2005 Salt Lake City Annual Meeting (October 16–19, 2005)

Paper No. 5
Presentation Time: 11:15 AM


UTSUNOMIYA, Satoshi, Department of Geological Sciences, Univ of Michigan, 1100 N. University Ave, Ann Arbor, MI 48109-1005 and EWING, Rodney C., Geological Sciences, University of Michigan, 2534 C.C little Building, 1100 N. University Avenue, Ann Arbor, MI 48109-1005, utu@umich.edu

U6+-minerals commonly form during the alteration of uraninite and spent nuclear fuel under oxidizing conditions. By the incorporation of actinides and fissiogenic elements into their structures, U6+-minerals maybe important in retarding the migration of radionuclides released during corrosion of spent nuclear fuel. Thus, the stability and the structural transformation of the U6+-minerals in radiation fields are of great interest. In this study, in order to examine the effects of ionizing radiation on U6+-minerals, electron irradiation (~8-33x1017 (e-/cm2/sec) at the room temperature) experiments were completed on: boltwoodite, K[(UO2)(SiO3OH)](H2O)1.5 kasolite, Pb[(UO2)(SiO4)](H2O) saléeite, Mg[(UO2)(PO4)]2(H2O)10 carnotite, K2(UO2)2(V2O8)(H2O)3 liebigite, Ca2[(UO2)(CO3)3](H2O)11 schoepite, [(UO2)8O2(OH)12](H2O)12. During the irradiation, boltwoodite, saléeite, and carnotite became amorphous at doses of 1-4x1010 Gray (Gy), while the amorphization dose (Dc) of kasolite, 50x1010 Gy, was about an order of magnitude higher than that of boltwoodite. This high Dc for kasolite is consistent with the hypothesis that the Dc increases as the mass of the inter-layer cation increases. Only amorphization, rather than chemical decomposition, occurred in boltwoodite, saléeite and carnotite, even at doses as high as 80x1010 Gy. In contrast, uraninite nanocrystallites began to form with a random orientation at ~43x1010 Gy in liebigite which had already become amorphous prior to irradiation in the vacuum of the TEM. For schoepite, the Dc was only 0.51x1010 Gy, and randomly oriented uraninite nanocrystallites formed at 7.8x1010 Gy which is approximately the same dose as compared with the Dcs for the other U6+-phases. Because the predicted cumulative dose by the ionizing radiation in spent nuclear fuel is ~107-108 Gy during the first 102-3 years after discharge, an additional contribution of ionizing radiation dose by α-decay events is needed in order to induce amorphization in these U6+-phases.