As discussed in Section 17.3, the choice of the appropriate core conversion ratio is related to the chosen strategy, i. e. a ‘high’ conversion ratio (CR>1) corresponds to a strategy of sustainable nuclear energy with waste minimization in a repository and stabilization of the MA inventory contained within the fuel cycle. A ‘low’ conversion ratio (CR -0.4-0.6) corresponds to a strategy of rapid TRU or MA inventory reduction (see Figs 17.5 and 17.6). ADSs correspond to cores with CR = 0 if an inert matrix fuel (IMF) is used as a driver.

17.1.1 Reactor type

The ADS in the schemes of Figs 17.5 and 17.6 can be considered as a ‘dedicated’ transmuter reactor. The ‘critical FR’ in Fig. 17.9 could be, for example, a FR that is progressively loaded with MA-containing fuel, with sodium as the coolant. The choice of the CR for the critical fast reactor determines whether the FR is to be

means ‘option’

Where

77.9 Scheme showing the different P&T options within the seven technical domains (on the left hand side) for the three main fuel cycle scenarios of Section 17.4 (across the top of the figure).

regarded as part of a sustainable system, as shown in Fig. 17.4, or as a transmuter reactor and an alternative to ADS (see Section 17.3). In fact, this is true regardless of the choice of coolant, so that gas or a liquid lead alloy could be substituted for sodium with no impact on the P&T implementation strategy, at least in an initial phase. No firm choices have been made at the present time and three specific prototypes are envisaged in Europe with missions related to transmutation:

In France, a Generation IV and actinide incineration demonstration prototype should be commissioned in the 2020 decade. This prototype, called ASTRID (Advanced Sodium Technological Reactor for Industrial Demonstration55 will probably replace the Phenix fast reactor and provide a means of testing homogeneous and heterogeneous minor actinide recycling modes, as described in Section 17.3.

The Myrrha project 56 is initially a 57 MW ADS with a sub-critical fast reactor core. The coolant is a liquid lead-bismuth alloy (Pb-Bi). The spallation target is also Pb-Bi. A schematic illustration is shown in Fig. 17.10.

An experimental gas-cooled fast neutron reactor ALLEGRO57 is also planned with a 2020 target date for the start of operation. Detailed design studies should start in 2013.