Fresh PWR fuel is ~4% U-235 and the rest is non-fissile uranium/cladding. ~95% of the potential energy still locked in the “waste” after spending ~2 years in the reactor. Breeder reactors would mean converting greater fraction of this mass into usable energy.

Running PWR core has be at +150 Bar to have +300*C outlet temp - so if something goes wrong it goes wrong like Fukushima. The fuel can stay in the core only until economics say running the plant at less than 100% design power isn’t profitable. Every 18/24 months the plant is needs to shutdown for maintance few a weeks to months. I don’t like PWRs.

“regular, i.e. non-breeder” MSRs that would just use uranium would be a massive improvement - both in safety and efficiency. Heat a massive silo of (secondary coolant) salt to +500*C with MSR, do the reactor repairs while this reserve runs the turbines, resume MSR. The issue is - politics, fear, and too little research in handling molten salts.