COMPLETE DOCUMENT (1862 kb) - OECD Nuclear Energy Agency

decrease is obtained in the radiotoxic inventory before 10 6 years. Thus there is no
immediate advantage in recycling neptunium, except as part of a strategy of systematically
incinerating all the MAs;
• If americium is recycled alone, only a moderate gain is achieved in comparison with
plutonium multi-recycling owing to the accumulation of curium. Nevertheless, while Pu
multi-recycling reduces the radiotoxic inventory of wastes by a factor of 5 to 10, this
reduction would be increased to a factor of 30 by recycling americium, without curium;
• Curium must therefore ultimately be considered, if a maximum inventory reduction is
intended. This could be achieved by fissioning the highly fissile 245 Cm. Yet, the very high
activity of 244 Cm (half-life 18 years) makes it very difficult to handle such a target. An
overall strategy could consider the separation of Cm and its interim storage for a century
or so to allow the 244 Cm to decay to 240 Pu and then recycle the remaining mixture
( 240 Pu/ 245 Cm).
If only plutonium is multi-recycled, the equilibrium obtained involves the accumulation of 300
to 600 t of Pu in the cycle depending on the type of dedicated reactor. This stabilisation of the mass of
Pu would be accompanied by a 2.5 to 10 fold increase in the mass of minor actinides produced. This
mass would be discharged with the wastes and would commensurably reduce the anticipated gain in
radiotoxicity to a factor of less than 10.
To make further headway, the MAs must be multi-recycled to a dedicated reactor, which
would increase the mass of Pu and MAs in the cycle at equilibrium, but which would reduce the masses
sent to the waste by a factor of nearly 100 in comparison with direct disposal.
However a residual mass of heavy nuclei would exist at equilibrium in the reactor and in the
different fuel cycle plants.
This concept of equilibrium mass in a nuclear reactor system implies that, in the case of
scheduled and progressive shutdown of the nuclear capability, it would theoretically be possible almost
to eliminate the mass of heavy nuclei present in the cycle, by shutting down first the Pu-producing
reactors, and then the Pu- and MA-consuming reactors as the inventory gradually decreases.
However, it must be understood that to implement such strategies would demand periods of
several decades or even centuries.
For strategies using incinerating reactors and reactors fuelled with enriched uranium, the
problem of natural uranium resources would arise within about fifty years.
A convertible reactor of the CAPRA type could perform equally well as a Pu consumer or a
breeder, and would help to switch rapidly from a strategy of plutonium limitation or reduction to a
strategy of plutonium use and regeneration or vice versa.
It must also be understood that physical studies of scenarios in no way imply their technical
and technological feasibility, which are the subject of a major R&D support programme, including the
development of an inert matrix for TRU targets, reactivity control in presence of high MA loadings.
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