UNESCO

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?

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 a standard reporting of the deep-time isotopic loadings, 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. Or that should be the ambition.
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.

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

Cornelius Holtorf attended the Webinar “Archaeological Cultural Heritage in the UNESCO Mandate” organized by the Polish National Commission for UNESCO, the UNESCO-UNITWIN Network on Culture in Emergencies and the University of Poznan (4 April 2025).

Cornelius Holtorf contributed to the consultation of the Swedish Commission for UNESCO concerning Sweden’s future collaboration with UNESCO (24 April 2025).

Cornelius Holtorf, gave an invited talk on “The Climate Heritage Paradox” for ca 90 participants in the national conference Heritage Horizons: Pathways to the Future by the Heritage Council of Ireland, held in Dublin, Ireland (1 May 2025).

Anders Högberg presented the research programme InKuiS – Innovative Cultural Entrepreneurship in Collaborative Co-creative Research, including the future-related project Earth Logic Design, at a conference organised by the Småland in Academy organised at Linnaeus University in Växjö (16 May 2025).

Cornelius Holtorf participated in a webinar of the “The Path to MONDIACULT 2025” series which is part of the preparations for MONDIACULT 2025, the UNESCO World Conference on Cultural Policies and Sustainable Development (19 May 2025). The 2025 edition of MONDIACULT in Barcelona will be pivotal in ensuring that culture is recognized as a standalone goal in the future United Nations development strategy.

Cornelius Holtorf contributed to a Consultation of the Heritage Adapts to Climate Alliance (HACA) on the UNFCCC process to develop indicators for measuring progress in adapting heritage sites and cultural practices to climate change (30 May 2025).

Cornelius Holtorf attended digitally a High level panel on future generations entitled “A Tribunal for Future Generations” held at the Hamburg Sustainability Conference 2025 and involving, among others, Guy Ryder (Under-Secretary-General, UN Executive Office) and Sophie Howe (The World’s first Future Generations Commissioner, for Wales) (2 June 2025).

Cornelius Holtorf and Anders Högberg held an informal meeting on heritage processes and futures literacy with Dr Anselm Tiggemann of the BGE Bundesgesellschaft für Endlagerung in Berlin to discuss future collaborations (9 June 2025).

Cornelius Holtorf attended digitally parts of The International Seminar on Heritage Interpretation and Presentation for Future Generations co-organized by the Institute of International Studies at Waseda University, Tokyo, Japan; the ICOMOS International Scientific Committee on Interpretation and Presentation of Cultural Heritage Sites, and the Our World Heritage initiative (14 June 2025).

Cornelius Holtorf ran a Future Workshop on “World heritage Southern Öland 25 years in the future” for 20+ students taking part in a course entitled “The World Heritage site of Southern Öland” at Ölands Folkhögskola, Skogsby, Öland, Sweden (18 June 2025).

Cornelius Holtorf arranged and participated in an exploratory meeting for future collaboration with Professor Tatsuyoshi Saijo, Kyoto University of Advanced Science (who has been developing Future Design) and Christine Kavazanjian, UNESCO Paris (representing UNESCO’s unit on Foresight and Futures Literacy), (19 June 2025).

Cornelius Holtorf took part in a meeting of the External Advisory Committee of the Flagship Initiative Transforming Cultural Heritage at the University of Heidelberg, Germany (20 June 2025).

Artikel i tidskriften Byggnadskultur (som är svenska byggnadsvårdsföreningens tidskrift). In Swedish.

In May, Anders Högberg was invited as keynote speaker at the National Library of Sweden. The invitation came from their Department for Research and Collection Management, which hosted a joint staff day. Högberg presented his research on heritage processes as futures-making practices. In his presentation Anders emphasised that we need new knowledge in order to rethink futures in novel ways. The discussion that followed on the presentation, largely focused on how we can create change to achieve this, what opportunities it might bring, but also which challenges we need to address in order to succeed.

National Library of Sweden. Photo Maria Aho