1. Prelude

The country which first develops the breeder reactor will have a great competitive advantage in atomic energy. Those words spoken by Enrico Fermi in 1945 may appear dated and no longer meaningful in 2023. The many difficulties experienced by the promoters of nuclear power with vigorous coordinated opposition from environmental groups, excesses and misplaced judgment on the part of regulators, horrible decisions by politicians and policy makers, selective blunders by utility industry management, poor performance by certain architect engineers/constructors, failure to implement an acceptable solution to waste disposal, and three accidents worldwide at nuclear power plants in the intervening years have definitely taken the bloom off the rose of what was once a promising technology. Today, it would appear that the future of electric energy production rests with renewables, particularly with wind turbines and solar plants while filling in gaps with combined cycle gas plants, and the continuing use of coal plants and nuclear plants that were constructed in the 1960s and 1970s until the total fleet of renewable power plants is put in place. This forecast may or may not reflect the reality of the renewables, depending on whether acceptable and economic energy storage can be developed and whether a reliable electricity supply can be maintained through sustained periods of darkness and calm. In 2020, renewables accounted for 20% of U.S. generation and 12% of U.S. consumption. The disparity between generation and consumption is a reflection on the availability of the renewables. If hydro and geothermal are removed from the picture, the difference probably becomes greater. Rather than moving toward complete reliance on renewables, it is more likely that the U.S. energy supply will continue to be diversified in the interest of both system reliability and economics.

In 2004, natural gas was extracted for the first time from the Marcellus shale, opening the floodgates of supply, particularly to electric utility companies deploying combined cycle plants. The combined cycle is somewhat unique among power generating options in that it achieves thermodynamic efficiencies approaching 60% and contributes up to 70% less CO2 to the atmosphere than an equivalently sized coal plant. At about $650/KWe capital cost, installed in very manageable 400 MWe increments, and with fuel cycle costs as low as 3¢/KW-hr., what’s not to like? The electric power industry currently represents 38% of the national consumption of about 31 trillion ft3 of natural gas per year. The percentage has been increasing steadily over the past ten years. The proven U.S. reserves are about 350 trillion ft3. So each time an electric company puts a combined cycle plant in service that is designed to operate for 40 years, it is betting that the proven reserves will increase by a factor of about 4 from their current values over the life of the plant. That doesn’t count the new combined cycle plants yet to be placed into service, which will deplete reserves faster. There will inevitably be a point in time when U.S. natural gas is in short supply, prices will increase dramatically, and electric utility companies will be compelled to curtail usage. Will those companies have another generating source they can put into service to replace their combined cycle plants? This nightmare has probably visited several electric utility company executives.

It appears likely that electric utility companies will soon be reassessing their positions on nuclear power, if they aren’t already. The use of nuclear power is easily justified by a resource argument and if the plants are properly designed, nuclear power can be justified by its superior economics and reliability. Nuclear power includes not just Light Water Reactors (LWRs) but also Liquid Metal Fast Breeder Reactors (LMFBRs). Fermi’s assertion is most likely as correct today as it was when he made it, as long as his word “develops” is assumed to imply that the development leads to a plant design that is economic and therefore actually deployed.

This monograph is intended to describe the technology and outline the history of LMFBRs for audiences generally familiar with LWRs. Most particularly, it is intended to identify a pathway for deployment of LMFBRs through a conceptual design approach which draws upon collective experience, recent innovation, and re-visitation of approaches previously considered that have been long lying dormant. The paper is also intended to suggest areas where further creative thought could be directed to improve the economic and operational performance of the concept to make it highly competitive with LWRs.

The climax of development of the breeder reactor in the United States was the Clinch River Breeder Reactor Plant (CRBRP) project, which was terminated by congressional action in 1983 primarily on economic grounds. The plant, as designed, was perceived to be too expensive and, unfortunately, it probably was. This raises the question of whether breeder reactors are inherently expensive or was the CRBRP design rendered in a fashion which led to excessive costs. Although engineers perform the actual design work, much of the way design develops is a direct result of the decisions of policy makers and upper level management. Ultimately, it is managers who are called upon to make many of the key decisions. Many decisions were made within a temporal context that was fleeting. At the time of the Clinch River Breeder Reactor Plant (CRBRP) project, the emphasis was reliability, not economics. When there was a choice between conservatism and cost reduction, conservatism always won. Economics was left for “commercialization”, i.e. some plant in the future. There is a more extensive treatment of the historical underpinnings in Appendix 7.

Although conservatism contributed to the plant’s demise, there was considerable useful work performed on the project, much of which continues to be available on the internet. The accessibility of CRBRP Preliminary Safety Analysis Report (PSAR) on the internet results in the availability of detailed CRBRP engineering descriptions and performance data and creates the opportunity to use CRBRP as a point of departure for many of the discussions contained herein. All references to CRBRP data that are drawn from the PSAR are not separately identified by reference in the text. There are some references to CRBRP data that are drawn from sources other than the PSAR and those have been footnoted.

The next LMFBR designed in the U.S. must be designed with the minimization of its capital cost in the forefront and a focus on plant operability that will be appealing to prospective electric utility company owners and operators. It would be desirable for it to make use of the breeding concept that is unique with the LMFBR in a fashion that dramatically improves the plant’s operability when compared to LWRs. The LMFBR has so many inherent advantages over the LWR there is good reason to expect that its capital cost would be equal to, less than, or even significantly less than a comparably sized LWR. Existing designs of LMFBRs fail to meet this objective. If the LMFBR has any possibility of attracting interest from skeptical potential users, it is essential that this objective be attained if deployment is to be accomplished within any reasonable time frame.

The purpose here is to propose a “design approach” which could possibly then be used as a basis for more serious design activity. There needs to be a context for this “design approach”, viz. a plant size and key parameters. Since the Superphénix reactor, completed in France near Lyon, is the largest LMFBR built and operated to date worldwide and comes perhaps the closest to realizing commercial application, its key parameters will be used – 3000 megawatts thermal (MWth) and superheated steam at a pressure of 2400 psig. Certain features of the Superphénix design proved to be a qualified success – notably the steam generators – and those will be carried forward into this proposed plant approach. As will be seen, these boundary conditions will prove to be sufficient for the purposes of this discussion. Meanwhile, there is more ground to be plowed with preliminaries.