Fred C. Montgomery

Electrically Biased NO x Sensing Elements with Coplanar Electrodes

Fabrication and characterization of electrically biased NO x sensing elements operative at 500-600°C are described. The sensing elements were produced by screen-printing Pt and transition metal oxide electrodes on yttria-stabilized zirconia substrates. DC electrical biasing greatly enhanced the response of the sensing elements to nitric oxide (NO), with voltage changes on the order of 10% observed as the sensing response to 450 ppmv NO at 600°C and 7 vol % O 2 . Voltage and current biasing techniques were employed with a sensing element using NiCr 2 O 4 as the oxide, and the computed changes in resistance due to NO were nearly identical, suggesting that the response mechanism of the elements is a change in dc electrical resistance. The sensing response was minimally affected by O 2 concentrations between 7 and 20 vol % at [NO] concentration levels from 0 to 1500 ppmv. These sensing elements and techniques may be useful in sensors for measuring [NO] at temperatures near 600°C.

Advanced electron microscopy study of fission product distribution in the failed SiC layer of a neutron irradiated TRISO coated particle

Tristructural isotropic (TRISO) coated particle fuel has been designed for application in hightemperature gas-cooled reactors (HTGR). TRISO particles for the HTGR fuel development effort underway at Idaho National Laboratory (INL) and Oak Ridge National Laboratory (ORNL) consist of a two-phase uranium oxide-uranium carbide (UCO) fuel kernel, a carbon buffer layer, an inner pyrolytic carbon (IPyC) layer, a SiC layer, and an outer PyC (OPyC) layer [1]. The first in a series of irradiation experiments (AGR-1) clearly shows release of certain metallic fission products, e.g., Ag and Pd, through intact TRISO coatings, with Cs generally well retained [1]. No significant chemical interaction was observed between Pd and SiC for UCO TRISO coated particles, which retained Cs [2].

Stable and selective sulfur dioxide sensing elements operating at 800–900 centigrade

Sensing behavior of electrochemical transducers for the detection of sulfur dioxide (SO2) is described. These elements operate at temperatures in the range 800-900 °C, and are constructed from oxide and precious metal electrodes on oxygenion conducting substrates. The responses to SO2 at oxygen contents around 5% can be large, with 25 ppm SO2 causing a 30-40% change in the sensing signal. This SO2 response is shown to be little affected by oxides of nitrogen (NOx), carbon monoxide, and propylene, present at the 100s of ppm level. Element stability is demonstrated over about 50 days of operation at temperature.

DETECTION OF SO2 AT HIGH TEMPERATURE WITH ELECTRICALLY BIASED, SOLID-ELECTROLYTE SENSING ELEMENTS

Design and operation of sensing elements for the detection of sulfur dioxide (SO2) at high temperature (800 900 oC) is described. The sensing elements consisted of three (two oxide and one Pt) electrodes on yttria-stabilized zirconia substrates. To operate the elements, a constant current (usually on the order of 0.1 mA) was driven between two of the electrodes and the voltage between one of these electrodes and the third electrode was monitored and used as the sensing signal. In one example, 31 ppm SO2 caused an approximately 40% change in the element output, and 2 ppm of SO2 could be easily detected. The cross-sensitivity to several interferents such as NOx was evaluated and found to be relatively small in comparison to the SO2 response.

Data Compilation for AGR-1 Variant 2 Compact Lot LEU01-48T-Z

This document is a compilation of characterization data for the AGR-1 variant 2 compact lot LEU01-48T-Z. The compacts were produced by ORNL for the Advanced Gas Reactor Fuel Development and Qualification (AGR) program for the first AGR irradiation test train (AGR-1). This compact lot was fabricated using particle composite LEU01-48T, which was a composite of three batches of TRISO-coated 350 {micro}m diameter 19.7% low enrichment uranium oxide/uranium carbide kernels (LEUCO). The AGR-1 TRISO-coated particles consist of a spherical kernel coated with an {approx} 50% dense carbon buffer layer (100 {micro}m nominal thickness), followed by a dense inner pyrocarbon layer (40 {micro}m nominal thickness), followed by a SiC layer (35 {micro}m nominal thickness), followed by another dense outer pyrocarbon layer (40 {micro}m nominal thickness). The kernels were obtained from BWXT and identified as composite G73D-20-69302. The BWXT kernel lot G73D-20-69302 was riffled into sublots for characterization and coating by ORNL and identified as LEU01-?? (where ?? is a series of integers beginning with 01). A data compilation for the AGR-1 variant 2 coated particle composite LEU01-48T can be found in ORNL/TM-2006/021. The AGR-1 Fuel Product Specification and Characterization Guidance (INL EDF-4380) provides the requirements necessary for acceptance of the fuel manufactured for the AGR-1 irradiation test. Section 6.2 of EDF-4380 provides the property requirements for the heat treated compacts. The Statistical Sampling Plan for AGR Fuel materials (INL EDF-4542) provides additional guidance regarding statistical methods for product acceptance and recommended sample sizes. The procedures for characterizing and qualifying the compacts are outlined in ORNL product inspection plan AGR-CHAR-PIP-05. The inspection report forms generated by this product inspection plan document the product acceptance for the property requirements listed in section 6.2 of EDF-4380.

