DOE OSTI2019
The DOE-NE AFC program broadly supports the creation of novel fuel forms including intermetallics, composites, and dopants for high uranium density compounds. While data can be obtained for key performance indicators such as thermal expansion and oxidation resistance in steam, fuel qualification remains a time intensive process. As such, accelerated fuel qualification methods are a recent focus of the program. By first looking at systems with known historical irradiation testing information, like UO 2 , the method of accelerated burnup testing can be validated, followed by use on novel materials with less information available, like silicides and nitrides. The biggest time delay in doing irradiation testing is reaching a “high burnup” fuel, to effectively model how the fuel will behave when it has been fully used. Reaching this point conventionally could take upwards of 30 years. Accelerated burnup would be approaching the threshold of “high burnup”, something on the order or 50GWd/MTU, more quickly, which although achievable in test reactors requires a decade to achieve using current irradiation testing schemes. To achieve this faster rate, the fuel is likely going to be subject to thermal effects commiserate with the increased heat by more fission. In a normal fuel pellet, this increased temperature would operate less efficiently because the thermal diffusivity of the pellet only allows it to transfer heat so quickly, thus causing a high centerline temperature and noticeable stress along the diameter of the pellet. Solutions could include smaller pellets, which would have a greater surface area giving off heat relative to their volume, or “shaped” fuel designs modifying the thermal behavior. The concept that drives the annular pellet design is reduction of the thermal gradient caused from the high “centerline” temperature at the center of a normal pellet to its surface. By removing the center of the pellet, the new centerline will instead be closer to an edge (whether that be the inner or outer edge), allowing cooling to wick away more heat than the traditional design. In an ideal world, the center of the pellet could also have a heat wick running through it allowing heat to be transported away from throughout the pellet. This increase in heat removal would allow the pellet to be subjected to higher energy output, and thus accelerate the burn-up process. UO 2 has been the staple fuel form of nuclear energy for decades, and replacement of this functionally understood material can only be done with sufficient fuel qualification. Increasing the burnup allows us to characterize new fuels with limited to no operational experience behind them, including carbides, nitrides, and silicide’s. Production of the unique geometries detailed herein will allow us to cut qualification times from multi-decadal experiments into the sub-decadal range, vastly increasing the quantity and quality of information available.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