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Science doesn't happen overnight, and Dave Petti, a fellow at DOE's Idaho National Laboratory, knows that better than many. As INL's technical director for TRISO fuel research, Petti and his team weathered a long dry spell before their project was resurrected in 2003 and reached an important milestone last month. Tri-isotopic fuel, or TRISO fuel, is a specialized nuclear fuel intended for high-temperature gas reactors. TRISO fuel is a spherical particle with uranium dioxide or uranium oxycarbide at its core. The core is coated with layers of carbon and silicon carbide — the TRISO coating — which act as "the primary containment" of fission products. The tiny particles, about one millimeter in diameter, are then embedded in graphite. TRISO fuel is unique because it can be fabricated with very few defects, survive severe accident conditions and — most importantly — fission far more uranium (called "burnup") than seen in previous research. As of early September, the TRISO fuel in INL's Advanced Test Reactor for more than 18 months had achieved 12.5 percent burnup — light water reactor fuel generally achieves no more than 3 or 4 percent burnup. This breakthrough didn't come easy. TRISO fuel testing was largely abandoned internationally in the early 1990s. The United States began having difficulties in that research area, and budget cuts effectively ended work toward solutions. The project was left for dead until 2003, when climate change and next-generation reactor goals prompted renewed interest in nuclear energy. "[Generation IV research] was the spark plug that started it," Petti said. Petti and his team were instructed to pick up TRISO research where they left off. They gleaned information from German records documenting 1980s breakthroughs to help them overcome barriers that had stalled the research. The overall aims of the TRISO project are within reach now, Petti said. INL hopes to achieve 16 to 17 percent burnup in June 2009, after which the fuel will go in for testing under accident condition simulations. "The goal of the project is to qualify fuel for use in gas reactors," Petti said. "So four to five years from now [it] should be well on its way."Submitted by DOE's Idaho National Laboratory |
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Check out the joint Fermilab/SLAC publication symmetry.
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PPPL Team Develops
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| The PPPL Lithium Dropper Team, from left (front row) includes Lane Roquemore, Dennis Mansfield (holding the Li dropper), and Henry Kugel; (second row) Mark Cropper and John Timberlake; (third row) Gretchen Zimmer and Doug LaBrie; (fourth row) Carl Bunting and Joe Winston; (fifth row) Tom Holoman and John Dong; and (top) Hans Schneider. Not shown are Tom Provost and the late Ray Gernhardt. |
You could call it a performance enhancer for the National Spherical Torus Experiment (NSTX) at the DOE's Princeton Plasma Physics Laboratory (PPPL).
The lithium powder dropper recently developed and tested by an NSTX team improves both plasma performance and duration. Plasma is a hot, gaseous state of matter used as the fuel to produce fusion energy - the power source of the sun and the stars.
Lithium, used for years in fusion devices as a coating on vacuum vessel walls, increases plasma performance by reducing impurities sputtering into the plasma. This benefit, though, is sometimes short-lived. Since lithium deactivates quickly, it sometimes loses its ability to boost the plasma performance during an entire discharge—or shot.
The problem is how to re-supply lithium halfway through and to the end of the plasma shot. "How do you keep the party going?" asks PPPL physicist Dennis Mansfield.
That's where the dropper comes in, shaking lithium into the plasma during the shot. Researchers tested the dropper at the end of NSTX operations last year, using pure lithium with thin coatings of carbonate. Pure lithium powder ignites in air and must be coated for stabilization for such experiments.
"The dropper concept is something fellow researcher Lane Roquemore and I were intrigued with a year or so ago," says Mansfield, who joined Roquemore in leading a team to explore the concept.
The group loaded a Lithium Powder Dropper with stabilized lithium metallic powder—spherical particles that don't stick together—for the experiments. It then dropped the 50-micron particles in a systematic and reproducible manner using a computer-controlled piezoelectric bending actuator operating at an acoustic resonance. Mansfield says researchers manipulate lithium at acoustic frequencies, which keeps the particles from "getting into traffic jams." The team demonstrated the controlled dropping with a laser diagnostic. The results: plasma confinement and shot length increased while the level of impurities shrank. The dropper allowed the plasma to receive a lithium boost during and toward the end.
Mansfield is developing proposals for the next NSTX campaign and plans to present a poster about the results at the November American Physical Society-Division of Plasma Physics meeting.
"It was a technical success. It was scientifically interesting and showed a glimmer of performance and a great deal of potential."
Submitted by DOE's Princeton Plasma Physics Laboratory