Digital Modernization of Oconee Nuclear Station
A report was developed to assist in identifying plant improvements to reduce the rate of trips and transients. This report outlined nonsafety control system modifications to add redundancy and eliminate single-failure vulnerabilities. As a result of the report, system upgrades were initiated on the integrated control system, the main turbine control system, the main generator voltage regulator, main feedwater pump control system, and control rod drive system.
The obsolescence of control and protection systems due to discontinued OEM support was another issue being addressed at the same time as the trip and transient report recommendations. Facility personnel determined that digital system upgrades were the best options to address obsolescence of the reactor protection system, engineered safeguards system, Keowee Hydroelectric Plant exciter, Keowee governor, turbine supervisory instrumentation, and pneumatic controllers and instrumentation.
The last input to the modernization project derived from the need to isolate feedwater during specific design basis events in order to improve plant response and prevent excessive cooling. To address this concern, a new safety-related digital automatic feedwater isolation system was designed.
A thorough modernization overhaul was approved to perform all identified upgrades over the course of a decade. These upgrades have positioned ONS as a leading U.S. nuclear power plant in the application of digital electronic technology. The remainder of this article provides a summary of each upgrade.
Integrated Control System
The integrated control system (ICS) controls reactor core power by regulating steam demand, control rod positions, and feedwater input. Digital upgrade of the ICS was performed by Duke Energy personnel using proven digital STAR modules from AREVA.
In addition, Duke Energy developed the control software by converting existing analog plant control algorithms and then implementing experience-based enhancements to improve plant operations. As part of the upgrade, redundancy was built into the hardware and software design.
This installation was completed by late 1998. No plant trips or transients have resulted from ICS equipment failures following this upgrade. Historically, it was not uncommon to have two reactor trips a year due to ICS component failures.
This installation of a digital ICS was the first in the industry for nuclear power plants.
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