Instrumentation & Controls, Nuclear, Reactors

Digital Safety

Issue 4 and Volume 114.

By Nancy Spring, Senior Editor

When the Nuclear Regulatory Commission approved a license amendment request to replace analog controls with a digital system at one of the country’s nuclear stations, the decision was hailed as a regulatory milestone by some.

Duke Energy Carolinas received NRC staff approval in late January to replace the 1970s-era analog, solid-state control for Oconee Nuclear Station’s reactor protection system (RPS) and engineered safeguard protection system (ESPS) with digital computer-based equipment. The $250 million upgrade is the first to receive NRC approval for an integrated digital RPS and ESPS instrumentation and control (I&C) system at a nuclear power plant in the U.S.

To say the NRC has been cautious in its attitude toward digital technology at the country’s nuclear power plants would be an understatement. It took a long time to reach the Oconee “milestone.”


  • Duke Energy Carolina’s application—the first the NRC received for digital control upgrades—has been in the works since January 2008 and the company has provided supplemental supporting information numerous times in the past two years. Duke actually submitted an application in 2006 that it later withdrew. The project first won internal approval at Duke in 2003.
  • The technology Duke chose, Areva’s Teleperm XS system, received generic approval from the NRC for use in all safety applications, including protection systems, in May 2000.
  • Areva has engineered, designed and implemented the I&C systems for all nuclear power plants currently in operation in Germany. Worldwide, 55 Teleperm XS units have been implemented or ordered since the first installation 10 years ago and Teleperm XX is included in the design for new nuclear plants. Still, NRC staff traveled to Germany to Teleperm XS production facilities to observe testing of the actual system.
  • The NRC previously approved single safety-related digital control upgrades, such as Wolf Creek nuclear power plant’s main steam and feedwater isolation system in 2009. But in February 2009, then-NRC commissioner Peter Lyons said the commission saw relatively little digital technology in the control room and none in the safety systems.


The rest of the nuclear world has been using digital controls for some time. In Japan, the first fully digital I&C system was integrated into the Kashiwazaki-Kariwa Unit 6 advanced boiling water reactor in 1996, followed by Kashiwazaki-Kariwa Unit 7. France, the U.K., Korea, Sweden and other countries have also implemented digital I&C systems in their nuclear power plants.

The NRC acknowledges on its website that digital I&C systems have been used in many applications in U.S. nuclear power plants, including feedwater control systems, recirculation control systems, demineralizer control systems, main turbine controls and other nonsafety systems. Oconee is different from all other U.S. installations because of the large scope of systems replaced. (A few safety applications have been installed, but they were not subject to NRC review.)

Clearly, NRC approval for safety-related digital systems wasn’t given lightly.

Robert Austin, program manager for instrumentation and control at the Electric Power Research Institute (EPRI), said the substantial review effort and time required to address NRC staff concerns and ultimately obtain NRC staff approval of Duke Energy Carolina’s application is an area requiring further improvement.

EPRI’s technical opinion is that the enabling research to demonstrate that the design, testing, installation and operation of safety-related digital protection systems can provide safe and reliable plant operation is complete and has been for some time.

“We are working with the Nuclear Energy Institute to more fully understand the NRC staff concerns with respect to the use of this technology and hopefully enable a more efficient and predictable licensing process for the use of digital technology in safety-related nuclear power plant applications,” said Austin.

If successful, he said, we can anticipate more widespread application of digital I&C technology by licensees.

Things might start to move quickly—relatively speaking, of course—as utilities decide to replace older analog systems. They have a choice of technologies, too. Besides Areva’s Teleperm system, the NRC has previously approved Westinghouse’s Common Qualified Platform (Common Q) and Invensys’ Triconex for safety-related applications, clearing the way for operating nuclear power plants to consider using them in retrofitting digital I&C systems.

The installation process at Oconee will begin in 2011. The new digital controls will be installed on the plant’s three operating units during scheduled refueling outages through 2013.

The rigorous analysis the NRC applied to this issue is characteristic and supports the reputation the U.S. nuclear industry has built for safety, reliability and efficiency. Now we can enter the digital age, albeit a little late.


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