Westinghouse Electric developing accident-tolerant fuel
May 4, 2014 12:00 AM
Westinghouse Specialty Metals Plant inspectors Kathie Beck and Melanie Shively
Westinghouse Specialty Metals Plant inspector Jason Lovas.
By Anya Litvak / Pittsburgh Post-Gazette
It can be difficult to talk about making nuclear plants safer without people inferring an immediate danger to the current fleet, says José Gutiérrez, senior vice president for nuclear fuel at Westinghouse Electric Co. in Cranberry.
“Airplanes are safe,” he said, “but tomorrow’s planes will be safer. Same with nuclear reactors. We’re totally convinced that today’s reactors are safe, but the next generation will be safer.”
For the past 10 years, Westinghouse has been working on designing something now called accident-tolerant fuel.
The company has spent nearly $10 million on the project and partnered with several large universities and companies all over the world to find new materials that can withstand high temperatures for longer periods, without melting down the core of a nuclear reactor.
When a tsunami ravaged the Fukushima Daiichi nuclear power station in Japan in March 2011, accident-tolerant fuel was catapulted to priority status at the U.S. Department of Energy. The following year, Congress gave the department 10 years to place this new generation of fuel into a commercial reactor.
Internally, Westinghouse is shooting for the same timeline.
This new fuel would be accident tolerant the same way that Westinghouse’s AP1000 nuclear reactor, currently being built in China and the U.S., is accident tolerant — both extend the period of time that a reactor can be without power, cooling and human intervention after a major accident.
The AP1000 can go for five to seven days using its passive cooling mechanisms that rely on gravity to keep the reactor core from overheating. The intent of accident tolerant fuel is to add more time to that span, allowing more time for responders to deliver help to the damaged site.
Better performing fuel
Nuclear fuel design hasn’t changed all that much since the atoms first split at the first commercial nuclear plant in Shippingport, Beaver County, some six decades ago, according to Kurt Terrani, staff scientist and Weinberg fellow with Oak Ridge National Laboratory in Tennessee, whose research is focused on testing and analyzing new designs.
The fueling process has been optimized and made more efficient, but the basics have remained the same.
The current design still relies on uranium oxide fuel pellets encased in zirconium metal tubes. A typical reactor core can have about 10 million fuel pellets, each the size of a pencil eraser, stacked on top of one another in fuel rods, also known as cladding. The life of a fuel rod is around five years. After that, it gets swapped out for a new one.
The term accident-tolerant fuel became popular after Fukushima, but companies have been looking at better fuel designs for years with the goal of improving fuel performance during non-catastrophic conditions, Mr. Terrani said.
Current light water reactors, the kind that Westinghouse makes, use zirconium-niobium in their cladding. It’s a sturdy material with anti-corrosive properties. But if it comes into contact with steam, it’s quick to produce hydrogen, which caused explosions at Fukushima.
The pellets themselves are made much like cupcakes, Mr. Gutiérrez explained. Uranium powder is mixed with some additives, placed in molds and “cooked” until it solidifies.
Westinghouse is researching the possibility of using a ceramic material, silicon carbide, in its cladding. It’s also thinking about a new type of pellet that’s denser and less likely to expand under high temperatures; expansion puts pressure on the fuel tube that holds it in place.
New fuels must perform better than current fuel, burn more efficiently and last longer — otherwise, nuclear plant operators won’t be willing to invest in a new, more expensive technology that might come in handy only in an extremely unlikely situation.
Safety is and always has been a major consideration of nuclear design, Mr. Terrani said, but commercial motivations must revolve around this basic fact: “You’re not building a fuel so you can expose it to a really severe accident. You’re building it so you can use it for five years to produce power.”
So the goal of a new fuel isn’t just to behave well during a horrible accident, but to be better than current fuel during regular operations.
Fuel must be 'seamless, viable'
Southern Co., a large U.S. utility currently building the first two American AP1000 plants in Georgia, is Westinghouse's partner on the fuel project. It will give the nuclear company the practical perspective on whether the fuel can be commercially viable.
“You have engineers that can develop very crazy ideas, but you need to know if it works in the plant,” Mr. Gutiérrez said.
Whatever shape it takes, the new fuel design must fit seamlessly in existing reactors and be able to be manufactured at current fuel production plants, like Westinghouse's specialty metals plant in Blairsville, Indiana County, which supplies 17 percent of the fuel tubes for all the world's reactors, according to plant manager Jim Cook.
It's a sprawling operation, employing 300 people over three shifts and churning out more than a million feet of pipe a year.
Change isn't new to the plant. In its early days, the facility used to make castings, turbine blades, magnets and latches before settling into zirconium-alloy tubes the late 1960s.
Mr. Gutiérrez said that if all goes well with the company's accident-tolerant fuel program, he'd like to see the new fuel tubes manufactured at Blairsville.
Mr. Cook can't picture what that would look like and says it's too early to talk about the implications for manufacturing.
"It might be a totally different process," he said. But wholesale changes are part of the plant's history, he added.
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