Korean researchers develop technology to predict long-term degradation of spent nuclear fuel storage containers

- Team identifies cause of aluminum alloy strength loss in dry storage containers

- Accelerated 10,000-hour testing enables long-term performance forecasting

A diagram of the KORAD-21 spent nuclear fuel transport and storage container. [Korea Radioactive Waste Agency]

South Korean researchers have developed a technology that can predict in advance how much the internal materials of spent nuclear fuel storage containers will weaken over decades.

The Korea Institute of Materials Science (KIMS) announced Tuesday that a joint research team led by Senior Researcher Lee Jun-ho of its Nuclear Safety Research Division and Professor Ban Chi-beom of Busan National University had identified the cause of long-term degradation in aluminum alloys used inside dry storage containers for spent nuclear fuel, and developed an evaluation technology to predict how the materials' performance will change over decades.

Spent nuclear fuel removed from reactors must be safely managed for an extended period before final disposal. Dry interim storage is a method in which spent fuel is placed in a specialized container and kept without water while residual heat is removed.

Inside the storage containers, structural components such as basket rails and shims support the spent fuel and maintain its arrangement. These parts are exposed to heat over long periods, but once the fuel is loaded they are difficult to inspect or replace directly, making it important to understand the materials' long-term performance in advance.

The 6061-T651 aluminum alloy used as an internal structural material is lightweight and has excellent thermal conductivity, but prolonged exposure to high temperatures can cause its strength and hardness to decline. This occurs through a phenomenon called "overaging," in which the nanoscale precipitates that harden the material grow larger and move farther apart.

The research team conducted accelerated testing by exposing the aluminum alloy to temperatures between 150 and 240 degrees Celsius for up to 10,000 hours.

The team observed that over time the nanoscale precipitates inside the alloy grew larger and the spacing between them widened, reducing the strengthening effect. The researchers also confirmed that these microstructural changes directly lead to measurable declines in strength and hardness.

Senior Researcher Lee Jun-ho (left) of the Korea Institute of Materials Science and Professor Ban Chi-beom of Busan National University. [Korea Institute of Materials Science]

The research team also derived a "time-temperature equivalence relationship," showing that similar degradation states can occur at different combinations of temperature and exposure time. This allowed them to propose a predictive method linking results from short-term, high-temperature accelerated tests to the material changes that would occur in actual long-term storage conditions.

The work opens a path to predicting how the physical properties of internal structural materials will change over extended use — without waiting decades for real-world storage tests.

The findings are expected to help evaluate the long-term safety of materials inside storage containers as South Korea moves to introduce domestic dry interim storage facilities for spent nuclear fuel. The data can also serve as foundational material for time-limited aging analyses (TLAA) and aging management programs (AMP), which analyze and manage performance changes caused by material aging.

"To store spent nuclear fuel safely over the long term, it is important to understand not only the initial performance of internal components but also how the materials change over time," Lee said. "This research is significant in that we have clarified the mechanism by which nanoscale changes lead to actual strength loss, and established a basis for predicting performance changes decades into the future."

The findings were published in the International Journal of Energy Research.

nbgkoo@heraldcorp.com