Scientists at Lawrence Berkeley National Laboratory and the Univ. of California at Berkeley conducted compression tests of copper specimens irradiated with high-energy protons, designed to model how damage from radiation affects the mechanical properties of copper. By using a specialized in situ mechanical testing device in a transmission electron microscope at the National Center for Electron Microscopy, the team could examine—with nanoscale resolution—the localized nature of this deformation. (Scales in nanometers, millionths of a meter) |
Nuclear power is a major component of our nation’s long-term clean-energy future,
but the technology has come under increased scrutiny in the wake of Japan’s recent Fukushima disaster. Indeed, many nations have
called for checks and “stress tests” to ensure nuclear plants are operating
safely.
In the United States,
about 20% of our electricity and almost 70% of the electricity from
emission-free sources, including renewable technologies and hydroelectric power
plants, is supplied by nuclear power. Along with power generation, many of the
world’s nuclear facilities are used for research, materials testing, or the
production of radioisotopes for the medical industry. The service life of
structural and functional material components in these facilities is therefore
crucial for ensuring reliable operation and safety.
Now scientists at Berkeley Lab, the Univ. of California
at Berkeley, and Los Alamos National Laboratory have devised a nanoscale
testing technique for irradiated materials that provides macroscale
materials-strength properties. This technique could help accelerate the
development of new materials for nuclear applications and reduce the amount of
material required for testing of facilities already in service.
“Nanoscale mechanical tests always give you higher strengths than the
macroscale, bulk values for a material. This is a problem if you actually want
use a nanoscale test to tell you something about the bulk-material properties,”
said Andrew Minor, a faculty scientist in the National Center
for Electron Microscopy (NCEM) and an associate professor in the materials
science and engineering department at UC Berkeley. “We have shown you can
actually get real properties from irradiated specimens as small as 400 nm in
dia., which really opens up the field of nuclear materials to take advantage of
nanoscale testing.”
Berkeley Lab scientist Andy Minor (left) and Peter Hosemann have devised a nanoscale testing technique for irradiated materials to provide macroscale materials-strength properties. This technique could help accelerate the development of new materials for nuclear applications, while reducing the amount of material required for testing facilities already in service. |
In this study, Minor and his colleagues conducted compression tests of
copper specimens irradiated with high-energy protons, designed to model how
damage from radiation affects the mechanical properties of copper. By using a
specialized in situ mechanical
testing device in a transmission electron microscope at NCEM, the team could
examine—with nanoscale resolution—the nature of the deformation and how it was
localized to just a few atomic planes.
Three-dimensional defects within the copper created by radiation can block
the motion of one-dimensional defects in the crystal structure, called
dislocations. This interaction causes irradiated materials to become brittle,
and alters the amount of force a material can withstand before it eventually
breaks. By translating nanoscale strength values into bulk properties, this
technique could help reactor designers find suitable materials for engineering
components in nuclear plants.
“This small-scale testing technique could help extend the lifetime of a
nuclear reactor,” said co-author Peter Hosemann, an assistant professor in the
nuclear engineering department at UC Berkeley. “By using a smaller specimen, we
limit any safety issues related to the handling of the test material and could
potentially measure the exact properties of a material already being used in a
40-year-old nuclear facility to make sure this structure lasts well into the
future.”
Minor adds, “Understanding how materials fail is a fundamental mechanistic
question. This proof of principle study gives us a model system from which we
can now start to explore real, practical materials applicable to nuclear
energy. By understanding the role of defects on the mechanical properties of
nuclear reactor materials, we can design materials that are more resistant to
radiation damage, leading to more advanced and safer nuclear technologies.”
