Large-scale nuclear materials study shapes national collaborations

In Kumar Sridharan‘s laboratory on the University of Wisconsin–Madison engineering campus, just one ill-timed sneeze might have catapulted his next three years’ worth of nuclear reactor materials research into oblivion.

A distinguished research professor of engineering physics, Sridharan and colleagues Yong Yang, Lizhen Tan and Kjetil Hildal spent summer 2008 preparing 500 smaller-than-a-sesame-seed samples for a unique study of how several traditional and cutting-edge materials fare in the harsh environment of a nuclear reactor.

“In terms of the number and diversity of samples being tested, this is one of the largest university-driven projects for studying the effects of radiation on materials in a national laboratory,” says Sridharan. “And, the samples are being irradiated in real-life conditions, as though they’d be in a nuclear reactor, which is a very unique opportunity for a university.”

The study, which includes about 20 different materials, could help researchers choose materials for the ultra-efficient nuclear reactors now under development. Unlike current reactors, these advanced reactors will operate at higher temperatures, pressures and radiation ranges, creating conditions today’s reactor materials can’t withstand.

“We’re trying to generate data that can be useful such that 10, 15, 20 years from now, the stage is set for somebody to build one of these advanced reactors,” says Todd Allen, a UW–Madison assistant professor of engineering physics.

Led by Sridharan and Heather MacLean, an Idaho National Laboratory (INL) engineer, the project is the first university-laboratory partnership at the recently created INL Advanced Test Reactor National Scientific User Facility.

In April 2007, the U.S. Department of Energy, which owns the test reactor, designated it as a national scientific user facility to support university, industry and national laboratory research of nuclear fuels and materials. In March 2008, UW–Madison’s Allen, a materials expert, also began serving as scientific director of the user facility.

The UW–Madison samples entered the INL test reactor in September 2008. Of the 500 samples, about half will be irradiated for one year, while the other half will remain in the test reactor until September 2010. Among the samples are steel, ceramics, amorphous alloys, and materials with a reinforced nanostructure for strength at high temperatures.

Depending on the material, each sample is receiving radiation at a constant temperature (ranging from 300 to 700 degrees Celsius). Many of the samples are under study at more than one temperature. INL engineers carefully arranged them in specially fabricated cylindrical capsules to ensure they receive even heat and radiation.

The samples are intentionally tiny; their small size enables researchers to analyze the effects of radiation via a technique called transmission electron microscopy. However, says Sridharan, the structural changes they will observe in the tiny disks are the same as those that would have occurred in “bulk” materials. “We are looking at the radiation response of a given material, which will be dictated by the material’s composition and structure, and not its size,” he says. “The project also includes tensile samples, which enable us to correlate these nanoscale structural changes to changes in bulk mechanical properties.”

Because the UW–Madison project is the first university project at the new INL user facility, Sridharan began planning with INL staff nine months earlier. “There are a lot of hurdles to be overcome before an experiment gets started,” he says.

For nearly six months, he and his colleagues participated in weekly teleconferences with INL staff. Not only did they prepare most of the samples, they also labeled each one and, among other data, provided INL staff the exact dimensions and composition of each sample. “Just telling them on the phone-or by e-mail-would not do it,” he says. “We had to actually reanalyze them and get them certified.”

The researchers’ experiences have laid the groundwork for the way in which other universities interact with INL. Since the UW–Madison experiment began, INL staff added three more university experiments to the reactor, and Sridharan has given lectures about how best to work with INL staff and prepare a research project for the user facility.

Now Sridharan and several research scientists and graduate students involved in the UW–Madison project are planning post-irradiation experiments for when the first batch of samples comes out of the reactor in September 2009. The project supplements the students’ on-campus research, which centers around using an ion beam to damage candidate reactor materials. “It gives them the chance to compare that with what happens in a real nuclear system,” says Allen, who splits his time between UW–Madison and INL and co-advises the students.

With INL staff, UW–Madison researchers will analyze their samples in Idaho-though Sridharan and colleagues at UW–Madison are developing analysis capabilities and hope to become a partner institution with the Advanced Test Reactor user facility. “We’re trying to establish this lab such that if INL has choke points-too many samples to analyze-they could send some of them here,” says Allen.

Because they lack the facilities and analysis capabilities, most universities can’t attempt research like as the UW–Madison project on their own. Ultimately, says Allen, the new partnerships enable universities to participate more fully in research with national laboratories, and in particular, the INL user facility. “Universities have not been able to define and lead major irradiation test programs as long as I have been involved in this field,” he says. “The UW experiment is the first in a number of projects where universities take the intellectual lead on a national level project.”

Collaborators on the UW–Madison project also include the University of Michigan, Penn State University, University of California, Oak Ridge National Laboratory, Los Alamos National Laboratory, Westinghouse, Gamma Engineering, and the Japan Atomic Energy Agency.