Helium solubility and behaviour in uranium dioxide

A mass spectrometry method for quantitative and kinetic analysis of gas release from nuclear materials and its application to helium desorption from UO2and fission gas release from irradiated fuel

“…A quantitative measurement of the gas accumulated in the HP sample chamber (1) is achieved by sampling the gas through the inlet (5) and the microvalve (13) to the low-pressure mass spectrometer chamber (7) and comparing its signals with the signal of a gas spike of the same element (introduced subsequently in the HP sample chamber), using a quadrupole mass spectrometer equipped with an electron bombardment ion source (6). The whole pumping system works in a closed circuit during the measurement process: once the gas is analysed in the mass spectrometer chamber (7), it is pumped immediately through the feedback (8) back to the HP sample chamber (1). This technique has the following advantages: it allows kinetic measurements, it yields the current integral of the gas released, it improves the sensitivity because the gas quantity sampled by the mass spectrometer can be significant versus the total quantity of gas collected without depleting the total quantity, and eventually it keeps the total inventory available for isotope ratio measurement at the end of the measurement.…”

“…In order to obtain a low background (a good vacuum) in the mass spectrometer chamber (7), two turbo pumps are installed in series (14) yielding a theoretical compression ratio in the range from 1 × 10 9 to 1 × 10 20 (sum of compression ratio of both turbo pumps) depending on the gas atomic mass and a pumping rate of ∼200 l s −1 . This system of feedback (8) ensures that the sample gas is never depleted and the measurement can thus be done continuously throughout the release process, allowing the determination of the release kinetics as well as long duration measurements.…”

“…Details of the sample preparation and infusion are given in Appendix and [8]. After the infusion, each sample was annealed and the released behaviour of Figure 5.…”

“…The same measurements on fresh nuclear fuel infused or implanted with gas, or on α-doped materials in which radiogenic helium gas is produced, permits on one hand to assess the solubility of the gas in the matrix [8], and on the other hand to determine the gas behaviour and its diffusion coefficient as a function of the annealing temperature, and to identify the release mechanisms.…”

A study of helium mobility in polycrystalline uranium dioxide

“…These may be put into four categories: actual differences in materials and/or material microstructures: grain or particle size, presence of grain boundaries, impurity or foreign element content, initial non-stoichiometry. the conditions under which the diffusion experiment is carried out (under vacuum: this study, [28,27,5]; under controlled oxygen partial pressure: [7]; at high pressure and in an inert gas environment: [2,3]). the overall strategy for introducing helium atoms in the samples (ion implantation: this study, [7]; radiogenic production: [27,5], high pressure and temperature infusion: [2,3,28,27]).…”