The Concept of Creating Verifiable Software for Nuclear Power Plant Process Instrumentation and Control Systems

In the today's world, process instrumentation and control systems (PICS) play a crucial role in ensuring safe and efficient operation of various facilities. This is especially the case for nuclear power plants (NPP), in which top priority is given to reliability and safety. One of the key aspects of software development for NPP PICS is verification, the process of confirming that the software meets the specified requirements and standards. The aim of the study is to demonstrate the concept of developing verifiable software for NPP PICS with due regard to the provisions of modern standards and regulatory documents. The focus is placed on elaborating a document called the Software Verification Plan. Its general structure is presented together with recommendations on the content of sections most important from the viewpoint of quality and safety assurance guarantees. An approach to defining the verification scope and depth depending on the impact of software on safety in accordance with different classification systems has been proposed. Matters concerned with ensuring independence of the verification process are discussed, and recommendations are given for developing an optimal matrix of independence in implementing the stages considering organizational forms of verification. The role and organizational structure are given, and their integration into a process-based approach to arranging the activities on verifying software for NPP PICS is shown. The successive stages in the lifecycle of software development for NPP PICS are compared with the verification stages, and the mechanism for ensuring the iterative nature of the verification process within the lifecycle individual stage is demonstrated. The conclusions have been drawn that the feasibility of verification is in principle possible through harmonizing the software development and verification methods, which, in its turn, opens the possibility to perform comprehensive monitoring of compliance with the requirements throughout all lifecycle stages of the NPP PICS software with promptly correcting any nonconformities that may arise.