ABSTRACT. It is widely recognized that the developing world is the next area for major energy demand growth, including demand for new and advanced nuclear energy systems. With limited existing industrial and grid infrastructures, there will be an important need for future nuclear energy systems that can provide small or moderate increments of electric power (10-700 MWe) on small or immature grids in developing nations. Most recently, the Global Nuclear Energy Partnership (GNEP) has identified, as one of its key objectives, the development and demonstration of concepts for small and medium sized reactors (SMRs) that can be globally deployed while assuring a high level of proliferation resistance. Lead-cooled systems offer several key advantages in meeting these goals. The small lead-cooled fast reactor concept known as the Small Secure Transportable Autonomous Reactor (SSTAR) reactor has been under ongoing development under the U.S. Generation IV Nuclear Energy Systems Initiative. It a system designed to provide energy security to developing nations while incorporating features to achieve nonproliferation aims, anticipating GNEP objectives. This paper presents the motivation for development of internationally deployable nuclear energy systems as well as a summary of one such system, SSTAR, which is the U.S. Generation IV Lead-cooled Fast Reactor system. INTRODUCTION.It is widely known that the developing world is the next area for major energy demand growth. This is the part of the world where population growth is high and, furthermore, the gap between the current levels of energy availability and the levels needed to sustain economic growth is also great. There is a diversity of different scenarios for supplky of expanded energy resources ranging from large and highlyt concentrated population centers of countries like China and india to remote and isolated communities (which also may be quite large). In addition, in many cases, existing electric grid capacity is limited and not readily able to accept lthe large increments of generating capacity represented by current central station nuclear power plants. Finally, industrial infrastructures are frequently limited and not able to provide the support needed for large central station plant construction, maintenenace and operation.

SUMMARYThe AFCI Options Study has examined the issues with the current use of nuclear power and collected and summarized the extensive results from previous studies for identifying the issues, the root causes, and the evaluation measures to be used for alternative fuel cycle and technology options. The importance of the fuel cycle strategy is discussed, as this directly affects the ability of an alternative fuel cycle to address the issues with nuclear power. The technology options are reviewed for the four major technology areas, fuel type (form and content), reactors and irradiation, processing, and disposal. The general capabilities of each option are summarized with respect to the potential effect that the option could have in addressing the nuclear power issues. The report concludes with a discussion of the decision framework for both nuclear fuel cycle strategies and the associated technology options, recognizing the overall advantages and limitations of various choices.A number of observations can be made at this stage of the AFCI Options Study. It is seen that the only fuel cycle strategy that can have a significant impact, i.e., an order of magnitude or more change, with respect to the nuclear power issues is continuous recycle of all transuranic (TRU) elements. There may be a special case for near-complete burnup of UNF that could also result in significant impact on the issues, making once-through and limited recycle strategies more attractive, since such an approach is essentially equivalent to a continuous recycle strategy where all TRU is recycled. However, after review of the technical issues, this possibility is considered impractical, maybe even impossible. Deciding the fuel cycle strategy is the important first step in considering alternative nuclear fuel cycle systems.Technology options exist for many areas of a nuclear fuel cycle. For fuel type, either uranium-based or thorium-based, it is only in the case of continuous recycle where these two fuel types exhibit different characteristics, and it is important to emphasize that this difference only exists for a fissile breeder strategy. The comparison between the thorium/U-233 and uranium/Pu-239 option shows that the thorium option would have lower, but probably not significantly lower, TRU inventory and disposal requirements, both having essentially equivalent proliferation risks. For these reasons, the choice between uraniumbased fuel and thorium-based fuels is seen basically as one of preference, with no fundamental difference in addressing the nuclear power issues. Since no infrastructure currently exists in the U.S. for thoriumbased fuels, and processing of thorium-based fuels is at a lower level of technical maturity when compared to processing of uranium-based fuels, costs and RD&D requirements for using thorium are anticipated to be higher. The availability and utilization of thorium-based fuels along with the uranium fuel technology in the U.S. would however make available more nuclear fuel resources for future nuclear expansion.

Many people have provided significant input for the preparation of this document. It is based, in large part, upon several basis documents, primarily including materials for radiation service, materials for high-temperature service, materials assessments, surveys and program plans for the different reactor systems and the microstructural analysis and modeling, and hightemperature structural design methodology crosscutting tasks. Text, tables, and figures from these documents have been incorporated into this report. The sheer number of contributors precludes their all being listed as authors, notwithstanding their significant input. To assist in providing appropriate attribution, those non-authors who contributed input from these and related sources are listed, with many thanks, below.

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