Maximizing nuclear power plant performance via mega-uprates and subsequent license renewal

Abstract

The goal of this thesis is 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 and life extensions afforded by advances in the state of the art of nuclear technology. America's commercial nuclear power plants were initially licensed for 40 years. A successful license renewal program is being executed to extend operational lifetimes to 60 years, which has supported the installation of more than 7000 MWe of generating capacity via power uprates. Yet improvements in instrumentation, analytical methods, operational strategies, materials, components, systems, and fuels enable plant operators to consider simultaneously extending plant lifetimes to 80 years, and further increasing plant generating capacity. Extending plant lifetimes requires certain plant structures, systems, and components (SSC) to be refurbished or replaced. Performing these changes with other plant upgrades required to provide a 25% or more power increase - a mega-uprate - can lead to improved returns and savings for investors, rate payers, and operators over the remainder of the plant's lifetime provided confidence in the plant's ability to operate through the remainder of the extended life can be demonstrated. A methodology was developed in this thesis to enable the analysis of 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 an 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 quantifies and propagates 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 introduced. 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 by increasing safety margins which reduces the need upgrade or replace plant systems. 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) technological readiness of high-performance plant components and systems; 3) experience with large power uprates; 4) cost uncertainties due to market conditions and technology risk; 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 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.