UNESCO

Beyond a Million Years: why high-level waste still needs shields—and memory

When it comes to high-level waste repositories, the old reassurance—“radioactivity falls back close to 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 or twenty thousand years. 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 dose at the surface of each piece as time rolls on.

A new paper looks squarely at that reality. Rather than only charting dose, 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 you can picture: roughly half a meter to nearly a meter at a million years, depending on the waste and the protection target.

• Spent fuel. For a representative multi-ton package (ignoring any cask shielding), about 67–93 cm of concrete is needed at one million years; after ~2.5 million years, substantial shielding—around 62–87 cm—remains necessary for the very long term.
• Vitrified waste. For a full-size cylinder, about 53–72 cm is needed at one million years. As shorter-lived contributors fade over tens of millions of years, the requirement settles to roughly 17–42 cm, persisting essentially indefinitely.
• Smaller isn’t safer. Even drill cores or fragments (say, 40 cm tall by 10 cm wide) still need shielding on the same order, because near-surface dose depends on what’s inside, not the item’s size.
• Scale matters. In France alone, there will be >50,000 vitrified cylinders. At a million years, unshielded drill cores from this mainstream inventory still translate into ~52–73 cm of required concrete.

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.

So what now?

1. Build for fragments. Don’t just model intact packages; assume cores, partial breaches, and erosion-revealed segments—and assign them shielding, too.
2. Specify the long-lived drivers. Make the deep-time isotopic loadings standard reporting fields, because they determine the shield.
3. 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.
4. 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.

The full article is accessible at https://lnu.diva-portal.org/smash/get/diva2:1989350/FULLTEXT01.pdf.

Referens: Claudio Pescatore (2025), Beyond a million years: Robust radiation shielding for high-level waste. Nukleonika, 70(3): 87-93. https://doi.org/10.2478/nuka-2024-0029