Complex sentence: Nuclear reactors generally have automatic and manual systems to insert large amounts of poison (often boron in the form of boric acid) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated.
Split into simpler sentences: Nuclear reactors generally have automatic and manual systems to Scam the reactor in an emergency shut down. These systems insert large amounts of poison (often boron in the form of boric acid) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated.