Half a Meter to a Meter: The Deep-Time Reality of Nuclear Waste
2025-08-21
Why high-level waste still needs shields — and memory beyond a million years
When it comes to high-level waste repositories, the old reassurance—“radioactivity falls back close to or below natural levels”—is misleading. Yes, if you total up all the radioactivity in a repository and compare it to the original ore, the sum may look modest after ten to a hundred thousand years, depending on waste type. But people (and animals) don’t meet sums. They meet things: individual containers, cores, and fragments that concentrate radioactivity. What matters—ethically and practically—is the radiation dose at the surface of each piece as time rolls on.

A new new paper looks squarely at that reality. Rather than only computing dose, a concept for radiation specialists, it asks a tangible question: how thick must a shield be to meet modern protection limits—not just now, but at one million years and beyond? Using concrete as the reference, the answer comes in units anybody can picture: roughly 50 to 90 centimeters at a million years, depending on the waste and the protection target.
- Namely, at one million years,
- Spent fuel about 67 to 93 centimeters of concrete is needed for a representative multi-ton package (ignoring any cask shielding)
- Vitrified waste about 53 to 72 centimeters is needed for a full-size cylinder.
- Beyond a million years, since uranium-238 lasts for billions of years, it sets the shielding needs to a practically constant non-zero value. In the absence of containers, concrete thickness requirements range between 17 and 42 cm for vitrified waste cylinders, and 62 to 87 cm for spent fuel.
- Smaller isn’t safer. Even drill cores (say, 40 cm tall by 10 cm wide) or fragments still need shielding on the same order, because near-surface dose depends on what’s inside, not the item’s size. At a million years, unshielded drill cores from these mainstream inventory still translate into ~48–67 cm of required concrete for vitrified waste; 46-72 cm for spent fuel drill cores.
- Scale matters. Numbers per item are only half the story. Program scale multiplies these requirements: for example, Sweden plans roughly 6,000 spent‑fuel canisters. In France, there will be >50,000 vitrified waste cylinders.

What this means in human terms
- Heritage, not waste alone. If descendants encounter these materials—by curiosity, drilling, erosion, or chance—they won’t face a vanishing hazard but an enduring one, beyond legal timeframes and planning horizons. Our commitment to protect future people “to levels comparable to today” becomes concrete—literally—in centimeters of real shielding.
- Justice and foresight. Thinking “per item” reframes responsibility. Are we designing containers—and contingencies—that keep each piece safe, including broken pieces? Are we documenting the long-lived contents that set deep-time dose? We should.
- Design humility. Landscapes move; encounters may occur. The ethical stance is not to promise a perfect fortress forever, but to equip future people with buffers that still work: robust, intelligible, maintainable shields—and the memory provisions (markers, archives, institutional handovers) to keep that knowledge alive. Also, acknowledge that danger never really fades away.
So what now?
- Build for fragments. Don’t just model intact packages; assume cores, partial breaches, and erosion-revealed segments—and assign them shielding, too.
- Specify the long-lived drivers. Make a standard reporting of the deep-time isotopic loadings, because they determine the shield.
- Design the message with the material. If safety demands 50–90 cm at a million years, our markings and archives should be designed to last—and be rediscoverable—on comparable horizons. Or that should be the ambition.
- Expand the lens. Apply similar analyses to long-lived “medium-level” wastes that carry significant long-term gamma issues.
Takeaway: this isn’t a new fear; it’s a clearer ethic. We owe the future not only sealed vaults and clever signs, but credible buffers—thicknesses you can measure with a ruler—matched to how matter behaves over time. The shield is not a metaphor; it’s a promise we can make, and keep.
Further reading
Claudio Pescatore, Beyond a million years: Robust radiation shielding for high-level waste Nukleonika, 70(3): 87-93, is accessible at
https://lnu.diva-portal.org/smash/get/diva2:1989350/FULLTEXT01.pdf

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