process –

SDP

• Incident Investigation (Management

Directive 8.3)*

• Notice of Enforcement Discretion

(NOED)

13

Oversight

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

*See Lectures 1-2, 7-1

Operational Experience

• Accident Sequence Precursor (ASP) Program

(Lecture 7-1)

• Emergent Issues (LIC-504)

• Generic Issues

14

Operational Experience

Emergent Issues

15LIC-504

Operational Experience

Generic Issues Program

• Addresses multi-facility issues affecting public health and safety, the common defense and security, or the environment (with respect to radiological health and safety

• Required by Congress; status and resolutions reported to Congress and the public

• Issues can be raised by public or by staff

• Three stages– Screening

– Assessment (including consideration of risk)

– Regulatory Office Implementation

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Operational Experience

https://www.nrc.gov/about-nrc/regulatory/gen-issues/dashboard.html#genericIssue/genericIssueDetails/3

Decision Support

• R&D and other technical support (see Lecture 8-2)

– Near-term regulatory application

– Longer-term anticipated need

• Risk-informed R&D prioritization: coming soon?

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Decision Support

Positive Outcomes from PRA*

• Actionable safety insights and lessons

– SLOCA > LLOCA => protecting against “worst case” design basis accident (DBA) doesn’t mean risk has been minimized

– Importance of SBO, auxiliary feedwater, human error, CCF, fires and external hazards

– Plant-specific nature of risk

• Changes that improved plant responses to actual events

• Improved plant performance

– Improved equipment reliability and plant performance under Maintenance Rule

– Reduced outage durations increased capacity factors

– Reduced worker doses (risk-informed in-service inspections)

• Increased objectivity of regulatory oversight (ROP)

18*Not all resulting from regulatory activities

Thought Exercises

Risk-Informed Technical Specifications

• The pre-outage unavailability growth curves look

linear. Under what conditions is this reasonable?

• The computed risk increases from extending an AOT

or STI is often very small. Why shouldn’t indefinite

extensions be allowed?

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