A deterministic approach for establishing a narrow band dynamic operating envelope to detect and locate hardware deterioration in nuclear power plants

Thesis(PhD (Nuclear Engineering))--North-West University, Potchefstroom Campus, 2013.Being able to detect and describe hardware deterioration in nuclear power plants benefits the nuclear industry tremendously as it would enable appropriate outage and maintenance planning. Being able to detect and describe this faulty behaviour also assists in fault analysis of nuclear power plants. This thesis describes the development of narrow band dynamic operating envelope that makes use of real-time simulated plant measurements and control operations to compare with actual plant measurements and control operations. By simulating the plant behaviour in real-time whilst comparing it with the real-time transient the plant is following, a second set of plant measurements is generated. The newly generated plant measurements represent plant measurements if the control system did not introduce control operations to nullify the effect of the fault. This enables the calculation of the unknown disturbance introduced into the plant as a fault condition. The benefit of such a system is that plant faults that are too small to detect (especially during transients when the plant operating point is moving around) can be identified. The behaviour of the control system is also continuously predicted so the effect of the control system compensating for fault effects (which in most cases hides the fault condition) is used to characterise the fault condition in terms of magnitude, position and subsystem being affected. The combination of the fault detection and fault characterisations produces a complete fault identification system. The approach is verified by making use of an implementation of the fault identification system on a simulated plant. Typical faults (small enough to go undetected for an extended period of time during a typical transient) are introduced into the virtual plant and continuously compared with another plant simulation, producing the same transient without the introduction of the fault. A comparison is done to evaluate the speed and detail provided by the fault identification system as opposed to the conventional plant protection system. Using the described methodology, the fault is detected and characterised before plant design limitations are reached or the fault is detected by the conventional protection system. In addition to the fault identification system, this research develops the functional requirements for a full scope engineering and training simulator that would allow the simulator to be fully utilised to simulate postulated accident scenarios, plan plant modification procedures as well as provide an in- transient real time reference for plant diagnostic systems. To ensure practical implementation of the system in the regulated nuclear industry, an implementation framework that keeps the conventional plant protection system intact, is created. It allows the implementation of narrow band dynamic operating envelope operating within the conventional operating envelope. The framework allows the implementation of the developed fault identification system and other plant diagnostic systems on existing nuclear power plants without impacting on existing nuclear power plant licences as well as the licensing process of new nuclear power plants.Doctora