A study of molybdenum behaviour in UO2 by X-ray absorption spectroscopy

Volatile fission product behaviour during thermal annealing of irradiated UO2 fuel oxidised up to U3O8

“…The vaporisation of the first group is detectable above 2000 K together with the vaporisation of the fuel matrix, the measured vaporisation enthalpies ranging between 501 and 548 kJ mol À1 , close to the enthalpy of vaporisation of Ln 2 O 3 [6]; the measured vapour pressures above irradiated fuel show an activity equal to their concentration in the fuel [7,8]. Atoms of the second group (Mo, Pd, Rh, Ru, Tc) precipitate in form of metallic particles mainly located in voids, bubbles, or at the grain boundary [9][10][11]. These metals have a low vapour pressure and are generally not released at low temperature from hypo to stoichiometric fuel.…”

EXAFS and XANES studies of americium dioxide with fluorite structure

“…The X-ray absorption fine structure (XAFS) technique including the extended X-ray absorption fine structure (EXAFS) and the X-ray absorption near-edge structure (XANES) is an excellent method for examining the local and electronic structures surrounding an actinide atom in oxide fuels [3][4][5][6][7]. In particular, XANES gives the information on the electronic structures of unoccupied molecular orbital.…”

“…In particular, XANES gives the information on the electronic structures of unoccupied molecular orbital. Martin and co-workers applied the XAFS technique to investigate the local structure of actinide atoms and simulated fission products in UO 2 and other oxide fuels [5][6][7]. They demonstrated the efficacy of the EXAFS to study the local structure of these minor constituents in the fuel matrixes.…”

BEHAVIORS OF MOLYBDENUM IN UO2FUEL MATRIX

“…The fission products could be categorized by groups: elements that form solid solutions with UO2, those that precipitate into a UO2 matrix in the forms of oxides or metals, and volatile elements [1,2]. Among the elements that precipitate into a UO2 matrix, molybdenum is the most abundant fission product since its fission yield is equivalent to that of xenon [2,3]. It is well known that molybdenum belongs to two categories at a time [4], either dissolving in the matrix or forming precipitates.…”

“…It exists as precipitates mainly located in voids, bubbles and grain boundaries [3,5,6], as well as a solid solution in UO2 spent fuel. In addition, it has a very particular role in the chemistry of nuclear fuel because the oxygen potential of Mo/MoO2 buffers the oxidation of uranium dioxide [2,3,7] when exposed to an oxidizing atmosphere. If oxygen potential is high enough (∆GO2 > ∆GMo), Mo may exist as an oxide form (MoO2) which causes a depletion of metallic precipitates.…”