11 Nuclear fuel cycle overview
We normally think about the nuclear fuel cycle as putting fuel in the reactor and then taking it out. Sometimes enrichment appears in the news, but not usually in a positive context.
The current nuclear fuel cycle consists of –
- Mining ore from the ground
- Conversion to [latex]UF_6[/latex]
- Enrichment from natural [latex]^{235}U[/latex] abundance to 3% – 5%
- Fuel fabrication [latex]UF_6 \rightarrow UO_2[/latex]
- Burning in reactor – fission
- Storage – wet and dry
- Reprocessing
- Fuel fabrication – [latex]MOX[/latex]
- Burning [latex]MOX[/latex]
- Back to storage
The United States does not currently reprocess used fuel. Once burned, fuel is stored in the used fuel pool for a time, then into dry storage. This is the same for any nation. Then, in the United States, it is expected that the stored fuel will be directly disposed in a repository. In a nation like France, the used fuel is chemically treated by the PUREX process to separate fission products from fissionable material; namely [latex]^{235}U[/latex] and [latex]^{239}Pu[/latex]. Then, these are fabricated to a new, mixed oxide or [latex]MOX[/latex] fuel to be fissioned in the reactor and repeat.
There are waste streams produced in the nuclear fuel cycle. Mill tailings result from the uranium ore extraction process. These are stored in ponds. For reprocessing, PUREX results in several liquid waste streams. These are vitrified into borosilicate glass. This is a material with over a half century of characterization. It is very stable with a low coefficient of thermal expansion. The vitrified waste is then disposed in the repository.
Advanced nuclear reactor concepts may have a different fuel cycle, but overall, is largely the same. The main difference would be the fuel fabrication for a molten salt or sodium fast reactor would be different than making uranium oxide fuel. Disposal will also always be needed, but the matrix; e.g., the borosilicate glass, may be a different material. Recycling processes could also be different, as production of metallic fuel or molten salt reactor fission product removal may use pyroprocessing, which uses electrochemistry to take advantage of the differences in the Gibbs free energy to extract fission products and TRUs from the used fuel.
Additional notes
- MIT Open Courseware – Systems analysis of the nuclear fuel cycle
- UC-Berkeley – Energy and society
- World Nuclear Association – Nuclear fuel cycle overview
- MIT Open Courseware – Nuclear reactor safety
- MIT Open Courseware – Integration of reactor design, operations, and safety<
- MIT Open Courseware – Nuclear science and engineering
Fuel cycle processes directed self-study course