Toward the performance assessment of advanced nuclear waste forms: temperature dependence of lanthanide borosilicate glass dissolution

Why safer nuclear waste storage matters

Modern nuclear reactors and future advanced designs can generate electricity without carbon emissions, but they also leave behind intensely radioactive waste that must be isolated from people and the environment for thousands of years. One of the most promising ways to do this is to lock the waste into specially designed glass, then store that glass deep underground. This study asks a simple but crucial question: how does one advanced type of nuclear waste glass behave in hot water over long times, and can we quantify that behavior well enough to trust our models of a future repository?

Locking radioactivity into glass

High-level radioactive waste is not stored as loose powder or liquid. Instead, it is typically melted into a robust glass that holds many different chemical elements in a tangled, solid network. International safety plans rely on several layers of protection: the waste is first immobilized in a durable glass, sealed in strong containers, and finally placed in carefully chosen rock formations deep below ground. To predict how well this system will work over hundreds of thousands of years, scientists build performance assessment models that simulate how quickly radioactive atoms might escape from the glass if water eventually reaches it. These models are only as good as the data fed into them, especially data on how temperature and water chemistry affect glass corrosion.

A new look at an advanced waste glass

The research focuses on lanthanide borosilicate (LaBS) glass, a class of materials designed to hold large amounts of difficult elements such as plutonium, americium, and curium. LaBS glasses are tougher and more heat-resistant than the more common waste glasses used for today’s reactors, and they can safely incorporate higher contents of radioactive metals because their structure already includes many lanthanide elements that absorb neutrons. The authors study a well-characterized sample called AmCm2-19, originally developed to immobilize americium- and curium-rich waste, and compare its behavior in water with a widely used reference glass known as International Simple Glass-1 (ISG-1). Both are exposed to pure water at temperatures from warm (50 °C) to very hot (250 °C) following a standardized durability test.

How heat changes the glass–water reaction

When glass sits in water, some of its building-block atoms slowly move into the liquid. By measuring how quickly key elements such as boron and silicon leave the glass, the team tracks its dissolution rate. For the AmCm2-19 glass, these release rates rise as the water becomes hotter but then level off around 150 °C. This flattening suggests the water has become saturated: it can no longer dissolve more of those elements, and a subtle, protective state is reached, possibly involving a thin alteration layer or new microscopic mineral phases. Interestingly, this advanced LaBS glass saturates the water with far lower concentrations of dissolved elements than the reference glass, pointing to different types of secondary compounds that may form in each system.

Peering into the glass and quantifying its resistance

To obtain numbers that modelers can use, the authors fit their temperature-dependent data to an Arrhenius relationship, which relates reaction rate to temperature. Using only conditions before saturation occurs (50 and 100 °C), they derive activation energies that describe how sensitive the dissolution rate is to temperature. For AmCm2-19, these values are modest, in the range of about 15–25 kilojoules per mole, and similar to those found in a few earlier LaBS compositions. In contrast, more conventional nuclear waste glasses often show much higher activation energies, meaning their reaction rates change more sharply with temperature. The team also studies how different lanthanide elements escape from the glass and finds that lighter lanthanides tend to leach more readily than heavier ones, reflecting how strongly they are held within the glass network.

Checking for hidden damage

Because the tests at high temperature suggest the water becomes saturated, the researchers perform a separate, more extreme experiment aimed at encouraging visible alteration products. They expose a fine powder of the AmCm2-19 glass to hot water at 200 °C for over two weeks, then examine the material with powder X-ray diffraction and electron microscopy. These methods can reveal new crystals or layers that might form on the glass surface. The measurements show only minor changes: a small pre-existing crystalline phase appears to diminish, and no obvious new crystals or thick surface coatings are detected. Elemental mapping of the glass surfaces before and after leaching also shows nearly identical compositions, implying that any protective alteration layer, if present, is extremely thin.

What this means for future waste repositories

From a lay perspective, the key message is that this advanced nuclear waste glass remains quite stable even in very hot water, and its deterioration slows once the surrounding liquid becomes saturated with dissolved components. The study provides some of the first detailed temperature-dependent numbers for how a LaBS glass dissolves, giving safety analysts better tools to predict its long-term behavior underground. While far more compositions and conditions must be explored, this work moves the field closer to waste forms and models that can be trusted to keep radioactivity locked away deep in the Earth for timescales far beyond any human planning horizon.

Citation: McLachlan, J.R., Stanley, D.A., Garcia, J.A. et al. Toward the performance assessment of advanced nuclear waste forms: temperature dependence of lanthanide borosilicate glass dissolution. npj Mater Degrad 10, 44 (2026). https://doi.org/10.1038/s41529-026-00756-1

Keywords: nuclear waste glass, lanthanide borosilicate, geological disposal, glass corrosion, high-level radioactive waste