Thursday, November 16, 2023

Graceful Aging

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EPRI research and pilot programs demonstrate how risk insights can enhance nuclear aging management programs.

Whether they acknowledge it or not, every human being is in the risk assessment business. For example, you perform a risk assessment every time you cross a street, decide to go on a trip, or consider a big life decision. Opting for a lightly trafficked route to school or work over a more crowded but quicker commute is a common daily dilemma. Another typical risk assessment is taking a vehicle for a routine tune-up or to diagnose a problem.

“There’s a ranking that goes on,” said Fernando Ferrante, who leads the Risk and Safety Management Program at EPRI. “You’re not going to let your brakes wear out. You’re not going to let your tire treads go bald. There are other things that you’re not going to ignore, like a broken mirror or your oil level, that could cause problems if they go unaddressed for a long time. But risk insights help prioritize where mechanics should focus their time and attention first.”

Risk assessments are part of everyone’s everyday life. When it comes to complex systems such as the electrical grid, sending astronauts to Mars, or operating commercial nuclear reactors, this work is done by risk analysts. They provide insights that can help make informed decisions when faced with competing priorities, costs and benefits, and uncertainties.

Long Operating Lives Elevates the Importance of Aging Management

Since 2019, EPRI has collaborated with the Nuclear Energy Institute (NEI) and member utilities Ameren and Constellation Energy to research and pilot the use of risk insights to improve aging management programs (AMPs) at nuclear power plants. One of the results of the ongoing work is the EPRI report, Leveraging Risk Insights for Aging Management Program Implementation.

As nuclear power plants operate longer, the role of AMPs in ensuring their safety and performance is elevated. Historically, AMPs have been guided by a deterministic philosophy, which was the common approach when most plants were built. A deterministic AMP is a prescriptive set of requirements directing how maintenance on plant systems, structures, and components (SSCs) is performed.

The deterministic philosophy worked well, particularly when large nuclear power plants had relatively little operating experience. However, because most plants have operated for decades, they have accumulated insights into how operations and design impact SSCs.

Those insights consider the frequency and impact of challenges to plant safety and performance and can complement deterministic approaches. For example, risk insights based on operational data and modeling give plant operators more flexibility to prioritize maintenance and other efforts on reactor components, systems, and operator actions based on their impact on safety and performance. Instead of being prescriptive, approaches informed by risk insights provide multiple approaches to achieving performance and safety objectives.

The fact that so many reactors have been operating for decades provides an opportunity to take advantage of risk insights. “It’s important to realize that when the first aging management programs were put together, there was limited information available about how many of these components may age,” said EPRI principal technical leader Emma Wong. “With limited information, it is reasonable to be more prescriptive, which led to more deterministic aging management programs.”

Decades of operating experiences and research have changed that, ushering in the possibility to translate that experience into risk insights that can be incorporated into AMPs. Indeed, Ferrante sees the work EPRI and its partners are pursuing not as a criticism of the deterministic AMPs that have worked so well but as opportunities to bolster them with research and real-world experience.

“We have all this engineering knowledge in terms of challenging areas for aging mechanisms in nuclear power plants,” Ferrante said. “We’re gathering that information and making it more risk prioritization oriented. You can use insights to shift your program from looking at everything the same way to asking what it will cost the plant if one component fails. And some components and structures are more important than others.”

The importance of integrating risk insights into AMPs is also underscored by the resource constraints nuclear power plant operators face today. While there is increasing interest in the potential for sensors and other technologies to monitor the aging of components in real-time, that capability has not yet been widely implemented or may not even exist for commercial use. “If you look at power plants today, they have fewer people and fewer resources but need to be able to manage more,” Wong said. “So, you need to be smarter about where you target your resources and time.”

A Framework to Apply Risk Insights

Risk insights have the potential to improve the efficiency and effectiveness of AMPs. However, applying insights consistently can be challenging. This is particularly true because different nuclear power plants’ SSCs vary considerably, which is why one of the most important outcomes of the research that went into the Leveraging Risk Insights for Aging Management Program Implementation report was the development of a framework to guide the application of risk insights in AMPs.

