In This Issue
Fall Issue of The Bridge on Nuclear Energy Revisited
September 15, 2020 Volume 50 Issue 3
The desire to reduce the carbon intensity of human activities and strengthen the resilience of infrastructure key to economic prosperity and geopolitical stability shines a new spotlight on the value and challenges of nuclear energy.

Sustaining the Value of the US Nuclear Power Fleet

Monday, September 21, 2020

Author: Bruce P. Hallbert and Kenneth Thomas

Sustaining the value of the US nuclear power fleet can be achieved through cost-effective, reliable operation to deliver diversity, robustness, environmental benefits, and national leadership. Many owners plan to operate nuclear plants for 60 years and more to capture this value. Doing so requires ensuring the integrity of key materials and the economic viability of these plants in current and future energy markets.


The fleet of US commercial nuclear power reactors has 96 operating plants (NRC 2019), many of them in their first period of extended operation (i.e., 40 years or more). Two sites have received approval for license renewal (from 60 to 80 years); another 6 plants have applied and 13 have announced similar intentions.

The fleet’s sustained operation can be achieved through continued reliable operation; effective maintenance and monitoring of vital structures, ­systems, and components (SSCs); and viable economics in current and future energy markets.

The Value of Continued Operations

Sustained operation of the US nuclear fleet provides needed and irreplaceable value through fuel source diversity, energy reliability, environmental sustainability, synergy with renewable forms of electricity, ­economic value, and vital national capabilities and leadership with nuclear power technologies.

In 2019 US nuclear reactors achieved a capacity factor of 93 percent, delivering over 800 million MWh to US residential consumers and industry—and avoiding 476 million metric tons of carbon emissions compared to fossil energy sources.[1] Nuclear energy supplies nearly 20 percent of US baseload electricity and 55 percent of US non-carbon-emitting electricity,[2] and can reliably supply energy when intermittent renewable sources (e.g., wind, solar) cannot. This is especially important in regions where intermittent sources are expected to increase their contributions to domestic electricity capacity (EIA 2019).

Communities surrounding nuclear plants benefit greatly. The Nuclear Energy Institute (NEI 2015) found that a typical nuclear plant generates approximately $470 million in sales of goods and services and almost $40 million in direct high-paying jobs annually. Tax revenue, reported to be about $67 million per site, supports local public schools, roads, and other infrastructure (NEI 2015). The Brattle Group estimates that the commercial nuclear industry accounts for 475,000 jobs and contributes $60 billion annually to US gross domestic product (Berkman and Murphy 2015).

Conversely, reports show that premature closures of commercial nuclear plants depress economic activity in the surrounding area (Stewart et al. 2014) and lead to higher electricity prices (Potomac Economics 2015), greater carbon emissions (Abel 2016; Content 2014), and substantial reductions in municipal operating budgets that depend on tax revenues from an operating nuclear plant (NEI 2017).

Keys to Sustainability

Sustaining the value and contribution of nuclear power to the nation’s energy mix involves addressing a number of challenges. Since more than half of existing plants are in their first period of extended operation it is vital to ensure that they can continue to perform needed functions. With several utilities planning to operate their nuclear plants beyond 60 years, additional information is needed to ensure the dependability of existing materials to function over longer service periods (Busby et al. 2014).

The nuclear power industry also faces economic challenges to continued operation. The move in many states to deregulated electricity markets (Warwick 2000, rev 2002) and the recent availability of inexpensive natural gas and influx of subsidized renewable energy (i.e., wind and solar) mean that some nuclear plants are operating in areas where the market price of electricity is below their production costs. The actual and announced shuttering of several operating nuclear plants has ensued, with more at risk. Improved plant efficiencies and reduced operating costs are imperative to sustain the existing fleet of light water reactors (LWRs).

Solutions for Continued Safe and Economic Operations

In 2007 the US Department of Energy (DOE), with the Electric Power Research Institute (EPRI) and other industry stakeholders, initiated planning that led to creation of the Light Water Reactor Sustainability (LWRS) Program (INL 2007). Since then, the DOE, EPRI, and US Nuclear Regulatory Commission (NRC), through memoranda of understanding, have been collaborating with nuclear industry stakeholders to support the continued safe and economic operation of US nuclear plants. The LWRS Program serves as the DOE Office of Nuclear Energy’s lead in these collaborative efforts and conducts research and development on materials, plant modernization, flexible plant operation and generation, risk-informed systems analysis, and physical security.

In the following sections we consider the need for dependable materials, cost-effective operation (including through modernization, diversified revenue, and risk-informed approaches), and physical security.

