Dynamic Analysis of Fuel Cycle Transitioning Page: 3 of 8
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Proceedings of Global 2009
Paris, France, September 6-11, 2009
Paper 9276this conversion ratio assumption was explored via
sensitivity studies. Both oxide and metal fuel forms were
considered for the fast reactors.
The transition analyses were all based on current U.S.
fuel cycle and LWR infrastructure, including current
inventories of used UOX fuel. Expansion of the current
100 GWe of installed reactor capacity started in 2015
based on 1.75% total annual compounded growth of
nuclear-based electricity generation. This growth provided
a doubling of nuclear electricity generation by 2060,
redoubling by 2100. The impact of this growth rate
assumption was assessed via sensitivity studies. Reactor
retirements after 60 years of operation were included in the
system dynamic analysis.
A geologic repository was assumed to open shortly
after fleet expansion started, for receipt of used LWR fuel
and high level waste. The initial repository capacity was
limited to disposal of 63,000 metric tonnes of initial heavy
metal per restrictions in the U.S. Nuclear Waste Policy
Act2. For all scenarios, inventories of used UOX fuel
accumulated through 2010 were assumed direct disposed
to reach this limit with additional used fuel and high level
waste allocated to "additional repository capacity". One
key impact of this assumption was the disposal of all
existing lower burn-up aged used fuels, simplifying the
analysis. All used UOX fuels discharged after 2010 were
assumed to have the same burnup of 51 MWth-days/kg-
iHM. LWR MOX-U/Pu fuels were assumed to have
similar burnup for compatibility in reactor reload cycles,
while the FR-TRU fuel at CR = 0.5 had a burnup of 132
MWth-days/kg-iHM. Both LWR fuels were cooled a
minimum of 10 years before separations or disposal, while
the FR-TRU fuel was cooled 2 years for on-site recycling
(primary assumption) and 10 years for centralized
recycling (sensitivity analysis).
Reprocessing of used LWR fuel was assumed to begin
in 2020 when the fuel discharged in 2010 reached the
minimum cooling time. Reprocessing capacity was
initially limited, restricting the production of MOX-U/Pu
and FR-TRU fuels. The availability of fuel feedstock is a
primary constraint on the rate of transition of the reactor
infrastructure from only LWRs to a mixed fleet of LWRs
and fast reactors. UOX reprocessing capacity was
expanded during the scenario such that no excess of cooled
fuel remained by 2100. MOX-U/Pu and FR-TRU
fabrication and reprocessing capacities were not
constrained. Natural uranium supply, conversion and
enrichment were not constrained, so when the rate of
construction of FRs was constrained by fuel availability
below the overall rate of fleet growth and replacement,
new UOX-fueled LWRs made up the deficit.Fast reactor introduction began shortly after 2030 for
the one-tier case. For the two-tier case, FRs were
introduced when the first MOX-U/Pu used fuel had cooled
and was available for reprocessing (~2037). In both cases,
construction was limited for the first decade to 1 GWe/year
new capacity for the first 5 years and 2 GWe/year for the
second 5 years.
The analysis was performed using the dynamic fuel
cycle simulation model VISIONS. VISION calculates the
mass flows of 81 isotopes and isotope groups of interest
for fuel composition, shielding, decay heat, and
radiotoxicity and includes decay calculations for isotopes
with half lives greater than 0.5 years. The model provided
facility and material information and annual data for total
electricity output, reactor capacity by type, natural uranium
and enrichment requirements, used fuel inventories, fresh
fuel fabrication and used fuel separations rates, and a
number of waste parameters.
III. FINDINGS
The primary results of the analyses include gradual
growth of total nuclear output with a slow transition from
all LWRs to a mixed fleet of LWRs and fast reactors in a
ratio approaching dynamic equilibrium. Figure 1 shows
the electricity generation by reactor type for the one- and
two-tier systems. These graphs show the exponential
growth pattern in all the analyses which is a reflection of
using an annual compounded growth rate. In both cases,
the amount of electricity generated by recycled materials is
small compared to that generated by UOX. The two-tier
system results in a slightly smaller amount of total
electricity being generated by recycled materials. This is
due to the time this material is sitting inactive in used LWR
MOX fuel.
The two-tier system also results in significantly fewer
fast reactors due to a number of factors. First, some of the
Pu that contributes to fast reactor cores in the one-tier
system is instead consumed during the LWR MOX pass.
Second, the time spent in the MOX pass delays the
construction of fast reactors, resulting in a lower dynamic
equilibrium ratio.
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Dixon, Brent; Piet, Steve; Shropshire, David & Matthern, Gretchen. Dynamic Analysis of Fuel Cycle Transitioning, article, September 1, 2009; [Idaho]. (https://digital.library.unt.edu/ark:/67531/metadc930888/m1/3/: accessed April 18, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.