SAPHIRE: A Comprehensive Tool for Probabilistic Risk and Reliability Assessment



Sapphire, an acronym for Systems Analysis Programs for Hands-on Integrated Reliability Evaluations, represents a significant advancement in the field of probabilistic risk and reliability assessment. Developed by the Idaho National Laboratory for the U.S. Nuclear Regulatory Commission (NRC), Sapphire has evolved over the decades into a sophisticated software tool that is integral for analyzing and evaluating the reliability of nuclear power plants and other critical infrastructure.

The Genesis of Sapphire

The development of SAPHIRE began in the mid-1980s, driven by two primary objectives set by the NRC. First, there was a need to demonstrate that Probabilistic Risk Assessment (PRA) information could be effectively managed and manipulated using the then-emerging microcomputer technology. Second, the NRC recognized the rapid advancements in PRA technology and sought an inexpensive and accessible platform to facilitate the education of PRA concepts to students and professionals in the field.

The initial version of what would become known as Sapphire was termed IRRAS (Integrated Reliability and Risk Analysis System). This early iteration was groundbreaking as it introduced capabilities to create, edit, and analyze graphical fault trees, significantly simplifying complex processes involved in risk assessment.

Evolution Through Versions

Over the years, SAPHIRE has undergone numerous upgrades, each adding layers of functionality and improving user experience. Here is a breakdown of its evolution:

  • 1987: Version 1 (IRRAS) – Introduced capabilities for drawing, editing, and analyzing graphical fault trees.
  • 1989: Version 2 – Integrated the ability to draw, edit, and analyze graphical event trees, expanding the scope of analysis.
  • 1990: Version 4 – This version marked significant analytical improvements and the formation of the IRRAS Users Group, fostering a community of users who could share insights and improve the software’s utility.
  • 1992: Version 5 – Transitioned to a 32-bit system which drastically reduced analysis time. New features included end state analysis and the integration of fire, flood, and seismic modules.
  • 1997: Version 6.x – Introduced a Windows user-interface, significantly enhancing usability. The plug-in feature was added, allowing analysts to expand built-in probability calculations.
  • 1999: Version 7.x – Improved the event tree “linking rules” and introduced dual language capability in the SAPHIRE database.
  • 2005-2010: Version 8.x – Development and subsequent release of SAPHIRE for Windows, providing tools tailored for both U.S. Government and industry use.

Key Features and Capabilities

Sapphire is designed to perform comprehensive risk and reliability assessments through a variety of analytical methods and tools. Some of its key features include:

  • Graphical Fault Tree and Event Tree Analysis – Enables users to visually map out complex processes and simulate different failure scenarios.
  • Rule-based Processing – Automates certain analytical tasks based on pre-defined rules, improving efficiency and consistency in the assessments.
  • Multi-processor Support – Allows the software to perform large-scale analyses more efficiently by leveraging multiple processors simultaneously.
  • End State Analysis – Helps determine the final condition of a system after various interactions and events, a crucial aspect of safety assessments.

Applications and Impact

Sapphire’s applications are vast, primarily focusing on the nuclear industry where reliability and risk assessments are critical for safe operations. It is used to evaluate the performance of nuclear reactor safety systems, predict potential failures, and plan preventive measures. The tool’s robust analytical capabilities make it an indispensable resource for risk managers and safety analysts who are responsible for maintaining high safety standards in nuclear facilities and other high-risk industries.


The continuous development of Sapphire over the past few decades underscores the critical need for advanced tools in the domain of risk and reliability assessments. From its inception as IRRAS to its current form as SAPHIRE, the software has not only adapted to changing technological landscapes but has also profoundly influenced the methodologies used in probabilistic risk assessments. Today, SAPHIRE stands as a testament to the progress in computational risk assessment, offering a blend of sophisticated features that help ensure the safety and reliability of critical infrastructure worldwide.


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