The dissolution of helium in La-doped UO2 as a surrogate of hypo-stoichiometric UO2

Abstract

In this work, the dissolution of helium in La-doped UO 2 samples was studied by helium infusion in an autoclave followed by thermal desorption (laser heating) coupled to mass spectrometer systems for the determination of helium release rate and the total helium quantity. Lanthanum was chosen as a dopant in UO 2 to study the effect of hypo-stoichiometry on helium solubility together with the impurity effect. Comparison of the dissolved He quantity from the samples with different La content showed that the dissolved He quantity slightly increases with increasing oxygen vacancy concentration in the samples.

Raman and X‐ray Studies of Uranium–Lanthanum‐Mixed Oxides Before and After Air Oxidation

“…Furthermore, although oxidation of pure and La‐doped UO 2 samples was performed under the same conditions (sample thickness, oxidation temperature, and time), oxidation of UO 2 could also depend on other parameters such as grain size, density, and orientation effect . The grain size of the current La‐doped UO 2 samples was in fact much smaller compared to undoped UO 2 (The average grain sizes of 6, 11, 22 at.% La‐doped UO 2 and undoped UO 2 samples are 3, 4, 7, and 14 μm, respectively . This would also explain a more rapid oxygen diffusion along grain boundaries than into the larger UO 2 grains …”

“…La‐doped UO 2 samples with three different compositions (6, 11, 22 mol%) were prepared by a sol–gel technique . Transmission electron microscopy observations on several grains of La‐doped UO 2 samples showed that all the samples have homogeneous compositions and no La or U oxide precipitates were present in the samples . The obtained powders were pressed at 110 MPa into a disk and the compacted disks were sintered at 1923 K for 6 h under 6% H 2 /94% Ar atmosphere to have (U 1− y 4+ ,La y 3+ )O 2− y /2 , that is, containing only U 4+ , and the O/M ratios of the three samples are thus O/M = 1.97, 1.945, ad 1.89, respectively.…”

“…61 The grain size of the current La-doped UO 2 samples was in fact much smaller compared to undoped UO 2 (The average grain sizes of 6, 11, 22 at.% La-doped UO 2 and undoped UO 2 samples are 3, 4, 7, and 14 lm, respectively. 17 This would also explain a more rapid oxygen diffusion along grain boundaries than into the larger UO 2 grains. 61 Thomas et al 15 showed that the presence of lanthanides in unirradiated UO 2 stabilizes the cubic M 4 O 9 crystal lattice during air oxidation at low temperature (175°C-195°C) and delays the formation of M 3 O 8 similar to the oxidation behavior of Light Water Reactor spent fuel.…”

Knudsen effusion mass spectrometry: Current and future approaches

“…313 Other examples demonstrate the measurement using KEMS of helium solubility in stoichiometric and hyper-stoichiometric UO 2 314 or in La-doped UO 2 as a surrogate of hypo-stoichiometric UO 2. 315 In the later study, the spent fuel storage/ disposal aspect is addressed. Diffusion and release properties of radiogenic helium need to be assessed for the prediction of material long-term behavior (spent fuel, radioisotopic thermal generator, actinide-bearing fuels).…”