Impact of alternative nuclear fuel cycle options on infrastructure and fuel requirements, actinide and waste inventories, and economics

Thesis (S.M. in Technology and Policy)--Massachusetts Institute of Technology, Engineering Systems Division, Technology and Policy Program; and, (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 222-223).The nuclear fuel once-through cycle (OTC) scheme currently practiced in the U.S. leads to accumulation of uranium, transuranic (TRU) and fission product inventories in the spent nuclear fuel. Various separation and recycling options can be envisioned in order to reduce these inventories while extracting additional energy and sending the ultimate waste to a repository. Choosing one of these options has direct implications for the infrastructure requirements, natural uranium consumption, actinide inventories in the system, waste repository needs and costs. In order to account for the complexity of the nuclear enterprise, a fuel cycle simulation code has been developed using system dynamics (CAFCA). An economic module was added using spreadsheets. Four main advanced fuel cycle schemes are assessed here within the context of the US market: 1) the twice-through cycle scheme (TTC): single-pass plutonium recycling in thermal spectrum LWRs using Mixed OXide (MOX) fuel; 2) Multi-recycling of TRU in sodium-cooled fast spectrum burner cores, characterized by a fissile conversion ratio lower than 1 (FBu); 3) Multi-recycling of TRU in sodium-cooled fast breeders with a conversion ratio of 1.23 (FBr); and 4) A two-tier scenario: a TTC scheme is practiced as a transition scheme to fast reactors. The base case scenario assumes annual nuclear energy demand growth rate of 2.5% from 2020 on. The technologies for plutonium separation as well as MOX fuel fabrication are assumed to be available in 2025 while the first commercial fast reactors, as well as the possibility to recycle their spent fuel, are assumed to be available in 2040.(cont.) For fast reactors, the cores are assumed to be TRU fueled, and the technology to separate the minor actinides is supposed to be available at the latest 5 years before deployment of fast reactors. Limits are applied on the building rate of reprocessing plants, which are also subject to a 80% minimum life-time loading factor requirement. It is found that, despite its higher cost, at the end of the century, the TTC scheme (single Pu-MOX recycle) does not lead to large improvements in terms of natural uranium consumption (16%), repository needs (considering both fission products and MA from reprocessing facilities, and spent MOX fuel) and TRU inventory reduction (although some shifting of TRU from storage to reactors occurs). This is especially significant because it is the only advanced fuel cycle option that can be deployed in large scale in the next few decades. However, if the primary reason for introduction of the more expensive fast reactors is resource enhancement and/or control of TRU in the nuclear waste, thermal reactor recycling allows the introduction of fast reactors to be delayed by 20-25 years. Moreover, once fast reactors are introduced, their deployment is accelerated compared to a 1-tier FR scenario. However, the two-tier scheme is the most expensive scheme as it combines the requirements of both the MOX technology and the FR technology. Sensitivity analyses were performed in order to assess the impact of secondary parameters. It is found that whatever the growth rate assumed, LWRs remain a significant part of the system at the end of the century, decades after fast breeders are introduced.(cont.) The reason is the fissile materials required for fabrication of start-up cores considerably affect the rate at which fast reactors can be deployed. As a result, the choice of the core design (compact core vs. large core) may be as significant as the choice of the conversion ratio. For example, the breeder scenario (CR=1.23) may lead to the same cumulative natural uranium consumption reduction (by 2100) as the self-sustaining reactors (CR=1.0) while leading to larger TRU inventory in the system and requiring greater fast reactor fuel reprocessing capacity. Allowing fast reactors to start with uranium only cores was not considered, as it will likely limit resource enhancement benefits of fast reactors. Still, in general, the higher the conversion ratio, the greater the fast reactor installed capacity, hence the greater the savings in natural uranium. Conversely, the best reduction in TRU from the OTC amount is obtained by the lower conversion ratio (45% for a pure burner with conversion ratio 0.0 by 2100). Doubling the minimum cooling time before reprocessing for all fuel types from 5 years to 10 years slows down the deployment of the fast reactors and therefore reduces their share in the total installed capacity. This is almost equivalent to replacing breeders with fast reactors with a conversion ratio of 0.75. Finally, the results show that starting the separation of the TRU 10 years prior to introduction of the fast reactors instead of 5 years provides a mid-term advantage (faster initial deployment) that vanishes within 25 years. In the long term, the fast reactor penetration results are insensitive to the assumed industrial capacity to build reprocessing facilities for the base case or at lower nuclear energy growth rates.(cont.) However, the assumed industrial capacity can be a real constraint if the nuclear energy growth rates are 4% or higher.by Laurent Guérin.S.M.S.M.in Technology and Polic