Layup Practices at EDF PWR Fleet and Future Developments

摘要

A proper lay-up can only be achieved by plant specific lay-up procedures. The layup control practices are necessary to prevent corrosion damage during shutdown and are an important part of the life time extension of a nuclear power plant. EDF operational experience in this area confirms that damage to plant equipment from improper layup procedures is a cause of reduced plant reliability and availability and can increase the corrosion products ingress into the SG during start-up. The plant preservation strategy applied across the EDF fleet is based on the following principles: - Anticipated time frame of the required layup: short-term outages can become long-term outages, and can necessitate the use of unplanned preservation techniques; - Dry layup for a long-term outage of the condensate/feedwater system: (1) condenser vacuum assisted draining at high temperature, (2) estimation of air requirements (flow rate, humidity...) to guarantee the optimum conditions inside the system. - Wet lay up for a short-term outage of the condensate/feedwater system: (1) system filled with operating medium, avoiding air ingress into the system, (2) injection of chemical agents if necessary. - Dry lay-up or wet lay up for the steam generators depending on maintenance work or radiation protection needed. This article presents the EDF layup program and the improvements in layup practices. It provides information on the layup procedures, best practices and recommendations, operating experience, considerations for different durations of outages; the implementation of a preservation working group, the selection of the systems that will be included in the lay-up program. Finally, future developments will be presented, such as the development of a 'convective model' to determine air requirements (humidity, flow rate...) and the drying rate to dry a heat exchanger.