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Engineering researcher seeking better way to reuse nuclear fuel

Prof. Patrick Pinhero is seated at his research group's Scanning Auger Microprobe (SAM). The SAM is an ultra-high vacuum (UHV) electron microscope capable of imaging features down to 25 nanometers (nm). It is fitted with cylindrical mirror analyzer (CMA) for determining the chemical composition of select points or areas within an image. In addition it possesses an ion milling system and a fracture stage for examining the near-surface and bulk interfaces.

As the nuclear power industry expands, a Mizzou Engineering faculty member is researching technology aimed at cutting the cost of reprocessing nuclear fuel so it can be used several times.

Associate Professor Patrick Pinhero aims to develop an electrochemical cell for reprocessing used nuclear fuel based on a low-cost alternative to the platinum required by current technology. Pinhero is testing a ceramic developed by Argonne National Laboratory—specifically, an inert conductive ceramic oxide—as well as the possibility of using thin layers of more costly metals such as platinum or gold.

“Gold and platinum are presently very expensive and becoming more so,” Pinhero said. “Finding an electrochemically well-behaved, low-cost alternative may save tens of millions of dollars in fuel reprocessing costs while making the process more efficient.”

Though used internationally, commercial reprocessing technologies have never gained a secure foothold in the United States due to their high cost and concerns that the plutonium they yield could give rise to nuclear weapons proliferation.

But as the country turns to nuclear power in response to rising oil prices and global warming fears, interest in technologies that would allow nuclear reactors to capture and use more of uranium’s potential energy has revived. The U.S. Department of Energy has increased funding and launched research initiatives during the last several years in hopes of encouraging the development of advanced nuclear fuel reprocessing techniques that would pave the way for an efficient means of creating fresh fuel from used uranium.

Financed by a Nuclear Regulatory Commission grant, Pinhero is investigating a so-called “dry” technology—that is, technology that operates outside water’s cooling and shielding properties—that would separate reusable uranium from spent nuclear fuel in an electrochemical cell.

The cell would operate like a scalding salt plating bath, separating the spent fuel’s remaining uranium and plutonium from radioactive wastes using an electric field tuned to those elements, he said. The uranium could then be reused at light-water reactors—which currently dominate reactor technology throughout the world—while the plutonium could be mixed with other elements to create fresh nuclear fuel for “fast” or “breeder” reactors, Pinhero said.

At the heart of Pinhero’s innovation is the ceramic material he plans to use for the cell’s anode, analogous to a battery’s positive terminal. Preliminary tests show that the Argonne lab’s proprietary ceramic may be stable enough to withstand the corrosive nature of the technique’s chemical reactions, he said.

Pinhero is performing detailed studies on anodes made of the Argonne ceramic, evaluating the material’s conductivity and its mechanical as well as other properties at the extremely high temperatures at which the electrochemical cell would operate. He plans to test and analyze several different ceramic anode prototypes, as well as anodes made of thin layers of platinum or gold.

Other factors Pinhero is examining focus on the voltage generating the cell’s electric field and the size of the cell’s anode as well as its cathode, which is roughly equivalent to a battery’s negative terminal.

“Our focus is on understanding the fundamental science so we can engineer systems that can be scaled up and integrated into a closed-loop nuclear fuel cycle,” Pinhero said.