Posts Tagged ‘Oak Ridge National Laboratory’
Wednesday, November 20, 2013 @ 04:11 PM gHale
By identifying fundamental forces that change plant structures during pretreatment processes used in the production of bioenergy, there may be more effective ways to convert woody plant matter into biofuels.
Pretreatment subjects plant material to extremely high temperature and pressure to break apart the protective gel of lignin and hemicellulose that surrounds sugary cellulose fibers.
“While pretreatments are used to make biomass more convertible, no pretreatment is perfect or complete,” said Department of Energy’s Oak Ridge National Laboratory’s (ORNL) Brian Davison, who was a coauthor of a research study and paper on the subject.
“Whereas the pretreatment can improve biomass digestion, it can also make a portion of the biomass more difficult to convert,” he said. “Our research provides insight into the mechanisms behind this ‘two steps forward, one step back’ process.” Also, pretreatment is the most expensive stage of biofuel production.
The team’s integration of experimental techniques including neutron scattering and X-ray analysis with supercomputer simulations revealed unexpected findings about what happens to water molecules trapped between cellulose fibers.
“As the biomass heats up, the bundle of fibers actually dehydrates — the water that’s in between the fibers gets pushed out,” said ORNL’s Paul Langan. “This is very counterintuitive because you are boiling something in water but simultaneously dehydrating it. It’s a really simple result, but it’s something no one expected.”
This process of dehydration causes the cellulose fibers to move closer together and become more crystalline, which makes them harder to break down.
In a second part of the study, the researchers analyzed the two polymers called lignin and hemicellulose that bond to form a tangled mesh around the cellulose bundles. According to the team’s experimental observations and simulations, the two polymers separate into different phases when heated during pretreatment.
“Lignin is hydrophobic so it repels water, and hemicellulose is hydrophilic, meaning it likes water,” Langan said. “Whenever you have a mixture of two polymers in water, one of which is hydrophilic and one hydrophobic, and you heat it up, they separate out into different phases.”
Understanding the role of these underlying physical factors — dehydration and phase separation — could enable scientists to engineer improved plants and pretreatment processes and ultimately bring down the costs of biofuel production.
“Our insight is that we have to find a balance which avoids cellulose dehydration but allows phase separation,” Langan said. “We know now what we have to achieve — we don’t yet know how that could be done, but we’ve provided clear and specific information to help us get there.”
Wednesday, October 30, 2013 @ 07:10 PM gHale
There could soon be new types of nuclear fuel pellets that would be safer in the event of a nuclear disaster.
New materials could end up encasing uranium-bearing fuel as an alternative to zirconium alloys, which have seen use as the outer layer of nuclear fuel pellets for the last 50 years, said a team of scientists from the University of Tennessee (UT) and Oak Ridge National Laboratory (ORNL), who will present their work at the AVS 60th International Symposium and Exhibition in Long Beach, CA.
Using sophisticated computer analyses, the UT and ORNL team identified the positive impact of several possible materials that exhibit resistance to high-temperature oxidation and failure, on reactor core evolution, thereby buying more time to cope in the event of a nuclear accident.
“At this stage there are several very intriguing options that are being explored,” said Steven J. Zinkle, the Governor’s Chair in the Department of Nuclear Engineering at the University of Tennessee and Oak Ridge National Laboratory. There is evidence that some of the new materials would reduce the oxidation by at least two orders of magnitude.
“That would be a game-changer,” he said. The materials examined include advanced steels, coated molybdenum and nuclear-grade silicon carbide composites (SiC fibers embedded in a SiC matrix).
The next step, he added, involves building actual fuel pins from these laboratory-tested materials and exposing them to irradiation inside a fission reactor. Once they perform as desired, the new fuel concepts would likely end up tested in a limited capacity in commercial reactors to then enable larger deployment possibilities.
Though it would take years before any new fuel concepts end up used commercially, given the rigorous and conservative qualification steps required, Zinkle said, these new materials may eventually replace the existing zirconium alloy cladding if they prove to be safer.
The typical core of a nuclear power plant uses the heat generated by fission of uranium and plutonium in fuel rods to heat and pressurize water. Steam then generates to drive steam turbines for electricity production. Water continuously circulates as a coolant to harness the thermal energy from the fuel and to keep the core from overheating.
The cooling pumps are a critical part of the reactor design because even when a nuclear reactor shuts down, the power it generates from radioactive decay of fission products remains at 1 percent of its peak for hours after shutdown. Given that nuclear power plants generate a staggering sum of energy under their nominal operating conditions (~4 GW of thermal energy), even one percent power levels after shutdown prove substantial. That’s why it’s essential to have cool water circulating continuously even after the shutdown occurs. Otherwise you risk overheating and ultimately melting the core – like leaving a pot boiling on the burner.
