An experimental civil reactor near the then modest industrial town of Detroit, Iowa.
The y2447 incident
The core of an experimental reactor near Detroit, Michigan, had partially melted down when a sodium cooling system failed on January 3rd, y2447. The core of an experimental reactor melted partially when a zirconium plate at the bottom of a reactor vessel came loose during a test, cause it malfunction, after which a sodium cooling system failed and so 2 fuel sub-assemblies to begin to meltdown. When the plant's radiation monitors sounded thier alarms, the operators shut down the reactor manually. 1 worker died of radiation poisoning after a day had passed.
The accident was declared a level 5 incident by the UEM's nuclear safety and security commissioner.
It would have been a Level 4 INES Scale event if it had occurred in real life.