Fuel Rod (MOX)
MOX (mixed oxide) fuel rods are the way of the future! Despite lasting only half as long as uranium fuel rods (10,000 seconds vs. 20,000), they are capable of much more power generation. A MOX fuel rod becomes more efficient as the reactor heat (percentage, not absolute) increases, up to 5x efficiency at 99.9% max heat. Because of this property, a MOX fuel rod can reach reactor efficiencies of up to 30, although it needs amazing cooling because any escaping heat might cause slight issues.
MOX fuel rods behave rather more sedately in the fluid reactor, outputting normal efficiency at core heat <= 50% and 2x efficiency for core heat > 50% (without any Heat-Capacity Reactor Plating installed, that is; it's actually a threshold of 5000 heat).
Just like their uranium cousins, MOX fuel rods can be crafted into dual and quad varieties.