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[Sandia Lab News]

Vol. 53, No. 13        June 29, 2001
[Sandia National Laboratories]

Albuquerque, New Mexico 87185-0165    ||   Livermore, California 94550-0969
Tonopah, Nevada; Nevada Test Site; Amarillo, Texas

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Microfluidic Pac-Man-like device interacts with blood cells Working on tomorrow's nuclear plant designs Interns research wireless networks

Sandia creates mechanized microfluidic device

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By Neal Singer

Inexpensive silicon microteeth that open and close like jaws to harmlessly deform red blood cells have been developed at Sandia.

The patent-pending microdevices, because of their constant munching, bear a strong resemblance to the computer game hero Pac-Man as their upper teeth slide back and forth in piston-like action across microchannels to momentarily trap unaware red blood cells against the lower teeth.

"We've shown we've created a micromachine that can interact at the scale of cells," says Sandia researcher Murat Okandan (1749).

The capability could add an extra tool to the growing capabilities of microfluidic devices, a billion-dollar industry. Microfluidic devices typically are limited in capabilities to examination of materials. But, says Murat, "We're trying to create conditions in which, on a massive scale, cells may be altered as well as examined."

The prototype device offers the possibility of considerable mechanical intervention at the cellular level because it operates rapidly and is so small that many units could operate in parallel in a small space. Ten complete units can fit in an area smaller than a household electric plug prong, and each microdevice can puncture 10 cells per second.

An immediate goal of Murat, who developed the device with Paul Galambos, Sita Mani, and Jay Jakubczak (all 1749), is to see whether the masticated red blood cells absorb fluorescent material.

If the material is readily absorbed, it means that Sandia researchers have created the first example of a continuous flow, mechanical cellular-membrane disrupter ever reported.

Enter, the needle

A near-time goal is to replace the microteeth with a hollow silicon needle now in development. The needles would rapidly inject DNA, RNA, or proteins (including drug molecules) into living cells at precise points of their anatomies and in large numbers, possibly changing the course of a disease or restoring lost functions.

Even if punctures have not occurred, "We've created a demonstration tool with very flexible technology that we hope will enable many designs and concepts," says Murat. "This device itself may generate considerable interest from the agriculture or genetic engineering marketplaces."

The cells punctured do not need to be blood cells but could be, say, stem cells -- cells able to change, given suitable direction -- possibly by gene implantation -- into many of the tissues of the human body, says Murat.

In terms of the number of living cells altered, the method potentially compares favorably with electrical or chemical techniques used to open cell walls for drug insertion; either of the latter methods kills large numbers of cells.

Also, microelectromechanical insertion is less expensive than these other methods. The devices -- powered by electrostatic actuators -- and the microchannels in which they function are so cheap to fabricate that, when mass-produced, a device could be thrown away after it is used once.

The depth and precise position of molecular insertion would be controlled by researchers who have located the cell's "sweet spot" by observing effects of the insertions.

Hundreds or thousands of units assembled in parallel, puncturing cells at the rate of 10 a second, could create a sizeable supply of enhanced material.

Why the device could be built

Inexpensive fabrication of the device became possible for two reasons: the capabilities of the Sandia MEMS SUMMiT V fabrication process -- a sequence of deposition, patterning, and etching -- to create complicated micromachines, and the use of silicon nitride to build insulated microchannels in that process.

An effective insulator is needed because microchannels of silicon, an electrical conductor, would short out electrodes that create electrical and magnetic fields used to analyze or manipulate the contents of the channel. By fabricating channels instead out of a version of silicon nitride, the researchers were able to avoid these problems.

Silicon nitride's other advantages are that it is transparent, allowing researchers optical examination of the experiments, and that it is a material commonly used in microelectronic device fabrication -- an important consideration.

Although the microdevices are fabricated step by step with lithographic processes well known to the semiconductor industry, the ability to easily make this complicated device is credited to the Sandia SUMMiT V fabrication process, which allows five-level micromachine construction to be quickly designed and implemented. The SUMMiT V process is the only one available worldwide that can construct five-level micromachine devices.

Another invisible ingredient in the mix was the expert MESA (Microsystems and Engineering Sciences Applications complex) fabrication teams that physically created the device. -- Neal Singer

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Sandia researchers helping define technology for tomorrow's nuclear power plants

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By John German

To envision the nuclear power plant of tomorrow, just look at the 103 plants operating in the US today.

Owners of current plants are petitioning the Nuclear Regulatory Commission (NRC) either to extend their current operating licenses by 20 years or to add capacity to existing plant sites.

