Light water reactor (LWR) fuel performance is limited by thermal and mechanical constraints associated with the design, fabrication,and operation of fuel in a nuclear reactor. These limits define the lifetime of the fuel, the maximum power at which the fuel can be operated, the probability of fuel structural failure over the fuel lifetime, and the transient performance of the fuel during an accident. A technique is explored that extends fuel performance by thermally bonding LWR fuel with a nonalkaline liquid-metal alloy. Current LWR fuel rod designs consist of enriched uranium oxide fuel pellets enclosed in a zirconium alloy cylindrical clad. The space between the pellets and the clad is filled by an inert gas (typically helium). Because of the low thermal conductivity of the gas, the gas space thermally insulates the fuel pellets from the reactor coolant outside the fuel rod, elevating the fuel temperatures. Filling the gap between the fuel and clad with a high-conductivity liquid metal thermally ''bonds'' the fuel to the cladding and eliminates the large temperature change across the gap while preserving the expansion and pellet-loading capabilities. The resultant lower fuel temperature has a direct impact on fuel performance. The application of liquid-bonding techniques to LWR fuel is explored to increase LWR fuel performance and safety. A modified version of the ESCORE fuel performance code (ESBOND) is developed to analyze the in-reactor performance of the liquid-metal-bonded fuel. An assessment of the technical feasibility of this concept for LWR fuel is presented, including the results of research into materials compatibility testing and the predicted lifetime performance of liquid-bonded LWR fuel. The results show that liquid-bonded boiling water reactor peak fuel temperatures are 400 degrees F lower at beginning of life and 200 degrees F lower aat end of life compared with conventional fuel. References: 12
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