When compounds in spent nuclear fuel break down, they can release radioactive elements into the ground and water. Scientists know that one fuel compound, neptunium dioxide, reacts with water, but they do not fully understand the process. This new study found that neptunium tends to dissolve where grains of the material come together, and larger grains are less likely to dissolve.
Scientists devised specialized X-ray mapping techniques. They determined that boundaries associated with regions where atoms are closely packed together most readily resist cracking. This analysis revealed that when a crack encounters such a boundary, it’s deflected to a less direct path and crack growth is slowed.