Still Not Risk Free
Even if everything went perfectly, this plan would still carry long term consequences. The energy and radiation released could interfere with future space travel. Generations from now, astronauts might unknowingly fly through leftover clouds of radioactive material.
We also do not fully understand how radioactive waste behaves in space. What if some of it ends up affecting other planets or moons? What if we are not alone in the universe, and our actions disturb something beyond our reach?