"It can take 10 years or more to build a plant, and no utility has requested a new plant for two decades," says Paul Pickard, Manager of Advanced Nuclear Concepts Dept. 6424. "Although significant operational improvements have been made, basic nuclear energy technology hasn't advanced much since the 1970s."

So for the next 10 to 20 years, he says, proposed new nuclear power plants are likely to look like advanced versions of today's water-cooled designs, with significant engineering and safety improvements. Other new plants could be adaptations of designs drawn up during the 1970s and '80s, such as gas-cooled pebble bed reactors.

Despite the lack of progress on the construction front, Sandia's behind-the-scenes R&D programs in nuclear power safety and advanced reactor technology are improving how today's nuclear power plants operate and helping define what plants might look like 25, 50, and 100 years from now.

New reactor concepts

"For the first time in more than a decade, significant research on new reactor concepts is beginning," says Tom Blejwas, Director of Nuclear and Risk Technologies Center 6400. "Fortunately, at Sandia we've kept our research capabilities alive primarily through continuing work in reactor safety for the NRC.

"Also, with the support of some Sandia VPs, about two years ago we began focusing our program development efforts on a rebirth of nuclear energy, and, consequently, we are well positioned for the next nuclear era," he says. "So the mere discussion of new nuclear power plant construction is exciting for us."

The first signs of new opportunities for Sandia have been small programs supported by Sen. Pete Domenici and sponsored by DOE's Nuclear Energy Research Initiative (NERI), as well as power plant optimization studies under DOE's Nuclear Energy Plant Optimization Program, says Tom. Sandia is participating in these growing programs while continuing its traditional reactor safety work, he says.

Understanding safety issues

The ongoing research in nuclear power plant safety, funded primarily by the NRC, provides experimental data to help regulators and operators predict and understand failures in containment vessels as well as computer modeling tools such as the MELCOR software developed at Sandia now in use around the world. (For more information, see www.sandia.gov/media/ NewsRel/NR2000/pccvtest.htm, www.sandia.gov/media/NewsRel/ NR2000/vessel.htm, and www. sandia.gov/media/NewsRel/NR2000/melcor.htm.)

Such reactor safety research could become increasingly important as aging takes its toll on older recertified power plants originally licensed for 40 years, and as the nation explores alternative reactor designs, says Paul.

NERI-funded research at Sandia, for example, is seeking to create self-diagnosing plant equipment that helps operators, with the aid of sensors and software modeling tools, predict how and when components such as valves, cables, and concrete might fail. (Contact: Felicia Duran, 6410)

(Programs involving shipping container performance, spent fuel storage, seismic analysis, fire risk assessments, risk-informed regulatory processes, and other technology areas also have contributed to the Labs' continued nuclear energy programs. Many of these contributions will be covered in future Lab News articles.)

Reducing investment risk

Meanwhile, interest in the US for new nuclear power plants is growing. But potential investors are wary of the high level of uncertainty and investment risk associated with plant construction.

Sandia is part of a multi-agency team looking for ways to reduce the risk of building new plants. The three-year project is funded by NERI and led by Duke Engineering.

Each plant is different, so regulatory certifications are tedious and unpredictable and can cause costly labor standdowns and procurement delays, says Gary Rochau, Manager of Modeling & Analysis Dept. 6415.

Sandia's role in the NERI project is to identify the leading risk factors that cause uncertainties in new plant design, procurement, construction, installation, and evaluation, then develop software analysis tools that help plant designers reduce the uncertainties.

"A tool could tell investors whether to expect a capital cost of $1 billion plus or minus a few million rather than $1 billion plus $1 billion or minus $100,000," says Gary. "It's taking a systems-level look at project management and finding ways to reduce risk, reduce cost, and reduce the time it takes to get a new plant on line."

Designing by analysis

So far the Sandia team has identified some important risk factors and has defined a method to put those factors into a software tool that will model the complicated set of considerations that determine risk.

Such a tool may help plan a construction project so that the regulatory issues are resolved before construction workers arrive, says Gary, or set up the procurement schedule so that pre-certified parts are delivered from the factory to the site. It could lend credibility to the notion that plant designs be modularized or standardized so they're alike from a regulatory standpoint, or to help choose one design over another.

"Software tools could tell us whether and by how much these changes would reduce time, cost, and risk," he says.

Another NERI project team led by Vince Luk (6420) has begun to develop a software tool that will model the physics of reactor pressure vessel designs. It is the first step toward a "design by analysis" approach that could one day speed up regulatory certifications for new plant designs, says Gary.

