Major challenges for P&T are the specification, fabrication and performance validation of transmutation fuels and targets. In addition to MA content and composition impact on P&T, it is necessary to have a comprehensive understanding of the fuel performance and behavior under a wide range of irradiation conditions and burn-ups. This understanding should encompass such effects as helium release, high-temperature gradients and cladding properties. Some of the current fuel type options for the different strategies discussed in this section are given in Table 17.6 (extracted from Ref. 58).

Notes:

*SFR: sodium-cooled fast reactor; LFR: liquid metal-cooled fast reactor; GFR: gas-cooled fast reactor; ADS: accelerator driven (sub-critical) system tASS: austenitic stainless steel; FMS: ferritic martensitic steel; ODS: oxide dispersion steel.

Issues related to different types of fuels for homogeneous recycling (oxide, metal, nitride, carbide) are being actively investigated and international comparisons are underway.

As for IMF, the main advantage of their utilization is the potential to destroy Pu and MAs more effectively than with the fuels containing U because this avoids further Pu production during irradiation. These fuels have been envisaged as ADS fuels and for the targets of the heterogeneous recycling mode (see Section 17.3).

In general, the criticality, radiation protection and cooling requirements, due to the presence of large amounts of isotopes with high decay heat and neutron production by spontaneous fission (both even-mass Pu isotopes and MAs) in the transmutation fuel, will determine the production capacity of a fabrication facility. In this respect the neutron production issue discussed in Sections 17.2 and 17.3 is a crucial one. In this respect, if one excludes the case of very high build-up of Cf-252 (see Section 17.2), curium is the most problematic element for fabrication plants. It is a powerful source of spontaneous neutrons and has a decay heat of 2.8 W/g from its main isotope, Cm-244, so that its handling is problematic. In terms of impact curium is followed by Pu-238, whose accumulation during recycling also raises similar issues, although to a lesser extent than curium. The next, in terms of difficulties, is Am-241. Appropriate (thick) neutron and у ray protection are needed, implying remote handling. The transport of fuel assemblies and in-reactor handling operations are also affected by these thermal and radiological constraints which, of course, would significantly raise costs.