Molybdenum Disilicide Oxidation Kinetics in High Temperature Steam

Technical Report · Wed Sep 07 00:00:00 EDT 2016

DOI:https://doi.org/10.2172/1323383· OSTI ID:1323383

Wood, Elizabeth Sooby ^[1]; Parker, Stephen Scott ^[1]; Nelson, Andrew Thomas ^[1]

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

The Fuel Cycle Research and Development program’s Advanced Fuels Campaign is currently supporting a range of experimental efforts aimed at the development and qualification of ‘accident tolerant’ nuclear fuel forms. One route to enhance the accident tolerance of nuclear fuel is to replace the zirconium alloy cladding, which is prone to rapid oxidation in steam at elevated temperatures, with a more oxidation-resistant cladding. Several cladding replacement solutions have been envisaged. The cladding can be completely replaced with a more oxidation resistant alloy, a layered approach can be used to optimize the strength, creep resistance, and oxidation tolerance of various materials, or the existing zirconium alloy cladding can be coated with a more oxidation-resistant material. Molybdenum is one candidate cladding material favored due to its high temperature creep resistance. However, it performs poorly under autoclave testing and suffers degradation under high temperature steam oxidation exposure. Development of composite cladding architectures consisting of a molybdenum core shielded by a molybdenum disilicide (MoSi₂) coating is hypothesized to improve the performance of a Mo-based cladding system. MoSi₂ was identified based on its high temperature oxidation resistance in O₂ atmospheres (e.g. air and “wet air”). However, its behavior in H₂O is less known. This report presents thermogravimetric analysis (TGA), scanning electron microscopy (SEM), and x-ray diffraction (XRD) results for MoSi₂ exposed to 670-1498 K water vapor. Synthetic air (80-20%, Ar-O₂) exposures were also performed, and those results are presented here for a comparative analysis. It was determined that MoSi₂ displays drastically different oxidation behavior in water vapor than in dry air. In the 670-1498 K temperature range, four distinct behaviors are observed. Parabolic oxidation is exhibited in only 670-773 K water vapor, a temperature range in which the material pests in dry O₂ environments. From 877-1084 K in water vapor, MoSi₂ undergoes rapid mass gain resulting in oxidation throughout the bulk of the sample at 980 K and 1084 K. The resulting material displays swelling and warping after the 980-1084 K exposures. A pre-passivation heat treatment performed at 1395 K was found capable of producing a coarse SiO₂ layer that limited pesting at lower temperatures in water vapor over the time periods investigated.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE Office of Nuclear Energy (NE)
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 1323383
• Report Number(s): LA-UR-15-26776; TRN: US1700280
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
ACCIDENT-TOLERANT NUCLEAR FUELS
WATER VAPOR
FUEL CANS
MOLYBDENUM
MOLYBDENUM SILICIDES
THERMAL GRAVIMETRIC ANALYSIS
OXIDATION
X-RAY DIFFRACTION
SCANNING ELECTRON MICROSCOPY
AIR
SILICON OXIDES
STEAM
CHEMICAL REACTION KINETICS
SWELLING
HEAT TREATMENTS
Material Science