Steven Krantz (2017):
Freshman composition teachers at Penn State like to tell their students of the engineers at Three Mile Island, who wrote to the governor of Pennsylvania three times to tell him that a nuclear disaster was in the making at their power plant. Their prose was so garbled that the poor governor could not determine what in the world they were talking about. The rest is history.
Googling I couldn't find much similar to the above claim. The closest I could find was this New York Times (1979) story: "Engineers Warned Builder of Danger Year Before Three Mile Island Accident". This story states merely that
Two engineers for the company that supplied the nuclear reactor that broke down at Three Mile Island said today that they had warned their superiors a year earlier
This story has nothing about any engineers writing to the governor or having "garbled" prose.
Edit: See also Mathes (1984, "Good Engineering + Poor Communication = Three Mile Island"). I can't find the full text, but from the abstract:
The accident at the Three Mile Island nuclear power plant resulted from a communication failure. ... The memo was sent to the wrong audience and was written in such a way as to preclude action. To a significant extent, the lack of effective response to his memorandum can be traced to his misinterpretation of the audiences for the memorandum. The resulting accident suggests that, no matter how good the engineering, it is not finished until organizations make decisions and take action. This requires effective communication.
(But again, there's no indication that anyone ever wrote to the Governor, much less "three times".)
