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Nuclear Fuels

A reactor’s ability to produce power efficiently is significantly affected by the composition and configuration of its fuel system. A nuclear fuel assembly consists of hundreds of thousands of uranium pellets, stacked and encapsulated within tubes called fuel rods or fuel pins which are then bundled together in various geometric arrangements.

There are many design considerations for the material composition and geometric configuration of the various components comprising a nuclear fuel system. Future designs for the fuel and the assembly or packaging of fuel will contribute to cleaner, cheaper and safer nuclear energy.

Today’s process for developing and testing new fuel systems is resource and time intensive. The process to manufacture the fuel, build an assembly, test it in a reactor, and evaluate its performance can take many years, involve many regulatory milestones and be quite costly. The Fuels focus area of NEAMS is dedicated to developing 3D, high resolution, multi-physics models and simulations to predict the evolution and performance of fuel systems that will help reduce some of these time and cost considerations.

These tools will help scientists and engineers understand the complex behavior of materials and their interaction with the fuel as well as how these behaviors change as one considers different length scales from micro-structural level to individual pellets to entire rods and bundles.  These tools will speed up the evaluation of the many different materials and configurations under consideration for packaging and handling of nuclear fuels by efficiently identifying designs unworthy of the long and costly testing process.


MARMOT is an application for simulating and understanding how materials such as nuclear fuel and its cladding change over time.  Specifically, MARMOT is able to capture how the microstructures of these materials evolve under irradiation by receiving inputs from more fundamental simulations at the atomic scale. These inputs are then used to generate new material properties and irradiation behaviors that can be used as inputs to engineering scale codes like BISON. By accurately capturing and passing specific properties from the lower length scales, MARMOT is then better able to model fuel performance at micron scale and in turn serve as a conduit to improve the predictive capability of the engineering scale tools.  For more detailed discussion on fuels modeling see the In Depth Article on Anatomy of a Nuclear Pin Assembly.


BISON is an application for simulating the performance of nuclear fuels at the engineering-scale under normal, off-normal, and accident conditions. BISON is designed to easily incorporate new material property and irradiation behavior models developed using MARMOT, making it increasingly predictive in nature. Together both BISON and MARMOT form the physics moduels of the Fuels Product Line.