Engineering topics

Kondrat, Kyle J.

Publications and source records attributed to Kondrat, Kyle J..

4 records

DOE OSTI2024

On the product phases and the reaction kinetics of carbothermic reduction of UO 2 +C at relatively low temperatures

The synthesis of UC using carbothermic reduction of UO 2 and C mixtures has been well studied at high temperatures. However, the product phase behavior of carbothermic reduction at low temperatures (≤1773 K) is not well studied. Such a study is important as low temperatures permit single phase UC synthesis without forming secondary higher carbides, and it further supports the knowledge base of the process that needs to be used for transuranic elements such as plutonium that have high vapor pressures at elevated temperatures. Therefore, a low temperature carbothermic reduction of two different C/UO 2 molar ratios under inert and reducing environments have been studied here. Two different sample holding crucibles, alumina (Al 2 O 3 ) and graphite, were also used here to differentiate the hypostoichiometric (UC 1-a ) and oxygen dissolved (UC 1-x O x ) uranium monocarbide phases adding more details on the two systems. Also, the reaction kinetics involved in the formation of UC via the carbothermic reduction of UO 2 +C using product phases instead of evolved gases such as carbon monoxide is reported here. Under inert atmospheres but with significant oxygen partial pressures, the low temperature carbothermic reduction of UO 2 +C produced up to 90 wt.% UC 1-x O x type oxycarbides as was confirmed by Xray powder diffraction. Reducing Ar-4%H 2 environments at these temperatures were not successful in synthesizing UC as it reduces the amount of C required for the carbothermic reduction, leaving UC phase at a non-equilibrium state. Inert atmospheres with low or negligible oxygen partial pressures on the other hand produced near stoichiometric UC at high phase purity, especially at 1673 – 1773 K temperature range. An activation energy of 377±75 kJmol -1 was also calculated using product phase concentrations of the carbothermic reduction of UO 2 +C under these inert Ar (g) atmospheres.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Special Nuclear Material Hold-up Measurement

Facilities that process special nuclear material (SNM) generally have a variety of equipment, shielding, and nearby radiation sources, which can pose challenges when performing nondestructive analysis (NDA) within the facility, as shown in Figure 1. In this figure, the left image features two individuals performing a holdup measurement of a large duct at a posting, utilizing a detector probe attached to a yardstick to reduce some aspect of the measurement uncertainty. Note that the distance to the holdup within the pipe from the posting cannot be accounted for. The right image similarly features several individuals guiding a holdup measurement of a ducting pipe several meters overhead, by attaching a detector probe to a long handle and lining that up with a posting on the outside of the pipe. SNM processing begets SNM holdup, and this difficulty with accurate NDA can result in unaccounted accumulation of SNM holdup within a process or area. Normal SNM processing operations can accumulate holdup within filters, pumps, pipes, ducts, other equipment, and facility support systems, as demonstrated by Figure 2. It is important for deactivation and decommissioning (D&D) gloveboxes and their ancillary equipment, material accountability, criticality safety, facility operations, waste management, radiation safety, and security to accurately characterize the location, composition, and quantity of this holdup to minimize these associated risks and potential diversion pathways. Current NDA techniques for assay of holdup are expensive, time consuming, and have high uncertainty.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2023

Crystallographic Study of Product Phases of Carbothermic Reduction and Nitridation of Hafnium Dioxide

Details of the carbothermic reduction/nitridation to synthesize hafnium nitride (HfN) and hafnium carbide (HfC) are scarce in the literature. Therefore, this current study was carried out to evaluate two pathways for synthesizing these two refractory materials: direct nitridation and carbothermic reduction/nitridation. Two mixtures of hafnium dioxide and carbon with C/HfO 2 molar ratios of 2.15 and 3.1 were nitridized directly using flowing nitrogen gas at elevated temperatures (1300–1700 °C). The 3.1 C/HfO 2 molar ratio mixture was also carbothermically reduced under flowing argon gas to synthesize HfC, which was converted into HfN by introducing a nitridation step under both N 2(g ) and N 2(g) -10% H 2(g) . X-ray diffraction results showed the formation of HfN at 1300 and 1400 °C and HfC 1–y N y at ≥1400 °C under direct nitridation of samples using a C/HfO 2 molar ratio of 2.15. These phase analysis data together with lower lattice strain and greater crystallite sizes of HfC 1–y N y that formed at higher temperatures suggested that the HfC 1–y N y phase is preferred over HfN at those temperatures. Carbothermic reduction of 3.1 C/HfO 2 molar ratio samples under an inert atmosphere produced single-phased HfC with no significant levels of dissolved oxygen. In conclusion, carbothermic reduction nitridation made two phases of different carbon levels (HfC 1–y N y and HfC 1–y 'N y ', where y' < y), while direct nitridation produced a single HfC 1–y N y phase under both N 2 and N 2 -10% H 2 cover gas environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2023

Trade Study of Nondestructive Assay Technologies

The purpose of this report is to summarize the capabilities of currently existing NDA technologies that can be applied to holdup measurements. Cataloguing the strengths and weaknesses of the existing state of the art is a necessary step towards setting goals for new technology development. The NDA technologies evaluated in this report include gamma imaging, non-imaging gamma detectors, and neutron coincidence counting. These technologies were chosen based on their potential for technological improvement or to be applied in different settings. Each technology will be analyzed on a set of evaluation criteria chosen to represent the most salient features of a detector system for holdup measurements. These criteria include sensitivity, energy resolution, angular resolution (for imaging technologies only), ease of use, and cost.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