Infusing Reliability Techniques into Software Safety Analysis

Software safety analysis for a large software intensive system is always a challenge. Software safety practitioners need to ensure that software related hazards are completely identified, controlled, and tracked. This paper discusses in detail how to incorporate the traditional reliability techniques into the entire software safety analysis process. In addition, this paper addresses how information can be effectively shared between the various practitioners involved in the software safety analyses. The author has successfully applied the approach to several aerospace applications. Examples are provided to illustrate the key steps of the proposed approach

MINIMAL CUT SETS IDENTIFICATION OF NUCLEAR SYSTEMS BY EVOLUTIONARY ALGORITHMS

Fault Trees (FTs) for the Probabilistic Safety Analysis (PSA) of real systems suffer from the combinatorial explosion of failure sets. Then, minimal cut sets (mcs) identification is not a trivial technical issue. In this work, we transform the search of the event sets leading to system failure and the identification of the mcs into an optimization problem. We do so by hierarchically looking for the minimum combination of cut sets that can guarantee the best coverage of all the minterms that make the system fail. A multiple-population, parallel search policy based on a Differential Evolution (DE) algorithm is developed and shown to be efficient for mcs identification, on a case study considering the Airlock System (AS) of CANDU reactor

Dynamic flowgraph methodology for reliability modelling of networked control systems: with application to a nuclear-based hydrogen production plant

The use of communication networks in digital control systems introduces stability and reliability concerns. Standard reliability and safety assessment methods need further modification to accommodate the issue in the reliability assessment of networked control systems. In this thesis, it is demonstrated that the Dynamic Flowgraph Methodology (DFM) can be extended to model networked control systems. The modelling of the communication network influence on the performance of the control system is presented. The areas that can affect the reliability of the control system are identified using the methodology. The thesis also presents the application of the DFM to a nuclear-based thermochemical water splitting process for hydrogen production, the Copper-Chlorine (Cu-Cl) cycle. The architecture of a networked control system and configuration of instrumentation and control systems for the hydrogen production plant are proposed in the thesis

Automatic Generation of Generalized Event Sequence Diagrams for Guiding Simulation Based Dynamic Probabilistic Risk Assessment of Complex Systems

Dynamic probabilistic risk assessment (DPRA) is a systematic and comprehensive methodology that has been used and refined over the past two decades to evaluate the risks associated with complex systems such as nuclear power plants, space missions, chemical plants, and military systems. A critical step in DPRA is generating risk scenarios which are used to enumerate and assess the probability of different outcomes. The classical approach to generating risk scenarios is not, however, sufficient to deal with the complexity of the above-mentioned systems. The primary contribution of this dissertation is in offering a new method for capturing different types of engineering knowledge and using them to automatically generate risk scenarios, presented in the form of generalized event sequence diagrams, for dynamic systems. This new method, as well as several important applications, is described in detail. The most important application is within a new framework for DPRA in which the risk simulation environment is guided to explore more interesting scenarios such as low-probability/high-consequence scenarios. Another application considered is the use of the method to enhance the process of risk-based design

Evaluation of the regulatory review process for the software development life cycle

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1997.Includes bibliographical references.by Andrew Patrick Gnau.M.S

A GUIDED SIMULATION METHODOLOGY FOR DYNAMIC PROBABILISTIC RISK ASSESSMENT OF COMPLEX SYSTEMS

Probabilistic risk assessment (PRA) is a systematic process of examining how engineered systems work to ensure safety. With the growth of the size of the dynamic systems and the complexity of the interactions between hardware, software, and humans, it is extremely difficult to enumerate the risky scenarios by the traditional PRA methods. Over the past 15 years, a host of DPRA methods have been proposed to serve as supplemental tools to traditional PRA to deal with complex dynamic systems. A new dynamic probabilistic risk assessment framework is proposed in this dissertation. In this framework a new exploration strategy is employed. The engineering knowledge of the system is explicitly used to guide the simulation to achieve higher efficiency and accuracy. The engineering knowledge is reflected in the "Planner" which is responsible for generating plans as a high level map to guide the simulation. A scheduler is responsible for guiding the simulation by controlling the timing and occurrence of the random events. During the simulation the possible random events are proposed to the scheduler at branch points. The scheduler decides which events are to be simulated. Scheduler would favor the events with higher values. The value of a proposed event depends on the information gain from exploring that scenario, and the importance factor of the scenario. The information gain is measured by the information entropy, and the importance factor is based on the engineering judgment. The simulation results are recorded and grouped for later studies. The planner may "learn" from the simulation results, and update the plan to guide further simulation. SIMPRA is the software package which implements the new methodology. It provides the users with a friendly interface and a rich DPRA library to aid in the construction of the simulation model. The engineering knowledge can be input into the Planner, which would generate a plan automatically. The scheduler would guide the simulation according to the plan. The simulation generates many accident event sequences and estimates of the end state probabilities

Development of a graphical approach to software requirements analysis

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 1998.Includes bibliographical references (p. 205-226).by Xinhui Chen.Ph.D

組織構造と作業戦略を考慮した作業チーム設計手法と最適化に関する研究

学位の種別:課程博士University of Tokyo(東京大学