Digital Instrumentation and Controls (I&C)
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Introduction
In 2021, the NRC has issued guidance, Design Review Guide (DRG): Instrumentation and Controls for Non-Light-Water Reactor (Non-LWR) Reviews for the NRC staff to use in reviewing the I&C portions of applications for advanced non-LWRs within the bounds of existing regulations. The DRG was developed to address the immediate needs associated with the non-LWR community. However, because the DRG is technology inclusive, it may be used for the review of LWR plant designs and other reactor technologies. The graphic is taken from the DRG, Figure X-1. The framework depicted in Figure X-1 above supports achieving the objectives of I&C system reviews, which are to confirm that: (1) the I&C system design includes the fundamental safety functions necessary to assure adequate safety during operation of a NPP under normal operation, transient, and accident conditions; (2) the I&C system safety functions, systems, and equipment have been properly classified, and appropriate performance as well as special treatment measures have been established; and, (3) an application demonstrates I&C system and equipment will be designed, fabricated, constructed, and tested in accordance with quality standards commensurate with the safety significance of the I&C functions to be performed.
On August 10, 2022, the NRC staff submitted SECY-22-0076, "Expansion of Current Policy on Potential Common Cause Failures in Digital Instrumentation and Control Systems" to recommend updating the current DI&C common cause failure (CCF) policy from SRM-SECY-93-087, "SECY-93-087 – Policy, Technical, and Licensing Issues Pertaining to Evolutionary and Advanced Light-Water Reactor (ALWR) Designs," dated July 21, 1993. Specifically, the NRC staff requested that the policy be expanded to allow the use of risk-informed approaches to justify an appropriate level of defense-in-depth and diversity for high safety significance DI&C systems. On May 25, 2023, the Commission approved the NRC staff’s recommendation with edits as contained in SRM-SECY-22-0076. In accordance with the Commission’s direction in SRM-SECY-22-0076, the NRC staff is updating Branch Technical Position 7-19, "Guidance for Evaluation of Defense in Depth and Diversity to Address Common-Cause Failure due to Latent Design Defects in Digital Safety Systems" for LWRs.
The NRC staff intends to use pre-application engagement and ongoing advanced reactor I&C workshops to address any questions or concerns related to the implementation of the Commission's revised policy on CCF. The NRC staff plans to revise the DRG, and possibly RG 1.233, in the future. The revision will address the differences in language discussed above and reflect any additional clarifications or improvements based on lessons learned by the NRC staff and prospective applicants, input received from the stakeholders during the ongoing advanced reactor I&C public workshops, and other interactions. The NRC staff believes this experience is necessary to understand what guidance on these matters would be of use to non-LWR applicants (e.g., on risk-informing the selection of critical safety functions). In the interim, the NRC staff will continue to address any questions or concerns from stakeholders in this area, including addressing the SRM-SECY-22-0076 policy in the applicable DI&C system design process.
Public Workshops on the I&C Licensing Framework for Advanced Reactors
In 2023, the NRC staff hosted public workshops with representatives from industry, the national laboratories, and others as part of the agency’s efforts to streamline reviews of future license applications and to ensure common understanding amongst the NRC staff, potential applicants, and the public. The workshop discussions related to specific industry questions regarding the Licensing Modernization Project (LMP) implementation for the design of I&C systems and the use of the DRG in preparing application submittals.