CANDU Heat Transport Maintenance and Life Management Program

Abstract

AECL has developed an integrated Plant Life Management (PLiM) Program and is assisting several CANDU reactor owners in its implementation. The PLiM initiatives are supported by design. procurement, construction, commissioning, regulatory and operations feedback, as well as an R&D program that provides support with regard to plant aging mechanisms, surveillance methodologies, mitigation methods, and improved inspection technologies. A specific example of the PLiM program effort is to ensure robust performance of the Heat Transport System (HTS). AECL has made efforts on several fronts to develop an integrated approach to monitoring, and maintaining the system performance. This includes efforts in system modelling, aging mechanism modelling, maintenance procedure development, and improved monitoring techniques. The heat transport system of a CANDU nuclear power plant requires monitoring throughout the plant life for efficient operation of the station. Successful monitoring of a station can identify the timing of preventative maintenance and the proper assessment of safety parameters to cater for changes that have occurred during operation. One of the key components of successful monitoring is the development of a thermal hydraulic plant model of each component in the primary heat transport system. In response to this need, AECL has developed system models with appropriate methodologies to predict HTS performance with respect to time. In conjunction with the development of predictive capabilities, AECL has identified several steam generator maintenance techniques to ensure long term performance. To quantify the impact of various maintenance activities, research has been conducted to establish deposit behaviour in steam generators and feeder pipes. This research enhances the ability to properly characterize the system conditions with time, making a significant contribution to overall maintenance management. Part of understanding the system characteristics and being able to model them, is the ability to obtain direct measurements of degradation mechanisms. Of particular interest is the distribution of deposit loading on the primary side of steam generators. AECL has developed a capability to easily provide this characterization, using eddy current probe technology. This paper discusses the overall approach developed at AECL to help understand and manage the maintenance requirements for the HTS. The discussion touches upon the basic modelling approach and the research being carried out to enhance the understanding of the key steam generator degradation mechanisms affecting HTS performance. Further, the paper will discuss the specific application of the primary side cleaning technology for application to CANDU plants. The paper will also demonstrate the application of the approach by looking at the recent primary side mechanical cleaning at Gentilly-2 NGS where there was a restoration of -5% of core flow and ~ -3 degrees C in reactor inlet header temperature (RIHT). Finally, the eddy current method developed to measure steam generator tube primary side fouling will be discussed. The technique, combined with the HTS performance models, is able to assist operators, maintainers and technical staff in planning when steam generator cleaning should be carried out. Results from the Gentilly-2 primary side clean are presented to illustrate the effectiveness of this approach.