Determination of oxygen-to-uranium ratios in hypo- and hyperstoichiometric uranium dioxide and tungsten-uranium dioxide

Thermodynamics of the O–U system: III – Critical assessment of phase diagram data in the U–UO2+x composition range

“…Table 1 Intrinsic uncertainties as summarized from Refs. [3][4][5] mainly), and finally will reach the congruent composition. These properties have been used:…”

“…Composition analysis of the samples may be performed by gravimetry either after reduction with pure H 2 at T > 1173 K [4] to UO 2±0.001 or by oxidation to U 3 O 8 (s) at atmospheric pressure. For this last case, Labroche et al [3,5] proposed an analysis of the different causes of errors, based on the Ackermann and Chang [6] work on the non-stoichiometry of the compound U 3 O 8Àz .…”

“…To avoid this, several authors used sintered pellets that are less reactive. According to Schaefer [4], the influence of humidity, when controlled, gave dx = ± 0.002. • For the reaction of precipitated U metal with air for UO 2Àx hypostoichiometric samples after cooling: dx = ± 0.002 is taken.…”

An Innovative High Thermal Conductivity Fuel Design

“…The defects in the UO 2 crystal lattice also act as phonon scattering centers, and reduce the thermal conductivity of UO 2 . In addition, hypostoichiometric UO 2 could contain uranium metal which could be highly reactive with other materials; hyperstoichiometric UO 2 may have an oxygen partial pressure sufficient to cause interaction with other materials [9]. The O/U ratio of an unknown UO 2.x powder can be determined by measuring the weight difference of UO 2.x and U 3 O 8 oxidized by UO 2.x , or UO 2.x and UO 2 reduced by UO 2.x (for hyperstoichiometric UO 2 ).…”

A comparative study on dissolution rate of sintered (Th–U)O2 pellets in nitric acid by microwave and conventional heating

“…6 Analytical methods routinely being used for O/M determination are the gas equilibration method, coulometric method and oxidation-reduction method. [7][8][9] To maintain neutron economy and fuel density it is necessary to have control on trace constituents in the fuel. For common metallic impurities, various analytical techniques like direct current arc emission spectroscopy (DC-Arc-AES), X-ray fluorescence (XRF), ion selective electrode (ISE) and atomic absorption spectroscopy have been employed.…”