| dc.description.abstract | 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. 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. 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. However, the assumed industrial capacity can be a real constraint if the nuclear energy
growth rates are 4% or higher. | en_US |
