Utilities that are considering expanding their generating capacity currently face the prospects of growing renewable standards, aging coal power plants, low but uncertain natural gas prices, proposed EPA carbon regulations, and the long term benefits afforded by energy fuel diversity. Combining these factors with the current economics and regulatory uncertainties associated with building new (large or small) nuclear power plants provides strong incentives for making the most of the operating commercial nuclear fleet in terms of lifetime and output. This lays the foundation for considering very large power uprates of 25% or more, referred to in this thesis as mega-uprates, in conjunction with life extension projects as the most affordable way of expanding nuclear energy generation in the near term. The goal of this thesis was to develop a methodology to evaluate the engineering and economic implications of maximizing performance of the United States’ commercial fleet of nuclear power plants. This methodology addresses aggressive power uprates in conjunction with life extensions afforded by advances in the state of the art of nuclear technology.
The U.S. commercial fleet of 100 operating nuclear reactors has an average age of 34 years. While they age past 40 years, they have established themselves as irreplaceable base load generating assets in America’s electrical infrastructure. All 100 reactors were originally licensed for 40 years; however, the margins engineered into the reactors, improved material management techniques, and better operating strategies have enabled many plants to seek license extensions to 60 years while motivating the industry to study the feasibility of life extension to 80 years and beyond. Life extension activities beyond 60 years are referred to as subsequent license renewal (SLR). Achieving lifetimes beyond 60 years, however, will require some structures, systems, and components (SSC) to be upgraded, replaced and/or overhauled due to either degradation or obsolescence. Additionally, utilities have been employing power uprates since the 1970s to increase the power output of their nuclear plants. Improved instrumentation, analytical methods, operational strategies, materials, components, systems, and fuels have enabled plant operators to increase the output of the operating commercial fleet by more than 7000 MWe since 1977; nearly 1000 MWe are expected to be added in the next five years as well. Many of the plants in the US commercial fleet may be able to accommodate more capacity, but doing so will require substantial upgrades to the plant, which may go beyond the collective uprate experience database.
A methodology was developed in this thesis to analyze the tradeoffs and implications of performing life extensions and mega-uprates together using probabilistic methods to address the uncertainties associated with these large-scale projects. This methodology evaluates the integrated design and capital asset management strategies for nuclear power plants to support decision-making to aggressively uprate and upgrade plants considering multivariate criteria, uncertainties, and multiple time-dependent options. Such a capability has significant value for evaluating future refurbishment and uprate options. This thesis resolves several outstanding design and analysis issues surrounding large-scale projects such as large power uprates, refurbishment, modernization, and subsequent license renewal by: (1) proposing improved statistical treatment of life-limiting component uncertainties; (2) evaluating plant-wide design approaches to realize power uprates greater than 20%; (3) improving the treatment of cost uncertainties, particularly those that arise from technology risk; (4) implementing an integrated decision framework that preserves uncertainties; and (5) enhancing the method’s accuracy and applicability by incorporating material improvements in the state of knowledge of the conditions that affect the plant’s performance. The methodology was implemented via a suite of computer codes referred to as the Integrated Plant Lifetime and Uprate Model – IPLUM – which was used to aid with these analyses.
Results of this thesis suggest that most nuclear power plants are capable of operating up to 80 years without replacing or refurbishing major life-limiting structures provided no major construction defects are present. Most PWRs can achieve 25%-40% uprates without introducing unfeasible design modifications. This thesis suggests that a four-loop Westinghouse plant can realize a 25% power uprate for a mean cost of about $1100/kWe installed. Additionally, new fuel technologies such as accident-tolerant cladding and higher density fuels may reduce the capital costs of these projects.
Combined life extension and mega-uprates may enable plant operators to install more than 20 GWe of nuclear capacity for less than the cost of building equivalent capacity in the form of new large reactors or small modular reactors. Mega-uprates also enable the expansion of carbon-free energy production with potentially superior economics to fossil fuel plants, while also enabling more flexible operational strategies such as load following. Additionally, the risk metrics of adding capacity via life extension and mega-uprates are reduced by upgrading existing plants instead of building new plants. Ultimately, the methods developed and used in this thesis highlight the sensitivities of a combined power uprate and life extension to: 1) plant degradation models and data; 2) technical readiness of high-performance plant components and systems; 3) experience with large power uprates; 4) cost uncertainties; and 5) future energy prices. Perturbations in any of these areas may introduce enough downside risk to negate the decision to implement these design options. Therefore it is essential that plant operators use confirmed plant condition information and identify contingencies specific to their plant, plans, and projects. Furthermore, a principal result of this work is enhanced quantification and characterization of the uncertainties associated with power uprates. The unique features of the net present value and return on investment probability density distributions produced by these analyses provide improved insights into the risks and rewards of large power uprates, which will allow plant owners to better understand and manage these risks