Nucleons: $235 + 1 = 236 = 144 + 89 + 3$. ✓ Protons: $92 = 56 + 36$. ✓ The products have greater binding energy per nucleon than uranium, so the total rest mass decreases; the mass defect appears as energy via $E = \Delta mc^2$, mostly as fragment kinetic energy.

Heavy nuclei need a high neutron-to-proton ratio for stability ($N/Z \approx 1.55$ for uranium); mid-mass stable nuclei need less ($\approx 1.3$). Fission fragments inherit uranium's ratio and are therefore neutron-rich for their size, decaying by $\beta^-$ emission (often in chains) towards stability.

Challenges: some products remain hazardous for thousands of years (long half-lives), and the waste generates heat requiring active cooling initially; secure isolation from groundwater and society is needed throughout. Strategy: interim cooling ponds followed by vitrification and deep geological repositories in stable rock formations (also acceptable: reprocessing to recover usable fuel).