“The scenario at each plant will always be different, but the framework provides a guideline to follow,” Wong said. “You can move down the flow chart approach to see if this works for you. It won’t work for everyone because not everyone will have enough information to use the framework. But the framework provides a tool that lets you gather information to see if it’s possible to use risk insights and benefit from them.”

For example, the framework involves collecting plant-specific information about SSCs and any existing knowledge about aging mechanisms and risk insights. The framework also leans heavily on operational lessons learned at the plant. This can result in a better understanding of the likelihood that there will be an SSC failure due to an aging effect and the potential consequences of a failure. All this information can then be used to inform AMP decisions and strategies, including the performance of maintenance, equipment replacement, and inspections.

There are several unique features of the framework. One is that it is focused on both safety and plant performance. This is a paradigm shift. “When you look at aging management for a license renewal, it’s all based on safety,” said Wong. “They don’t look at whether your plant will run optimally. We’re looking at the enterprise risk management of the whole system. Safety is paramount, but operational performance is also up there.”

Another unique aspect of the framework is that it is built to continuously incorporate new risk insights that are developed because of ongoing operational experience and research. Indeed, the framework acknowledges that AMPs should include a constantly refreshed feedback loop that integrates an improved understanding of how SSCs age and what can be done to mitigate the risks of aging.

Applying Risk Insights in the Real World

Developing a framework that can be applied at any nuclear power plant was an important first step in seizing the benefits of risk insights. But it was also essential to apply it in real-world scenarios. This was done in a pilot project at Constellation Energy’s Limerick Generating Station in Pennsylvania, where the framework was applied to the utility’s selective leaching AMP. It was also incorporated into the AMP for medium-voltage cables at Ameren’s Callaway Energy Center in Missouri.

The results were encouraging. At a high level, researchers estimate that implementation of the framework could save Constellation $2 million and Ameren $600,000 over 20 years of extended plant operations.

At Constellation’s Limerick Generating Station, applying the framework resulted in a more holistic asset maintenance and management approach. For example, the framework utilizes information about component degradation and existing risk tools to create a technical basis to modify the testing and inspection recommendations that plant owners committed to secure a 20-year license extension.

The pilots utilized a component-specific approach versus the more standard general risk analysis that would be used in a deterministic AMP. This resulted in a component-specific analysis of degradation risk that built a technical justification for AMP action.

For example, at Limerick, the utility recognized the need to integrate components not traditionally associated with safety into the AMP. “They looked at everything to see what would degrade and impact plant operation, not just safety,” said Drew Mantey, an EPRI senior principal project manager. “The framework led them to look at ways to better their asset and aging management.”

At Ameren’s Callaway Energy Center, the framework helped build a justification for testing cables less frequently than what would be dictated by a deterministic AMP. “We did this pilot to show that there was potentially a rationale for extending testing frequencies that are set at six years to 10 years,” Mantey said.

As helpful as the pilots were in validating the relevance and value of the framework in the two plants, they also helped confirm its versatility. That’s because one pilot applied selective leaching risk insights to the framework while the other used insights specific to medium-voltage cables. “It allowed us to look at different risk tools, which was good because it shows how the framework can be applied with different inputs,” Mantey said.

Now that the potential of risk insights to improve AMPs has been demonstrated, lessons from the pilot projects and EPRI’s research are being incorporated into a how-to guide for other utilities to use. The work is being led by EPRI and the NEI’s License Renewal Task Force. Additional pilot projects are also under consideration.

One of the most important lessons from the pilots was about the importance of communication. “Sometimes silos can arise where engineers and risk analysts may not fully understand the benefits of using risk insights,” Wong said. “Sometimes the experts involved may feel like they don’t speak the same language. But we saw in both pilots that one way to overcome this hurdle is to successfully communicate by sharing the information transparently and clearly with each other.”

EPRI Technical Experts:

Emma Wong, Fernando Ferrante, Drew Mantey
For more information, contact