Oklo, the Earth's Two-billion-year-old only Known Natural Nuclear Reactor (2018)

Original Article ↗ Hacker News Discussion ↗

Information gaps and use of LLMs vs Wikipedia

  • Several commenters note the IAEA article is light on quantitative details (ore size, total energy, timing, observability).
  • Wikipedia is cited as a much better technical source (e.g., ~100 kW average thermal output over hundreds of thousands of years).
  • Some defend using tools like Claude/Perplexity with web search for structured explanations and better discovery, others say “just use a search engine” and warn against unverified LLM outputs.
  • One analogy: LLMs are like lossy compression of knowledge, so you shouldn’t expect precise, reference-grade answers.

Uranium enrichment, early Earth, and cosmic origin

  • Discussion of why natural reactors were possible 1.7–1.8 billion years ago: higher natural U‑235 fraction then, plus water moderation and special ore geometry.
  • People link the current 0.720% U‑235 ratio to nucleosynthesis in supernovae and radioactive decay timescales.
  • It’s noted that “fresh” supernova debris has more U‑235 than U‑238; over billions of years U‑235 decays faster, flipping that ratio.
  • Debate over whether all Uranium on Earth came from a single or many supernovae; consensus in-thread leans toward multiple events well-mixed in the proto-solar cloud.

Oklo and nuclear power advocacy/skepticism

  • Some see “100 kW for hundreds of thousands of years, naturally contained” as a powerful pro‑nuclear talking point.
  • Pro‑nuclear comments emphasize dense, stable, low day‑to‑day risk power, and argue that economic models undervalue very long-lived assets.
  • Skeptical comments stress high capital costs, increasing lifecycle costs (decommissioning, waste), and low-probability but extremely expensive accidents (e.g., Fukushima cleanup scale).

Waste burial and long‑term safety

  • Oklo is cited as evidence that fission products can remain underground for billions of years; skeptics counter that groundwater interactions occurred and “safe now” took 2 billion years.
  • Long exchange on deep geological repositories:
    • Pro side: burying waste ~0.5–1 km deep in stable bedrock with no aquifer makes leakage extremely implausible; some repositories (e.g., in Finland, US defense waste sites) already exist.
    • Skeptical side: real-world failures (flooded or unstable mines, mishandled barrels), transport risks, need for continuous safety culture, political/economic corner-cutting, and unknown long-term geology.
    • Also a distinction between “can be done safely” vs “will be done safely under real institutions.”

Discovery, measurements, and classification

  • The slight depletion (0.717% vs ~0.720%) mattered because arms-control accounting required precise U‑235 balance, prompting investigation.
  • Commenters are curious about the measurement uncertainty and enrichment impact of such a small delta.
  • Clarification that “natural nuclear reactor” here means fission on Earth’s crust, not stellar fusion.

Miscellaneous

  • Lighthearted speculation about ancient or time-traveling civilizations causing Oklo.
  • Reference to Oklo the startup as a cleverly named nuclear company that hasn’t yet operated a reactor.