The FuTure oF nuclear Fuel cycle - MIT Energy Initiative
The FuTure oF nuclear Fuel cycle - MIT Energy Initiative
The FuTure oF nuclear Fuel cycle - MIT Energy Initiative
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the once-through <strong>Fuel</strong> Cycle for light-Water reactors<br />
Most of the world’s reactors are light water reactors that use<br />
a once-through open fuel <strong>cycle</strong>. This fuel <strong>cycle</strong> consists of<br />
seven steps.<br />
• Uranium mining and milling. uranium is the starting fuel<br />
for all fuel <strong>cycle</strong>s. uranium mining and milling is similar to<br />
the mining and milling of copper, zinc, and other metals.<br />
uranium is often found with copper, phosphates, and other<br />
minerals; thus, it is often a co-product of other mining<br />
operations. about 200 tons of natural uranium is mined to<br />
fuel a 1000-MW(e) light-water reactor for one year.<br />
• Uranium conversion. <strong>The</strong> uranium is chemically purified<br />
and converted into the chemical form of uranium hexafluoride<br />
(uF 6 )<br />
• Uranium enrichment. uranium contains two major<br />
isotopes: uranium-235 and uranium-238. uranium-235<br />
is the initial fissile fuel for <strong>nuclear</strong> reactors. natural uranium<br />
contains only 0.7% uranium-235. In the uranium<br />
enrichment process, natural uranium is converted into<br />
an enriched uranium product stream containing 3 to 5%<br />
uranium-235 and depleted uranium that contains ~0.3%<br />
uranium-235.<br />
• <strong>Fuel</strong> fabrication. <strong>The</strong> enriched uranium is converted into<br />
the chemical form of uranium dioxide and fabricated into<br />
<strong>nuclear</strong> fuel. a typical lWr requires ~20 tons of enriched<br />
uranium fuel per year.<br />
• Light-water reactor. When fresh fuel with uranium-235 is<br />
loaded into a reactor, the fissioning of uranium-235 produces<br />
heat. <strong>The</strong> fuel also contains uranium-238, which<br />
upon absorption of neutrons produces plutonium-239, a<br />
readily fissionable material like uranium-235 that also fissions<br />
to produce heat. Just before the fuel is discharged<br />
from the reactor as SnF, about half the energy being generated<br />
is from the fissioning of plutonium-239 that was created<br />
in the reactor. <strong>The</strong> heat is converted into electricity.<br />
• Interim storage of spent <strong>nuclear</strong> fuel (SNF). a typical<br />
lWr fuel assembly remains in the reactor for three to four<br />
years. upon discharge of the SnF, it contains ~0.8% uranium-235,<br />
~1% plutonium, ~5% fission products, and the<br />
rest is mostly uranium-238. <strong>The</strong> SnF is stored for several<br />
decades to reduce radioactivity and radioactive decay<br />
heat before disposal.<br />
• Waste disposal. If no advanced fuel <strong>cycle</strong> is deployed that<br />
can use plutonium and uranium-238, then the SnF would<br />
be considered a waste that ultimately must be sent to a<br />
geological repository for disposal.<br />
Figure 2.1 once-through <strong>Fuel</strong> Cycle<br />
Mining &<br />
Milling<br />
Conversion<br />
Enrichment<br />
<strong>Fuel</strong><br />
Fabrication<br />
Light Water<br />
<strong>The</strong>rmal Reactor<br />
Interim<br />
Storage<br />
Waste<br />
Disposal<br />
20 <strong>MIT</strong> STudy on <strong>The</strong> <strong>FuTure</strong> <strong>oF</strong> <strong>nuclear</strong> <strong>Fuel</strong> <strong>cycle</strong>