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Use of Risk in Nuclear Regulation

For assessing public safety and developing regulations for nuclear reactors and materials, the NRC traditionally used a deterministic approach that asked (1) What can go wrong? and (2) What are the consequences? Now, new information for assessing risks also allows NRC to ask "How likely is it that something will go wrong?"

New techniques for measuring, analyzing, and ranking public health risks make it possible for the NRC to incorporate risk insights into its regulations. By risk-informing its regulations and regulatory processes, NRC can focus the attention of its licensees on those design and operational issues most important to safety and move away from prescriptive regulations based on conservative engineering judgments toward regulations focused on issues that significantly contribute to safety. See reactors or materials and waste, also listed in the box at the top of this page, for specific information in each of these areas.

• Background
• Status
• Public Involvement
• Process Description
• Regulations and Guidance
• Related Documents and Other Resources

Background

Current NRC regulations are based largely on deterministic analyses developed without the benefit of quantitative or measurable estimates of risk. Most NRC regulatory requirements were developed in the early stages of reactor technology development, and thus were based on limited experience, testing programs, and expert judgment, in conjunction with conservative design margins and the principle of defense-in-depth to protect public health and safety. The deterministic approach asks two questions: (1) What can go wrong? and (2) What are the consequences? This approach assumes that adverse conditions can occur and requires plant designs to include safety systems capable of preventing or minimizing accident consequences.

Although the deterministic approach has been successful in protecting public health and safety, Probabilistic Risk Analysis (PRA) considers these questions in a more comprehensive manner by examining a more broad spectrum of initiating events and their frequency and now asks the additional question, "How likely is it that something will go wrong?" PRA then analyzes the consequences of the scenarios and ranks the consequences by their frequency, giving a measure of risk (see NRC’s Strategic Plan (specifically Nuclear Reactor Safety Performance Goal Bullets 3 and 4 in Vol. 2, Part 2) and Final Policy Statement on Probabilistic Risk Assessment) [Volumes 1 and 2].

Status

The NRC is actively moving toward increasing the use of risk insights and information in three strategic arenas (Nuclear Reactor Safety, Nuclear Materials Safety, and Nuclear Waste Safety.)

In the Reactor Safety Arena, risk-informed activities occur in five broad categories: (1) applicable regulations, (2) licensing process, (3) revised oversight process, (4) regulatory guidance, and (5) risk analysis tools, methods and data. Activities within these categories include revisions to technical requirements in the regulations; risk-informed technical specifications; a new framework for inspection, assessment, and enforcement actions; guidance on risk-informed inservice inspections; and improved standardized plant analysis risk models.

Licensed activities addressed under the Materials and Waste Safety Arenas include uranium recovery, sealed sources and devices, irradiators, interim storage of spent fuel, transportation of radioactive materials, disposal of spent fuel, decommissioning, waste disposal, medical use of isotopes, nuclear fuel fabrication, and uranium enrichment. This diversity of regulated activities presents special challenges because a single approach to "risk-informing"the materials and waste regulatory applications is not practical.

The Risk-Informed Regulation Implementation Plan (RIRIP ). For each initiative, the RIRIP provides background, objectives, tasks, resource allocations, schedules, and status. This information is updated semi-annually.

Public Involvement

In line with the NRC's goal of increasing public confidence, the agency is considering risk-informed regulation openly, giving the public and the nuclear industry clear and accurate information and a meaningful role in the process. Information on risk-informed regulation is provided to the public through this Web site’s technical and programmatic information and About Meetings Open to the Public and News and Information pages and the RIRIP summary and detailed individual project information.

Process Description

NRC identified regulatory activities that could benefit from applying risk information to them and made these activities the basis for the agency's overall strategy for risk-informing its regulations.

Next, the NRC assigned revision of the related regulation to the appropriate staff experts who determined an approach for risk-informing that regulation. The risk-informed approach enhances the traditional deterministic approach by:

• explicitly considering a broader range of safety challenges
• prioritizing the challenges on the basis of risk significance, operating experience, and engineering judgment
• considering a broader range of counter measures to mitigate the challenges
• explicitly identifying and quantifying uncertainties in analyses
• testing the sensitivity of the results to key assumptions.

A risk-informed regulatory approach is also used to identify insufficient conservatism and provide a basis for additional requirements or regulatory actions. After determining the regulatory approach, the staff experts follow standard administrative processes for revising the regulation.

Related Regulations and Guidance

The Commission PRA Policy Statement encourages greater use of PRA to improve safety decision making and regulatory efficiency, including the use of PRA to support decisions to modify an individual plant's licensing basis.

In addition to the regulations listed, the following Regulatory Guides (RG) and Standard Review Plan (SRP) references provide guidance on the use of PRA findings and risk insights in support of licensee requests for changes to a plant’s licensing basis (i.e., license amendments and technical specification changes).

The Commission PRA Policy Statement encourages greater use of risk information, for example:

• Section 36 in Part 50, Technical specifications (10 CFR 50.36)
• Section 65 in Part 50, Requirements for monitoring the effectiveness of maintenance at nuclear power plants (10 CFR 50.65),
• Section 23 in Part 100, Reactor Site Criteria (10 CFR 100.23)
• Regulatory Guide (RG) 1.174 on licensing basis
• RG 1.175 on inservice testing
• RG 1.176 on graded quality assurance
• RG 1.177 on technical specifications
• RG 1.178 on inservice inspection
• Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants
• Chapter 19 , "Use of PRA in Plant-Specific, Risk-Informed Decisionmaking: General Guidance"
• Chapter 3.9.7 , "Risk Informed Inservice Testing"
• Chapter 16.1 , "Risk-Informed Decisionmaking: Technical Specifications"
• Chapter 3.9.8 , "Trial Use for the Review of Risk-Informed Inservice Inspection Piping"
• NMSS Standard Review Plan for Fuel Cycle

Related Documents and Other Resources

• White Paper on Risk-Informed and Performance-Based Regulation
• Performance Assessments
• Safety Goal Policy Statement
• Reactor Oversight Process (NUREG-1649, Rev. 3)
• SECY-99-100, "Framework for Risk-informed Regulation in the Office of Nuclear Material Safety and Safeguards"
• SECY-98-144, "Risk-Informed and Performance Based Regulation"
• SECY-98-300, "Options for Risk-informed Revisions to 10 CFR Part 50 - "Domestic Licensing of Production and Utilization Facilities"
• SECY-00-0198, "Status Report on Study of Risk-Informed Changes to the Technical Requirements of 10 CFR Part 50 (Option 3) and Recommendations on Risk-Informed Changes to 10 CFR 50.44 (Combustible Gas Control)"
• SECY-00-0194, "Risk-Informing Special Treatment Requirements"
• SECY-00-0162, "Addressing PRA Quality in Risk-Informed Activities"
• "Plan for Using Risk Information in the Materials and Waste Arenas: Case Studies"

Links or references are provided to other documents in each of the activities discussed in the RIRIP.

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Last revised Monday, June 23, 2003