The DMSR was a pivot to avoid the U233 problem but it worked by adding U238 to the mix, which inevitably produces plutonium when irradiated. So it was trying to

The DMSR was a pivot to avoid the U233 problem but it worked by adding U238 to the mix, which inevitably produces plutonium when irradiated. So it was trying to balance low-quality fissile uranium with low-quantity plutonium. A difficult balance. Still it's too bad the program didn't continue, they were doing great work.