by Carl Fisher, Areva Reactors and Services, and Michael E. Bailey, Oconee Nuclear Station
Because nuclear power plants are licensed to operate for long periods, how does one address obsolescence issues in systems built decades ago? As consumers switched from telephone landlines to mobile phones and from typewriters to computers, the nuclear industry is moving from outdated analog technology to newer, more modern digital systems. Digital technology already plays a leading role in many other industries, such as aviation, automotive and Navy nuclear.
Transitioning to digital technology is critical to addressing obsolescence in the current nuclear fleet and is further increasing the safety and reliability of U.S. nuclear power plants. An industry-leading example of this transformation is Duke Energy Corp.’s Oconee Nuclear Station. This station is the first and only U.S. commercial nuclear station to employ digital technology for a comprehensive system upgrade. Two years have passed since the station transitioned to a digital instrumentation and control (I&C) system, during which time Oconee has experienced improved safety, reliability and plant availability.
Advanced digital technology helps address the increasing obsolescence of analog systems–many of which were designed and built decades ago–and are becoming costly to maintain. Manufacturers that originally produced analog systems are discontinuing support for older equipment.
In Oconee’s case, Duke Energy recognized the benefits of operating the station beyond its original 40-year license and applied for and received a license from the Nuclear Regulatory Commission (NRC) that permits operation through 2034. Duke realized it would need to make significant upgrades to operate Oconee reliably and cost-effectively into the 21st century.
As part of its overall refurbishment program, Duke completed the installation of Areva’s digital safety-related Reactor Protection System and Engineered Safety Protection System for Oconee’s Unit 1 in June 2011. Duke subsequently completed installation of this technology in Unit 3 in 2012 and will complete installation in Unit 2 in 2013.
A Successful Installation
As an integral part of overall plant operations, upgrading to a digital I&C system is a significant undertaking for plant modernization projects, as well as new plant construction. As the first digital I&C project to receive approval from the NRC, the project at Oconee focused on the changing regulatory environment. Introducing a proven, global technology as a conceptual design in the U.S. market and translating it in clear requirements for a regulatory arena presented challenges. Although nonsafety-related digital control and monitoring systems have been installed in nuclear plants for years, the NRC needed to develop new guidance for safety-related digital systems because existing regulations did not address the new features and capabilities.
As with any first-of-a-kind nuclear plant enhancement, the Oconee project team noted the importance of working with the NRC immediately. It was critical for the project team to understand the NRC’s expectations for its standard review plan and interim guidance. Constant, open communication throughout the licensing process from conceptual design to functional acceptance built the foundation of a successful transition.
Protecting a Digital System
During the licensing and commissioning of the digital I&C system, Duke and Areva conducted thorough reviews of cybersecurity issues. An upgraded digital system provides physical and software barriers, defense-in-depth and diversity methods to provide cybersecurity for these digital assets. Procedures at Oconee control access to these critical digital assets and protect from malicious attacks from outsiders and insiders.
The NRC review confirmed the digital I&C system meets federal cybersecurity requirements to isolate the system from threats such as hackers and viruses. The safety-related systems are isolated from the Internet to prevent such threats.
Offering Valuable Benefits
While helping the nuclear industry address obsolescence, upgrading to a digital I&C system offers other significant benefits, including improved plant safety and reliability. These systems improve operations with system self-diagnostics, automated testing, online maintenance, enhanced redundancy and more readily available information.
The digital I&C system has improved overall plant reliability and performance with its advanced operator interfaces and controls and maintenance interfaces. In addition, the system provides enhanced levels of system redundancy, modern manufacturing quality that meets the latest standards, and self-monitoring to ensure system health and proper operation.
The Reactor Protection System monitors inputs related to reactor core operation, such as coolant pressure, temperature, power and flow, while the Engineered Safety Protection System monitors other inputs, such as coolant and containment pressure, and actuates engineering safety features, such as cooling water injection and containment isolation and cooling. Combined, these new systems improve safety by ensuring that reliable trips are initiated when needed and spurious plant trips are avoided.
Making Day-to-day Operations More Efficient
As a result of implementing an advanced, digital I&C system, tasks such as conducting surveillances are performed automatically by the system, which reduces the need for the plant operator to perform this function in the control room.
Maintenance activities that previously took three to four hours per channel for the nuclear instrumentation now take only 30 minutes per channel. As a result, system engineers have more information available to them. Further, the system enhancements eliminated quarterly functional testing and daily channel checks, which reduced the number of labor hours needed for the online testing.
The Reactor Protection and Engineered Safety Protection Systems operate mainly in the background and activate only when events are evolving too quickly for plant operators to respond.
Planning for an Upgrade to Digital Technology
As nuclear plants age and utilities need to upgrade to digital technology to ensure continued safe operation, utilities need to allow adequate planning time and consider industry experience in designing, licensing and installing digital equipment. Defining detailed functional requirements at the beginning of a project helps ensure project success and avoid rework and delays.
The key to success in a digital I&C upgrade project such as the one at Oconee is to have a clear vision of what is needed. Engage all station stakeholders early and often in developing requirement specifications. Mock-ups and simulations help ensure all functions to be performed by the new system are properly identified and defined in the equipment specification.
In addition, operator training is critical to project upgrade success.
A duplicate training system was installed to train operators on the new system and allow them to enhance its design prior to production. By having the duplicate system available early in the project, testing could be conducted simultaneously with design and implementation, which expedited the functional acceptance of the system.
As new ideas surface after the initial phase of developing the new system requirements, project teams should ensure these new ideas are properly reviewed and approved. Seemingly simple changes can require revisions to many documents, which could increase costs much.
Ensuring Plant Reliability
As the NRC continues to approve extensions of nuclear plants’ operating licenses, it is becoming increasingly important for the industry to embrace the transition to digital technology. Proven digital protection systems are in place at nuclear plants around the world to increase capability, longevity, safety and reliability. The newer, more modern digital technology helps ensure the reliability of key plant safety functions today and for years.
Carl Fisher is vice president of hardware modernizations and nuclear parts center for AREVA Reactors and Services.
Michael E. Bailey is reactor and electrical systems engineering manager at Oconee Nuclear Station.