Digital I&C

Purpose

Digital Instrumentation and Control (I&C) is expected to be used increasingly in not only advanced reactors, but also to plant modifications for current LWRs in operation, therefore research into digital I&C's effect on plant risk is a high priority in the development of ARs.

Scope

With the development of digital I&C to replace non-digital mechanisms of control comes different modes of failure but also different modes of success. Digital I&C has the potential to lower plant risk while also presenting new protective measures that need to be taken such as developing a cybersecurity network.

Digital I&C

EPRI is developing an approach to deploy digital I&C systems in advanced reactors (see EPRI 3002008018 [55]). The results of using this approach will help to identify areas where additional research is needed in order to properly account for their impact on risk.

• The approach applies systems engineering methods to improve the design of digital instrumentation and control (I&C) systems.
• The process identifies emergent behavior and potential issues / errors to digital I&C systems using Hazards and Consequences Analysis (HAZCADS) which integrates the Systems Theoretic Process Analysis (STPA) method to identify unsafe control actions (UCAs).
• The approach determines risks for system “misbehavior” and uses bounding risk assessments to assign risk reduction targets (RRTs) for each UCA. UCAs produce direct impacts on plant equipment and thus can be directly mapped to failures modeled in the plant PRA.
• The approach then identifies and establishes control methods (technical or administrative) to minimize the identified risks.

Since advanced reactors will employ significantly more automation than the existing fleet of LWRs, the assessment of human actions (their application and likelihoods) may be different than what has become standard for PRAs of existing plants. Driving questions:

• How applicable are existing HRA methods to the digital environment?
• Can the HRA methods be updated to assess digital systems and operator actions using them?
• Due to the increased use of automation, it is postulated that EoCs can become a more important (potentially the dominant) source of human error and it is possible that other tools (e.g., STPA) may be better suited to examine EoCs and eliminate them in the design process.

Another piece of developing digital I&C for advanced reactors will be how to secure and protect the control of the reactor. This will likely involve developing a cybersecurity system alongside components that are controlled by Digital I&C

EPRI Activities

• EPRI Digital Instrumentation and Control Implementation (New/Existing Plants)