Some people talk about "dropping it into the sun", but the energy required is approximately more like "lifting it all the way up there". It takes a lot of kW to push a dump truck full of nuclear waste up to six or seven miles a second, and if something goes wrong, all that energy tends to go into spreading everything around the landscape.

The explosion of a Delta II rocket in 1997 shows the amount of energy released:

https://www.youtube.com/watch?v=z_aHEit-SqA

Because you really don't want a rocket full of concentrated nuclear waste to blow up on the launch pad or in the atmosphere.

Because it might not make it there.