{"id": "card_n_22f6cb5bf619", "kind": "note", "title": "Fission — 82 terajoules in a kilogram", "body": "Split uranium-235 and each atom yields ~200 MeV. Scaled by Avogadro's number (exact\nsince 2019), sealed: 82 TJ per kilogram — 2.737 million times coal at 30 MJ/kg: https://narrowhighway.com/s/8a5e89ab13bc499f39240c64360d90c34a65a291c91c73fcac4fc976131b17c5 .\nThat ratio is why a reactor refuels in years, not trainloads per day, and why a few kilograms\nmattered so terribly in 1945. The chain reaction (each fission freeing 2–3 neutrons),\ncriticality, and moderation are engineering on top of measured cross-sections; which\nfragments appear, and their decay heat, are ENSDF tables — nature measured, never derived\nin one line. The energy arithmetic above, though, is receipts.", "source": {"label": "Concordance assay — 2026-07-09", "url": "https://narrowhighway.com/s/8a5e89ab13bc499f39240c64360d90c34a65a291c91c73fcac4fc976131b17c5", "ref": "nuclear_dig", "authority_tier": "engine_derived"}, "shelf": "science", "box": "nuclear", "bands": ["fission", "uranium-235", "200 mev", "energy density", "82 tj/kg", "reactor", "chain reaction", "criticality"], "connections": [], "author": "engine", "created_at": "2026-07-10T01:19:38.918200+00:00", "updated_at": "2026-07-10T01:19:38.918200+00:00", "visibility": "public", "lifecycle_stage": "public", "volatility": "permanent", "surface": "secular", "metrics": {"paperclips_count": 0, "helpful_count": 0, "not_helpful_count": 0, "cite_count": 0, "walks_through_count": 0, "flagged_count": 0}, "source_hash": "3e364c9a6c27e933dbee8e95df4c6bdab6f5655f35590dc3e6f92d425973b8d8"}