Thermodynamic and composition changes in UO2±x (x< 0.005) at 1950 K

Thermodynamics of the O–U system. IV – Critical assessment of chemical potentials in the U–UO2.01 composition range

“…For studies performed with CO/CO 2 = 10/1 gaseous flow equilibrium compositions, Markin et al [47], Wheeler [50] and Wheeler and Jones [51], the final composition is located in the oxygen potential vertical change in stoichiometric UO 2 . This composition was estimated first by the authors [47,50] to be very accurate, %± 0.001 and later to be ± 0.003 (see Fig.…”

“…This composition was estimated first by the authors [47,50] to be very accurate, %± 0.001 and later to be ± 0.003 (see Fig. 2 in [51]), but as the comparison with other methods, like H 2 /H 2 O flow ratios or hydrogenation into UH 3 , gives results to within 0.005 [51], we adopt a total uncertainty d(O/U) = ±0.005. As the silica sheath is opened in an argon filled glove box, and the sample is firstly slightly oxidized to UO 2+x by a known amount of O 2 (volumetric method) before reduction, there is no uncertainty due to air exposure (see Table 5).…”

“…For pyrometric measurements [45][46][47][48][49][50][51], the stability of the temperature control added to the pyrometric readings and necessary calibration procedures lead to dT $ ±15 K. For W/Re thermocouples [52], we would prefer to increase slightly the estimates of the authors up to dT = ±10 K.…”

Effects of Fuel Oxidation and Dissolution on Volatile Fission Product Release under Severe Accident Conditions

“…Equilibrium deviation (x e of UO 2þxe ) from stoichiometric UO 2 of the fuel is evaluated as a function of the oxygen potential 14) of the test atmosphere with the Lindemer-Besmann model. 15) Oxidation rate to move to the equilibrium is then calculated as a function of surface area to volume ratio (S/V) and temperature with the model developed by Cox et al, 16) and deviation (x of UO 2þx ) from stoichiometric UO 2 can be estimated at each time during the test.…”

“…The oxidation of stoichiometric UO 2 to UO 2þx by steam and the resulting change in the diffusion coefficient could be calculated from their separate effect studies as follows. [14][15][16]20) The oxygen partial pressure in the atmosphere gas is obtained from Wheeler and Jones formula in a hydrogen and steam mixture, 14) ln…”