As I've learned more, the energy from a single atom is not much. They split nitrogen long before uranium but it didn't really matter. You need the chain reaction of uranium.
From Gemini:
The energy released from a single uranium atom splitting is an infinitesimally tiny fraction of what's needed to even warm a mug of water. You would need the simultaneous fission of approximately 1.96 quadrillion (1,960,000,000,000,000) uranium atoms to heat a single mug of water.
*JFC what's up with the downvotes? Because I used Gemini?