The key P&T feasibility issues are, it appears, found in fuel cycle performance. Table 17.4 presents two key parameters — decay heat and neutron production after post-irradiation cooling — which largely determine the ease of the fuel fabrication step. Data are shown for some of the transmutation strategies considered previously, comparing these with standard PWR fuel.

The MA/Pu ratios in Table 17.4 correspond to different TRU management strategies. The MA/Pu ratio of -0.1 is used because it corresponds approximately to the TRU composition of PWR fuel at discharge. The ratio MA/Pu -1 corresponds to the case of a fuel with a high MA content, which could be loaded in a dedicated transmuter (FR or ADS).

In the case of homogeneous recycling in PWRs and FRs, the large difference in the neutron source at fabrication is essentially due to the impact of the 252Cf spontaneous neutron fission (-1012 n/g/s) contribution, due to the different mechanisms of its build-up in the two different types of spectrum (see Fig. 17.2). Since 252Cf is a very powerful neutron emitter (see Table 17.1), it results in an unacceptably high neutron source at fuel fabrication. This is one of the factors that suggests that grouped TRU transmutation in thermal reactors should be avoided.6

Moreover, the strong increase in the decay heat and neutron source values observed for a) all low CR critical FRs with high MA/Pu loading ratios, b) TRU target heterogeneous recycling with more than -10% MAs in the target and c) U-free loaded ADSs, can also result in very significant penalties on the associated specific fuel cycle (spent fuel handling, fuel fabrication, etc.). However, it should be noticed that the specific fuel cycle associated with those systems will be only a limited part of the overall fuel cycle, as will be discussed later (Sections 17.4.1 and 17.4.2).