Afaik, the fuel cost is a fairly small portion of the cost of reactor produced power.
Hence there is no strong push to reduce fuel costs.
Increased fuel life, to reduce refuelling downtime, would be more attractive. The more serious understanding of what fuel composition it would take to achieve this is beyond me. One could envision thorium getting used to breed U 233, I don't know whether that would extend the fuel life. Some expert might want to contribute and let us know.