Development of System and Component Life Management Techniques for Optimal Design and Maintenance of Power Plants

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Power Plant performance is a function of design, operational environment, and maintenance. Today, the demand for rigorous safety and high efficiency is pushing the envelope of power plants, particularly nuclear plants with the result of significant increases in cost of maintenance. Decision making for new power plants or continued operation of existing power plants is shrouded with uncertainty due to changes in standards. In addition, the existing plants are entering the last 25% of their life and ageing effects are becoming significant and difficult to predict. This affects plant performance by requiring a higher level of inspections, or replacements, many of which turn out to be either ineffective or unnecessary. Hence, there is a strong need for an improved ability to predict effects of plant ageing and the ability to diagnose ageing. Significant research is conducted international on plant ageing phenomena concentrating mostly on understanding material and chemistry relationships with the environment. This important research leads to a better understanding of failure mechanisms and the ability to predict failure mechanisms. However, there are other impacts of ageing on the plant performance, such as impact on cooling flow or heat transfer which affects safety margins. Thus in some cases, the actual failure condition is not necessarily the life limiting factor for the component or system. On the other hand, many of the models used in design remain significantly conservative for analyzing plant safety. The end result is that it is not truly possible to optimize the overall plant performance due to the large amounts of uncertainty.The key objective of this research program is to develop life management techniques to be used both in design and in operations and maintenance to increase the overall reliability of the plant. To achieve this long term objective, it is necessary to study the following areas: (1) Improved methods for detecting ageing conditions in plant systems and components, and (2) Perform experiments on simulated aged systems/components to determine impact on thermalhydraulics and safety margins. This work will then allow development of predictive models that combine knowledge of plant design, plant condition, and ageing effects. For the detection of ageing conditions, our research group already has diagnostic systems such as ultrasonic tomography, capacitance tomography, neutron radiography, and thermography. These techniques will be applied to various combinations of components and environments to develop improved inspection methods. The work will be combined with image processing methods for improved quantitative analysis as this is currently a weakness in the inspection program.The experimental program will incorporate methods for representing ageing effects. We have developed three techniques to change the surface conditions to simulate mechanical ageing/impact damage, surface deformation using a deformable plastic, and a biological compound for simulating the effects of biofouling. The experiments will measure the impact of the aged condition on coolant flow, three dimensional flow disturbance, and pressure drop. Models for thermalhydraulics as a function of the ageing condition will be developed.Life management models will be developed for a select set of systems and components. Contacts with OPG will be able to provide some data regarding the conditions of some portions of the plant.The novelty of this work is that it will involve multiple disciplines involving mechanical and other stresses, interaction with materials and chemistry, and thermalhydraulic behaviour.