An Integrated Framework for Risk Assessment of High Safety Significant Safety-related Digital Instrumentation and Control Systems in Nuclear Power Plants: Methodology and Demonstration

Abstract

This report documents the activities performed by Idaho National Laboratory (INL) during Fiscal Year (FY) 2022 for the U.S. Department of Energy (DOE) Light Water Reactor Sustainability (LWRS) Program, Risk Informed Systems Analysis (RISA) Pathway, digital instrumentation and control (DI&C) risk assessment project. In FY 2019, the RISA Pathway initiated a project to develop a risk assessment strategy for delivering a technical basis to support effective and secure DI&C technologies for digital upgrades/designs. A framework was proposed for this strategy, which aims to (1) provide a best-estimate, risk-informed capability to quantitatively and accurately estimate the risk impact of plant modernization, considering the introduction of high safety-significant safety-related (HSSSR) DI&C systems, (2) support and supplement existing risk-informed DI&C design guides by providing quantitative risk information and evidence, (3) offer a capability of design architecture evaluation of various DI&C systems, (4) assure the long-term safety and reliability of HSSSR DI&C systems, and (5) reduce uncertainty in costs and support integration of DI&C systems in the plant.

Advanced Human-System Interface Risk Analysis Based on Redundancy-Guided Systems-Theoretic Hazard Analysis and Human Reliability Analysis

“…Table I summarizes the various HSI-related PSFs, as well as the capabilities of four different HRA methods to properly evaluate these PSFs. These four methods are the Standardized Plant Analysis Risk HRA [2], Cause-based Decision Tree (CBDT) [11], Cognitive Reliability and Error Analysis Method [12], and Integrated Human Event Analysis System for Event and Condition Assessment (IDHEAS-ECA) [13]. In HRA, practitioners review the HSIs required for human actions, determine their PSF levels, then use them to estimate the final HEPs.…”

“…RESHA's outputted summaries of HSI conditions are generated as fault trees (i.e., HSI fault trees). The quantitative values in the fault trees come from [13], as well as from the unavailability equations suggested by the fault tree theory of PRA [13]. HRA methods are used to quantify a human action in the two different HSI conditions.…”

“…The details of these diagrams were assumed based on the APR1400 DI&C system. First, in the figure, the QIAS-P is simplified into a diagram, having already been analyzed in our previous study [13]. The information from the QIAS-P is provided to the QIAS-N processor and the IPS server.…”

An Integrated Framework for Risk Assessment of Safety-related Digital Instrumentation and Control Systems in Nuclear Power Plants: Methodology Refinement and Exploration

“…Results are obtained based on limited design information and testing data. [1], [2], [3], [4], [5]. The LWRS program, sponsored by the U.S. DOE and coordinated through a variety of mechanisms and interactions with industry, vendors, suppliers, regulatory agencies, and other industry research and development (R&D) organizations, conducts research to develop technologies and other solutions to improve economics and reliability, sustain safety, and extend the operation of nation's fleet of nuclear power plants (NPPs).…”

“…In other words, are there any critical failures or failure combinations existing in the system that may lead to the DI&C system completely losing its function? A seven-step process, shown in [4], illustrates the workflow of RESHA in the proposed framework for the hazard analysis of DI&C systems, especially for software CCF analysis of highly redundant safety-related DI&C systems.…”