Lindemer, Terrence | Search NASA

DOE OSTI2015

Triso coating development progress for uranium nitride kernels

In support of fully ceramic matrix (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 UN kernels [3]. The nitride kernels are used to increase fissile density in these SiC-matrix fuel pellets with details described elsewhere [4]. The advanced gas reactor (AGR) program at ORNL used fluidized bed chemical vapor deposition (FBCVD) techniques for TRISO coating of UCO (two phase mixture of UO2 and UCx) kernels [5]. Similar techniques were employed for coating of the UN kernels, however significant changes in processing conditions were required to maintain acceptable coating properties due to physical property and dimensional differences between the UCO and UN kernels (Table 1).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2015

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

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 H2 in the entire process.

36 MATERIALS SCIENCE↗