Rule #1: Don't Drop Things in a Nuclear ReactorHow a missing rulebook nearly caused a meltdown.

From the show

It really happened

In 1993, a 130lb piece of a crane fell into an active nuclear reactor. For nine hours, operators hesitated to shut it down because no procedure existed for such an event. This is the story of an incredible oversight at the Wylfa power station, where the lack of a simple instruction—'if a large metal object falls into the core, turn it off'—risked a catastrophe.