Then the robot becomes highly radioactive. What do you do with it then?
Dig out a mountain cavern for the disposal of the highly radioactive waster.
You haul it away to some remote location and let it sit for the next 100,000 years. A desert climate is preferable.
And the equipment you used to haul away the dead robot is also contaminated. You park it with the dead robot.
With current technology, any machine working in the hot zone will have a very short lifetime until the control systems fail (Minutes to Hours). Then it must be pulled out of the way for work to continue. Even steel becomes brittle and shatters after a while.
You will need a lot of single-use robots and disposal vehicles.