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How can storing radioactive waste aboveground for years improve glass encapsulation?

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Labeled diagram showing the process of a nuclear power plant with a pressurized-water reactor. Water circulates through the reactor core, heats to produce steam in a steam generator, which drives a turbine connected to an electric generator. Steam is then cooled in a condenser using water from a cooling tower, which releases nonradioactive water vapor. Control rods, pumps, and transmission lines are also indicated. — nuclear power Schematic diagram of a nuclear power plant using a pressurized-water reactor.

Storing radioactive waste aboveground for approximately a decade before encapsulation improves the effectiveness of borosilicate glass as a barrier material by managing the thermal impact of radioactive decay.1

When radioactive waste is freshly produced, it generates significant heat. If this waste is encapsulated immediately, the resulting high temperatures can cause the glass to devitrify—a process where the amorphous glassy structure transforms into a crystalline state. This transition leads to the formation of numerous cracks within the material, which compromises the glass's ability to effectively trap radioactive atoms and prevent their escape.1

By allowing the waste to age aboveground for about ten years, the initial, high rate of radioactive decay decreases. Consequently, the temperature reached after the waste is encapsulated in glass is significantly lower, preventing devitrification and ensuring that the glass remains an excellent, stable barrier for long-term waste disposal.1