That’s basically what happened at Fukushima. On March 11, 2011, engineers at the plant managed to initially safely shut down the plant following a massive earthquake, but then a large tsunami knocked out the backup generators running the water pumps an hour later. What followed were explosions associated with hydrogen generated from the reduction of steam during high temperature oxidation of core materials, and releases of radioactive fission products. The accident displaced the local population and will take years and require a significant cost to clean-up.
Fukushima has had a profound impact on the safety culture of the industry, said Zinkle. Despite the fact that not a single U.S. nuclear power plant was unsafe or shut down in the wake of the accident, the Nuclear Regulatory Commission has issued new requirements to enhance their safety, including increasing the requirements for backup power generation on site.
Monday, August 27, 2012 @ 05:08 PM gHale
Knowing the position of missing oxygen atoms could be the key to cheaper solid oxide fuel cells with longer lifetimes.
That means new microscopy research could enable scientists to map these vacancies at an atomic scale.
Although fuel cells hold promise as an efficient energy conversion technology, they have yet to reach mainstream markets because of their high price tag and limited lifespans.
Overcoming these barriers requires a fundamental understanding of fuel cells, which produce electricity through a chemical reaction between oxygen and a fuel. As conducting oxygen ions move through the fuel cell, they travel through vacancies where oxygen atoms used to be. The distribution, arrangement and geometry of such oxygen vacancies in fuel cell materials should affect the efficiency of the overall device, researchers said.
“A big part of making a better fuel cell is to understand what the oxygen vacancies do inside the material: How fast they move, how they order, how they interact with interfaces and defects,” said Department of Energy’s Oak Ridge National Laboratory’s (ORNL) Albina Borisevich. “The question is how to study them. It’s one thing to see an atom of one type on the background of atoms of a different type. But in this case, you want to see if there are a few atoms missing. Seeing a void is much more difficult.”
ORNL scientists used scanning transmission electron microscopy to determine the distribution of oxygen vacancies in a fuel cell cathode material below the level of a single unit cell. The team verified its findings with theoretical calculations and neutron experiments at the lab’s Spallation Neutron Source.
“Even though the vacancy doesn’t generate any signal in the electron micrograph, it’s still a big disturbance in the structure,” Borisevich said. “You can see that the lattice expands where vacancies are present. So we tracked the lattice expansion around vacancies and compared it with theoretical models, and we were able to develop a calibration for this type of material.”
By providing a means to study vacancies at an atomic scale, the ORNL technique will help inform the development of improved fuel cell technologies in a systematic and deliberate fashion, in contrast to trial and error approaches.
Beyond its relevance to applications in fuel cells and information storage and logic devices, ORNL coauthor Sergei Kalinin said the team’s research is also building a bridge between two scientific communities that traditionally have had little in common.
“From my perspective, it is physics marrying electrochemistry,” Kalinin said. “The idea is that vacancies are important for energy, and vacancies are important for physics. The materials that physicists like to study are exactly the same as the materials used for fuel cells, and unless we understand how vacancies behave at interfaces, ferroic domain walls, and in thin films, we will not be able to fully appreciate the physics of these systems.”
Tuesday, May 15, 2012 @ 03:05 PM gHale
There is now a new way to accurately measure gas bubbles in pipelines.
In the end, it all comes down to safety as the ability to measure gas bubbles in pipelines is vital to the manufacturing, power and petrochemical industries.
In the case of harvesting petrochemicals from the seabed, warning of bubbles present in the harvested crude is crucial because otherwise when these bubbles come up from the seabed (where pressure is very high) to the surface where the rig is, the reduction in pressure causes these bubbles to expand and could cause a “blow out.” A blow out is the sudden release of oil and/or gas from a well and issues with the blow out preventer were key in Deepwater Horizon oil spill in the Gulf of Mexico in 2010.
Currently, the most popular technique for estimating the gas bubble size distribution (BSD) is to send sound waves through the bubble liquid and compare the measured attenuation of the sound wave (loss in amplitude as it propagates) with that predicted by theory.
The key problem is the theory assumes the bubbles exist in an infinite body of liquid. If in fact the bubbles are in a pipe, then the assumptions of the theory do not match the conditions of the experiment. That could lead to errors in the estimation of the bubble population.
There is now a new method, which takes into account that bubbles exist in a pipe, said Professor Tim Leighton from the Institute of Sound and Vibration Research at the University of Southampton, who is leading a project team.
Leighton and his team started the work as part of an ongoing program to devise ways of accurately estimating the BSD for the mercury-filled steel pipelines of the target test facility (TTF) of the $1.4 billion Spallation Neutron Source (SNS) at Oak Ridge National Laboratory (ORNL), one of the most powerful pulsed neutron sources in the world.
