Testing the shelf-life of nuclear reactors

Testing the shelf-life of nuclear reactors

NEWS mobility. Theoretical calculations suggest great potential while experimental evidence for one compound revealed charge carrier mobilities as la...

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mobility. Theoretical calculations suggest great potential while experimental evidence for one compound revealed charge carrier mobilities as large as 6.1 cm2 V 1 s 1 and current on/off ratios of 107, the team reports. In efforts to explain the nature of stability in these compounds, researchers at University of California Los Angeles led by Ken Houk carried out DFT (density functional theory) calculations. Calculations from the Houk group corroborate experimental

Materials Today  Volume 17, Number 8  October 2014

results and indicate that bistetracene is about 5 orders of magnitude (about 70 000 times) less reactive than pentacene in Diels–Alder reactions with [60]fullerene [Y. Cao, et al. J. Am. Chem. Soc. 136 (2014) 10743–10751]. The researchers’ relatively straightforward synthetic scheme for making these compounds bodes well for the construction of even larger polyacenes in this class and they are now working on building such molecules with relatively high numbers of

Clar aromatic sextets for further testing in high performance organic electronic devices. ‘‘Further studies include structure–property relationships of even larger conjugated cores,’’ Briseno told us. ‘‘We will also employ these stable building blocks to synthesize polymer semiconductors. These compounds will find use in large-area, roll-to-roll manufacturing of electronic devices.’’ David Bradley

Testing the shelf-life of nuclear reactors Researchers at the University of Michigan, Ann Arbor, Los Alamos National Laboratory, Idaho National Laboratory, Idaho Falls and TerraPower based in Bellevue, Washington, have demonstrated the power of high-energy beams of charged particles (ions). The ions can rapidly and consistently damage samples of ferritic-martensitic steel, the material used in certain nuclear reactor components. The significance of the result is that the breakdown closely replicates that seen when high-energy neutrons from a nuclear reactor interact with the material – damage accrues in a matter of days, rather than decades. The structural components of advanced reactors such as the sodium fast reactor and the traveling wave nuclear reactor must be able to withstand the extreme levels of radioactivity from the fission reaction itself at temperatures well above 400 8C. Unfortunately, standard tests of such components are expensive, require increasingly rare test reactors and test periods that are

impractical. Moreover, the samples themselves also become radioactive making subsequent studies and examination time consuming and expensive. Nevertheless, understanding how these structural components are affected by radiation at the microscopic level is critical to building long-lasting, robust and safe nuclear reactors. To demonstrate the proof of principle with ion beams instead of conventional reactor irradiation, the team of researchers preloaded reactor components of ferriticmartensitic steel with atoms of helium gas, to simulate alpha particles. They irradiated the samples with an ion beam from a particle accelerator at 5 million electronvolts energy and a temperature of 4608C for several hours, and after which used transmission electron microscopy (TEM) to characterize the damage caused by the energetic ions penetrating the steel and observed microscopic holes (voids), dislocations and precipitates within the

steel – none of which were present before ion irradiation. Comparing this ion-beam damage with that seen in actual components of the same batch of steel used in a sodium fast reactor during the period 1985–1992, it was found that the types of defects (as well as their sizes and numbers) caused by neutron bombardment from the nuclear reaction to be closely reproduced by that with the ion beam experiments. Lead author Gary Was hopes that their research will help develop ‘‘a stronger understanding of how to use ion irradiation to emulate neutron irradiation to enable the rapid development of new materials for advanced reactors as principal sources of clean energy’’. With additional work, a rapid, standardized experimental procedure may be developed for the routine evaluation of materials, facilitating the creation of more resilient components for nuclear reactors of the not-so-distant future. David Bradley

Squishy robots could revolutionize search-and-rescue Researchers have developed a phase-changing material made from wax and foam that could lead to a new generation of low-cost robots able to switch between hard and soft states to move through small gaps. The innovative material could find uses in building deformable surgical robots that can pass through the body without causing any damage, or squeeze through the rubble of buildings looking for survivors during search-and-rescue operations. With growing interest in soft robotics and shape-shifting systems, much research 368

Three 3D-printed soft, flexible scaffolds.

is going into the most effective way to achieve components of variable strength and stiffness. Since many existing robotic systems are comprised of rigid components, which limit their movement, the team wanted to develop components that allow robots to better conform to the environment and achieve significant changes in shape and volume to improve their capabilities. To produce their material, the scientists from MIT, the Max Planck Institute and Stony Brook University, in collaboration with a robotics company, coated low-cost