The FuTure oF nuclear Fuel cycle - MIT Energy Initiative

Twice-Through Cycle
Table 7.3 shows the levelized cost for the Twice-Through Cycle. In the Twice-Through Cycle
raw uranium is first fabricated into uranium-oxide fuel (UOX) for use in a light water reactor.
This is called the first pass of the fuel in a reactor. Then the spent fuel is reprocessed, and
plutonium, whether in isolation or mixed with uranium, is fabricated into a mixed-oxide
fuel (MOX) for reuse in a light water reactor. This is called the second pass of the fuel in a
reactor. Of course, the MOX fuel forms only a part of the fuel core of the second reactor.
The table shows the levelized cost for both: lines [1]-[11] detail the LCOE for the first pass,
the UOX fuel in a light water reactor, while lines [12]-[19] detail the LCOE for the second
pass, the MOX fuel in a light water reactor.
For the first pass reactor burning fresh UOX fuel, the front-end fuel costs, reactor costs and
non-fuel operating and maintenance costs are identical to those for the Once-Through Cycle—lines
[1]-[5]. However, the back-end fuel cycle costs are different since the spent fuel
is sent for reprocessing. The costs of reprocessing the spent UOX fuel are included as a part
of the back-end fuel cycle cost for the first pass—line [6]. The reprocessing produces three
streams: uranium, plutonium and high level waste. The high level waste contains the fission
products, minor actinides and impurities. The cost of disposing of this high level waste
stream is included as a part of the back-end fuel cycle cost for the first pass—line [7]. A
credit for the value of the recovered uranium, which can be used in the fabrication of fresh
UOX fuel, is included as a part of the back-end fuel cycle cost for the first pass—line [8].
The size of this credit is determined by the price of raw uranium for which the reprocessed
uranium is a substitute, and the differential cost of fabricating UOX from reprocessed uranium.
The analysis also requires a credit for the value of the recovered plutonium which will
be used to fabricate MOX fuel for the second pass—line [9]. Since the MOX fuel is used to
produce electricity that substitutes for electricity produced with UOX fuel, the size of the
credit will be such that the LCOE for the first pass and the LCOE for the second pass are
exactly equal—i.e., line [11] will equal line [19]. Line [20] shows this credit measured as a
price per unit of plutonium, $ -15,734/kg. Line [9] shows this credit measured as a value
per unit of electricity, $ -0.14 mill/kWh. The fact that the price of the separated plutonium
is negative, as is the credit obtained by the first reactor, implies that the first reactor pays
for the plutonium to be taken away. The total back-end fuel cycle cost for the first pass is
2.87 mill/kWh—line [10]. This is a much higher cost of disposal than in the Once-Through
Cycle.
The total levelized cost for the first pass reactor in the Twice-Through Cycle is 85.38 mill/
kWh, which is higher than in the Once-Through Cycle. The difference between the two is
entirely due to the higher cost of disposing of the spent fuel by reprocessing as opposed to
sending the complete spent fuel package directly to a repository.
For the second pass reactor burning MOX fuel, the front-end fuel cost is composed of the
purchase of depleted uranium, a credit for taking the separated plutonium, and the cost of
fabricating the MOX fuel. These items are shown in lines [12]-[14] and the total is shown
in line [15]. This second pass has a much lower front-end fuel cycle cost than the first
pass—3.02 mill/kWh as opposed to 7.11 mill/kWh for the first pass. This is primarily due to
the fact that the second pass reactor owner will be paid to take the separated plutonium. The
payment equals 4.39 mill/kWh—line [13]—and is a significant help in offsetting the high
cost of fabricating the MOX fuel. The levelized reactor capital and operating costs—lines
[16] and [17]—are exactly the same whether the reactor is burning UOX fuel or MOX fuel.
104 MIT STudy on The FuTure oF nuclear Fuel cycle