Dependable Materials

Research by the LWRS Program aims to enhance understanding and prediction of long-term environmental degradation and behavior of materials in nuclear power plants and to provide methods to assess and monitor SSC performance. Materials research focuses on reactor metals, concrete, cables, and potential mitigation strategies (i.e., repair and replacement). Collectively, the following research activities are developing techniques and methods to address damage that occurs during the extended service life of reactor metals and other ­materials, and to offer candidate replacement materials when such repairs are needed.


Aging of reactor pressure vessel (RPV) steels results in radiation-induced hardening, manifested as increases in the ductile-brittle fracture temperature (DT) for the remainder of a plant’s service life. A primary objective of the LWRS Program’s research is to develop a robust physical model to accurately predict transition temperatures at high fluence (at least 1020 neutrons/cm2, with energy E > 1 MeV) for vessel-relevant fluxes pertinent to extended plant operations.

Understanding the role of alloy composition, flux, and total fluence is important because current regulatory models (e.g., both the Eason-Odette-Nanstad-Yamamoto model and the new American Society for Testing and Materials E900 Standard) may underpredict hardening in steels at high fluence levels.

In 2018 the LWRS Program completed development of an updated model for DT at high fluence. The improved predictive models of RPV steel embrittlement were used to develop a multiphysics model, named ­Grizzly (Spencer et al. 2018), a simulation tool that accounts for aging effects on material properties and the overall thermomechanical response of the RPV to loading.


The properties of concrete in a radiation field change over time because of ongoing changes in the microstructure driven by radiation conditions (spectra, flux, fluence), temperature, moisture content, and loading conditions. Research is being conducted to improve understanding of chemistry and radiation-induced degradation mechanisms and the levels of irradiation that the concrete structures may experience when the reactor life exceeds 60 years.

The Microstructure-Oriented Scientific Analysis of Irradiated Concrete (MOSAIC) software tool was developed to assess the susceptibility of plant-specific concrete to radiation-induced structural degradation (Giorla 2017). The MOSAIC tool incorporates the response of concrete and its components to temperature, moisture, constraint, radiation, creep, and composition variations.

Efforts are continuing to develop a method for use in establishing risk-informed guidelines to evaluate the performance of aging safety-related concrete SSCs.


Cable-aging research aims to increase understanding of the mechanisms that result in changes to cable performance and to enable more accurate assessments of these changes for use in managing in-service materials during extended operations. Investigators seek to characterize the interaction of environmental and material properties on the performance of cables and to develop improved nondestructive examination (NDE) techniques of in situ cable materials.

The goals of this research are to produce a predictive model of cable aging and degradation and to deliver NDE methods that can be qualified to ensure cable integrity through industry cable-aging management programs.

Mitigation Strategies

Potential mitigation techniques include weld repair, postirradiation annealing, water-chemistry modifications, and replacement options for the use of new materials with reduced susceptibility to various modes of degradation.

Cost-Effective Operation

A number of nuclear plants are undertaking efforts to improve their long-term competitive positions to address the challenges of operating in a price point–dominated market. These include initiatives to reduce operating costs through greater efficiencies in plant operation and to diversify and increase sources of revenue. The LWRS Program and others are working with owner-operators to spearhead efforts that will be viable for others in the industry.

Creating Efficiencies Through Modernization

Since most plants were constructed years ago, their instrumentation and human-machine interfaces rely on analog technologies, such as those shown in figure 1. Replacing them is broadly perceived as involving significant technical and regulatory uncertainty, which may translate into project delays and substantially higher costs for these refurbishments.

LWRS Program research addresses critical gaps in technology development and deployment to reduce risks and costs and support deployment of new digital instrumentation and control technologies. ­Rather than merely replacing aging technologies with more modern technologies that perform exactly the same functions, digital approaches—and associated strategies, technical bases, and cost justifications—are being developed to transition to more technology-centric (i.e., automated) and less labor-centric (i.e., manual) plant operation. These modernizations both enable significant operating cost reductions and improve human-system and overall plant performance.

Figure 1 

Plants are participating in R&D activities in which new technologies are developed and validated for use (figure 1). Vendors, suppliers, and owner-operators are similarly contributing to efforts to reduce costs through automated system performance monitoring. The Technology-Enabled Risk-Informed Maintenance Strategy (TERMS) draws on their input to integrate advances in online automated asset monitoring, data analysis techniques, and risk assessment methods to reduce maintenance costs (Agarwal 2018). TERMS is also developing technology to enhance the reliability of plant systems, lower maintenance costs, reduce downtime, and increase power generation—and revenue—by increasing plant availability.

Diversifying Revenue

Opportunities may exist in the near future for nuclear power plants to revolutionize their operating paradigm and diversify their revenue by dispatching either thermal or electrical energy to produce nonelectrical products. The LWRS Program is collaborating with plants to explore the technical feasibility and economic viability of such a game-changing development by investigating and evaluating technologies and markets near specific nuclear plants that could directly supply energy to industrial users.