Defining the future plant

But investors in the next generation of newly designed nuclear power plants, perhaps 30 to 50 years out, envision utopian plants that meet several general criteria: inherent or passive safety, proliferation resistance, high efficiencies, long fuel burn times, minimized waste streams, multiple uses, and fuel sustainability. (See "High ideals for future nuclear power plants" at left.)

High efficiency metal- or gas-cooled reactors, pebble bed reactors, and breeder reactors -- such as those demonstrated or in use in other countries -- may meet many of the criteria, says Paul.

Sandia has studied safety and engineering issues associated with each of these reactor types, and some of that research continues in support of the DOE "Generation IV" program to evaluate options for next-generation, advanced nuclear power plants.

For example, Sandia is conducting an LDRD-funded study on the feasibility of highly efficient, passively safe, high-temperature gas reactors, says Paul. Such systems take advantage of the inherent design characteristics of the reactor to achieve safety and efficiency, minimizing the need for additional complex safety systems.

"You can't keep adding layers of engineered systems and have the plants remain cost competitive," he says. "Next-generation plant designers should ask 'what's the most robust and simplest way to do this and how can we get the cost down without compromising safety?'"

Fission batteries

Labs researchers also are developing new, futuristic concepts for generating nuclear power that represent major departures from current nuclear energy technology and that would meet many of the criteria.

One concept, called Direct Energy Conversion, seeks to generate electricity from fission without first boiling water. (In a boiling water reactor common in the US today, heat from fission reactions in the reactor core converts water to steam, the pressurized steam drives a turbine, and the turbine's rotational energy drives a generator. See illustration at left.)

As part of a NERI-funded project, a Sandia-led team has developed three concepts for direct energy conversion "fission batteries" that produce electrical current directly from fission. Essentially, positively charged heavy atoms and electrons released during fission reactions in the fuel are separated and collected by electrodes, creating a usable voltage.

This separation, a big technical challenge, says Gary, might be accomplished either by directing differently charged particles in opposite directions using magnetic fields (borrowed from Sandia's pulsed power research) or by separating differently charged fragments using charged mesh filters.

The result is a self-contained, current-producing ball, tube, or chamber with an anode and a cathode. Some of the concepts, such as the grapefruit-size ball called a Magnetically Insulated Fission Electric Cell, are potentially mass manufacturable, can be stacked together into arrays that could produce perhaps 60 megawatts of electricity, and theoretically are capable of 60-percent conversion efficiencies. A cell the size of a golf ball might produce six times the energy of a D-cell battery.

"The basic physics behind these ideas was demonstrated in the 1950s and 60s, but recent advances in technology could make them practical," says Gary.

"We're now building engineering models to see how much power we can get out of each one," he says. "By August we are to down-select one concept for NERI. But none of these ideas is bad, so we'll look at using them each in different applications."

Seeking a limitless energy source

Although uranium potentially represents a larger energy resource than fossil fuel reserves, ultimately, even uranium is a finite resource, reminds Paul. In part because of the abundance of fuel, fusion has long been considered the ultimate nuclear energy source.

A 30-year international R&D program in fusion energy has explored magnetic confinement fusion and inertial confinement fusion approaches, but each candidate technology has presented researchers with formidable technical challenges.

Sandia's favored approach to fusion energy, based on a scaled-up version of the Labs' Z machine, likewise has its challenges, but many of the challenges are in the engineering, rather than the physics, arena.

"We've shown with our Z accelerator that the physics is on course for demonstration of fusion," says Gary.

"We believe we can contain the explosion. We believe we can get the energy densities that are needed. So it's an engineering problem but a big one."

An accelerator that could rapidly repeat high-yield pulsed fusion of deuterium and tritium would represent an essentially limitless supply of energy for mankind, he says. (Deuterium and tritium are heavy isotopes of hydrogen. Deuterium is abundant in nature and tritium can be manufactured by the power plant.)

Palo Verde times two

One LDRD-funded partnership among Centers 6400, 1600, and 14100, the University of Wisconsin, UC Davis, UC Berkeley, the University of New Mexico, and General Atomics seeks ways to feasibly accomplish cheap, repetitive pulsed power quickly enough to provide uninterrupted electricity, including the need for mass-manufactured target assemblies. (Gary Rochau, 6415)

Another LDRD project seeks to develop a recyclable transmission line, which along with the target assemblies would be destroyed with each shot. (Steve Slutz, 1674)

Labs researchers envision a ring of 12 scaled-up Z-style accelerators each popping off one pulse every 10 seconds to generate the electricity, with a target distribution area in the center to rapidly deliver mass-produced target inserts. The entire plant might take up an area the size of the Palo Verde nuclear plant near Phoenix and would produce as much as six gigawatts of electricity (twice the Palo Verde output). Its primary byproduct would be tritium, a short-lived radioisotope and a primary fuel component for the plant.

