Conference Proceedings Paper
EC6 for Darlington as a Managed-Enhancements Replication Project
9th International Conference on CANDU® Maintenance - 2011 December 04-06
Mike Soulard (Candu Energy Inc.)
CANDU 6 design has a well-deserved reputation for lifetime performance and on-time, on-schedule construction. Candu Energy is finalizing development of an upgraded reactor product, the Enhanced CANDU 6* (EC6*), which incorporates the CANDU 6’s well-proven features, and adds enhancements that make the reactor even more safe and easier to operate. The EC6 is the only mid-sized reactor (700 MWe class) with a proven pedigree that meets modern reactor expectations and regulatory standards. It is sized for smaller grids and also has outstanding fuel-cycle capability.
Some of the key features incorporated into the EC6 include increasing the plant’s power output, shortening the overall project schedule, addressing obsolescence issues, optimizing maintenance outages and incorporating lessons learnt through feedback obtained from the operating plants. The EC6 utilizes modern computers and a distributed control system housed in an advanced control room which, along with automated testing and on-line diagnostics, make the plant easier and safer to operate, with minimal operator intervention. An array of health monitoring equipment are also installed to foretell impending equipment problems, which can be acted upon, avoiding complications that could result in forced shutdowns. Improvements to the fire protection system and enhanced security features will further protect the assets. Containment and seismic capability are upgraded to meet modern standards. The first deployment of the EC6 is anticipated inCanada; other markets are also being pursued.
The EC6 reactor is designed for a target lifetime capacity factor of 92% including 94% year-to-year and a 1% Forced Loss Rate. Since the number and duration of maintenance outages impact plant capacity factors, periodic short duration maintenance outages of less than a month once every 36 months is a key target of the EC6 reactor. This objective is achieved by automating a number of tasks such as shutdown systems testing. The majority of these activities can be undertaken with the reactor at power.
Enhancements incorporated into the EC6 design to improve performance and facilitate maintenance include:
- Use of improved material and plant chemistry specifications based on operating experience from CANDU plants, e.g. life-limiting components such as HTS feeders and headers have been enhanced with higher chromium content to limit the effect of feeder corrosion.
- Implementation of advanced computer control systems for monitoring, display, diagnostics and annunciation and improvement of configuration management capability.
- Utilization of SMART CANDU™ modules for monitoring plant chemistry of systems and components, equipment status monitoring, and providing predictive maintenance capability.
- Ensuring capability for return to full power on restoration of the electrical grid. The EC6 reactor has the capability to continue operating and delivering house load without connection to the grid, therefore enabling a rapid return to production of power upon reconnection.
- A maintenance-based design strategy. This program incorporates lessons learned and ensures maintainability of systems and components. It defines an improved maintenance program to ensure plant conditions are diagnosed and maintained within their design performance limits. This results in improved preventive maintenance and reduced forced outages at a rate of less than five days/year.
- Improved plant maintenance with provisions for electrical, water and air supplies that are built-in for on-power and normal shutdown maintenance.
- Shielding in radiologically controlled areas is provided to minimize worker exposure and occupational dose.
- Improved equipment selection and system design based on probabilistic safety evaluations using three-year outage intervals.
- The EC6 design offers a target life of 60 years with one mid-life refurbishment of certain critical equipment, such as the fuel channels and feeders. This objective is achieved by elongating the fuel channel bearings, thickening the pressure tube slightly, increasing the feeder wall thickness, using improved equipment and materials, better plant chemistry, and more active monitoring of critical plant parameters. All life-limiting factors have been evaluated and addressed, supported by extensive studies. By essentially doubling the useful life of the reactor, the plant owners are assured of a long-term supply of their electricity needs with an improved return of assets
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