The research explores how measured phase speeds and attenuations in bubbly liquid in a pipe might invert to estimate the BSD (independently measured using an optical technique). This new technique, appropriate for pipelines such as TTF, gives good BSD estimations if the frequency range is sufficiently broad.
“The SNS facility was built with the expectation that every so often it would need to be shut down and the now highly radioactive container of the mercury replaced by a new one, because its steel embrittles from radiation damage,” Leighton said. “However, because the proton beam impacts the mercury and generates shock waves, which cause cavitation bubbles to collapse in the mercury and erode the steel, the replacement may need to be more often than originally planned at full operating power. Indeed, achieving full design power is in jeopardy.
“With downtime associated with unplanned container replacement worth around $12 million, engineers at the facility are considering introducing helium bubbles, of the correct size and number, into the mercury to help absorb the shock waves before they hit the wall, so that the cavitation bubbles do not erode the steel. Oak Ridge National Laboratory (ORNL) and the Science and Facilities Research Council (Rutherford Appleton Laboratory, RAL) commissioned us as part of their program to devise instruments to check that their bubble generators can deliver the correct number and size of bubbles to the location where they will protect the pipelines from erosion.
“This paper reports on the method we devised half-way through the research contract. It works, but just after we designed it the 2008 global financial crash occurred, and funds were no longer available to build the device into the mercury pipelines of ORNL. A more affordable solution had to be found, which is what we are now working on. The original design has been put on hold for when the world is in a healthier financial state. This has been a fantastic opportunity to work with nuclear scientists and engineers from ORNL and RAL.”
Monday, May 14, 2012 @ 02:05 PM gHale
A carbon nanotube sponge that can soak up oil in water with incredible efficiency is now in the works.
Carbon nanotubes, which consist of atom-thick sheets of carbon rolled into cylinders, have captured scientific attention because of their high strength, potential high conductivity and light weight. However, producing nanotubes in bulk for specialized applications often faced limitations because of difficulties in controlling the growth process as well as dispersing and sorting the produced nanotubes. Not anymore.
That is because Bobby Sumpter at the Department of Energy’s (DOE’s) Oak Ridge National Laboratory (ORNL) was part of a multi-institutional research team that set out to grow large clumps of nanotubes by selectively substituting boron atoms into the otherwise pure carbon lattice.
Sumpter and Vincent Meunier, now of Rensselaer Polytechnic Institute (RPI), conducted simulations on supercomputers, including Jaguar at ORNL’s Leadership Computing Facility, to understand how the addition of boron would affect the carbon nanotube structure.
“Any time you put a different atom inside the hexagonal carbon lattice, which is a chicken wire-like network, you disrupt that network because those atoms don’t necessarily want to be part of the chicken wire structure,” Sumpter said. “Boron has a different number of valence electrons, which results in curvature changes that trigger a different type of growth.”
Simulations and lab experiments showed the addition of boron atoms encouraged the formation of “elbow” junctions that help the nanotubes grow into a 3-D network.
“Instead of a forest of straight tubes, you create an interconnected, woven sponge-like material,” Sumpter said. “Because it is interconnected, it becomes three-dimensionally strong, instead of only one-dimensionally strong along the tube axis.”
Further experiments showed the team’s material, which is visible to the human eye, is extremely efficient at absorbing oil in contaminated seawater because it attracts oil and repels water.
“It loves carbon because it is primarily carbon,” Sumpter said. “Depending on the density of oil to water content and the density of the sponge network, it will absorb up to 100 times its weight in oil.”
The material’s mechanical flexibility, magnetic properties, and strength lend it additional appeal as a potential technology to aid in oil spill cleanup, Sumpter said.
“You can reuse the material over and over again because it’s so robust,” he said. “Burning it does not substantially decrease its ability to absorb oil, and squeezing it like a sponge doesn’t damage it either.”
The material’s magnetic properties, a result of the team’s use of an iron catalyst during the nanotube growth process, means a magnet can easily control it or remove it in an oil cleanup scenario. This ability is an improvement over existing substances used in oil removal, which usually stay behind after cleanup and can degrade the environment.
The experimental team submitted a patent application on the technology through Rice University. A research paper entitled “Covalently bonded three-dimensional carbon nanotube solids via boron induced nanojunctions,” is also available.
The research team included researchers from ORNL, Rice University; Universidade de Vigo, Spain; RPI; University of Illinois at Urbana-Champaign; Instituto de Microelectronica de Madrid, Spain; Air Force Office of Scientific Research Laboratory; Arizona State University; Universite Catholique de Louvain, Belgium; The Pennsylvania State University; and Shinshu University, Japan.
Thursday, March 22, 2012 @ 03:03 PM gHale
Computer systems of the agency in charge of America’s nuclear weapons stockpile are “under constant attack” and face millions of hacking attempts daily, said officials at the National Nuclear Security Administration (NNSA).
