UI prof leading project on material that can better withstand reactor accident

URBANA — University of Illinois researchers have won a $3.5 million grant to develop cladding for nuclear fuel rods that can better withstand a reactor accident.

Brent Heuser, UI professor of nuclear, plasma and radiological engineering, is principal investigator for the grant from the U.S. Department of Energy's Nuclear Energy University Programs.

Five partners from academia, government and industry will collaborate on the work: the University of Florida, University of Michigan, manufacturer ATI Wah Chang in Oregon, Idaho National Laboratory, and the University of Manchester. The United Kingdom is providing more than $1.5 million for collaborative research.

The project will develop and test cladding material with greater accident tolerance, improving nuclear safety, according to Heuser.

The Zircaloy cladding used in the industry, developed in the 1960s, is a blend of zirconium and tin that is resistant to corrosion. But researchers would like to prevent oxidation during what the industry calls "off-normal events," or accidents, Heuser said.

When a reactor core heats up and the cladding is exposed to steam, it forms zirconium oxide. That reaction leaves behind hydrogen, which is volatile and can lead to an explosion and heat up the fuel even more, he said.

The goal is to modify the cladding so that the oxidation reaction is inhibited, he said. It will be tested under realistic scenarios mimicking the conditions of temperature and steam exposure during an accident, he said.

The Energy Department and the nuclear industry wanted to be proactive following the nuclear disaster at Japan's Fukushima Power Plant in March 2011, Heuser said.

A tsunami caused by a massive earthquake disabled emergency generators at the power plant, disrupting the pumps that circulated cooled water to the reactor, which eventually overheated.

"What happened in Fukushima really can't happen in the United States," Heuser said. "They had some design flaws. Their barrier wasn't high enough for the magnitude of the tsunami they saw. They simply didn't anticipate a flooding of their critical power supplies."

Few of the 104 nuclear reactors in the United States are located along the coasts, and those have proper barriers and redundancies to protect against that scenario, he said.

A more likely event in the United States involves a loss of coolant from mechanical problems, such as a pump failure or a break in a water line, though Heuser emphasized that the industry is safe.

"Light water reactors are inherently safe in general," Heuser said. "If you can make the fuel accident-tolerant, then you've improved the system."

Cladding is the first line of defense during an accident. It consists of long, skinny rods, about a half-inch in diameter and perhaps 3 or 4 meters long, that contain nuclear fuel pellets, he said. The rods are welded and capped on the top and bottom and combined in groups of 100 to form an "assembly." A reactor core is made up of 100 to 150 assemblies.

Decades of testing and experience have produced cladding that maintains its mechanical integrity long after the fuel is spent, he said. Nuclear reactor operators constantly monitor water chemistry to be sure the rods aren't corroding and their integrity is maintained, he added.

When exposed to high temperatures, the oxidation appears on the surface of the cladding. One solution is to develop a coating that adheres to the cladding that won't oxidize and can withstand the nuclear environment, he said.

The other is to develop self-healing cladding, a technique used in other applications. That would involve changing the composition of the Zircaloy slightly to include elements that could rise to the surface when the cladding heats up and change its composition to stop the oxide reaction, Heuser said.

"We're going to investigate both," he said.

Having ATI Wah Chang, which manufactures the cladding, as an industry partner is crucial, he said.

Illinois has 11 reactors, providing 48 percent of the state's electrical power.

"We are one of the largest, if not the largest, nuclear states. It's important that we're doing this research so we can educate students in nuclear engineering and nuclear energy, and improve safety," Heuser said.

Department of Energy officials said the award will support nuclear energy research and development and student investment, and help ensure that "secure, safe and efficient nuclear energy is part of the U.S. energy portfolio."

"The Illinois award announced today will help train and educate our future energy leaders, while developing the innovations we need to create new jobs and export opportunities for American-made nuclear technologies," Secretary Steven Chu said in a release.

Heuser and UI Professor James Stubbins last year received a grant of nearly $1 million to study how cladding performs once it's put in long-term storage, in partnership with Texas A&M University.

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