Silicon Carbide Oxidation in Steam up to 2 MPa

Abstract

Growth and microstructure of a protective or nonprotective SiO2 scale and the subsequent volatilization of scale formed on high‐purity chemical vapor deposited (CVD) SiC and nuclear‐grade SiC/SiC composites have been studied during high‐temperature 100% steam exposure. The environmental parameters of interest were temperature from 1200°C to 1700°C, pressure of 0.1 to 2 MPa and flow velocities of 0.23 to 145 cm/s. Scale microstructure was characterized via electron microscopy and X‐ray diffractometry. The Arrhenius dependence of the parabolic oxidation and linear volatilization rate constants were determined. The linear volatilization rate exhibited a strong dependence on steam partial pressure with a weaker dependence on flow velocity. At high steam pressures, the oxide scale developed substantial porosity, which significantly accelerated material recession. The dominant oxide phase for the conditions studied was cristobalite. The oxidation behavior of SiC/SiC composite was strongly dependent on the state of the surface, specifically whether steam could find easy entry into the material via surface‐exposed interface layers. For the case where these as‐machined interfaces were surface coated with matrix CVD SiC, composite recession was found to be essentially that of high‐purity CVD SiC.

Preliminary safety analysis of the PWR with accident-tolerant fuels during severe accident conditions

“…Improved oxidation resistance of the ATF cladding typically takes effect in the mid-phase of a loss of active core cooling accident when the rate of core heatup and combustible gas production could be suppressed. The oxidation characteristics of SiC in water vapor have been increasingly studied, which suggests that a paralinear oxidation model (Opila and Hann, 1997;Opila, 2003;Terrani et al, 2014) could be applied. The oxidation of SiC in water vapor starts from the formation of protective silica (SiO 2 ) scale and production of H 2 and carbon monoxide gas (CO):…”

“…The rate constants are usually expressed on the basis of Arrhenius' relationship A expðÀB=RTÞ. To model the oxidation kinetics of SiC cladding, in the present study we adopt the following relationships derived by Terrani et al (2014) based on high-temperature SiC oxidation experiments during exposure to pure steam:…”

Material Selection for Accident Tolerant Fuel Cladding

“…The silica scale formed on SiC has excellent steam oxidation resistance up to at least 1973 K (1700°C) [13] but many other aspects of its utilization as nuclear fuel cladding, including thermo-mechanical reliability [21] and hydrothermal corrosion resistance, have not yet been proven sufficient. [22] Figure 2 illustrates the rates shown in Figure 1 at 1373 K and 1473 K (1100°C and 1200°C) in 1 bar steam.…”

“…Oxidation experiments were conducted in three different systems: (1) thermal gravimetric analysis (TGA) in 1 bar of Ar-50 pct H 2 O or dry air at 1473 K (1200°C), using a Cahn model 1000 microbalance with a quartz tube, (2) magnetic suspension TGA using a Rubotherm DynTHERM LP-HT-II instrument where the alumina test chamber was fully isolated with dry air or 100 pct steam at 1073 K to 1773 K (800°C to 1500°C), and (3) a high-temperature [maximum 1973 K (1700°C)] test rig consisting of a vertical alumina tube with two resistively heated furnaces where steam or air entered the bottom of the tube and was preheated to 1273 K to 1573 K (1000°C to 1300°C) by the first furnace and the specimen was held in the second furnace in an alumina holder attached to the top tube using an alumina pin. [13] For the TGA experiments, the specimen was suspended with a Pt-Rh wire, which experienced little evaporation in steam or Ar-50 pct H 2 O. The deionized water used to generate steam was not Ar-bubbled or filtered as is typically done for~873 K (600°C) steam testing, thus the O 2 content was~10 ppm.…”

“…Figure 1 provides an overview of the steam oxidation kinetic data of the various fuel cladding candidates. [4,13,[15][16][17] The data were fitted to an Arrhenius relationship [4,13,[15][16][17] with the resulting oxidation activation energies noted. Current results for MAX phase materials are also shown.…”