Assessment of semi-empirical potentials for the U-Si system

Technical Report · Wed Feb 03 00:00:00 EST 2016

DOI:https://doi.org/10.2172/1237245· OSTI ID:1237245

Baskes, Michael I. ^[1]; Andersson, Anders David ^[1]

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1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)

Accident tolerant fuels (ATF) are being developed in response to the Fukushima Daiichi accident in Japan. One of the options being pursued is U-Si fuels, such as the U₃Si₂ and U₃Si₅ compounds, which benefit from high thermal conductivity (metallic) compared to the UO2 fuel (semi-conductor) used in current Light Water Reactors (LWRs). The U-Si fuels also have higher fissile density. In order to perform meaningful engineering scale nuclear fuel performance simulations, the material properties of the fuel, including the response to irradiation environments, must be known. Unfortunately, the data available for U-Si fuels are rather limited, in particular for the temperature range where LWRs would operate. The ATF HIP is using multi-scale modeling and simulations to address this knowledge gap. Even though Density Functional Theory (DFT) calculations can provide useful answers to a subset of problems, they are computationally too costly for many others, including properties governing microstructure evolution and irradiation effects. For the latter, semi-empirical potentials are typically used. Unfortunately, there is currently no potential for the U-Si system. In this brief report we present initial results from the development of a U-Si semi-empirical potential based on the Modified Embedded Atom Method (MEAM). The potential should reproduce relevant parts of the U-Si phase diagram as well as defect properties important in irradiation environments. This work also serves as an assessment of the general challenges associated with the U-Si system, which will be valuable for the efforts to develop a U-Si Tersoff potential undertaken by Idaho National Laboratory (also part of the ATF HIP). Going forward the main potential development activity will reside at INL and the work presented here is meant to provide input data and guidelines for that activity. The main focus of our work is on the U₃Si₂ and U3Si₅ compounds, because they are the main nuclear fuel candidates. U₃Si₅ is derived from USi₂ in the AlB₂ structure by creating 1/6 vacant sites on Si sublattice. The ordering of these vacancies will not be studied in any detail here.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1237245
• Report Number(s): LA-UR-15-26949; TRN: US1600298
• Country of Publication: United States
• Language: English

Related Subjects

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
ACCIDENT-TOLERANT NUCLEAR FUELS
URANIUM SILICIDES
POTENTIALS
WATER MODERATED REACTORS
URANIUM DIOXIDE
DENSITY FUNCTIONAL METHOD
ALUMINIUM BORIDES
PHASE DIAGRAMS
THERMAL CONDUCTIVITY
EVALUATION
COST
IRRADIATION
WATER COOLED REACTORS
COMPARATIVE EVALUATIONS
DENSITY
COMPUTERIZED SIMULATION
DEFECTS
TIME DEPENDENCE
MICROSTRUCTURE
PERFORMANCE