Nuclear engineers strive for safer fuel in response to Fukushima
ATLANTA — The explosions that damaged a crippled Japanese nuclear plant during a disaster that forced mass evacuations in 2011 show what can happen when nuclear fuel overheats.
In response to the Fukushima Dai-ichi accident, Washington dramatically increased funding to develop tougher protective skins for nuclear fuel, hoping to spur innovation in designs that hadn't changed much in years. While the Department of Energy was spending $2 million before the accident on future fuel designs, the funding reached as high as $30 million afterward.
Now, scientists at multiple institutes are in the middle of developing designs that could start finding their way into test reactors as soon as this summer, to be followed by larger tests.
The goal is to create nuclear fuel that is more resistant to damage and melting in extreme situations and less prone to a chemical reaction that makes its metal wrapping brittle and produces explosive hydrogen gas. If researchers succeed, their work could give plant workers more time to keep an accident from spiraling into a meltdown. The work is no cure-all to prevent accidents, but it's a way of reducing risk.
“It's basically buying time for the reactor,” said Andrew Griffith, the Energy Department's director for fuel cycle research and development. “It's basically an insurance policy.”
Scientists are considering a range of improvements.
Some are proposing fundamental departures. The Electric Power Research Institute is experimenting with cladding made of molybdenum, which maintains its strength in higher temperatures than the current zirconium alloys. A stronger metal would do a better job keeping fuel from melting and slumping in a reactor during extreme accidents.
Engineers at the University of Tennessee are trying to coat cladding with ceramics that can withstand higher temperatures than the existing cladding, and Westinghouse Electric Co. hopes to use silicon carbide as the base for its claddings in future fuel designs.
Quicker improvements may come from changing existing fuel designs. A nuclear engineer at the University of Illinois, Brent Heuser, received federal funding to develop coatings that could be applied to cladding to prevent the chemical reaction that produces hydrogen and weakens the cladding. His team is interested in “self-healing” fuel, which has added materials that migrate to the surface of a fuel rod during an accident and form a protective coating.
To get around the economic obstacles, some researchers hope to offset the extra cost of the protection measures by combining them with fuel that produces more energy before it must be replaced. Others, like Heuser, say regulators would need to force utilities to use the safer products.