Immobilization plays a central role in unbuilding projects that involve unruly toxicity. In the twenty-first century, unbuilding by design has become commonplace as former industrialized facilities are decommissioned and dismantled. While many of these industries have histories of negligent contamination, contemporary regulatory bodies both national and international now routinely seek assurances regarding the safe-guarding of human and other-than-human life.  However, the dynamic qualities of toxic matter pose challenges. Legal frameworks set standards, and monitoring institutions seek to ensure compliance, but many of the contaminants to be disposed of resist containment (Müeller and Nielsen 2023). And perhaps nowhere more obviously than in the nuclear industry, an industry that only recently began to contemplate its own future, and where legacy wastes are not fully documented or understood and the properties of future wastes have yet to be determined.

In the United Kingdom, the first generation of nuclear power stations were built without decommissioning plans. The civil nuclear energy program of the Cold War era emerged from the state preoccupation with the production of plutonium for the manufacture of nuclear weapons. As the current director of one of these early stations recently commented to me: “they just assumed that the wastes would disappear.”

Contemporary nuclear waste management programs effectively re-engineer the radioactive materials, either by changing the chemical make-up to reduce volatility, or by changing the form, from gas or liquid to solids. The most common immobilization practices, especially for the lower-level wastes, follow the popular industry mantra “if in doubt grout”!  More expensive techniques with greater stabilization include vitrification and/or ceramic encapsulation. In all cases the modification of the waste forms changes the energetic force of the radioactive particles. It slows them down and creates the potential for them to degrade in situ.

Nevertheless, the question of how to ensure the integrity of the immobilized forms over hundreds of thousands of years remains. In the United Kingdom, the decision was taken to support deep geological disposal, a choice that has been widely adopted internationally. The fundamental promise of a Geological Disposal Facility (GDF) is that it will isolate the highest-level radioactive wastes by burying them deep underground at a depth of between 200-1,000m. The GDF is conceptualized as a multi-barrier system. Once rendered solid, the wastes will be placed in copper or steel cannisters, and the cannisters in turn will be buried deep in the host rock, surrounded by additional barriers of impermeable bentonite clay. The aim is to create an engineered technology of passive safety whereby the combined layers will ensure that no further human care is needed once the materials are sealed deep underground. The scientists focus on the relationship between the ongoing mobilities of the wastes and the heterogeneous environmental conditions of their layered containment. They work to understand the groundwater flows, and the ways in which the porosity and the chemistry of the rock, the bentonite, the concrete and the metal containers might enhance or limit the movement of the radionuclides.

Geologists are enrolled to identify “suitable” host rocks to form the ultimate and most enduring barrier. In their search for suitable rocks geologists look for a combination of qualities that include an optimal balance of stability, strength, and impermeability. They also look for evidence of prior disturbance from which they project the probability of future change: fault lines or fissures that might diminish rock strength or channel water; seismic activity; and proximity to underground resources that might otherwise attract the attention of future generations. They calculate the depth of previous ice ages, and the vulnerability of the surface facilities and entrance shafts or tunnels that need to be secure for around two hundred years until the construction and operational phases are complete and the GDF is definitively closed. However, it is the geological time horizon that provides the ultimate assurance. If the rock does not move or allow movement for millions of years, then even the highest-level radioactive wastes will decay and thus effectively disappear. After all, a few hundred thousand years barely registers on the geological timescale.

However, while the design of the GDF holds out the promise of disappearance, the challenges of its material realization highlight the ongoing necessity of managing multiple very apparent material relations in the more immediate future. The unbuilding of a nuclear power station requires the building of new and extensive infrastructures of disposal: interim storage, treatment plants, containerization technologies, exploratory surveys and bore holes, transport links, access ways and disposal vaults, the recruitment, training, and retention of a skilled workforce, and the political and social alliances needed to secure the funding, the regulatory permissions and the social acceptance required to secure a site. Key to immobilization is a change of speed. But immobilization is relative and relational. It fails when leaks occur not only within the material structures but also in the social fabric that produces and sustains them (Harvey 2025).

In this collection we are interested in thinking with unbuilding as an open concept oriented to the disruption of normative theorizations of the future, especially the notion that the future can be designed into being as the product of human intentionality. The GDF is no exception. Its intrinsic stability can be forecast with respect to the very low risk of seismic or glacial disturbance. The integrity of the rock can be analyzed, and the uncertainties of heterogeneous formations can be avoided. Human intrusion on the other hand remains a probability. There are no semiotic solutions for communication with future populations living beyond the scope of contemporary imaginations. It is highly unlikely that archaeologists and/or explorers from the distant future would be deterred by warning signs, even if they were intelligible. And it is not beyond the bounds of possibility that the unbuilding of a GDF could serve to produce materials for an as yet unknown purpose. Thus, while immobilization supports projects for the containment and disposal of radioactive wastes, it also draws attention to the unknowability of future environmental rhythms and relations on which the technological promise of disappearance ultimately depends.