The agency faces cyber attacks from a “full spectrum” of hackers, said Thomas D’Agostino, head of the agency.
“They’re from other countries’ [governments], but we also get fairly sophisticated non-state actors as well,” he said. “The [nuclear] labs are under constant attack, the Department of Energy is under constant attack.”
A spokesman for the agency said the Nuclear Security Enterprise experiences up to 10 million “security significant cyber security events” each day.
“Of the security significant events, less than one hundredth of a percent can be categorized as successful attacks against the Nuclear Security Enterprise computing infrastructure,” the spokesman said, which puts the maximum number at 1,000 daily.
The agency wants to beef up its cyber security budget from $126 million in 2012 to $155 million in 2013 and has developed an “incident response center” responsible for identifying and mitigating cyber security attacks.
In April of last year, the Department of Energy’s Oak Ridge National Laboratory was successfully hacked and several megabytes of data stolen, D’Agostino said. Internet access for lab workers ended up disconnected following the breach.
Adam Segal, a cyber security expert with the Council on Foreign Relations, said it’s likely that a majority of those 10 million daily attacks are automated bots “constantly scanning the Internet looking for vulnerabilities.”
“The numbers are kind of inflated on that front,” Segal said, adding that it’s extremely unlikely that hackers would be able to remotely launch a nuclear warhead, because those systems are “airgapped” or disconnected from standard Internet systems. But the Stuxnet computer worm, discovered in 2010, widely spread to supposedly-secure uranium enrichment plants in Iran, Indonesia and India, shutting those systems down.
The NNSA said they are not aware of any viruses or malware that could remotely launch a nuclear warhead, but the “Stuxnet worm is a very real example of how sophisticated malware can cause physical damage to industrial systems.”
Segal said Stuxnet was a lesson — no matter how secure a computer system is, it can always suffer a breach.
“Stuxnet showed that airgapping is not a perfect defense,” Segal said. “Even in secure systems, people stick in their thumb drives, they go back and forth between computers. They can find vulnerabilities that way. If people put enough attention to it, they can possibly be penetrated.”
D’Agostino said with the agency facing so many hacking attempts, its employees have to remain vigilant.
“All it takes is one person to let their guard down,” he said. “This is going to be, in my view, an ever-growing area of concern.”
Segal said any successful hackers would likely have to have an intimate knowledge of the programming languages used by the Department of Energy.
“There’d probably have to be a state-based actor behind it. You have to understand a lot about the systems,” he said. “Hacking into the Department of Energy and looking for nuclear secrets — how to build a bomb — is probably much easier than trying to take over a bomb or a launch code, and probably of more interest to the Russians or the Chinese or the Iranians.”
Friday, September 9, 2011 @ 11:09 AM gHale
There is a new battery under development that could increase power, energy density and safety while dramatically reducing charge time, and have an impact on the smart grid.
Titanium dioxide creates a highly desirable material that increases surface area and features a fast charge-discharge capability for lithium ion batteries, according to a team of researchers from the Oak Ridge National Laboratory. Compared to conventional technologies, the differences in charge time and capacity are striking.
“We can charge our battery to 50 percent of full capacity in six minutes while the traditional graphite-based lithium ion battery would be just 10 percent charged at the same current,” said Hansan Liu, of Oak Ridge’s Chemical Sciences Division.
Compared to commercial lithium titanate material, the ORNL compound also boasts a higher capacity – 256 vs. 165 milliampere hour per gram – and a sloping discharge voltage that is good for controlling state of charge. This characteristic combined with the fact oxide materials are extremely safe and long-lasting alternatives to commercial graphite make it well-suited for hybrid electric vehicles and other high-power applications.
The results could also have special significance for applications in stationary energy storage systems for solar and wind power, and for smart grids. The titanium dioxide with a bronze polymorph also has the advantage of being potentially inexpensive, Liu said.
At the heart of the breakthrough is the novel architecture of titanium dioxide, named mesoporous TiO2-B microspheres, which features channels and pores that allow for unimpeded flow of ions with a capacitor-like mechanism. Consequently, a lithium ion battery that substitutes TiO2-B for the graphite electrode charges and discharges quickly.
“Theoretical studies have uncovered that this pseudocapacitive behavior originates from the unique sites and energetics of lithium absorption and diffusion in TiO2-B structure,” Liu and his team wrote in a paper entitled “Mesoporous TiO2-B Microspheres with Superior Rate Performance for Lithium Ion Batteries.”
Paranthaman noted the microsphere shape of the material allows for traditional electrode fabrication and creates compact electrode layers, said Parans Paranthaman also of the Oak Ridge Chemical Sciences Division. He also added the production process of this material is complex and involves many steps, so more research remains to determine whether it is scalable.