Jason M. Harp

RERTR-12 Post-irradiation Examination Summary Report

The following report contains the results and conclusions for the post irradiation examinations performed on RERTR-12 Insertion 2 experiment plates. These exams include eddy-current testing to measure oxide growth; neutron radiography for evaluating the condition of the fuel prior to sectioning and determination of fuel relocation and geometry changes; gamma scanning to provide relative measurements for burnup and indication of fuel- and fission-product relocation; profilometry to measure dimensional changes of the fuel plate; analytical chemistry to benchmark the physics burnup calculations; metallography to examine the microstructural changes in the fuel, interlayer and cladding; and microhardness testing to determine the material-property changes of the fuel and cladding. These characterization activities are tailored specifically to define: • The mechanical response of fuel meat, cladding, and interlayers, including diffusion barrier integrity • Whether geometry is stable and predictable; that changes in channel gap do not compromise ability to cool fuel • That fuel performance is known and predictable • A limited set of physical properties that are important for the analysis of fuel burnup limits • Whether swelling is stable and predictable.

Thermal and transport properties of U 3 Si 2

Abstract We have studied U 3 Si 2 by means of the heat capacity, electrical resistivity, Seebeck and Hall effects, and thermal conductivity in the temperature range 2–300 K and in magnetic fields up to 9 T. All the results obtained point to delocalized nature of 5 f -electrons in this material. The low temperature heat capacity is enhanced ( γ el  ∼ 150 mJ/mol-K 2 ) and shows an upturn in C p /T (T), characteristic of spin fluctuations. The thermal conductivity of U 3 Si 2 is ∼8.5 W/m-K at room temperature and we show that the electronic part dominates heat transport above 300 K as expected for a metallic system, although the lattice contribution cannot be completely neglected.

Interdiffusion Behavior of FeCrAl with U 3 Si 2

Advanced steels, including FeCrAl are being considered as an alternative to the standard light water fuel (LWR) cladding, Zircalloy. FeCrAl has superior mechanical and thermal properties and oxidation resistance relative to the Zircalloy standard . Uranium Silicide (U3Si2) is a candidate to replace uranium oxide (UO2) as LWR fuel because of its higher thermal conductivity and higher fissile density relative to the current standard, UO2. The interdiffusion behavior between FeCrAl and U3Si2 is investigated in this study. Commercially available FeCrAl, along with pellets fabricated at the Idaho National Laboratory were placed in diffusion couples. Individual tests have been run at temperatures ranging from 500 ℃ to 1000 ℃ for 30 h and 100 h. The interdiffusion is analyzed with an optical microscope and scanning electron microscope (SEM). Uniform and planar diffusion regions along the material interface are illustrated with backscatter electron micrographs and energy-dispersive X-ray spectroscopy (EDS).

Thermal Properties Measurement Report

The Thermal Properties Measurement Report summarizes the research, development, installation, and initial use of significant experimental thermal property characterization capabilities at the INL in FY 2015. These new capabilities were used to characterize a U3Si2 (candidate Accident Tolerant) fuel sample fabricated at the INL. The ability to perform measurements at various length scales is important and provides additional data that is not currently in the literature. However, the real value of the data will be in accomplishing a phenomenological understanding of the thermal conductivity in fuels and the ties to predictive modeling. Thus, the MARMOT advanced modeling and simulation capability was utilized to illustrate how the microstructural data can be modeled and compared with bulk characterization data. A scientific method was established for thermal property measurement capability on irradiated nuclear fuel samples, which will be installed in the Irradiated Material Characterization Laboratory (IMCL).