>Feynman had discovered that the Y-12 Plant was storing uranium nitrate solution enriched in U-235 in drums holding 300 to 3,000 gallons. After performing some calculations, the young physicist determined that the drums were placed in potentially unsafe arrangements in a number of buildings.[0]

Looks like fluids again, not warheads.

https://exploreoakridge.com/how-a-26-year-old-physicist-may-...