Experience with fast breeders shows that a typical [48] 1.2 GWe reactor requires an initial inventory of 5 tons of plutonium. A 1200 MWe reactor

produces around 0.25 tons of plutonium annually, corresponding to a doubling time of 20 years. However this value of the doubling time does not take into account the reprocessing stage. The longer the cooling time of the used fuel before reprocessing, the longer the effective doubling time. As an example, if the residence time of the plutonium in the reactor is 4 years, and the cooling time also 4 years, the plutonium inventory is doubled, and so is the doubling time. The transition from a PWR — (BWR-) based system to a fast reactor system was studied. It was assumed that a strong PWR programme starts in 2010, first breeders starting progressively in 2020. By 2030 no new PWRs are connected to the grid, leaving the field to fast reactors. Figure 2.7 shows the evolution of the reactor park cor­responding to a plutonium production of 250kg/GWe by the PWRs and 200kg/GWe by the fast breeders.

A cooling time of 1 year was assumed. The target of 9000 GWe by 2050 can be reached. For longer cooling times it is found that the target cannot be reached. Cooling times as short as 1 year are probably not possible with standard aqueous reprocessing and would require pyro-chemical reprocessing. After 2050 the PWRs would be phased out progressively and the doubling time of the FR could be adjusted to the desirable evolution of the reactor park. In figure 2.7 a 1.5% annual increase of the nuclear park was assumed.

Figure 2.8 shows the plutonium stockpile outside the reactors. It displays three regimes. First the Pu inventory increases slowly until 2030 as

a result of the production by the increasing PWR (BWR) park. The decrease between 2030 and 2050 reflects the sharp increase in the number of fast reactors. The increase after 2050 is due to the slower increase of the number of fast reactors. Instead of keeping the total plutonium stockpile at such a high value, it could be possible to use the excess neutrons for the transmutation of fission products, for example. Alternatively, reactor sizes could be reduced, giving more flexibility to the power system.

In our scenario the last PWR reactors will be phased out in 2070. At that time the total amount of natural uranium used would reach 12 million tons, close to the presently estimated reserves. This means that the number and lifetime of the PWR park cannot be considered as an easily adjustable variable to achieve the strong increase of nuclear power between 2030 and 2050. This increase will be difficult to achieve and requires the early development of breeders, as well as the availability of as much reprocessed plutonium as possible. The generalization of MOx incineration has to be weighed against this requirement. Similarly, incinerating plutonium in HTR reactors may be counterproductive if spent fuel reprocessing is not possible. Until the development of breeder reactors the best use of reproces­sing facilities might be the fabrication of Pu-Th fuels for PWRs, producing 233U, which could be used as described in section 4.2.2.

Of course, accepting a lower value for the target in 2050 would make things easier. For example, a target of 7000 GWe could be reached with a doubling time of 32.5 years. Another possibility would be to increase the share of more efficient plutonium-producing reactors such as the CANDUs.