The FuTure oF nuclear Fuel cycle - MIT Energy Initiative

For the sake of simplicity, we use a single model of a reference 1000 MWe LWR, and assume
a unique set of parameters for the fuel cycle. Data about the fuel requirements are taken
from [Hoffman et al., 2005]. In reality, there are many sizes of LWRs, and their fuel cycles
also differ according to their fuel management. Table 6.1 summarizes the characteristics
of interest for the reference LWR (scaled to a 1000 MWe unit) as well as all other reactors
considered in this study.The sidebar describes the fuel details (fuel compositions, mass flow
rates, etc.) used in the analysis.
Table 6.1 Characteristics of The Reference Power Plants
plant and CyCle deSCription
liGht Water
reaCtorS
FaSt breeder
reaCtor
FaSt burner reaCtor
Thermal Power (MWt) 2,966 2,632 2,632
Thermal efficiency 33.7% 38% 38%
electrical output (MWe) 1000 1000 1,000
conversion ratio 0.6 1.23 0.0 0.5 0.75 1.0
cycle length (eFPd) 1 500 700 132 2 221 2 232 2 370
average number of batches 3 3 (+ blankets) 8.33 5.82 5.95 3.41
average irradiation time (eFPd) 1,500 1,785 (2380 for the 1,099 1,286 1,380 1,262
blankets)
discharge Burn up (MWd/kghM) 50 103.23 293.9 131.9 99.6 73.0
notes
1. eFPd: effective Full Power days. 2. Fuel cycle lengths less than about a year are not attractive for utilities, as they require
frequent refueling and limit the capacity factor.
The Twice-Through Fuel Cycle (single pass MOX in thermal reactors)
LWRs may be fueled with Mixed Oxide (MOX) assemblies. MOX is a mixture of Plutonium/Americium
1 oxide (PuO 2 /AmO 2 ) and depleted (or natural) uranium oxide (UO 2 ).
Unlike uranium, plutonium can be found in only trace quantities in nature, but is formed
in reactors. About half of the plutonium produced in a LWR is fissioned in that reactor
(typically contributing about one fourth of the energy produced over the irradiation of a
UO 2 batch), or decays in situ. However, a significant amount (typically about 1% w of the
total heavy metal) remains in the discharged spent UO 2 fuel.
Hence, the twice-through cycle (denoted TTC) is intrinsically a limited recycling scheme.
After a minimum cooling time, the fuel discharged from UO 2 fueled LWRs is sent to reprocessing
plants where both the uranium (which typically constitutes 99% w of the heavy metal
in used UO 2 fuel) and the plutonium are extracted. The minor actinides are sent along
with the fission products to interim storage for ultimate disposal.The plutonium is sent
to MOX fabrication plants (possibly co-located with the reprocessing plant) for MOX pin
fabrication.MOX assemblies are then loaded in LWRs for electricity production. Depending
on the capability of the reactor and the policy choice, the core can be fully loaded with
MOX assemblies, or only partially loaded (typically 30%). In the latter case, the remainder
is constituted of traditional UO 2 assemblies. Very few of the existing U.S reactors, so-called
Generation II reactors, are licensed to be loaded with MOX assemblies.
chapter 6: analysis of Fuel cycle options 73