Self-repairing materials may soon make nuclear reactors a whole lot safer

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Washington, March 26 (ANI): As a result of research by Los Alamos National Laboratory scientists, self-repairing materials within nuclear reactors may one day become a reality.

Los Alamos researchers report a surprising mechanism that allows nanocrystalline materials to heal themselves after suffering radiation-induced damage.

Nanocrystalline materials are those created from nanosized particles, in this case copper particles.

Nanocrystalline materials consist of a mixture of grains and the interface between those grains, called grain boundaries.

When designing nuclear reactors or the materials that go into them, one of the key challenges is finding materials that can withstand an outrageously extreme environment.

In addition to constant bombardment by radiation, reactor materials may be subjected to extremes in temperature, physical stress, and corrosive conditions.

Exposure to high radiation alone produces significant damage at the nanoscale, as it can cause individual atoms or groups of atoms to be jarred out of place.

Each vagrant atom becomes known as an interstitial.

The empty space left behind by the displaced atom is known as a vacancy. Consequently, every interstitial created also creates one vacancy.

As these defects build up over time in a material, effects such as swelling, hardening or embrittlement can manifest in the material and lead to catastrophic failure.

Therefore, designing materials that can withstand radiation-induced damage is very important for improving the reliability, safety and lifespan of nuclear energy systems.

Because nanocrystalline materials contain a large fraction of grain boundaries - which are thought to act as sinks that absorb and remove defects - scientists have expected that these materials should be more radiation tolerant than their larger-grain counterparts.

Recent computer simulations by the Los Alamos researchers describe the never-before-observed phenomenon of a "loading-unloading" effect at grain boundaries in nanocrystalline materials.

This loading-unloading effect allows for effective self-healing of radiation-induced defects.

Using three different computer simulation methods, the researchers looked at the interaction between defects and grain boundaries on time scales ranging from picoseconds to microseconds.

On the shorter timescales, radiation-damaged materials underwent a "loading" process at the grain boundaries, in which interstitial atoms became trapped-or loaded-into the grain oundary.

Under these conditions, the subsequent number of accumulated vacancies in the bulk material occurred in amounts much greater than would have occurred in bulk materials in which a boundary didn't exist.

After trapping interstitials, the grain boundary later "unloaded" interstitials back into vacancies near the grain boundary.

In doing so, the process annihilates both types of defects - healing the material. (ANI)

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