Three people died testing a prototype, possibly a murder/suicide:
https://en.m.wikipedia.org/wiki/SL-1
This was the last time someone died in a reactor accident in the US
Edit: they also installed one reactor at the Army's secret ICBM ice lair in Greenland:
https://en.m.wikipedia.org/wiki/Project_Iceworm
Three people died testing a prototype, possibly a murder/suicide: https://en.m.wikipedia.org/wiki/SL-1 This was the last time someone died in a reactor accident in the US
Edit: they also installed one reactor at the Army's secret ICBM ice lair in Greenland: https://en.m.wikipedia.org/wiki/Project_Iceworm
This was the last time someone died in a reactor accident in the US... so far!