A jumper in the wrong place or an ice-cube relay being removed can ultimately have similar effects. Ban fingers too?
A properly designed system has one set of PLCs for primary control, and a separate one as a supervisory system to ensure basic functionality always is online. The secondary system wouldn't control pump speed, but it would ensure coolant is flowing of the system is on.
It would be relatively easy to keep a nuclear power plant from operating at peak efficiency, but unless IKEA or WalMart have started making reactors forcing more serious effects remotely is nearly impossible.