THERMAL CONDUCTIVITY OF POLYCRYSTALLINE ZIRCONIUM NITRIDE AS A FUNCTION OF TEMPERATURE, POROSITY, AND OXYGEN IMPURITY LEVEL

Conference · Wed Jan 31 00:00:00 EST 2007

OSTI ID:985881

STANEK, CHRISTOPHER R ^[1]; MCCLELLAN, KENNETH J ^[1]; MORALES, LUIS A ^[1]; BYLER, DARRIN D ^[1]; VOIT, STEWART L ^[1]; HENDERSON, JACK B ^[1]

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1. Los Alamos National Laboratory

The U.S. Department of Energy is currently investigating routes that will allow for a closed fuel cycle. One key benefit of a closed fuel cycle is significant reductions in the radiotoxicity of high-level waste via transmutation of minor actinides in fast spectrum reactors or accelerator driven systems. Mononitrides (MN, where M = Zr, U, Np, Pu, Am, Cm, etc.) are candidates for transmutation fuel materials due to significant radiation tolerance and high thermal conductivity, both important characteristics for high burn-up fuels. ZrN is of interest as a candidate matrix material for future dispersion fuels, a diluent in actinide-bearing fuels, and a surrogate material that enables efficient assessment of some trends in thermo-physical properties of mononitrides. ZrN-based, actinide-bearing nitride fuels, e.g. (Pu, Np, Am)N-36wt%ZrN, have been irradiated in the Advanced Test Reactor (ATR) at INL in the AFC-AE test and are scheduled for insertion in the Phenix reactor for the FUTURIX-FTA experiment. Pure ZrN matrix material is also scheduled for insertion in the FUTURIX-MI materials irradiation experiment. Therefore, it is important to understand the thermophysical properties of unirradiated polycrystalline ZrN as a function of porosity (density and pore distribution) as well as stoichiometry. Specific heat, thermal expansion and thermal diffusivity have been measured in ZrN samples with different bulk densities and oxygen impurity levels. For the samples, thermal conductivity was calculated as the product of the bulk density, specific heat and thern1al diffusivity. Properties were measured over at least the temperature range of room temperature to 1200 C in samples with densities ranging from roughly 85 to 95% of theoretical density. Over this temperature range, the linear thermal expansion coefficient was {approx}10 x 10{sup -6}/C, specific heat increased from {approx}0.4 to 0.5 J/(g K), and thermal diffusivity increased from {approx}3 to 6 mm{sup 2}/s. For the densities studied, this corresponded to thermal conductivity increasing from {approx}7 to 20 W/(m K) from room temperature to 1200 C. As expected, thermal conductivity of the polycrystalline ZrN varied with density and a significant effect on the measured properties was observed for samples with different oxygen impurity levels. The implications of the observed trends in thermophysical properties with porosity and oxygen impurity level will be discussed in the context of nitride fuel fabrication and performance as well as with respect to fuel property characterization.

• Research Organization: Los Alamos National Laboratory (LANL), Los Alamos, NM (United States)
• Sponsoring Organization: USDOE National Nuclear Security Administration (NNSA)
• DOE Contract Number: AC52-06NA25396
• OSTI ID: 985881
• Report Number(s): LA-UR-07-0703; TRN: US1006262
• Resource Relation: Conference: GLOBAL 2007: ADVANCED NUCLEAR FUEL CYCLES AND SYSTEMS ; 200709 ; BOISE
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACCELERATORS
ACTINIDES
BULK DENSITY
FABRICATION
FUEL CYCLE
IRRADIATION
MATRIX MATERIALS
NITRIDES
NUCLEAR FUELS
OXYGEN
PHENIX REACTOR
POROSITY
RADIATIONS
SOLVENTS
SPECIFIC HEAT
STOICHIOMETRY
TEST REACTORS
THERMAL CONDUCTIVITY
THERMAL DIFFUSIVITY
THERMAL EXPANSION
TRANSMUTATION
WASTES
ZIRCONIUM NITRIDES