Carbothermic Synthesis of ~820- m UN Kernels. Investigation of Process Variables

Abstract

This report details the continued investigation of process variables involved in converting sol-gel-derived, urainia-carbon microspheres to ~820-µm-dia. UN fuel kernels in flow-through, vertical refractory-metal crucibles at temperatures up to 2123 K. Experiments included calcining of air-dried UO 3-H 2 O-C microspheres in Ar and H 2-containing gases, conversion of the resulting UO 2-C kernels to dense UO 2 :2UC in the same gases and vacuum, and its conversion in N 2 to in UC 1-x N x. The thermodynamics of the relevant reactions were applied extensively to interpret and control the process variables. Producing the precursor UO 2 :2UC kernel of ~96% theoretical density was required, but its subsequent conversion to UC 1-x N x at 2123 K was not accompanied by sintering and resulted in ~83-86% of theoretical density. Decreasing the UC 1-x N x kernel carbide component via HCN evolution was shown to be quantitatively consistent with present and past experiments and the only useful application of H 2 in the entire process.

Production of near‐full density uranium nitride microspheres with a hot isostatic press

“…Depleted uranium nitride (DUN) microspheres with diameters ranging from 420 to 858 microns and TD between 87% and 91% TD with closed porosity were synthesized in an effort to quantify process variables for fabrication of UN kernels for FCM fuel . For this work, 3 different batches, summarized in Table , were chosen to investigate increasing density with a HIP postprocessing step.…”

Examination of HIP for production of high density UN kernels

“…Kernels produced in FY15 and FY16 [6] consistently resulted in between 86-88% TD UN microspheres with closed porosity. For this work, three different batches, summarized in Table 1, were chosen to investigate increasing density with a HIP post processing step.…”

“…Depleted uranium nitride (UN) microspheres with diameters ranging from 420 to 858 microns and TD between 87 and 91 percent were synthesized in FY15 and FY16 part of a larger effort to explore fabrication routes for Fully Ceramic Microencapsulated (FCM) fuel [4][5][6]. This work investigates the viability of a post processing step with a hot isostatic press (HIP) shown in Fig.…”

Fabrication and Characterization of Surrogate TRISO Particles Using 800μm ZrO₂ Kernels

“…In support of fully ceramic microencapsulated (FCM) fuel development [1][2], coating development work is ongoing at the Oak Ridge National Laboratory (ORNL) to produce tri-structural isotropic (TRISO) coated fuel particles with both UN kernels [3] and surrogate (uranium-free) kernels. The nitride kernels are used to increase fissile density in these SiC-matrix fuel pellets with details described elsewhere [4].…”