الفهرس 
IntroductionOnly 14 pages are availabe for public view
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Abstract
In this thesis, a Safety-Critical Software Development Framework (SCSDF) is presented to be used in the developing of the Safety Critical Software System (SCSS) for NPPs. The presented SCSDF helps the practitioners to develop the SCSSs for NPPs in accordance with the proposed phases, processes, approaches, and methodologies with the target of making the system safe, risk-free, and fail-safe. This SCSDF is an integrated framework dedicated for NPPs and consists of seven phases. The SCSSs development processes mandate to get several milestones such as software requirements, software design, software coding (implementation), software testing, and software integration. In addition to software planning phase that focuses on safety analysis plan, software commissioning phase with associated tests, and software updating phase with associated safety processes.
Considering the existing standards and the currently used frameworks are a conceptual structure without details. In the meantime, the presented SCSDF can be considered as a projection of known standards for SCSS applied in NPPs applications, to specifically generate more safety-oriented and reliable development processes.
The presented SCSDF presents the Non Functional Requirements (NFRs) model specified for NPPs based on safety system classification and graded approach, which assigns the quality attributes and the set of suitable requirements to a given system based on its importance to safety. This model helps in enhancing the system overall safety without increasing the system complexity and useless implementation cost.
The presented SCSDF technically puts most important software safety related definitions on stage and handles problems related to these definitions with one and unique SCSDF. For example, during the software design process, SCSDF handles the single-point failures, Common Cause Failure (CCF) and encourages modularity. As a part of the SCSDF, fault detection, and fault tolerance improve not only the safety but also the system reliability.
The presented SCSDF simplifies design and coding processes of NPPs software development lifecycle as it provides smooth and straightforward methodologies, which apply logical, abstract and flow-based development steps to decrease complications and increase understandability. This distinguishing nature of the SCSDF contributes to the elimination of risks which might be caused by the complex architectural design and coding. SCSDF presents a hazard analysis approach, which definitely represents one of the contributions of this thesis for both academia and industry. The presented hazard
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analysis approach based on qualitatively and semi-quantitatively contributes towards a better understanding of fault types, root causes of the main failures and the severity of software failures. Furthermore, studying software failure trends can help practitioners to identify software components that require more V&V and may need fault tolerance mechanisms. Considering the reliability of the Reactor Protection System (RPS) software, the applied SCSDF proves that, it can handle single-point failures by applying the failure analysis approach, applying the safety constraints, applying the V&V, and taking the appropriate measures to detect, correct the errors and considering the latent errors. Additionally, it increases the system reliability and reduces risks of single point failures and the CCF.
The introduced factors in the maintenance phase that shall be assessed and considered during software maintenance, in addition to the presented safety processes that shall be performed during software updating or maintenance contribute toward sustain the safety of the SCSS and accordingly the critical system.
RPS is considered as the most important safety system of NPPs. The RPS system is intensively based on complex software programming. In this thesis, the RPS simulation was developed with successful achievements and proves that the RPS design based on the presented SCSDF enhance and sustain the system safety level by identifying failure conditions of the software.
The reliability of RPS software is explored mathematically in the form of failure rate. The SCSDF is used to develop the RPS software applications and the failure rate of this application is calculated to be 1.7*10-11 compared to 10-7 of previously developed RPS software application. With this almost negligible failure rate value, the reliability and dependability and consequently safety of the RPS software application is 100% of the failure-free operation.