| Summary: | Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering; and, (S.M.)--Massachusetts Institute of Technology, Engineering Systems Division, 2008. === Includes bibliographical references (p. 202-204). === A system dynamics simulation technique is applied to generate a new version of the CAFCA code to study the mass flow in the nuclear fuel cycle, and the impact of different options for advanced reactors and fuel recycling facilities on the accumulation of the transuranics (TRU) inventory. Several aspects of the nuclear fuel cycle are studied for the US and for Brazil. This includes the impact of advanced nuclear technologies' introduction, under a prescribed industrial construction capacity, on uranium resources, the need for uranium enrichment, demand for fuel reprocessing facilities, and total cost of electricity over the next one hundred years. Introduction of fuel recycling can reduce the growing demand for uranium, and the long-term need for storage of radioactive spent fuel. However, the timing of introduction of recycling is important for proper technology development, and that is reflected in the assessments. The nuclear fuel cycle is modeled as a high level structure diagram, which provides an overview of the interconnections among its blocks without showing all the details, and as a structure-policy diagram which details the decision rules applied to the structure. The high level structure diagram represents the nuclear fuel cycle; the fleet of thermal and fast reactors; the separation and reprocessing plants; the waste repository; the spent fuel storage; and the paths for the fuel and waste mass transfer. In addition, an economic model is added to study different cases under the same assumptions. The economic model is based on the forecasted need for advanced reactors and recycling facilities, assuming that all costs are recovered within the nuclear energy system. === (cont.) Different recycling technology options are included in the code: (1) Thermal recycling in LWRs using Combined Non-Fertile and UO₂ Fuel (CONFU), (2) Recycling of TRU in fertilefree fast cores of Actinide Burner Reactors (ABR); and (3) Fast recycling of TRU with UO₂ in self-sustaining Gas-cooled Fast Reactors (GFR). Case studies for different advanced technology introduction dates and for distinct TRU depletion rates are examined. In particular, the code is equipped to simulate the introduction of two recycling technology options with a prescribed allocation of the TRU supply between them. The simulation results show that early introduction of the GFR recycling scheme leads to the most significant reduction in uranium consumption, and enrichment requirements, thus delaying the depletion date of uranium ore. The GFR technology requires less uranium resources due to U recycling and near unity fissile conversion ratio. However, in a non-breeding reactor system, the consumption of U continues to grow, and the TRU needed to start fast reactors will be growing at a constrained rate. On the other hand, the CONFU recycling scheme keeps the TRU inventory in the entire system well below other schemes, and guarantees equilibrium between the generation and consumption of transuranics without investments in fast reactors. Also, it reduces the TRU sent to the repository for disposal by orders of magnitude. The ABR scheme does the same but requires the introduction of fast reactors. Nevertheless, the CONFU and ABR schemes have no significant impact on the amount of uranium resources consumption or enrichment requirements. CONFU incinerates more TRU than the GFR and ABR schemes during the simulation period. Economic analysis indicates that the CONFU technology is more attractive at current uranium prices, and that fast recycling becomes as attractive as thermal recycling at higher uranium prices. === (cont.) The results also show that if a nuclear fuel cycle state/reactor state collaboration with Brazil is started, there will be a significant impact on the U.S. cumulative TRU inventory at interim storage, enrichment requirements, uranium consumption, and number of advanced fuel facilities. The results show that a nuclear partnership without the introduction of advanced nuclear technologies would not have advantages for the U.S. Furthermore, a nuclear collaboration allows a higher ratio of fast reactors to total installed nuclear electric capacity in the U.S. === by Rodney Busquim e Silva. === S.M.
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