Volume 18, No. 1 - Spring 2009
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Nuclear Energy

Student Researcher

Aims to

Improve

DESIGN

of Nuclear Reactors

By Mellina Stucky

Jeff Hetherly

Photo by: Mike Woodruff

With a graduate fellowship from the U.S. Department of Energy, Jeff Hetherly will use computer models and simulations to study the effects of radiation on stainless steel.

A love of computers and computer gaming initially led Jeff Hetherly down a path toward a computer science degree. How­ever, the prospect of using computer modeling as it applies to physical theory won him over, and instead he chose to study physics, earning his bachelor of science from UNT, magna cum laude, in May 2008.

"I've always been interested in physical theory and equations," Hetherly says. "Computer modeling is a direct application of that."

Hetherly now is continuing his education at UNT, pursuing a master of science in physics simultaneously with a doctor of philosophy in materials science and engineering.

He was the only student from Texas and one of nine from across the nation to be awarded a $45,000 two-year graduate fellowship from the U.S. Department of Energy Advanced Fuel Cycle Initiative last May. The overall mission of the AFCI is to make nuclear fuels more efficient and the waste they produce less harmful to the environment.

Structural Integrity

The funds allow Hetherly to study how long-term exposure to radiation can cause the materials used to build nuclear reactors to deform. He is focusing specifically on the effects of radiation on nano-structured stainless steel, and his findings may be used to support the design of future nuclear reactors.

"Hetherly's research is important to the AFCI program because stainless steel is the predominant material of construction for future fast reactors," says James Bresee, senior technology specialist with the U.S. Department of Energy.

Hetherly explains that in a fast reactor, as opposed to a more conventional thermal reactor, the fission chain reaction is sustained without slowing, or moderating, the neutrons.

"The absence of a moderator requires fuels that are more dense, but it allows higher energy production per atom of fuel, resulting in a more efficient use of re­sources," he says.

Although many conventional nuclear reactors are built with stainless steels, materials in fast reactors are exposed to higher radiation levels. Radiation exposure eventually causes the steel to bulge, reducing its structural integrity.

"Newer ways of processing stainless steel potentially solve the problem," Hetherly says, "but the steels haven't been fully tested, and physical experiments are very expensive. Accurate computer modeling offers a relatively low-cost way to reduce the number of experiments needed to test them."

Modeling Radiation Effects

Under the guidance of Srinivasan Srivilliputhur, assistant professor of materials science and engineering, and Duncan Weathers, associate professor of physics, Hetherly uses computer models and simulations to examine how the new stainless steels react to high doses of radiation.

"With the models, we are able to track each atom's position in an artificial sample," he says. "This allows us to see where each atom goes when it is hit with radiation and how well the sample retains its shape. With scientists at Los Alamos National Laboratory, we can speed up the simulation to see how the material will react over long periods of time."

A mathematical program Hetherly is writing will be tested on the Center for Advanced Scientific Computing and Modeling computer cluster at UNT. He also will run his calculations on supercomputer clusters at the Texas Advanced Computing Center in Austin and Lawrence Livermore National Laboratory in Liver­more, Calif.

"Using the supercomputers, I can manipulate more atoms in the same amount of time or the same amount of atoms in less time," Hetherly says.

A Safer Energy Source

As an increasing number of developing countries plan to use nuclear power as a way of supplying energy, it has become necessary to ensure that these plants have less impact on the environment.

"More countries are building new nuclear power plants and are experimenting with ways to reprocess and use the waste from older plants for fuel," Hetherly says.

Spent fuel rods are the most radioactive of all nuclear wastes, and that radioactivity takes thousands of years to decay. By identifying building materials that absorb fewer radioactive atoms and predicting the lifespan of materials used in new fast nuclear reactors, Hetherly's research will allow more efficient structures to be built. If the materials do not have to be replaced as often, fewer nuclear waste storage facilities will be needed, resulting in tremendous cost savings for the industry as well as good news for the environment.

"With these new materials, it would take much less time for the harmful radioactive material to decay in underground storage," Hetherly says.

Networking and National Labs

Hetherly competed for the AFCI fellowship against more than 100 top students in science and engineering fields from universities including the Massachusetts Institute of Technology and the University of California at Berkeley. In the summer, he traveled with the other new AFCI fellows to visit the DOE headquarters in Washington, D.C., and Argonne National Laboratory in Illinois.

"I encourage the AFCI fellows to work with national labs and the DOE headquarters and to network with each other," says Cathy Dixon, coordinator of the fellowship program and director of the University Research Alliance at West Texas A&M. "The students chosen for the program are the cream of the crop, and they will work together throughout their careers."

Hetherly says he is looking forward to working with the other fellows and learning from contacts at the national labs.

"It's a wonderful opportunity."

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