The cost of producing high-pressure steam for industrial use is estimated to be $4.00–$5.25 per 1000 lb of steam ($5.25–$11.00 per 1000 kg of steam), depending on plant type and operating costs as shown in figure 2. This is 15–45 percent lower than the cost of producing steam using a natural gas package boiler before any credits for CO2 emissions reduction are applied.

Figure 2

Because demand is increasing for low-carbon-emission products, hydrogen is being considered because it is a clean fuel, is used in a variety of materials manufacturing and chemicals production, and can be used for trucks and cars that run on hydrogen-powered fuel cells.

A design and evaluation study that coupled either a low-temperature electrolysis plant or a high-­temperature steam electrolysis plant to a nuclear plant identified two business opportunities for LWR-supported electrolysis: (1) smaller plants would produce hydrogen for fuel-cell vehicle filling stations where low-temperature ­electrolysis plants can be competitive with natural gas steam reforming plants; (2) at industrial plants that use a large amount of hydrogen, steam electrolysis was shown to be competitive with large-scale natural gas steam reforming plants (Boardman et al. 2019).

Recent DOE awards demonstrate movement toward a future in which nuclear plants devote more of their operations to produce hydrogen or other products. These projects emphasize low-temperature electrolysis using polymer electrolyte membrane cells, but options are being considered for other hydrogen production systems.

The LWRS Program also completed an independent evaluation of the production of fertilizers, steel, and synthetic fuels using hydrogen produced by LWRs and CO2 from ethanol plants.

Using Risk-Informed Approaches to Reduce Costs

Since the transition in the late 1980s to greater use of risk-informed approaches to safety assessment and management, there has been a gradual openness to use them in many aspects of nuclear plant operation and maintenance. This shift may support greater flexibility in managing plant operations within established safety margins.

LWRS collaborations with owner-operators, EPRI, and others are investigating improvements in resilience for nuclear power plants, cost and risk categorization applications, and margin recovery and operating cost reduction. Each involves the development of advanced analytical methods and tools, tested in collaborative projects to ensure that the results can be used by other owner-operators.

One project is exploring how advanced technologies may enhance the resilience of LWRs (Ma et al. 2019). The study is considering accident-tolerant fuel, industry investments in diverse and flexible coping strategies implemented as a result of post-Fukushima enhancements, and passive cooling technologies for improved decay heat removal. The performance of these measures is being analyzed by new tools that integrate probabilistic risk assessment and thermal hydraulic analysis to demonstrate benefits for plant operation and safety. Collectively these may improve economics by offering the potential to recategorize some safety-related SSCs as nonsafety and reduce operating costs.

Physical Security

Implementation of enhanced physical security requirements to protect against an attack at US nuclear power plants after September 11, 2001, resulted in larger onsite physical security forces and costs that are comparatively high relative to other operational costs. LWRS Program research to improve efficiencies and optimize costs to ensure physical security at commercial plants includes risk-informed approaches to physical security.

Current industry practices in plant physical security assessments use “target sets” and security modeling tools to analyze the timelines and effectiveness of a given security posture (i.e., physical security elements and the typical means for their use) against a defined adversary. The integration of analyses of physical protection with plant system responses enables modeling of the timeline from the start of an attack to radiological and other consequences of concern. The LWRS Program is studying ways to achieve this integration to improve the technical basis for stakeholders’ decisions so that they both optimize physical security and realize operation and maintenance cost benefits.


The LWRS Program and collaborating organizations conduct research, development, and technology demonstrations to achieve progress in key areas needed for the continued operation of nuclear power plants. These activities and their accomplishments directly support the mission of the LWRS Program on behalf of the DOE Office of Nuclear Energy: to develop science-based methods and tools for the reliable and economical long-term operation of the nation’s high-performing fleet of commercial nuclear power plants.

Nuclear power has reliably and safely supplied approximately 20 percent of electrical generation in the United States over the past two decades. It remains the country’s single largest producer of non-greenhouse-gas-emitting electricity, supports the resilience of the electricity grid at a time of increasing growth in intermittent energy sources, and is transitioning to generate other needed nonelectric products. It provides value to the national economy and local communities through numerous direct benefits.

Sustaining the operation and value of the existing US nuclear fleet is a national imperative requiring the efforts of a broad cross section of stakeholders such as the DOE, NRC, EPRI, owner-operators, vendors, and suppliers to the commercial nuclear power industry.


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[1]  Nuclear Energy Institute, US Nuclear Generating Statistics, 1971–2019, generati ng-statistics

[2]  US Energy Information Administration, What is US electricity generation by energy source?,

About the Author:Bruce Hallbert is national technical director of the DOE-sponsored Light Water Reactor Sustainability Program and Kenneth Thomas is a senior research staff member, both at Idaho National Laboratory.