Irradiation induced volume change in UN2

Matrix swelling rate and cavity volume balance of UO2 fuels at high burn-up

“…where a 3 12 is the average atomic volume in UO 2 [18], a is the lattice constant, z is the number of sites explored per gas-atom jump, d is the width of the boundary, n is a grain-boundary diffusion enhancement factor, and K is the flux of gas-atoms per unit area of grain boundary. The intergranular bubble nucleation and growth formulation incorporated here is based on the assumption that, although the effect of radiation-induced re-solution on intergranular bubble behavior is not negligible, a reasonable approximation can be obtained by neglecting such effect in the governing equations [19].…”

“…Regarding the gas in dynamic solution, the hypothesis has been made following Matzke [20,21] that gas atoms in the UO 2 lattice become effectively bound to the so-called Schottky trios, i.e., electrically neutral defect complexes consisting of one uranium vacancy and two oxygen vacancies. Thus, corresponding to the ad-atoms on surfaces associated with the Schottky defects [18], for every bound Xe atom (i.e., every atom in dynamic solution) a bulk volume increase of 3 atomic volumes was considered. Since, as mentioned above, the average atomic volume in UO 2 is given approximately by a 3 /12 (a = UO 2 lattice constant) [18], the volume increment assigned per trapped Xe atom is around 4.1 · 10 À23 cm 3 /atom.…”

“…Thus, corresponding to the ad-atoms on surfaces associated with the Schottky defects [18], for every bound Xe atom (i.e., every atom in dynamic solution) a bulk volume increase of 3 atomic volumes was considered. Since, as mentioned above, the average atomic volume in UO 2 is given approximately by a 3 /12 (a = UO 2 lattice constant) [18], the volume increment assigned per trapped Xe atom is around 4.1 · 10 À23 cm 3 /atom. This volume is certainly much smaller than that occupied by Xe atoms in bubbles, as calculated both under Van der Waals (8.5 · 10 À23 cm 3 / atom) or HS-EOS (5.3-6.0 · 10 À23 cm 3 /atom) conditions (see Section 3.2).…”

Thermal recovery mechanisms of UO2 lattices by defect annihilation

“…In the previous study [1], swelling mechanisms of the uranium dioxide crystal with ingrowth of irradiation induced defects is studied by molecular dynamics (MD) simulation method and compared with experimental results [2,3,4]. Neutron and alpha-particle irradiation induced defects are investigated and it was shown that main reason for the lattice swelling is the obstruction type defects.…”

A physical description of fission product behavior fuels for advanced power reactors.

“…As the bubble population continues to grow, single atoms will eventually have a higher likelihood of being captured into an existing nucleus rather than meeting another single atom. The grain boundary concentration per unit volume can be approximated by 12 is the average atomic volume in UO 2 [22], a is the lattice constant, z is the number of sites visited per gas-atom jump, δ is the width of the boundary, ζ is a grain boundary diffusion factor and K is the flux of gas-atoms per unit area of grain boundary.…”