Safety testing of AGR-2 UO2 compacts 3-3-2 and 3-4-2

Post-irradiation examination (PIE) is in progress on tristructural-isotropic (TRISO) coated-particle fuel compacts from the Advanced Gas Reactor (AGR) Fuel Development and Qualification Program second irradiation experiment (AGR-2) [Collin 2014]. The AGR-2 PIE will build upon new information and understanding acquired throughout the recently-concluded six-year AGR-1 PIE campaign [Demkowicz et al. 2015] and establish a database for the different AGR-2 fuel designs.

PIE on safety-tested AGR-1 compact 4-2-2

Post-irradiation examination (PIE) is being performed in support of tristructural isotropic (TRISO) coated particle fuel development and qualification for High-Temperature Gas-cooled Reactors (HTGRs). AGR-1 was the first in a series of TRISO fuel irradiation experiments initiated in 2006 under the Advanced Gas Reactor (AGR) Fuel Development and Qualification Program; this work continues to be funded by the Department of Energys Office of Nuclear Energy as part of the Advanced Reactor Technologies (ART) initiative. AGR-1 fuel compacts were fabricated at Oak Ridge National Laboratory (ORNL) in 2006 and irradiated for three years in the Idaho National Laboratory (INL) Advanced Test Reactor (ATR) to demonstrate and evaluate fuel performance under HTGR irradiation conditions. PIE is being performed at INL and ORNL to study how the fuel behaved during irradiation, and to examine fuel performance during exposure to elevated temperatures at or above temperatures that could occur during a depressurized conduction cooldown event. This report summarizes safety testing of irradiated AGR-1 Compact 5-1-1 in the ORNL Core Conduction Cooldown Test Facility (CCCTF) and post-safety testing PIE.

Development of a Radial Deconsolidation Method

A series of experiments have been initiated to determine the retention or mobility of fission products* in AGR fuel compacts [Petti, et al. 2010]. This information is needed to refine fission product transport models. The AGR-3/4 irradiation test involved half-inch-long compacts that each contained twenty designed-to-fail (DTF) particles, with 20-μm thick carbon-coated kernels whose coatings were deliberately fabricated such that they would crack under irradiation, providing a known source of post-irradiation isotopes. The DTF particles in these compacts were axially distributed along the compact centerline so that the diffusion of fission products released from the DTF kernels would be radially symmetric [Hunn, et al. 2012; Hunn et al. 2011; Kercher, et al. 2011; Hunn, et al. 2007]. Compacts containing DTF particles were irradiated at Idaho National Laboratory (INL) at the Advanced Test Reactor (ATR) [Collin, 2015]. Analysis of the diffusion of these various post-irradiation isotopes through the compact requires a method to radially deconsolidate the compacts so that nested-annular volumes may be analyzed for post-irradiation isotope inventory in the compact matrix, TRISO outer pyrolytic carbon (OPyC), and DTF kernels. An effective radial deconsolidation method and apparatus appropriate to this application has been developed and parametrically characterized.

Multi-tier Analysis of SiC Breaches in Safety-Tested AGR-1 TRISO Fuel Particles

Tristructural isotropic (TRISO) coated particle fuel development is being supported by the US Department of Energy, Office of Nuclear Energy. The development plan includes a series of irradiations to qualify TRISO fuel. The first irradiation, AGR-1, included fuel fabricated at Oak Ridge National Laboratory (ORNL) and irradiated in the Advanced Test Reactor at the Idaho National Laboratory (INL). The TRISO fuel design consisted of a uranium carbide/uranium oxide kernel surrounded by concentric coating layers of carbonaceous buffer, inner pyrolitic carbon (IPyC), silicon carbide (SiC), and outer pyrolitic carbon (OPyC). Particles were then over-coated with carbonaceous matrix material and pressed into a cylindrical compact, with each compact containing greater than 4100 TRISO particles. A total of 72 compacts were included in AGR-1 and the irradiation was completed in November 2009 after ~620 effective full power days [1].

High-T NOx Sensing Elements Using Conductive Oxides and Pt

Development of NOx sensing elements intended for operation at T ∼600 °C are described. The elements were fabricated by depositing co-planar La1-x Srx BO3 (B = Cr, Fe) and Pt electrodes on yttria-stabilized zirconia substrates. Characterization of the elements included response to NO2 and NO as well as the [O2 ] dependence of the NO2 response. Much stronger (∼ 40 mV for 450 ppm NO2 in 7 vol% O2 at 600 °C) sensing responses were observed for NO2 than NO, indicating these elements are best suited for detection of NO2 . Pronounced asymmetries were observed between the NO2 step response and recovery times for the elements, with temperature being the primary variable governing the recovery times in the temperature range 500–700 °C.Copyright