Saturday, November 17, 2012

Advanced Materials and Design Tools for NextGen Nuclear Reactors

Nuclear reactors take a lot of punishment in the way of heat and sub-atomic particles. More durable materials would allow reactors to have longer lifetimes -- reducing overall costs and increasing profits.

Nano-engineered materials have the potential to resist damage from heat and irradiation for longer periods of time than conventional materials currently used.
In order to build the next generation of nuclear reactors, materials scientists are trying to unlock the secrets of certain materials that are radiation-damage tolerant. Now researchers at the California Institute of Technology (Caltech) have brought new understanding to one of those secrets—how the interfaces between two carefully selected metals can absorb, or heal, radiation damage.

... During nuclear irradiation, energetic particles like neutrons and ions displace atoms from their regular lattice sites within the metals that make up a reactor, setting off cascades of collisions that ultimately damage materials such as steel. One of the byproducts of this process is the formation of helium bubbles. Since helium does not dissolve within solid materials, it forms pressurized gas bubbles that can coalesce, making the material porous, brittle, and therefore susceptible to breakage.

Some nano-engineered materials are able to resist such damage and may, for example, prevent helium bubbles from coalescing into larger voids. For instance, some metallic nanolaminates—materials made up of extremely thin alternating layers of different metals—are able to absorb various types of radiation-induced defects at the interfaces between the layers because of the mismatch that exists between their crystal structures.

... in a metallic nanolaminate material, small helium bubbles are able to migrate to an interface, which is never more than a few tens of nanometers away, essentially healing the material. "What we're showing is that it doesn't matter if the bubble is within the interface or uniformly distributed—the pillars don't ever fail in a catastrophic, abrupt fashion," Greer says.

She notes that the implanted helium bubbles—which are described in the Advanced Functional Materials paper—were one to two nanometers in diameter; in future studies, the group will repeat the experiment with larger bubbles at higher temperatures in order to represent additional conditions related to radiation damage.

In the Small paper, the researchers showed that even nanopillars made entirely of copper, with no layering of metals, exhibited irradiation-induced hardening. _R&D Mag
Advanced computational design tools provide another way in which future generations of nuclear reactors can be made safer and more durable:
... many of the highly complex physical phenomena that affect reactor performance and safety remained somewhat of a mystery. It wasn't possible to "see" what was taking place inside this very harsh environment—until now.

Researchers are using some of the world's most powerful computers at the Argonne Leadership Computing Facility to take a leap forward in nuclear reactor design, analysis and engineering. Their efforts could shave millions of dollars off the cost of reactor design, development, preparation for licensing, and construction.

Researchers have developed a suite of computer tools, called the Simulation-based High-efficiency Advanced Reactor Prototyping (SHARP) Reactor Performance and Safety Simulation Suite, that numerically mimic and allow researchers to "see" the physical processes that occur in a nuclear reactor core. SHARP users can build complex virtual reactor models, which can run the reactor through a variety of operational or accident scenarios that would be impractical or impossible in the real world. _PO
US national energy labs utilise some of the most advanced hardware and software computer tools in the world -- including the ORNL Titan supercomputer, the world's most advanced. As mentioned here previously, the Titan will be used to design better nuclear reactors, along with a few other energy related tasks.



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