Ensuring Safety-Critical Software Excellence in Next-Generation Nuclear Systems

The two-legged approach to the substantiation of computer-based systems important to safety (CBSIS), preferred by the UK nuclear regulator, has led to additional effort needed to justify the use of software, particularly through the application of independent confidence-building measures (ICBMs). The economic viability of SMRs is challenged by additional ICBM requirements whose cost does not scale with SMR reactor power, and the late application of UK-specific additional testing and analysis is considered to be inconsistent with systems engineering good practice.

This report provides a summary of a critical analysis of literature (including international standards) and engagement with a number of leading experts in software assurance. It considers a practical framework (VARIA) for the assurance of software used in nuclear CBSIS. It builds on good practice used in the nuclear sector and in other industries for software assurance and the critical role independent scrutiny plays. It identifies where assurance activities can be conducted earlier in the development lifecycle to reduce project risk.

The VARIA framework highlights ways to reduce testing and assurance costs within the traditional two-legged approach, while still showing that the risks of using CBSIS are reduced to as low as reasonably practicable (ALARP), without compromising safety or security standards. It provides a proactive mechanism to capture evidence as it is produced, identify evidentiary gaps early or allow for the implementation of a system architecture to manage the resulting risk.

Read the full report here.