"If this worked, it would be clean, there would be no long-lived radioactive waste, and you can't make bombs out of tritium alone," says Gary. "We would have more fuel than we could ever use."

"That's the ultimate nuclear power plant," adds Paul. "A fusion power plant is a long way out on the horizon, and there are of course major hurdles, but this approach provides a promising alternative path to achieving the fusion energy goal." -- John German

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Sandia interns begin to research wireless networks

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By Nancy Garcia

Participants in the Embedded Reasoning Institute have seen the future, and that future is wireless.

Six upper-division students have begun a summer internship in the new institute to explore wireless networks of computers so small, they can be "worn" as easily as a cell phone or personal data assistant, or PDA, (such as a Palm Pilot). The students will investigate design and development of these small, computerized embedded systems connected by wireless networks.

The research includes work on the wireless hardware as well as development of software that uses artificial intelligence features to learn and reach decisions.

"The students are really excited about it," says Christine Yang (8920), who coordinates the institute. Fellow mentors are Rob Armstrong (8920), Nina Berry (8920), Carmen Pancerella (8920), and Ron Kyker (8411). "This is a growing field," Christine continues. For instance, there is a new publication dedicated to open source embedded solutions, the Embedded Linux Journal. Embedded systems are already offered in some cell phones, in which incorporation of global positioning systems allows the service provider to send emergency roadside assistance, even if the caller is lost.

Smart appliances, wearable computers

People also talk about "smart" appliances, such as a refrigerator that knows when the milk is running low, or a snack machine that recognizes it needs to stock up on corn chips. National security applications of these emerging technologies might include using wireless networks to gather information on sensors in flight tests.

In the interdisciplinary, upper-division summer institute, the students are working on very basic frameworks for computer-based situational understanding, Christine says. The Tiqit computer, developed at the Stanford Wearable Computing Laboratory, is being used as an example of a potential platform. Roughly as powerful as a desktop computer (although not as quick), it fits in the palm of a hand and can display to a monitor, provide access to the Internet, and support a World Wide Web server. The students' fields range from electrical engineering to computer science, so that as a group, they can address hardware and software or integration issues, Nina says.

Howard Hirano (16000) of the Advanced Concepts Group and Carmen have already briefed the students on a proposed device that will monitor a wearer's health-and-safety status. Dubbed "My Friend," this computerized device, integrating both hardware and software, could track physiological measures such as pulse and heart rate, recognizing when the wearer (or health provider) should be aware that the wearer's physiological condition warrants attention.

Ron will be briefing the interns on Bluetooth, an emerging new wireless technology that permits creation of networks between different devices, say, between a cell phone, a PDA, and a computer. The group will be developing a wireless distributed sensor network for collecting health sensor data using this new hardware/software standard.

"Bluetooth, initially developed by the Swedish cell phone company Ericsson, is an exciting and enabling technology for many new applications." Ron says, "and we're going to play with it and find out what it can do."

Graduate students Katie Moor and Pippin Wolfe (both 8920), who are returning for their second summer at Sandia, along with graduate student Brian Lambert (8920), are looking at capturing and analyzing data from a fingertip oxygen sensor typically used in diagnostic monitoring. (Both sensors and a microprocessor could be wirelessly networked on the individual wearing them in a "personal area network.")

Three college-level students are also in the program this summer: Eric Burns, Stephen Elliott, and Chris Kershaw (all 8920). Working alongside them is Hillary Davis (8920), a student who is entering her senior year of high school and participated in the Sandia Go Figure math contest. She was also an outstanding achievement winner this year in the Sandia Women's Committee Math/Science Awards.

The interdisciplinary approach is intended to provide an R&D incubator so students can combine skills to produce solutions to a collection of innovative projects provided by their Sandia mentors.

For instance, Nina has a particular interest in artificial intelligence, software that learns and can function through the activity of programmed entities called agents.

"There's an exciting potential for software advancements using artificial intelligence techniques like neural networks and agent-based networks to recognize abnormalities and patterns for sensor interpretation," Nina says. "We want to ask, "What kind of intelligence can we add to this reasoning?"

The culmination of these summer activities will be the establishment of future projects in sensor and IT (information technology) research that will attract potential employees for Sandia's future. -- Nancy Garcia

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Last modified: July 2, 2001

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