US operator urges faster changes to I&C rules holding back digitization
The Nuclear Regulatory Commission (NRC) must accelerate rule changes on digitizing safety control systems and update software failure assumptions so plant operators can implement lower-cost digital systems, John Connelly, Engineering Manager of Capital Projects at Exelon Nuclear, told Nuclear Energy Insider.
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U.S. nuclear utilities have called for the modification of regulations on digital safety-related instrumentation and control (I&C) systems so that they can cut costs and improve competitiveness amid low power prices.
Nuclear generation costs have risen by 28% over the last 12 years, according to the Nuclear Energy Institute (NEI), and this is impacting the competitiveness of nuclear power in a market which is being increasingly penetrated by natural gas and renewable energy.
Operators must embrace digitization of nuclear work practices if they are to cut operating costs by 30% by 2018, a target set by the NEI in its 2015 Delivering the Nuclear Promise (DNP) initiative.
Switching over to digital technology has a direct impact on unplanned outage times, Connelly told Nuclear Energy Insider.
“Historical analysis showed that moving analog systems into the digital domain resulted in a 95% reduction in forced loss rate,” he said.
US nuclear plant capacity factors
Source: Nuclear Energy Institute (NEI).
Some 39% of nuclear firms see a lack U.S. regulatory progress as the biggest challenge to implementing digital technologies and processes, according to a recent survey by Nuclear Energy Insider.
Current regulations create unnecessary costs and regulatory uncertainty for operators looking to implement digital technology to improve market competitiveness, Connelly said.
Operators are concerned about lengthy regulatory processes given the current tough power market conditions. Between 2011 and 2013 Duke Energy converted the reactor control and protection systems of its three-reactor Oconee Nuclear Station in South Carolina to digital systems but the NRC review process took five years, according to the NEI.
Exelon began upgrading feedwater systems at Dresden, LaSalle, Limerick and Quad Cities non-safety systems in the 1990s. The upgrades were regarded as non-safety systems and therefore required limited regulatory approval according to regulation 10 CFR 50.59, which guides how licensees can make changes to their facilities and procedures. The regulatory process for digitization projects is far more onerous but changes are on the way.
NRC action
The Nuclear Regulatory Commission (NRC) has prioritized new modified regulation on Digital Instrumentation & Control (DI&C) and safety-related systems and in May the regulator published an Integrated Action Plan (IAP).
Constructive dialogue and coordinated activities with operators has allowed the regulator to identify the most important regulatory changes, according to Connelly, who serves as Chairman of NEI’s Technical and Regulatory Issues Task Force.
The regulator has focused on key Modernization Plans (MP) to address near-term, critical digital I&C needs, NRC staff told Nuclear Energy Insider.
The table below shows priority MPs in the IAP are to be completed in 2016-17.
Priority projects in the NRC's Integrated Action Plan (IAP)
Data source: Nuclear Regulatory Commission (NRC).
Some strategies include a holistic review of more performance-based, technology-neutral approaches, NRC staff said, as well as further integration of multiple guidance documents.
NRC also plans to streamline license review processes based on lessons learned from recent licensing experience and ongoing research. The regulator will also use new analytical approaches to address the safety of evolving digital systems, NRC staff said.
Failure rates
Issues relating to the application of rules on Software Common-Cause Failures (SCCF) and the 10 CFR 50.59 regulations are the most urgent, as they represent the greatest regulatory barriers to integrating digital software and hardware into a plant’s safety-related systems, Connelly said.
Digitizing a safety system generally cannot be done under 10 CFR 50.59 because the criteria of BTP 7-19 assumes a SCCF probability of 1 (SCCF will occur), unless the licensee can unequivocally demonstrate a SCCF will not occur by either demonstrating internal system ‘diversity’ or designing a sufficiently simple system, he said. Diversity reduces SCCFs by designing redundancy that still allows the digital system to function.
The current regulatory assumptions create a significant barrier to implementing DI&C and are inconsistent with operators experience and independent research conducted by EPRI, Connelly said. The EPRI report provides practical guidance on addressing a full range of potential SCCFs.
Even the simplest of safety system modernizations are subject to the digital licensing process which is complex, lengthy and introduces financial risk, Connelly said. A Licence Amendment Request does not receive approval until completion of the Factory Acceptance Test, which occurs late in the project life cycle after significant funds have been spent, he said.
“This is completely inconsistent with the processes used for new reactors – Part 52 - and introduces financial risk that most licensees simply cannot tolerate,” Connelly noted.
The NRC’s IAP recognises the process must become more streamlined, informed of current best practices and scalable.
NRC staff said there was no proposal to change the underlying 10 CFR 50.59, but industry has proposed a revision to the guidance which clarifies the types of digital system changes that require a license amendment.
The NRC is also reviewing current regulation on the scope of common cause failures and will propose any appropriate updates that enable nuclear firms to design more effective systems, NRC staff said.
By Karen Thomas