The FuTure oF nuclear Fuel cycle - MIT Energy Initiative

With few exceptions, the existing closed fuel cycle technologies require the separation of
pure plutonium or plutonium/uranium mixtures from SNF before fabrication of new fuel
because of technical and economic constraints in the production of new nuclear fuel assemblies.
Nuclear fuel assemblies are highly engineered components that require extensive
quality assurance. This is much easier to do this when starting with pure materials rather
than with impure materials containing fission products with high radiation limits. In most
cases separation of pure fissile materials such as plutonium is not a fundamental requirement
of closed fuel cycles but rather a consequence of existing fuel fabrication technology
limits.
Different closed fuel cycles have radically different types of reactors and fuels; however, the
same backend fuel cycle technologies are used for separating different types of SNF into
product streams and converting wastes into acceptable waste forms for disposal. This is
because all SNF contains the same actinides and fission products with the same requirements
for acceptable waste forms. In contrast, the fuel fabrication technology is fuel cycle
and reactor specific.
A product slate is critical to the design, configuration, and operations of the separations
and waste treatment units in a recycling plant. The product slate will depend on the SNF
feed material, the selected recycling reactors (fast or thermal reactors), the recycle strategy
(total or partial-closed cycle), fuel reactor fuel configurations (homogeneous or heterogeneous),
type of recycled fuel (metal, oxides, other ceramics, etc.), as well as target materials/
configuration. Ultimately, it is the recycle fuel fabrication and waste disposal methods that
provide the specifications for what are the form and composition of the products coming
out of a recycling plant.
Separations and Waste Treatment
The larger the number of products desired from SNF, the more complex the recycling plant.
A recycling plant incorporates separations to produce desired products and waste management
facilities. Traditional functions encountered in recycling facilities are listed in Table
E.1 for both aqueous and electrochemical (pyrochemical) processes.
p Aqueous processing. The fuel is dissolved in a low-temperature aqueous acid solution
with various organic extractants used to separate products from the aqueous solution.
The process can be scaled to very large sizes (7000 tons SNF/year)
p Electrochemical (pyrochemical) processing. The fuel is dissolved in a high-temperature salt
with electrochemical methods used to “plate-out” metallic products. The process is usually
operated as a batch process with multiple lines to meet throughput requirements.
Commercially only one type of recycling facility exists, that which recovers plutonium from
LWR spent fuel for production of MOX fuel (recycle of plutonium back to LWRs). Three
complete commercial recycling plants have been built which include the separations and
waste treatment portions, but all lack treatment for selected off-gases and tritiated water:
p LaHague (France): 2 trains of 800 tons LWR SNF/year
p Sellafield THORP (Great Britain): 1200 tons LWR SNF/year
p Rokkasho (Japan): 800 tons LWR SNF/year
appendix e: Status of Fuel cycle Technologies 231