Interferes with the solid state electronics in the robot.
So build one with tubes. Or 'valves' as the foreigners say.
And the components no doubt are already hardened/shielded to the maximum extent practical. It would be feasible to implement the robot mechanical functions using hydraulics, but the sensors and cameras are another matter. That unprecedented level of radiation (within the scope of man’s activities) is going to do funky things to a broad range of materials: solid, liquid, and gaseous.