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etrievable conditions, is therefore a method to keep the decisions on this
source term in the hands of future generations without increasing the risk.
Transmutation of properly conditioned targets could in principle be
undertaken in the future if dedicated burner reactors become available.
Reprocessing provides access to some fission products that are important
radiological source terms. Existing technologies enable partitioning and conditioning
of these radionuclides into appropriate matrices to be disposed of in
suitable repository conditions if available.
The advanced fuel cycle with P&T incorporated is the most comprehensive
approach. It requires dedicated fuel cycle and reactor facilities that go
far beyond current nuclear technology. In particular, the transmutation
approach calls for the development of FR burners and/or accelerator driven
system (ADS) facilities, which may take 20–30 years to become industrially
available. This option is the only one that offers a final solution to sustainable
nuclear energy production.
A serious situation would occur if recycling were interrupted after, for
example, 50 or 100 years. In this scenario the enrichment of plutonium in the
nuclear energy generating plants would have reached an equilibrium level and
the whole inventory must be disposed of at that time. Recycling of TRUs in a
composite fleet of nuclear reactors, comprising LWRs and FRs, depends on a
long term energy policy with a continuous political and economic backing of
nuclear energy in the global energy mix.
The impact of this ‘interruption’ scenario on the design of a repository is
far reaching: the radiotoxicity of the nuclear fuel streams after long term
irradiation is multiplied by several orders of magnitude, the heat dissipation
requirement is much higher and the effect of the long term radiotoxicity
reduction is not attained for a period of several hundred years, as determined
by the residual concentration and the decay time of 238 Pu.
The most important decay chain [7] from a radiological point of view is
the 4n + l decay chain, comprising 245 Cm, 241 Pu, 241 Am and 237 Np. The 4n + 3
decay chain includes, for example, 243 Cm and 239 Pu, and the 4n chain includes
244 Cm and 240 Pu (Figs 3 and 4).
In conclusion, the decision to operate the P&T fuel cycle should be
supported over a sufficiently long period (70–100 years), until equilibrium is
established between generation and consumption of TRUs, otherwise an interruption
would imply multiplication of the radiotoxic inventory.
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