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Nuclear industry explores accident-resistant fuel

By Associated Press

LAST UPDATED: 12:27 p.m. HST, Jun 14, 2014

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, the U.S. government 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 U.S. Department of Energy was spending $2 million before the accident on future fuel designs, the funding reached as much 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, followed by larger tests later on.

The goal is to create nuclear fuel that 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 that releases harmful radiation. 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 in the government- and industry-funded efforts are experimenting with multiple solutions before narrowing their focus on the most-promising technologies.

Nuclear fuel has remained similar for decades. Uranium dioxide is compressed into a pellet about the size of a fingertip. Those pellets are stacked into fuel rods up to 15 feet long and placed in a tube, called cladding, made from zirconium alloy. That metal cladding resists corrosion in a reactor, holds up against heat and serves as a barrier that keeps radioactive elements in place without cutting too much into the energy produced by a nuclear plant.

Nuclear fuel is supposed to withstand accident conditions, but the disaster at the Fukushima Dai-ichi plant shows how it can fail when pushed to extremes.

After an earthquake, tsunami waves crashed over the plant's seawall and disabled the electrical gear needed to run reactor cooling systems. When the cooling systems and backups stopped working, the reactors overheated. As water levels dropped, the metal cladding around the fuel reacted with steam and oxidized, producing hydrogen gas. Scientists blame that escaping hydrogen gas for causing multiple explosions that damaged the facility.

The same reaction also produces heat, further contributing to the extreme temperatures that allowed fuel to melt and radioactive byproducts to escape. Some oxidation occurs during a reactor's normal operation, but nowhere near the levels that occur in an extreme accident.

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 nuclear 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, while 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 U.S. funding to develop coatings that could be applied to existing cladding to prevent the chemical reaction that produces hydrogen, heat and weakens the cladding. His team is also 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.

Any change must make financial sense. Adding safety improvements costs more money. That's not attractive to cost-conscious utilities since the existing cladding already meets federal safety rules.

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.

"It's often where businesses and regulatory bodies butt heads," Heuser said.

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atilter wrote:
connect the dots - into the future! can (will) anyone remember the way electricity is being produced today? increased safety -> decreased probability of disaster -> increased use of nuclear solutions to produce electricity -> decreased costs in production -> decreased usage rates -> less profit motive -> disappearance of electrical utilities producing electricity (more toward distribution grids) -> decreased popularity of stock investments in monopolistic electric utilities!
on June 14,2014 | 12:43PM
OldDiver wrote:
When insurance companies are willing to insure nuclear power plants is when they will be safe to operate. Until then count me out.
on June 14,2014 | 12:50PM
livinginhawaii wrote:
You do realize that Oahu has more nuclear reactors per person than most states in the nation? If you are "counted out" just curious as to why you continue to live in such a place....
on June 14,2014 | 01:30PM
HanabataDays wrote:
Since Hawai`i has no commercial nuclear power generating plants at all, you must be referring to the reactors in the boomers at Pearl. That's a totally different safety scenario, and the insurance situation isn't the least bit comparable. Just wanted to be sure everyone was clear on your meaning, since you chose to play footsie on the details.
on June 14,2014 | 02:25PM
sailfish1 wrote:
That's not really true because most of the nuclear submarines and/or ships are not in Hawaii at any given time.
on June 14,2014 | 07:42PM
HanabataDays wrote:
A bit surprised the article made no mention of pebble-bed reactors. They haven't proven themselves in the real world yet, but seem to be worthy of ongoing research. There's a fair amount of controversy about them, and Wikipedia's a reasonably neutral starting point to learn more details.
on June 14,2014 | 02:33PM
what wrote:
People should realize that Fukushima was designed on a 1950s reactor design. Modern designs would not have had problems Fukushima did. Also realize that the other worst nuclear disaster, Chernobyl, was one of the worst designed nuclear reactors in terms of safety in the history of mankind.
on June 14,2014 | 02:58PM
kaiakea wrote:
"...Others like Heuser say regulators would need to force utilities to use the safer products. "It's often where businesses and regulatory bodies butt heads," Heuser said." Although I agree that the safest materials should be found, the systems that keep the public safe also need to be strengthened. There was too much of the profit motive implicated in the Fukushima disaster that could have been offset by stronger rules. Regulatory agencies need to be completely separate from the profit arm of the industry or we will continue to have more and worse accidents.
on June 14,2014 | 04:12PM
Mythman wrote:
on June 14,2014 | 04:37PM
krusha wrote:
Yep, that is the answer a lot safer than uranium. http://en.wikipedia.org/wiki/Thorium
on June 14,2014 | 06:36PM
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