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New Light-Water Reactors Sub-Arena

New light-water reactors (LWRs) comprise one of four sub-arenas that the staff of the U.S. Nuclear Regulatory Commission (NRC) identified in considering which areas of the reactor safety arena to target for greater use of risk information. This page summarizes the following aspects of this sub-arena:


Implement risk-informed and performance-based activities to address the PRA elements of Title 10, Part 52, of the Code of Federal Regulations (10 CFR Part 52), and to increase the effectiveness and efficiency of the design certification, licensing, and oversight activities that the NRC staff conducts for new LWRs.

This objective has two main parts:

  • First, this objective involves using the plant-specific PRA to implement risk-informed and performance-based programs. For example, the maintenance rule (10 CFR 50.65) will utilize the PRA to a great extent. Other examples include initiatives that a new reactor licensee may voluntarily pursue, such as risk-informed technical specification completion time, risk-informed in-service inspection, or special treatment under 10 CFR 50.69.
  • Second, this objective involves using risk insights and PRA results to improve the NRC's effectiveness and efficiency in the licensing and oversight processes. For example, the staff will use risk insights, in conjunction with other considerations, to focus its review of a new reactor license application on those aspects that are important to risk. Other examples include developing risk-informed acceptance criteria for applications and adopting a risk-informed approach to sampling the inspection, testing, analysis, and acceptance criteria (ITAAC) to confirm the acceptability of the as-built plant.

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The risk-informed and performance-based activities (listed below) for this sub-arena satisfy the following screening criteria:

  • The stated objective will help to improve the effectiveness and efficiency of the NRC's regulatory process, while increasing nuclear plant safety and reducing unnecessary regulatory burden.
  • The bases for developing a risk-informed and performance-based regulatory structure for licensing and oversight of new LWRs are articulated in several Commission documents, policy statements, and processes (including the 10 CFR Part 52 rulemaking).
  • Goals and activities to meet the objective for this sub-arena will be performance-based, to the extent that they meet the following four criteria:
    1. measurable parameters to monitor performance
    2. objective criteria to assess performance
    3. flexibility to allow licensees to determine how to meet the performance criteria
    4. no immediate safety concern as a result of failure to meet the performance criteria

An applicant for a combined license (COL) for a new LWR is required to perform a PRA. The NRC staff expects such PRAs to be used for the following purposes:

  • Identify risk-informed safety insights.
  • Demonstrate how risk compares to the Commission's goals.
  • Assess the balance between accident prevention and mitigation.
  • Identify and address vulnerabilities, reduce risk contributors, and select among design alternatives during the design phase.
  • Demonstrate that the plant design represents a reduction in risk (compared to existing operating plants).
  • Demonstrate that the design addresses the requirements in 10 CFR 50.34(f), as they relate to Three Mile Island (TMI).

PRA results and insights are used to support the following programs (among others):

  • Regulatory Treatment of Non-Safety Systems (RTNSS)
  • Inspection, test, analysis, and acceptance criteria (ITAAC)
  • Reliability Assurance Program (RAP)
  • Future aspects of regulatory oversight, technical specifications, the maintenance rule (10 CFR 50.65), and others

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The following goals are derived from the Commission's policy statements and guidance, which reflect the current phase of NRC and industry development, as well as the current implementation of risk-informed activities:

  • Ensure (during the design certification phase) that the applicant used risk-informed safety insights to select among alternative features, operational strategies, and design options to reduce or eliminate the significant risk contributors of existing operating plants.
  • Ensure that the risk associated with the design compares favorably with the Commission's goals of less than 1E-04/year for core damage frequency (CDF) and less than 1E-06/year for large release frequency (LRF).
  • Using the results and insights from the PRA, ensure that the COL applicant supported the RTNSS process, including the identification of structures, systems, and components (SSCs).
  • Using the results and insights from the PRA, ensure that the COL holder supported regulatory oversight processes, as well as programs associated with plant operations (such as technical specifications, reliability assurance, human factors, and maintenance rule implementation).
  • Using the results and insights from the PRA, ensure that the applicant identified and supported the development of specifications and performance objectives for plant design, construction, inspection, and operation (such as the ITAAC, RAP, technical specifications, and COL action items and interface requirements).

Risk-Informed and Performance-Based Activities

The following table specifies the ongoing licensing initiatives, projects, and activities that the staff of the U.S. Nuclear Regulatory Commission (NRC) has targeted for greater use of risk information in the New Light-Water Reactors Sub-Arena within the Reactor Safety Arena.

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Initiative, Program or Project Project Description and Major Activities Status
Development of ISG on PRA technical adequacy for ALWRs "Develop Interim Staff Guidance (ISG) DC/COL-ISG-028, "Assessing the Technical Adequacy of the Advanced Light-Water Reactor (ALWR) Probabilistic Risk Assessment for the Design Certification Application and Combined License Application," to provide guidance on how the applicants can use the ASME/ANS PRA Standard (RA-Sa-2009) for assessing the technical adequacy of their PRA. This ISG supplements RG 1.200 to address the pre-operational phases (e.g., Part 52 licensing) and large release frequency (LRF) for ALWRs. It is expected to be incorporated into RG 1.200, RG 1.206, and SRP 19.0, following the issuance of next edition of PRA Standard. ACRS Subcommittee on Reliability and PRA was briefed on this ISG prior to the issuance for public comment. Risk Basis: The ISG is needed because the existing PRA Standard was developed based on current operating reactors. This guidance provides consistent consideration of the PRA Standard in assessing the technical adequacy of the PRA needed for Part 52 Design Certification/Construction Operating License (DC/COL) applications." Issued for public comment on October 14, 2014. Expected to be incorporated into PRA Standard in Fall 2016.
Evaluate and develop risk-informed regulatory guidance for new reactors

In response to SRM-SECY-12-0081, "Risk-Informed Regulatory Framework for New Reactors," the staff submitted SECY-13-0137, "Recommendations for Risk-informing the Reactor Oversight Process (ROP) for New Reactors." In that SECY paper the staff recommended the development of an integrated risk-informed approach for evaluating the safety significance of inspection findings for new reactor designs.
Risk Basis: The use of relative risk metrics that would provide a more risk-informed approach to the determination of the significance of inspection findings for new reactors are being considered.

More information
Development of Standardized Plant Analysis Risk (SPAR) Models for New LWRs Develop design-specific SPAR models for new and advanced reactor designs. Internal events, at-power, SPAR models have been developed for the AP1000, ABWR (GE and Toshiba), US APWR, and EPR designs. In addition, some models have been extended by adding a shutdown model to the ABWR-Toshiba model and a flooding, fire, and low power shutdown models to the AP1000 SPAR model. Planned future activities include development of SPAR models for additional designs, including small modular PWRs (e.g., mPower) and extension of existing SPAR models to include additional scope considerations. The staff provided the Commission with an update of these activities included in SECY-14-0107, "Status of the Accident Sequence Precursor Program and the Standardized Plant Analysis Risk Models," dated October 6, 2014.
Risk Basis: The staff may use new reactor SPAR models to perform risk assessments to inform potential risk-informed applications for Combined Licenses (COLs), focus construction inspection scope, or assess the significance of construction inspection findings. Once the plants begin operation, independent assessments using SPAR models will be used by the staff for the evaluation of operational findings and events similar to the assessments performed for current operating reactors.

To request additional information, Contact Us About Risk-Informed, Performance-Based Regulation.

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Page Last Reviewed/Updated Friday, April 01, 2016