Uranium Oxide Mass Loss Rate in Water for an Interface Under Alpha-Irradiation
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C. Corbel
a,
J-F Lucchini b, G. Sattonnay a, M-F Barthe ¢, F. Huet
d,
p. Dehaudt
d,
C. Ardoisa, B.Hickela, J.L.Paulb a
CEA Saclay, DSMIDRECAM/SCM/ Laboratoire CEA de radiolyse b CEA
Marcoule, DCCIDRRVISCDILECM ¢CERI-CNRS, Orleans d CEA
Grenoble, DTP/SECC
ABSTRACT
This work uses an external alpha beam to irradiate an uranium oxide/water interface and investigates the release of uranium in aerated deionized water under alpha irradiation. A high energy alpha beam delivered by a cyclotron (CERI-CNRS) goes through the oxide and emerges in the water with a 20 MeV energy. First results are reported here showing that the uranium mass loss rate increases by three orders of magnitude in aerated deionized water under high flux (Ž_3.3x1 010 xr..cmT2 .S'I). INTRODUCTION The environmental assessment of nuclear spent-fuel (UOX) disposal requires a prediction of release rates of uranium once contact between spent fuel and groundwater is established. A first step in the modelling is to replace spent fuel by uranium oxide (UO=) and use the release rates predicted for uranium oxide submitted to the same leaching conditions as spent fuel. The reliability of such an approach is however questionable due to the difference in the radioactivity of UOX and UO 2 . Spent fuel is a gamma, beta and alpha radioactive material with an activity depending on its bum-up and storing age. The decay time for spent fuel to recover the value of its initial alpha activity as fresh fuel is over more than one million of years. The strong gamma and beta activity of spent fuel decrease by more than three orders of magnitudes in the first few hundred years after disposal. Since the metallic container is expected to survive this period, ground water reaching spent fuel after this period will be subjected mainly to alpha radiolysis [1]. At the spent fuel//water interface, the water composition is modified by the radiolytic species produced by the emerging alpha particules and the spent fuel structure is modified by the defects produced by the alpha particules along their track. Reliable estimates of the uranium release rates due to alpha activity are still lacking although the dissolution of UO2 doped with alpha emitters [2,3] or irradiated by a low flux alpha source [4,5] has been earlier investigated.
41 Mat. Res. Soc. Symp. Proc. Vol. 608 © 2000 Materials Research Society
This work proposes a new approach to investigate how alpha emission from a U02 surface may affect the release of uranium at the U0 2/H20 interface. The production
rate of defects in U0 2 and radiolytic species in H20 are controlled by the alpha energy, stopping power and flux. To monitor these three physical quantities at the UO2/H20 interface, we use an alpha-beam supplied by a cyclotron. The beam passes through the U0 2 disk and emerges into the water in contact with the disk. Depending on initial beam energy and disk thickness, the beam energy at the interface can be adjusted between 0 - 20 MeV. The beam has however a narrow energy distribution at the interface due to strag
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