Irradiation experience on prototype fast reactor (PFR) Pu/UO 2 fuel now extends to over 64000 pins covering a range of cladding and wrapper materials of relevance to the commercial fast reactor (CFR) with a leading sub-assembly at 16 per cent burn-up. With consistent high-power running achieved the forward loading of the PFR core is being planned with fuel and materials targeted for 20 per cent burn-up and beyond and the first sub-assemblies of these designs are already under irradiation.