What are risk-informed, performance-based principles?

Risk-Informed, Performance-Based (RIPB) principles enable an economical implementation of a graded approach so that resources and higher quality expectations are associated with the most important activities contributing to the desired outcome (e.g. safety, economics, plant availability).

What is risk-informed decision making?

It is a process where risk insights are considered together with other sources of insights (e.g.deterministic analysis, safety margin, engineering design features) that considers a broad set of potential challenges to safety and provides a logical means for prioritizing these challenges.

A risk assessment is needed to make a risk-informed decision. An assessment will look at three parts:

  1. The likelihood of occurrence of an event.
  2. The likelihood of an adverse response to that event whether by a structural failure, loss of coolant, component failure, etc.
  3. The magnitude of the consequences resulting from the adverse failure (e.g. loss of life, economic damages, environmental damages, etc.) if that occurs.

Insights gained from conducting a risk assessment can then allow for better resource allocation by focusing on more risk-significant issues identified in the assessment.

The consensus in the engineering community is that a risk-informed analysis is the best source of information for priority setting and resource allocation.

What is a Performance-based approach?

An approach that relies upon the desired, measurable results or performance outcomes based on objective criteria rather than a prescriptive process, technique, or procedure.

Basically, performance-based approaches seek to explicitly identify performance objectives that collectively represent the desired outcome of a project and look at the result of a design or regulation to assess the performance. It formally allows for more flexibility in meeting performance criteria.

A performance-based approach must follow some basic steps:

  1. Establish the means for defining objectives, identifying parameters to be observed, and setting performance criteria
  2. Monitor performance to ensure allowable margins are not compromised
  3. Verify that expected outcomes are realized. Expectations of performance may be set through simulations and/or prototype tests.

The engineering community believes that focusing on the performance objectives instead of a prescriptive “how-to” design approach will allow for more innovation in methods without sacrificing adequacy of safety requirements.

What do the regulators say?

The U.S. Nuclear Regulatory Commission (NRC) has been working to add RIPB regulations since 1994 with the development of the Probabilistic Risk Assessment Implementation Plan. That’s because the majority of the regulations are based on deterministic and prescriptive requirements i.e. what can go wrong and how to fix the problem. The majority of the current regulations were developed without considering numerical estimates of risk. Without incorporating risk assessments into the regulations, the NRC assumed that undesirable events can occur and required plant designers to include safety systems and defense-in-depth principles capable of preventing and/or mitigating the consequences of accidents.

In 1999, the NRC adopted the following definition: An approach in which risk insights, engineering analysis and judgment including the principle of defense-in-depth and the incorporation of safety margins, and performance history are used, to (1) focus attention on the most important activities, (2) establish objective criteria for evaluating performance, (3) develop measurable or calculable parameters for monitoring system and licensee performance, (4) provide flexibility to determine how to meet the established performance criteria in a way that will encourage and reward improved outcomes, and (5) focus on the results as the primary basis for safety decision-making. [SRM-SECY-98-0144].

The current belief is that using RIPB concepts will guide NRC requirements and regulatory attention to the issues that are most important to the health and safety of the public and the environment; and identify performance measures that ensure an adequate safety margin.

Position statements

ANS published Position Statement 46, Risk-informed and performance-based regulations for nuclear power plants, in 2017 in support of RIPB regulations. With this position statement ANS "supports and advocates for Risk-Informed and Performance-Based (RIPB) safety design and licensing approaches because such approaches will assure protection of public health and safety in the most effective, efficient, and transparent manner. The RIPB approach is a set of methodologies that work to realize graded safety along with efficient priority setting.”

The ANS/ASME Joint Committee on Nuclear Risk Management (JCNRM)

The ANS/ASME Joint Committee on Nuclear Risk Management (JCNRM) Consensus Committee focuses on writing consensus standards that establish safety and risk criteria and methods for completion of probabilistic risk analysis (PRA) and risk assessments. The flagship standard for the JCNRM is ANSI/ASME/ANS RA-S-2008(R2019), Standards for level 1/large early release frequency probabilistic risk assessment for nuclear power plant applications, which is currently being revised. The other big project currently in production is the ASME/ANS RA-S-1.4-2013, Probabilistic risk assessment standard for advanced non-light water reactor (NLWR) nuclear power plants. In September 2019, the JCNRM decoupled the NLWR standard from the next edition of the Level 1/LERF standard to ensure it would be available by the end of 2020 to support regulatory applications.

Risk-informed, Performance-based Principles and Policy Committee (RP3C)

The ANS Standards Board has established the Risk-informed, Performance-based Principles and Policy Committee (RP3C) as a committee that reports directly to the Standards Board. The RP3C is responsible for the identification and oversight of the development and implementation of the ANS Risk-Informed and Performance-Based Standards Plan that establishes the approaches, priorities, responsibilities and schedules for implementation of risk-informed and performance-based principles in ANS standards. These principles are applicable to standards that address the design, construction, operation, evaluation and analysis, decontamination and decommissioning, waste management, and environmental restoration for nuclear facilities.

Further Reading

from nuclear news

The nexus between safety and operational performance. ­­­Over the past 20 years, the nuclear industry’s efforts to improve plant performance have taken a risk-informed approach that focuses resources on the most safety-significant issues.

Risk-informed, performance-based safety: Past, present, and future. Risk-informed and performance-based approaches to nuclear safety have saved money and improved safety for current reactors and have the potential to offer even greater benefits for advanced reactors.

other documents and pages

Last modified October 20, 2020, 9:40pm CDT