Power Surge: Uranium alloy fuel for TerraPower

Posted: July 18, 2012 - 9:45am | Y-12 Report | Volume 9, Issue 1 | 2012

Since 2010, Y‑12 has provided TerraPower with technical support in the fabrication methods for uranium alloy fuel to be used in a new traveling wave nuclear reactor that can run for more than 30 years without refueling. Image of reactor power concept, used with permission of TerraPower, LLC.

Y‑12's nuclear expertise, expanding since the site's integral role in the Manhattan Project, is positioning the Y‑12 Complex at the forefront of what Sen. Lamar Alexander repeatedly asserts is needed — “a new Manhattan Project for clean energy independence.”

TerraPower, a private company backed by Microsoft founder Bill Gates, is developing next-generation nuclear reactor technology. And Y‑12, armed with its expertise in uranium, is providing TerraPower with technical support.

“We have the facilities, infrastructure and skills needed to create the test fuel.”

This new class of nuclear reactor offers benefits missing from today's light water reactors, TerraPower asserts. The new reactor costs less to build and operate; lowers proliferation risks by reducing the need for enriched uranium; converts depleted uranium to usable fuel as it operates; uses liquid sodium as a coolant, which is inherently safer than water; and can run more than 30 years without refueling.

Founded in 2008, TerraPower has completed a conceptual design of a sodium-cooled fast reactor and plans to commercialize the technology in the next 10 years.

TerraPower estimates that its “traveling wave reactor” could convert a single 8-metric-ton canister of depleted uranium into enough electricity to power 2.5 million U.S. homes for a year. More than 30,000 cylinders of depleted uranium are stored in Paducah, Ky., and huge stockpiles also exist around the world.

A 'Perfect Match'

Y‑12's role is to investigate different approaches to making metallic uranium-zirconium slugs, the fuel for the traveling wave reactor.

The TWR requires a small amount of enriched uranium in metallic form to start a chain wave reaction that slowly burns depleted uranium to maintain power levels. This enriched fuel is fundamental to this type of reactor design. Y‑12's decades of experience in working with enriched uranium and metallic uranium alloys make the site one of only a handful in the nation that can support this work.

“We cast, machine, microwave and perform many other operations with metallic uranium, so we have the facilities, infrastructure and skills needed to create the test fuel,” said John Creasy, Y‑12's advanced reactor and materials design expert.

Moreover, as the nation's storehouse for enriched uranium, Y‑12 has access to the special nuclear material needed for the TWR. The reactor requires metallic uranium that is on average 10 to 12 percent enriched; however, the commercial nuclear power industry is licensed to operate using uranium that is less than 5 percent enriched.

“The feed material TerraPower needs has to come from downblended weapons-grade uranium or must be obtained elsewhere and worked at Y‑12. In either case, working with enriched uranium alloys is our specialty, so we're a perfect match for the job,” said Chris Robinson, director of Y‑12's Nuclear Material Initiatives. “Y‑12 will downblend enriched uranium from former nuclear weapons to create the feed material for the slugs or help obtain the needed enriched uranium required to produce the driver fuel.”

Fuel slugs, each about the diameter of a pencil, can be made several ways. Using different methods, Y‑12 will create sample slugs and then “down select” the best-performing, most cost-effective approach.

In March 2012, TerraPower and Y‑12 signed a five-year Work for Others agreement. Through this agreement, Y‑12 will fabricate sample fuel pins for testing within a research sodium fast reactor. Russia's BOR‑60 experimental reactor, a sodium fast reactor similar to the TWR, will irradiate the pins as part of TerraPower's multiyear fuel testing program. How well the fuel performs will be analyzed. “This testing is crucial to developing fuel and materials that will stand up in a 30- to 50-year operating environment,” Robinson said.

The technology behind the TWR has evolved since the 1950s, but only recently has the reactor been shown to work — at least in a virtual environment. Using computer science expertise from Microsoft and from TerraPower's parent company, Intellectual Ventures, reactor physicists built models and performed complex computations to simulate how the reactor works.

Now ready to build a pilot plant, TerraPower is in talks with several nations — countries committed to putting nuclear on their power grid — to host the reactor. Even though the first plant is planned to be constructed outside the U.S., TerraPower is using a number of U.S. companies, national labs and universities to further the design, including Y‑12. In the meantime, the company supports the Nuclear Regulatory Commission's efforts to establish guidance for future certification and licensing of next-generation plants in the U.S.

Tens of thousands of fuel pins, much longer than those used in the BOR‑60 reactor, will be needed to form the core of the pilot reactor. Y‑12 is working with TerraPower and others to develop a fuel fabrication line for the pilot plant.

Y‑12's fuels and materials work “is essential,” said TerraPower CEO John Gilleland. “Y‑12 has the reputation, capabilities and potential capacity to develop the specific fuel type the TWR needs and then scale up processes to provide the amount of metallic uranium fuel slugs for the first TWR core,” he said. “By working closely with Y‑12, with their years of experience with metallic uranium, TerraPower will be able to ensure the design performs as expected but, as importantly, can be manufactured in a cost-effective manner.”

Nuclear energy resurgence

Developing fuel slugs and test pins for TerraPower is in line with Y‑12's strategic goal to create specialty fuels involving enrichments greater than commercially available ones.

“Doing this work for TerraPower is a natural extension of performing our national security missions,” said Lloyd Jollay, who heads Y‑12's Nuclear Materials Applications group. “Because this is a commercial venture, new ways of looking at our business processes are necessary. We have done defense work for so many decades that people are excited to work on new challenges.”

“It's invigorating to be involved in the nuclear energy resurgence,” Robinson said. “I'm excited to be part of taking a game-changing design that uses all of our capabilities from the Cold War era and putting them into a technology that advances the future of nuclear power.”

Q&A with TerraPower CEO John Gilleland

How will the U.S. benefit from sending the fuel Y‑12 creates to Russia's BOR‑60 experimental reactor for testing?

JG: There is limited fast neutron irradiation capacity in the world. The BOR‑60 reactor is a reliable irradiation platform that is used by many international organizations. TerraPower will irradiate small fuel pins with materials and critical dimensions identical to those that will be used in the TWR. This will allow irradiation results to be obtained to support our design calculations and in advance of licensing the first TWR.

How do you get beyond the fear factor, especially after the Fukushima Daiichi nuclear power plant disaster in 2011, when it comes to the public's perception of nuclear energy?

JG: The earthquake and tsunami tragedy in Japan that led to the Fukushima accident has become a hurdle that reactor designers must address, even though the conditions were clearly beyond the prescribed design basis. The TWR is a true Generation IV reactor with safety systems that exceed any reactor currently operating or under construction. TerraPower has reviewed the TWR design and made some modifications to ensure that the reactor would safely shut down and continue to passively cool during such a “beyond design basis accident.” The TerraPower TWR uses passive cooling and therefore remains safe in “station blackout conditions.” With that said, the nuclear industry worldwide has been impacted by the events at Fukushima. We continue to believe that nuclear power is essential to the global electrical power generation mix both for environmental and economic purposes.